Low C/N Municipal Wastewater Simultaneous Nitrification And Internal Denitrification Denitrification And Phosphorus Removal Performance And Optimization Research

The increasing production of municipal sewage and its low C/N ratio water quality characteristic make it difficult for traditional denitrification and phosphorus removal processes to meet their strict discharge standards.Due to the shortcomings of traditional biological nitrogen and phosphorus removal technologies,it is particularly important to develop new technologies for nitrogen and phosphorus removal with low consumption and high efficiency.The topic of this study was to start up the simultaneous nitrification-endogenous denitrification and phosphorous removal?SNEDPR?system using low C/N ratio municipal sewage based on the sequencing batch reactor?SBR?.SNEDPR-SBR technology was considered as a promising process achieving high efficient nitrogen and phosphorus removal,by enhanceing the storage of internal carbon sources to achieve a“one carbon dual use”approach.Furthermore,by controlling the concentration of different influent matrix and operating mode,as well as investigating the relationship between nitrogen and phosphorus removal performance and population dynamics of functional microorganisms of the SNEDPR system,this study might provide a theoretical support for the stable operation and application of SNEDPR-SBR process.At the same time,this study also achieved the feasibility of treating for municipal and nitrite sewage by enhancing the performance of DPAOs?denitrifying phosphorus accumulating organisms?,which coupledPDPR system with SNED system.?1?In order to achieve an efficient nutrient removal,an extended anaerobic/low aerobic?dissolved oxygen:0.5¹.0mg/L?sequencing batch reactor?SBR?fed with municipal sewage was started up and optimized by regulating the influent C/N ratio.The population dynamics of functionalmicroorganisms were also analyzed.Results indicated thatwhen the influent C/N ratio raised from 4.3 to 5.15,the N and P removal performance of the system became better with total nitrogen?TN?and PO₄^3--P removal efficiencies up to 89.3%and 90.6%,respectively;with C/N ratio reduced to<3,the nutrient removal performance decreased firstly and then increased in the following operation.However,the effect of low C/N on the phosphorus removal performance of PAOs?phosphorous accumulating organisms?was higher than the endogenousdenitrification capability of DGAOs?denitrifying glycogen accumulating organisms?,showed as the TN and PO₄^3--P removal efficiency reduced to 21.4%and 3.4%firstly,and lately increased to 92.9%and94.1%gradually.In the stable phase of the system,the average phosphorus release per COD and SNED efficiency reached to 437.1mg/L and 89.1%respectively,with the average effluent concentration of NH₄⁺-N,NO_x^--N and PO₄^3--P was 0,4.4,and 0.2mg/L,respectively.After 136-day operation,PAOs,GAO,AOB?ammonia oxidizing bacteria?and NOB?nitrite oxidizing bacteria?accounted for8.9%,8.3%,2.15%and 7.5%of total biomass,respectively,which ensured the P uptake,nitrification and denitrification.Additionally,the occurrence of simultaneous partial nitrification-endogenous denitrification at the low aerobic stage of the system interpreted the efficient nutrient removal from low C/N?<3?wastewater.?2?A sequencing batch reactor?SBR?fed with municipal sewage was studied under by adjusting different C/P ratios?10,15,20,30 and 60?to analyze the competition mechanism of GAOs and PAOs.The experimental results showed that a proper reduction of the influent C/P ratio?C/P ratio reduced from 60 to 30?could enhance the competitive advantages of phosphorus accumulating organisms?PAOs?in the SNEDPR system,and the highest phosphorus removal efficiency was achieved at C/P ratio of 30,with the anaerobic phosphorus release rate?PRR?and the aerobic phosphorus uptake rate?PUR?reached to 3.5mg/?g·h?and 4.2mg/?g·h?respectively,and the average effluent PO₄^3--P concentration lower than 0.3 mg/L,the percentage of PAOs in contribution to store the endogenesis carbon(P_PAO,An)reached to 88.1%;but a poor performance of phosphorus removal appeared with a further reduction of influent C/P ratios to 10,both the PO₄^3--P removal efficiency and P_PAO,An reduced from 38.1%and 82.4%to 3.1%and 5.3%,respectively,the PRR and PUR just at 0.2mg/?g·h?and 0.24mg/?g·h?,respectively.The performance of COD removal was not affected by decreasing influent C/P ratios showing as an average COD removal efficiency was stabilized at 85%.In addition,the performance of nitrification became poorer with the C/P ratios reduced from 60 to 20,as the effluent NH₄⁺-N and NO₂^--N concentration increased from 0 and 6.9 mg/L to 5.1mg/L and 16.2 mg/L;and then the nitrificaton performance recovered when the C/P ratios went lower to 10,but the nitrite accumulation had been disturbed shown as both the effluent NH₄⁺-N and NO₂^--N concentration reduced to 0,meanwhile the effluent NO₃^--N concentration increased from 0.08 mg/L to 14.1mg/L.The SNED efficiency decreased from 62.1%to 36.4%firstly and then raised to 56.4%lately.The advantage competition of glycogen accumulating organisms?GAOs?could be improved when the influent C/P ratio lower than 15,and the enhancement of the GAOs endogenous denitrification ability might explain the recovery denitrification performance of the system at the influent C/P ratios downed from 20 to 10.?3?An extended anaerobic/low aerobic?dissolved oxygen:0.5¹.0mg/L?sequencing batch reactor?SBR?fed with municipal sewage was studied,with four different SRT?5d,10d,15d,25d?conditions.The experimental results showed that A shorter SRT could enhance the competitive advantage of PAOs in the system with the SRTT?10d,but when the SRT less than 10d denitrifying bacteria could more more active than DPAOs;and when the SRT=15d and 10d,the performance of phosphorus removal was both in a high level,especially when SRT=10d,the average PPAOs,An was 68.4%,PRA and PUA reached to 31.9mg/L and 34.3mg/L,respectively.The performance of nitrification of the system was not affected in different SRT conditions,meanwhile,the TN removal efficiency and SNED efficiency was the highest compared to the four SRT,with the average TN removal efficiency and SNED efficiency reached to 89.6%and 71.8%,respectively.During the SRT?10d,the performance of COD removal could not vary with different SRT conditions,shown as the COD removal efficiency reached higher than 78%.However,the COD removal efficiency was not stable under shorter SRT.In contrast,the ability of system to resist the changes in the influent loads was improved under the longer SRT operation.The system appeared to the best sludge settling ability under the SRT=15d,with SV and SVI was 20%and 64mL/g,and the MLSS improved with the extended SRT operation;although the capability of the system under long SRT shown a better resistance to shock loads but a poorer settling performance.?4?Combination PDPR system with SNED system in an anaerobic/anoxic/aerobic operated SBR was proposed for deep-level nutrient removal in municipal and nitrite sewage treatment without external carbon addition.In anaerobic stage enriched with partial denitrifyingphosphorus-and-glycogen accumulating organisms?DPAOs and GAOs,DGAOs?stored organic maters as intracellular carbons with the COD_intra efficiency reached to 88.2%.And in the following anoxic stage mainly conducted partial denitrification and phosphorus removal?PDPR?with the average PO₄^3--P removal efficiency and NO₂^--N removal efficiency was 98.9%and 99.2%?PDPR efficiency reached to 100%?.GAOs contributed to SNED process in the following aerobic stage by utilizing the residual intracellular polymers achieved NO₂^--N to N₂ lead to the better performance of nitrogen removal under high nitrite,with SNED efficiency up to 68.5%.High-throughput sequencing analysis revealed that genera of Candidatus_Competibacter and Defluviicoccus?reported as GAOs?were detected accounted for 10.15%.Nitrosomonas?deemed as AOB?occupied 3.48%and the percentage Nitrospira?NOB?only occupied by 1.54%.The dominant position of Dechloromonas,Candidatus_Microthrix and Candidatus_Accumulibacter?⁵.36%?,which representative PAOs and DPAOs explained the stable performance on phosphorus removal.