A ^ j l l (JA^jJl Ail I UiU

Sudan Academy of Sciences (SAS) Atomic Energy Research Coordination Council

Disinfection of Sewage Water and Sludge using Gamma Radiation

By

Rihab Moawia Ali Musaad B.Sc. (Chemistry & Zoology)

Faculty of Science, University of Khartoum (2002)

Higher Diploma (Chemistry) Faculty of Science, University of Khartoum (2004)

A thesis submitted to Sudan Academy of Science in fulfillment of the requirements for the degree of Master of Science in Radiation

Chemistry

Supervisor: Dr. Adam Khatir Sam

I

Disinfection of Sewage Water and Sludge using Gamma Radiation

By Rihab Moawia Ali Musaad

Examination committee

Title Supervisor

External examiner

Internal examiner

Name Dr. Adam Khatir Sam

Dr. Hassan Ibrahim Nimir

Dr. Isam Salih Mohamccl

Signature

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II

(Dedication

To my betoved

Mother

in

Acknowledgments

With a deep sense of gratitude, I wish to express my sincere thanks to my supervisor,

Dr. Adam Khatir Sam for his continuous great help, confidence, encouragement and

absolute patience during all the steps of this study.

No Doubt, he provided me all his time, the essential knowledge that hardly could be

found and the planning and executing the works in time, which made my work more

clear and easy to be achieved.

My sincere thanks are due to Dr. El-Gundy for providing me constant encouragement

and the useful advices and help during my work in the Veterinary Research Centre. In

addition, I would like to thank with my deep sense of gratefulness, Dr Jammaa and his

workers for everything that they have done to me.

My thanks are also due to the members of Central Laboratory in Soba. My thanks are

also due to the members of microbiology laboratory in department of botany at

University of Khartoum. And special thanks to Dr Fathi Alrabaa, department of

zoology.

Special thanks, with deep sense of love to my friends and colleagues at SAEC for the

great help that they always providing me, specially my dear friend Ashraf Salih who

helped me, moreover; my thanks expended to Dr.Isam Salih for his assistance to

complete my thesis.

Actually, there are no suitable words to thanks my family, who gave me whatever I

need; love, care, encouragement and motivations to complete my study. I would like

to share this moment of happiness with my mother, father, sisters and brothers.

Finally, I would like to thanks all whose direct and indirect support helped me

completing my thesis in time.

IV

Abstract This study has been carried out to assess the efficiency of gamma radiation in

disinfecting sewage water and sludge from harmful pathogenic bacteria (e.g.

Streptococcus, Salmonella, Shigella, total E-coli and total Coliform), parasites

(Ascaris ova) as well as its ability to degrade organic matter (BOD).

Samples were exposed to gamma-radiation doses ranging from 0.5 to 8 KGy using

Co cell. Amongst pathogenic bacteria which are subjected to different doses of

gamma-radiation Streptococcus faecalis revealed to be the most resistance bacterial

indicator since complete elimination of these bacteria could be attained at 3.5 KGy

while total E-coli shown to be the most sensitive with lethal dose at 2 KGy.

The radiation doses that required for reducing the bacterial population by 90% (Dio)

and 50% (D50) were determined for each species. The Dio values found ranged from

0.75 KGy for Streptococcus and 2.75 KGy for Total count bacteria. On the other

hand, D50 fall within the range of 0.5 KGy for total count bacteria, total Coliform and

Streptococcus; and 1.0 KGy for total H-coli.

With regard to the efficiency of radiation treatment to destroy Ascaris ova viability it

was found that no larvae were viable after exposure to 1.0 KGy following incubation

of exposed ova for four weeks period.

V

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VI

TABLE OF CONTENTS DEDICATION Ill ACKNOWLEDGEMENTS IV ABSTRACT V ARABIC ABSTRACT VI LIST OF TABLES X LIST OF FIGURES XI

CHAPTER ONE: INTRODUCTION 1

1.1 Component of wastewater 2 1.1.1 Organisms 2 1.1.2 Organic matter 2 1.1.3 Oil and grease 3 1.1.4 Inorganic 3 1.1.5 Nutrients 4 1.1.6 Solids 4 1.1.7 Gases 4 1.2 Wastewater Characteristics 4 1.2.1 Temperature 5 1.2.2 pi 1 5 1.2.3 Flow 5 1.3 Health risks 5 1.4 Wastewater Treatment Methods 7 1.4.1 Conventional treatment methods 8 1.4.1.1 Activated sludge and oxidation 9 1.4.1.2 Chlorination 9 1.4.1.3 Ozone 10 1.4.2 Radiation method 10 1.4.2.1 Mechanism of gamma-ray in sewage sludge 11 1.4.2.2 The benefit 13 1.4.2.3 The disadvantages 14 1.5 The radiation chemistry theory 15 1.5.1 Chemical effects of ionizing radiation 15 1.6 Water Radiolysis 20 1.7 Literature Review 23

CHAPTER TWO EXPERMENTAL TECHNNIQUES. . . 38

2.1 The Cobalt-60 irradiator 38 2.1.1 Principle of operation 40 2.1.2 Dosimetry systems 40 2.2 Material and Methods 40 2.2.1 Area of study 40 2.3 Sample collection and preparation 43 2.4 Sample Irradiation 45

VII

2.5 Sample Measurements 45 2.5.1 Biological Oxygen Demand (BOD5) 45 2.5.2 Bacterial Count 46 2.5.2.1 Surface viable count of bacteria 47 2.5.3 Parasites test (Ascaris lumbrecoids) 47 2.5.3.1 Procedure for determination of Heleminth ova in wastewater 48

sludge 2.5.3.2 Viability 48

CHAPTER THREE: RESULT AND DSCUSSION 49

3.1 Biochemical Oxygen Demand (BOD5) 49 3.2 pH 49 3.3 Effect of radiation on survival of bacteria 50 3.4 Ascaris 54

CONCLUSIONS 64 REFERNCES 65

VIII

List of Tables

TABLE 1-1: HALF-THICKNESS VALUE FOR GAMMA 17

TABLE 1-2: LET VALUES FOR GAMMA-RADIATION 18

TABLE (3-1): (BOD) OF WASTEWATER EFFLUENTS BEFORE AND AFTER GAMMA IRRADIATION 5 6

TABLE 3.2: STATISTICAL SUMMARY OF BACTERIA COUNTS (CFU/ML)

BEFORE AND AFTER GAMMA IRRADIATION OF SEWAGE WATER FROM SOBA

SEWAGE TREATMENT PLANT 57

TABLE (3-3): THE INFLUENCE OF GAMMA RADIATION ON THE

DEVOLVEMENT OF ASCARIS EGGS 58

IX

List of Figures

FIG. 1.1: FORMATION OF FREE RADICAL SPECIES IN WATER BY MEANS OF

IONIZING RADIATION 21

FIG.2. 1: MDSN NORDION GAMMA CELL 222 EXCEL 39

FIG. 2.2: LAYOUT OF KHARTOUM SEWAGE REHABILITATION PLANT 42

FIG. 2.3: RUTTNER WATER SAMPLER 44

FIG.3 .1: THE PLOT OF RATIO PERCENTAGE AGAINST Y-DOSE FOR TOTAL

COUNTS BACTERIA 59

FIG.3.2: THE PLOT OF RATIO PERCENTAGE AGAINST Y-DOSE FOR TOTAL

COUNTS BACTERIA 60

FIG.3 .3: THE PLOT OF RATIO PERCENTAGE AGAINST Y-DOSE FOR TOTAL

COLIFORMS 61

FIG. 3.4: THE PLOT OF RATIO PERCEN TAGE AGAINST Y-DOSE FOR TOTAL E-

COLI 62

FIG. 3.5: THE PLOT OF RATIO PERCENTAGE AGAINST Y-DOSE FOR

STREPTOCOCCUS 63

x

Chapter One

Introduction

Until today no data lias been appeared in open literature addressing the topic of radiation

treatment of sewage waste in Sudan. This study is the first of its kind in Sudan aimed at

establishing base-line data on gamma-dose levels and the irradiating geometries needed

to disinfect and improve the quality of sewage waste water and sludge for possible re-use

in irrigation.

Wastewater is defined as the water borne wastes of a community; it contains

approximately 99.9% pure water and 0.1% pollutants by weight. All the water used in the

home that goes down the drains or into the sewage collection system is wastewater

sewage, stormwater and water that have been used for various purposes around the

community. Unless properly treated, wastewater can harm public health and the

environment. Wastewater is mostly water by weight; other materials make up only a

small portion of wastewater, but can be present in large enough quantities to endanger

public health and the environment, because practically anything that can be Hushed down

a toilet, drain, or sewer can be found in wastewater, even household sewage contains

many potential pollutants (Nicholas, 2001). If human wastes were the only things

entering the sewage treatment plant, then sewage sludge would contain only nutrients and

should undoubtedly be returned to the land. Unfortunately, most sewage treatment plants

receive industrial toxic wastes, which contain some potentially harmful components

including heavy metals such as cadmium, lead and mercury which are then mixed with

the human wastes, creating a pernicious mixture of nutrients. The wastewater

components that should be of most concern to homeowners and communities are those

that have the potential to cause disease or detrimental environmental effects. Most

communities generate wastewater from both residential and nonresidential sources

(Catherine el al. 1997).

Water used in toilets, showers, baths, kitchen sinks and laundries in homes and offices is

domestic wastewater. There are two types of domestic sewage: blackwater, or wastewater

1

from toilets, and gray water, which is wastewater from all sources except toilets. Black

water and gray water have different characteristics, but both contain pollutants and

disease-causing agents that require treatment. Nonresidential wastewater in small

communities is generated by such diverse sources as offices, businesses, department

stores, restaurants, schools, hospitals, farms, manufacturers, and other commercial,

industrial, and institutional entities. Slormwater is a nonresidential source and carries

trash and other pollutants from streets, as well as pesticides and fertilizers from yards and

fields. (Nicholas, 2001)

1.1 Component of wastewater

1.1.1 Organisms

Many different types of organisms live in wastewater and some are essential contributors

to the treatment. A variety of bacteria, protozoa, and worms work to breakdown certain

carbon-based (organic) pollutants in wastewater by consuming them. Through this

process, organisms turn wastes into carbon dioxide, water, or new cell growth. Bacteria

and other microorganisms are particularly plentiful in wastewater and accomplish most of

the treatment. Most wastewater treatment systems are designed to rely in large part on

biological processes (Catherine et al. 1997)

1.1.2 Organic matter

Organic materials are found everywhere in the environment. They are composed of the

carbon-based chemicals that are the building blocks of most living things. Organic

materials in wastewater originate from plants, animals, or synthetic organic compounds,

and enter wastewater in human wastes, paper products, detergents, cosmetics, foods, and

from agricultural, commercial, and industrial sources.

Organic compounds normally are some combination of carbon, hydrogen, oxygen,

nitrogen, and other elements. Many organics are proteins, carbohydrates, or fats and are

biodegradable, which means they can be consumed and brokendown by organisms.

2

However, even biodegradable materials can cause pollution. In fact, too much organic

matter in wastewater can be devastating to receiving waters

1.1.3 Oil and grease

Fatty organic materials from animals, vegetables, and petroleum also are not quickly

broken down by bacteria and can cause pollution in receiving environments. When large

amounts of oils and greases are discharged to receiving waters from community systems,

they increase Biological Oxygen Demand (BOD) and they may float to the surface and

harden, causing aesthetically unpleasing conditions. They also can trap trash, plants, and

other materials, causing foul odors, attracting flies and mosquitoes and other disease

vectors. In some cases, too much oil and grease causes septic conditions in ponds and

lakes by preventing oxygen from the atmosphere from reaching the water.

1.1.4 Inorganic

Inorganic minerals, metals, and compounds, such as sodium, potassium, calcium,

magnesium, cadmium, copper, lead, nickel, and zinc are common in wastewater from

both residential and nonresidential sources. They can originate from a variety of sources

in the community including industrial and commercial sources, stormwater, and inflow

and infiltration from cracked pipes and leaky manhole covers. Most inorganic substances

are relatively stable, and cannot be broken down easily by organisms in wastewater.

Large amounts of many inorganic substances can contaminate soil and water. Some are

toxic to animals and humans and may accumulate in the environment. For this reason,

extra-treatment steps are often required to remove inorganic materials from industrial

wastewater sources. For example, heavy metals which are discharged with many types of

industrial wastewaters are difficult to remove by conventional treatment methods.

Although acute poisonings from heavy metals in drinking water are rare, potential long-

term health effects of ingesting small amounts of some inorganic substances over an

extended period of time are possible.

3

1.1.5 Nutrients

Wastewater often contains large amounts of the nutrients nitrogen and phosphorus in the

form of nitrate and phosphate, which promote plant growth.

1.1.6 Solids

Solid materials in wastewater can consist of organic and/or inorganic materials and

organisms. The solids must be significantly reduced by treatment or they can increase

Biological Oxygen Demand (BOD) when discharged to receiving waters and provide

places for microorganisms to escape disinfection, they also can clog soil absorption fields

in onsite systems.

1.1.7 Gases

Certain gases in wastewater can cause odors, affect treatment, or are potentially

dangerous. Mclhanc gas, for example; is a byproduct of anaerobic biological treatment

and is highly combustible. Special precautions need to be taken near septic tanks,

manholes, treatment plants, and other areas where wastewater gases can collect.

In addition to the many substances found in wastewater, there are other characteristics

system designers and operators use to evaluate wastewater, for example; the color, odor,

and turbidity of wastewater give clues about the amount and type of pollutants present

and treatment necessary.

1.2 Wastewater Characteristics

In addition to the many substances found in wastewater, there are other characteristics

system designers and operators use to evaluate wastewater. For example, the color, odor,

and turbidity of wastewater give clues about the amount and type of pollutants present

and treatment necessary.

The following are some other important wastewater characteristics that can affect public

health and the environment, as well as the design, cost, and effectiveness of treatment

4

1.2.1 Temperature

The best temperatures for wastewater treatment probably range from 77 to 95° F. In

general, biological treatment activity accelerates in warm temperatures and slows in cool

temperatures, but extreme hot or cold can stop treatment processes altogether.

1.2.2 pH

The acidity or alkalinity of wastewater affects both treatment and the environment. Low

pH indicates increasing acidity; while a high pH indicates increasing alkalinity (a pH of 7

is neutral). The pH of wastewater needs to remain between 6 and 9 to protect organisms.

Acids and other substances that alter pH can inactivate treatment processes when they

enter wastewater from industrial or commercial sources. (Catherine et al. 1997)

1.2.3 Flow

Whether a system serves a single home or an entire community, it must be able to handle

fluctuations in the quantity and quality of wastewater it receives to ensure proper

treatment is provided at all times.

1.3 Health risks

Many disease-causing viruses, parasites, and bacteria also are present in wastewater and

enter from almost anywhere in the community. These pathogens often originate from

people and animals that are infected with or are carriers of a disease. Graywater and

blackvvatcr from typical homes contain enough pathogens to pose a risk to public health.

Other likely sources in communities include hospitals, schools, farms, and food

processing plants.

Some illnesses from wastewalcr-related sources are relatively common. Gastroenteritis

can result from a variety of pathogens in wastewater, and cases of illnesses caused by the

parasitic protozoa Giardia lambia and Cryptosporidium. Other important wastewater-

related diseases include hepatitis A, typhoid, polio, cholera, and dysentery. Outbreaks of

these diseases can occur as a result of drinking water from wells polluted by wastewater,

5

eating contaminated fish, or recreational activities in polluted waters. Some illnesses can

be spread by animals and insects that come in contact with wastewater.

Even municipal drinking water sources are not completely immune to health risks from

wastewater pathogens. Drinking water treatment efforts can become overwhelmed when

water resources are heavily polluted by wastewater. For this reason, wastewater treatment

is as important to public health as drinking water treatment. A properly designed, sized,

installed and maintained on site wastewater treatment system should safely remove and

treat wastewater from a home. Untreated or improperly treated wastewater is a risk to

people through direct contact with sewage, or animals (Hies, dogs, cat, etc.) that have

been in direct contact with sewage. Also, untreated or improperly treated wastewater is a

threat to human health and the environment when it pollutes surface water or

groundwater (Mala, 2002).

Sewage system has to be established to collect the waste material; however, providing

sewers for the cities is not a complete solution of the problem of excreta disposal,

because sewage disposal into water resources or land would actually lead to the spreading

of intestinal diseases and other environmental hazards.

The character and degree of wastewater treatment depend on the raw water whether it is

from factories or residential, and also on the system used. If wastewater is to be used for

irrigation of agriculture crops, in an instructed manner, including a high degree fruit and

vegetables usually consumed uncooked, disinfection is necessary to inactivate the

pathogens. Additional processes may be required to remove certain resistant protozoan or

helminthes.

In many advanced countries directives requires that the sludge, before applying to

agricultural land must undergo on appropriate process to kill-off disease causing

organisms, which may be present in the sludge (Pathogens). Sewage sludge contains

various pathogenic organisms that capable to induce several human diseases. And

propagate in the enteric or urinary systems humans and are discharged in feces or urine

pose the greatest risk to public health with regard to the use and disposal of sewage

sludge. Such as; Bacteria include different species: Salmonella typhi (enteric fever,

tyhoicl), Vibrio cholera (Cholera), and E.coli (Infantile diarrhoea); Parasites: Helminthes

6

ova occur universally in raw sewage, including those of Taenia, Ascaris lumbricoides etc.

helminthes infections which can be transmitted by sewage are those whose causative

agents (ova or larvae) escape from the bodies of infected persons in their excreta, and are

then capable of infecting other human beings, either directly or after passage through one

or more intermediate hosts and Giardia Lamblia (Giariasis), and lastly Viruses: Reovirus

(Fever,Resiratory infections, Diarrhoea), Echovirus (Rash and Fever), Adenovirus

Resiratory andEye Infectons), Rotavirus (Diarrhea,Vomiting),( El-Motaium, 2000).

Sludge contains a broad suite of heavy metals and concentration which vary from sludge

to sludge. The heavy metals enter sewage from industrial applications often in inorganic

forms. Once combined with municipal wastes, the metals are absorbed onto the organic

materials, precipitate with iron and aluminum oxides or precipitate with carbonates

sulfides and phosphates (Alibhai, 1985). Various characteristics of each metal often

limited the health hazard associated with land application.

Several methods are available, including anaerobic digestion, composting, liming, and

thermal disinfection (Hijkal el al, 1979; Strauch, el al, 1985). These methods aim at

making the sludge biologically and chemically safe. But these conventional methods

seem to be insufficient to eliminate the pathogens from wastewater (EL-Fouly 1996).

1.4 Wastewater Treatment Methods

The goal of wastewater treatment is to remove as much of the floating and biodegradable

pollutants and disease-causing agents in wastewater as possible to minimize the risks to

public health and impact on the environment.

Fundamental studies have shown that complete degradation of biologically resistant

compounds disinfection of sewage sludge as well as killing of microorganisms can be

achieved by ionizing radiation treatment (Getoff, 1995). Gamma rays are of the latter

type and are suitable for the treatment of sewage because of the lack of residual

radioactivity left in the material irradiated, irradiation of the effluent with gamma photons

from Cobalt-60 results in zero residual radioactivities.

In many small communities, wastewater treatment often takes place in onsite systems,

such as septic systems. It also may be collected and transported through a network of

7

sewers to small decentralized treatment systems or to a central community treatment

plant. Some communities use a combination of options.

Wastewater has been adversely affected in quality by anthropogenic influence. Sewage is

correctly the subset of wastewater that is contaminated with feces or urine but is often

used to mean any waste water. For technical purposes waste waters can be divided into

urban and industrial wastewaters from industries and it varies with the type and size of

industry (Boari, 1997).

Many countries there is an increasing demand on irrigation water by municipal waste

water which represent a reasonable source value in effluent sewage, which contain of

high population of pathogenic organisms and disinfection treatments instead of contained

valuable nutrients, minor elements and organic matter of great importance for plant

growth as well as very necessary to obtain products safe on their reutilization in

agricultural purposes (El-Fouly et al. 1996).

Sewage sludge is the mud-like material that remains after bacteria have digested the

human wastes that flow from into local sewage system. It contains many nutrients

beneficial to plant growth, such as nitrogen, potassium phosphorus and certain trace

minerals. If human wastes were the only things entering the sewage treatment plant, then

sewage sludge would contain only nutrients and should undoubtedly be returned to the

land. Unfortunately, most sewage treatment plants receive industrial toxic wastes, which

contain some potentially harmful components including heavy metals such as cadmium,

lead and mercury which are then mixed with the human wastes, creating a pernicious

mixture of nutrients and industrial poisons. Moreover, sewage sludge contains toxic

organic matter such as chlorinated hydrocarbon dioxins and furans, together with

pathogenic microorganisms. Increase in population, industrial activities, extensive use of

pesticides and other chemical for cultivation are caused increasing load of pollution on

the environment.

1.4.1 Conventional treatment methods

Sewage is generally treated before its disposal on land or in water. Various methods of

sewage and sludge disinfection which are commonly used, like conventional sewage-

treatment plants, thermal disinfection, composting of sewage or chlorination, all have one

8

or more disadvantage (Hejkal et al., 1979; 1981; Krishnamurthy, 1980; Russ and Yanko,

1981).

Several conventional methods are known to be applied for water disinfection, but till now

these methods seem to be insufficient to eliminate the pathogens from wastewater. There

is ample evidence that excreta and wastewater, especially in developing countries, do

contain high concentrations of excreted pathogens (Feachem, 1983). Many of these

pathogens can survive in these materials for some lime and can also withstand most

conventional treatment processes. Many conventional methods have been used for

recycling and reutilized the waste water for many benifitial purposes. Such as trickling

filters, (Sabharvval et a\. 2004, and Reimers et al. 1980)

1.4.1.1 Activated sludge and oxidation

Activated sludge and oxidation can not produce an effluent which complies with the

guidelines for controlling helminth eggs. Similary, they can not meet the bacterial

standards, unless the effluent is chlorinated. Chemical treatment of wastewater only

exchanges one type of pollution for another.

1.4.1.2 Chlorination

Chlorine used in sufficient quantities to kill large percentages of bacteria and also the

pollutes in water, so that it stunts plant growth, kills oysters and other shellfish, and in

general makes the effluent far less useful (David et al. 1972). The application of the

chlorine compounds to water or waste water, usually for the purpose of pathogens

reduction (Hejkal et al., 1979; 1981; Krishnamurthy, 1980; Russ and Yanko, 1981). In

some circumstances, chlorination may also provide chemical oxidation and odour control.

Disinfection is generally operated by chlorination with Ch or NaOCI. In addition to this,

the usage of various chlorine-containing presticides and other chemicals as well as

fertilizer in modern agriculture, contributes to contamination of ground water. The killing

of microorganisms containing humic compounds by chlorination lead to the formation of

various halogenated hydrocarbons (Rook et al. 1974).

9

1.4.1.3 Ozone

Ozone used to disinfect wastewater, or as tertiary treatment, does not increase the odor,

color, or salt content of the plant effluent. In relatively pure potable water, ozone has a

half life from about 20 to 80 minutes, depending on the Chemical Oxygen Demand

(COD) remaining in the water. At normal temperature, ozone residuals rapidly disappear

if any COD is present. The disadvantages of using ozone include high cost, possible air

pollution from escaping ozone and high electrical consumption.

1.4.2 Radiation method

One of the recent methods of rendering sewage and sludge free of pathogens is the use of

ionizing radiation (Epp 1975; Wizigmann and Wiiursching, 1975; Brandon, 1976;

Brandon et al., 1977; Ward, 1977, 1981; Krishnamurthy, 1980, 1981; Suess et al., 1983;

Iya and Krishnamurthy, 1984). Radiation processing refers to the use of radiation as a

source of energy for industrial processing and comprises the application of ionizing

radiation on physics, chemistry, biology and microbiology Holds (Sampa, et al. 2005).

The basic types of irradiation systems, which are currently being used in waste treatment

operations or being studied for these purposes include gamma-radiation, electron-beam,

ultraviolet and X-rays.

Several technical scale irradiation plants have been established in different countries,

some using 137Cs as a source. In several industrialized countries, use of 137Cs for this

purpose is an efficient means of reusing this radioisotope which is produced in substantial

quantities as a by-product of reprocessing of defense and power nuclear fuel wastes. At

present sufficient technical data is available on gamma treatment of sludge's, permitting

its application on the demonstration or commercial scale, but a few gaps in knowledge

still exist especially for the practical application of electron beam technology

(FAO/IAEA, 1995).

Ultraviolet irradiation systems have regained popularity at wastewater treatment plants as

an alternative to chlorine. These systems have undergone improvements that resulted in

more robust equipment and more reliable operation. The possible application of x-ray-

10

whose use well established for medical diagnosis and cancer therapy for the treatment of

wastes has been investigated. However, the technology has not yet been applied for this

purpose (swinwood el al. 1994). It has been known for decades as the most powerful

sterilizing agent for small to moderate volumes of industrial liquids and air, killing most

micro-organisms quickly, and now at a reasonable cost. But the application to secondary

treated sewage has taken many years to achieve, because of the large volumes and the

suspended solids.

Electron beam accelerators and gamma irradiators with Cobalt-60, isotope produced in

nuclear reactor are used as radiation sources. The two types of radiation sources are

routinely used in radiation processing technology, gamma radiation from artificially

produced radioactive isotope Cobalt-60 and high energy electrons produced by

accelerators. The choice of one or the other depends on the process and on economic

considerations and both satisfy the main industrial requirements (Sampa, 2005).

Differences between gamma rays from Cobalt-60 sources and electron beams are dose

rale and penetration of radiation. In general gamma irradiators are used for the irradiation

of high-density and large-volume materials while electron beams are suitable for the

irradiation of thin materials such as plastic films and surface coatings (Makuuchi, 1992).

It is important to clarify that one of the main requirements is well satisfied, the radiation

with these radiation sources do not produce any radioactivity in the irradiated material

land, and the irradiated products are safe for use immediately after irradiation. This

process is competitive for processing some material, present a competitive cost and is

safe technology for environment, for operating personnel and for end-users (Markovic,

1988).

1.4.2.1 Mechanism of gamma-ray in sewage sludge

Radiation technology is now a credible option for dealing with problems of health hazard

pollutants in sewage sludge. The pathogens present in the sewage sludges can also be

effectively removed from the sewage sludge by exposing it to high energy radiation from

radioactive sources such as cobalt-60. The radiation treatment of sewage sludge, can offer

11

an efficient, simple and reliable method to produce pathogen free sludge. Which can

further up graded to produce a value added bio fertilizer and allow recycling of the waste

products. Therefore, irradiation of sewage sludge as a tertiary treatment process has been

investigated sine early seventies (Suess,e/ al, 1975, Rawat, et al, 1977).

The high- energy gamma radiation from radioactive sources such as Cobalt- has the

ability to inactivate the pathogens with a very high degree of reliability, and clean and

efficient manner (Sabharwal, et al. 2004). These rays penetrate and pass through the

sludge, inactivating microorganisms and decomposing various organic compounds

without leaving in any residual radioactivity or making the sludge radioactive. The

finished product "clean sludge" can be utilized as an organic, sanitary fertilizer/soil

conditioner or use as an animal feed. Recently, the use of ionizing radiation has proven

to be effective in hygenization of sewage sludge (kabila, et al. 1981; Pandya et al. 1987).

Gamma irradiation of sewage sludge, in addition to removing harmful pathogenic

organisms, can lead to changes in physical and chemical properties (Suss, et al 1983; El-

Motaium, 2000).

Radiation treatments applied on effluent and on poudrettc showed that the lethal effect of

gamma rays on the different microbial groups under investigation increased with

increasing the radiation dose. Treating wastewater with gamma radiation may contribute,

in one step, the disinfecting sewage effluent and poudrette from pathogens.

There are two factors affect the process of removal of pollutants from wastewater, firstly

radiation condition in high doses the decomposition of pollutant an achieved in high

percentage and vice verse. The second factor is the composition of wastewater, rich waste

water with pollutant demand high doses to insure most of pollutants were decomposed

(Han, et «/.2004). The clean sludge would minimize the risk of pathogenic

microorganisms, harmful release of nitrogen compounds and emission of halocarbons

that are potential important contributors to global climate change. Therefore, sludge

irradiation-pasteurization may be the most environmentally and economically handling

and treatment. For example: 3KGy of absorbed dose in sewage sludge removes 99.99%

of pathogenic bacteria, which are other wise responsible for causing diseases such as

cholera, typhoid, dysentery etc. Contrary to the conventional processes, the radiation

treatment of sewage sludge kills the pathogens in simple, efficient and reliable way.

12

Sludge free from pathogens has potential to be used as manure in agriculture fields.

While the continuous use of chemical fertilizers deteriorates the quality and fertility of

the soil as it contains useful soil conditioning materials. And the radiation processed

sludge material is free of any dour.

1.4.2.2 The benefit

Development of integrated sludge management techniques would help in achieving the

twin benefits of recovering the resource value of sludge for use a safe fertilizer in

agricultural practice and combating the nation-wide public health and sanitary

engineering problems of safe disposal of sewage sludge (Iya and Krishnamurthy, 1984).

The irradiation of sludge offers some unique advantages over conventional processing

techniques. As accelerators become relatively less expensive and as wastes become more

of a problem, irradiation of sludge will likely become a common practice. Irradiation

pasteurization of sewage has the following advantages:

a- No heat energy is required

b- The process and equipment is simple, reliable and easily controlled;

c- No addition of chemical substances;

d- Corrosion and deterioration of dewatering properties are minimized in contrast to

thermal pasteurization treatment;

e- Radiation effectively inactivates sludge pathogens;

f- Radiation induced decomposition of various organic compounds such as phenols,

chlorinated hydrocarbons, dye stuffs, etc, in water represents a new and very

efficient possibility for elimination of the steadily increasing pollution (Getoff and

Lulz.1985).

g- Sterilized sewage could be reused as a valuable fertilizer or as a cattle feed

supplement (Krishnamurthy, 1985).

h- The use radiation technology for environmental protections becoming

increasingly important.

Irradiation-disinfection of municipal sewage sludge offers the obvious benefit of

eliminating potentially harmful organisms to allow waste to be recycled. In cases where

sludge meets regulatory requirements for fertilizer or soil conditioner use or fed

13

supplemented use sludge irradiation-disinfection may be the most environmentally and

economically sound solution. It can help free-up valuable landfill and incinerator capacity

recycles sludge into a useful soil product, reduce plant-operating costs.

The benefits of sludge utilization, rather than disposal are being realized to a limited

degree through land application and composting. The cost effective and reliable

elimination or reduction can be a stumbling block to achieving more successful

utilization. Ionizing radiation was selected because of its potential to provide multiple

benefits with regard to wastewater treatment and sludge management.The ability of

ionizing radiation to compete with chemical treatment based on performance standards

has been acknowledged, and economic analyses confirmed that radiation techniques for

waste treatment are competitive with existing advanced treatment technologies (Maloof

1988, McKeown, 1996).

The use of radiation as a multipurpose treatment tool within a wastewater treatment

facility has the potential to beneficially impact several aspects of operation. For instance,

the ability of irradiation to eliminate toxic chemicals and break down recalcitrant

organics is well known, therefore, it is expected that irradiation will (a) facilitate

biodegradation,(b) enhance sedimentation to produce solids that thicken

readily,(c)increase process loading rates by enhancing sludge conditioning

characteristics, and(d) reduce waste sludge volumes by controlling the excessive growth

of filamentous bulking organisms, without large amount of chemical polymers that add

mass.

1.4.2.3 The disadvantages

The perception of higher capital costs than others techniques, more training and safety

precautions for operators and concern about reliability of source of irradiation. Radiation

technology has uniform occupational safety standards in all countries and on the other

hand, the competitive technique using ethlene oxide (Etox) is applied with varying

degrees of safety standards in countries at different stages of industrial development, the

main problems associated with the use of (Etox) are risk to operating personnel, risk to

patients due to residues, and risk to general population due to environmental problem.

14

1.5 The radiation chemistry theory

The radiation chemistry may be defined as the study of the chemical effects produced in a

system by absorption of ionizing radiation. Included this definition are the chemical

effects produced by radiation from radioactive nuclei (a, [3 and y-rays), by high- energy

charged particles (electrons, protons, deuterons, etc.) and by electromagnetic radiation of

short wavelength less than about 250A (i.e., with an energy greater than about 50 electron

volts).

Electromagnetic radiation of rather longer wavelength, in the ultraviolet and visible light

regions of the spectrum may also initiate chemical reactions, though in this case

ionization does not occur and reaction is brought about via electronic excited species.

The high energy photons and particles are not selective and may react with any molecules

lying in their path, raising it to any one of its possible ionizing or excited states. The

radiation chemical reaction may be complicated further by effects due to the high initial

concentration of ionized and excited species in the tracks, particularly in the liquid and

solid phases.

Ions and excited molecules are also formed by electric discharge in gases and give rise to

chemical effects similar to those produced by ionizing radiation. However, it is not

simple matter to measure the energy transferred to the active species and experimental

results are qualitative rather than quantitative; they are generally treated separately from

radiation chemistry.

1.5.1 Chemical effects of ionizing radiation

The radiation sources used in radiation chemistry studies can be divided into two groups:

those employing natural or artificial radioactive isotopes and those which employed

particle accelerators. The first group includes the classical radiation sources, radium and

radon, and also the more recently discovered and used artificial radioactive isotopes such

ascobalt-60 (Co-60), casesium-137, and strontium-90.

The radioisotope most commonly employed in industrial applications is Co-60 which

undergoes |3-decay with l/2 = 5.2 year emitting two gamma photons of energy 1.17 and

15

1.33 MeV. With this energy the Compton Effect is prominent and for materials made of

atoms with low atomic number (C, H, N, O, etc..) is essentially the only significant

mechanism of interaction in water. The Compton Effect is prominent importance between

0.1 and 4 MeV.

Gamma-rays are electromagnetic radiation of nuclear origin with short wavelength in the

region of 3x10"9 cm to 3x10"" cm. It is more convenient to describe the radiation in terms

of energy than wavelength since it is absorbed from the radiation that is basically of

interest, and the relationship between them is given as follow in:

E = hcA. (1.1)

Where h is Planck's constant, c is velocity of light and A. is the wave length. According to

this relationship, energy range of gamma-rays becomes approximately 40 KeV to 4 MeV.

The y-rays emitted by radioactive isotopes are either monoenergetic or have a small

number of discrete energy (e.g: Co-60 which gives equal numbers of y- photons of

energy 1.3332 and 1.173 MeV).

Unlike a & (3 particles, which lose their energy gradually through number of small energy

transfer, y-rays tend to lose the greater part of their energy through a single interaction.

The result is that whereas monoenergetic a-particles and electrons are showed down by

thin absorbers rather than absorbed in the same situation. Parts of the incident y-rays are

completely absorbed but remainder are transmitting through a sheet of absorbing material

as shown by (eq. 2):

N = Nie"llx (1.2)

Where Nj is the number of incident photons, x is the thickness of the absorber, and u. is

the total absorption coefficient of the material. Gamma-rays have not a definite range in

the matter; so another concept; the half-thickness value (half-value thickness) often used

to relate the photons transmitted by one half. It can be calculated from (eq.2) if the

absorption coefficient is known (the half value layer 0.963/u.).Some of the half-thickness

values for coball-60 and cesium-137 of y-rays are given in Table 1.1.

16

Table 1-1: Half- value thickness for gamma (Nelms, el al., 1956)

Isotope

Caesium-137

Cobalt-60

Density

absorber

Photon energy

MeV

0.66

1.25

Half- value thickness (cm)

Water

8.1

11

1.0

aluminum

3.4

4.6

2.72

Concrete

3.8

5.2

2.35

Lead

0.57

1.06

11.34

An indication of the linear rale of energy loss by a charged particle and the density of

ionization in the particle track is given by the specific ionization, the total number of ion

pairs produced in a gas unit length of track. The specific ionization includes both ions

produced in the primary particle track and those produced by a-rays.

Linear energy transfer (LET) is thus can be defined as, the linear-rate of loss of energy

(locally absorbed) by an ionizing particle traversing a material medium (ICRU, 1959),

and a rough average value calculated by dividing the total energy of a particle by its path

length. Several factors contribute to the roughness of this average value. In the llrst place,

the rate of energy loss by a particle changes as it is slowed down, and the LCI" will vary

at different positions along the track. Secondly, energy lost by the primary particle in a

particular section of the track is not necessarily absorbed locally but may be transferred in

part to a- rays or to secondary electromagnetic radiation.

y-and X-ray transfer all their energy to the medium through secondary electrons having a

wide range of energies and LET.

Table 1.2 gives average values for the Linear Energy Transfer (LET) of the secondary

electrons produced by the absorption of y-radiation in water, which are calculated using

an average energy for the secondary electrons. Gamma-rays does not form a track of

charged particles and hence the LET is not directly applicable to the y-radiation itself.

In addition to absorption by matter both u and [3 particles and electromagnetic radiation,

from the point sources decrease in intensity as the square of the distance from the source

as this distance is increased, this is the familiar inverse square relationship of photometry.

The absorption of radiation by matter and the decrease in intensity with distance may be

treated independently.

17

Tabic 1-2: LET values for gamma-radiation (Nelms, el «/.1956)

Isotope

Caesium-137

Cobalt-60

Photon energy (MeV)

0.66

1.25

Average LET in water (KeV/u.)

0.39

0.27

As a matter of Tact, it is essential to an understanding of radiation chemisry phenomena,

the basic knowledge of the processes by which ionizing radiation interact with matter,

since the chemical effect are direct consequence of the absorption of energy from the

radiation. In this section the principle interaction of ionizing radiation (electromagnetic,

in particular), with matter will be outlined.

Unlike charged particles, which generally lose energy almost continuously through a

large number of small energy transfers as they pass through matter, photons of

electromagnetic radiation tend to lose a relatively large amount of energy whenever they

interact with matter. However, not all incident photons will interact with any finite

thickness of matter, and those which do not interact suffer no change and are transmitted

with their original direction and energy. The effect of the absorbing matter (neglecting for

the moment the photons which do interact) is therefore to reduce the number of photons

transmitted, and thus to reduce the intensity of the radiation passing through it. By

intensity are generally ergs per square centimeter per second.

The reduction in electromagnetic radiation intensity (dl) on passing through a small

thickness (dx) of absorber is given by:

dl = -I, M dx (1.3)

Where 1; is the initial intensity of the incident radiation and LI is the total linear absorption

coefficient (unit cm"1) of the material. The linear absorption coefficient is thus the

fraction of the incident. Photons are directed from the incident beam by unit thickness of

absorber; it is a constant for a given material and for radiation of a given energy but

varies from material to material and for different photon energies.

The total absorption coefficient is the sum of a number of partial coefficients representing

various processes of absorption. These processes include; the photoelectric effect, the

18

Compton Effect, pair production, coherent scattering, and photonuclear reactions. The

first three of these processes are the most importance; each process depends very much

on the photon energy and the atomic number of the stopping material.

a. The photoelectric effect

Low-energy photons are absorbed mainly by photoelectric absorption. In this type of

interaction the entire energy of the photon (II0) is transferred to single atomic electron,

which is ejected from the atom with energy equal to the difference between the photon

energy and the binding energy (Eg) of the electron in the atom:

EC = E°-EB (1.4)

In photons with low energies, the electrons are ejected predominantly at right angles to

the direction of the incoming photon, but as the energy increases; the distribution shifts

increasingly toward the forward direction. Energy and momentum must be conserved and

this is made possible by the recoil of the reminder of the atoms, so that photoelectric

interaction is not possible with free electrons.

If the incident photon has sufficient energy, it is generally the most tightly bound electron

in the atom that is ejected (i.e. an electron from the K. shell). Interactions with K-

electrons account for about 80% of the photoelectric absorption for photons with the

energies greater than the K-shell binding energy; most of the reminder of the interactions

are with L-electrons. The vacancy created by loss of an electron from an inner atomic

shell will be filled by an electron from an outer shell, with emission of characteristic X-

radiation (fluorescent radiation) or of low energy Auger electrons.

Photoelectric absorption is most probable for high atomic number materials and for low

photon energies.

b. The Compton Effect

In the Complon Effect a photon interacts with an electron, which may be losely bound or

free, so that the electrons is accelerated and the photon deflected with reduced energy.

The energy and momentum of the incident photon are shared between the scattered

photon and the recoil electron. The direction in which the electron recoils is

19

predominantly that of the incident photon, and is more nearly so the higher the fraction of

the photon energy it carries away and the higher the incident photon energy.

c. Pair-production

Pair production involves the complete absorption of a photon in the vicinity of an atomic

nucleus or, less frequently, an electron with the production of two particles, an electron

and positron. The energy of the photon less the rest energies of the two particles is

divided between the kinetic energy of the electron and positron (the small amount of

energy transferred to the nucleus is nearly always neglected).

Momentum is shared by the recoiling nucleus. The positron is in a similar manner to an

electron and eventually combines with an electron, the particles being replaced by two

0.51 MeV y-rays (annihilation radiation) emitted in opposite directions.

tl. Photonuclcar reactions

At energies about 8 MeV for high-Z materials, and in the region of 10 to 20 MeV for

low-Z materials, photons have sufficient energy to eject a neutron from the nucleus of an

atom. The cross-section of these reactions is zero for photon energies below the binding

energy of the particles and then generally small compared with the Compton and pair

production cross-section at the same energy, through the neutrons which are ejected may

be significant in practice because of their considerable range.

Natural lead, for example can undergo a (y, n) reaction with threshold energy of 7.9

MeV. The photonuclear cross-section shows a maximum at 13.7 MeV and at this energy

has a value about 4.3% of that for the combined Compton and pair production processes.

1.6 Water Radiolysis

As it has been mentioned before, the primary effect of high energy radiation is ionization

and to some extent excitation of the atoms and molecules. The radiations release

gradually their energy through the medium giving rise to a track of reactive species (ions,

excited molecules, radicals, electrons) whose reactions are responsible for irreversible

chemical transformation of matter radiolysis (TCEO, 2004).

20

H20

Ionizing Radiation

Excitation

1 H.O*

+H20 •

i r+oir

-rH20 <—

Oil

Ionisation

I UJX +e

+H20

*- ntn

+H30+

Fig.1.1: Formation of free radical species in water by means of ionizing radiation

Although, wastewater is usually characterized by rather high solute concentrations as

compared to ground or drinking water with regard to the effect of ionizing radiation

wastewater has also to be classified as dilute aqueous solution. When dilute aqueous

solution are irradiated practically all the energy absorbed is deposited in water molecules

and the observed chemical changes are brought about indirectly via the free radical

species formed in water by so-called water radiolysis. Direct action due to energy

deposited directly in solute is generally unimportant in dilute solutions. The effect of

ionizing radiation on water, which is known to result in the formation of molecular

species and free radicals, as well as some ions. For pollutant decomposition and

microorganism inactivation, respectively just the free radical species are of interest. The

21

differences between pollutants and microorganisms are more dominating; a discussion

concerning the effect of free radicals must be performed separately.

The free radicals formed during water radiolysis are highly reactive, the OH radicals are

the most powerful oxidant known to occur in water, and the same is valid for the

hydrated electron e~aq as recluctant. In consequence these radicals do not only react with

target pollutants but also with many other solutes contained in the water, even with some

inorganic ions like bicarbonate and nitrate.

As a sequence of the interaction between ionizing radiation (electrons y-rays) and water

electronically exited and ionized molecules are formed. Subsequently this leads to the

production of several very reactive primary species' (OH, e"aq, IT) and molecular

products (Hi, H2O2).

In the presence of oxygen in water the reducing species, H-atoms and the "solvated

electrons" (e"aq) are converted into oxidizing species, perhydroxyde radical anions (0%),

the last one together with the OH -radicals can initiate degradation of water pollutants

(GetolTNikola, 1995)

The ionizing radiation interacts with matter in two ways: directly and indirectly. In direct

interaction, the ionizing radiation interacts with critical molecules like DNA and proteins

present in the microorganism causing cell death. During indirect interaction, radiolysis

products of water results in the formation of highly reactive intermediates which then

react with the target biomolecules culminating in the cell death.

H20 — • OH', IT e"ai„ H2, H2O2

OH', 11, e"lK| + DNA (in microorganism) —> Damage to DNA,

Present of oxygen is important in the process as the oxygen is a known radio-scnsilizer

which helps in fixing the radiation damage done to cells thereby inhibiting theirself repair

mechanism and resulting in inactivation of the microorganism (Pikaev el al., 1997).

Both cobalt-60 and cesium-137 produce gamma photons which could be used for the

treatment of sewage. Two cause's results to use cobalt-60 irradiation, both of which

result from gamma photons, which is activate chemical molecules and typically cause

ionization to occur by the interaction with the orbiting electrons. As a result, small

molecules may be broken into shorter chains and/or so activated that the potential for

v)

chemical reactions is increased. In the connection with this effect, the gamma photons

also produce ozone, peroxide, hydroxide ions, and oxygen ions in even pure water.

These products of irradiation are very strong oxidants the result of the ionization and

absorption of energy into the molecular chain structure in the resent of the production of

the oxidants produce possible synergistic effects that result in a breakup of the chemical

molecular structures and the killing of bacteria and irradiation is only economically

practical way of treating a fluid to kill viruses and have the fluid remain usable. Gamma

irradiation has been more widely used in wastewater treatment applications (Borrely et

al., 1998; Gehringer and Eschweiler 1998; Graino and Magnavacca, 1998) for both

radiation sources (gamma and electron beam), energetic photons interact primarily with

the water in the activated sludge matrix. The radiolytic ionization of water is represented

by the following (Waite et al., 1997).

H2-> OH + e"aq + IT + H202 + H2 (g) + H30+

Only the observed radiation energy can initiate physical, chemical or biological effects.

The energy absorption in a medium e.g. water, takes place in l()"15 s. In the course of

which the dose distribution is not uniform because of electron scattering and the "build

up" effects occurring during the interaction between radiation and matter.

1.7 Literature Review

El-Motaium (2000a) has reviewed nuclear techniques (gamma radiation and electron

beam) which have been recently introduced for sewage sludge treatment. These methods

are gaining worldwide recognition as a means of pathogen disinfection, organic

pollutants degradation and improving sewage water quality. The use of gamma radiation

and electron beam has proved to be more effective in sewage sludge treatment than the

conventional methods. Ionizing radiation has been recognized as a fast and reliable

means for pathogen removal by several authors (e.g. Kapila et al. 1981; Pandya et al.

1987; El-Motaium et al. 2000b; Abo-Elseoud et al. 2004). Sufficient data are available

for gamma radiation treatment of sludge, permitting its application on commercial scale.

The possibility of beneficial and safe recycling of gamma-irradiated sludge in agricultural

uses was documented by Chang (1997). He has indicated the occurrence of faecal

23

pollution and the presence of microbial pathogens. It has been concluded that Faecal

coliform could be used as reliable indicator for bacterial pathogens. Also he concluded

the reduction of pathogens in sewage sludge by radiation is a function of the absorbed

dose and may be described by first order reaction. He has reported the mechanism by

which gamma radiation induces ionization in biological tissue resulting in the production

of free radicals that cause denaturation of cell protoplasm damage cause inaclivation of

most pathogens, being single-cell organisms.

Ascaris eggs are frequently used as an indicator organism to test; El-Motaium et ul.

(2005) investigated the efficiency of a particular treatment. The lethal dose was found to

vary between the two types of radiation; lower dose of gamma radiation was required

relative to the electron beam to achieve the same pathogen removal. The effectiveness of

irradiation in destroying pathogens in sludge has also been studied by several researchers

(e.g. Trump et al. 1984); Hurley et cd. 1979 and Sivinskl983). Moreover, the heavy

metals are less available for plants from irradiated raw sludge (Kirkham 1980). Also,

Farag and El-Mongy, (1993) proved that irradiation disinfection of manure, for example

cow and poultry manure, offer the obvious benefit of eliminating potentially harm fill

organisms and can be used as ingredients in livestock feed. This would minimize the risk

of pathogenic organisms, environmental pollution and may offer economical returns. In

general, doses of 5 to 20 KGy inactivate most of the bacterial pathogens and

helmiminthic parasites.

Gauthier and Archibald (2000) found that coliform bacteria have long been used to

indicate of fecal contamination of water and thus health hazard. The fecal streptococci

(entcrococci), alternative indicator of fecal health hazards, were common in all mills in

the absence of sewage whereas salmoncllas were not found. Therefore, they

recommended the use of total coliform, fecal coliform, enterococci, or E. coli counts as

indicators of fecal contamination.

Irradiation-pasteurization of sludge can be carried out in gamma irradiator with cobalt-60

source, which emits gamma rays. These rays penetrate and pass through the sludge,

Inactivating microorganisms and decomposing various organic compounds without

24

leaving in any residual radioactivity or making the sludge radioactive. These technologies

of irradiation-pasteurization have been shown to be quickly, efficiently and reliably deal

with potential health hazards materials in sewage sludge (Farag et al. 2007).

According to the results reported by Al-Ani and Al-Khalidy (2006), irradiation by

gamma radiation with doses ranging from 100 to 500 Krad was proved to be efficient in

reducing some of the physical contaminants. The organic contaminants were degraded

and reduced to about 12% of their original concentrations. Authors concluded that

irradiation technology could effectively modify the characteristics of the wastewater to

such levels that arc compatible with Iraqi disposal standards. However, experimental

pilot plant study is required to optimize the cost of wastewater treatment through the use

of this technology. Rawat et al. (1997), was also observed that a gamma radiation dose of

2 KGy could effectively reduce the coli form load in raw sewage to acceptable safe levels

of less than 100 CFU/ml. The treated effluents from the primary and final settling tanks

were found require lower closes of radiation as the initial microbial load in the treated

effluents was low compared to that in the raw sewage. Recycling municipal sludge by

gamma radiation may offer economical returns. Several authors have discussed the

relative costs of sludge irradiation (Hurley et al. 1979, Ballantine 1978, Piccinini et

a/. 1982).

An experiment was conducted At Virginia key wastewater plant in Miami to study the

efficiency of gamma radiation in reducing the microbial load in the chlorinated effluent

and dewatered sludge by Abdel Karem el al. (1996). In the chlorinated effluent, total

counts faccalis were eliminated with 2 KGy while I KGy was sufficient to eradicate total

col'iform. Regarding the dewatered sludge, a dose of 6 KGy was quite sufficient to

decrease total counts from 6X10^ to few cells/g. whereas total coli form could not be

detected after irradiation with 2KGy. Another experiment was carried-out to compare the

effect of gamma radiation with that of electron beam on microbial groups in chlorinated

effluent. At any given dose of radiation, gamma rays proved to be more lethal than

electron beam for all types of organisms. On the other hand, Streptococcus faecalis

revealed to be the most resistant bacterial indicator since complete elimination of these

bacteria could be attained at 4 KGy while 2.5 KGy level was quite sufficient to eradicate

25

coliform bacteria including the fecal types. They stated that the 4 KGy radiation dose is

convenient level sufficient to destroy pathogenic bacteria present in sewage.

Watanabc and Takehsa (1984) recommended that 5 KGy dose could be considered as an

adequate disinfection dose. Ahlstrom (1985) demonstrated that irradiation is an effective

means for reducing pathogens in sewage sludge to levels where sludge reuse in public

areas meets criteria for protection of the public health. Raw domestic wastewater contains

about 10 coliforms per 100 ml and some 10" helminthes eggs per liter where helminthes

infections are prevalent (Mara and Cairncross, 1989).

In a study, at Zenein station at Egypt, (EL-Fouly el al. 1996) reported microbiological

analysis which was carried out for an extended period of time and found that treating

wastewater with gamma radiation may contribute, in one step, the disinfecting sewage

effluent and poudrctte from pathogens. Me found that the counts of total microorganisms

and those of specific microbial groups in the already treated wastewater at the outlet of

the station were quite comparable to those detected in raw sewage at the inlet. From

which he slated that sewage treatment in this station is insufficient. Radiation treatments

which he applied on effluent and on poudrette showed that the lethal effect of gamma

rays on the different microbial groups under investigation increased with increasing the

radiation dose.

Research activities in different countries have demonstrated that inactivation of fecal

coli-fonns in secondary effluent from municipal sewage can be obtained with doses less

than 1 KGy. While conventional disinfections are adversely affected by the water matrix,

radiation processing for bacteria inactivation is generally unaffected by matrix.

Therefore, radiation processing has a clear advantage over the existing methods for

municipal wastewater disinfection (IAEA, 2004).

Application of irradiation together with any of the other lethal factors, particularly the

ilevaled temperature and the addition of chlorine proved to be very effective in

eradicating bacterial indicators in sewage. A dose of 2 KGy was found quite effective if

sewage was heated to 50 °C or treated with 3 ppm chlorine. Radiation doses of 0.5 and

26

1.0 KGy were similarly effective in presence of 6 and 10 ppm chlorine, respectively (EL-

Fouly <;/«/. 1996)

Scott el al. (1985) and Tsuru (1979) demonstrated that irradiation is an effective means

for reducing pathogens in sewage sludge to levels where sludge reuse in public areas

meets criteria for protection of the public health. It is known that conventional composts

contain I02 to 104 count/g of total coliforms, but the compost made from irradiated

sludge dose not contain coli form at all. In a report made by, Brandon el al. (1977) it was

indicated that the apparent D|0 value (the amount of irradiation required to inactivate 90%

of a population of a particular organism or group of organisms) for total coli forms in

dried raw sludge varied from 17 to 353 KRad. However, in liquid sludge the Dio value

for coliforms was consistently 20 to 30 KRad. Also found to be inactivated by 30 KRad

as Salmonella species in liquid digested sludge.

Richard el al. (1981) determined the radiation inactivation rate of several classes of

indigenous microorganisms in dewatered raw sludge. He found that the indigenous fecal

streptococci were quite resistant lo ionizing radiation in sludge expected. However, their

resistance decreased some what with dewatering. The largest effect he found was with

salmonella typhimurium, whose radiation resistance approximately doubled in dried

sludge. However, he did not find excessively large Dm values for any bacterial species

tested.

The feasibility of using l0Co gamma irradiation to inactivate total coliforms, fecal

coliforms, Escherichia coliform, in hard-shelled clams, Mcrcenaria merccnaria, was

investigated by Ilarewood el al. (1994). 'Hie results of the three trials made indicated

average Dm values of 1.32 KGy for total coliforms, 1.39 KGy for fecal coliforms, 1.54

KGy for E. coli,. Irradiation doses of > 0.5 KGy were significantly found lethal to the

shellfish.

Various methods of sewage and sludge disinfection which are commonly used, like

conventional sewage-treatment plants, thermal disinfection, composting of sewage or

chlorination, all have one or more disadvantage (Hejkal el al. 1979, 1981;

27

Krishnamurthy, 1980; Russ & Yanko, 1981). One of the recent methods of rendering

sewage and sludge free of pathogens is the use of ionising radiation (Epp, 1975;

Wizigmann & Wiiursching, 1975; Brandon, 1976; Brandon et al. 1977; Ward, 1977,

1981; Suess et al. 1983; lya & Krishnamurthy, 1984). Earlier it was that reported that, the

use of ionizing radiation is one of the recent methods of rendering sewage free of

pathogens (Kapila et al. 1981; Pandya et al. 1987). Gamma irradiation of sewage sludge,

besides removing harmful pathogenic organisms, might also lead to changes in its

physical and chemical properties (Suess et al. 1983).

McCaslin and Sivinski (1980) found that 1 Mrad of gamma irradiation effectively

destroys pathogenic bacteria and parasites in dried sewage sludge. The Dm for total

coliform was found to be higher, 0.50 KGy, using electron beam than using gamma

radiation, 0.25 KGy (El-Motaium et al. 2005). The Dio for total coliform in sludge was

found 0.67 KGy using gamma radiations (El-Motaium et al. 2000). Virus was found to

have relatively high resistance to inactivation by ionizing radiation (Chang, 1997). The

Dio value was found 2.5 KGy for virus inactivalion in sewage sludge. The results

reported by Tree et al. (2003), clearly conllrmed that enterococci were more resistant to

chlorination than E. coll and that both were more rapidly inactivated than the viruses

examined. The potential for usage of ionizing radiation for destruction of pathogens in

sewage has been reviewed (Piadong 1992; Phillip 1999).

The reuse of irradiated sewage water and sludge is environmentally safe for recycling in

agriculture. Irradiated sewage sludge proved to be a good organic fertilizer for sandy and

calcareous soils without any need to mineral fertilizer. Irradiated sewage sludge

resemble a slow release fertilizer capable for sustaining crop production without harming

the environment (El-Motaium, 2006)

McKinney and co-workers (1958) reported that the survival of Salmonella in sludge in

seeded bench-scale digesters was dependent on the density of the initial population,

available nutrients, and detention time. Brandon et al. (1976) investigated that regrowth

of Salmonella species can occur, even in material that consists of as much as 60% solids.

Reduction of bacteria and E.coli in sludge was rapidly carried out with irradiation dose

28

by Joo Lee, et al. (2002). Within irradiation close of 3 KGy large portion of

microorganisms was found to become inactive.

The sensitivity of enrichment procedures may have been similarly limited. For example,

only one Shigella organism was recovered from the attempted Shigella isolations. Wang

el al. (1966) found that temperature was a vital factor in determining the probability of

Shigella survival in sewage treatment, with higher temperatures decreasing survival. The

recovery of only a single isolate from digested sludge is therefore not surprising.

In study conducted by Bachir el al. (2003), samples of concentrated municipal sewage

sludge, stored for 2, 4 and 6 months, with different moisture contents were exposed to

different doses of gamma irradiation. The results indicated that in all tested sewage

sludge samples, bacterial pathogens including Ilnterobacter sp., Salmonella sp., and

Escherichia coli were initially detected. Al l doses reduced the total counts of

microorganisms. Dio of total count decreased with increase in the moisture content of the

sewage sludge, therefore the cost per unit could be decreased to half when wet sewage

sludge (about 50% moisture) was used.

Suess and Kesscl, 1977, Waite et al. 1997, Sedlacek, 1985, Maloof 1988, Chaychian et

al. 1997. It has also been demonstrated that ionizing radiation can alter the physical

properties of wastewater sludge particles to enhance dewater ability and biodegrability

through the action of radiation - induced free radical chemistry (Etzel et al. 1969;

Sedlacek el al. 1985; Kurucz et al. 1991; Wang 1993 ;). Pardya et al. (1989) suggested

that gamma radiation induced inactivation of toxic substance(s) in sludge.

Ionizing radiation was selected by several authors because of its potential to provide

multiple benefits with regard to wastewater treatment and sludge management. At doses

from 2-6 KGy, irradiation has been used successfully to achieve a variety of treatment

objectives, including toxic chemical destruction (Meeroff et al. 2004; Kurucz et al. 1995;

Cooper et al. 1992), flue gas treatment (Frank 1995), The ability of ionizing radiation to

compete with chemical treatment based on performance standards was acknowledged,

29

and economic analyses confirmed that radiation techniques for waste treatment are

competitive with existing advanced treatment technologies (McKeown 1996).

Farooq el al. (1993) examined the sensitivity of a wastewater population of total

coliforms present in raw sewage and secondary effluent after irradiating with similar

doses delivered by a high-energy electron beam and gamma -radiation. The electron

beam study was conducted on a large scale at the Virginia Key Wastewater Treatment

Plant, Miami, Fla. The reduction of test organism was observed at an electron beam dose

of 500 KRads, while at reductions were observed at the same dose utilizing the gamma-

source.

Mecroff el al. (2004) analysis of beneficial effects from preliminary studies and pilot

tests demonstrated that a dose of 2-3 KGy would be potentially successful for bulking

control and to a lesser degree enhanced thickening and radiation-assisted anaerobic

digestion (Daniel el al. 2004).

Giuliani el al. (2005) implemented irradiation of municipal sludge for safe disposal and

agricultural use. They reported thai the process parameters were adjusted to effectively

eliminate coliform bacteria in the sludge and to prevent their re-growth. Irradiated sludge

was found to be free of fecal coliform and could be directly disposed after drying in a

landfill or used as manure. AFRA (2006) with an increased interest in the utilization of

sewage for agriculture, an evaluation of the effect of sewage treatment processes on the

survival of intestinal parasites of great public health importance. I lala (2000) indicated

that at sewage plant in Sudan, hookworms and Ascaris were the most occurring parasites,

whereas others were found rarely and reflected that transmitted helminthcs diseases in

this area were mainly due to Ascaris and hookworms

Pikaev (1997) found that 3-5 KGy of ionizing radiation was adequate to completely

inactivate pathogens in sewage sludge. A dose of 10 KGy is required by USIZPA (1993)

for Ascaris ova elimination from sludge. Brandon (1979) indicated that 1 mRad was a

sufficient dose to ensure the inactivation of Ascaris eggs naturally present in digested

sludge filter cake and in composted sludge. Suess (1977) has reported a dose of 3 KGy

30

for sludge decontamination but Takehisa (1980) and Hashimoto el al. (1988) found that 5

KGy was the appropriate disinfection dose for dewatered sludge. Ascaris sum (the

roundworm of pigs) has eggs that are morphologically indistinct from those of the human

parasite Ascais lumbricoides and the life-cycles of the parasites are very similar. Since,

the eggs of Ascarids are more resistant to sewage treatment processes than those of other

helminthes (Carrington, el al. 1991). For parasites one criterion for safe sludge disposal is

the viability of Ascaris sp ova have therefore been chosen as "indicators" for inactivation

studies. These pathogens can be destroyed by high temperature (Pike et al. 1988) or

chemical means lime treatment (Scliuch el al. 1985).

One criterion for the safe sludge disposal is the viability of Ascaris sp. eggs (thick-shell

nematode eggs) which is ubiquitous and relatively resistance to most forms of treatment

(Enigk el al. 1975; Holl 1975). Therefore, it has been chosen as " indicator" for

inactivation studies (e.g. Geller, 1982). Horak (1993) using accelerated electrons, after 8

weeks of incubation the morphological and developmental status of eggs was determined.

And the destruction of embryos within eggs was observed at doses over 1.1 KGy.

Untreated wastewater sampled from Damascus sewage water treatment plant containing

nematode Ascaris lumbricoides ova were treated using gamma irradiation by Shamma el

al. (2002) at doses between 1.5 and 8 KGy. Immediately after irradiation morphological

and developmental status of eggs was examined microscopically. These eggs were

incubated for 8 weeks after this period no larvae were observed. Capizzi et al. (1999)

have investigated that the efficiency of radiation treatment to destroy Ascaris ova

viability and found that no ova were viable after exposure to 0.75 KGy (D90 at 0.39).

Although, the outer coat of the Ascaris ovum had a protective effect at low doses (0.20

KGy) no difference in ova viability was observed at 0.30 KGy.

The sensitivity of Ascaris sum to radiation was reported by Seivinski (1975), Yeager and

Ward (1980) and Brandon (1978) who used doses of 0.95, 1.0 and 1.5 KGy, respectively,

However, in conflicting reports on the radiation sensitivity of Ascaris ova, higher doses

were recommended by Keller (1983), Hess and Breer (1976) and Heuer and Hofmann

31

(1979) who used over 3.0 KGy. Burger et al. (1978) and Enigk et al. (1975) established

that doses of 4.0 and 4.8 KGy respectively, are necessary for the destruction of ova from

Ascaris species. It is probable that the differences in radiation sensitivity of such Ascaris

ova could be explained by the different types of sludge in which the ova were irradiated.

The most important factors affecting the viability of the eggs at one of the treatment

plants were exposure time and solid content, while other factors showed no statistically

significant influence. Results of the other treatment plant showed that, besides exposure

time and solid content, sludge pH, drying bed temperature and air temperature were

significantly affecting the viability of the eggs (Plachy and Juris, 1995).

Gamma-rays effectively disinfected microorganisms and completely removed them at a

dose of 0.3 KGy (Jung et al. 2002). The combination of gamma-rays and titanium

dioxide significantly improved the treatment process.

Ahlstrom (1985) found that irradiation did not increase the extractability and plant uptake

of a broad range of nutrients and heavy metals from sludge-amended soils. This finding

was supported by the results of rZI-Motaium and Badawy (2000) in Egypt, however, more

studies are required in order to quantify this finding and understand the mechanisms

involved.

Katzenelson et al. (1976) described risks of communicable disease infections associated

with usage of waste water irrigation in agricultural settlements and illustrates the

necessity for improved technology to minimize pathogen hazards in recycling sewage

products to agricultural usage. The production of sludge clearly varies with the type of

processing. Primary treatment produces 80 g/d of raw sludge solids per capita, primary

plus secondary produces 120 g/d and primary plus secondary plus tertiary produces 150

g/d(Gazso, 1991).

Electron beam irradiation for effluent reclamation represents a true alternative to

chemical and UV treatment, as compared to chemical disinfection it proved to be a clean

technology without formation of hazardous by -products; as compared to UV irradiation

electron beam irradiation is technically much more simple, almost insensitive to color,

32

suspended soils or gas bubbles in the effluent stream, and moreover, to effluent

composition and fouling characteristics, respectively (IAEA, 2003).

The physicochemical parameters of the effluents such as electrical conductivity, total

hardness, biochemical oxygen demand (BOD) and dissolved oxygen remained largely

unaltered after exposure to gamma irradiation. These effluents could hence be gainfully

employed in agricultural practice after radiation disinfection (Rawat el al. 2002). The

improvement of the quality by determining the changes in organic matter as indicated by

the measurement of biochemical oxygen demand (BOD) and total organic carbon (TOC).

Sludge were obtained from a Riyadh wastewater treatment plant and studied using a

laboratory scale 60CO gamma (Basfar el al.2002). Similarly, it was demonstrated by the

reduction in bacteria and BOD, provided adequate disinfection while increasing the water

quality. A dose of 1 KGy resulted in reduction of 99.8% of the total coliform. For fecal

coli form a dose 1 KGy resulted in a reduction of 99.3%.complete in activation of both

total and fecal coliform with no regrowth was achieved at a dose of 1.3 KGy. For both

samples (before and after chlorination) the 5-day BOD5 was measured resulted in a

reduction of 23% and 24% at 4kGy. The reduction at 4 KGy was significant as this was

the close that has been shown to the target for waste water disinfection using the electron

beam process (Faroog el al. 1993).

A pilot plant was developed for the reclamation and reuse of secondary effluent from a

sewage treatment plant. Gamma-irradiation showed effective organic contaminant

decomposition and this resulted in the reduction of 5-day biochemical oxygen demand

(BOD5), color, chemical oxygen demand (CODs) and total organic carbon (TOC). The

average reduction in BOD5, TOC, which was obtained after 12 operations, was 52, and

67, respectively. The Environmental Protection Authority (EPA) sets the standards for

water quality for water being discharged, generally for BOD5 < 20 mg/E, 80% of the

time (Plachy and Juris, 1995). Jung el al. (2002), reduced BOD by 85% irrespective of

absorbed dose and the removals of COD were 64%, at a dose of 15 KGy.

It has been demonstrated that ionizing radiation can alter the physical properties of

wastewater sludge particles to enhance dewaterabilty and biodegradability through the

action of radiation-induced free radical chemistry (Etzel el al. 1969; Kurucz et al. 1991;

33

Waite et al. 1997; Sedlacek 1985; Wang 1993). Joo Lee et al. (2002) studied the radiation

effects on the physical characteristic of the sewage sludge in order to obtain information

which will be used for study on the enhancement of the sludge's dewaterability. Water

content in sludge cake could be reduced by irradiation at the dose of 10 KGy. Several

researchers have recently studied the radiation technology to reduce water in sludge cake

but most of the radiation processes have been focused on eliminating the organic and

biological contaminants of sludge. Aurelie et al. (2003) carried out the fundamental study

on radiation effects based on enhancement of sludge dewaterability and evaluated the

physical characteristics of sludge affecting dehydration. Suss et al. (1983) found that

gamma irradiation of sewage sludge, in addition to removing harmful pathogenic

organisms; can lead to changes in physical and chemical properties.

Brandon (1979) evaluated the different methods of sludge stabilization and found that

aerobic and anaerobic digestion are not very effective in reducing pathogens, lime

treatment requires that a high pH be reached and maintained, heat treatment was effective

but expensive and energy intensive, composting require all of the composting sludge

reached an adequate temperature for pathogens inactivation. It was obvious that

irradiation of sewage sludge ensure the safe recycle of sewage sludge.

El-Gohary et al. (1995) have employed conventional techniques used in water and

wastewater treatments can produce high quality water; however, the application of these

techniques to reclamation in a large scale is limited due to economic and maintenance

problems. On the contrary, radiation treatment using gamma-rays or electron beams is a

simple and efficient technique that can remove a wide variety of organic contaminants

and disinfect harmful microorganisms as well (Borrcly et al. 1998). Radiation techniques

have been widely studied to purify natural and polluted drinking water and to disinfect

sewage sludge, but application of this technique to the reclamation of sewage effluent is

not well developed because the water usually contains high concentrations of various

pollutants (Pikaev, 1997). ncreasing amount of sewage sludge; more legislative

regulation of its disposal have stimulated the need for developing new technologies to

process sewage sludge efficiently and economically (Wang et al. 2007). One ideal

consideration is to recycle it after proper treatment. Radiation technology is regarded to

34

be a promising alternative for its high efficiency in pathogen inactivation, organic

pollutants oxidation, odor nuisance elimination and some other characteristics

enhancement, which will facilitate the down-stream process of sludge treatment and

disposal.

The ionizing radiation treatment of sewage and redundant activated sludges at doses

ranging from 5 to 10 KGy was shown to decrease the specific resistance to filtration, the

potential of colloidal particles, and the bound water content of sewage sludge and to

increase the amount of highly molecular substances of filtrate (Vysotskaya and

Shevchuk, 1986). Borrely el al. (1998) described the potential of using ionizing radiation

to disinfect sewage and sludge, as well as the possibilities of recycling natural resources

and their by-products. Me presented a brief review on the development of radiolytic

treatment of wastewaters with electron beam accelerators or Co gamma sources to

eliminate organic and biological contaminants from liquid and solid wastes. Suitable

radiation doses were suggested for each particular case. Investigations performed in many

countries showed that irradiation with a suitable dose of gamma or electron beam

radiation makes sewage sludges sanitary safe and usable as soil fertilizer immediately

after treatment (Chmielewski, 2005).

Trump el al. (2002) reported effects of biological, chemical and physical studies.

Electron treatment was suggested as an alternative to chlorination of municipal liquid

wastes after electron treatment to provide disinfection. Disposal of sewage sludge was

recommended as an agricultural resource by subsurface land injection, or as a nutrient for

fish populations. The data obtained by Vysotskaya el al. (2002) showed that the sludge's

dewatering improvement is due to a decrease in the stability of colloid systems. Low

doses were more effective in this respect, than higher ones.

(Al-Ani and Al-Khalidy, 2006) carried out a study using different doses of radiation to

treat wastewater samples collected from the AL-Rustamia wastewater treatment plant in

Baghdad city. According to their results, irradiation by gamma radiation with a dose

ranging from 100 to 500 KRad was efficient in reducing some of the physical

contaminants. The organic contaminants were degraded and reduced to about 12% of

35

their original concentrations. Generally, irradiation technology could effectively modify

the characteristics of the wastewater to such levels that are compatible with Iraqi disposal

standards. The results of the study also showed that, an experimental pilot plant study is

required to optimize the cost of wastewater treatment through the use of this technology.

Radiation technologies applying gamma sources and electron accelerators for material

modification are well-established processes (TECD. 2005). There are over 160 gamma

industrial irradiators and 1300 electron industrial accelerators in operation worldwide.

Very important and promising applications concern environmental protection-

technology, being a clean and environment friendly process, helps to curb radiation

pollutants' emission as well. The industrial plant for wastewater treatment is under

development in Korea and a pilot plant for sewage sludge irradiation has been in

operation in India for many years.

Aladawi, et al. (2005) investigated the effect of UV radiation on the development of

Ascaris lumbricoides larvae, eggs were exposed to increasing UV doses. Filtered

wastewater from the secondary effluent taken from the Damascus wastewater treatment

plant (DWTP) was used as irradiation and incubation medium. The progressive and

accelerated embryonation stages were microscopically observed. Results indicated that

the UV radiation accelerated the development of larvae with increasing UV dose.

Preliminary information about the relationship between the UV radiation dose and rate of

embryonation was also presented

The impacts of UV irradiation, gamma irradiation, and a combination of both on

Escherichia coli inactivation in primary and secondary wastewater effluents were

investigated by Kochhar (1981). Gamma irradiation of previously UV irradiated samples

indicated that particle-associated microorganisms, which are protected from UV, can be

inactivated by ionizing radiation at a rale similar to that for free microorganism

inactivation. An estimation of the energy required for disinfection indicated that, in

general, the required energy and the energy cost for E. coli inactivation using ionizing

radiation are considerably higher than those for UV radiation. Udupa el al. (1994) also

investigated the impacts of UV irradiation, gamma irradiation, and a combination of both

36

on Escherichia coli inactivation in primary and secondary wastewater effluents. UV doses

of 35 and 62 J/m were required for a 1 -log inactivation of E. coli in the primary and

secondary wastewater samples, respectively. A gamma dose of 170 Gy (J/kg) was

required for a 1 -log inactivation of E. coli in both wastewater samples. Variation in

gamma radiation dose rates did not have a significant impact on the extent of inactivation

at a given total dose. Gamma irradiation of previously UV-irradiated samples indicated

that particle-associated microorganisms, which are protected from UV, can be inactivated

by ionizing radiation at a rate similar to that for free microorganism inactivation. An

estimation of the energy required for disinfection indicated that, in general, the required

energy and the energy cost for E. coli inactivation using ionizing radiation are

considerably higher than those for UV radiation.

37

Chapter Two

Experimental Techniques

2.1 The Cobalt-60 irradiator

Cobalt-60 can be obtained with activities as high as 20 to 40 curies per gram though an

activity of 1 to 5 curies per gram is more usual. The Cobalt-59 from which it is prepared

through 59Co (n,y) bnCo reaction is generally irradiated in a reactor in the form of

pellets, or thin discs to give a uniformly active material and these are assembled into

radiation sources the desired size.

The containers in which the Cobalt-60 assembled also serve to filter out emitted (3-

particles (Spinks el al. 1990; Swallow et al.960). Currently, gamma irradiators installed

with an energy source of radioactive Coball-60 are used in the areas of sterilization of

medical products, consumer goods, disinfection of sewage sludge and degradation of

toxics in soils (Swinwood, el al. 1994).

In this study we have used MSD Nordion "Gamma cell 220 Excel" for irradiating the

sewage water samples. The cell is surrounded by 25 cm lead shield for protection

purposes. The cell is in the form of hollow cylinder into which the sample is introduced

by means of the moving drawer, spiral lubes through the drawer allow wires and small

tubes to be led into the irradiation cavity without the escape of radiation (Fig. 2.1).

38

StiftSdlog source* container

.,.,. Samp'« loadhQ

Same*

dffv*

Fig. 2 . 1 : M S D Nord ion "Gamma cell 220 Excel"

39

2.1.1 Principle of operation 60Co undergoes naturally [3"decay to the Ni60*, which loses its excitation energy by

emission y-photons with two energies (1332.5 and 1172.3 KeV), and these processes can

be seen in the below scheme: 6oCo6o __> «)Nil |1 + p 6oNi + y i + Y2 ( t l / : = 5.2 y)

Irradiation of the effluent with gamma photons from cobalt-60 results in zero residual

radioactivity.

Gamma radiation (60Co) and electron beam (accelerator) has been successfully used for

alleviation of environmental pollution. Such alleviation includes: disinfection of harmful

pathogens, degradation of toxic organic pollutants, and destruction of seed weed and

reduction of soluble heavy metals, odor and BOD & COD (El-Motaium, 2006). Gamma

rays from 60Co pass through sludge, killing microorganisms and parasites. They do not

leave any residue in or on the sludge, and they do not make the sludge "radioactive." The

irradiation process will not change moisture content, or the levels of nutrients and heavy

metals its sole function is to eliminate pathogenic organisms (Swinwood, 1994).

2.1.2 Dosimetry systems

The reference source is calibrated by using Fricke Dosimetry, and the dosimeter signal is

then converted to absorbed dose or dose rate in water by computations based on cavity

theory. The reference source is used to irradiate the routine dosimeter under identical

conditions, and the calibration is usually expressed in terms of dose or dose rate in water,

rather than in terms of dose or dose rate in the dosimeter medium. The routine dosimeter

is then exposed together with the product in the irradiation facility, although the

irradiation conditions (i.e. energy spectrum and geometry) may be markedly different

from those of the calibration.

2.2 Material and Methods

2.2.1 Area of study

This study was carried out in the sewage rehabilitation project located in the green belt

area at southern part of Khartoum state (lat.!5° 36', long. 32° 33', Alt.380 m). It covers

•40

the Green belt Plant in Salama area where all samples were collected from. The plant is

some 400 meters from the eastern border of the green belt. The plant serves areas in

Khartoum that includes Al-Amarat, Khartoum Centre, Khartoum-2, Khartoum-3,

hospitals and part of the industrial area. The population in this area is about 1 million

people.

The investigation was carried out at the inlet of the sewage rehabilitation plant (Fig. 2.2).

It consists of the following parts:

a. Primary (Anaerobic) pond

The conditions in the pond are mostly anaerobic and alkaline. Bacteria associated with

anaerobic ponds are Clostridium and many sulphate reducing and methane-forming

bacteria and methano serocine (Reid, 1982; Ahmed, 1992).

b. Secondary (facultative) ponds

The major organisms inhabiting this pond are aerobic and anaerobic bacteria, blue green

algae and green algae. However, the aerobic condition prevail more towards the surface

of pond water (Mala, 2000).

c. Tertiary (maturation) ponds

Its medium is basically alkaline. This pond is characterized by being completely aerobic

(El Hassan, 1993).

(1. Canal

The canal is a long stretch of water, fairly narrow (3 m in width), to which water flows

from the tertiary ponds to feed the irrigated areas of the green-belt where the bank area

rich in vegetation.

41

2.3 Sample collection and preparation

A total of 150 wastewater samples and sludge's were collected from untreated water of

inlet of the green belt plant. The samples were taken using Ruttner water sampler shown

in Fig. 2.3. Samples were placed in sterilized glass bottles (250 ml and 500 ml) and

transported to the laboratory in ice container for a period of two years (October 2005-

August 2007). pH was immediately measured in the field with the aid of portable pH-

meter.

The sampler used was locally made and it consists of one liter galvanized cylindrical

container fixed to a heavy iron base at the lower end of a holder consisting of a three

meters long tough but light metallic tubing two centimeters in diameter.

To know of which depth the water sample will be taken, the holder was marked at

intervals of one decimeter each, with the zero mark adjacent to the open end of the

container. Three centimeter from the upper rim of the container four windows, each 2 x 2

cm were cut to allow entry of water at the required depth. The lid, which was made to

permit up and down movement in and out of the upper part of the container, had a deep

(7 cm) lower rim, that when allowed to be inserted in the container closes firmly its four

windows. This prevents contamination of the water samples taken at the required depth

by water from other depth.

The lid was fixed to two springs attached to fixed points on a metallic rod which in turn

was fixed to a long steel string attached to a simple lever system fixed one meter from the

upper free end of the holder. At the required depth, when the lever is pressed the lid

moves upwards getting out of the container and its windows firmly.

43

NEWPUMBING STATION

ft 3

SERIES 2

T

INLET CHAMBER AND

SCREEN O-RID

_y Y_

POND 1

Y Y V

POND 1

POND 2

POND3 o o

EXISTING-PUMBING STATION

Dfctritutiai Cnunbi «1

SERIES 1

DETR1BUTI0N CHAMBER HI

POND 1

T

POND 1

POND 2

T POND 3

OUTLET CHAMBER

fc-1 0500

1-1

3 DISHARGE CANAL

KHARTOUM SEWERAGE REHABILITATION PROJECT

FIG SOBA SEWAGE TREATMENT PLANT GENERAL PLAN

Fig. 2.2: Layout of Khartoum sewage rehabilitation plant

42

at rest

V; in action

scale marks

window

heavy base

u

', spring

V\ \m i m h=4

container opened

h=^

Fig. 2.3: Ruttner Water Sampler

44

2.4 Sample Irradiation

Experiments were conducted to study the effect of y-radiation on organic matter (BOD),

different microbial groups and parasites. Representative samples were exposed to

increasing doses of gamma radiation ranging from 0.5 to 8 KGy using gamma cell with

dose rate of 1.22 Gy/sec as determined using Frecke dosimeter. The pathogens groups

and BOD were determined before and after irradiation.

2.5 Sample Measurements

2.5.1 Biological Oxygen Demand (BODs)

Principle of the test:

Biochemical oxygen demand (BOD) is one of the main indicators of the quantity of

pollutants present; a parameter used to measure the amount of oxygen that will be

consumed by microorganisms during the biological reaction of oxygen with organic

material. Test is typically conducted under specified conditions and may then also be

refer to as BOD5'

The Biological oxygen demand (BOD) test is used to determine the relative oxygen

requirements for wastewater, effluent and polluted water. It measures the change over

five days in dissolve oxygen (DO) concentration in a stopper bottle completely filled with

the waste or a dilution of it. A special dilution water is used which is buffered to pH 7.2

and contains essential inorganic nutrients.

Sterile 500-mI bottles were thrown in each of the ponds, using a rope, and filled with the

water sample. Airtight incubation bottles of 300 ml capacity with tapered and pointed

glass stoppers and flared mouth were filled with sample, to overflowing and incubated at

the specified temperature (20±l °C) for 5-clays. Dissolved oxygen (D.O) was measured

initially and after incubation, and the BOD was computed from the difference between

initial and final (D.O). Because the initial (D.O) was determined immediately after the

dilution was made, all oxygen uptake, including that occurring during the 15 min was

included in the (BOD) measurement.

45

Dilution of the samples was carried out by placing one liter of distilled water in a

measuring cylinder, and 2-ml each of phosphate buffer, MgSC>4, CaCb, and FeCl3

solutions were added (these act as substitute nutrients for living organisms in diluted

water samples). Saturation with dissolved oxygen was then performed using an electrical

aerator. The stopper from the BOD bottle was removed. 2ml of manganese sulphate

solution and alkali iodide azide solution were added, and with care to exclude air bubbles

was shaken to suspend the precipitate. When the floe had settled, the bottle was

unstoppered and 2 ml of concentrated H2SO4 were added to the solution. The floe then

dissolved and the bottle contents turned yellow. 200 ml of the bottle contents were

titrated with N/40 (0.025 N) sodium thiosulphate was then added dropwise until the

colour changed from blue to colourless. Dissolved oxygen concentration in mg/1 was

calculated as follows:

n/) _ "^ °f thioMiIphate x 0.025 normality of sodium thiosulphate (N)

BOD bottles containing the diluted sewage sample were then incubated at 20±1 °C, after

5 days incubation, final (DO) was determined using (he iodomctric Test. IJOD (nig/I) was

calculated according to the following equation:

BOD = ^ ^ - x dilution factor(l/1000) P

D = DO of diluted sample immediately after preparation (mg/l)

d = DO of diluted sample after 5 days incubation at 20 °C (mg/1),

P = decimal volumetric fraction of sample used,

(Note: two replicates for each test were performed).

2.5.2 Bacterial Count

Microbiological examination of wastewater sample is to determine sanitary quality. Tests

for detection and enumeration of indicator organisms, rather than pathogens, are used.

Experience has established of the significance of coli form group density as a criterion of

the degree of pollution and thus of sanitary quality. 5 wastewater samples were taken in

46

250 ml sterile glass bottle twice per week for total bacteria and some typesU^H^^B

bacteria were determined, using different media according to types of bacteria before and

after irradiation as detailed below.

2.5.2.1 Surface viable count of bacteria

As described by miles and Misra method (1938), the inoculums were deposited as drops

from a calibrated dropping pipette. Each drop was 0.02 ml in volumes was allowed to fall

from a height of 2-3cm onto the medium. The drop was spreads over an area of 1.5-2.0

cm diameter each of the six lobed plates received one drop (0.2 ml) of each dilution in

separate numbered sectors. The counts were made in the drops areas showing the largest

number of discrete colonies without confluence (up to 20 or more colonies), the mean of

the sex counts gives the viable count of the dilution in 50ul. Therefore, the colony

forming unit per ml (CFU) suspension is counted x 50 x dilution number.

The count of viable bacteria in the sample depends on the use of selective media for each

bacterium. Neutron Agar for total count bacteria, EMBA (Eosin Methyl Blue Agar) was

used to estimate the counts of total E-coli, and inoculate XLD and SS (Salmonella

Shigella) for Salmonella Spp. and Shigella spp. The medium used for counting

Streptococcus is Azide blood agar and for total coliform bacteria MacConky agar media

was used.

2.5.3 Parasites test (Ascaris lumbrecoids)

Ascaris lumbrecoids is a warm that causes infection, in man all over the world. Million of

people are annually reported to and infected. The infection causes heavy losses in

resources and mortalities (WHO, 1989).

Different radiation doses were used in this study (1, 3, 5 and 8 KGy). 1500 g of the

sludge samples were distributed in 5 sterile bottles (jam bottles). This was chosen to suit

the cell volume in the gamma irradiation machine. Control bottles of sludge were placed

aside.

Ascaris (female uterus) produce about 200,000 Eggs/day (Gerald et al, 2005). Our

calculations were about 100 eggs/g and the plant is receiving about 9 million of

gallon/day.

47

2.5.3.1 Procedure for determination of Helminthes ova in wastewater sludge

Once a week on the same day as described by Dominique, el al (1990) each 2 g sample of

sludge was carefully suspended in 22 ml of flotation solution and was then transferred to

two 12 ml centrifuge tubes which had their tops ground flat. The tubes were filled with

reagent (Z11S04) until a slight meniscus was formed at the top, on which a 22 x 22 mm

cover slip was placed. The two tubes were then centrifuged at 150 x g for 3 min. The

cover slides were removed and placed on microscopic slide for microscopic examination

(slide-1), and replaced by new cover slips before a second centrifuge at 150 x g for 3 min

(slide-2), and finally the three cover slips from each tube were examined under the

microscope at magnification of x 100.

2.5.3.2 Viability

The number of ova was estimated using three 2 g portions of each of the irradiated and

control sludge, and then they were incubated in Petri dishes at room temperature for a

period of 4 weeks. Innervation was measured by the ability of fertilized eggs to

embryonate during the 4 weeks after treatment. The average number of ova after

incubation was constant in irradiated samples, but development was evident in control as

indicated by the presence of larvae.

48

Chapter Three

Results and Discussion

For the ease of reference the result obtained here for pathogens (some types of bacteria

and Ascaris) and organic matter (BOD5) of sewage water collected from inlet of sewage

plant located south of Khartoum at Salamah area are discussed under subheadings detail

of which will be given blew.

3.1 Biochemical Oxygen Demand (BOD5)

BOD5 was measured using titrimetric method and the obtained data are presented in

Table (3-1). Reduction in organic matter contents (BOD5) was due to gamma irradiation

with different doses (0 - 2.5 KGy). It is obvious that the percent reduction increases with

increasing gamma dose. Jinho et al. (2002) reduced BOD by 85% irrespective of

absorbed dose. However, Baslar et al. (2002) found a reduction of 24% at 4 KGy. The

reduction at 4 KGy is significant as this is the dose that has been shown to be the target

for wastewater disinfection using the electron beam process (Faroog et al. 1993; Basfar

and Abdel Rehim, 2002). Using gamma radiation, Jung et al. (2002) indicated that

biodegradable organic materials can easily be decomposed even at a low absorbed dose

(100 Gy). The reduction in BOD caused by radiation could be due to its direct and /or

indirect effect on the destruction of organic material (Cooper et al. 2001). The indirect

effect is due to free radicals produced by water radiolysis i.e. IT, 011.

3.2 pH

The pl-1 of the raw sewage was found to in the range between 5.2 and 5.8. This indicates

that the medium is acidic most probably due to input of industrial wastewater.

49

3.3 Effect of radiation on survival of bacteria

Preliminary experiments to establish the relative sensitivity of the total bacteria, total

coliforms and various pathogenic bacteria (E-coli, streptococcus, salmonella and shigella)

to irradiation indicated that, all test organisms in raw sewage were virtually eliminated at

dose level of 500 Krad obtained from sewage water in Salamah area presented in graphs

and will be discussed below.

Table 3.2 shows the statistical summary of bacteria counts (CFU/ml) before and after

irradiation in Soba irradiation cell.

Total count of bacteria in zero KGy falls within the range of 25x10 - 3E+008 CFU/ml with

a mean value of 28. lxl07±83.19x 106 in total viable counts of bacteria and (0.2-16.9)103

CFU/ml with a mean value of (39.58±72.45)102 at 0.5 KGy. It is apparent that the mean

value of the total bacteria decreased rapidly after irradiation with a dose of 0.5 KGy, until

it reaches the mean value of 87±92 CFU/ml at dose of 3.5 KGy. This tends to confirm

that the gamma rays have a clear disinfection effects on total viable counts. It should be

in place to note that the minimum value measured in the sewage water for total viable

bacteria is at 3.5 KCJy.

E-coli counts ranged from (I lxlO4- 24xl04) with the mean value of (63xl03±46xl03)

CFU/ml at 0.0 KGy, (46xl0-50xl02) with a mean value of (24.8-23.1)102 CFU/ml at 2.5

KGy. The argument stated above for E-coli indicating similar for mean and STD

(standard Deviation). On the other hand, that of Streptococcus falls within the range of

(80-2300)10"" CFU/ml which is greater relative to that of E-coli, with a mean value of

(11.15) 102 CFU/ml.

Many samples at different days were collected from the sewage water and then exposed

by gamma rays, ranges from 0.5 to 7.5 KGy. Approximate Dm and D50 values were also

estimated. Since Dm values represent minimum dosages effecting 90% inactivation of the

populations involved, irradiation closes for the subsequent quantitative experiments were

selected to generate data reflecting a 90% to 99.99% activation range. The Dm and D50

values for various pathogens in raw sewage ranged from 0.75-2.75 KGy and 0.5-1.0

KGy, respectively. The rating of the test organisms in decreasing order of radiosensitivity

was as follows: E-coli, coliforms and streptococcus, respectively.

50

As a result of increased exposure of gamma ray, the number of microorganisms

decreased according to the simple curves shown in graphs (3.1-3.5). Each microorganism

in this study showed different lethal dose that causes total sterilization, from the other

microorganisms. This leads to the point that, the microorganisms have different response

for radiation. When they were exposed with a dose of 0.5 KGy their number decreased by

50%.

The D50 and D !0 for total viable counts in Fig (3.1) found to be 0.5 and 2.75 KGy when

were placed in sewage water. As the micros exposed to dose of 1.5 KGy shown in the

results, when the total count were exposed to 1.5 KGy, the E-coli found to have less

sensitive response to the dose compared to the rest of the population. The E-coli were

decreased by 90.5%.

In the sewage water, D5o and D|0 were 1.0 and 1.48 KGy for the E-coli and 0.5, 2.0 KGy

for total coliforms. Streptococcus showed significant resistance to radiation, where the

number of population was decreased by 100 % when exposed to 3.5 KGy. D50 and Dio

were recorded to be 0.50 and 0.75 KGy, respectively.

Data for the number of the irradiated microorganisms before and after irradiation are

shown in Table (3.2). D50 and Dio are shown in graph (3.1-3.5). From the results, it is

clearly observed that all the investigated organisms are influenced by y-rays. Although

D50 and Dm have changed among the population, it can be said that the studied

microorganism have different response to radiation. Microorganisms were completely

removed at dose of 4.5 KGy; regrowth of microorganisms was not detected in this system

only at this dose. This excellent disinfection as compared with chlorination or Ozonation

alone may be due to the high redox potential of the reactive radicals such as hydroxyl

radicals produced during gamma-irradiation (Bensason el al, 1983). The population

showed steady decrease when exposed to 0.5 and 1.0 and 3.0 KGy, by50%, 70% and

90% respectively. It was found that 4.5 KGy be a lethal dose for the total count. Abdel

Karem el al (1996) in chlorinated effluent a dose of 6 KGy was quite sufficient to

decrease total count from 6xl05 to few cells/g. It could be stated that the 4 KGy radiation

dose is an optimum level sufficient to destroy pathogenic bacteria present in sewage. El-

Fouly et al (1996) and Hashimoto et al (1988) found that 5 KGy is the appropriate

disinfection dose for dewatered sludge, whereas El-Motaium et al, (2005), found that a

51

dose of 1 KGy and 6 KGy are sufficient for disinfection of sewage water and sewage

sludge respectively. The adequate disinfection dose is considered to be 5 KGy (Watanabe

and Takehsa 1984) Ahlstrom (1985) Farooq et al 1993), 500 Krad. At doses from 2-6

KGy, irradiation has been used successfully to achieve a variety of treatment objectives,

including chemical destruction (Cooper et al 1992, Kurilcz et al 1995. (Pikaev 1997), the

opinion of radiation scientists, 3-5 KGy of ionizing radiation is adequate to completely

inactivate pathogens in sewage sludge.

One can notice that the close needed to kill bacteria in sewage water in other studies made

is lower than the close in this study but as the same as their treated sludge and we belief

this may due to the fact that sludge in which bacteria is found in this study is untreated

and brought waste water from untreated area, which was proven by anther experiment on

different day the data showed that the lethal dose of total counts bacteria is 2.0 KGy and

Dio, D50 are 1.0 and 0.5 respectively (Fig3.1)

Nevertheless, total coliforms bacteria including E-Coli were more sensitive for to

radiation where the counts decreased to a bout 98 % when exposed to 1.75 KGy. Upon

using 3.5 KGy Slrepto has shown greater resistance to high doses than E-Coli. When

using 2.5 KGy to irradiate Strepto, the counts were decreased to 2.8x104 CFU/ml. The

dose 3.5 KGy was found to be lethal for Strepto. On other hand, Salmonella was found to

be the most sensitive organism where 1.5 KGy was enough to eliminate. The lethal dose

of Salmonella was found be 1.5 KGy whereas in a study made by Brandon, el al (1977)

the lethal dose was 30 Krad in liquid digested sludge.

The E-coli (Fig. 3.4) found to have less sensitive response to the dose compared to the

rest of the population. D50 and Dm were found to be 1.0 and 1.5 respectively, agreement

with earlier study by Harewood, et al (1994), they indicated that average Dm values of

1.54 KGy for E-coli. The Dm value in this study for E-Coli do not agree with the lower

Dio value (Dm= 0.37) reported earlier by Luizzo et al (1967). This discrepancy may be

due to difference in treatment method and contamination. Basfar (2002) used a dose of

1.0 KGy which resulted in a reduction of 99.3%. Such as E. coli tend to diminish rapidly

(Loweetal. 1956).

Figure 3.3 shows the inactivation of Coliform. Rawat et al (1997) observed that a gamma

radiation dose of 2 KGy could effectively reduce the coliform from final settling tank and

52

Dio was 0.22 Gy agreements with earlier reports. Burkhardt (1992) reported that Dio

values of 0.18 KGy in phosphate buffer. Marewood and Riffey (1994) reported average

Dm values of 1.75, 1.32 KGy for total Coliform, and Abdel Karem et al (1996) in

chlorinated effluent total coli form could not be detected after irradiation could not be

detected after irradiation with 2 KGy, whereas El-Fouly et al (1996) found 2.5 KGy level

was quite sufficient to eradicate coliform bacteria. Brandon, et al (1977) for total

coliforms in dried raw sludge varied from 17 to 353 Krad. Harewood, et al, (1994) found

Dio values of 1.32 KGy for total coliforms, 1.39 KGy for fecal coliforms, and 1.54 KGy

for E. coli.

As shown in the Fig. (3.5) Streptococcus showed significant resistance to radiation,

where the number of population was decreased by 103 cell/ml when exposed to 2.5 KGy.

D50 and Dm were recorded to be 520 and 800 Gy, respectively. The radioresistance of

strepto was well recognized by Udupa et al, (1994) and may possibly be attributed to the

ability of the streptococci to repair DNA breaks induced by radiation. Yeager and O'

Brien (1983) further observed Strepto to be the most radioresistant of six enteric bacteria

studied at all moisture levels. S. faecal is and oilier fecal Streptococci have been

consistently found to be more resistant to ionizing radiation than most other bacteria

associated with sewage (Brandon, et al 1978, Etzel, 1969, Kristof, et al. 1970, Lowe, et al

1956, Reidenour, et al 1956, Roberts, et al 1974, Touhill, et al 1969 and Richard, 1981

and El-Fouly 1996).

Fig (3.2) for total count bacteria by different days shows the lethal dose of 2.75 KGy.

Shigella Spp. was not found because of difficulties associated with detection of this

bacterium in waste water, long distance from the sampling site to the irradiator and

detection lab, as well as influence by temperature. As in the results reported by Donald et

al (1980) also were unable to detect Shigella Spp. in sewage water samples. Our recovery

experiments suggest that Shigella do not survive well in wastewater. This would decrease

the probability that this organism would be present in the waste applied to land. However,

we can not exclude the possibility that the method used by us and other workers is not

sufficiently sensitive to permit isolation, because of this lack of isolation of Shigella Spp.

from original waste or from sludge; we are unable to reach any conclusion about the

presence or absence of this pathogen or about the relative risks involved.

53

3.4 Ascaris

In the present study ova of helminthes were found in raw sewage (Ascaris lumbricoids).

The mean number of this species ranges between 45-80 eggs per liter. The parasites

burden in the sludge was finding to be 100 eggs/g. The irradiation was made and the

effect of the radiation detected compared to the control after incubation and no larvae

were recovered at dose >1.0 KGy (see Table 3-3). Capizza, el a/.(1999) found life larvae

in the rate of radiation below 0.75 KGy. That is to say if we used less doses it could have

destroyed the embryos used in their experiment eggs with their coating (shell) and eggs

without coats. They found at the rale of 0.2 KGy that the coated egg to be less destroyed,

but at 0.3 KGy the effect is equal. In our experiment we did not compare between coated

and uncoated eggs.

In our study we made it to simulate the effect naturally in the plant and a possible

irradiation to make it. Sivinski( 1975) used 0.95 KGy dose from a cobalt 60 source

whereas 1 Iorak( 1994) reported similar observations using a dose of 1.1 KGy employing

accelerated electrons and Enigik, el al (1975) used 4.8 KGy and found it necessary to

destroy the Ascaris eggs. Shamma el al 2002) using gamma irradiation dose between 1.5

and 8 KGy) and incubated for 8 weeks, after the period no larvae were observed. Enigk

(1975) on the other hand was reported that the viability of Ascaris eggs was not affected

by the 0.3 KGy and the number of viable eggs after irradiation with this dose was similar

to the control.

Brandon (1978) indicated that Ascaris ova are sensitive to gamma radiation with Dc)n

values in liquid and composed sludge at about 0.5 KGy. Yeager and O' Brien (1983)

using ovum obtained from pig faeces, reported a D90 of 0.45 KGy for ovum without outer

coat. However, in conflicting reports on the radiation sensitivity of Ascaris eggs, higher

doses were recommended by Keller (1983), Hess and Breer(1976) and Heuer and

Hofmann (1979) who used doses over 300 krad (i.e. 3.0 KGy). Burger el al. (1978) and

Enigk el al. (1975) established that doses of 400 and 480 Krad (i.e. 4.0 and 4.8 KGy),

respectively, are necessary for the destruction of eggs from Ascaris species. It is probable

that the differences in radiation sensitivity of such Ascaris eggs could be explained by the

54

different types of sludge in which the eggs were irradiated. Water content greatly

influences the radiation sensitivity of the organisms present (Koubik et al; 1987).

Unfortunately, the type of sludge used in the experiments reported by Burger et al. (1978)

and Enigk et al. (1975) was not characterized.

55

Table (3-1): Physical properties (BOD) of wastewater effluents before and after

gamma irradiation

y-Dose (KGy)

0.0

0.5

1.0

1.5

2.0

2.25

2.5

BOD(mg/l)

750

700

600

550

500

450

350

Reduction (%)

0.0

6.66

20.00

26.6

33.33

40

53.33

56

Table 3.2: Statistical summary of Bacteria counts (CFU/ml) before and after gamma

irradiation of sewage water from Soba sewage treatment plant (No. 62 samples)

\ Statistics

Bacteria \ ^

type \ .

Total bacteria count

Coliforni

Escherichia. Coli

Streptococcus

y-Dose

(KCy)

0.0

0.50

1.5

1.75

2.00

2.25

2.50

2.75

3.00

3.25

3.5

0.0

0.50

1.5

2.50

0.0

0.50

1.5

1.75

2.00

2.25

2.50

0.0

0.50

1.5

Mean±Std.

( CFU/ml)

28.1 x 107± 83.19.x 10"

39.58 x I 0 : ± 72.45.x I0 :

42.48 x 102± 64.96x 102

37.20x 102± 52.04.x I0 :

18.75.x I02 ± 21.56 x I02

52.6 x 10±25 .3x 10

76.6.x 10 ± 76.4 x 10

50.5.x 10 ± 37.4.x 10

37.0.x 10±31.1 x 10

42.0 i 10.0

87.0 ±92.0

11.8 x 101 ± 84.60xl02

71.26.x 102±32.89xl02

25.50.x 10 :± 39.6x10

95.0.x 10 ±35.0x10

63.9x10'±46.27x10-'

62.5x10'± 10.60x10'

14.5x10'± 10.14x10'

60.37x102± 84.32.\ I02

I5.03xl02±2l. l6.xl02

75.2x10 ± 10.57x10"

24.86.x l()2± 23.08.x I02

10.15x10" ± 17.19x10"

I1.9.xl04± 15.69.x 104

62.50x 102± 17.67xl02

Maximum

(CFU/ml)

3 x 108

16.90 x 10'

16 x 101

74 x 102

34 x 102

80 x 10

22.9 x I02

77x 10

59.0x10

50.00

27.0x10

21.30x10'

94.52.x I02

30.00xl02

12.00.x 102

ll.OOxlO4

70.00x10J

23.00xl03

12.00x10'

30.x 102

15.0xl02

50.00x I02

30.0x10"

23.00x104

75.00x102

Minimum

( CFU/ml)

25.0 x 10

20.0 x 10

70.00

40.00

35.0 x 10

30.0 x 10

27.0.x 10

24.0 x 10

15.0 x 10

35.00

20.00

24.x I02

48.0xl02

22.50xl02

55.0x10

24.0.x I02

55.0xl&3

15.0x10

75.00

0.7x10

0.4x10

46.0x10

15.0x10'

80.0x102

50.0xl02

Note: full data tables are given in appendix, CFU: means colony forming unit

57

Total Counts

100.00-,

Dose (KGy)

Fig. 3.1: The plot of ratio percentage against y-dose for Total counts

Bacteria

59

type: total count

100.00

20.00-

0.00-

D50

D10

1 1 1 —1 1 1 1 1 1— 00 1.00 2.00 2.25 2.75 3.00 3.25 3.50 3.75 4.00

Dose (KGy)

Fig. 3.2: The plot of ratio percentage against y-dose for Total counts

Bacteria

60

Total Coliform

100.00

n i i r 1.50 2.50 3.50 4.00

Dose (KGy)

Fig. 3.3: The plot of ratio percentage against y-dose for Total coliforms

61

type: E-coli

100.00-

90.00-

80.00-

0> U) flj

c 0) o k . (D

o ra £

70.00

60.00

50.00

40.00

30.00-

20.00-

10.00

0.00

Dose (KGy)

Fig. 3.4: The plot of ratio percentage against y-dose for Total E-coli

62

type: Sterptococuse

erce

ntag

<

Q.

Rat

io

100.00-

90.00-

80.00-

70.00-

60.00-

40.00-

30.00-

20.00-

10.00-

0.00-

\

\

\ D50 I

\

\ D10

^ ^ i i i i i i i i i ~ r i i i i

.00 .50 .75 1.25 1.50 2.25 2.50 2.75 3.00 3.25 3.50 4.50 5.50 6.50 7.50

Dose (KGy)

Fig. 3.5: The plot of ratio percentage against y-dose for Total

Streptococcus

63

Conclusions

Based on the results obtained on y-radiation treatment of sewage water and sludge, the

following concluding remarks could be drawn:

a. Gamma-irradiation has shown to be effective in removing organic contamination

and disinfect pathogenic bacteria from the sewage water and sludge.

b. Amongst the pathogenic bacteria studied E. coli is more sensitive to radiation,

whereas Streptococcus is more resistant.

c. Ascaris ova are demonstrated to be non-viable after exposure to irradiation dose

of 0.1 KGy.

d. Gamma-irradiation opens door for possible reuse of irradiated sewage water and

sludge for agriculture

e. This area of research is of potential interest and hence further detailed studies

need to be considered on large scale basis

Recommendations:

We recommend that Khartoum Slate Authorities:

a. To revisit the biological disinfection method currently employed at Khartoum

sewage water treatment plant as there is no different seen in bacteria counts for

samples taking from inlet and outlet.

b. The facility area must be bordered by protective areas to keep the waste water to

limit access of people and animals so as to avoid spreading of waste water and

sludge during Hood season.

64

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