Enhanced Production Of Short-Chain Fatty Acids From Excess Sludge By Combined Free Nitrous Acid And Alkyl Polyglucoside Treatment

With the rapid development of China’s sewage treatment industry,the number of urban sewage treatment plants in China is increasing,resulting in more and more surplus sludge production.The sludge contains a lot of toxic and harmful substances,and improper disposal can cause environmental problems.Therefore,the remaining sludge treatment needs to be solved.The anaerobic fermentation of sludge produces Short Chain Fatty Acids（SCFAs）,which can be used as an inexpensive carbon source for biological nitrogen and phosphorus removal in sewage,and at the same time realize the resource reduction and reduction of sludge.The use of sludge anaerobic fermentation to produce acid is an important way to realize sludge resource utilization,and has broad application prospects.In view of the low acid yield of sludge anaerobic fermentation,this study used Free nitrous acid（FNA）pretreatment combined with Alkyl polyglycosides（APG）to promote the anaerobic fermentation of excess sludge to produce acid.The effect of APG dosage on the acid production process of anaerobic fermentation of excess sludge under single APG treatment conditions was studied.Effect of FNA concentration on the process of acid production of anaerobic fermentation of excess sludge by FNA pretreatment and APG treatment of excess sludge.Mechanism of FNA Pretreatment and APG treatment of excess sludge for acid production.The high-throughput sequencing technology was used to assist the analysis of microbial community structure.The following conclusions were obtained:（1）Under the condition of temperature 30℃ and initial fermentation pH=7.00,the dosage of APG increased from 0.025 to 0.150 gAPG/gVSS,the yield of SCFAs increased with the increase of APG dosage,and the yield of SCFAs production reached the maximum at6 days of sludge fermentation.At the same time,when the APG dosage was from0gAPG/gVSS to 0.075gAPG/gVSS,the ratio of SCFAs production,dissolved NH₄⁺-N concentration,organic matter reduction rate and acetic acid and propionic acid to total acid amount increased significantly with the increase of APG dosage.Increasing,the ratio of valeric acid and isovaleric acid decreased with the increase of APG dosage.However,when APG dosage was from 0.075gAPG/gVSS to 0.150gAPG/gVSS,the yield of SCFAs,the dissolved NH₄⁺-N concentration,the reduction rate of organic matter and the ratio of acetic acid and propionic acid to total acid content were not significantly increased with the increase of APG dosage.（2）Under the condition of temperature 30℃,after 2 days of FNA pretreatment,APG was added,initial fermentation pH=7.00,APG dosage was 0.050 gAPG/gVSS and 0.075 g APG/gVSS,the effect of FNA concentration on the acid production process of anaerobic fermentation of excess sludge was studied.The results showed that the dosage of APG was0.075gAPG/gVSS,the concentration of FNA was 0.653mg/L,and the yield of SCFAs was the highest at 5 days of fermentation,which was 324.94±1.98mg COD/gVSS,which was 5.53,1.92 and 1.55 times of that of blank group,FNA group and APG group,and the reduction rate of sludge organic matter was 35.19±0.80%.（3）FNA pretreatment combined with APG treatment can promote the dissolution process,hydrolysis process and acidification process of anaerobic fermentation of residual sludge;significantly inhibit the activity of methanogens and the activity of protease andα-glucosidase in anaerobic fermentation of excess sludge can be improved.Qualitative and quantitative analysis of DOM in fermentation broth of FNA pretreatment and APG treatment of excess sludge by three-dimensional fluorescence spectroscopy.It was found that FNA+APG treatment promoted the cracking of sludge and enhanced the release of degradable organic matter in sludge.（4）Using high-throughputsequencingtechnologytoanalyzethestructural characteristics of microbial flora under different treatment conditions from the perspective of microbial community,the results show that:FNA pretreatment combined with APG treatment can reduces the diversity of microbial flora,and the functional microorganisms of the fermentation system are enriched.At the phylum level,compared with the blank group,the samples processed were enriched in Proteobacteria,Firmicutes and Actinobacteria,among which the Firmicutes increased the most.At the class level,the percentages of Alphaproteobacria,Gammaproteobacria,Clostridia and Bacilli increased.The percentage of Anaerolineae and Betaproteobacteria associated with SCFA consumption was reduced,and the proportion was the lowest in the FNA+APG group.At the genus level,the proportion of Enterococcus,Clostridium Anaerofilum,Methylocystis,Aquihabitans,Shigella and other bacteria in the FNA+APG group was significantly increased,and the proportions of Phaeodactylibacter and Terrimonas were significantly reduced.In summary,from the point of view of sludge acid production,fermentation time,organic matter reduction rate and economic efficiency,FNA pretreatment for 2 days,APG was added,APG dosage was 0.075gAPG/gVSS,initial fermentation pH=7.00,FNA concentration was 0.653mg/L,and fermentation was 5d as the optimal process conditions for FNA and APG to treat excess sludge for acid production.The method can simultaneously realize the resource utilization and reduction of sludge,and provides technical guidance for the treatment of sewage sludge.