Assessment of a combined UASB and MBR process for treating wastewater from a seafood factory at different temperatures

A combined upflow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR) bench-scale system was studied for treating wastewater generated in a seafood production facility. Hydraulic retention time in the UASB + MBR varied between 14 and 50 h. COD in the wastewater ranged between 500 and 3,000 mg/L. Despite the strong variability in the wastewater characteristics, the system was able to remove the organic carbon compounds and solids, stably complying in-force effluent discharge limits. This fact demonstrated the ability of the MBR post-treatment to polish the COD coming from the UASB reactor even when this methanogenic stage did not operate properly. Also, the effect of the temperature in the anaerobic UASB stage was evaluated, and organic removal rates up to 6 kgCOD/(m3 d) and COD methanation percentages larger than 90% were obtained. The presence of quaternary ammonium compounds, which are used as biocides for cleaning in the production line, inhibited biological processes, especially in the anaerobic methanogenesis and nitrification stages.