Realization And Optimization Of Nitrogen Removal In Mainstream A~2O Process By Biofilm Enhancement

Anaerobic/Anoxic/Oxic Reactor（A²O）has a simple structure and can achieve simultaneous nitrogen and phosphorus removal.It is commonly used in wastewater treatment plants,but the treatment effect is difficult to meet the increasingly strict water discharge standards.Besides,a large amount of energy is consumed in the aeration stage of the A²O process,which causes a huge waste.Therefore,it is necessary to combine a more efficient and energy-saving treatment process to save energy and reduce consumption in the WWTPs,and to achieve’carbon neutrality’and’peak carbon dioxide emissions’.The use of ANAMMOX to enhance the nitrogen removal of municipal wastewater is one of the current research hotspots in 21th century.Compared to traditional nitrification/denitrification processes,the anammox process has three distinct advantages:（i）partial oxidation of ammonia to nitrite,reducing aeration requirements by 60%;（ii）almost 100%savings of carbon source required for denitrification;（iii）80%reduction in excess sludge production.Therefore,it’s a promising method to reduce the demand for carbon sources of the influent wastewater by using the anammox process,thereby improving the nitrogen removal efficiency.This study aimed to enhance total nitrogen removal efficiency in IFAS reactor to treat domestic wastewater.The mechanism of biofilm and floc sludge on the removal of pollutants was explored,the microbial community characteristics of biofilms and activated sludge and the enrichment characteristics of anammox bacteria were investigated.In addition,the influence of C/N ratio on the pollutant removal performance of the system was explored.The regulation of influent carbon sources provided a feasible method to improve contaminant removal efficiency in treating domestic wastewater with low C/N ratio.1.The continuous flow IFAS reactor was rapidly started up and stabilized,and high nitrogen and organic removal efficiencies were achievedThe IFAS-A²O process was rapidly started up through sludge inoculation and the using of fixed biofilm carriers.The TIN removal load was（0.10±0.03）kg N·m^-3·d^-1,and the average removal rate of TIN and COD was 65-75%and 79%,respectively,showing stable performance during 127 days of operation.Affected by the low temperature in winter,the MLSS of the system was declined and the nitrogen removal performance was destroyed.During the operation,it was found that the appropriate HRT was 14-15 hours.In addition,the reduction of flocculent sludge resulted in a significant decrease in the TIN removal rate（only 52%）.In this study,the flocculent sludge was the main contributor to nitrification of the system,while the nitrification capacity of biofilm was weak.With the recovery of MLSS,the average TIN removal rate increased to 74%.After removing all biofilm carriers for 121 days,the TIN removal rate and COD removal rate remained around 70%and 80%.A phenomenon was also consistent with the above speculation,that the flocculent sludge was the main contributor of nitrification in this system.2.During the operation of the IFAS process,the source of microorganisms in the suspended sludge was the initial inoculation of the biofilm,and the microorganisms in the biofilm were continuously succeeded in different functional areasThe microbial community distribution of biofilm and suspended sludge in the IFAS reactor was investigated.According to high-throughput sequencing data,the main genera of AOB,NOB and An AOB were Nitrosomonas;Nitrospira,Nitrotoga and Candidatus Brocadia.Nitrosomonas were mainly distributed in the aerobic biofilm,accounting for 0.97%;Nitrospira and Nitrotoga also had the highest relative abundance（1.38%and 0.59%）in the aerobic biofilm,followed by activated sludge（0.46%and0.16%）,the figures in the remaining samples were lower.Candidatus Brocadia had the highest relative abundance（0.43%）in the aerobic biofilm,followed by the anoxic biofilm,the activated sludge and the anaerobic biofilm,indicating that the biofilm in the reactor together with the micro-aerobic/aerobic environment was conducive to the occurrence of anammox process.Besides,the aerobic and anoxic areas in the IFAS-A²O reactor may be potential hot areas for anammox to occur.In addition,according to the PCo A analysis,the environmental conditions of different functional areas drove the continuous succession of microbial communities,which made the spatial distribution of microbial community more complicated,and improved the NRE of the system.3.COD/N ratio was an important factor of the nitrogen removal performance in IFAS reactor,and precise regulation of carbon source was an important way to enhance the nitrogen removal capacity.The key factors of the coagulation process were investigated,and the pollutant removal performance was optimized by controlling influent organic loadThe influence of the dosage of coagulant aid,stirring method and stirring time on the coagulation process was investigated.The optimal dosage of PAC and PAM were200 mg·L^-1 and 8 mg·L^-1,respectively.The optimal stirring speed in this experiment was 80 r·min^-1.By controlling the organic load of influent water,the pollutant removal was optimized.As the influent organic load was increased from 0.31 kg·m^-3·d^-1 to 0.37kg·m^-3·d^-1,NRL was improved to 0.08 kg N·m^-3·d^-1.The controllable adjustment of the influent carbon source was a promising way to strengthen the nitrogen removal capacity of the process.