Influence of hydraulic retention time on the operation of a submerged membrane sequencing batch reactor (SM-SBR) for the treatment of greywater

This study describes the experience received in operating an SM-SBR under different hydraulic retention times for the treatment of synthetic greywater. The pilot scale SM-SBR with a working volume of VR = 500 L is operated with hydraulic retention times of 33, 24 and 12 h, and a volumetric exchange ratio of ~0.25. The removal of COD, ammonia, total nitrogen is investigated for the different set-ups. Despite the low COD in greywater, the treatment performance of the reactor is always sufficient to meet reuse guidelines. The biomass concentration increases slowly, although no excess sludge has been taken out (except sampling). Therefore, the sludge age is assumed to be >360 d.

Synthetic greywater was treated in an SMSBR with anoxic and aerobic phases for denitrification and nitrification. Low loading rates resulted in low oTS concentration at the beginning, but increasing loading rates yielded oTS concentrations where an MBR is applicable. NUR and AUR values were comparable to literature data and suggested that nitrogen removal is generally feasible in these systems. The TN removal efficiency achieved under the different HRT illustrated the success of an optimised cycle and phase times as operational parameters. Moreover, a further optimisation potential to an HRT of 8 h was indicated. The low growth rate must be taken into consideration when designing an SMSBR for greywater treatment. Abbreviations GW greywater SM-SBR submerged membrane sequencing batch reactor VER volumetric exchange ratio SRT sludge retention time HRT hydraulic retention time TMP transmembrane pressure PVDF polyvinylidene fluoride PES polyethersulfone