| dc.description.abstract | Energy is an important issue in human society. Since the oil crisis, every countries have to look for alternative sources of energy. Agricultural waste is usually treated by incineration or landfill. These methods have caused severe ecological problems involving air and water pollution. Anaerobic fermentation is a biological process that converts agricultural waste into biomethane. It is a mature and stable technology for the treatment of organic fraction of various waste materials.
Nowaday, most of the anaerobic fermentation plants in Taiwan are single-stage anaerobic fermentation. All anaerobic fermentation microbial groups are fermented in the same system. There are many different microbial groups in the anaerobic fermentation process, so it is a more complex system. Acid-producing bacteria and methanogens are suitable for growth in different environments. The volatile fatty acids produced by acid-producing bacteria will acidify the environment and inhibit the activity of methanogens. When methanogens produce methane, they will increasing the pH value of the environment and also affect the activity of acid-producing bacteria. Therefore, by separating the acid-producing stage and the methane-producing stage into two separate systems, they can be fermented in a suitable environment to find each optimal conditions for the stage. When substrate with high solid concentration in anaerobic fermentation, the problems of poor mass transfer and excessive acidification will occur in the fermentation process. Research have found that biochar can become a support medium for immobilization of biomass, so it can improve the growth of microbes and increase the buffering capacity of the anaerobic fermentation system by providing alkalinity.
In this study, it is found that adding biochar to the two-stage anaerobic fermentation of agricultural waste can increase the concentration of volatile fatty acids by 32.5% and shorten the fermentation days. In addition, in the process of making biochar, the biochar is grinded, or different pyrolysis temperature and pyrolysis time are changed, to explore the impact of different biochar on the two-stage anaerobic fermentation of agricultural waste. According to the experimental results, after the biochar being grinded, it can increase the concentration of volatile fatty acids by 32.6%. Also, the addition of biochar to the acid-producing stage at a pyrolysis temperature of 500℃ and a pyrolysis time of 2 hour is a more optimal biochar parameter. Finally, it is found that when the amount of biochar increased to 30%, the concentration of volatile fatty acids will also increase 35%. In addition, the effect of adding biochar on the methanogenesis stage was explored through simulation, and it is found that adding biochar can improve the growth of methanogens and increase the methane concentration in a shorter fermentation time. After increasing the amount of biochar, the methane production gets higher. The final cumulative methane production is 579.2 mL, compared to the control group by increasing 42%. | en_US |