Study On The Efficiency And Mechanism Of Enhancing Co-digestion Of Sewage Sludge And Food Waste By AnMBR

The single substrate anaerobic digestion of sewage sludge and food waste respectively has technical bottlenecks.For example,the single substrate anaerobic digestion efficiency is low and the methane production rate is low due to insufficient carbon source,difficult cell cracking and high concentration of inhibitory substances in the residual sludge;while the kitchen waste is easily acidified due to carbohydrates,insufficient nitrogen source and high lipid content.The high load single substrate anaerobic digestion system is prone to acid accumulation and unstable operation.Multi-substrate anaerobic co-digestion has the advantages of regulating the ratio of carbon to nitrogen,increasing the diversity of microbial community and diluting the concentration of inhibitory substances,which can solve the deficiencies of single-substrate anaerobic digestion and improve the methane production.It is an effective method to treat food waste and sewage sludge at present.However,the synergistic mechanism of anaerobic co-digestion still needs further exploration.Therefore,a batch experiment was carried out in this paper to reveal the promoting mechanism of anaerobic co-digestion of sewage sludge and food waste to produce methane by using a dynamic model,and a high-solid anaerobic membrane bioreactor（AnMBR）process was constructed.Based on the process experiment,the influence of organic load（OLR）on the efficiency of AnMBR in treating sewage sludge and food waste was explored.The main conclusions are as follows:（1）Batch biochemical methanogenic potential（BMP）experiment was carried out to investigate the influence of feedstock ratio on methanogenic performance combined with methanogenic dynamic model.The results show that when Se S（sewage sludge）:When FW（food waste）ratio was 0.5:0.5（VS）,the cumulative methane production was 208.4m L/g VS,4.65 and 2.57 times of Se S and FW single-substrate anaerobic digestion,respectively.However,when FW ratio was higher than 40%,the methane production did not increase further.The maximum methanogenesis rate（R_m）under this substrate ratio condition was 39.5 m L/g VS/d,which was 7.1 times and 3.2 times higher than Se S and FW single substrate anaerobic digestion,respectively.In addition,the lag time of methanogenesis（λ）is 0.18 d,which is the lowest among all the ratios.The optimal matrix ratio was 0.5:0.5 by methanogenesis kinetics analysis,and the anaerobic digestion process of residual sludge was promoted by adding proper amount of kitchen waste.（2）The high solid AnMBR process was constructed,and the influence of OLR（1,2,4,8,11 g COD/L/d）on the process performance was investigated.The results show that with OLR from 1 to 11 g COD/L/d,the methane production rate increases from 300to 2563 m LCH₄/L/d,and the methane production rate also changes with the mean value of 263.1 to 301.5 m LCH₄/g COD_fed.It is found that the methane production rate is the highest when OLR is 4 g COD/L/d.Is 301.5 m LCH₄/g COD_fed;With the increase of OLR,the conversion of organic matter in the four stages of anaerobic digestion first increased and then decreased.The conversion of organic matter in the medium OLR（OLR=4g COD/L/d）was the highest,which were 78.8%,86.6%,86.9%and 86.1%,respectively.Its hydrolysis rate is the highest among the four stages,so it is considered that the high rate of methane production at this stage is due to the high rate of hydrolysis.Under high load condition（OLR=11 g COD/L/d）,dissolved organic matter starts to accumulate in the system,especially protein organic matter,which is the main factor affecting the methanogenesis rate.In the first four stages,the membrane pollution was small（TMPt≤0.3k Pa）,while in the fifth stage,the membrane pollution became significant,from slow pollution to fast pollution（TMPt≥1.8k Pa）.SEM-EDX（Scanning Electron Mictogi-X-ray Energy Dispersive Analysis）analysis shows that after physical and chemical cleaning the surface of the contaminated membrane becomes smooth,the membrane holes are clearly visible,and the pollutant elements such as C,P and Fe are significantly reduced.（3）Macrogenetic sequencing was used to analyze the evolution of microbial communities at different stages of AnMBR operation.Studies showed that at the phylum level,the relative abundance of Thermotogae and Bacteroidetes increased with the increase of OLR,while the relative abundance of Chloroflexi decreased.For archaea,the relative abundance of Methanosarcina decreased with the increase of OLR,while the relative abundance of hydrotrophic Methanoculleus increased gradually,indicating that the contribution of H₂/CO₂ methanogenic metabolic pathway increased gradually.The analysis of key genes related to methanogenesis showed that the gene expression was most active at 4 and 8 g COD/L/d,and was significantly inhibited at 11 g COD/L/d.（4）COD balance analysis and energy budget balance analysis are carried out based on the operation results of high solid AnMBR treatment of residual sludge and kitchen waste co-digestion process.Under all OLR conditions,COD converted to CH₄ is higher than 70%,indicating that AnMBR process is superior to traditional anaerobic digestion technology in methane recovery.Energy budget balance analysis shows that when OLR is 1,2,4,8 and 11 COD/L/d,AnMBR process achieves 19.4,20.6,22.5,20.9 and 20.3k J/g VS energy surplus.Heating（E_H）accounts for the largest proportion of energy consumption,followed by aeration cycle（E_B）.Accounting for 55.8%and 25.4%of total energy consumption,respectively.