利用前處理與共消化提升微藻厭氧消化之沼氣產量研究

Abstract

微藻於生質沼氣上的應用是一種具有發展潛力的微藻生質能利用方式，本研究透過微藻的油脂萃取以及高溫稀酸水解兩種前處理來改善微藻的生物降解性，提升厭氧消化沼氣產量。從水解與厭氧消化的結果顯示，萃油後的藻渣比起未經處理的藻體具有較佳的水解可受性，提高後續高溫稀酸水解的水解效果，並且有效的縮短微藻厭氧消化的試程，而萃出的藻油可做為生質柴油的材料。最佳的高溫稀酸水解條件為120 ℃搭配0.5 ℃硫酸處理10分鐘，可將微藻與藻渣的可溶性有機物分別從11 %提升至19 %和9 %提升至46 %。比較不同前處理之微藻於S/I ratio = 1的條件下進行產氣實驗的結果，微藻的油脂萃取與高溫稀酸處理各提升10 %與52 %的甲烷產量，而複合上述兩種前處理可以提升102 %甲烷產量。此外，本研究利用添加生質柴油的副產物粗甘油與微藻進行共消化調整進料中的碳氮比(C/N Ratio)以改善微藻碳氮比過低的缺點。結果以調整碳氮比至5.24，可達到最高的甲烷提升量42 %。綜合以上之前處理與共消化之效益，可有效的將微藻厭氧消化的甲烷產量提升1.5倍，達到理論轉換值350 mL CH4/g CODadd的65 %，有效的改善微藻於厭氧消化的應用性。本研究透過變性梯度凝膠電泳(DGGE)分析不同前處理之進料對厭氧汙泥菌相的影響，經定序和比對參與厭氧汙泥中已知的古生甲烷菌族群為Methanosaeta與Methanosarcinales，主要參與甲烷化作用。而細菌群中，有大量的水解菌Bacteroidetes及Firmicutes，以及酸化菌酸化菌Syntrophus與Smithella，硫還原菌為Deltaproteobacteria。

Anaerobic digestion of microalgae will be a potential component of microalgae biofuel production system. In this study, a batch anaerobic digestion was conducted to evaluate the effects of lipid extraction (LE) and thermal-chemical hydrolysis (TCH) for enhancing methane yield from microalgae. The results exhibited that lipid extraction could reduce the HRT (Hydraulic Retention Time) of anaerobic digestion and promote the potential of TCH. The optimum condition of TCH was carried out at 0.5 % (w/w) sulfuric acid and 120 ℃ temperatures. Thermal-chemical hydrolysis increased biodegradability of microalgae and LE residue from 11 % to 19 % and 9 % to 46 %, respectively. When digestion of microalgae was S/I ratio = 1, TCH and the LE process increased methane yield, up to 52 % and 10 % respectively. The combination effect increased yield by 102 % over that of the raw microalgae (93.5 ± 6.0 mL CH4 / g CODadd). In addition, we replaced a part of microalgae with crude glycerol to adjust the C/N Ratio of feeding. However, co-digestion with crude glycerol and microalgae increased 42 % of methane production at a C/N Ratio of 5.24. After pretreatments and co-digestion of microalgae, the conversion rate of COD to methane increased from 27 % to 77 %. Then, microbial community shifts were determined by denaturing gradient gel electrophoresis (DGGE). Microbial community structures showed continuous shifts within five bacterial phyla and three archaea. Bacteroidetes-like and Firmicutes-like organisms, appeared to be responsible for degradation of microalgae. Syntrophus-like and Smithella-like organisms involved acidogenesis or syntrophic acid degradation. And, Deltaproteobacteria- like organisms produced hydrogen sulfide (H2S) in biogas. Both hydrogenotrophic and aceticlastic methanogens appear to have been involved in the methanogenesis with the acidogenic products, such as Methanosaeta and Methanosarcinales.