Chemist: Hassan EL-Nagar Hassan

B Sc. in Chemistry,1997, Faculty of Science.

Diploma In Materials Science

Project Title: (Metal Ions Uptake Efficiency of Chemically Prepared

Polyamide)

M.Sc degree in Polymer Science under the guidance of Professor Dr.

Ali gad (Institute of Graduate Studies and Research –Materials Science

Dep., Alx. University)

Project Title: Evaluation of the Thermal Stability of some Prepared

Polymers

Head Section in Utilities Sector (ANRPC) (Alex. National Refining and

Petrochemicals Co

Alexandria National Refining &Petrochemicals Co. (ANRPC)

Technical Affairs

Utilities Sector

Case study about

Grey fragile bacterial colonies in open

recirculation cooling water system

Presented by

Chemist /Hassan EL-Nagar Hassan

Abstract

High biological growth was found at the bottom basins of the different cells and it was

observed as expansion of grey fragile bacterial colonies. High probability of H2S is a by –

product of their metabolism, the “rotten egg’’ odour associated with sulphur compound is

an indication that bacteria may be present in the open recirculation cooling water system.

High depletion of cathodic inhibitor (Zinc residual) even after we were increased the dose

rate of cathodic inhibitor (Zinc chloride, Carboxylated/Sulfonated terpolymer) to double,

High depletion of anodic inhibitor (Orthophosphates residual) even after we were increased

the dose rate of anodic inhibitor (Phosphonate, Polymer, Acrylic acid Polymer, Sodium

salts) to double, High depletion of mixed inhibitor (Zinc residual and Orthophosphates

residual) even after we were increased the dose rate of mixed inhibitor (Phosphate/Zinc

with Phosphonate, Polymer, and Azole), High amount from the undesired accumulation of

deposits of a biological nature on the heat exchangers. Such deposits can contain micro

(microfouling) or microorganisms (macrofouling) , High depletion of residual chlorine

even after we were increased oxidizing biocides (Sodium hypochlorite NaOCl) and non

oxidizing biocides (Isothiazolines) to double, High probability of H2S gas leakage within

the industrial processing and High corrosion rate (10 MPY) that measured through the

corrosion coupons rack (Low carbon steel C1010). Therefore we were inspected for

detection of H2S leakage and /or Sulfate-reducing bacteria (SRB) by collecting water

samples from each point of suspicious to perform chemical and biological analyses at

chemistry administration and ANRPC Laboratory. From analyses it was found that sulfate

1

reducing bacteria (SRB) is a cause of this problem. To solve that problem through

replacement H2SO4 (which used as pH control) by HCl, Drain for each cells (A, B&C)

individually and comprehensive cleaning for the cells (A,B&C) manually and chemically

by applying shock doses of sodium hypochlorite 12% (100 ppm) instead of continuous

injection for three months then to be reduced to 50 ppm continuous injection and

Nonoxidizing biocides (Isothiazolines) (50 ppm /20 days), Inspection for H2S leakage by

comprehensive inspection for all heat exchangers as well as equipments containing this gas,

to detect and block that leakage. High dose was applied from cathodic, anodic and mixed

inhibitor. As a result of this action the Corrosion rate is 2.2 MPY and Grey fragile bacterial

colonies in open recirculation cooling water system disappeared.

2

Introduction-I

3

Case history -II

Industry: Refining &Petrochemicals

Specimen Location: Bacterial colonies from the out of service cell basin in open

recirculation cooling water system

Time in Service : 12 Years

Sample Specifications: Gray Fragile Bacterial Colonies

Problem identification -III

High biological growth was found at the bottom basins of the different

cells and it was observed as expansion of grey fragile bacterial colonies.

High probability of H2S is a by –product of their metabolism, the “rotten

egg’’ odour associated with sulphur compound is an indication that

bacteria may be present in the open recirculation cooling water system.

High depletion of cathodic inhibitor (Zinc residual) even after we were

increased the dose rate of cathodic inhibitor (Zinc salt) to double.

High depletion of anodic inhibitor (Orthophosphates residual) even after

we were increased the dose rate of anodic inhibitor (Phosphonate) to

double.

High corrosion rate (10 MPY) that measured through the corrosion

coupons rack (Low carbon steel C1010).

High probability of H2S gas leakage within the industrial processing.

4

High amount from the undesired accumulation of deposits of a biological

nature on the heat exchangers. Such deposits can contain micro

(microfouling) or microorganisms (macrofouling).

High depletion of residual Chlorine even after we were increased

Oxidizing Biocides (Sodium hypochlorite NaOCl) and non Oxidizing

Biocides to double.

Therefore we were inspected for detection of H2S leakage and /or Sulfate-

reducing bacteria (SRB) by collecting water samples from each point of

suspicious to perform chemical and biological analyses at chemistry

administration and ANRPC Laboratory.

Sample Point -II.1I

Water source used as makeup (Storage tank and potable water).

Cooling water supply

Cooling water return

Bacterial colonies from bottom the out of service cell

E01 (deethanizer condenser )

E03 (Sour water treatment )

E08 (Amine cooler)

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Results -I.2II

1- ANRPC Laboratory

Test

Sample

Make up

Supply

Cooling

Water

Return

Cooling

Water

pH @ 25 ⁰C 7.2 8.4 8.3

Conductivity µs/cm 565 2170 2165

T.Hardness (ppm) 135 620 630

P-Alkalinity (ppm) NIL 20 18

m-Alkalinity (ppm) 160 188 185

Chloride (ppm) 52 290 300

Ortophosphate (ppm) NIL 1.3 1.2

Residual Zn (ppm) NIL 0.72 0.65

Residual Chlorine (ppm) 0.4 0.01 0.01

H2S (ppm) NIL NIL NIL

Iron (ppm) NIL 0.5 0.5

COD NIL 36 40

BOD NIL 5 6

E08 outlet

E08 inlet

E03 outlet

E03 inlet

E01 outlet

E01 inlet

Test

Sample

8.7 8.7 8.7 8.7 8.8 8.7 pH @ 25 ⁰C

2187 2179 2183 2171 2180 2170 Conductivity µs/cm

NIL NIL NIL NIL NIL NIL H2S (ppm)

Where Eo1 (Deethanizer Condenser), Eo3 (Sour water treatment) and Eo8

(Amine cooler)

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2- Chemistry administration

Sample Point : Bacterial colonies from bottom the out of

service cell

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III.3- Results and Discussions

The analyses that were done at chemistry administration confirmed the

following suspicious as the prospected source of the problem:

High nitrates concentration (140 ppm) in the open recirculation water,

although normal is not being exceeded (31 ppm).

High sulfate concentration (330 ppm) in the open recirculation water,

confirms the existence of Sulfate reducing bacteria (SRB) and /or

H2S.

Total aerobic bacteria (20 Col. /ml), although normal is not being

exceeded (10 Col./ml).

Total anaerobic bacteria (17 Col./ml), although normal is not being

exceeded (10 Col. /ml).

Absence of algae growth within the cooling water samples analyzed.

High Chemical oxygen demand (COD) (8145 ppm), although normal

is not being exceeded (100 ppm).

High Biological oxygen demand (BOD) (1000 ppm), although normal

is not being exceeded (60 ppm).

Therefore high COD & BOD indicated the existence of H2S and /or

Sulfate reducing bacteria (SRB). SRB are nonpathogenic and they are

anaerobic bacteria, but they are capable of causing severe corrosion of

iron material in a water system because they produce enzymes which

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have the power to accelerate the reduction of sulfate compounds to

corrosive hydrogen sulphide (eq.1).

SO4-2

+ 8 e -+ 4H2O S

2- + 8 OH

- (1)

Confirmed existence of SRB in both the cooling water sample taken

from different points as well as form Grey fragile bacterial colonies

that was observed in the cell basin.

Existence of SRB in the cooling water sample due to reduction of

sulphate to the corrosive hydrogen sulphide and decreasing of pH

value.

P-Alkalinity was not found this indicated the M-Alkalinity is HCO3-1

due to formation H2CO3 and decreasing in pH value.

IV- Solutions

Replacement H2SO4 (which used as pH control) by HCl (which used

as pH control).

Drain for each cells (A, B&C) individually and comprehensive

cleaning for the cells (A,B&C) manually and chemically by applying

shock doses of sodium hypochlorite 12% (100 ppm) instead of

continuous injection for three months then to be reduced to 50 ppm

continuous injection .

9

Inspection for H2S leakage by comprehensive inspection for all heat

exchangers as well as equipments containing this gas, to detect and

block that leakage.

High dose was applied from cathodic inhibitor (9 ppm) (Zinc

chloride, Carboxylated/Sulfonated terpolymer), anodic inhibitor

(7 ppm) (Phosphonate, Polymer, Acrylic acid Polymer, Sodium salts)

and mixed inhibitor (6 ppm) (Phosphate/Zinc with Phosphonate,

Polymer, and Azole) for two months.

High dose was applied from oxidizing biocides (NaOCl) (100 ppm)

and Nonoxidizing biocides (Isothiazolines) (50 ppm /20 days)

Take a random samples from the water make up source ,supply

cooling water and return cooling water to analyze COD,BOD,H2S

,total aerobic bacteria (Dip slides) (one per week) .

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V-Results before and after upgrading

(A)

(B)

Figure 1(A&B): Zinc (ppm) before and after upgrading

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(A)

(B)

Figure 2(A&B): Phosphate (ppm) before and after upgrading

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(A)

(B)

Figure 3(A&B): Iron (ppm) before and after upgrading

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(A)

(B)

Figure 4(A&B): Ryzanar stability index before and after upgrading

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(A)

(B)

Figure 5(A&B): Langelier saturation index before and after upgrading

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(A)

(B)

Figure 6(A&B): Rate of Corrosion (MPY) before and after upgrading

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(A)

(B)

Figure 7(A&B): Total aerobic bacteria (CFU/ml) before and

after upgrading

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VI-Forms of Grey fragile bacterial colonies and Corrosion Coupons

(A)

(B)

Figure 8(A&B): Grey fragile bacterial colonies in water

jacket cooling in air reciprocating compressors

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(A): After one month

(B): After three months

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(C): After six months

(D): After nine months

Figure 9(A, B, C &D): Corrosion Coupons

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Conclusions

1- In the case SRB prefers using HCl (pH control) instead

H2SO4 .Where SRB obtains their energy from the anaerobic

reduction of sulfates.

2- Stagnant water and flow condition will increased the

Specific growth rate of SRB.

3- Low pH value (7) is optimum condition to increase the

Specific growth rate of SRB

4- Cooling tower cells that are not in the working preferred

not to leave without operating continuously water flow.

5- In the case SRB prefer using bromine instead chlorine

where chlorine consumed by ammonia, sulfides, iron and

hydrocarbons

6- In the case SRB we suggested

Prefer using Glutaraldehyde compounds (non-oxidizing

biocide) where which it is especially effective in controlling

slime forming bacteria, SRB and algae.