以乾式厭氧消化進行廚餘產沼氣之研究

Abstract

本研究以實驗室規模乾式厭氧反應器生產沼氣，評估廚餘在不同醱酵條件下的產氣效果及有機廢棄物處理效率，同時利用變性梯度凝膠電泳觀察菌相變化。本研究亦針對乾式厭氧消化後殘餘沼渣進行各項基本測試及肥料分析，並以種子發芽率試驗及結球白菜植栽試驗評估沼渣腐熟度及其肥效。 研究結果顯示，厭氧消化廚餘在中溫（35°C）及高溫（55°C）皆可達60%以上理論甲烷轉換效率，中溫與高溫條件最終產沼氣量並無明顯差異，但高溫醱酵生產沼氣速率為中溫醱酵的兩倍以上；進一步調整反應器循環水淋洗頻率來優化沼氣產量，沼氣產量隨循環水淋洗頻率增加而上升，在高溫（55°C）、高淋洗頻率（3L/1Hr）條件下進行醱酵，十天內生化甲烷潛力值即可達到520 L/Kg-VSadd；然而連續操作乾式厭氧反應器時，循環水中氨氮累積將導致沼氣產量減少，本研究發現以稀釋方式控制循環水氨氮濃度低於1,500 mg/L，可穩定維持系統沼氣生產量達80%以上。菌相分析結果顯示植菌源雖相同，但經醱酵溫度提高，乾式反應器內菌相有明顯改變，然而改變淋洗頻率並不影響菌相分布。此外，高溫厭氧醱酵後沼渣經種子發芽率試驗結果證實已腐熟，經沼渣成份分析發現有機質含量低於市售有機肥，但透過植栽測試沼渣肥效仍有助於作物生長。

In this study, we established a lab-scale dry anaerobic fermentation reactor for biogas production form kitchen waste, and evaluated the biogas production potential in different reactor condition, the microbial community was investigated by denaturing gradient gel electrophoresis (DGGE). In addition, we analyzed the characteristics of fermentation residues, the seed germination and planting was tested for being ferterlizer. The results revealed mesophilic condition as well as thermophilic condition produced same biogas amount until 23th day of fermentation, but the biogas production rate under thermophilic condition (55°C) was twice times faster than mesophilic condition (35°C). As increasing rinsing rate of circulating water, the better biogas production was harvested, biogas production efficiency with thermophilic and high rinsing rate reached 520L/kg-VSadd/10days, which was an extremely high biomethane potential for dry anaerobic fermentation reactor. Furthermore, an inhibition of biogas production in continuously operation has been confirmed by the cumulative ammonia concentration in circulating water, we had improved the system with at least 80% efficiency of biogas production in continuously operation by diluting the ammonia concentration less than 1500 mg/L in circulating water. In the microbial community analysis, DGGE revealed the distribution patterns of 16s rRNA were various between mesophilic and thermophilic condition but remained constant under different rinsing rate. Seed germination test had confirmed the maturity of the fermentation residues, but the organic content in residues is less than the commercially organic fertilizer, yet the fermentation residues was positive in conducive to crop growth.