| 摘要: | 能源是人類社會重要的議題之一，自從石油危機以來，各國紛紛尋找替代能源。農業廢物通常通過焚燒或掩埋的方式進行處理。這些方法造成了嚴重的生態問題，包括空氣汙染和水污染。厭氧發酵是一種將農業廢棄物轉化為生物甲烷的生物過程。它是一種成熟穩定的處理各種廢棄物有機物部分的技術。
目前在台灣大部分的厭氧發酵工廠多為單階段厭氧發酵槽，所有厭氧發酵的微生物群皆在同一個系統進行發酵，由於在厭氧發酵過程中有許多不同的微生物群參與，所以厭氧發酵是一個較複雜的系統。其中水解產酸菌與產甲烷菌彼此適合生長的環境並不相同，產酸菌產生的揮發性脂肪酸會使環境酸化，出現抑制產甲烷菌活性的情況，而產甲烷菌在產生甲烷時，會使環境pH值提高，同樣也會影響到產酸菌的活性，所以透過將水解產酸階段與產甲烷階段分離成兩個各自的系統，讓不同的微生物群可以在各自合適的環境進行發酵，並找尋到各階段最適化的條件。在處理固體濃度較高的厭氧發酵時，發酵過程中會出現質傳不良和過度酸化的問題。研究發現，生物碳可以成為生物質固定化的支持介質，改善微生物群的生長，以幫助底物降解，增加揮發性脂肪酸濃度，還可透過提供鹼度來增加厭氧發酵系統的緩衝能力。
在本研究中，發現在農業廢棄物進行兩階段厭氧發酵中添加生物碳可以提升揮發性脂肪酸濃度32.5%，並且縮短發酵天數。此外，在製作生物碳的過程中，將生物碳經磨碎處理、或改變不同的熱裂解溫度和熱裂解時間，來探討不同的生物碳對農業廢棄物進行兩階段厭氧發酵的影響。根據實驗結果，生物碳經磨碎處理後可以提升揮發性脂肪酸濃度32.6%，並且以500℃的熱裂解溫度和2小時的熱解時間製作的生物碳添加於產酸階段是較為合適的製作生物碳參數。最後討論了生物碳添加量對厭氧發酵產酸階段的影響，發現隨著生物碳添加量的增加會提升揮發性脂肪酸濃度，當生物碳添加量增加到30%時，揮發性脂肪酸的濃度提升了35%。另外，透過模擬的方式來探討添加生物碳對產甲烷階段的影響，發現添加生物碳能夠改善產甲烷菌的生長，在較短的發酵時間內提升甲烷濃度，並且將生物碳添加量增加後，觀察到沼氣產量的增加，進一步提升每日甲烷產量，最終累積甲烷產量為579.2 mL，相較於控制組提升了42%。
;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%. |
