Fate of surfactants in membranebioreactors and conventionalactivated sludge plants

Two membrane bioreactors (MBRs) were operated at high sludge retention time (SRT) (between 30 and 75 d) in parallel to a conventional activated sludge plant (CASP) conducted at SRT ) 10 d. The fate of linear alkylbenzene sulfonate (LAS), nonylphenol ethoxylates (NPnEO, n ) 1-15), nonylphenoxy carboxylates (NPnEC, n ) 1-2), and nonylphenol (NP) in these systems was investigated. All systems were very efficient in the removal ofLAS(around 99%).Theanalysis of varianceshowed that the difference in the removal efficiency of LAS in the CASP and the MBR operated at SRT ) 65-75 d (respectively 99.0 ( 0.43 and 99.8 ( 0.11) were significant (p < 0.05), confirming the importance of SRT in the removal of LAS. Comparison between the CASP and the MBRs in the removal efficiency of nonylphenolic compounds were conducted considering NP3-15EO, the sum of NP1-15EO, NP1-2EC, and nonylphenol (NP). In all cases MBRs were more efficient than the CASP. In the case of NP the removal was about 76 ( 7.5% for the CASP and 90% ( 12.1 and 82 ( 8.7% for the MBRs. Better performance of MBRs in the removal of nonylphenolic compoundscanbeattributed toabetter degradation. For example, if the sum of NP1-15EO and NP1-2EC is considered, estimated biodegradation was about 48% for the CASP and 72% for MBRs.