3단계 발효시스템을 이용한 음식폐기물로부터 바이오가스의 생산 및 이를 이용한 메탄산화세균의 배양

Abstract

The three stage methane fermentation system was constructed based on the fermentation system developed in our laboratory. This system consisted of hydrolysis, anaerobic acid and methane fermenter. The first stage was a semi-anaerobic hydrolysis/acidogenic process which converted food wastes into complex organics such as carbohydrates, fats and proteins. The operation temperature, hydraulic retention time (HRT) and total chemical oxygen demand (tCOD) were 45℃, 2 days and 78,542 mg/L, respectively. The second stage was an anaerobic acidogenic process which produced organic acids such as butyric acid, lactic acid and acetic acid, as well as ethanol. The operation temperature, HRT, and tCOD were 35℃, 2 days and 72,151 mg/L. In the third stage, strictly anaerobic methane fermentation, biogas was produced by methanogenic bacterium using organic acids including acetic acid. Biogas consisted of methane and carbon dioxide with 78 % methane proportion. The operation temperature, HRT, and tCOD for methanogenesis were 47℃, 12 days, and 8,412 mg/L. The effects of initial COD concentration of food waste and HRT of first stage and second stage on the organic acid productions were examined. When the initial COD concentration of food waste was about 120,000 mg/L and HRT of the first stage and second stage were 24 : 72, the total amount of organic acid was about 12,500 mg/L. When the initial COD concentration of food waste was about 70,000 mg/L and HRT of the first stage and second stage were 36 : 90, the total amount of organic acid was about 14,000 mg/L. When the initial COD concentration of food waste was about 50,000 mg/L and HRT of the first stage and second stage were 24 : 72, the total amount of organic acid was about 9,000 mg/L. The production of organic acid by the inoculation of Clostridium perfringens was examined during the second stage anaerobic acid fermentation. 4.5 g/L organic acid was produced without inoculation of C. perfringens in the batch experiment. On the other hand, when C. perfringens was inoculated and the pH is adjusted to 6.5 or not, total production of organic acids were 32.0 and 24.5 g/L, respectively. The production of organic acid was 7.0 g/L when the C. perfringens was not inoculated through the repetitive batch experiment. On the other hand, the production of organic acid were 25.0 and 11.5 g/L when C. perfringens was inoculated and the pH is adjusted to 6.5 or not, respectively. Finally, the methanotrophic bacterium isolated from the soil was identified as Methylosinus sp. JH and cultured using the biogas produced by the three stage methane fermentation system and pure methane. The proportion of methane and oxygen were 43 : 57 and 51 : 49 in biogas and pure methane used for cultivation. When Methylosinus sp. JH was cultured using the biogas and pure methane, the growth rate was not changed significantly. The result of this experiment suggests, it is appropriate to cultivate methanotrophic bacteria using the produced biogas.