Effect of sludge recirculation pattern on biological nutrient removal by a prototype IT/BF-MBR (inclined tube/biofilm-membrane bioreactor) and microbial population characteristics

Abstract

A novel prototype IT/BF-MBR (inclined-tube/biofilm - membrane bioreactor) was developed as a single compact reactor for biological nutrient removal and building wastewater reuse. The system consists of three compartments; first-stage biofilm compartment (Tube 1), second-stage biofilm compartment (Tube 2) and aerobic membrane compartment. The wastewater from a 20-floor building in Chulalongkorn University was fed to the system at organic loading rate of 1.6 kg COD/m3-day. The IT/BF-MBR was operated with hydraulic retention time, HRT of 4.4 h. In this study, influence of two sludge recirculation patterns on biological nutrient removal was investigated. Sludge recirculation pattern 1 was the sludge recirculation from aerobic compartment to the front Tube 1 and Tube 2 compartments at the same flowrate. For the sludge recirculation pattern 2, the sludge recirculation was from aerobic compartment to Tube 2 and from Tube 2 to Tube 1. Total sludge recirculation rates for both slude recirculation patterns were kept at 200% of feed flowrate,Qin. From long-term system operation, it was found that the sludge recirculation pattern 2 could achieve higher phosphorus removal efficiency due to more complete anaerobic condition inside Tube 1. COD, nitrogen and phosphorus removal efficiencies were 95.0, 96.4 and 94.0%, respectively. Moreover, real-time PCR assay was performed for the microbial population quantification of ammonia oxidizing bacteria (AOB), Nitrospira and Candidatus Accumulibacter inside the IT/BF-MBR system. Furthermore, the quality of treated effluent could comply with the water reuse standards for toilet flushing purpose.