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The effect of thermal pretreatment on the characteristics of degradation of waste activated slduge (WAS) in anaerobic digestion was investigated by laboratory-scale batch and continuous experiments at 35±1°C. The pretreatment temperatures of WAS ranged from 62 to 175°C and the pretreatment times were 15, 30, 60, 90 and 120 minutes. The organic particulates in WAS were solubilized to soluble carbohydrates, lipids and proteins or converted into the lower molecular weight compounds, such as volatile fatty acids, by the thermal pretreatment. Through the thermal pretreatment. the anaerobic degradability of WAS and the gas production from WAS were greatly increased, and the retention time necessary for anaerobic digestion was possible to be reduced by 5 days. The optimum pretreatment temperature and pretreatment time for the upgrading of anaerobic digestion of WAS were 170°C and 60 minutes, respectively. At this pretreatment condition, the COD removal and the gas production were markedly increased. At the digester with retention time from 5 to 10 days, the COD removal efficiency reached over 60% and gas production ranged from 223 to 235ml·gCOD−1 which were about 2 times those of the control. The numbers of methanogenic bacteria existing at retention times from 1.5 to 10.0 days ranged from 107 to 108 MPN·ml−1, and reached the maximum population level at the retention time of 5 days. The increase in solubilization and anaerobic degradation of major organic compounds in WAS by thermal pretreatment decreased in the following order: carbohydrates > proteins > lipids.

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The characteristics of the degradation of cellulose, soluble starch, and glucose in the acidogenic phase and the effects of the substrate loading rate and biological solids retention time on the methanogenic phase of anaerobic digestion were investigated. The results obtained from continuous experiments using laboratory-scale anaerobic chemostat reactors elucidated the true rate-limiting step of anaerobic digestion. The specific rate of substrate utilization decreased in the following order: glucose, soluble starch, acetic acid, and cellulose. The rate of the hydrolysis of cellulose was so low that this was shown to be the rate-limiting step in overall anaerobic digestion. Among methanogenic bacteria Methanosarcina would provide a higher substrate utilization rate than Methanothrix, and the maximum allowable substrate loading rate in the methanogenic phase was 11.2 g acetic acid/L day.

The purpose of this study is to investigate the biological hydrogen production potential of individual organic fraction of municipal solid wastes (OFMSW) by batch experiments. Seven varieties of typical organic solid wastes including rice, cabbage, carrot, egg, lean meat, fat and chicken skin were selected to estimate the hydrogen production potential. Among the OFMSW, carbohydrate produced the most hydrogen through biological hydrogen fermentation compared with proteins or lipids. Subsequently, the biological hydrogen production potentials of some individual carbohydrate were measured: cabbage, 26.3-61.7 mL/g-VS; carrot, 44.9-70.7 mL/g-VS; and rice, 19.3-96.0 mL/g-VS. The hydrogen percentages of the total biogas produced from cabbage, carrot and rice were 33.9-55.1%, 27.7-46.8% and 44.0-45.6%, respectively.

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