Study On Anaerobic Digestion By Solid Method With Waste Activated Sludge To Produce Methane

At present, disposal capacity of China's urban sewage treatment is increasing rapidly. In urban sewage treatment, sewage is made up of 0.02% of slude. The organic matter content of waste activated sludge(WAS)is 10 times than the urban sewage, organic compounds of bio-degradation is 59%-88% of the total organic solid, which is good matrix of anaerobic digestion.Effects of various pretreatments on methane production were studied with waste activated sludge. The results showed that the speed of gas production was the highest at the first four hours after alkali protease pretreatment, which was 3.29 ml/gVS per hour. When waste activated sludge was thermally treated in an autoclave, the accumulative gas production was 45.80 ml/gVS, which was the highest as compared to the gas production in other pretreatments. It was also 230% higher than that of the control group. After microwave irradiation, the methane content was 62.26%, which was the highest compared with the other pretreatments and increased 130% than that of the control group.Effects of different addition of kitchen wastes(KW)on anaerobic digestion with waste activated sludge were investigated under medium temperature. It indicated that the ratio of carbon and nitrogen (C/N), extracellular polymeric substance(sEPS)and other physiological and biochemical indicators could be improved significantly in anaerobic digestive system with the addition of KW increasing. Especially, when the mass ratio of WAS and KW was 2.0:1, the accumulative gas production was 156.56 ml/gVS and the methane content was 67.52%, which were 4.7 and 1.5 times higher than that of the control group of waste activated sludge anaerobic digested alone, respectively. The mixed digestion of WAS and KW not only improved hydrolytic environment and anaerobic digestibility, but also obtained more biogas production.When the addition of Ni was 0.0025ug/gWAS, it played a larger role of gas production in anaerobic digestion with WAS. The addition of Ni enabled the advantages of menthanogens to change, it dominated by mathanosata to methanosarcina dominant in anaerobic digestion.After microwave(MW)pretreatment, adding KW and the trace element Ni, gas production and methane contents were gradually improved. Gas production of MW, MW + KW and KW + Ni + MW were 62.90 ml/gVS, 159.64ml/gVS, 168.22ml/gVS, which were 1.3 times, 4.8 times and 5.2 times higher than 27.26 ml/gVS of the control group. Methane contents were 56.83%, 69.52% and 72.35%, increased 0.8 times, 1.2 times and 1.3 times compared to 30.95% of the control group, reseparately.