Effects Of Phosphorus Chemical Recovery From Side-stream Aqueous Phase On Reversed A~2/O Biological System

Nitrogen and phosphorus are the main source of nutrient for biological growth,but they are the main factors that contributed to water eutrophication.With the discharge standards is becoming more and more strict,the effluent of phosphorus is difficult to achieve the national level A discharge standard in the plant,chemical phosphorus removal need more costs.Phosphorus is a kind of non-renewable and irreplaceable natural resources.With the development of economy,this makes the phosphorus resources shortage even more critical.In terms of the phosphorus cyclic utilization,the implementation of discharge standard and the control of eutrophication,the simultaneous chemical phosphorus precipitation is the best choice of phosphorus removal in biological system.The side-stream chemical phosphorus precipitation can result in P stripping for PAOs.However,the effects of P recovery on the biological treatment system and microbial community structure must be investigated in the reversed A~2/O(anoxic-anaerobic-aerobic)system.In this paper,the reversed A~2/O system with simultaneous chemical phosphorus precipitation was used to carry out phosphorus recovery under the synthesized wastewater.The effects of different side-stream ratio on biological nitrogen and phosphorus removal were studied,and the changes of microbial community structure were analyzed.The study is considered to provide theoretical reference for the application under simultaneous side-stream chemical phosphorus precipitation process.The main results and conclusions are made as follows:(1)Simultaneous side-stream chemical phosphorus precipitation had little effect on the efficiency of ammonia and COD removal.The performance of nitrogen and phosphorus removal had been improved in the system,obviously.While theside-stream ratio was 20%,the rate of phosphorus releasing and uptaking was the highest,which was reduced with the increasing of side-stream ratio gradually.The high side-stream ratio could not guarantee the stable and sustainable operation of the system.(2)The phosphorus content of sludge decreased with the increase of side-stream ratio,and the trend of SVI of the system was negatively correlated with the phosphorus content of sludge.The ratio of the side-stream had big influence on the size of activated sludge and the settling performance of sludge.The grain size began to decrease,the sludge distribution was loose,the sedimentation performance was deteriorated,which resulted in sludge bulking.The low side-stream ratio could help to improve the settling of the system.Simultaneous side-stream chemical phosphorus removal promoted the growth of filamentous bacteria in the system,and the number of protozoa also increased with the increase of side-stream ratio.(3)With the increase of side-stream ratio,the phosphate concentration decreased in the anaerobic stage gradually,and the PHA content was significantly decreased in the sludge,and the trend of glycogen was opposite.(4)The reversed A~2/O system with simultaneous chemical phosphorus precipitation process had its unique advantages,which could improve the performance of nitrogen and phosphorus removal and achieve considerable amount of phosphorus recovery.Comprehensive comparison of the operating conditions under different side-stream ratioes,the side-stream ratio should not be too large,the best side-stream ratio should be controlled about 20%.(5)In the simultaneous side-streaming chemical phosphorus removal system,the microbial diversity increased with the increase of the side-stream ratio,and the proportion of microorganisms in the system that retained of inoculate sludge decreased.The system mainly existed proteobacteria as the dominant microorganism,and the The changes of abundance on α-proteobacteria,β-proteobacteria andγ-proteobacteria and Cytophagia were consistent with the results of nitrogen and phosphorus removal.(6)Simultaneous chemical phosphorus precipitation had some influence on the relative abundance of function bacterial in the system.With the increase ofside-stream ratio,the abundance of Dechloromonas increased from 0.05% to 7.95%.The bacterial abundance of Acinetobacter was reduced from 2.31% to 0.21% with the side-stream.The abundance of the Thiothrix increased from 0.01% to 4.32%,which was the main cause of sludge bulking.The efficiency of nitrogen and phosphorus removal efficiency and sludge performance were closely related to the evolution of function bacterial.