Comparative assessment of the phytoremediation rates of some aquatic macrophytes in an aquaculture...

CHAPTER ONE

INTRODUCTION

1.1 Background

Aquaculture can be described as the cultivation and harvest of aquatic plants and

animals of which the fish culture is most common in Nigeria. There are however,

three categories of fish culture systems; open, semi-closed and closed systems. Open

system culture refers to fish farming in surface water bodies like rivers, lakes, seas

etc. Semi-closed systems refer to culture system in which water enters the culture

unit once and is discharged after use. Closed systems are aquaculture systems where

water is reconditioned and recycled into a culture unit. Some aquaculture methods

require much more water than others. In which ever method used, a large quantity of

effluent containing pollutants that are hazardous to the fish environment is produced.

For the open and semi-closed systems, pollutant laden effluent is naturally

remediated while for the closed system it needs appropriate measures for

remediation.

Nigeria is one of the largest fish consumers in the world with over 1.5 million tonnes

of fish consumed annually as she imports over 900,000 metric tonnes of fish and while

her domestic fish catch is estimated at 450,000 metric tonnes/year (Jim 2003, Ezenwa

and Anyanwu, 2003). The over dependence on imported fish has adversely affected

her economy and mostly foreign reserves (Davies et al. 2008). Adebayo and Adesoji

(2008) inferred that since fish supplies from open water and lagoons continue to fall

and human population rise, fish farming will present an effective way of generating

food and income from declining land spaces.

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The commercial fish farming in Nigeria is done more in semi-closed concrete or

plastic tanks, dug-out ponds, etc. especially in areas where influent water is not

limited. Effluents from semi-closed systems are usually discharged in the open or dug-

out pits which pollute the surface and groundwater.

The treatment of aquaculture effluent especially of the closed system type is

necessary because, in many areas, water is a limited resource and depending on the

receiving water body, the total mass loading of nutrients from effluents can

contribute to significant environmental degradation (Adler et al. 2000 and Redding et

al. 1997). Closed recirculating aquaculture systems are usually used where new

water supplies are limited or expensive (i.e. high pumping or treatment costs), the

possibility of introducing pathogens or contaminants into the system with influent

water is high, effluent disposal capacity is limited, or where the operators want to

practice strict control over water quality and temperature within the fish culture

system (Lawson, 1997).

(Huguemin and Colt, 1989) reported that the universal attribute of closed aquaculture

system is that fishes are restrained at high densities. Normal culture is 61-122 kg/m3,

but densities even in some small scale experimental systems are beyond 545 kg/m3.

1.2 Treatment Processes for Recycling Effluent

The major treatment processes used in recirculating systems are screening, settling,

granular media filtration, biological filtration, aeration and disinfection. Solids in

effluents are usually eliminated using screening, sedimentation and granular media

filtration.

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Biological filtration is the heart of any recirculating aquaculture system and is used for

nitrogen control (i.e. ammonia and nitrite). It is the technique that makes use of living

organisms to remove a substance from a liquid solution and systems which utilize

algae and higher green plants to filter water are usually in closed method hydroponic

systems.

Hydroponics can be defined as the cultivation of plants in nutrient enriched water

without soil or with the support of a medium such as gravel, Rockwool, perlite etc.

The plants roots are placed on this medium which is completely inert to support the

plant and the root from being constantly immersed in water or nutrient solution, and

also access to oxygen. Plants growing in hydroponic chambers receive their nutrients

from the nutrient solution for healthy growth. In temperate regions, people can

cultivate some of their vegetables all year round in indoor hydroponic gardens

(www.myhydroponicgarden.net).

1.3 The Use of Aquatic Plants for Water Treatment

The conventional wastewater treatment plants of activated carbon, electro

dialysis, ion exchange, reverse osmosis etc. are expensive to install, operate and

maintain especially in developing countries like Nigeria, hence, the use of aquatic

macrophytes for wastewater purification is a viable alternative. Aquatic

macrophytes enhance wastewater treatment by acting as a medium for bacterial

growth, by filtering/adsorbing suspended particulate matter and removing

inorganic nutrients from the wastewater (Sooknah and Wilkie, 2004). Some

aquatic macrophytes have been successfully used for effluent treatment (Jung

2002 and Snow and Ghaly 2008b).

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Common examples of these aquatic macrophytes in Nigeria include; water

hyacinth, water lettuce, water lily, duckweed, ferns etc.

Water Hyacinth (Eichornia Crassipes) is a common tropical aquatic plant found

in most fresh water bodies. According to www.aquaplant.com, it is a free floating

perennial plant that can grow up to a height of 91.5 cm. The dark green leave’s

blades are circular to elliptical in shape attached to a spongy, inflated petiole.

Underneath the water surface is a thick, heavily branched, dark fibrous root

system. It has striking blue to violet flowers located on a terminal spike. It is a

very aggressive invader and can form thick mats which can cover the entire

surface of a pond frequently, causing oxygen depletion.

In nutrient rich waters, such as polluted ponds or lakes for instance, the report

shows that the plant can grow so quickly that the surface covered by the mats

doubles every 4-7 days (www.idrc.ca/fr/ev).

Water hyacinth obtain their nutrients directly from the water and have been used

for wastewater treatment facilities. He further reported that they prefer to grow

most prolifically in nutrient-enriched waters (Grodowitz, 1998).

Jung (2002) in his report concluded that wastewater drain from livestock farms

contained large quantities of nitrogen, phosphorus and soluble inorganic

compounds which are difficult to remove by conventional cleaning treatment such

as filters. They can be effectively removed by plants, particularly water hyacinth

and water dropwort.

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Grodowitz (1998) stated that with the increasing popularity of water gardening

and home ponds, water hyacinth is now sold by many Washington (US) nurseries

for its unusual appearance, attractive flowers and ability to remove nutrients from

the water.

Another commonly used aquatic plant for water treatment is the Duckweed

(Lemnaceae sp.). Ruenglertpanyakul et al. (2004) inferred that duckweed has a

high capacity to adsorb nutrients from water and it is easy to manage in the ponds

because of its small size and is highly productive with high protein content when

cultivated in nutrient-rich water and has potential as fish food in the development

of a low-cost aquaculture system. Skillicorn et al. (1993) reported that duckweed-

based wastewater treatment systems provide genuine solutions to such problems.

They are economical to install, operate and maintain. They do not require

imported components. They are functionally simple, yet robust in operation; and

they can provide tertiary treatment performance equal or superior to conventional

wastewater treatment systems now recommended for large-scale applications.

The report also indicated that duckweed wastewater treatment systems remove, by

bioaccumulation, as much as 99 percent of the nutrients and dissolved solids

contained in wastewater.

1.4 Theoretical Development

1.4.1 Nitrogenous Toxins in Aquaculture

The accumulation of some nitrogenous compound in a closed aquaculture system

such as un-ionized ammonia (NH3), ionized ammonium (NH4+), nitrite (NO2

-),

and nitrate (NO3-) are of great interest. Lawson (1997) reported that, the major

forms of nitrogen and their effects in aquaculture systems are as follows:

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Table 1.1 Major Forms of Nitrogen and their Effect on Aquatic life

Forms Effects

Nitrogen gas (N2) Inert gas with no significant effect. Organic nitrogen Decays to release ammonia.

Un-ionized ammonia (NH3) Highly toxic to aquatic animals.

Ionized ammonium (NH4+)

Non-toxic to aquatic animals except at very high concentrations.

Total ammonia (NH3 + NH4+) Converted to nitrite by nitrifying bacteria.

Nitrite (NO2-)

Highly toxic to aquatic animals; converted to nitrate by nitrifying bacteria.

Nitrate (NO3-)

Non-toxic to aquatic animals except at very high concentration; readily available to aquatic plants.

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Fish feeds and the metabolic wastes of the fish which causes water quality

degradation are the main sources of Nitrogen. Such wastes include ammonia,

urea, CO2, organic faecal material etc. The organic faecal material is further

degraded to produce additional ammonia, nitrites (NO2-) and nitrates (NO3). These

substances depress water pH, increase turbidity, deplete dissolved oxygen, and

make the water more toxic to the fish. The more severe the culture practice, the

greater the impact and the rate of waste production in an aquaculture system. It

also depends on the fish species, life stage, system biomass and the type and

amount of feed given to the fish. The gills of the fishes excrete un-ionized

ammonia (NH3) which is quickly absorbed by phytoplankton and aquatic plants.

According to Tucker and Robinson (1990), ammonia is not a problem in fish

ponds having good phytoplankton bloom, but can be problematic in ponds if the

feeding rate exceeds 56kg/ha/day. When the amount of ammonia released is more

than the plant requirement, the excess is oxidized by nitrifying bacteria.

1.4.2 Toxin Kinetics

Nitrification can be defined as the oxidation of ammonia to nitrate with nitrite

formed as an intermediate product. The conversion of ammonia to nitrate is an

aerobic process. Denitrification occurs when anaerobic conditions develop and

nitrate is converted back to ammonia.

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Painter (1970) reported at least five types of bacteria capable of oxidizing

ammonia to nitrite which were Nitrosomonas, Nitrosococcus, Nitrosospira,

Nitrosocystis and Nitrosogloea, of which, Nitrosomonas was the most valid and

two of its major species were Nitrosomonas europea and Nitrosomonas

monocella.

Nitrification is a two-stage aerobic process. The first stage is the conversion of

ammonia to nitrite by Nitrosomonas bacteria (USEPA, 1975 and WPCF, 1983)

The chemical reaction is shown by the equation (1)

NH4+ + 1.5O2 → 2H+ + H2O + NO2 (1)

The oxidation of nitrite is a single-step process that uses oxygen from water to

form nitrate and only molecular oxygen as an electron acceptor (Atlas and Bartha,

1987). The chemical reaction is shown in equation (2)

NO2 + 0.5O2 → NO3 (2)

For closed recirculation system, oxygen is limited and there is the possibility of

nitrite accumulation. Oxygen is slightly soluble in water and causes a slow rate of

diffusion of atmospheric oxygen into water and so water contains only small

amount of dissolved oxygen available for the respiration of aquatic life.

Nitrification requires oxygen and this process is very efficient when dissolved

oxygen is near saturation. When dissolved oxygen level declines as a result of

nitrification, the behavioral and physiological responses of the fishes change.

They become less active and can stop feeding in other to conserve energy and

their remaining metabolic oxygen (Tucker and Robinson, 1990).

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If dissolved oxygen level continues to decline, the fishes may die. The chemical

reactions in Equations 1 and 2 release energy that is used by Nitrosomonas and

Nitrobacter to produce new cell growth. Since nitrification is an acid-forming

process, water in closed systems are buffered to prevent a decline in pH.

1.5 Definition of Problem

As reported by Tchobanoglous et al. (2003) the percentage of freshwater in the

world is about 3% and its depletion by continued population growth, uneven

distribution of water resources have necessitated the search for new sources of

water supply, contamination of both surface and groundwater by human activities,

while ensuring water conservation and an efficient re-use of the existing water

supplies. In developed countries, the re-use of treated effluent from municipal

wastewater treatment plant is considered as a reliable water resource.

Phosphates and nitrates are among the major pollutants in these wastewaters.

They can cause algal bloom which depletes dissolved oxygen and affects aquatic

life. Nitrates are very soluble in water and its leaching into surface and

groundwater can cause severe impact on potable water quality. Referral to

www.dnr.state.wi.us/org, infants who are fed with water or formula made with

water that is high in nitrate can develop a condition that is known as

Methemoglobinemia in medicine. People who have heart or lung disease, certain

inherited enzyme defects, or cancer may be more sensitive to the toxic effects of

nitrate than others.

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In developing countries like Nigeria, the method of controlling ammonia and its

by-product is a limiting factor for a successful commercial aquaculture. The

technology for an advanced biological treatment of fish tank effluent is

uneconomical and also the complex nature of the nitrogen cycle to local fish

farmers has caused the disposal of aquaculture wastewater indiscriminately or

unprofessionally, thereby increasing the concentrations of ammonia, nitrites,

nitrates and other contaminants in surface and groundwater above the permissible

level. The ineffectiveness of relevant regulatory agencies contributes to the non-

compliance of the approved standards for wastewater disposal and so the

attendant effect as a result of these could cause an epidemic.

1.6 Justification

Some aquatic macrophytes have revealed potentials of nutrient removal from

different types of wastewater. The comparative assessment of nature’s

phytoremediation rates by some tropical aquatic macrophytes in aquaculture

effluent is what this work is focused on.

This assessment will help in recommending a more suitable aquatic plant to be

used for biological filtration. The use of aquatic plants for the purification of

aquaculture effluent will be a viable alternative to conventional wastewater

treatment plants. The advantage of using aquatic plant for purification is that the

water resources are conserved as the environment is naturally controlled by the

plant creating a mutually beneficial, symbiotic relationship with the aquatic

animal.

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This research is multidisciplinary and its findings will help aquaculturists,

wastewater managers, environmentalists etc. in the design, construction and

management of water resources for commercial aquaculture, farms, domestic and

municipal supplies. Aquatic plants while being used for wastewater treatment can

also be harvested, dried and used as mulch, briquettes, feeds for livestock etc.

1.7 Objectives

• determine the nutrient level of an aquaculture effluent.

• evaluate and record the phytoremediation rates of the selected aquatic

macrophytes.

• compute and compare the effects of retention times on phytoremediation rates

with two-way analysis of variance (ANOVA) at 95% confidence level using

Excel spreadsheet.

1.8 Scope of work

This research project is focused on the reduction of nutrient/pollution load of the

aquaculture effluent in the hydroponic units using aquatic macrophytes which are

water hyacinth (Eichornia crassipes), water lettuce (Pistia stratiotes), and

morning glory (Ipomea asarifolia).

The selected pollutants measured are Total Suspended Solids (TSS), Total

Dissolved Solids (TDS), Ammonium-nitrogen (NH4+-N), Nitrite - nitrogen (NO2

--

N), Nitrate-nitrogen (NO3--N), Orthophosphate-phosphorus (PO4

3--P), Chemical

Oxygen Demand (COD), pH, and Electrical Conductivity (EC).

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CHAPTER TWO

LITERATURE REVIEW

2.1 Wastewater Treatment

The importance of water as a global resource for human life is irrefutable. It

follows then that the need to manage and protect this resource has been

recognized for centuries, such that it is now a conservation priority the world

over. Advancements in the efficiency, convenience and sanitation of human

society have owed directly to the development and distribution of large-scale

dependable supplies of high-quality potable water (Oswald, 1988b).

Unfortunately, these same developments have also allowed for the convenient

aqueous disposal of objectionable, infectious and toxic wastes away from their

points of origin and, most commonly, into the nearest natural body of water

(Oswald, 1988b; Shiny et al., 2005). It is this aqueous waste, or ‘wastewater’, and

the processes involved with its remediation that form the basis of this project.

A prominent threat to global water quality in general is its contamination with

human derived wastes of residential, industrial and commercial origins. This is

particularly the case for freshwater resources, where human-derived wastewaters

are one of the major sources of contamination and pollution (Craggs et al., 1996).

In recent times, a general decline in environmental water quality—a consequence

of anthropogenic interactions—has given rise to significant environmental

problems and public health concerns (Hoffmann, 1998). These pollution-

associated issues have, therefore, justifiably received increasing levels of

attention, to the extent that they are nowadays of major concern to modern society

(de la Noüe et al., 1992).

More recently, the application and enforcement of environmental laws governing

wastewater and its discharge has become increasingly more stringent due to

heightened public pressure as well as inputs from concerned governing bodies and

agencies (Middlebrooks et al., 1974; de la Noüe et al., 1992).

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This increased regulatory pressure has served as the historical driving force

behind initial changes to waste water treatment technologies and indeed general

waste treatment philosophy (Middle brooks et al., 1974) and will no doubt

continue to drive process and technological advancements into the future, or as

long as the pollution-associated problems remain. This has however triggered the

use of alternative methods for the treatment of effluents of which

phytoremediation using some aquatic macrophytes such as water hyacinth, water

lettuce, fern, duckweed, and recently morning glory is a latest economic trend.

Snow and Ghaly (2008) used aquatic macrophytes such as water hyacinth, water

lettuce and parrot’s feather plants to examine for their abilities to remove

nutrients from aquaculture wastewater at two retention times. During the

experiment, the aquatic plants grew rapidly and appeared healthy with green

color. At hydraulic retention times (HRTs) of 6 and 12 days, the average water

hyacinth, water lettuce and parrot’s feather yields were 83, 51 and 51 g (dm) m-2

and 49, 29 and 22 g (dm) m-2, respectively. The aquatic plants were able to

significantly reduce the pollution load of the aquaculture wastewater. The TS,

COD, NH4+-N, NO2

--N, NO3--N and PO4

3--P reductions ranged from 21.4 to

48.0%, from 71.1 to 89.5%, from 55.9 to 76.0%, from 49.6 to 90.6%, from 34.5 to

54.4% and from 64.5 to 76.8%, respectively. Generally, the reductions increased

with longer retention times and were highest in compartments containing water

hyacinth followed by compartments containing water lettuce and parrot’s feather.

In terms of COD, NO3--N and PO4

3--P, the effluent leaving the hydroponics

system was suitable for reuse in aquaculture. However, at the end of the

experiment it was inferred that effluent had slightly high levels of TS, NH3-N,

NO2--N and pH.

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Ajayi and Ogunbayo (2012) investigated the effectiveness of water hyacinth in

wastewater treatment. After a 5-week simple experiment, in which water

hyacinths were planted in wastewater samples obtained from three different

industries, the average removal of pollutants were found to be 53.03%, 64.41%,

65.4%, 47.22%, 94.67% and 30.30% for Total Suspended Solids (TSS),

Biochemical Oxygen Demand (BOD), Dissolved Oxygen (DO), nitrate-nitrogen,

cadmium and iron respectively.

Kamal (2009) studied the efficiency of constructed wetland to treat pollutant in

Palm Oil Mill Effluent (POME). Parameters concerned were ammonia-nitrogen

(NH3-N) and orthophosphate (PO4

3-). In this study, lab scale of free water surface

was constructed by using water lettuce (Pistia stratiotes) as wetland plant and

gravel as filter. This experiment consisted of two systems which were without and

with cycle. Each system was conducted on four stages; first and third stage used

gravel as a filter whereas second and fourth stage used constructed wetland to

remove the pollutant. This experiment was conducted with different

concentrations of sample which were 100% concentration and 80% concentration.

For the first system (without cycle) which was 10 days of treatment, 93.36% of

NH3-N and 79.54% of PO43- had been removed from 100% sample concentration

while 90.95% of NH3-N and 78.52% of PO4

3- removed from 80% of sample

concentration. For the second system (with cycle) which is 20 days of treatment,

the optimum days of treatment was 15 days which gave the optimum results of

98.39% of NH3-N and 83.12% of from 100% sample concentration whereas

96.37% of NH3-N and 80% of PO4

3- removed from 80% sample concentration.

From the results, they showed that the percent removal of NH3-N were much

higher than PO43-. As a conclusion, it was stated that constructed wetland could be

used as industrial waste treatment and also gives high efficiency in removal of

contaminant in POME.

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Kutty, Ngatenah and Malakahmad (2009) carried out an experiment to determine

the removal efficiency of water hyacinth in polishing nitrate and phosphorus, as

well as chemical oxygen demand (COD) and ammonia. based on the knowledge

that water hyacinth is considered as the most efficient aquatic plant used in

removing vast range of pollutants such as organic matters, nutrients and heavy

metals.

Water hyacinth was cultivated in the treatment house in a reactor tank of

approximately 90(L) x 40(W) x 25(H) in dimension and built with three

compartments. Three water hyacinths were placed in each compartments and

water sample in each compartment were collected in every two days. The plant

observation was conducted by weight measurement, plant uptake and new young

shoot development.

Water hyacinth effectively removed approximately 49% of COD, 81% of

ammonia, 67% of phosphorus and 92% of nitrate. It also showed significant

growth rate at starting from day 6 with 0.33 shoot/day and they kept developing

up to 0.38 shoot/day at the end of day 24. From the studies conducted, it was

proved that water hyacinth is capable of polishing the effluent of municipal

wastewater which contains undesirable amount of nitrate and phosphorus

concentration.

2.2 Utility of Macrophytes in Phytoremediation

Macrophytes are beneficial to lake because they provide food and shelter for fish

and aquatic invertebrates. They also provide oxygen which helps in overall like

functioning and provide feed for some fish and other wildlife, macrophytes are

considered as important components of the aquatic ecosystem not only as a food

source for aquatic invertebrates but because they also act as efficient

accumulation of heavy metals, (fostne and whittman, 1979) therefore it is very

important to understand the function of macrophytes in ecosyetems.

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The use of aquatic vascular plants for heavy metal phytoremedictation is very

over emphasized for the treatment of industrial effluent before discharge into the

aquatic ecosystems. Because only an aquatic plants can flourish in aquatic

environment, naturally requiring simple mineral nutrients and sunlight, they can

be conveniently tested for their phytoremediation potential.

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CHAPTER THREE

METHODOLOGY

3.1 Experimental Materials

The chosen aquatic macrophytes for the experiment were Water hyacinth, Water

lettuce and Morning glory. Suitable quantities of these plants in their natural state

were randomly and carefully obtained from nearby streams, lakes and ponds

within and around Gbarian/Ekpetiama – Yenagoa, L.G.A in Bayelsa State. The

reason for this was to take care of the age and varietal differences.

Aquaculture effluent was obtained from Tuksmari Fish Farms, No. 20 Elelenwo

Street G.R.A Phase 1 Port Harcourt, Rivers State with coordinate (N4.82660

E6.99590) using Nokia E71 Smartphone, and transported to the aquaculture

effluent tank in the experimental site. The effluent was mixed properly and

analyzed to determine its nutrient concentration.

3.2 Experimental Apparatus

The experimental apparatus constituted of an aquaculture effluent tank,

mechanical aerator, screen and hydroponic units.

3.2.1 Aquaculture Effluent Tank

A plastic storage drum was used as the aquaculture effluent tank and as a

sedimentation tank. This tank was left static for few hours to settle out all

settleable solids which came from faecal material and uneaten food.

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3.2.2 Mechanical Aerator

The essence of the mechanical aerator was to supply air by aeration to remove

odour, convert soluble salts to their insoluble state, and increase dissolved oxygen

thus helping in the oxidation of ammonia to nitrates for the availability in plant

uptake.

3.2.3 Screen

A screen was attached to the discharge of the aquaculture effluent tank so as to

intercept uneaten food, faecal and floating materials.

3.2.4 Hydroponic Units

Shallow plastic troughs were used containing measured quantity to ensure enough

contact with the effluent. The troughs were wide enough to accommodate the

plant growth within the experimental period.

3.3 Experimental Procedure

The experimental site was the Soil and Water Conservation Laboratory-

Agricultural and Environmental Engineering Department, Niger Delta University

Wilberforce Island, Bayelsa State Nigeria. Located in the mangrove swamp

vegetative zone, the town has a tropical climate with two seasons: the wet season

from March to October and the dry season between November and April. The

experiment however began December 16, 2011 and terminated January 13, 2012.

The three aquatic macrophytes were placed in non-flow hydroponic units

containing the aquaculture effluent in order to obtain data on the effect of

treatment retention time on nutrient depletion rates within the effluent.

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The experiment was designed in a completely randomized 4 x 4 experimental

pattern, with 4 replicates. This was thus, conducted using 16 hydroponic units

each containing 6 liters of aquaculture effluent out of which 4 units containing

effluent only, was used as control.

The plants were first washed and stored in a tank with clean water to avoid pre-

contamination carry-over effects. Each hydroponic unit was then stocked with

appropriate plants of approximately same age and varietal specie.

The total hydroponic units for the experiment were 12 in addition to 4 units

containing effluent only (the control). The essence of the control was to ascertain

if remediation was caused by factors other than the aquatic macrophytes.

In order to maintain Dissolved Oxygen (DO) in the hydroponic units, mechanical

aeration using air pump and bubble wand were applied every three days for 10

minutes, throughout the experimental period of 28-days.

During the experimental period, water samples were collected at days 7, 14, 21,

and 28 from each unit and refrigerated in labeled bottles until they were analyzed

in the laboratory.

3.4 Analyses

All samples collected were analyzed to determine the following; pH, Electrical

Conductivity using portable hand-held kits, TDS, TSS, NH4 +-N, NO2--N, NO3

--

N, PO43— P and COD using standard methods in the Chemical Sciences

Laboratory, Niger Delta University Wilberforce Island, Bayelsa State. A two-way

analysis of variance (ANOVA) was used for the comparison with the aid of Excel

spreadsheet.

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CHAPTER 4

RESULTS AND DISCUSSION

4.1 Laboratory Preparations

At the end of the experiment, samples were sent to the laboratory for analysis and

observations were made as to the behavior and rate of remediation by the selected

aquatic macrophytes. The laboratory results were however computed using initial

sample collected before the commencement of the experiment and subsequent

data gotten at various hydraulic retention times.

4.2 Plant growth:

At the initial stage of the experiment, the aquatic macrophytes in their various

hydroponic units performed very well and appeared healthy with green colour.

The water hyacinth (plates 4.1a, 4.1b, 4.1c and 4.1d) and water lettuce (plates

4.2a, 4.2b, 4.2c and 4.2d) produced numerous daughter plants by vegetative

propagation and morning glory grew rapidly across the water surface forming

numerous branches and nodes. Between days 7-14 of the experiment, the surface

area of compartments containing water hyacinth, lettuce and morning glory

(plates 4.3a, 4.3b, 4.3c and 4.3d) were completely covered. It was also observed

that there were significant increases in the size of individual macrophytes due to

nutrient absorption.

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4.2.1 Water hyacinth progress in the course of the experiment

Plate 4.1(a) Water Hyacinth (Day 1) Plate 4.1(b) Water Hyacinth (Day 14)

Plate 4.1(c) Water Hyacinth (Day 21) Plate 4.1(d) Water Hyacinth (Day 28)

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4.2.2 Water lettuce progress in the course of the experiment

Plate 4.2(a) Water lettuce (Day1) Plate 4.2(b) Water lettuce (Day14)

Plate 4.2(c) Water lettuce (Day 21) Plate 4.2(d) Water lettuce (Day28)

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4.1.3 Morning glory progress in course of the experiment

Plate 4.3(a) Morning glory (Day 1) Plate 4.3(b) Morning glory (Day14)

Plate 4.3(c) Morning glory (Day21) Plate 4.3(d) Morning glory (Day28)

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4.3 Effluent quality:

Table 4.6 shows the effluent and influent Total Suspended Solids (TSS), Total

Dissolved Solids (TDS), Chemical Oxygen Demand(COD), Ammonium - (NH4+),

Nitrite (NO2-), Nitrate - (NO3

- -N), Orthophosphate (PO4 -P), pH , and Electrical

Conductivity (E.C) and the nutrient removal efficiencies of each water quality

parameter. The effects of plant type and hydraulic retention time on the reductions

of the parameters were tested using a two-way analysis of variance (ANOVA)

using Excel spreadsheet.

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Table 4.1 Chemical constituents of the aquaculture effluent

Parameter (mg L-1) Value

Total Suspended Solids 12.60

Total Dissolved Solids 2010.00

Chemical Oxygen Demand 108.00

Ammonium-Nitrogen 0.05

Nitrite-Nitrogen 0.34

Nitrate-Nitrogen 0.56

Orthophosphate 0.40

pH 6.40

EC (μs cm-1) 4020.00

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Table 4.2 Mean Values for Pollutant Reduction by Water Hyacinth

Hydraulic Retention Time (Days)

Parameters mg/L 0 7 14 21 28

Total Suspended So/.lids 12.60 5.80 5.75 2.75 4.71

Total Dissolved Solids 2010.00 638.25 199 94.55 61.25

Chemical Oxygen Demand 108.00 161.75 143.25 114.13 104.13

Ammonium-Nitrogen 0.05 0.0175 0.0075 0.005 0.005

Nitrite-Nitrogen 0.34 0.12 0.079 0.075 0.052

Nitrate-Nitrogen 0.56 0.079 0.063 0.0065 0.015

Orthophosphate 0.40 0.18 0.13 0.078 0.048

pH 6.40 5.82 5.66 5.50 5.46

Electrical Conductivity(μs cm-1) 4020.00 1276.50 379.50 189.33 122.48

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Table 4.3 Mean Values for Phytoremediation by Water Lettuce



Total Suspended Solids 12.60 3.93 7.78 2.30 5.30

Total Dissolved Solids 2010.00 851.50 232.00 76.46 222.60





Orthophosphate 0.40 0.30 0.195 0.195 0.095

pH 6.40 6.15 5.85 5.97 5.48

Electrical Conductivity(μs cm-1) 4020.00 1703 466.75 152.88 445.2

27

Table 4.4 Mean Values for Phytoremediation by Morning glory

HYDRAULIC RETENTION TIME (DAYS)








Orthophosphate 0.40 0.76 0.03 0.21 0.17

pH 6.40 6.11 5.68 6.19 4.27

Electrical Conductivity (μs cm-1) 4020.00 1957.25 625 304.50 229.75

28

Table 4.5 Mean Values for Control









Orthophosphate 0.40 0.36 0.23 0.19 0.22

pH 6.40 6.52 6.68 7.075 6.28

Electrical Conductivity (μs cm-1) 4020.00 2016.75 1273.75 1222.25 1383.50

29

Table 4.6 - Water Quality parameters for Total Dissolved Solids and Total Suspended Solids Parameter HRT days Treatment Influent

(mg L-1) Effluent (mg L-1)

Reduction (mg L-1) (%)

TDS 7 Control 2010 1008.50 1001.50 50 Water hyacinth 2010 638.25 1371.75 68 Water lettuce 2010 851.50 1158.50 58 Morning glory 2010 978.75 1031.25 51 14 Control 2010 636.75 1373.25 68 Water hyacinth 2010 199.00 1811.00 90 Water lettuce 2010 232.00 1778.00 88 Morning glory 2010 245.75 1764.25 88 21 Control 2010 487.50 1522.50 76 Water hyacinth 2010 94.55 1915.45 95 Water lettuce 2010 76.45 1933.55 96 Morning glory 2010 152.25 1857.75 92 28 Control 2010 691.75 1318.25 65 Water hyacinth 2010 61.25 1948.75 97 Water lettuce 2010 222.60 1787.40 89 Morning glory 2010 114.75 1895.25 94 TSS 7 Control 12.60 5.05 7.55 60 Water hyacinth 12.60 5.80 6.80 54 Water lettuce 12.60 3.93 8.67 69 Morning glory 12.60 4.74 7.86 63 14 Control 12.60 6.38 6.22 49 Water hyacinth 12.60 5.75 6.85 54 Water lettuce 12.60 7.78 4.82 38 Morning glory 12.60 3.36 9.24 73 21 Control 12.60 5.48 7.12 57 Water hyacinth 12.60 2.75 9.85 78 Water lettuce 12.60 2.30 10.30 82 Morning glory 12.60 4.31 8.29 66 28 Control 12.60 3.28 9.32 74 Water hyacinth 12.60 4.71 7.89 63 Water lettuce 12.60 5.30 7.30 58 Morning glory 12.60 7.43 5.17 41

30

Table 4.6.1 - Water Quality parameters for Nitrite (NO2) and Nitrate (NO3) NO2 7 Control 0.34 0.33 0.01 3 Water hyacinth 0.34 0.12 0.22 65 Water lettuce 0.34 0.19 0.15 44 Morning glory 0.34 0.21 0.13 38 14 Control 0.34 0.15 0.19 56 Water hyacinth 0.34 0.08 0.26 76 Water lettuce 0.34 0.10 0.24 71 Morning glory 0.34 0.12 0.22 65 21 Control 0.34 0.14 0.20 59 Water hyacinth 0.34 0.08 0.26 76 Water lettuce 0.34 0.09 0.25 74 Morning glory 0.34 0.08 0.26 76 28 Control 0.34 0.17 0.17 50 Water hyacinth 0.34 0.05 0.29 85 Water lettuce 0.34 0.10 0.24 71 Morning glory 0.34 0.09 0.25 74 NO3 7 Control 0.56 0.21 0.35 63 Water hyacinth 0.56 0.08 0.48 86 Water lettuce 0.56 0.20 0.36 64 Morning glory 0.56 0.15 0.41 73 14 Control 0.56 0.14 0.42 75 Water hyacinth 0.56 0.06 0.50 89 Water lettuce 0.56 0.05 0.51 91 Morning glory 0.56 0.11 0.45 80 21 Control 0.56 0.13 0.43 77 Water hyacinth 0.56 0.01 0.55 98 Water lettuce 0.56 0.04 0.52 93 Morning glory 0.56 0.07 0.49 88 28 Control 0.56 0.15 0.41 73 Water hyacinth 0.56 0.02 0.44 79 Water lettuce 0.56 0.05 0.51 91 Morning glory 0.56 0.06 0.50 89

31

Table 4.6.2 Water Quality parameters for Ammonium (NH4) and Orthophosphate (PO4) NH4 7 Control 0.05 0.03 0.02 40 Water hyacinth 0.05 0.02 0.03 60 Water lettuce 0.05 0.02 0.03 60 Morning glory 0.05 0.04 0.01 20 14 Control 0.05 0.02 0.03 60 Water hyacinth 0.05 0.01 0.04 80 Water lettuce 0.05 0.01 0.04 80 Morning glory 0.05 0.01 0.04 80 21 Control 0.05 0.02 0.03 60 Water hyacinth 0.05 0.01 0.04 80 Water lettuce 0.05 0.01 0.04 80 Morning glory 0.05 0.01 0.04 80 28 Control 0.05 0.03 0.03 60 Water hyacinth 0.05 0.01 0.04 80 Water lettuce 0.05 0.02 0.03 60 Morning glory 0.05 0.01 0.04 80 PO4 7 Control 0.40 0.36 0.04 10 Water hyacinth 0.40 0.18 0.22 55 Water lettuce 0.40 0.30 0.10 25 Morning glory 0.40 0.76 -0.36 -90 14 Control 0.40 0.23 0.17 43 Water hyacinth 0.40 0.13 0.27 68 Water lettuce 0.40 0.20 0.20 50 Morning glory 0.40 0.03 0.37 93 21 Control 0.40 0.19 0.21 53 Water hyacinth 0.40 0.08 0.32 80 Water lettuce 0.40 0.20 0.20 50 Morning glory 0.40 0.21 0.19 48 28 Control 0.40 0.22 0.18 45 Water hyacinth 0.40 0.05 0.35 88 Water lettuce 0.40 0.10 0.30 75 Morning glory 0.40 0.17 0.23 58

32

Table 4.6.3 Water Quality parameters for Chemical Oxygen Demand and pH COD 7 Control 108.00 122.00 -14.00 -13 Water hyacinth 108.00 161.75 -53.75 -50 Water lettuce 108.00 140.00 -32.00 -23 Morning glory 108.00 140.25 -32.25 -30 14 Control 108.00 98.80 9.20 9 Water hyacinth 108.00 143.25 -35.25 -33 Water lettuce 108.00 74.50 33.50 31 Morning glory 108.00 88.75 19.20 18 21 Control 108.00 110.75 -2.75 -3 Water hyacinth 108.00 114.13 -6.13 -5 Water lettuce 108.00 58.50 49.50 46 Morning glory 108.00 44.50 63.50 59 28 Control 108.00 115.00 -7.00 -6 Water hyacinth 108.00 104.13 3.87 4 Water lettuce 108.00 65.00 43.00 40 Morning glory 108.00 33.63 74.37 69 pH 7 Control 6.40 6.52 -0.12 -2 Water hyacinth 6.40 5.82 0.58 9 Water lettuce 6.40 6.15 0.25 4 Morning glory 6.40 6.11 0.29 5 14 Control 6.40 6.68 -0.28 -4 Water hyacinth 6.40 5.66 0.74 12 Water lettuce 6.40 5.58 0.82 13 Morning glory 6.40 5.68 0.72 11 21 Control 6.40 7.01 0.61 10 Water hyacinth 6.40 5.50 0.90 14 Water lettuce 6.40 5.97 0.43 7 Morning glory 6.40 6.16 0.24 4 28 Control 6.40 6.28 0.12 2 Water hyacinth 6.40 5.46 0.94 15 Water lettuce 6.40 5.48 0.92 14 Morning glory 6.40 4.27 2.13 33

33

Table 4.6.4 - Water Quality Parameters for Electrical Conductivity E.C 7 Control 4020 2016.75 2003.25 50 Water hyacinth 4020 1276.50 2743.50 68 Water lettuce 4020 1703.00 2317.00 58 Morning glory 4020 1957.25 2062.75 51 14 Control 4020 1273.75 2746.25 68 Water hyacinth 4020 379.50 3640.50 91 Water lettuce 4020 466.75 3553.25 88 Morning glory 4020 625.00 3395.00 84 21 Control 4020 1222.25 2797.75 67 Water hyacinth 4020 189.33 3830.67 95 Water lettuce 4020 152.88 3867.12 96 Morning glory 4020 304.50 3715.50 92 28 Control 4020 1383.50 2636.50 66 Water hyacinth 4020 122.48 3897.52 97 Water lettuce 4020 152.88 3867.12 96 Morning glory 4020 229.75 3790.25 94

34

4.3.1 Total Solids:

This is the sum of Total Dissolved Solids and Total Suspended Solids. The

average total solid concentration in the aquaculture wastewater for Total

Dissolved Solids (TDS) and Total Suspended Solids (TSS) were 2010 mgL-1 and

12.6 mgL-1 respectively. At hydraulic retention times of 7 and 14 days the

average reductions from the controls and compartments containing water

hyacinth, water lettuce and morning glory were 50,68,58 and 51% for TDS; 68,

90, 88 and 88% for TSS respectively. The reductions were however higher in the

compartments containing water hyacinth followed by water lettuce and morning

glory. Figure 4.4 and 4.41 shows a clear graphical representation of the plant

behavior at various retention times. The results of ANOVA displayed also shows

that for TSS there was no significant difference while for TDS there was

significant difference.

35

FIG. 4.1 TSS Phytoremediation rates at various hydraulic retention times

0

1

2

3

4

5

6

7

8

9

DAY 7 DAY 14 DAY 21 DAY 28

TSS

Con

cent

ratio

n m

g/L

Sample Days

WATER HYACINTH WATER LETTUCEMORNING GLORY CONTROL

36

Table 4.7 Results of a two-way ANOVA for TSS reductions as affected by plant type and hydraulic retention time

Source of Variation

SS df MS F P-value F crit

Rows 10.91644 3 3.638813 0.760747 0.586238 9.276628 Columns 0.035113 1 0.035113 0.007341 0.93712 10.12796 Error 14.34964 3 4.783213 Total 25.30119 7

37

FIG. 4.2 TDS Phytoremediation Rates at Various Hydraulic Retention Times.

0

200

400

600

800

1000

1200


TD

S C

once

ntra

tion

(mg/

L)

Sample Days


38

Table 4.8 Results of a two-way ANOVA for TDS reductions as affected by plant type and hydraulic retention time

Source of Variation


Rows 839564 3 279854.7 54.53244 0.00408 9.276628 Columns 1483.763 1 1483.763 0.289126 0.628109 10.12796 Error 15395.68 3 5131.894 Total 856443.4 7

39

4.4 Chemical Oxygen Demand:

The aquaculture wastewater had an average chemical oxygen demand (COD)

concentration of 108 mg L-1. Uneaten or regurgitated food and faecal production

are the major sources of organic matter in aquaculture effluents. Both the plant

type and the HRT had significant effects on the COD reduction. The COD

removal was higher in the compartments containing water lettuce between days

7and 14 followed by morning glory between days 21 and 28.

At HRTs of 7 and 14 days, the average COD reductions from the controls and the

compartments containing water hyacinth, water lettuce and morning glory were , -

13, -50, -23, and -30% and 9, -33, 31 and 18% respectively, while days 21 and 28

were -6, 4, 40 and 69%. The COD reductions increased as hydraulic retention

time was increased.

Figure 4.5 shows a clear graphical representation of the plant behavior at various

retention times. The results of ANOVA displayed also shows that there was

significant difference.

Sooknah and Wilkie (2004) investigated the use of water hyacinth and water

lettuce plants for reducing the nutrient content of an anaerobically digested dairy

manure and reported COD reductions of 65.8, 80.5 and 79.6% in the control and

in the compartments containing water hyacinth and water lettuce after 31 days.

40

FIG 4.3 COD Phytoremediation Rates at Various Hydraulic Retention Times.

0

20

40

60

80

100

120

140

160

180


CO

D c

once

ntra

tion

(mg/

L)

Sample Days


41

Table 4.9 Results of a two-way ANOVA for COD reductions as affected by plant type and hydraulic retention time

Source of Variation



42

4.2.3 Ammonium – Nitrogen:

The aquaculture wastewater contained 0.05 mg L-1 ammonium – nitrogen

(NH4+-N). In fish and shellfish, ammonia is the major nitrogenous waste product

of protein catabolism, and it is excreted primarily in un-ionized form (NH3)

through the gills. Ammonium is also produced through the microbial

decomposition of fish faeces and uneaten food in a process called

ammonification.

Ammonification refers to a series of biological transformations that convert

organically bound nitrogen to ammonium – nitrogen under both aerobic and

anaerobic conditions. The reactions involved in the decomposition release energy

which can then be utilized by the microorganisms for growth and reproduction or

to sustain metabolic functions.

The results of the analyses in Figure 4.6 and Table 4.9 shows that NH4+-N

reductions were significantly affected by plant type, but were not significantly

influenced by hydraulic retention time. At HRTs of 7 and 14 days, the average

NH4+-N reductions from the controls and the compartments containing water

hyacinth, water lettuce and morning glory were 40 , 60, 60,and 20% and 60, 80,

80 and 80% respectively, while days 21-28, the reductions were 60, 80, 80 and

80% and 60, 80, 60 and 80% respectively.

43

FIG 4.4 NH4+ Phytoremediation Rates at various Hydraulic Retention Times.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14


NH

4+ co

ncen

trat

ion

(mg/

L)

Sample Days


44

Table 4.10 Results of a two-way ANOVA for NH4+ reductions as affected by plant type

and hydraulic retention time Source of Variation



45

4.3.4 Nitrite – Nitrogen:

The aquaculture wastewater had an average nitrite – nitrogen (NO2- -N)

concentration of 0.338 mg L-1. Nitrification was facilitated by the continuous

aeration of the system compartments during the experiments. At hydraulic

retention times of 7 and 14 days, the average NO2--N reductions from the controls

and the compartments containing water hyacinth, water lettuce and morning glory

were 3, 65, 44 and 38% and 56, 76, 71 and 65%, respectively. The results of the

statistical analyses presented in Table 4.5 shows that plant type and the HRT had

significant effects on NO2--N reductions. The NO2

--N removal was higher in the

compartments containing water hyacinth followed by the compartments

containing water lettuce and morning glory, although the difference between the

three selected aquatic macrophytes were not much. The NO2- - N reductions

increased with the longer retention time.

46

FIG. 4.5 NO2- Phytoremediation Rates at various Hydraulic Retention Times

0

1

2

3

4

5

6

7

8


NO

2- con

cent

ratio

n (m

g/L

)

Sample Days WATER HYACINTH WATER LETTUCEMORNING GLORY CONTROL

47

Table 4.11 Results of a two-way ANOVA for NO2- reductions as affected by plant type

and hydraulic retention time Source of Variation


Rows 0.016826 3 0.005609 29.50055 0.009979 9.276628 Columns 2.81E-05 1 2.81E-05 0.147929 0.726168 10.12796 Error 0.00057 3 0.00019 Total 0.017425 7

48

4.3.5 Nitrate – Nitrogen:

The aquaculture wastewater had an average nitrate – nitrogen (NO3- -N)

concentration of 0.56 mg L-1. NO3- -N accumulates in aquaculture systems as a

result of nitrification (Poxton, and Allouse, 1982; Ackefors, Huner, and Konikoff;

1994). At HRT of 28days, the average NO3—N reductions from the controls and

the compartments containing water hyacinth, water lettuce and morning glory

were 73, 79, 91 and 89% respectively. The results of the statistical analyses

presented in Figure 4.8 shows that both plant type and HRT had slight significant

effects on NO3-—N reductions. The NO3

-—N removal was higher in the

compartments containing morning glory followed by the compartments

containing water hyacinth and water lettuce. NO3—N reductions increased with

the longer retention time.

(Jo, Ma, and Kim; 2002) evaluated the potential of water lettuce and water

hyacinth plants for removal of NO3-—N from an intensive recirculating

aquaculture system effluent over a 48 hour period and found that the NO3-—N

concentration in the wastewater was reduced from 21.4 to 17.4 and 17.9 mg L-1,

respectively. NO3-—N is not acutely toxic to fish. The average NO3

-—N

concentrations in the final effluents from the hydroponics system were 0.41, 0.44,

0.51 and 0.50 mg L-1 at day 28 for control, water hyacinth, water lettuce and

morning glory, respectively.

Poxton (2003) recommended that NO3-—N concentrations do not exceed

50 mg L-1 in waters used for the culture of fish and shellfish.

49

FIG.4.6 NO3- Phytoremediation Rates at various Hydraulic Retention Times.

0

0.05

0.1

0.15

0.2

0.25


NO

3- Con

cent

ratr

atio

n (m

g/L

)

Sample Days


50

Table 4.12 Results of a two-way ANOVA for NO3- reductions as affected by plant type and

hydraulic retention time. Source of Variation


Rows 0.016716 3 0.005572 0. 32288 0.253417 9.276628 Columns 0.002485 1 0.002485 1.03599 0.383693 10.12796 Error 0.007196 3 0.002399 Total 0.026398 7

51

4.3.6 Orthophosphate – Phosphorus:

The aquaculture wastewater contained 0.4 mg L-1 phosphate – phosphorus (PO43--

P). Phosphorus occurs in aquaculture wastewater primarily as soluble and

insoluble phosphates in both organic and inorganic forms (EPA. 2000). The main

inorganic form is soluble orthophosphate, which exists in different states (H2PO4-,

HPO42-, and PO4

3--P) depending on the pH of the medium (Mitsch, and Gosselink,

2000).

At HRTs of 7 and 14 days, the average PO43--P reductions from the controls and

the compartments containing water hyacinth, water lettuce and morning glory

were -10, 55, 25 and -90% and 43, 68, 50 and 93%, respectively. Hydraulic

Retention Time had significant effects on PO43--P removal.

The PO43--P removal was higher in the compartments containing water hyacinth

at day 7 followed by the compartments containing water lettuce and the morning

glory which had 90% increase, but at day 14, reduction was higher in hydroponic

unit containing morning glory followed by water hyacinth and then water lettuce.

The PO43--P reductions were influenced by hydraulic retention time and increased

as HRT was increased.

52

FIG 4.7 PO43- Phytoremediation Rates at various Hydraulic Retention Times.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8


PO43-

Con

cent

ratio

n (m

g/L

)


53

Table 4.13 Results of a two-way ANOVA for PO43--P reductions as affected by plant type

and hydraulic retention time

Source of Variation



54

4.4 pH:

The aquaculture wastewater had an average pH of 6.4. At hydraulic retention

times of 7 and 14 days, the pH of the final effluent leaving the system was -2, 9,

4, and 5% and

-4, 12, 13 and 11 for the controls and compartments containing water hyacinth,

water lettuce and morning glory, respectively. This can be inferred that the

effluent at the initial state was acidic in nature and was able to reduce acidity level

of the effluent.

According to (Lawson 1995; and Meande 1989) the pH of waters used for the

culture of fish and shellfish should range from 6.5 to 8.0. When the pH of the

growth medium rises above 9.0, it begins to adversely affect most aquatic species,

and a pH in the range of

11.0 – 11.5 is lethal to all species of fish (Poxton and Allouse; 1982) When pH

falls within the range of 5.0 – 6.0, rainbow trout, salmonids and molluscs become

rare, the rate of organic matter decomposition declines because the fungi and

bacteria responsible for degradation are not acid tolerant, and most green algae,

diatoms, snails and phytoplankton disappear (Poxton, 2003). Most fish eggs will

not hatch when the pH of the surrounding environment reaches 5.0. Changes in

water chemistry may also occur as a result of a decrease in pH ( Poxton M. J and

Allouse S. B; 1982) Waters suitable for reuse in an aquaculture facility were not

produced.

55

FIG 4.8 pH levels at various Hydraulic Retention Times

0

1

2

3

4

5

6

7

8


pH

Lev

el

Sample Days


56

Table 4.14 Results of a two-way ANOVA for pH changes as affected by plant type and hydraulic retention time

Source of Variation



57

4.5 Electrical Conductivity:

Electrical conductivity (EC) is a measure of the ability of water to conduct an

electric current and depends on:

Concentration of the ions (higher concentration, higher EC)

Temperature of the solution (high temperature, higher EC)

The determination of the electrical conductivity is a rapid and convenient means

of estimating the concentration of ions in solution.

The aquaculture effluent had an average electric conductivity of 4020 μs cm-1 .In

the course of the experiment, there were reductions in the constituents of

electrical conductivity in the various hydroponic units as time increased. Table

4.9 and Figure 4.11 shows that there was significant effects of plant type and

Hydraulic Retention Time.Reduction in the compartments containing control,

water hyacinth, water lettuce and morning glory for days 7 and 14 were 50, 68, 58

and 51% and58, 91, 88 and 84%.Water hyacinth proved to be the most effective

followed by water lettuce and then morning glory.

58

FIG 4.9 Electrical Conductivity Phytoremediation Rates at various Hydraulic Retention

Times.

0

500

1000

1500

2000

2500

DAY 7 DAY14 DAY 21 DAY 28

Ele

ctri

cal C

ondu

ctiv

ity (µ

s cm

-1)

Sample Days


59

Table 4.15 Results of a two-way ANOVA for E.C changes as affected by plant type and hydraulic retention time

Source of Variation


Rows 3298884 3 1099628 51.2644 0.004467 9.276628 Columns 15196.35 1 15196.35 0.70845 0.46176 10.12796 Error 64350.38 3 21450.13 Total 3378430 7

60

CHAPTER 5

CONCLUSION AND RECOMMENDATION

5.1 CONCLUSION

Untreated wastewater generally contains high levels of organic material, numerous

pathogenic micro-organisms, as well as nutrients and toxic compounds which entails

environmental and health hazards and, consequently, must immediately be treated

appropriately before discharge. The ultimate goal of this work was to comparatively

assess the phytoremediation rates of Water hyacinth, Water lettuce and Morning glory

in an aquaculture effluent.

From the comparative assessment, it was inferred that the selected macrophytes were

capable and efficient enough to reduce the pollutant levels in aquaculture effluent.

Parameters analyzed were Total Suspended Solids (TSS), Total Dissolved Solids

(TDS), Ammonium-nitrogen (NH4+-N), Nitrite - nitrogen (NO2

--N), Nitrate-nitrogen

(NO3--N), Orthophosphate-phosphorus (PO4

3--P), Chemical Oxygen Demand (COD),

pH, and Electrical Conductivity (EC).

It was also observed that reductions were highest in hydroponic units containing water

hyacinth followed by water lettuce and then morning glory. Water hyacinth being the

most efficient at HRT day 28 was able to reduce TDS by 97%, TSS by 63%, NO2 by

85%, with slight variation in the reduction of NO3 by 79% against water lettuce with

91%. Also NH4 was reduced by 80% for both water hyacinth and morning glory; water

hyacinth reduced 88% PO4, COD by 4% with morning glory dominating by 69%

reduction.

61

5.2 RECOMMENDATION

The conventional wastewater treatment plants of activated carbon, electro dialysis, ion

exchange, reverse osmosis etc. are expensive to install, operate and maintain especially

in developing countries like Nigeria. Hence, the use of aquatic macrophytes for

wastewater purification is a viable alternative. Aquatic macrophytes enhance

wastewater treatment by acting as a medium for bacterial growth, by filtering/adsorbing

suspended particulate matter and removing inorganic nutrients from the wastewater.

This assessment will help in recommending a more suitable aquatic plant to be used for

treatment of aquaculture effluent. The use of aquatic plants for the purification of

aquaculture effluent will be a viable alternative to conventional wastewater treatment

plants. The advantage of using aquatic plant for purification is that the water resources

are conserved as the environment is naturally controlled by the plant creating a

mutually beneficial, symbiotic relationship with the aquatic animal.

This research project has however provided several useful outcomes that can assist in

future guidelines for effective, ecologically friendly and economic methods of

wastewater purification.

• The selected aquatic macrophytes should be used because they are effective in the

improvement of water quality.

• They can be used for treatment of other types of wastewater.

• They should be used because they are economically friendly and inexpensive and are

easy to operate even by the rural dwellers.

62

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Snow, A. M and Ghaly, A. E (2008a) Use of barley for the purification of aquaculture wastewater in a hydroponic system. American Journal of Environmental Sciences. Vol. 4(2): 89-102.

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Snow, A. M and Ghaly, A. E (2008b) A comparative study of the purification of aquaculture wastewater using water hyacinth, water lettuce and parrot’s feather. American Journal of Applied Sciences. Vol. 5(4): 440-453.

Sooknah, R. D and Wilkie, A. C (2004) Nutrients removal by floating aquatic macrophytes cultured in anaerobically digested flushed dairy manure wastewater. Ecological Engineering. 22: 27-24.

Tchobanoglous, G., Burton, F.L and Stensel, H.D (2003) Wastewater Engineering. Treatment and Re-use Tata Mc Graw-Hill publishing company Ltd. New Delhi Tucker, C. S and Robinson, E. H (1990) Channel Catfish Handbook. New York: Van Nostrand Reinhold

Ruenglertpanyakul, W., Attasat, S and Wanichpongpan, P (2004) Nutrient Removal from Shrimp Farm Effluent by Aquatic Plants. Water Science and Technology. IWA Publishing. Vol 50. No 6. pp 321-330 U. S. Environmental Protection Agency (USEPA) (1975) Process Design Manual for Nitrogen Control. Washington DC: USEPA, Office of Technology Transfer

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http://www.myhydroponicgarden.net/

http://www.dnr.state.wi.us/org

http://www.idrc.ca/fr/ev

APPENDICES

APPENDIX I

HARVESTING OF THE WATER HYACINTH

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TURNING THE AQUACULTURE EFFLUENT INTO THE EFFLUENT TANK

APPENDIX II

THE EFFLUENT TANK READY TO DISCHARGE MEASURED QUANTITY OF EFFLUENT FOR USE IN THE EXPERIMENT.

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COLLECTION OF MEASURED QUANTITY OF THE EFFLUENT TO BE PUT INTO

HYDROPONIC UNITS.

APPENDIX III

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CAREFULLY RANDOMIZING AND PLACEMENT OF AQUATIC MACROPHYTES IN VARIOUS HYDROPONIC UNITS

AERATION DURING THE EXPERIMENTAL PERIOD

APPENDIX IV

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SAMPLE COLLECTION IN PROGRESS

FINAL SAMPLES COLLECTED FOR LABORATORY ANALYSIS ON DAY 28

APPENDIX V

Effects of the Water hyacinth on some physicochemical characteristics of the aquaculture effluent for the Hydraulic Retention Times

70

Sample code and

HRT(days)

Effluent Parameter (mg L-1)

pH

E.C (μs cm-1)

TDS

TSS

NO2

NO3

NH4

PO4

COD

A1-7 5.62 940 470 14.00 0.143 0.018 0.02 0.24 150

A2-7 5.78 1901 950 6.00 0.135 0.15 0.01 0.4 201

A3-7 5.53 1063 532 2.4 0.124 0.088 0 0.04 168

A4-7 6.35 1202 601 0.8 0.077 0.06 0.04 0.04 128

MEAN 5.82 1276.5 638.25 5.8 0.12 0.079 0.0175

0.18 161.75

A1-14 5.68 167 84 5 0.044 0.011 0.01 0.18 78

A2-14 6.25 879 440 10 0.077 0.08 0.01 0.1 185

A3-14 5.37 328 164 3.8 0.147 0.015 0.01 0.2 180

A4-14 5.34 216 108 4.2 0.046 0.01 0 0.02 130

MEAN 5.66 379.5 199 5.75 0.079 0.063 0.0075

0.13 143.25

A1-21 4.67 114 57 2 0.1 0.012 0.02 0.08 68

A2-21 6.34 514 257 4 0.077 0.011 0 0.21 170

A3-21 5.58 544 272 2.5 0.087 0.003 0 0.02 140

A4-21 5.41 74.9 37 2.5 0.035 0 0 0 78.5

MEAN 5.50 189.33 94.55 2.75 0.075 0.0065 0.005 0.078 114.13

A1-28 5.45 122 61 2.4 0.053 0.01 0.01 0.05 105

A2-28 5.73 225 5.73 225 0.082 0.01 0 0.1 105

A3-28 5.19 68 5.19 68 0.035 0.001 0 0.02 138

A4-28 5.47 74.9 5.47 74.9 0.037 0.04 0.01 0.02 68.5

MEAN 5.46 122.48 5.46 122.48 0.052 0.015 0.005 0.048 104.13

APPENDIX VI

Effects of the Water lettuce on some physicochemical characteristics of the aquaculture effluent for the various Hydraulic Retention Times

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Sample code and HRT(days)


pH

E.C (μs cm-1)

TDS

TSS

NO2

NO3

NH4

PO4

COD

B1-7 6.47 1456 728 8.40 0.184 0.122 0.01 0.38 140.0

B2-7 5.86 1862 931 2.00 0.194 0.170 0.02 0.40 130.0

B3-7 5.90 1841 920 4.50 0.183 0.200 0.01 0.35 170.0

B4-7 6.36 1653 827 0.80 0.194 0.32 0.04 0.068 120.0

MEAN 6.15 1703 851.50

3.93 0.19 0.203 0.02 0.30 140

B1-14 6.02 208 104 12.50 0.102 0.02 0.010 0.04 58.0

B2-14 5.56 470 230 3.40 0.108 0.094 0.02 0.10 106.0

B3-14 6.12 313 156 0.80 0.083 0.068 0.00 0.10 55.0

B4-14 5.68 876 438 14.40 0.102 0.022 0.01 0.54 80.0

MEAN 5.85 466.75 232.00

7.78 0.099 0.051 0.01 0.195 74.75

B1-21 6.35 118 59 2.50 0.151 0.015 0.00 0.50 60.0

B2-21 5.92 97.5 48.8 4.00 0.048 0.003 0.00 0.02 84.0

B3-21 5.91 244 122 2.50 0.048 0.043 0.01 0.02 60.0

B4-21 5.72 152.0 76 1.2 0.108 0.08 0.01 0.24 30.0

MEAN 5.97 152.88 76.45 2.30 0.089 0.042 0.005 0.195 58.50

B1-28 5.31 1282 641 1.20 0.072 0.012 0.00 0.14 120.0

B2-28 5.39 150 75 4.40 0.073 0.004 0.01 0.01 40.0

B3-28 5.61 102.8 51.4 3.10 0.051 0.059 0.01 0.05 50.0

B4-28 5.62 246 123 12.50 0.194 0.018 0.04 0.18 50.0

MEAN 5.48 445.2 222.6 5.30 0.103 0.048 0.015 0.095 65.00

APPENDIX VI

Effects of the Morning glory on some physicochemical characteristics of the aquaculture effluent for the various Hydraulic Retention Times

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Sample code and

HRT(days)


pH

E.C (μs cm-1)

TDS

TSS

NO2

NO3

NH4

PO4

COD

C1-7 5.41 2420 1210 2.85 0.212 0.138 0.04 1.28 120.0 C2-7 6.42 1993 997 4.00 0.255 0.165 0.02 0.62 201.00

C3-7 5.80 2100 1050 3.60 0.183 0.074 0.04 0.74 90.00

C4-7 6.80 1316 658 8.50 0.172 0.240 0.04 0.38 150.00

MEAN 6.11 1957.25 978.75 4.74 0.21 0.15 0.035 0.76 140.25

C1-14 5.34 568 284 1.80 0.218 0.20 0.01 0.33 90.00

C2-14 6.24 535 268 2.80 0.068 0.120 0.01 0.15 75.00

C3-14 5.62 657 329 5.05 0.083 0.059 0.01 0.44 70.00

C4-14 5.51 740 370 3.80 0.121 0.078 0.02 0.28 120.00

MEAN 5.68 625 245.75 3.36 0.12 0.11 0.01 0.03 88.75

C1-21 6.20 278 138 2.40 0.105 0.076 0.02 0.18

20.00

C2-21 6.00 217 109 3.50 0.048 0.074 0.00 0.10

40.00

C3-21 6.24 4.09 205 0.85 0.060 0.063 0.00 0.32 62.00

C4-21 6.32 314 157 10.50 0.102 0.045 0.01 0.25 56.00

MEAN 6.19 304.5 152.25 4.31 0.079 0.065 0.0075 0.21 44.5

C1-28 5.66 194 97 14.50 0.077 0.155 0.02 0.30

32.00

C2-28 5.59 212 106 4.2 0.074 0.370 0.01 0.05 30.00

C3-28 5.81 301 150 5.60 0.121 0.078 0.00 0.16 40.50

C4-28 5.58 212 106 5.40 0.075 0.018 0.02 0.16 32.00

MEAN 4.27 229.75 114.75 7.43 0.087 0.16 0.13 0.17 33.63

APPENDIX VIII

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Effects of the Control on some physicochemical characteristics of the aquaculture effluent for the various Hydraulic Retention Times

Sample code

and HRT(days)


pH

E.COND (μs cm-1)

TDS

TSS

NO2

NO3

NH4

PO4

COD

D1-7 6.71 2510 1255 0.68 0.254 0.205 0.08 0.84 130

D2-7 6.98 1528 791 6.80 0.378 0.197 0.02 0.28 110

D3-7 5.90 1815 908 8.40 0.431 0.25 0.01 0.18 120

D4-7 6.50 2160 1080 4.30 0.288 0.125 0.02 0.13 128

MEAN 6.52 2016.75 1008.50 5.045 0.33 0.21 0.031 0.36 122.00

D1-14 7.24 1179 589 0.56 0.089 0.180 0.02 0.48 110

D2-14 7.00 1208 604 12.30 0.269 0.120 0.02 0.24 60

D3-14 6.24 1184 592 2.50 0.112 0.100

0.01 0.12 140

D4-14 6.24 1524 762 10.16 0.121 0.150 0.02 0.08 85

MEAN 6.68 1273.75 636.75 6.38 0.15 0.14 0.018 0.23 98.75

D1-21 7.10 1188 594 2.05 0.114 0.132 0.03 0.36 120

D2-21 7.11 1321 661 4.20 0.178 0.102 0.01 0.26 78

D3-21 7.06 1100 550 11.38 0.109 0.085 0.01 0.08 130

D4-21 7.03 1280 640 4.30 0.169 0.210 0.03 0.05 115

MEAN 7.075 1222.25 487.5 5.48 0.143 0.13 0.02 0.19 110.75

D1-28 6.24 1415 707 3.20 0.218

0.110 0.04 0.42 125

D2-28 6.34 1390 695 2.82 0.58 0.121 0.02 0.18 80

D3-28 6.21 1222 611 450 0.115 0.105 0.01 0.11 120

D4-28 6.31 1507 745 2.60 0.208 0.280 0.04 0.15 135

MEAN 6.28 1383.5 691.75 3.28 0.17 0.15 0.03 0.22 115.00

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