Study On Operation Condition Optimization And Membrane Fouling Control Of A~2/O-MBR Process For Phosphorus-containing Wastewater Treatment

In recent years,a large amount of nitrogen and phosphorus were discharged into receiving water bodies,resulting in eutrophication,which in return led to pollution incidents such as water bloom and red tide.In order to control the pollution,discharge standards of nitrogen and phosphorus are getting more and more severe,so a large number of urban sewage treatment plants cannot meet the standard and need a renewal.Taking the upgrades of a wastewater treatment station of a convention center using biological contact oxidation process in Dalian as an example,the performance of upgrading A~2/O-MBR process on the treatment of low-carbon and high-phosphorus domestic wastewater with large fluctuations in water quality was investigated,and the effects of carbon source addition in anaerobic pool and poly aluminium chloride addition in MBR membrane pool on the removal of nitrogen and phosphorus were explored.Finally,the intermittent operation mode and membrane cleaning method were optimized.The main results obtained were as follows:(1)After the low-carbon and high-phosphorus domestic wastewater was treated by A~2/O-MBR process,the concentrations of COD,ammonia nitrogen and total nitrogen effluent concentrations could comply with the“Liaoning Province Integrated Wastewater Discharge Standard”.However,the total removal efficiency of phosphorus was still poor and the effluent concentration of total phosphorus could not meet the standard.Thus,further optimized operation was necessary.(2)When adding starch as a supplementary carbon source in the anaerobic tank of A~2/O-MBR process,the removal rate of total nitrogen and total phosphorus increased,while the total phosphorus effluent still could not meet the discharge standard.Thus,poly aluminium chloride was added in the MBR membrane pool to increase the removal of phosphorus.Results showed that a total phosphorus removal could reach up to 97.8%and phosphorus concentrations were kept stable at the range of 0.03~0.41 mg/L in the effluent,which met the discharge standards.(3)The intermittent operation mode of MBR membrane effluent could affect the transmembrane pressure.The growth rate of transmembrane pressure increased with the increase of self-priming pump running time and decreased with the increase of stopping time.When the membrane cleaning scheme of hydraulic backflushing 15 min+500 mg/L NaClO alkali washing 2 h+0.1%hydrochloric acid washing for 2 h was applied,a cleaning efficiency of 95.3%for membrane filtration resistance was achieved.By optimizing the operational conditions of additional carbon source and chemical dephosphorization agent in A~2/O-MBR process,a low-carbon and high-phosphorus domestic wastewater can be treated and the effluent could meet discharge standard.With the optimization of intermittent operation mode and membrane cleaning method,the system could run stably.This study can provide important references for the upgrading of the low C/P domestic wastewater treatment plant.