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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1972
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Reference:
Composition 0
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Principles of method if other than guideline:
River samples were collected and determined amounts of urea were added to the river water. Biodegradation of the test item was observed for 14 days. The degree of nitrification was determined.
GLP compliance:
no
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on inoculum:
Freshly collected river waters, designated A, B, C and D, of varying composition were employed to evaluate the biodegradation of urea. Their composition varied for relevant constituents as follows (mg/L): ammoniacal N, 0.03 - 0.40; nitrite N,0.02 - 0.08; nitrate N, 1.2 - 8.8; pH, 7.6 - 8.3; alkalinity as CaCO3, 100 - 220; hardness as CaCO3,120 - 380.
Duration of test (contact time):
14 d
Initial conc.:
2 mg/L
Initial conc.:
8 mg/L
Initial conc.:
15 mg/L
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
A series of 1 L samples of the four rivers were fortified with two or all three of the 2 mg/L, 8 mg/L and 15 mg/L levels of urea and allowed to stand in water baths at two to four of the temperatures 4 ± 0.5 °C, 8 ± 0.5 °C, 12 ± 0.5 °C and 20 ± 0.5 °C. A steady stream of moist air was passed over each solution in the series, a “blank” flask containing deionized water being interposed between each series of flasks at different temperatures. Aliquots (50 mL) were withdrawn from each flask after 1, 2, 4, 7, 10 and 14 days and the ammoniacal N and urea content determined. After 14 days the volume of solution remaining was measured, and, where small volume changes were apparent, allowances for evaporation or condensation on a time basis were made to the ammonia N and urea values. Nitrite N, nitrate N and pH were also measured on completion of each trial.
Key result
Parameter:
% degradation (test mat. analysis)
Value:
>= 95 - <= 100
Sampling time:
8 d
Remarks on result:
other: at 20 °C
Details on results:
The nitrification of the test item was determined. The total concentration of nitrogen as urea at the beginning was around 3.75 mg/L and after 14 days ot was degraded to 0.85 mg/L. Respectively, the amount of nitrites and nitrates increased - from 0.02 to 2.1 mg/L for nitrites, and from 8.8 to 10.8 mg/L for nitrates. Whereas, the ammonia present in the test system decreased from 0.40 to 0.09 mg/L.

River A

For river water A breakdown of urea occurred only at 20 °C and was complete within 8 days for all levels of urea employed (2, 8 and 15 mg/L); the rate of biodegradation appears to be non-linear, little loss of urea occurring in the first 2 days but increasing rapidly thereafter. At 4, 8 and 12 °C no degradation was observed.

River B

At 20 °C, for the 2 and 8 mg/L levels of urea the rate was gradual for up to 10 days and afterwards increased rapidly, while for the 15 mg/L level the breakdown curve was similar to river water A. At 12 °C, breakdown commenced effectively only after 10 - 11 days and appeared to continue at a constant rate for the next 3 - 4 days irrespective of the level of urea present. No loss of urea occurred at 8 °C.

River C

In river water C urea was degraded in a similar fashion to river water B at 20 °C, after 6 - 7 days after the start initiation urea at level 8 mg/L started to rapidly degrade. By the 14th day around 95 % degradation was observed. No loss of urea occurred at lower temperatures.

River D

River water D showed no loss of urea at any temperature and any tested concentration.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
In conclusion, urea is readily biodegradable in river water under environmental conditions.
Executive summary:

The biodegradability of urea was inspected in four river samples. The procedure followed was similar to the one in OECD TG 301D. In closed bottles 50 mL river water samples were mixed with urea at concentrations of 2, 8 and 15 mg/L. The bottles were incubated at 4, 8, 12 and 20 °C. The biodegradation was measured for 14 days. In river water A and B, the test item showed rapid degradation at 20 °C after around 8 - 10 days and by day 14 was completely degraded. In river water C degradation was observed only at 20 °C and in river water D no degradation at any temperature of test concentrations was observed. In lower temperature in river waters A and B slower degradation ( at 12 °C) or no degradation (at 4 and 8 °C) at all was observed. These results show that the degradation of urea depends on the microorganisms present in the natural water and on the temperature of the environment. At environmental conditions of 20 °C and pH 7 - 8, urea showed high degradation in a 14-day test period. Therefore, the test item is considered as readily biodegradable.

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
Please refer to section 13 for "Read-Across justification".
Reason / purpose:
read-across source
Related information:
Composition 1
Test material information:
Composition 1
Key result
Parameter:
% degradation (test mat. analysis)
Value:
>= 95 - <= 100
Sampling time:
8 d
Remarks on result:
other: at 20 °C
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
Please refer to section 13 for "Read-Across justification".
Reason / purpose:
read-across source
Related information:
Composition 1
Test material information:
Composition 1
Key result
Parameter:
% degradation (test mat. analysis)
Value:
>= 80 - <= 99
Sampling time:
30 min
Key result
Parameter:
BOD5
Value:
>= 120 - <= 180 other: mg/L paper mill affluent
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1997
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Reference:
Composition 0
Principles of method if other than guideline:
Method: lab scale continuous STP reactor
GLP compliance:
no
Remarks:
Study is well documented and follows sound scientific principles.
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
Combined mill primary clarifier effluent was obtained from Howe Sound Pulp and Paper (Port Mellon, BC) during TCF(totally chlorine-free) bleaching operations and stored at 4 °C until use. Combined mill effluent is comprised of approximately 75 % (by volume) kraft mill effluent and 25 % TMP (thermomechanical pulping) effluent, and is treated by primary and secondary treatment prior to discharge. Two batches of primary treated effluent were obtained for this study.
Duration of test (contact time):
30 h
Initial conc.:
>= 5 - <= 1 000 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Parameter followed for biodegradation estimation:
other: BOD and toxicity
Details on study design:
Several methods of gauging reactor acclimation to hydrogen peroxide were performed throughout the study. Activated sludge mixed liquor samples from continuous reactor were shocked with varying concentrations of hydrogen peroxide. Reactor used was a lab-scale 3.5-litre working volume activated sludge reactor treating combined mill effluent was operated continuously over a period of six months. Reactor temperature 34 °C, hydraulic retention time 30 hours, solids retention time 5 days, nutrient addition (BOD:N:P) = 100:5:1, feed pH = 6.5 - 7.5.
Reference substance:
not specified
Key result
Parameter:
% degradation (test mat. analysis)
Value:
>= 80 - <= 99
Sampling time:
30 min
Key result
Parameter:
BOD5
Value:
>= 120 - <= 180 other: mg/L paper mill affluent

In the test increasing concentrations (5 - 1000 mg/L influent) of peroxide were continually added to a reactor treating combined TCF (Total Chlorine Free)-bleached kraft mill effluent. Treatment efficiency, as measured by removal of BOD, chemical oxygen demand (COD) and toxicity, was found to be unaffected by hydrogen peroxide concentrations of up to 1000 mg/L. The ability of activated sludge to tolerate sudden increases in hydrogen peroxide concentration was determined by measuring the viability of the sludge by measuring its oxygen uptake rate (OUR). Oxygen uptake rate of activated sludge samples, especially when unacclimated, were found to decrease dramatically when subject to shock loads of hydrogen peroxide. The OUR of unacclimated activated sludge was inhibited by sudden exposure to shock doses of hydrogen peroxide. The effect was reversible, with full recovery of metabolic activity restored within approx. 10 hours of exposure to the initial shock dose of 960 mg/L. OUR was decreased by 25 % with 100 mg/L load, 50% with 320 mg/L load, and 70% with 960 mg/L load. Activated sludge that had been acclimated to hydrogen peroxide in the reactor feed was more resistant to hydrogen peroxide shock loading.  Sludge acclimated to 500 mg/L hydrogen peroxide had about 20% OUR decrease with 320 mg/L shock load. The rate of peroxide reduction in effluent appears to be inversely related to the initial concentration of hydrogen peroxide. First order rate constants varied from about 0.05 to 0.15/min with 200 mg/L load. Autoclaved sludge yielded negligible rates of peroxide degradation over a 12 h period, providing that viable microorganisms are required to maintain demonstrable rates of peroxide degradation in STP. Catalase -equivalent induction in activated sludge was also monitored and it was found to increase with increasing hydrogen peroxide feed concentration. The presence of over 20 mg/L hydrogen peroxide in bleached kraft mill (BKM) effluent was found to decrease the biological oxygen demand (BOD) by up to 25%. The complete decomposition of hydrogen peroxide concentration up to 1000 mg/L was not found to have an effect upon the effluent toxicity as measured by Microtox-test.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Based on this test it can be concluded that activated sludge is able to treat totally chlorine free bleached kraft mill effluent that contains high concentrations of hydrogen peroxide.
Executive summary:

A test on the effect of hydrogen peroxide on the efficiency of activated sludge from a paper mill was carried out in a lab scale continuous STP reactor. Untreated effluent from a paper mill was used in the reactor and hydrogen peroxide was added by gradually increasing the concentration from 0 to 1000 mg/L. Treatment efficiency, as measured by removal of BOD, chemical oxygen demand (COD) and toxicity was found to be affected by hydrogen peroxide concentration of up to 1000 mg/L effluent in disproportionality to the amount of hydrogen peroxide in the effluent. Peroxide-induced reductions in effluent BOD may impair the efficiency of the effluent treatment in an activated sludge STP. Especially shock loads of hydrogen peroxide may adversely affect the activity of the activated sludge. On the other hand, activated sludge can be acclimated to the presence of high concentrations of hydrogen peroxide and is able to maintain viability.

Description of key information

The test item is considered to be readily biodegradable, based on the ready biodegradability of its degradation products.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The ready biodegradability of the test item was addressed with a read-across approach to its degradation products - urea and hydrogen peroxide. The test item is not stable and decomposes rapidly to urea and H2O2, therefore, the read-across to both substances is considered acceptable.

Urea

The biodegradability of urea was inspected in four river samples. The procedure followed was similar to the one in OECD TG 301D. In closed bottles 50 mL river water samples were mixed with urea at concentrations of 2, 8 and 15 mg/L. The bottles were incubated at 4, 8, 12 and 20 °C. The biodegradation was measured for 14 days. In river water A and B, the test item showed rapid degradation at 20 °C after around 8 - 10 days and by day 14 was completely degraded. In river water C degradation was observed only at 20 °C and in river water D no degradation at any temperature of test concentrations was observed. In lower temperature in river waters A and B slower degradation ( at 12 °C) or no degradation (at 4 and 8 °C) at all was observed. These results show that the degradation of urea depends on the microorganisms present in the natural water and on the temperature of the environment. At environmental conditions of 20 °C and pH 7 - 8, urea showed high degradation in a 14-day test period. Therefore, the test item is considered as readily biodegradable.

Hydrogen peroxide (H2O2)

A test on the effect of hydrogen peroxide on the efficiency of activated sludge from a paper mill was carried out in a lab scale continuous STP reactor. Untreated effluent from a paper mill was used in the reactor and hydrogen peroxide was added by gradually increasing the concentration from 0 to 1000 mg/L. Treatment efficiency, as measured by removal of BOD, chemical oxygen demand (COD) and toxicity was found to be affected by hydrogen peroxide concentration of up to 1000 mg/L effluent in disproportionality to the amount of hydrogen peroxide in the effluent. Peroxide-induced reductions in effluent BOD may impair the efficiency of the effluent treatment in an activated sludge STP. Especially shock loads of hydrogen peroxide may adversely affect the activity of the activated sludge. On the other hand, activated sludge can be acclimated to the presence of high concentrations of hydrogen peroxide and is able to maintain viability.

In conclusion, the test item is considered to be readily biodegradable, based on the ready biodegradability of its degradation products.