Registration Dossier

Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
biodegradation in water: sewage treatment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2018-11-05 to 2019-01-09
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 303 A (Simulation Test - Aerobic Sewage Treatment. A: Activated Sludge Units)
Version / remarks:
22nd January 2001)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on source and properties of surface water:
n.a.
Details on source and properties of sediment:
n.a.
Details on inoculum:
- Details on collection (e.g. location, sampling depth, contamination history, procedure): Municipal sewage treatment plant, 31137 Hildesheim, Germany
The activated sludge was washed once with tap water and maintained in an aerobic condition by aeration at room temperature until use. At test start the concentration was 2.9 g DW/L.

Domestic sewage with a DOC of 95 - 146 mg/L was used as organic medium.
Domestic sewage was collected from the primary sedimentation tank of the treatment plant. At sampling the sewage was filtered to remove coarse particles. The DOC and pH value were measured from each batch. Each batch was stored at about 4°C to reduce microbial activity. Domestic sewage of the same source as for activated sludge was used.
Duration of test (contact time):
30 d
Initial conc.:
0.5 mg/L
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: 372 mL
- Additional substrate: no
- Test temperature: 21.0 - 23.6°C
- pH: 6.09 - 7.16
- Suspended solids concentration: 2.9 9 DW/L
Domestic sewage with a DOC of 95 - 146 mg/L was used as organic medium.
Domestic sewage was collected from the primary sedimentation tank of the treatment plant. At sampling the sewage was filtered to remove coarse particles. The DOC and pH value were measured from each batch. Each batch was stored at about 4°C to reduce microbial activity. Domestic sewage of the same source as for activated sludge was used.
DOC adjustment of the domestic sewage with synthetic sewage was not necessary.

The system was started with activated sludge with a dry weight of 2.9 9 DW/L in the aeration vessel. Test volume in the aeration vessel was 372 mL. To re-suspend activated sludge adhering to the walls of the
aeration vessel, a magnetic bar was placed inside the aeration vessel permanently. For resuspension, the magnetic bar was swiped over the glass walls with a second magnetic bar from outside of the vessel.
Throughout the test the sludge adhering to the walls of the activated sludge units were re-suspended daily. Regularly, all tubes and tubing were checked and cleaned to prevent a growth of biofilm a far as possible.
Due to the geometry of the air-lift pump, slight 1055 of sludge occurred until day 14, furthermore the sedimentation capacity decreased. Therefore fresh sludge was added on day 9 (test start) and day 15 (day 6 of test item application) to the aeration vessel.

Sludge retention time (SRT) 10 d
1/10 of the volume (37.2 mL) ofthe activated sludge in the aeration vessel was removed as surplus sludge once per day directly from the aeration vessel by a syringe.

Application:
After a period in which the system had stabilized and the removal of DOC of the organic medium was efficient (> 80 %), dosing of the test item solution in the aeration vessel of the test item unit was started. The test item was continuously applied to the aeration vessel by a syringe pump. As the stock solution was added directly to the activated sludge unit, no biodegradation occurred before it reached the aeration vessel.
The elimination, sorption and primary degradation of the test item was determined by UPLC-MS/MS.

TEST SYSTEM
- Culturing apparatus: Activated sludge unit consisting of an aeration vessel (approx. 500 mL, activated sludge volume 372 mL) and a separator (approx. 250 mL)
- Number of culture flasks/concentration: 1
- Method used to create aerobic conditions: The aeration vessel was aerated continuously. Airflow was adjusted to maintain an oxygen level of at least 2 mg/L and was ensured by strong bubbling in the aeration vessel.



Test performance:
After the activated sludge units had stabilized, the dosage of the test item was started (2018-1114). After six days (from 2018-11-20 on) the nominal influent concentration of the test item was reduced because the sludge structure was impacted.
After eight days of test item application, the plateau phase was started. The plateau phase lasted about three weeks and in total 16 samplings of the effluent and sludge were done. Influent (each new stock solution), effluent and sludge samples were analysed by UPLC-MS/MS.
The mean elimination of the test item in the effluent during the plateau phase was 99.29 % of the influent concentration (95 % CI: 99.18 - 99.40). The mean load of the test item in the sludge during the plateau phase was 0.12 % of total influent load (95 % CI: 0.06 - 0.18). The mean concentration of the test item in the sludge during the plateau phase was 9.96 µg/g DW (95 % CI: 5.88 - 14.03).
The mean load of the test item in the sludge during the plateau phase was 0.12 % of total influent load (95 % CI: 0.06 - 0.18). The mean concentration of the test item in the sludge during the plateau phase was 9.96 µg/g DW (95 % CI: 5.88 - 14.03).
Based on these data it can be concluded that the main elimination process of the test item in a sewage treatment plant is biodegradation.
% Degr.:
>= 73 - <= 84
Parameter:
DOC removal
Remarks on result:
other: daily elimination
Transformation products:
not measured
Details on results:
The biodegradation of the organic medium was calculated from the difference of influent and effluent DOC.
DOC values of the effluent were determined from composite effluent samples taken over a period of 24 h. Therefore, influent DOC and effluent DOC of the following 24 h were used for the calculation of elimination.
During acclimatisation, the activated sludge unit had stabilized and biodegradation of the DOC of the organic medium became efficient (> 80 % after 1 day).
In the course of the study the biodegradation oscillated in the range of 73 - 84 %. The slight decrease was probably due to variations in the quality and composition of the organic medium. Nevertheless, the unit worked stable and efficiently throughout the study.
Results with reference substance:
n.a.

DOC Concentration and Degradation of the Organic Medium

Study day

Day of Test Item Application

DOC

Elimination DB[%]

Influent CM [mg C/L]

Effluent E0 [mg C/L]

0

-9

129.1

21.4

83

1

-8

21.1

84

2

-7

20.2

84

3

-6

112.8

16.6

87

4

-5

14.6

87

7

-2

16.7

85

9

0

21.8

81

10

1

95.1

26.0

73

11

2

28.3

70

14

3

26.3

72

15

4

97.4

27.6

72

16

5

24.9

74

17

6

23.2

76

18

7

23.4

76

21

12

145.5

36.5

75

22

13

37.8

74

23

14

135.8

37.0

73

24

15

36.3

73

25

16

36.8

73

28

19

142.4

28.0

80

29

20

27.5

81

30

21

27.1

81

31

22

124.7

27.9

78

32

23

27.5

78

35

26

30.1

76

36

27

122.9

25.4

79

37

28

20.8

83

38

29

21.0

83

39

30

20.2

84

 

 

 

Oxygen Concentration, pH-Value and Temperature in the Activated Sludge

Study day

Day of Test Item Application

Parameter

pH

Temperature [°C]

O2[mg/L]

3

-6

6.59

23.6

6.48

11

2

6.19

22.8

4.84

17

8

6.09

22.9

5.87

24

15

6.60

21.0

5.82

31

22

6.32

22.5

6.24

38

29

7.16

22.4

-

- = not determined, due to technical reason

The pH of the activated sludge at test start was 7.40. The pH of the activated sludge used for adjustment was 7.35.

At day 3 of the study the pH of the activated sludge unit was 6.59. During adaptation and plateau phase (day 2 - day 22 of test item application) the pH was< 7.0. The decrease of the pH had no influence on the degradation capacity of the activated sludge.

At the end of the study the pH was 7.16 and therefore in the range of 7.5 ± 0.5.

The temperature in the aeration vessels was in the range of 21.0 - 22.7 °C throughout the study.

Validity criteria fulfilled:
yes
Conclusions:
Based on the analysis of the test item C16 Alkylamidopropyltrimethylammonium Chloride in the effluent, the mean elimination rate at the plateau phase in relation to the total influent concentration was calculated. The elimination of the test item in the effluent was 99.29 % (95 % CI: 99.18-99.40) in a continuously operating activated sludge unit. The mean load of the test item in the sludge during the plateau phase was 0.12 % (95 % CI: 0.06 - 0.18). The mean concentration of the test item in the sludge during the plateau phase was 9.96 µg/g DW (95 % CI: 5.88 - 14.03).
lt can be concluded that the main elimination process of the test item in a sewage treatment plant is biodegradation.
Executive summary:

The elimination and primary degradation of the test item C16 Alkylamidopropyltrimethylammonium Chloride in an activated sludge unit was determined according to OECD guideline 303 A.

The elimination and primary degradation of C16 Alkylamidopropyltrimethylammonium Chloride by aerobic microorganisms was determined in a continuously operating laboratory activated sludge unit simulating the activated sludge process.

The activated sludge unit was started with an activated sludge content of 2.9 g/L DW. After a short acclimatization period of the activated sludge (DOC elimination> 80 %), the application of C16 Alkylamidopropyltrimethylammonium Chloride was started. Samples of the effluent and sludge were taken at regular intervals and UPLC-MS/MS analysis was carried out to determine the effluent concentration and fraction adsorbed on the activated sludge to determine elimination of the test item.

During acclimatization, the activated sludge unit was inoculated with activated sludge. The DOC elimination of the organic medium reached a degradation rate > 80 % already after 1 day. The dosage of the test item was started after an acclimatization period of 8 days.

The nominal concentration of the test item stock solution was 500 mg/L. At test start the nominal test concentration was 1.0 mg/L.The stock solution was dosed at a constant rate of 124 µL/h into the activated sludge unit. Because the influent concentration of 1.0 mg/L impacted the sludge structure, the nominal test item concentration was adapted on day 6 of adaptation period. Consequently, the stock solution was dosed at a constant rate of 62 µL/h into the activated sludge unit, resulting in an influent concentration of 0.5 mg/L test item.

Based on the analysis of the test item in the effluent, the mean elimination rate at the plateau phase in relation to the total influent concentration was calculated. The elimination of the test item was 99.29 % of the influent concentration (95 % CI: 99.18 - 99.40) in a continuously operating activated sludge unit. The mean load of the test item in the sludge during the plateau phase was 0.12 % of total influent load (95 % CI: 0.06 - 0.18). The mean concentration of the test item in the sludge during the plateau phase was 9.96 µg/g DW (95 % CI: 5.88 - 14.03).

Description of key information

mean elimination: 99.29%of the influent concentration (95 % CI: 99.18 - 99.40) during plateau phase

mean load in the sludge during plateau phase: 0.12 % of total influent load (95 % CI: 0.06 - 0.18)

mean concentration of test item in the sludge during the plateau phase: 9.96 µg/gDW (95% CI: 5.88 - 14.03)

Key value for chemical safety assessment

Additional information

The elimination and primary degradation of the test item C16 Alkylamidopropyltrimethylammonium Chloride in an activated sludge unit was determined according to OECD guideline 303 A.

The elimination and primary degradation of C16 Alkylamidopropyltrimethylammonium Chloride by aerobic microorganisms was determined in a continuously operating laboratory activated sludge unit simulating the activated sludge process.

The activated sludge unit was started with an activated sludge content of 2.9 g/L DW. After a short acclimatization period of the activated sludge (DOC elimination> 80 %), the application of C16 Alkylamidopropyltrimethylammonium Chloride was started. Samples of the effluent and sludge were taken at regular intervals and UPLC-MS/MS analysis was carried out to determine the effluent concentration and fraction adsorbed on the activated sludge to determine elimination of the test item.

During acclimatization, the activated sludge unit was inoculated with activated sludge. The DOC elimination of the organic medium reached a degradation rate > 80 % already after 1 day. The dosage of the test item was started after an acclimatization period of 8 days.

The nominal concentration of the test item stock solution was 500 mg/L. At test start the nominal test concentration was 1.0 mg/L.The stock solution was dosed at a constant rate of 124 µL/h into the activated sludge unit. Because the influent concentration of 1.0 mg/L impacted the sludge structure, the nominal test item concentration was adapted on day 6 of adaptation period. Consequently, the stock solution was dosed at a constant rate of 62 µL/h into the activated sludge unit, resulting in an influent concentration of 0.5 mg/L test item.

Based on the analysis of the test item in the effluent, the mean elimination rate at the plateau phase in relation to the total influent concentration was calculated. The elimination of the test item was 99.29 % of the influent concentration (95 % CI: 99.18 - 99.40) in a continuously operating activated sludge unit. The mean load of the test item in the sludge during the plateau phase was 0.12 % of total influent load (95 % CI: 0.06 - 0.18). The mean concentration of the test item in the sludge during the plateau phase was 9.96 µg/gDW (95 % CI: 5.88 - 14.03).