Determination of quorum-sensing signal substances in water and solid phases of activated sludge systems using liquid chromatography–mass spectrometry

The detection of acyl homoserine lactones (AHLs) in activated sludge is essential for clarifying their function in wastewater treatment processes. An LC–MS/MS method was developed for the detection of AHLs in both the aqueous and solid phases of activated sludge. In addition, the effects of proteases and extracellular polymeric substances (EPS) on the detection of AHLs were evaluated by adding protease inhibitors and extracting EPS, respectively. Recoveries of each AHL were improved by adding 50μL of protease inhibitor, and recoveries were also improved from 0 to 56.9% to 24.2%–105.8% by EPS extraction. Applying the developed method to determine the type and concentration of AHLs showed that C4-HSL, C6-HSL, C8-HSL and 3-oxo-C8-HSL were widely detected in a suspended activated sludge system. The dominant AHL was C8-HSL, with a highest concentration of 304.3ng/L. C4-HSL was mainly distributed in the aqueous phase, whereas C6-HSL, C8-HSL and 3-oxo-C8-HSL were preferentially distributed in the sludge phase. [Display omitted]