Nitrogen Removal Performances Of A Polyvinylidene Fluoride Membrane-aerated Biofilm Reactor

Some problems exist in traditional nitrogen removal technology, such as long technology process, complexe control and large aera, and so on. Membrane-aerated biofilm reactor (MABR) is considered as a novel technology, overcoming these shortcomings, which combines membrane technology and biofilm.In this study, a MABR with polyvinylidene fluoride (PVDF) hollow fiber membrane was developed. The MABR realized the simultaneous nitrification and denitrification (SND) through mass transfer in opposite direction of aeration. The nitrogen removal was studied under different influent loads and C/N ratios. The feasibility of MABR to treat the wastewater with a low C/N ratio was analyzed. Moreover, the microorganism diversity under the typical operating conditions and the microbial community ecological succession were investigated.The bioattaching property of different membrane materials showed that the attached biomass on PVDF membrane was 0.71 g TOC/m2, showing an excellent biomass attaching property. Results of MABR system with the increase of influent NH4+-N concentration from 30 to 120 mg/L showed that the MABR had outstanding COD removal ability, and the COD removal was always higher than 85%. Nitrogen removal was significantly affected by the influent NH4+-N concentration. The limitation of influent NH4+-N concentration for this MABR system was 70 mg/L with a maximum specific NH4+-N conversion rate of 55.67 kg/m3-d and specific TN removal rate of 52.87 kg/m3·d, which were both higher than other traditional wastewater treatments.Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) results showed that the bacteria community diversity was obvious in the biofilm of MABR system because of the coexistence of aerobic and anaerobic environment. Apart from various ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, Nitrosomonas sp. and Planctomycetes sp. were found, which might conduct naerobic Ammonium Oxidation (ANAMMOX) with partial nitrification under oxygen limited condition.The operation parameters of MABR were optimized, and results for indicated that the optimal HRT was 24 h, the optimal aeration pressure was 0.025 MPa with air aeration. Under the optimal operating conditions, the removal of COD, NH4+-N, TN was 92.21%,96.80% and 83.75%, respectively. Besides, the MABR system showed good stability under the shock load.The MABR system was used to treat the wastewater with a low C/N ratio. Results showed that the MABR system effectively treated the wastewater with a low C/N ratio of 5:1 with a removal of COD, NH4+-N, TN of 84.29%,96.07% and 85.59%, respectively. The MABR system provided sufficient electron donor for denitrification to achieve SND and save carbon source. PCR-DGGE results showed that the microorganism associated with biofilm formation, denitrification and ANAMMOX process changed obviously. Thus, denitrification and ANAMMOX process were greatly affected by the influent C/N ratio.