Advanced analysis of membrane-bioreactor performance with aerobic-anoxic cycling

Mathematical modeling and intensive chemical analysis are used to quantify the relationships among the heterotrophic bacteria, autotrophic bacteria, a nd key inorganic (NH4+-N and NO3--N) and organic (COD) compounds of municip al wastewater treated in a pilot-scale membrane bioreactor (MBR) operated w ith aerobic-anoxic cycles. Key features of the model for MBR are no biomass in the effluent, partial removal of biomass-associated products by the mem brane, and D.O. cycling with 9 mg/L during aeration period and 0.5 mg/L for the anoxic period. The model explains the key trends in the cyclic data: N H4+-N is consumed only during aerobic periods and rises steadily during ano xic period; NO3--N is produced only during aerobic periods, but declines in anoxic periods; The soluble COD in treated water mainly consists of BAP an d is relatively constant through the cycle. Advantages of introducing an an oxic cycle to the continuous flow MBR process are reduction of total efflue nt nitrogen, oxygen consumption, and sludge production as a consequence of denitrification. On the other hand, the anoxic period causes an increase in the average effluent NH4+-N. (C) 1998. Published by Elsevier Science Ltd. All rights reserved.