Study On The Productive Application And Optimization Of Semi-centralized Sewage Treatment System

The main water supply and drainage system in China is the traditional centralized model,which belongs to the "terminal pollutant treatment" structure.It can not realize the reuse of water resources and the energy consumption of the system is high.This system belongs to the resource consumption model.The new semi-centralized water supply and drainage model which based on the separation of sewage source,treatment and recycling of water resources has attracted more attention in recent years because of its advantages,for example high resource utilization,low energy consumption and low pollutant discharge.There are few researches on the plant-scale semi-centralized sewage treatment and lack of practical data.This paper takes the Qingdao Shiyuan semi-centralized sewage treatment system as the research object.The operation of the black water and gray water treatment system which based on the membrane bioreactor?MBR?had been conducted and optimized.The denitrification and dephosphorization of black and gray water systems were studied by means of testing and simulating the operation to investigate the removal efficiency of nitrogen and phosphorus pollutants in each reactor.Especially,the effects of recirculation ratio,dissolved oxygen and sludge concentration on the denitrification and dephosphorization of black water system were further investigated in detail to seek the best parameter to run the system.At the same time,the microbial population structure of black and gray water treatment system were analyzed to auxiliarily debug the system operation.The research results indicated:?1?The removal efficiency of COD and NH₄⁺-N in black water system were 97.1% and 99.2% respectively.Since the low influent SCOD/TN of biochemical system,the performance of nitrogen and phosphorus were ineffective.The effluent concentration of TN and TP were 17.5 mg/L and 5.2 mg/L and the removal efficiency were 83.3% and 45.8% respectively.The removal efficiency of COD,TN,NH₄⁺-N and TP in gray water syetem were 96.6%,90.3%,99.2% and 93.3% respectively;But when the influent TCOD/TN> 20,the effluent concentration of NH₄⁺-N and TN increased to 10.6mg/L and 13.4mg/L,then the NO.2 reaction zone should be adjusted to aeration state to satisfy the DO requirement of oxidation and nitration.?2?The effect of internal recirculation ratio and dissolved oxygen on the denitrification performance of the system was investigated.When recirculation ratio was 500%,the denitrification performance was the best.The effluent TN concentration was 15.8mg/L and the TN removal efficiency was 84.6% which was higher than the recirculation ratio were 300% and 700% by 5.6% and 3.8% respectively.When the dissolved oxygen?DO?concentration is less than 0.50mg/L,the nitrification efficiency is obviously inhibited and reduced to 43.3%.When the DO were 0.60-0.75 mg/L,1.5-2.0 mg/L and 3.5-4.0 mg/L,the nitrification rate increased gradually,and the nitrification rates were 90.2%,96.5% and 97.8% respectively.?3?The Simultaneous Nitrification and Denitrification?SND?experiment showed that when the DO concentration was gradually reduced to 0.6-0.75 mg/L,the average TN removal efficiency increased up to 90.6%,which was 14.5% higher than that at high DO level,and the TN removal efficiency via SND???SNDTN??in the aerobic zone was 56.1%.In addition,the internal recirculation ratio and sludge concentration were influential to SND level and TN removal efficiencies.When the internal recirculation ratio decreased from 300% to 200%,the TN removal efficiency decreased from 90.2% to 83.7%,and further decreased to 82.8% with increasing internal recirculation ratio to 500%.When the sludge concentration in the aerobic zone decreased from 9000±300 mg/L to 6000±300 mg/L,??SNDTN?decreased from 58.8% to 8.1% and TN removal efficiency decreased from 88.8% to 76.0%.?4?The experiment of chemical method to enhance the phosphorus removal capacity showed that the removal efficiency of phosphorus increased from 28.8% to 89.9% after the addition of FeCl3.In addition,it had little effect on the denitrification performance of the black water system.?5?The experiment of enhancing the nitrogen removal efficiency of black water system by adding organic carbon source into the prepositive denitrification and rear denitrifying zone showed that the adding organic carbon source into the rear denitrifying zone could obviously improve the TN removal capacity of the system,the TN concentration of the effluent reduced to 13.5mg/L,the removal efficiency increased from 78.9% to 88.8%.The average amount of TN which was removed in the rear denitrifying zone was 13.1mg/L.?6?The microbial population structure of black and gray water system was analyzed by Miseq high-throughput sequencing technology.It was found that with the increase of reaction temperature and influent load,the ACE,Chao and Shannon indices of the two systems increased,indicating that the diversity of microbial population and the diversity of the community increased.The typical PAO was Acinetobacter and its amount was only 8.76% of the phosphorus bacteria number..It caused that the phosphorus removal efficiency was ineffective.The proportion of phosphorus-removing bacteria in the gray water system was 1.91%,which was equivalent to the amount of denitrifier bacteria?2.08%?.Since the contradiction between the organic source competition was more moderate,the performance of phosphorus removal of the gray water system was effective.