Performance of an anaerobic sequencing batch reactor operating under high organic loading in treatment of biodiesel wastewater

Studies reporting the performance of anaerobic sequencing batch reactor (AnSBR) operating with high organic loadings are scarce. This study aimed to contribute to the technical and scientific literature by reporting the experience obtained when biodiesel wastewater was treated in an AnSBR applying organic loading rates (OLR) above those commonly used in batch reactor projects. For this, physicochemical and chromatographic analysis of the effluent were carried out. Further, the biomass was assessed chemically and morphologically, along with bacterial diversity characteristics. Supported by these analyses, the system performance was discussed in terms of COD remotion efficiency and buffering capacity. The AnSBR reached 10% of COD removal at the steady-state, which caused the biomass defragmentation and facilitated washout. This suggests that the startup and operation of AnSBR under optimized conditions with an average applied OLR of 11.3 g_COD L^-1 d^-1 worked as a pressure for the microbiota selection, stimulating the production of total volatile acids, which promoted system reduction efficiency and souring. In this context, food/microorganism ratios above 1.0 g_COD g_TVS ^-1 d^-1 can favor acidogenic activity, and total volatile acids/bicarbonate alkalinity concentration ratios above 1.9 may indicate acidification. The addition of support material for immobilizing/increasing biomass retention and/or operation under two-stage may be interesting alternatives for increasing AnSBR efficiencies under high OLRs.