Hyperhaline Municipal Wastewater Treatment of a Processing Zone through Pilot-Scale A/O MBR, Part II: Nitrogen and Phosphorous Removal

Abstract

An integrated anoxic/aerobic membrane bio-reactor (A/O MBR) was designed to treat hyperhaline municipal wastewater from a processing zone of Tianjin, China. The removal performance of the system to ammonia nitrogen (NH3-N), total nitrogen (TN) and total phosphorus (TP) was investigated, and the contribution of membrane and microbes to pollutant removal was evaluated and discussed. The adaptability of the system to a high-loading nitrogen impact was also studied. Experimental results show that the removal efficiencies of NH3-N and TN of the A/O MBR system were approximately 95% and 50%-70%, respectively, during the four-month investigation period. Very good removal is mainly contributed to the microbial degradation. Membrane interception to nitrogenous matters is insignificant. The contribution of membrane interception is to keep nitrifying bacteria (having a long generation cycle) in the reactor, thus strengthening nitrogen removal. Total phosphorus removal of the A/O MBR system is as high as 60%-80%. Such high removal of TP is unexpected since there was only once sludge discharge from the system during four-month operation period, that is traditional biological phosphorus removal cannot be achieved. Nontraditional biological functions (including sludge particle adsorption to phosphoric matters and microbial assimilation) and membrane interception to insoluble phosphoric matters (mainly organic phosphorus and a small quantity of phosphorus complex) are the main mechanisms of TP removal of the A/O MBR system. Moreover, biological function is predominant, therefore sludge concentration in the reactor is increased and TP removal is enhanced.