Comprehensive Utilization Of Urban Organic Waste High Temperature Anaerobic Digestion Process And Residue Studies

In recent years, anaerobic digestion of municipal solid waste (MSW) was developed and established in developed countries, especially in Europe;among that, method of Dranco, Kompogas and Valorga process have been industrialized. On basis of domestic and abroad references, there have been some integrated and systematic researches, such as breaking and sorting technologies of MSW, anaerobic process of MSW, and comprehensive utilization of anaerobic residue, completed in this dissertation. The objective of the study was that it can find a feasible way to treat and recycle MSW scientifically.The researches have been studied about the microbiology, thermodynamics of microbes and biochemical process of anaerobic technology for treating MSW. Firstly, there was a illustration of the relation between △G' and hydrogen partial pressure, and also some discussion about the effect of hydrogen partial pressure on interspecies hydrogen transfer. Then there were some emphatic study about the anaerobic thermophile species and its biochemical mechanism of thermo-stabilization. Finally, there were some discussion about the routes of anaerobic biochemical degradation of OFMSW such as hydrolysis, acidification and methanogenesis in the paper.The breaking and sorting experiments were carried out for MSW from the settlement in Kunming University of Science and Technology. The efficiency of breaking and sorting equipment was 64.04% for separating organic fractions of municipal solid waste (OFMSW). The analyses were taken about the physical compositions and organic chemical components of MSW respectively by hand-sorted and machine-sorted method. Based on the data from the test, it was 72% and 64% respectively for the biodegradable fractions (BF) of selected organic waste components in hand-sorted and machine-sorted MSW, with 0.795 L/gTS and 0.733 L/gTS respectively as the maximum theoretical biogas. The biochemical methane potential (BMP) ofhand-sorted and machine-sorted MSW were 199.1mLCH4/gVS and 162.4mLCH4/gVS in the mesophilic conditions, 232.4 mLCH4/gVS and 180.6 mLCIWgVS in the thermophilic conditions.The results of batch experiments under the semi-dry anaerobic digestion of OFMSW (TS = 15.5%, without diluting or drying) showed that it was 55°C for the optimum temperature. The parameters were gotten such as 287.7mL/gVSadd for biogas production rate, 66.9% for average methane concentration in biogas,about 1.5d for start-up time, 10'2 for the fecal coliform and 100% for mortality rate of bellyworm ovum under thermophilic (55 °C ) conditions, which exceeded the mesophilic and psychrophilic conditions. The inactivation of pathogenic bacteria in the residue under thermophilic condition was in accordance with the criterion in GB8172-87.Laboratory-scale experiment was carried out to assess the influence of temperature fluctuation on thermophilic anaerobic digestion of OFMSW. Heating failure was simulated through decreasing suddenly temperature from 55 °C to 20 "C (approx. room temperature in Kunming city). The duration of low temperatures were 1, 5, 12, 24h and 15d respectively in the experiments. The following results could be found out that biogas production was almost stopped and VFAs such as acetate, propionate accumulated rapidly, accompanied by pH decrease. Temperature decline not only affected the methanogensis but also the hydrolysis and acidification. But the system could be restored during some time after the temperature came back to 55°C , which showed that the thermophilic microorganisms was highly resilient to temperature fluctuation.On the contrary, when the temperature of thermophilic anaerobic process increased from 55°C to 65°C and 75°C respectively, with 15 days as high temperature interval, the results showed that thermophilic process could acclimatize itself to the condition of high temperature of 65°C and hardly affect the stability of process. As the temperature exceeded the maximi limit of growth, the ecosystem of microorganisms were ruined due to A hyperthermia temperature of 75°C in the reactor, which resulted in failureof anaerobic process.The batch anaerobic digestion kinetics model which dominated by hydrolysis have been deduced based on the cumulative biogas yield in different reaction temperatures. The activation energy of anaerobic hydrolysis of OFMSW was 36.84kJ/mol. The biodegrading rate of OFMSW in the anaerobic reactor was quicker than it in landfill.There was a comparison about the active performance of anaerobic thermophilic digestion between four source of inoculum such as sewer sludge, septic tank bottom sludge, aerobic activated sludge and mesophilic anaerobic sludge. The experiments through three incubated times were investigated the activity of inoculum. The results showed that activity of mesophilic anaerobic sludge and septic tank bottom sludge exceeded the others, which was emphasized by the test of specific methanogenic activity (SMA) and ammonia IC50 values. It was interested that septic tank bottom sludge could be used as the inoculum of thermophilic anaerobic digestion in case of the lack of mesophilic or thermophilic sludge.The batch experiment was investigated to find out the proportions of TS and inoculum ratio in the reactors. The results showed a positive correlation between the TS and inoculum ratio. The higher TS in feed of the municipal solid waste was, the more inoculum feed shoud be needed to stabilize the anaerobic process and enhance the biodegradability of OFMSW. And the appropriate TS fed in the reactor were 15%~25%.The proportions of OFMSW and manure on performance of thermophilic anaerobic co-digestion were investigated in the experiments. The appropriate proptortions of MSW and manure was 60/40 (based on weight content). The N and P content variation in the reactors during the thermophilic anaerobic co-digestion process were investigated too. There were little lost at the end of fermentation.The utilization of anaerobic digestion residue from OFMSW was discussed. The percentage of organic substance in the residue was 52.24% . The amount of heavy metal in the residue was accorded with the criterion in GB8172-87. Laboratory-scale experiment was investigated to produce theorganic-inorganic compound fertilizer No.l* and 2* by compounding the anaerobic digestion residue with the inorganic fertilizer. The main nutrient index of two fertilizers can meet relevant standards in GB18877-2002. Five kinds of flowers, which were Gerbera jamesonii, Primula, Portulaca grandiflora, Dianthus caryophyllus .L. and Antirrhiuum murjust were chosen to assess the fertility of organic-inorganic compound fertilizer No.l* and 2 . Compared with the inorganic fertilizer, organic-inorganic fertilizer had better growth influence on flowers.