Experimental Study On Low C/N Domestic Sewage By Combined Multi-level AO Process And MBR

While the urban sewage discharge volume and treatment scale are increasing with the increase of urbanization rate,the effluent standards of sewage treatment plants have also been greatly improved,the urban sewage treatment plants in the transformation of stably reaching the first level A standard are faced with the problems of low carbon and nitrogen ratio,which affects the ability of biological denitrification,and the low water temperature in winter,which affects the problems of biological nitrification and denitrification capacity.The multi-stage A/O-MBR combined process has the advantages of multi-stage A/O processan and the MBR process,high efficiency of denitrification in the influent water,low energy consumption of non-nitrating liquid reflux,high efficiency solid-liquid separation,stable water discharge,and flexible control.which is favored in many stably reaching the first level A standard process?In this study,a multi-stage A/O-MBR combination process was used to treat low-carbon-to-nitrogen-ratio urban domestic wastewater,The method of reducing the hydraulic retention time and doesn't discharge excess sludge was used to increase the sludge concentration to the normal operating concentration,during the increase of sludge concentration,the effects of process treatment and sludge characteristics were changed;after the completion of the system start-up period,the effects of sludge return ratio,SRT,DO,and other process parameters on the removal efficiency of system pollutants were studied;Increased internal circulation measures to improve nitrogen and phosphorus removal efficiency,analyzed the enhanced effect of denitrifying phosphorus removal,analyzed the effects of sludge mixture characteristics and process parameters on membrane fouling,and studied the method of hydraulic backwash and chemical on-line cleaning for membrane flux.Recovery situation.The results show that:?1?During the start-up of the system,the sludge concentration in the reactor was increased from 2500 mg/L to 5000 mg/L due to the system's non-rejection operation and retention of the membrane pool,but the sludge activity decreased.The MLVSS/MLSS value decreased from the initial 0.85 to 0.79,and the total SOUR value decreased from the initial 22.5 mg O₂/?g MLVSS·h?to the final 19.68 mg O₂/?g MLVSS·h?.During the start-up period of the system,the effluent COD,NH₄⁺-N,and TN concentrations of the system gradually decreased,and the TP slowly increased.The effluent COD,NH₄⁺-N,TN,and TP concentrations were 53.16,7.09,16.24,and 2.40 mg/L,unable to reaching the first level A standard?2?Sludge return ratio,SRT,DO optimization study found that the sludge return ratio and the system COD removal efficiency is positively related;and NH₄⁺-N,TN,TP removal effect is negatively correlated,the optimal reflux ratio is 50%.SRT has no significant effect on COD removal efficiency of the system;it is positively correlated with the removal efficiency of NH₄⁺-N and TN,but SRT too long will also reduce the removal efficiency;and negatively related to the removal efficiency of TP,considering the optimal efficiency of simultaneous nitrogen and phosphorus removal,It is better to choose SRT as 20 d,the effluent TN can reach the first level A standard stably,and the TP can reach he first level B standard.The optimal reflux ratio is 1.5 mg/L.The efficiency of nitrogen and phosphorus removal was best.The average concentration of COD,NH₄⁺-N,TN and TP in the effluent system were 28.20,2.06,12.48,and 0.93 mg/L,The effluent COD,NH₄⁺-N,and TN Can reach the first level A standard,the effluent TP reach he first level B standard.?3?It was found in the process of enhanced phosphorus removal that after the process improvement,the system had no significant effect on the removal efficiency of COD and NH₄⁺-N.The average removal rates were 89.55% and 98.38%,respectively;the system TN removal rate was slightly increased,and the removal rate was improved.from the initial 76.92% to 80.31%,the removal rate of the system TP increased significantly,and the removal rate increased from the initial 74.81% to 90.55%.By the 40 th day,the effluent COD,NH₄⁺-N,TN,and TP concentrations of the system were 26.63,1.12,10.33,and 0.48 mg/L,respectively,all reaching the first level A standard.Through sludge static analysis experiments,it was found that the change of the operating mode made the phosphorus-accumulating bacteria and the denitrifying phosphorus-accumulating bacteria proliferate,and the proportion of denitrifying phosphorus-accumulating bacteria in the phosphorus-accumulating bacteria increased from 15% in the initial period to 24%.?4?With the increase of sludge concentration and sludge age,the increase rate of TMP is increasing,and the time for TMP to reach the set cleaning pressure is gradually shortened.The system has a SRT of 10 d and the TMP average growth rate is 1.22KPa/d.The appropriate aeration volume of the MBR reaction tank in this system is 0.10Nm³/h.Considering both the effective control of the increase in membrane resistance and ensuring that the required amount of water is met,the optimum drawdown time ratio is determined to be 8 min: 2 min.The recovery effect of water backwash on membrane flux increased with the increase of the backwash time,but when the backwash time was extended to 4min,the recovery of membrane flux no longer increased significantly.The simple hydraulic cleaning can only alleviate the membrane fouling and is not enough to eliminate the membrane fouling.Chemical cleaning of contaminated membranes with 0.2% Na Cl O solution can restore the membrane flux to 99.5% of the initial state.