A Study On The Methanogenic Process And Mechanism Of Co-anaerobic Digestion Of Sludge And N,N-Dimethylformamide

With the rapid development of the urbanization process in China and the improvement of environmental standards,the output of residual sludge,a by-product of wastewater treatment plants(WWTPs),continues to increase.So,its reasonable treatment and disposal have become a prominent environmental problem that needs to be solved urgently.Anaerobic digestion(AD)is a typical method to realize sludge innocuous,resource utilization,and stabilization treatment,it can simultaneously treat the refractory organic pollutants contained in the sludge.N.Ndimethylformamide(DMF)is widely used as a "universal solvent" in the chemical industry.It is a typical pollutant in chemical industry wastewater,and its biodegradability is very low.Because of this,based on the anaerobic digestion technology route,this paper researched the co-anaerobic digestion of residual sludge and DMF wastewater,and an efficient and stable coanaerobic digestion system of residual sludge and DMF wastewater was established.The study first adopted the co-cultivation method to domesticate the substrate with DMF degradation ability under mesophilic condition,and the influence of DMF and residual sludge concentration on the domestication process has been investigated.Then,the sequencing batch experiment method(Batch)was used to study the mesophilic co-anaerobic digestion behavior between the residual sludge and DMF under different inoculation substrates,different inoculation ratios,residual sludge concentration,and initial pH conditions.By using precision barometer and gas chromatography to detect the biogas output of the reactor and the methane and carbon dioxide concentration in the biogas;by using high-performance liquid chromatography to detect the DMF contents in the fermentation broth;by using gas chromatography,electrode method,Phenol-Sulfuric acid method,Folin-phenol method,Nessler’s reagent spectrophotometric method,etc.,respectively detected the changes of shortchain fatty acids(SCFAs),pH,EC,carbohydrates,protein,ammonia nitrogen content and other indicators in the fermentation broth.It has been adopted the high-throughput sequencing methods analyzed the microbial community structure in the domesticated substrate and the sequencing batch anaerobic digestion experiment respectively;based on these,the mechanism of co-anaerobic digestion of sludge and DMF has been discussed.The results showed that:(1)During the co-cultivation of residual sludge and DMF,DMF containing 1.25 ‰,2.5‰,5 ‰(V/V)in the reactor did not significantly inhibit the anaerobic digestion of sludge.The conversion rates of methane(R2=0.997)and carbon dioxide(R2=0.980)corresponding to DMF degradation were 443.43 mL/g and 57.96 mL/g,respectively.The biogas production behavior in the co-cultivation process showed obvious three-stage characteristics.The time of three stages of biogas production in the parallel group was also different,and the increase of residual sludge concentration in the reactor was helpful to narrow this difference.Proteobacteria,actinobacteria and Chloroflexi are the dominant bacteria phyla,and Euryarchaeota is the dominant archaea phyla in the microbial community of domesticated substrate.(2)In the sequencing batch anaerobic experiment,the highest ratio of 1:4 domesticated substrate inoculation was helpful for the start of co-anaerobic digestion.The inoculation of the domesticated substrate eliminated the time difference in the three stages of biogas production in parallel groups,and improves the stability of the system.The increase in the concentration of the residual sludge in the reactor shortened the time required for the degradation of DMF and the biogas production also increased.Under the condition of adding 25.13(g TS)/L of residual sludge,the DMF of 2362 mg/L in the reactors was completely degraded with 4 days,which was 7 days shorter than that of the group without residual sludge added.The initial pH has significant effects on the co-anaerobic system.When the initial pH<6 or>8,the degradation of DMF was significantly inhibited.The analysis of the microbial community showed that the succession of the archaeal community occurred in Co-anaerobic digestion.the Halobacterota was the dominant archaeal phyla in the process of DMF degradation,and the Euryarchaeota was the dominant archaeal phyla after DMF degradation.Methanosarcina unclassified_f__Methanosarcinaceae and Methanomethylovorans plays a major role in the degradation of DMF in co-anaerobic digestion.They convert DMF hydrolysates(formic acid and dimethylamine)into CH4,CO2 and ammonia nitrogen.(3)Based on the co-anaerobic digestion result in batch experiment,a two-stage coanaerobic digestion system for the sludge and DMF treatment was constructed.The system operation results showed that the complete degradation of 4000 mg/L DMF was achieved in the 48-h operation cycle.The cumulative biogas production of each operation cycle was the same,and the system can maintain long-term stable operation under high DMF load.In short,the co-anaerobic digestion of sludge and DMF effectively improves the DMF anaerobic degradation and the overall biogas yield.The two-stage co-anaerobic treatment system further enhances the advantages of co-anaerobic digestion in the sludge and DMF treatment process.This study also provides an effective technical method and theoretical support for the collaborative treatment of sludge and various refractory organics.