Performance of membrane bioreactor to different hydraulic shock loadings

Abstract

A Membrane Bioreactor (MBR) treating simulated sewage was operated and stabilised for a period of 60 days at an organic loading rate of 3.6 g/COD/day and Hydraulic Retention Time (HRT) of 8 h, during which the MBR showed 95% removal of Chemical Oxygen Demand (COD), 98% removal of Total Organic Carbon (TOC) and TSS, 91% removal of Total Kjeldahl Nitrogen (TKN) and 30% removal of phosphate. The responses of the MBR to different hydraulic shock loadings were studied. The HRT was reduced to 4 h, 2 h, 1 h and 0.8 h to simulate two, four, eight and tenfold increase in flow rate, respectively, for a period of 12 h. During the shock load the influent COD concentration was maintained constant. Under the hydraulic shocks, the COD removal efficiency temporarily reduced to between 92% and 81% and the TOC removal efficiency reduced to between 80% and 48%. TOC removal efficiency was very poor at tenfold hydraulic shock. The TKN and phosphate removal efficiency were slightly affected at twofold hydraulic shock, showing a removal efficiency of 76% and 24%, respectively. The nitrogen and phosphate removal was highly affected at higher shock loads with very high TKN and phosphate concentration in the effluent. The system took much longer time (around 7 to 14 days) to recover in terms of nutrient removal for higher shock loads. The biomass was not at all affected at two, four and eightfold increase in flow rate. The high biomass and sludge retention of the MBR is advantageous to withstand such high and sudden hydraulic shocks, with its ability to recover faster than any other biological reactor.