Optimization Study On Mesophilic Anaerobic Co-digestion Of Food Wastes And Sludge

The "dual carbon" goal is put forward and the demand for energy transformation is becoming more and more urgent.Reforming the energy utilization system,resource utilization and clean disposal of organic solid waste have become urgent problems to be solved at present.Anaerobic digestion can not only clean and efficiently dispose of organic solid waste,but also convert biomass energy in organic solid waste into clean energy – biogas.Thus,energy utilization will be improved and the proportion of biomass energy in the energy consumption structure will be enlarged.However,the current anaerobic digestion has the disadvantages of low gas production rate and unstable system.The cooperative anaerobic digestion of various organic solid wastes can optimize the anaerobic digestion system to a certain extent,but the optimal ratio of various organic solid wastes has not yet been achieved.It is proved that at the same time,anaerobic digestion under high load is still easy to "destabilize",resulting in gas production inhibition and even system collapse.Therefore,this paper explores a high organic load synergistic anaerobic digestion technology for stable and efficient operation.The mechanism of gas production inhibition in highload continuous anaerobic digestion was investigated by sequencing batch experiments on the optimal ratio of different materials.The problem of easy instability of the high-load anaerobic digester system is optimized by the method of biogas slurry reflux,and the continuous coordinated mesophilic anaerobic digestion of various organic solid wastes such as catering waste,kitchen waste and sludge under high load is stabilized.Run efficiently.It provides a reference for the actual engineering of anaerobic digestion using high concentration materials.To improve the gas production rate and system stability of anaerobic digestion,a sequencing batch anaerobic digestion experiment was first carried out with different ratios of catering waste,kitchen waste,and sludge to determine the optimal material ratio.The results show that the synergistic anaerobic digestion of various organic solid wastes can increase the methane production and improve the stability of the anaerobic digestion system.With the enlargement of kitchen waste proportion,the cumulative methane production first increased and then decreased.Sludge: catering waste: kitchen waste = 4:1:5(calculated by TS)is the best ratio,and the cumulative methane production is the highest at this time,which is 9780 m L,and the ratio of sludge: catering waste: kitchen waste is 4:3:3,2:2:6 and 1:1:8 were improved by 10.90%,74.67%,and 373.74%,respectively.Secondly,based on the optimal ratio,the mechanism of gas production inhibition in the anaerobic digestion system under high organic load was also explored.)two-stage continuous anaerobic digestion experiment.The results show that the synergistic anaerobic digestion of multiple organic solid wastes with high load has higher gas production rate and methane production potential than low load,but the continuous high-concentration feed will cause slight gas production inhibition,which is manifested as methane concentration and the continued decline in daily methane production.The inhibitory mechanism is that high concentrations of VFA will cause toxicity to methanogens,especially acetic acid-trophic methanogens,resulting in a decrease in the abundance and activity of methanogens,which directly affects the gas production rate.The VFA concentrations of S2-2(30th day)and S2-3(39th day)in high load stage increased from16280mg/L to 18580mg/L,exceeding the inhibition threshold of 18000 mg/L,and the relative abundance of methanogens increased by 97.9% decreased by 89.8%,the relative abundance of acetate-trophic methanogen Methanimicrococcus decreased from 52.7% to 20.5%,and the methane concentration continued to decrease from 48.45% to 42.77%;The average gas production rate decreased by 13% compared with the average gas production rate of 2000,and there was a slight gas production inhibition,and the gas production efficiency and system stability decreased.Finally,aiming at the problem of high-load gas production inhibition,the optimization effect of biogas slurry reflux on a high-load anaerobic digestion system was studied.Based on the optimal ratio,the high-load continuous synergistic mesophilic anaerobic digestion experiment of biogas slurry reflux was carried out.The results show that the application of biogas slurry reflux can optimize the gas production of high-load systems.The gas production rate in the backflow stage of biogas slurry was 35.0L/d,which was 9.38% higher than the 32.0L/d in the high-load stage.The methane concentration(51.41%)in the backflow stage of biogas slurry was significantly higher than that under high load(44.86%).The application of biogas slurry reflux can improve the stability of the anaerobic fermentation system and relieve the inhibition of gas production under high load.On the 14 th to 19 th day of the biogas slurry reflux stage,the methane concentration dropped from 55.01% to 48.18%,the daily methane production dropped from35.0L/d to 32.5 L/d,the acetic acid concentration dropped from 1035mg/L to 705mg/L,and the ammonia nitrogen concentration dropped from 35.0L/d to 32.5L/d.From 2540mg/L to 3330mg/L,the gas production rate and system stability decreased.However,in the last 5 days,the methane recovered to 55.46%,the daily methane production increased to 40.0 L/d,the VFA concentration and ammonia nitrogen concentration returned to normal levels,and the gas production inhibition state was lifted.In this paper,the research shows that by proving the gas production inhibition mechanism and applying a variety of optimization methods,the continuous coordinated mesophilic anaerobic digestion of various organic solid wastes can be realized stably and efficiently for a long time under high load.Higher gas production rate and system stability can also be achieved.