Simultaneous High-Efficient Biological Phosphorus Removal And Phosphorus Recovery Of Chemical Precipitation Combined With BNR Process Subjected To Low Consumption

Phosphorus is one of the indispensable elements of life.Due to its nonvolatility,phosphorus moves from land to ocean in a unidirectional line in nature.Eutrophication of waterbody and the shortage of phosphorus resources have become the focus and hotspot in the field of wastewater treatment.Over-aeration of biological nutrient removal（BNR）system not only causes unnecessary waste of energy,but also leads to system failure and effluent phosphorus substandard.In this study established a chemical phosphorus recovery method through magnesium ammonium phosphate（MAP）precipitation coupling with mainstream BNR process subjected to low consumptionwas established to investigate simultaneous biological phosphorus removal and phosphorus recovery performance under different conditions.The feasibility of efficient synchronous biological phosphorus removal and phosphorus recovery of long-term side-stream phosphorus recovery combined with low-consumption mainstream BNR process was evaluated and the optimal operation parameters were determined.The main reason for phosphorus removal and recovery performances decline were analyzed based on changes of microbial community structure in mainstream biological treatment process and metabolism mechanism transformation of functional microorganisms,which provided theoretical and data support for ractical application of this technology.Besides,the study has certain guiding significance to achieve carbon peak and carbon neutralization for China.The main results of the study are as follows:1.Low dissolved oxygen（DO）had no influence on the stable phosphorus removal of BNR system.Total phosphorus in effluent could meet grade A of the comprehensive wastewater discharging standard,though DO concentration was controled at under ultra-low condition(0.1mg·L^-1).It was feasible to carry out phosphorus removal efficiently in the BNR system with low consumption.Besides,low DO was benificial to sludge reduction.Chemical precipitation could promote a stable biological phosphorus removal performance of overaerated BNR system with no failure occurring in a long period（107 days）.Furthermore,a phosphorus recovery product which was mainly composed of struvite and magnesium phosphate crystals was prodeced in the side-stream reaction tank under the optimal conditions.2.The removal of COD and ammonia nitrogen was not influenced in the mainstream overaerated BNR system with the long-term chemical precipitation phosphorus recovery in side-stream.Nevertheless,total nitrogen removal efficiency was gradually increased due to the enhancement of denitrification capacity during anaerobic period.With the increase of side-stream frequency,the anaerobic phosphorus release and aerobic phosphorus uptake capacity of polyphosphate accumulating organisms（PAOs）decreased.Long-term extracting1/2 anaerobic supernatant to side-stream tank,especially,could lead to the mainstream BNR system lose the advantage of stable and efficient phosphorus removal gradually.As a result,intermittent extraction or appropriate reduction of side-stream ratio was suggested to gurantee synchronous phosphorus removal and phosphorus recovery.In addition,long-term extraction of anaerobic supernatant for phosphorus recovery was beneficial to sludge reduction and had little effect on sludge settling performance.3.Low dissolved oxygen concentration(DO=1.0mg·L^-1,1.0mg·L^-1,0.2mg·L^-1)and side-stream ratio（m=0,1/4,1/3,1/2）had little effect on the removal efficiency of COD and ammonium,but the removal efficiency of TN was improved due to the enhancement of simultaneous nitrification and denitrification capacity in the mainstream BNR system.Also,the phosphorus removal performance at DO=1.0 mg·L^-1 and 0.6 mg·L^-1 stages was stable and efficient though phosphorus release capacity decreased gradually with DO.When DO≥0.6mg·L^-1,higher phosphorus recovery efficiency could be achieved at higher side-stream ratio.However,the optimal conditions with DO=1.0 mg·L^-1 of and side-stream ratio=1/3 was determined in view of the reliability of the combined process and stability of effluent water quality.4.Compared with influent C/P ratio,the amount of carbon source and phosphorus were the main factors affecting biological phosphorus removal performance of the mainstream BNR system subjected tolow consumption.However,the change of influent carbon source and phosphorus concentration had little influence on the removal of TN in the mainstream system.The effluent TN could stably meet the requirements of Grade A of the Discharge Standard of Pollutants from Urban Wastewater Treatment Plants（GB18918-2002）.High phosphorus release amount was more favorable for side-stream phosphorus recovery.Besides,C/P=400/8 was considered to be the reasonable influent quality given the phosphorus recovery potential and effluent standard requirements of low-consumption mainstream BNR system.5.The introduction of side-stream phosphorus recovery process during anaerobic phase had little effect on nitrogen and COD removal performance no matter the low-consumption mainstream BNR system was operated at room temperature（22±1℃）or low temperature（14±1℃）.The room temperature mainstream low-consumption system operated at 22℃was found to be more stable in biological phosphorus removal during side-stream phosphorus recovery period.There was little difference in phosphorus recovery potential between BNR systems at room temperature and low temperature,but it was not desirable to implement side-stream phosphorus recovery strategy in BNR systems operating at low temperature and low consumption considering the stability of mainstream BNR systems.6.The change of microbial community structure in the low-consumption mainstream BNR system before and after long-term side-stream phosphorus recovery were analyzed by molecular biological methods.It was found that the richness of microbial population did not change significantly.The microbial community structure,however,was more uneven.The analysis of microorganisms at genus level showed that Candidatus Accumulibacter which was the dominant PAOs and Nitrospira which performed nitrification reduced after long-term side-stream extraction.Nevertheless,other potential microbes which could removal nitrogen and phosphorus like Dechloromonas and Flavobacterium increased instead,indicating that the side-stream phosphorus deprivation could change the microbial population structure of the low-consumption mainstream system to a large extent.These results supported the main reason of phosphorus removal variation of the mainstream system.