Simultaneous removal of organic substances and nitrogen in pilot-scale submerged membrane bioreactors treating digested traditional Chinese medicine wastewater

Abstract

Influence of dissolved oxygen (DO) concentration on organic substances and nitrogen removal was investigated in pilot-scale submerged membrane bioreactors (SMBRs) degrading digested traditional Chinese medicine (TCM) wastewater. The DO concentration for each SMBR was maintained at 0.6, 1.2, 3.0 and 5.0 mg/L, respectively. Experimental results indicated that DO had an important effect on the chemical oxygen demand (COD) removal and nitrogen conversion. Simultaneous nitrification and denitrification were able to be accomplished in the continuous-aeration SMBRs by controlling ambient DO concentration. It is postulated that, because of the oxygen diffusion limitation, an anoxic micro-zone was formed inside the flocs where the denitrification occurred. From four tested DO levels, the optimal DO concentration favoring COD and total nitrogen removal was found to be 1.2 mg/L. At that DO level, more than 96% COD and 90% total nitrogen were degraded. A model was developed for the SMBR process of degrading the digested TCM effluent, taking into account the biological degradation and membrane separation. The model well fitted the laboratory data, and was able to simulate the removal of COD and nitrogen. It is suggested that the model proposed could reflect and manage the operation of SMBR treating a certain kind of industrial wastewaters.