Conversion Mechanisms of Carbon, Nitrogen, and Phosphorus in Ozone-Fixed-Bed and Membrane Bioreactors for Deep Treatment of Municipal Tail Water

Abstract

An ozone-oyster shell fixed-bed bioreactor (OFBR) and a membrane bioreactor (MBR) were constructed and operated for about half a year for the deep treatment of municipal tail water. Pilot-scale test results showed that the combined OFBR-MBR had high removal efficiencies for carbon, ammonium, and phosphorus, and mean removal efficiencies for chemical oxygen demand, ammonium, total nitrogen, and total phosphorus (TP) were 75%, 99%, 20%, and 40%, respectively. Refractory organics in the municipal tail water were transformed to biodegradable organics in the OFBR, and the MBR effectively intercepted the surplus micro-molecular organics and microbes. Ammonium was mostly converted to nitrate, ∼10% of which was released as nitrogen gas through nitrification and denitrification by commonly known aerobic ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and denitrifying bacteria in the OFBR-MBR. The sludge was enriched in TP, which could be removed via surplus sludge discharge when sludge loading increased to overload amounts. Total removal depended on the uptake of phosphorus-accumulating organisms in the aerobic phase. Conversion mechanisms of carbon, nitrogen, and phosphorus in the OFBR-MBR system might be further adjusted to optimize process operation parameters, which might result in greater application of this system.