| Compared with landfill, incineration and compost, anaerobic digestion of organic fraction of municipal solid waste (OFMSW) could recover clean energy in the process of treating waste, resulted in remarkable energy benefit, economy benefit, eco-environment benefit and social benefit, so that it was considered as the most reasonable and efficient way of resource utilization. However, when this technology was used to treat OFMSW, due to the complexity and variability of OFMSW, there was a lot of difficulty and limitation to need to overcome.It was well-known that the OFMSW was a complex waste, rich in starch, cellulose, xylan, fat and protein, and if any constituent of them was pre-degraded, there would be good for anaerobic digestion (AD). So based on some reports related at home and abroad, in this dissertation, the influence of hydrolase pretreatment on anaerobic digestion was investigated to promote OFMSW pre-hydrolysis, so that the complexity of OFMSW was minimized, and the efficency of AD was increased. More impotant was to develop an approach to hydrolase pretreatment applied to AD.In carrying out this research, firstly, a hydrolase kinetic analysis method with the degree of hydrolysis (DH) as index function and a Modified Gomperts Model (MGM) for anaerobic digestion were set up. And then, by using hydrolase kinetic analysis method, amylase, cellulase, hemicelluase, lipase, protease and mixed hydrolytic enzyme were respectively used to estimate the influence of them on DH of OFMSW. Finally, by means of MGM, the influence of hydrolase pretreatment on anaerobic digestion of OFMSW was investigated. Some research results as follows:(1) The hydrolase kinetic analysis method with the degree of hydrolysis as index function could be used to analyze and estimate the influence of hydrolase dosage, substrate concentration, hydrolytic time, and hydrolytic temperature on DH of OFMSW.(2) Based on anaerobic digestion Modified Gomperts Model, the kinetic parameters of OFMSW digestion was obtained that could be used to analyze and estimate the influence of hydrolase pretreatment on anaerobic digestion of OFMSW. This attempt would provide a new method for AD research and data analysis.(3) The experiment results from influence of feedstock to inoculum ratio (FIR) and the digestive concentration (DC) on anaerobic digestion of OFMSW, showed that the FIR from 1.5:1 to 2.5:1 and the DC from 4% to 8% were very good for OFMSW digestion.(4) The experiment results from change of hydrolase activities in OFMSW digestion, indicated that various hydrolytic enzyme activities had a closely relationship with biogas rate. With the increase and decrease of enzyme activity, biogas rate would correspondingly increase and decrease, the peak values of enzyme activity and biogas rate almost occured at the time.(5) The experiment results from a-amylase pretreatment applied to OFMSW digestion, demonstrated that under neutral pH value, the optimum hydrolytic condition for a-amylase was:enzyme dosage 100U/gVS, substrate VS concentration 10%, hydrolytic time 60min and temperature 80℃, and at this conditions, the DH was 9.15%. When using a-amylase pretreatment to OFMSW for anaerobic digestion, the optimum pretreatment condition for a-amylase was:under neutral pH value, enzyme dosage 100U/gVS, substrate VS concentration 8%, pretreatment time 60min and temperature 70℃, and at this conditions, compared with without any pretreatment group, the maximal accumulative biogas yield and VS biogas potential were increased by 17.0%, and the maximal biogas rate and VS biogas rate were increased by 21.4%.(6) The experiment results from cellulose pretreatment applied to OFMSW digestion showed that the optimum hydrolytic condition for cellulase was:enzyme dosage 120U/gVS, substrate VS concentration 8%, hydrolytic time 24h, temperature 60℃and pH value 5.6, and at this conditions, the DH was 23.8%. When using cellulase pretreatment to OFMSW for anaerobic digestion, the optimum pretreatment condition for cellulase was:enzyme dosage 140U/gVS, substrate VS concentration 10%, pretreatment time 24h, temperature 50℃, and pH value 5.6, and at this conditions, compared with without any pretreatment group, the maximal accumulative biogas yield and VS biogas potential were increased by 29.0%, and the maximal biogas rate and VS biogas rate were increased by25.7%.(7) The experiment results from xylan pretreatment applied to OFMSW digestion, showed that the optimum hydrolytic condition for hemi-cellulase was:enzyme dosage 200 thousand U/gVS, substrate VS concentration 10%, hydrolytic time 12h, temperature 50℃and pH value 7.0, and at this conditions, the DH was 32.2%. When using hemi-cellulase pretreatment to OFMSW for anaerobic digestion, the optimum pretreatment condition for hemi-cellulase was: under neutral pH value, enzyme dosage 150 thousand U/gVS, substrate VS concentration 12%, pretreatment time 16h, temperature 50℃, and at this conditions, compared with without any pretreatment group, the maximal accumulative biogas yield and VS biogas potential were increased by 15.4%, and the maximal biogas rate and VS biogas rate were increased by19.2%.(8) The experiment results from lipase pretreatment applied to OFMSW digestion, showed that the optimum hydrolytic condition for lipase was:under neutral pH value, enzyme dosage 60U/gVS, substrate VS concentration 8%, hydrolytic time 12h and temperature 50℃, and at this conditions, the DH was 34.8%. When using lipase pretreatment to OFMSW for anaerobic digestion, the optimum pretreatment condition for lipase was:under neutral pH value, enzyme dosage 80U/gVS, substrate VS concentration 10%, pretreatment time 16h and temperature 50℃, and at this conditions, compared with without any pretreatment group, the maximal accumulative biogas yield and VS biogas potential were increased by 14.6%, and the maximal biogas rate and VS biogas rate were increased by13.9%.(9) The experiment results from protease pretreatment applied to OFMSW digestion, showed that the optimum hydrolytic condition for lipase was:under neutral pH value, enzyme dosage 12.5×103U/gVS, substrate VS concentration 8%, hydrolytic time 12h and temperature 50℃, and at this conditions, the DH was 14.3%. When using protease pretreatment to OFMSW for anaerobic digestion, the optimum pretreatment condition for lipase was:under neutral pH value, enzyme dosage 10x103 U/gVS, substrate VS concentration 10%, pretreatment time 12h and temperature 40℃, and at this conditions, compared with without any pretreatment group, the maximal accumulative biogas yield and VS biogas potential were increased by 16.8%, and the maximal biogas rate and VS biogas rate were increased by18.8%.(10) The experiment results from mixed hydrolase pretreatment applied to OFMSW digestion, showed that hemi-cellulase had a maximum contribution of 61.7%to the degree of hydrolysis, followed by a-amylase 17.2%, cellulase smallest only 1.33%. When using mixed hydrolase pretreatment to OFMSW for anaerobic digestion, with regard to the extent of influence of different hydrolases on accumulative biogas yield, VS biogas potential, biogas rate and VS biogas rate, a-amylase was the largest one of them, next hemi-cellulase or y-amylase, and lipase was the smallest one. Hence, ingredients in mixed hydrolases should take into consideration a-amylase, hemi-cellulase or y-amylase firstly.These results above were only a little bit achievements being made in this experimental research, but there still were many problems to further explore and perfect for hydrolase pretreatment technology if it would was applied to OFMSW anaerobic digestion.
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