Biological Nitrogen Removal By Coupling Zeolite Adsorption/regeneration And Modified A/O Process

In the past thirty years,China's economy is developing rapidly concomitantly with urbanization and industrialization.Subsequently,environmental problems especially in wastewater pollution are increasingly standing out and showing out-break in local regions.After“The Action Plan for Prevention and Treatment of Water Pollution”was promulgated in 2015,the discharge standard for nitrogen and phosphorus has become more stringent.However,in most towns,total nitrogen removal in municipal wastewater treatment do not meet the standard.Currently,A/O process is a widely used technology in nitrogen removal,which has the advantage in simple process flow and easy control.Generally,increasing internal reflux ratio could improve nitrogen removal efficiency,but increase operation cost.Additionally,internal reflux makes it hard to remove 90%of nitrogen due to the introduction of dissolved oxygen into anoxic phase.In this study,we presented a novel design by coupling zeolite adsorption/regeneration and modified A/O process to achieve deep nitrogen removal.Therefore,we carried out a series of investigations as follows:?1?characterization of zeolites in terms of specific surface area and pore size distribution,and selection of desired zeolites for ammonia adsorption in terms of particle size,adsorption time,dosage,pH,COD concentration,salinity and temperature;?2?determination of the optimal operating parameters by investigating the coupled process in COD,NH3-N and TN removal efficiencies in orthogonal experiment,where dissolved oxygen?DO?,internal reflux?r?and return sludge were chosen as the influencing factors;?3?under optimal operating conditions,investigation of the treatment efficacy of the coupled process with synthetic and real municipal wastewater.Therefore,we used a specific surface analyzer and a scanning electron spectroscopy to characterize zeolites used in this study and investigate the effect of influencing factors such as DO,r and R on COD,NH₃-N and TN removal efficiencies through the coupled process.Meanwhile,under optimal operating conditions,we investigated the efficacy of the coupled process in treating real municipal wastewater.It can be concluded that:?1?the optimal conditions for zeolites to remove ammonia nitrogen could be achieved with particle size of 5 mm,dosage of 30 g/L,COD concentration below 500 mg/L,temperature more than 25 ^oC and adsorption equilibrium time set at 0.1?0.2 h,and the modified zeolites with particle size of 5 mm had the maximum of surface area and roughness;?2?the major influencing factors to TN and NH₃-N removals were r and DO,respectively,while COD removal efficiencies were achieved at higher levels despite of the influencing factors;Through orthogonal experiment,DO at 1 mg/L,r at 100%and R at 100%were selected as the operating parameters for effectively remove carbon and nitrogen;?3?effluent COD,NH₃-N and TN all met the first grade Municipal Wastewater Treatment Plant?GB 18918-2002?when the coupled process was applied to treat real municipal wastewater,with TN removal efficiency up to 91%.Above all,the coupling zeolite adsorption/regeneration and modified A/O process could achieve deep nitrogen removal,which was proved to be cost effective and overcome the disadvantage of traditional A/O process.Hence,it provide a promising approach for deep nitrogen removal from wastewater.