農畜固態廢棄物厭氧共消化之探討

陳榮星(Jung-hsing Chen)

指導教授 ： 王鯤生 ； 林居慶

國立中央大學/工學院/環境工程研究所/博士(2015年)

摘要

有機固體廢棄物產自於農業活動，包括家畜排泄物(例如牛和豬的糞便)和木質纖維材料(例如稻稈)，已不再被被認為是廢棄物，因為它們是穩定的生質物來源，藉由厭氧處理而轉變為有用的燃料(例如甲烷、氫氣和乙醇)，可作為不同的再生能源應用。然而傳統的厭氧處理程序係採「濕式」消化，而不是應用「乾式」(或稱為「固態」)消化。因此有必要開發一種新技術，它不僅能有效處理農業廢棄棄，而且是更為穩定有效操作的方式。本研究建立一套固態厭氧消化滲漉系統，並應用共消化方法來促進生質氣體產出。具體而言，使用最佳化設計方法進行牛糞發酵產氫，而其關鍵因子會影響豬糞和紙漿或稻稈在滲漉系統所進行共消化的評價和鑑定。
就產氫而言，應用田口方法的水準設定及L18矩陣直交表，來定義影響高溫厭氧發酵的主要影響因子(溫度及pH值)，接著按所定義的最適溫度及pH條件，以響應表面法的中心組成設計，預測氫氣含量、氫氣產生量及比氫氣產出。結果顯示控制系統在溫度和pH值分別在60℃和5.20±0.21時，可得最適的產氫濃度54.64±11.45(%)、氫氣產生率405.54±93.61(mL-H2/L/d)和比氫氣產出10.25±1.96 (mL-H2/g-VS)。
就產甲烷而言，決定最適固體停留時間為6天後，以半連續試驗進行豬糞和紙漿共消化，期能提升甲烷產出之質與量，結果顯示紙漿和豬糞在濕重比50 : 50時，得到高甲烷濃度57.53 %，進而比較紙漿和豬糞共消化與單獨豬糞消化，分別提升了甲烷濃度5.8%、甲烷產生量35.61 %和比甲烷產出49.22 %。除了紙漿，稻稈被用於產甲烷滲漉系統的進料基質，結果顯示當兩種預酸化和未酸化稻桿均質化為相同粒子大小時，得到相同的甲烷產出水準，建議稻稈的預酸化處理不是「生質物到甲烷」轉換系統的條件，尤其在滲透性(水力傳導度)測試裏顯示進料物的孔洞性也許才是整個調控甲烷產出的關鍵因子。另外，在系統的最高甲烷產生率和甲烷濃度的多源基因體分析顯示Methanosarcinales 和Methanobacterials是古生菌的主要菌群，符合在系統中檢測到乙酸的核算水準，比較意外的是，高溫菌Thermoplasmatales 在古生菌的所佔比例偏低。

關鍵字

牛糞 ； 田口方法 ； 響應表面法 ； 豬糞 ； 紙漿 ； 稻稈 ； 滲漉系統 ； 多源基因體

並列摘要

Organic solid wastes resulted from agricultural activities including livestock droppings (such as cow and pig manures) and lignocellulosic materials (such as rice straws) are no longer considered as “wastes”, because they are stable biomass sources that can be anaerobically treated and converted to useful fuels (such as methane, hydrogen, and ethanol) as renewable energy for a variety of applications. However, conventional anaerobic treatment processes have been conducted with “wet-state” digestion, instead of “dry-state” (or “solid-state”) digestion. As a result, there is a need to develop a new technology that not only can efficiently treat the agricultural wastes but can also be operated in a more sustainable fashion. In this study, a percolating solid-state anaerobic digestion system was established, and co-digestion approaches were employed to improve the biogas production. Specifically, fermentation of cow manure using the optimal design methodology was conducted to produce hydrogen, and the key factors that would influence co-digestion of pig manure (PM) mixed with paper & pulp sludge (PPS) or rice stalks (RS) to generate methane in the percolating system were evaluated and identified.
For the hydrogen production, the Taguchi method with level settings and an L18 orthogonal array to identify the primary factors affecting thermophilic anaerobic fermentation (temperature and pH value) was employed, followed by the central composite design of response surface methodology to predict the hydrogen content and production and to identify the optimal temperature and pH conditions. Results show that controlling the system at the ideal temperature and pH of 60C and 5.20±0.21 respectively resulted in the optimal hydrogen concentration of 54.64±11.45%, hydrogen generation rate of 405.54±93.61 mL-H2/L/d, and specific hydrogen yield of 10.25±1.96 mL-H2/g-VS.
For the methane production, after determining that the optimal solid retention time was 6 days, semi-continuous experiments were conducted to co-digest PM and PPS in hopes of increasing the quality and quantity of methane generation. Results indicated that a wet weight ratio of 50:50 for PPS and PM produced the highest methane concentration of 57.53%; further, co-digestion of PPS and PM increased methane concentration, methane yield, and specific methane production rate by 5.8%, 35.61%, and 49.22%, respectively, in comparison with those from the digestion of PM alone. Apart from PPS, RS were used as the feedstock substrate for methane production in the percolating system. Results show that when both pre-acidified and un-acidified rice straw were homogenized to the same particle size, similar methane-production levels were obtained, suggesting that pre-acidification of RS is not a prerequisite for the “biomass to methane” conversion in this system; moreover, results from permeability (or hydraulic conductivity) tests showed that porosity of the feedstock may be the key factor in modulating the overall methane production. In addition, metagenomic analysis revealed that the highest methane production rate and methane concentration were obtained from the systems where Mechanosarcinal and Methanobacterial dominated the archaean communities, in accord with elevated levels of acetate detected in these systems. Surprisingly, Thermoplasmatales, the thermophiles, only occupied a lower proportion of the archaean community.

並列關鍵字

cow manure ； Taguchi method ； response surface methodology ； pig manure ； pulp and paper sludge ； rice straw ； percolating system ； Metagenomics

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