利用臭氧與高壓循環系統破裂藻體以提高厭氧消化之甲烷產能

Abstract

本論文研究前處理破裂藻體結構對於微藻進行厭氧消化產甲烷之影響。前處理包含臭氧與高壓循環系統，高壓輔助系統是一種利用增壓與減壓反覆循環製造快速壓差以破裂藻類細胞結構的前處理方式。厭氧消化將微藻轉化成沼氣，其效率受藻類水解時間影響，臭氧與高壓循環系統釋放藻體內部基質，縮短厭氧消化水解時間。臭氧破裂藻類效果可藉由水中綠色素消失判定所需的臭氧曝氣時間，做為最適合的厭氧消化產氣進料，臭氧破裂淡水藻的處理效率(COD Solubilisation)可達19.63%，海水藻可達52.16%。然而，處理效率與水體中化學需氧量的分布無相對應關係，SCOD隨著曝臭氧時間上升再下降，TCOD隨著臭氧反應時間下降。 藻類厭氧消化產氣系統不適用於高鹽度的海水藻，鹽度抑制厭氧消化菌活性，造成產氣量下降，使用海水藻作為厭氧產氣基質來源時，需選擇耐鹽度性高的厭氧污泥，或將液體中的鹽度去除。假設空白系統中的產氣量皆為污泥自行分解的產氣量時，進行厭氧消化試驗，在148.40 g厭氧污泥乾重對應1 g的藻類固體乾重的厭氧消化實驗參數下，淡水藻做微生物發酵基質，添加10.52 mg 藻類COD，將甲烷濃度由16.38%提升至22.15%，而添加9.2 mg經臭氧破裂後藻類的COD，將甲烷濃度提升至20.67%，結果顯示臭氧破裂藻類進行厭氧消化，對於最終甲烷濃度提高無明顯的效果。 濃縮藻類可以提高厭氧消化產甲烷濃度，將藻液濃縮使COD提高為原本的2.47倍，產出的甲烷濃度為濃縮前的2.18倍，表示增加COD進料提供更多反應基質。

In order to enhance the efficiency of anaerobic digestion, the effects of ozonation and high-pressure extraction were studied on microalgae. High-pressure extraction was performed with mildly elevated pressure in consecutive cycles of compression and decompression as pretreatment. Anaerobic digestion converts the organics present in microalgae into biogas, but the efficiency and the digestion rate are limited by the hydrolysis. Biodegradability of microalgae could be low depending on the nature of the cell wall, thus pretreatment was applied to rupture the cell wall in order to improve biodegradability efficiencies. Chemical oxygen demand (COD) and matter solubilisation caused by pretreatments was focused on organic solids. In terms of ozone pretreatment, COD solubilisation was 19.63% and 52.16% on flesh water algae and sea water algae, respectively. No significant relationship between COD solubilisation and SCOD/TCOD was observed, however, it was found that SCOD increased with ozone feeding time and then decreased, while TCOD decreased with ozone feeding time. In this study, anaerobic bacteria are unable to adapt the saline environment, and have low capability to deal with sea microalgae that has high saline contents. The experimental results showed that the methane production decreased when salt content is higher. However, if anaerobic digestion is used to treat the saline wastewater, the capability of anaerobic bacteria must be enhanced or remove the saline content. In flesh water algae system, the final methane concentrations increased from 16.38 to 22.15% when adding 10.52 mg COD of algae; the final methane concentrations increased to 20.67% when adding 9.2 mg COD of algae with ozone pretreatment. The result suggested that ozone extraction did not have significant impact on methane production. The final methane concentrations increased from 4.23 to 9.21% when the COD concentration of microalgae increased from 511 to 1262 mg/L. It could be concluded that inoculum/substrate ratio had a considerable effect on methane production.