Performance And Mechanism Of Integrated Efficient Nitrogen Removal Coupled Sludge Reduction Process In Municipal Wastewater

Anaerobic ammonia oxidation（Anammox）is regarded as the most promising nitrogen removal process,which is expected to solve the problems of high energy consumption,large sludge yield and difficult to achieve low-cost advanced nitrogen removal in traditional biological nitrogen removal process.Partial nitrification and anammox coupled denitrification is a common anammox combination process.But this process still has some problems such as large sludge yield.Sludge fermentation can achieve sludge reduction,and the fermentation products can be used as the carbon source of denitrification process.It is expected that anammox process and sludge fermentation can be coupled to achieve an integrated efficient sewage nitrogen removal synchronous sludge reduction.Based on the above analysis,the feasibility of the integrated simultaneous partial nitrification,anammox,denitrification and fermentation（SNADF）process was studied,and the effects of different dissolved oxygen（DO）on the system and its mechanism were investigated.Subsequently,the feasibility of treating exogenous sludge with SNADF system was explored.Finally,the effects of temperature fluctuation on nitrogen removal efficiency and microbial community in SNADF system were studied.The main research results and conclusions of this paper are as follows:（1）In order to explore the feasibility of SNADF process,sequencing batch reactor（SBR）SNADF system treating simulated sewage was started up through inoculating nitrification activated sludge and anammox granular under intermittent aeration condition.The experimental results showed that when the concentration of DO was 0.1-0.3 mg/L,the average total nitrogen removal efficiency was 63.9%and the observed sludge yield was 0.0268kg MLSS/kg COD.When the DO was increased to 0.4-0.6 mg/L,the average total nitrogen removal efficiency could be increased to 92.8%,and the observed sludge yield was 0.1474kg MLSS/kg COD.In situ test and metagenomic analysis results showed that there was fermentation reaction in the reactor,and the fermentation mainly stopped at the acid production stage,which provided suitable carbon source for partial denitrification,promoted the partial denitrifying-anammox reaction,and improved the nitrogen removal performance.High-throughput results showed that Nitrosomonas,Candidatus＿Competibacter,Candidatus＿Brocadia and other nitrogen removal-related bacteria could be enriched to a certain extent with the increase of DO concentration,which significantly improved the nitrogen removal effect.The relative abundance of the main fermentation bacteria Comamonadaceae,Anaerolineaceae and Saprospiraceae decreased with the increase of DO,which weakened the sludge reduction effect.Considering the simultaneous sludge reduction and nitrogen removal,the appropriate DO concentration for SNADF process was 0.4～0.6mg/L.（2）In order to explore the feasibility of treating exogenous sludge by SNADF process,three SNADF reactors were run in parallel.Municipal sludge and thermal hydrolysis sludge with the mass of 10%of the total sludge in the reactor were added to SBR2 and SBR3 on a20-day cycle,respectively.SBR1 was used as the blank group.The experimental results showed that the average total nitrogen removal efficiency of three reactors could reach 92.8%,93.4%and 94.6%,respectively.The Y_obs of three reactors are 0.0268,-0.0639,-0.16914kg MLSS/kg COD and 0.14736,0.11047,0.050519 kg MLSS/kg COD during two different phases,respectively.This indicated that the addition of exogenous municipal sludge and thermal hydrolysis sludge would not adversely affect the SNADF process,but promote the nitrogen removal and sludge reduction performance to a certain extent.Through the analysis of bacterial community and functional genes,it was found that the abundances of genes related to the conversion of pyruvate to acetic acid in three reactors were 66894,66240 and 65662hits,respectively,while the abundances of key functional genes related to methane generation were 348,384,and 280 hits,respectively,and the abundance difference between the two types of functional genes was large.This indicated that there was fermentation in all three reactors and the fermentation mainly stopped at the acid production stage to produce easily degraded organic matter for nitrogen metabolism.In addition,the variation trends of nitrogen removal bacteria and nitrogen metabolization-related genes in the three reactors were the same.The q PCR results showed that anaerobic ammonia oxidizing bacteria（An AOB）was enriched in all three reactors.The enrichment degree of An AOB in SBR2 and SBR3 was greater than that of SBR1,which indicated that adding exogenous municipal sludge and thermal hydrolysis sludge would not have adverse effects on the nitrogen removal bacteria and functional genes,and might also promote the enrichment of An AOB and efficient nitrogen removal.（3）In order to investigate the effect of temperature on the nitrogen removal performance and f bacterial community in SNADF process,the temperature was gradually reduced from32℃to 16℃with a 20-day cycle and a gradient of 4℃.The results showed that the average total nitrogen removal efficiency at 32℃,28℃,24℃,20℃and 16℃were 94.88%,94.72%,94.89%,92.01%and 83.12%,respectively.It is proved that SNADF process can maintain a relatively efficient nitrogen removal level at low temperature.High throughput analysis showed that the relative abundance of Candidatus＿Brocadia,the dominant bacteria of An AOB,increased from 0.09%to 0.18%when the temperature decreased from 32℃to16℃,which further indicated that low temperature had limited effect on the SNADF system.At the same time,the relative abundance of Nitrosomonas,the dominant bacteria of AOB,increased from 0.16%to 1.63%,which might provide a guarantee for nitrogen removal by anammox at low temperature.The relative abundance of Candidatus＿Competibacter,the dominant partial denitrification bacteria,decreased from 51.22%to 24.17%,however,it was still the dominant bacteria in SNADF system.The relative abundance of denitrifying bacteria Thauera and Amaricoccus increased from 0.01%and 0.25%to 2.90%and 5.66%,respectively,which provided guarantee for efficient nitrogen removal and growth of An AOB at low temperature.