Optimization And Mathematical Modeling On The Carbon And Nitrogen Removal Performance Of MABR

Membrane-aerated biofilm reactor(MABR)integrates the gas-permeable membrane and the biofilm to achieve and stabilize the formation of redox-stratified microniche by individually regulating the counter-diffusional mass transfer between the electron acceptor and donor.It's conducive to improving the oxygen transfer and utilization efficiencies and realize the simultaneous nitrification and denitrification(SND)process,highlighting the technical advantages in the field of carbon and nitrogen removal for wastewater treatment.The two-stage MABR system was integrated and constructed through the reflux system to investigate the treatment feasibility for the synthetic wastewater,COD and ammonium concentrations of which were 300 mg/L and 35 mg/L,respectively.The process parameters were gradually determined for the effective performance,including the aeration pressure of 0.015 MPa for MABR-1 and 0.040 MPa for MABR-2,the water inflow of 0.75 L/h and the reflux ratio of 200%.During the continuous operation,the ammonia loading impact on the systematic stability was conducted with stable removal performance of soluble organics and ammonia achieved.Water quality of the bulk liquid and operational parameters of the system would significantly affect the compositional,structural and functional characteristics of the membrane-aerated biofilm,further associated with the mass transfer process and degradation pathway of the carbon and nitrogen substances.Hence the treatment performance changes.Based on the biofilm modeling,effects of oxygen transfer coefficient,intra-membrane aeration pressure and concentration of soluble organics on the SND process were analyzed to further elucidate the optimization mechanism and regulation measure for the conversion and removal performance of carbon and nitrogen substances.Results indicated that the oxygen transfer coefficient would impact the growth and/or competition among microbes and then the structure and function of the biofilm.It's essential to provide sufficient oxygen for facilitating the conversion efficiency of ammonium and then the removal of total nitrogen.Growth activity of heterotrophic bacteria would be regulated by the concentration of soluble organics in the bulk liquid,further impacting the growth and/or competition between ammonia-oxidizing microbes and nitrite-oxidizing bacteria during the ammonium conversion process.Under certain concentration of soluble organics,feasibility of oxygen supply and nitrogen oxide would alter the synergetic-and-competitive growth among the facultative heterotrophs,and then mediate the short-cut nitrogen removal pathway.But incomplete denitrification mediated by the heterotrophic bacteria under insufficient organics supply was the main source of accumulation of nitrogenous intermediates.Besides,the biofilm thickness would influence the mass transfer and degradation process within the membrane-aerated biofilm and then change the distribution of active microbes.For the thinner biofilm,the short-cut nitrogen removal via the nitrite reduction was the dominant removal pathway.However,the carbon source should be supplemented to enhance the conversion of nitrous oxide.Researches on the biofilm modeling were potentially conducive to the performance optimization and practical application of the membrane-aerated biofilm.