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Biodegradation in water and sediment: simulation tests

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No STP simulation test has been performed for tallow bis(hydroxyethyl)amine oxide (CAS no 61791 -46 -6) instead the available STP simulation test results of oleyl bis(hydroxyethyl)amine (CAS no 25307 -17 -9) are read across. This read across is considered to be justified as both substances have a similar structure, are readily biodegrable, have a negligible vapour pressure and have a similar sorption. Based on the slightly higher mean Kd of 4526 L/kg for oleyl bis(hydroxyethyl)amine the removal via sorption for tallow bis(hydroxyethyl)amine oxide which has a mean Kd of 2271 L/kg will be slightly lower than for oleyl bis(hydroxyethyl)amine. This lower sorption will however immediately compensated via additional biodegradation. Using the results of the STP simulation study from the source chemical oleyl bis(hydroxyethyl)amine for read across to the target chemical tallow bis(hydohydroxyethyl)amine oxide can be considered as a realistic worst-case approach.

In the STP (sewage treatment plant) simulation study with 2,2’(octadec-9-enylimino)-bisethanol (25307-17-9) more than 99.999% removal was observed using specific chemical analyses (LCMS/MS) of the effluent during day 44 to 48 (n=5). Also  the sorption to sludge was measured and this accounted for 0.16 % of the total removal which means that 99.83% is removed by biodegradation.

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Biodegradation in a sewage treatment simulation test:

More than 99.999% removal is observed for Oleyl bis(hydroxyethyl) amine (2,2’(octadec-9 -enylimino)-bisethanol; 25307-17-9) in waste water treatment simulation test. From this removal 99.83% is removed via biodegradation and 0.16 % via sorption.

The removal of Oleyl bis(2 -hydroxyethyl)amine in biological treatment plants was simulated in a continuously-fed activated sludge (CAS) unit fed with domestic wastewater spiked with Oleyl bis(2 -hydroxyethyl)amine (AkzoNobel, 2010). Oleyl bis(2-hydroxyethyl)amine was exposed to micro-organisms maintained by addition of domestic wastewater in the CAS test. Oleyl bis(2 -hydroxyethyl)amine was spiked at a nominal influent concentration of 50 mg/L (37.0 mg/L carbon; calculated) for a period of 48 days and included a control fed with domestic wastewater only.

The immediate high removal percentages can be attributed to adsorption and probably biodegradation. The mean removal percentage of oleyl bis(2-hydroxyethyl)amine calculated over 15 measurements obtained from day 34 to 48 of the test was 102±0.8% (95% confidence interval). These high removal percentages strongly indicate that oleyl bis(2-hydroxyethyl)amine is biodegraded completely. Formation of water soluble compounds during biological treatment of oleyl bis(2-hydroxyethyl)amine can be excluded. An accurate assessment of the removal of oleyl bis(2-hydroxyethyl)amine was established with specific analyses. The mean removal percentage of oleyl bis(2-hydroxyethyl)amine in the test unit was quantified from day 44 to 48 and was more than 99.999% using octadecenyl bis(2-hydroxyethyl) amine as representative component for the whole substance as a worst-case. These analyses demonstrate that the removal of octadecenyl bis(2-hydroxyethyl)amine is complete. Octadecenyl bis(2-hydroxyethyl)amine concentrations in the mixed liquid suspended solids (activated sludge) of the reactor sampled on days 47 and 48 were 3.2 mg/L. Mean removal percentages of octadecenyl bis(2-hydroxyethyl)amine from the influent through adsorption onto sludge assessed in two samples was therefore 0.16% demonstrating that octadecenyl bis(2-hydroxyethyl)amine is primarily removed by biodegradation.

In conclusion, the CAS test demonstrates that oleyl bis(2-hydroxyethyl)amine is almost completely removed from the wastewater in conventional biological wastewater treatment plants. Oleyl bis(2 -hydroxyethyl)amine is primarily removed by biodegradation.

 

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