Soluble microbial products (SMPs) in the effluent from a submerged anaerobic membrane bioreactor (SAMBR) under different HRTs and transient loading conditions

This study investigated the performance of a submerged anaerobic membrane bioreactor (SAMBR) fed with synthetic wastewater (544 ± 22 mgCOD/L) operating at different hydraulic retention times (HRTs-12 h, 8 h, 6 h, 4 h, 2 h, and 1 h) at both steady state, and under transient load conditions (2 and 1 h), and the SMPs produced under these conditions. COD removal at decreasing HRTs (12 h, 8 h, 6 h, 4 h, and 2 h) was high (>94%), but decreased to 80% when operating at 1 h HRT. VFAs accumulated when the HRT was decreased to 2 h and 1 h, accounting for 69% and 89% of the effluent COD, respectively. Effluent SMPs accounted for an average of 14 ± 2 mgCOD/L at steady state, but this fluctuated more during transient conditions (12 ± 6 mgCOD/L). The COD equivalent of dissolved methane in the effluent was 17% at 4 h HRT, exceeding the saturation value of methane. Low MW compounds were identified using gas chromatography–mass spectrometry (GC–MS), with solid phase extraction (SPE) as the pre-treatment. 120 compounds were identified in the effluent at steady state, and were alkanes (39), alkenes (3), esters (11), alcohols (7), nitrogenated compounds (11), phenols (11), and others (9). Increases in cyclooctasulfur, N-butyl-benzenesulfonamide, alkanes, 1-naphthalenol, camphor, 2-methylphenol, and (Z)-9-octadecenamide were also found during transient conditions, and these compounds were not found in the feed; hence it is possible that these compounds were produced by microorganism as by-products from substrate utilization