Effects Of Exposure To Linear Anionic Surfactants On Anammox Biomass Activity

Anaerobic ammonium oxidation (anammox) is now widely recognized as an important biological process for nitrogen removal from wastewaters, which can directly convert NH4+-N to N2 gas with NO2--N as electron acceptor under anaerobic conditions. Compared with the conventional nitrification-denitrification process, anammox process has significant advantages, such as no demand for oxygen and organic carbon, low sludge production and no CO2 emissions. However, the high requirements for the wastewater and long-term start-up period still restrict the industrial applications of anammox process. Surfactant is one kind of organic compounds with biotoxicity and widely used in industry and daily life, extremely linear anionic surfactants (LAS). The wastewater treated with anammox process inevitably contains surfactants, such as textile wastewater, petroleum wastewater. For this case, this study investigated the toxicity of surfactants on anammox bacteria and the possibility of applying anammox process on treating nitrogen-rich wastewater containing LAS.This work demonstrates the feasibility of nitrogen removal from wastewater containing linear anionic surfactants, such as sodium dodecyl benzene sulfonate (SDBS) and sodium deodecyl sulfate (SDS), by using anammox process. Experimental results showed that exposed to SDS caused irreversible inhibition on anammox activity and further nitrogen removal rate (NRR), which decreased from 6.7 ± 0.6 to 1.4 ± 0.1 mg-NgVSS-1h-1 as the dosages of SDS increased from 0 to 150 mg/L. However, NRR was not significantly affected in the presence of SDBS. Further investigation indicated that exposed to both SDBS and SDS did not induce membrane damage to anammox cells. Enzyme activity assays proved that the nitrite reductase (NIR) activity of anammox biomass was suppressed by SDS and SDS ranging from 50 to 150 mg/L resulted in a sharp decrease in the NIR activity, which were 58.8 ± 8.2%,37.0 ± 6.6% and 16.2 ± 4.9% of the control, respectively. The NIR suppression was positively correlated with NRR inhibition, suggesting that the negative influence on anammox biomass was induced by NIR denatured exposed to SDS.The long-term biotoxicity of SDBS and SDS on anammox bacteria was studied. The results demonstrated that the nitrogen removal rate didn't decrease when the concentration of SDBS and SDS reached 50 mg/L. When the SDS addition increased to 100 mg/L, the TN removal rate sharply reduced to 0.30 kg-N/m3/d, only about 50% of the control. However, part of the anammox bacteria exposed in SDS and SDBS appear black, while the control is still deep red, indicating that the cells are still affected by the toxicity of surfactant. These findings proved that it is necessary to consider the content of surfactant in the wastewater in the application of anammox process.