730 Hydrotesting Engineering

R.B. Chen holds a masters degree in biology and works as a senior lab scientist inSaudi Aramcos Laboratory Research and Development Center. Prior to Saudi Aramcoshe was affiliated with Conocos Research and Development Department. She has published and presented several papers internationally. E.Y. Chen holds a Ph.D. inmaterial science from Georgia Institute of Technology and is a NACE InternationalAccredited Corrosion Specialist. He is a senior engineering consultant with SaudiAramcos Consulting Services Department. He was a research scientist with Conocobefore joining Saudi Aramco. He has published extensively in international technicalsocieties journals.

Reprinted with permission from the 1997 SPE/EPA Exploration and ProductionEnvironmental Conference, Dallas, March 35, 1997.

A B S T R A C T

Pipelines must be properly laid up to prevent corrosion damage during

mothballing or following a hydrostatic test prior to commissioning.

Among all the lay-up procedures, wet lay-up using chemically treated

water is generally considered the most cost-effective approach. This

is particularly true for major sub-sea pipelines. To implement the

procedure, a number of oil field chemicals, including bactericide,

are added to the water. However, at the end of the lay-up period,

it has become increasingly difficult to discharge bactericide-treated

water because of environmental concerns.

WET LAY -UP FLUID: CAN IT BE BOTH CORROSION PREVENTIVEAND ENVIRONMENTALLY FRIENDLY?

by R.B. Chen and E.Y. Chen

A standard procedure for wet lay-up, which can be easily

implemented in the field and is also environmentally acceptable,

remains to be established. For this reason, a study was conducted

to examine the efficacy and stability of different types of bacteri-

cides for wet lay-up application. Methods of removing the

bactericide residuals remaining in the water at the end of lay-up

were investigated using the Microtox assay system. The study was

intended to demonstrate that a properly treated wet lay-up fluid

could be safely discharged into the environment.

This paper reviews the current practices of hydrostatic testing

and lay-up for cross-country and sub-sea pipelines. The paper also

presents the study results and recommendations on treatment of

wet lay-up fluids.

INTRODUCT ION

Among all the alternatives of laying up a pipeline for mothballing

or following a hydrostatic test prior to commissioning, wet lay-up

using chemically treated water is considered the most cost-effective

approach. The water is usually treated with oxygen scavenger and

bactericide to minimize corrosion damage. However, at the end

of the lay-up period (which can be a few years), disposal of

bactericide-treated water has created environmental concerns

because of the potential toxic impact to the receiving environment.

Procedures for disposal of such water have yet to be resolved.

Bactericide used for wet lay-up application should provide

adequate long-term corrosion protection and is environmentally

acceptable as well. However, studies have shown that the most

effective bactericides in terms of antimicrobial performance were

highly toxic to marine organisms, whereas the least toxic bactericides

performed poorly in microbial growth inhibition tests (Whale and

Whitham 1991). These results suggest that it is unlikely to find a

chemical which can meet both requirements (highly effective

antimicrobially and with the lowest aquatic toxicity).

A more practical approach to resolve this problem is probably

to use physical or chemical methods to detoxify the bactericide-

treated water, reducing the toxicity to below detectable limit prior

to discharge. This approach should be more economical compared

to other options, such as (1) dry lay-up; (2) reducing or eliminating

bactericide treatment in the water, thereby taking the risk of

corrosion damage during the lay-up period; (3) discharging bacte-

ricide-treated water into a lined evaporation pond; (4) rescheduling

hydrostatic testing; or (5) using high-pH water without bactericide

for wet lay-up.

To render a detoxification program cost-effective in field

operations, a number of criteria must be considered:

1. implementability of the procedure

2. duration of the procedure (completion should occur within a

very short time period, such as minutes, not hours or days)

3. toxicity and biodegradability of the selected neutralizing

agent (the neutralizing agent should be non-toxic as well as

biodegradable to minimize potential environmental impact if

over-treatment takes place)

4. capability to treat a large quantity of water on site

5. cost

6. safety

7. maintenance

8. transport

Many of the detoxification procedures reported in the literature

(Notarfonzo and Stevens 1996; Oil & Gas Journal 1995; Beckmanand Tacetta 1995) or recommended by the chemical suppliers

could require weeks for significant detoxification to occur, rather

than hours or minutes as desired in field operations. Others require

holding tanks or additional facilities for treatment of the dis-

charged water.

This study was initiated to investigate ways for treatment of wet

lay-up fluids, minimizing the environmental impact upon disposal

of chemically treated water. The objectives of the study are:

1. To identify chemical treatment packages for use in wet

lay-up application.

2. To examine the feasibility of removing the bactericide

residuals remaining in the water following wet lay-up for

safe disposal into the environment.

METHODSMicrotox assay system

The Microtox toxicity analysis system (Model 2055) utilizes a

bioluminescent marine bacterium (Vibrio fischeri) as the test organism.The system is designed for quick assessment of acute toxicity of

aqueous samples, or extracts of solid samples. The toxicity of a

sample is assessed based on changes in the bioluminescent activity

of the test bacteria following exposure to toxicants for five to 15

minutes. The reduction in light output from these organisms is

directly related to the toxicity of the sample. Results are expressed

as Gamma values (Light-Loss Effect); higher Gamma values repre-

sent higher toxicity. Based on Gamma values measured at various

dilutions of the sample, an EC50 (Effective Concentration resulting

in 50% reduction in light output, i.e., Gamma = 1.0) can be deter-

mined for a specified exposure time. Higher EC50 values represent

lower toxicity. EC50 concentrations with statistical information

(95% confidence range) are calculated by the Microtox data

reduction software provided by the manufacturer.

Bactericide performance evaluation

To select a chemical treatment package for wet lay-up applications,

a number of requirements have to be considered: (1) effectiveness

of the chemical for long-term corrosion protection, (2) compatibility

with oxygen scavenger, (3) chemical stability and (4) environmental

acceptability.

The antimicrobial performance of the selected treatment pack-

ages was assessed in a laboratory planktonic time-kill test. The test

60 S A U D I A R A M C O J O U R N A L O F T E C H N O L O G Y W I N T E R 1 9 9 7 / 9 8

was conducted at ambient temperature in deoxygenated Arabian

Gulf water (total dissolved solids in the range of 42,000 mg/L).

Each chemical was tested at 50, 100, 250 and 500 ppm (as

received) in the presence of 50 ppm oxygen scavenger. Either

ammonium bisulfite scavenger or liquid carbonhydrazide was used

based on recommendations from the chemical suppliers.

The test inocula consist of General Aerobic Bacteria (GAB) and

Sulfate-Reducing Bacteria (SRB) cultures isolated from the scraping

solids in Saudi Aramcos seawater injection system. Prior to inocu-

lation into the test water, the bacteria were sub-cultured successively

at three-day intervals by transferring them into fresh growth

media. One corrosion coupon (half of the regular strip type,

2 7/8 in 7/16 in 1/8 in) was added to each test bottle containing

300 mL test water. This produced a volume-to-surface area ratio

of 6 in, which would simulate a 24-in-diameter pipeline. Multiple

sets of test bottles were prepared for each test condition for analysis

at time zero, and following three months and eight months of

incubation. Controls for this test program contained oxygen

scavenger only, with no bactericide added. All test bottles were

kept at ambient temperature and covered with foil to prevent

photodegradation.

The analysis program after three months exposure included

SRB and GAB populations, Microtox toxicity, bactericide residuals

concentration, and corrosion coupon weight-loss measurements.

After eight months, toxicity and bactericide residuals for selected

chemicals were determined to study bactericide stability. SRB and

GAB populations were determined by the triplicate decimal serial

dilution method using growth media prepared in Arabian Gulf

water. Results are expressed as Most Probable Number (MPN) SRB

or GAB per mL. The toxicity of test water was assessed by the

Microtox assay at 20C using Arabian Gulf water as the receiving

water. Results are expressed as EC50-5 minute concentrations or

Gamma-5 minute values. The residual concentration of quaternary

phosphonium-based bactericide was analyzed by titration.

Biguanide concentration was determined using a colorimetric

method. The corrosion rate was determined based on corrosion

coupon weight-loss measurements.

Detoxification

Detoxification of the bactericide-treated water after three months

exposure was evaluated using the following methods:

dilution with seawater (1:2, 1:10, 1:50, 1:250)

aeration for one hour at ambient temperature

exposure to sunlight for one hour

raising water pH to 9 and 10

filtration with glass-fiber filter

adsorption by activated carbon followed by filtration with

glass-fiber filter

adsorption by sand followed by filtration with glass-fiber filter

use of oxidizing agent (chlorine)

Each method was tested with a 10 mL aliquot from bottles

showing effective microbial control. The overall toxicity remaining

in the aliquot following the detoxification treatment was determined

by the Microtox assay. Each sample was analyzed immediately

following the treatment. The results are expressed as 5-minute

Gamma values (light-loss effect). Data are compared with controls

which received no neutralization treatment, i.e., direct discharge.

The impact of each treatment and the toxicity of the neutralizing

agent (chlorine) in Arabian Gulf water were also assessed.

For sand and activated carbon treatments, the time allowed for

each reaction was kept to a minimum (minutes). Each 10 mL

aliquot was treated with 1 g sandy soil collected from a nearby

land farm site. For carbon adsorption, 0.01 g activated carbon was

used for each treatment. Because of the color, turbidity and partic-

ulates present in the treated sample (which would interfere with

Microtox bacteria bioluminescence measurements), the aliquot was

filtered through a glass-fiber filter prior to toxicity determination.

The effect of filtration alone on the overall toxicity of the test

water was also examined.

Neutralization of bactericide residuals by chlorine was evaluated

at chlorine concentrations ranging from 0.5 ppm to 20 ppm. The

contact time for each treatment was kept to a minimum (minutes).

Chlorine concentration was determined by Hach DREL/2000

spectrophotometer. In addition to toxicity measurement, the effec-

tiveness of chlorine neutralization of biguanide and quaternary

phosphonium residuals was also monitored by chemical analysis as

described previously.

RESULTSSelection of bactericide

1. Identification of current technology for wet lay-upTo identify current treatment technology, nine chemical and

oil companies were contacted worldwide. Based on their

recommendations, six bactericide/oxygen scavenger packages

were selected for evaluation. The active ingredient of these

products and the recommended detoxification procedures are

summarized in table 1. The performance of these treatment

packages is compared with polymeric biguanide hydrochloride,

a bactericide which has previously been used in Saudi Aramcos

mothballing operations.

2. Bactericide ecotoxicityThe acute toxicity data of the bactericides included in the test

program are summarized in table 2. The data were generated by

the manufacturers or independent laboratories using a wide

range of marine and freshwater organisms (i.e., fish, shrimp,

crustaceans, mussels, etc.) as the test species. Toxicity of these

products assessed based on responses from the Microtox bacte-

ria are presented in table 3. All bactericides are ranked from the

least toxic (1) to the most toxic (6) based on their LC50-96

hours or EC50-5 minute values; higher LC50 or EC50 values

S A U D I A R A M C O J O U R N A L O F T E C H N O L O G Y W I N T E R 1 9 9 7 / 9 8 61

represent lower toxicity. Data show that despite the wide range

of species tested and the test protocols used in these bioassays,

the Microtox toxicity results correlate reasonably well with

fish/shrimp bioassay results.

3. Bactericide antimicrobial performance and toxic impactThe results of the planktonic time-kill test following three

months exposure are presented in fig. 1. Two bactericides

(quaternary phosphonium salt and polymeric biguanide) provided

complete kill of General Aerobic Bacteria (GAB) and Sulfate-

Reducing Bacteria (SRB) at the lowest concentration tested (50

ppm as received). Two other chemicals (organobromide and

thiocyanate) also showed complete kill, but only at much higher

concentrations (500 and 250 ppm, respectively). The other two

chemicals either resulted in no kill at the highest concentration

tested or were effective against SRB but not GAB. The mini-

mum effective concentration for each chemical producing a

complete kill is summarized in table 4.

The toxicity, bactericide residuals, and corrosion-rate data

determined after three months are shown in table 5. The results

show that biguanide-treated waters were the most toxic of all

the waters tested, as indicated by the lowest EC50 values

(EC50-5 minute concentrations ranging from 12.2 to 1.5%).

The glyoxal-, combination-package- and organobromide-treated

waters were relatively nontoxic (EC50-5 minute concentrations

approaching or greater than 50%). The corrosion rates observed

after the three-month incubation period were all within accept-

able limits (500 500

Polymeric Biguanide

chemicals of all products tested, according to the ecotoxicity

data (tables 2 and 3). But these two bactericides were not the

most effective chemicals against bacteria at the end of the

three-month exposure period. The toxicity rank of all bactericide-

treated waters after three months was different compared to the

ecotoxicity rank of the neat chemicals. The changes of toxicity

in the waters during the three-month incubation based on

Microtox assessment and chemical analysis are discussed in

Section 5, Bactericide Stability.

Based on the bactericidal effectiveness test results, four

chemicals (quaternary phosphonium, biguanide, organobromide

and thiocyanate) were selected for further evaluations of their

compatibility with oxygen scavenger, chemical stability and

bactericide neutralization.

4. Compatibility with oxygen scavengerThe toxicity of quaternary phosphonium-, biguanide-,

organobromide- and thiocyanate-based bactericides tested as

bactericide alone, and also in the presence of oxygen scavenger,

by the Microtox assay is shown in table 6. Data show that the

presence of the oxygen scavenger could affect the toxicity of

the bactericides. For quaternary phosphonium-, biguanide- and

thiocyanate-based products, the presence of oxygen scavenger


Control(0 ppm) 50 ppm 100 ppm 250 ppm 500 ppm

Glyoxal 3.36 5.36 5.88 3.97 2.88Q. Phosphonium 3.97 -0.4 -0.4 0.36 0.36Combination 4.23 4.97 2.63 3.97 4.36Biguanide 3.97 -0.4 -0.4 -0.4 -0.4Organobromide 5.36 4.18 3.63 3.97 -0.4Thiocyanate 5.36 4.63 1.63 -0.4 -0.4

Control(0 ppm) 50 ppm 100 ppm 250 ppm 500 ppm

Glyoxal 5.36 -0.4 -0.4 -0.4 -0.4Q. Phosphonium 3.63 -0.4 -0.4 -0.4 -0.4Combination 4.32 4.63 4.36 5.18 3.97Biguanide 3.63 -0.4 -0.4 -0.4 -0.4Organobromide 3.97 -0.4 -0.4 -0.4 -0.4Thiocyanate 3.97 -0.4 -0.05 -0.4 -0.4

GAB

(Log

MPN

/mL)

SRB

(Log

MPN

/mL)

Glyoxal Q. Phosphonium Combination Biguanide Organobromide Thiocyanate

Glyoxal Q. Phosphonium Combination Biguanide Organobromide Thiocyanate

GAB

Control (0 ppm) 50 ppm 100 ppm 250 ppm 500 ppm

SRB

Control (0 ppm) 50 ppm 100 ppm 250 ppm 500 ppm

87

654

32

1

0-1

87

654

32

1

0-1

Fig. 1. Bactericide performance evaluation results after 3 months exposure


1 Controls 1, 2, 3 contain oxygen scavenger only (no bactericide). All oxygen scavengers are tested at 50 ppm. 2 Bactericide concentrations (as received).

TIME 0 TIME 0 3 MONTHS 3 MONTHS 3 MONTHS 3 MONTHSEC50-5 min. EC50-15 min. EC50-5 min. EC50-15 min. Res. Rem. Corr. Rate

(%) (%) (%) (%) (ppm) (mpy)Control 11 >50 >50 33.6 24.3 0.50

2 >50 >50 >50 >50 0.53

3 >50 >50 48.5 35.6 0.42

Glyoxal

50 ppm2 >50 >50 36.2 22.8 0.42

100 ppm >50 >50 49.0 26.3 0.74

250 ppm >50 >50 >50 >50 0.40

500 ppm >50 >50 >50 19.9 0.50

Quaternary Phosphonium

50 ppm 35.9 12.8 39.1 28.0 15 0.67

100 ppm 34.2 22.0 47.0 41.3 0.88

250 ppm 27.5 14.6 21.0 11.8 0.72

500 ppm 13.8 9.8 21.6 9.3 60 0.74

Combination Package

50 ppm >50 >50 >50 >50 0.56

100 ppm 43.1 30.6 42.9 32.9 0.50

250 ppm 13.1 9.6 28.6 18.7 0.47

500 ppm 7.8 5.9 >50 >50 0.64

Polymeric Biguanide

50 ppm 7.7 4.6 12.2 6.7 46 0.56

100 ppm 5.4 3.5 5.3 3.0 0.51

250 ppm 2.6 1.5 2.5 1.8 0.46

500 ppm 1.5 1.0 1.5 1.0 0.35

Organobromide

50 ppm >50 >50 >50 >50 0.45

100 ppm >50 >50 55.0 37.2 0.49

250 ppm 2.1 1.5 48.7 38.6 0.45

500 ppm 1.1 0.7 55.1 39.8 0.76

Thiocyanate

50 ppm 16.2 8.8 35.9 23.1 0.20

100 ppm 6.1 3.6 25.5 17.7 0.14

250 ppm 11.4 6.4 42.6 30.9 0.15

500 ppm 3.2 1.9 18.9 16.6 0.30

TABLE 5.BACTERICIDE PERFORMANCE EVALUATION RESULTS

AFTER THREE MONTHS EXPOSURE-TOXICITY, CHEMICAL RESIDUALS, CORROSION RATES

enhanced the acute toxicity of the chemicals, as indicated by

higher Gamma values. For organobromide-based bactericide,

the toxicity was significantly reduced when oxygen scavenger

(carbonhydrazide) was mixed with the bactericide. Similar

observations have been reported by other investigators when

organobromide biocide was mixed with ammonium bisulfite

oxygen scavenger (Whale and Whitman 1991). It is also indi-

cated in the literature that DBNPA (dibromonitrilopropionamide,

the active ingredient of the organobromide biocide tested) was

degraded by a number of sulfur-containing species such as sulfite,

bisulfite, thiosulfate and sulfide (Exner, Burk and Kyriacou 1973).

These compounds debrominated DBNPA instantaneously to

form cyanoacetamide. Because of the incompatibility with

oxygen scavengers, organobromide-based bactericide at present

is not recommended for wet lay-up applications.


Bactericide + Bactericide Bisulfite Oxygen Bactericide +

Alone Scavenger2 Carbonhydrazide2

Seawater 2.30 0.10

Quaternary Phosphonium 0.38 1.54 (50 ppm)Polymeric 8.01 95 Biguanide (10 ppm)Organobromide 5.54 0.58(2.5 ppm)Thiocyanate 1.41 1.83(1.0 ppm)

TABLE 6. COMPARISON OF BACTERICIDE TOXICITY

WITH AND WITHOUT OXYGEN SCAVENGER1

1 All results presented as Gamma-5 min. values (light-loss effect); highervalues represent higher toxicity.

2 Oxygen scavengers are tested at 50 ppm.

RESIDUAL RESIDUALTOXICITY1 TOXICITY1 TOXICITY1 REMAINING2 REMAINING2

Time 0 3 Months 8 Months 3 Months 8 Months

Control 1 >50 33.6 23.8

2 >50 >50 33.8

3 >50 48.5 43.5

Quaternary Phosphonium

50 ppm 35.9 39.1 31.2 15 ppm (30%) 8 ppm (16%)100 ppm 34.2 47.0 24.1 9 ppm (9%)250 ppm 27.5 21.0 >50 17 ppm (7%)500 ppm 13.8 21.6 20.6 60 ppm (12%) 24 ppm (5%)

Polymeric Biguanide

50 ppm 7.7 12.2 6.4 46 ppm (92%) 44 ppm (88%)100 ppm 5.4 5.3 5.4 67 ppm (67%)250 ppm 2.6 2.5 2.1 155 ppm (62%)500 ppm 1.5 1.5 1.2 270 ppm (54%)

Organobromide

50 ppm >50 >50 >50

100 ppm >50 55.0 36.4

250 ppm 2.1 48.7 47.0

500 ppm 1.1 55.1 46.7

Thiocyanate

50 ppm 16.2 35.9 >50

100 ppm 6.1 25.5 >50

250 ppm 11.4 42.6 >50

500 ppm 3.2 18.9 >50

TABLE 7. BACTERICIDE STABILITY DURING EIGHT MONTHS EXPOSURE

1 All toxicity results presented as EC50-5 min. (%). 2 Quaternary phosphonium determined by titration; biguanide determined colorimetrically.

5. Bactericide stabilityComparing the three-month and eight-month EC50 data with

the initial toxicity determined at time zero, no significant

changes have been observed in the biguanide- and quaternary

phosphonium-treated waters during the eight-month incubation

period (table 7). Further analyses of the active ingredients of

the bactericides using chemical methods show that significant

amounts of PHMB (polyhexamethylene biguanide) remained

after three months and eight months, which support the Microtox

toxicity results. In quaternary phosphonium-treated waters,

however, only a small amount of THPS (tetrakishydroxymethyl

phosphonium sulfate) could be detected analytically, but the

overall toxicity of the water remains relatively unchanged.

These results suggest that the active ingredient THPS has con-

verted or degraded to some intermediate products which are no

longer measurable by chemical method, but remain toxic.

For organobromide- and thiocyanate-treated waters, the

overall toxicity has been reduced significantly, with EC50 values

increasing over the eight-month incubation period (see table 7).

According to the literature, organobromide is a fast-acting

chemical designed to provide a rapid kill of a wide variety of

microorganisms (Exner, Burk and Kyriacou 1973). It is generally

used in industrial recirculating and once-through cooling water

systems, paper mills, metalworking fluids, and air washer systems.

It decomposes relatively fast by a number of chemical and bio-

logical mechanisms, such as hydrolysis, photodegradation and

reaction with sulfur-containing compounds.

Detoxification of bactericide-treated water

Results of detoxification of quaternary phosphonium, biguanide,

organobromide and thiocyanate residuals remaining in the water

following the three-month incubation period are summarized in

table 8. The effect of the detoxification treatments on seawater

itself is also shown in table 8. For direct discharge with no further

detoxification treatment, the four waters showed various degrees

of toxic impact on the Microtox bacteria, with Gamma-5 minute

values ranging from 0.68 to 9.76. The toxicity levels were reduced

to below the detection limit (Gamma-5 minutes 0.05 or EC5, the

concentration giving a 5% reduction in light output) when the

waters were diluted by approximately a factor of 50.

Data in table 8 also show that although biguanide-treated water

is highly toxic to the Microtox bacteria, biguanide residuals appear

to be the most adsorbable of the four chemicals evaluated. Compared

to the untreated control, treatment with glass-fiber filter significantly

reduced the toxicity of the residual. Further treatment with sand or

activated carbon resulted in additional reduction of the toxicity in

the water. Aeration/oxidation or exposure to sunlight had only a

slight effect on detoxification of the water. It appears that in addi-

tion to dilution, biguanide residual can be effectively removed by

precipitation and/or adsorption onto carbon, sand/clay particles or

other inert materials, presumably due to its cationic nature.

For quaternary phosphonium, organobromide and thiocyanate

residuals, the only treatment that effectively eliminated the toxicity

in the water was carbon adsorption (Gamma-5 minute values

reduced to 100 1.40 1.03

Raising pH to 10 2.88 3.69 10.7

Filtration 100 >100 9.94 100

TABLE 8. DETOXIFICATION OF BACTERICIDE RESIDUALS FOLLOWING THREE MONTHS EXPOSURE (MICROTOX TOXICITY ANALYSIS RESULTS1)

1 All results (except dilution factors) presented in Gamma-5 min. values (light-loss effect); higher values represent higher toxicity. Each bottle tested at 50% dilution.2 Initial treatment concentrations at time zero: Q. phosphonium, 50 ppm; biguanide, 50 ppm; organobromide, 500 ppm; thiocyanate, 250 ppm.3 Gamma-5 min. values reduced to

have very little effect compared to the untreated controls, suggesting

that these procedures can not be completed within minutes or

seconds as desired by field operations.

Use of an oxidizing agent such as chlorine has been proposed

as a potential method for removal of bactericide residuals. Results

in table 9 show that the addition of chlorine was able to neutralize

quaternary phosphonium and biguanide residuals based on chemical

analysis of the active ingredient of freshly prepared bactericide

solutions. However, the water remained toxic following chlorine

treatment (table 8). The toxicity could be a result of the toxic

effect of the neutralizing agent itself, as shown in table 8 (tested

with seawater alone). The toxicity could also suggest that the

by-products formed from the oxidation reactions are toxic.

DISCUSSIONSTreatment of wet lay-up fluid

Selection of bactericide for use in the treatment of wet lay-up

fluid should be based on the following criteria: (1) effectiveness

of the chemical for providing long-term microbial control,

(2) compatibility with all chemicals used, (3) chemical stability

and (4) environmental acceptability. In this study, environmental

acceptability was evaluated based on Microtox acute toxicity

assessment of the neat chemicals and the chemical residuals

remaining after three months and eight months exposure. It is

recognized that toxicity of a chemical is only one aspect of

environmental acceptability; other factors (biodegradability,

bioaccumulation potential) also play a role in the overall assessment

of environmental impact. However, the most common acute

impact is toxicity. Toxicity is widely used in the industry as a stan-

dard parameter for chemical characterization. It is one of the prime

requirements of many regulatory schemes (Whale and Whitman).

Results of this study show that the long-term performance of

the bactericides against oil field bacteria generally correlates with

the toxicity assessment of the chemicals based on short-term

responses from the Microtox bacteria, except in chemicals with

low stability. The most effective chemicals with the best bactericidal

efficacy and chemical stability are toxic to the Microtox bacteria;

the chemicals with the lowest toxicity are ineffective in terms of

bacteria control. It appears that bactericide detoxification (chemi-

cally and physically) would have to be included as part of the wet

lay-up chemical treatment package, if all four chemical selection

criteria are to be met. The final procedure selected to treat wet

lay-up fluid should be a balance based on both cost and environ-

mental considerations.

Detoxification of bactericide-treated water

A number of procedures have been recommended in the literature

and by chemical suppliers for detoxification of the bactericides

tested in this program. These include raising pH, oxidation/

aeration, exposure to sunlight, hydrolysis and degradation to

transform the active ingredients to less toxic components. Results

of this study suggest that these methods would require days and

weeks of time for significant detoxification to occur, rather than

minutes or seconds as desired by field operations. Additional facilities

such as holding tanks are also required for aeration, oxidation or

photodegradation reactions. Furthermore, the potential environ-

mental impact of the final degradation products, including algal

bloom, eutrophication, etc., is largely unknown. These factors

should be considered in the selection of a treatment package and

its detoxification procedure for wet lay-up.

Based on responses from the Microtox bacteria, carbon adsorp-

tion appears to be the most promising of all the detoxification

methods evaluated. This method effectively removed the residual

toxicity of all four bactericide-containing waters tested within a

short period of time (minutes). Liquid-phase purification with

carbon adsorption has long been cost-effectively applied to process

streams, drinking water, groundwater and municipal and industrial

wastewater (Beckman and Tacetta). Activated carbon adsorption

systems have also been used to treat pipeline hydrotest water con-

taining BTEX (benzene, toluene, ethylbenzene and xylene) on site

for surface discharge (Oil and Gas Journal). This technologyreportedly has a number of advantages: effective, relatively low

cost, safe, portable, durable, simple to operate and easy to main-

tain. However, because of the large quantity of water to be treated

in most of Saudi Aramcos operations and the types of organic

molecules to be removed, the feasibility of implementing such

system on site, and the cost required, should be further investigated.

Use of an oxidizing agent such as chlorine for detoxification

does not appear to be a viable option, since chlorine is highly toxic

to the Microtox organisms, and the reaction products may also

be toxic. In evaluating chemical neutralization procedures, it is

important that the selected neutralizing chemicals are relatively

nontoxic and biodegradable. Otherwise, overtreatment would


Q. Phosphonium Biguanide(ppm) (ppm)

No Treatment2 48 41

Chlorine 0.5 ppm 48 39

1 ppm 50 36

2 ppm 50 25

5 ppm 50

create a new problem. Based on these considerations, it appears

that bactericide detoxification by chlorination is unlikely to be

easily implemented in the field.

Application of the Microtox assay system

The Microtox assay is designed for quick assessment of acute

toxicity (typically for an exposure time of five to 15 minutes) based

on changes in luminescence activities from a marine bacterium.

The one problem often faced in interpreting Microtox data is the

correlation of toxic responses between bacteria and other biological

species indigenous to the local environment. As indicated in the

literature (Bulich, Greene and Isenberg 1981; and Indorato, Snyder

and Usionowicz 1984), the Microtox results are generally consid-

ered comparable to standard fish/shrimp kill test results. In this

study the acute toxicity of the test bactericides determined by the

Microtox system and those reported by the chemical suppliers

based on a wide range of marine and freshwater species correlate

reasonably well. The Microtox assay results also correlate with the

antimicrobial performance of the bactericides observed in the

planktonic time-kill test.

As mentioned previously, the Microtox assay measures the overall/

combined toxicity of a water sample, including the bactericide

residual and any degradation by-products formed during the lay-up

period. Compared to chemical analysis of bactericide residuals, this

provides a more accurate assessment of the potential environmental

impact. The Microtox analysis system is especially suitable for

measuring the relative changes in aquatic toxicity of an environment

because it is quick and simple to use. The results of this study have

demonstrated that the Microtox assay system is an invaluable tool

in assessing the toxicity of bactericide-treated waters, the effective-

ness of chemical treatment in lay-up operations, and in developing

toxicity-reduction strategies.

CONCLUSION

Laboratory evaluation of wet lay-up treatment packages indi-

cates that the most effective chemicals in terms of bactericidal

effectiveness and chemical stability are most toxic based on

Microtox assay results. An effective bactericide detoxification

procedure is required as part of the wet lay-up chemical treat-

ment package. The final treatment procedure should be

based on both cost and environmental considerations.

On an equal concentration basis, biguanide- and quaternary

phosphonium-based bactericides are the most effective of all

chemicals tested. Biguanide is also found to be most stable

during the eight-month study.

Carbon adsorption is an effective way to rapidly remove the

toxicity of bactericide residuals. Of all methods evaluated,

this is the only technology which effectively detoxified all

four chemically treated waters.

In addition to carbon adsorption, the toxicity of biguanide

residuals can also be reduced by sand or glass-fiber filter

treatments. While biguanide-treated water is the most toxic

of all bactericides tested, the residuals appear to have the

highest adsorption capacity.

To remove the toxicity by dilution, a factor of approximately

1:50 is required for safe discharge of bactericide-treated water

following lay-up.

Bactericide detoxification by hydrolysis, oxidation, pH

adjustment and/or photodegradation cannot be accomplished

within minutes or seconds as desired by field operations.

Bactericide detoxification by chlorine does not appear to be a

viable option for field application because of the toxic nature

of chlorine and/or its oxidation products.

The Microtox assay system is an invaluable tool in assessing

the overall environmental impact of bactericide-treated

waters and developing toxicity reduction strategies.

ACKNOWLEDGMENTS

The authors would like to thank Mahfoud A. Al-Ghamdi of Saudi

Aramco Lab R&D Center for his significant contributions to this

study.

REFERENCESBeckman, W.K. and J.J. Tacetta. 1995. Pretreatment Is a Crucial

First Step: An introduction to physical and chemical treatmentprocesses. International Ground Water Technology (December).

Bulich, A.A.; M.W. Greene; and D.L. Isenberg. 1981. Reliabilityof the bacterial luminescence assay for determination of thetoxicity of pure compounds and complex effluents. AquaticToxicity and Hazard Assessment: Fourth Conference, ASTM STP 737.D.R. Branson and K.L. Dickson, eds., American Society forTesting and Materials, p338.

Exner, J.H.; G.A. Burk; and D. Kyriacou. 1973. Rates and prod-ucts of decomposition of 2,2-dibromo-3-ditrilopropionamide.J. Agr. Food Chem. v.21, p838.

Indorato, A.M.; K.B. Snyder; and P.J. Usionowicz. 1984.Toxicity screening using Microtox analyzer. Toxicity ScreeningProcedures Using Bacterial Systems, D. Liu and B.J. Dutka, eds.,New York:Marcel Dekker Inc. p37.

Notarfonzo, R. and R.D.S. Stevens. 1996. UV/oxidation is aquiet, clean destroyer: Contaminated water is detoxified withno need for secondary disposal. International Ground WaterTechnology. April.

Oil & Gas Journal. 1995. Pipeline treats hydrotest water on sitewith carbon adsorption, January. p92.

Whale, G.F. and T.S. Whitham. 1991. Methods for assessingpipeline corrosion prevention chemicals on the basis of antimi-crobial performance and acute toxicity to marine organisms.Paper presented at the First International Conference onHealth, Safety and Environment, The Netherlands, Nov. 10-14.


Documents

730 Hydrotesting Engineering