On the complete aerobic microbial mineralization of linear alkylbenzene sulfonate

The xenobiotic organic compounds linear alkylbenzene sulfonates (LAS) are among the most thoroughly investigated with respect to biodegradability. Previous studies have shown that LAS are relatively rapidly degraded under aerobic conditions, but only very slowly or not at all degraded under anaerobic conditions. In the present work, the degree of primary and ultimate biodegradation of LAS by consortia of aerobic microorganisms was examined. The quantification of primary biodegradation was conducted via analysis of the LAS content in the mixed liquor, which was based on microwave-assisted-extraction (MAE) followed by solid phase extraction with liquid chromatography coupled with a fluorescence detector (HPLC-FD). The ultimate biodegradability of LAS was examined by measuring both the disappearance of the test compound and the formation of carbon dioxide using the OECD method 301B or the sulphate. It was found that the established enriched mixed microbial population was capable for complete mineralization of all LAS, as verified by the sulfate production as well as the application of the OECD method and the carbon mass balances carried out throughout the course of the conducted experiments. In particular, any intermediate compound formed during LAS biodegradation was rapidly decomposed, making any intermediate accumulation temporal.

Based on the results of this investigation, it can be concluded that the established enriched mixed microbial population, originating from activated sludge, revealed a great ability to degrade the aromatic surfactant LAS. The comparison with the respective reduction of LAS in an abiotic control verified that the LAS elimination was exclusively due to their biodegradation. The results from the LAS mineralization kinetic experiments showed that the LAS degradation profile was repeatable. The abiotic control did not indicate that any significant physicochemical LAS reduction occurred during the experiment. By monitoring the DOC in the mixed liquor during the experiment, it was proved that LAS were mineralized completely and there were no persistent metabolites. The mineralization of LAS during aerobic degradation was also verified through carbon mass balances, as well as sulfate production. Therefore, native microorganisms proliferating in typical wastewater treatment plants are able to completely degrade and mineralize LAS present in raw wastewater under the provision that adequate hydraulic retention time (HRT) is provided for aerobic biological treatment. It can also be concluded that under the typical conditions of short HRTs (in the range of few hours) applied in most typical WWTPs, LAS ultimate biodegradation may be hard to succeed and therefore high concentrations of undegraded LAS or their metabolites may be found in the treated effluents in case that high LAS concentration levels are present in the raw wastewater and depending, of course, on the amount of acclimatized biomass available for LAS mineralization.