瘤胃纖維分解菌和甲烷菌共培養於農業廢棄物產製甲烷之可行性評估

Abstract

氣候變遷、能源危機和化石燃料枯竭促使了再生能源的發展。甲烷是一個有潛力的燃料而且它在所有碳氫化合物中具有最高氫碳比，相對於石油為更乾淨且環保的燃料。甲烷是在沼澤、垃圾掩埋場和動物的腸胃道等厭氧環境中由甲烷菌所產生。瘤胃含有大量的微生物所以對草料很強的消化能力。它同樣在發酵的時後會產生可觀量的甲烷。本研究之目的是將來自瘤胃內的纖維分解菌和甲烷菌共培養於農業廢棄物上產生甲烷，以期作為一個產生再生能源的方法。 Ruminococcus albus 7 (ATCC 27210) 是瘤胃內主要的纖維分解菌之一，能夠產生乙酸、氫氣和二氧化碳。Methanosarcina barkeri (BCRC 19175) 是存在於很多厭氧環境的甲烷菌，能夠使用氫氣、二氧化碳和乙酸作為能量來源生長。在本實驗中，選擇稻稈、玉米稈和粗糠，作為基質單獨培養R. albus 7和其與M. barkeri共培養。在不同時間點測pH值、產氣體積和收集氣體、培養液和固形物樣品然後分析氣體組成、揮發性脂肪酸和纖維組成。結果中，R. albus 7能夠消化玉米稈和稻稈，但是對於粗糠的消化能力很低。R. albus 7和M. barkeri共培養於稻稈可以顯著提高纖維素的消化率和乙酸濃度 (P < 0.05)。在產氣部分，M. barkeri的存在能夠降低氫氣和二氧化碳的產量及產生甲烷。共培養於稻稈、玉米稈和粗糠中的甲烷產率分別為0.4 mmol/g-DM、0.3 mmol/g-DM和0.13 mmol/g-DM。但甲烷只有在發酵前期產生，而且 M. barkeri生長不理想。 根據本研究結果，以R. albus 7和M. barkeri共培養將部分農業廢棄物轉換成甲烷之效果不理想。

Climate change, energy crisis and fossil fuel depletion are driving the development of renewable energy. Methane is one of the potential fuel and it has the highest hydrogen to carbon ratio in all hydrocarbons, is a relatively clean fuel and more eco-friendly than oil. Methane is produced by methanogens in the anaerobic environment such as, swamps, land fills and the intestinal tracts of animals. Rumen has a great ability to digest grass by its abundant microorganisms. It also produce considerable methane during fermenting. The aim of the present study is to coculture the rumen cellulolytic bacteria and methanogen on the agricultural wastes and produce methane as a way to make renewable energy. Ruminococcus albus 7 (ATCC 27210) is one of the main fibrolytic bacteria in rumen and produces acetic acid, hydrogen and carbon dioxide. Methanosarcina barkeri (BCRC 19175) presences in many anaerobic environment and it can use hydrogen, carbon dioxide and acetic acid as energy sources for growing. In this experiment we chose rice straw, corn stover and rice hull as the biomass for culturing R. albus 7 alone and its coculturing with M. barkeri. We measured the pH, gas production and collected the gases, broth and solids and analyzed the gas compositions, volatile fatty acids and fiber compositions at different time points. In our results, R. albus 7 was able to digest corn stover and rice stover but had a low ability to digest rice hull. Coculturing with M. barkeri could promote the cellulose digestibility and the concentration of acetic acid on rice straw significantly (P < 0.05), but not on corn stover. According to the gas product, the presence of M. barkeri decreased yield of hydrogen and carbon dioxide and produced methane. The methane yield of coculturing on rice straw, corn stover and rice hull were 0.4 mmol/g-DM, 0.3 mmol/g-DM and 0.13 mmol/g-DM, respectively. But the methane was only produced at the early stage of fermenting and the growth of M. barkeri wasn’t ideal. The current research demonstrated that the result of coculturing R. albus 7 and M. barkeri to turn the agricultural wastes to methane is not ideal.