The Effects of the Concentrations of Iron, Phosphate, and Organic Nitrogen on the Yield of Hydrogen Produced from Anaerobic Digestion of Organic Wastes Using Grass Compost as the Seeding Material

[[abstract]]再生能源為自然界可以循環滋生的能源，由於價格昂貴且不普及，目前尚無法取代傳統的化石燃料，由於其污染性低且可減少溫室氣體的排放，所以仍有研究及發展的空間。氫氣是一種潔淨的替代能源，燃燒後產生水而不會生成其它有害副產物，經由燃料電池可直接轉換為電能利用，因此具有發展潛力，預計在公元2020年後，將可進入能源市場中。 產生氫能的方式很多，其中以生質氫能最受到重視。生質氫能是利用微生物將生質物或廢棄物的有機質分解轉化以產生氫氣，生質物產氫不僅可以潔淨的方式生產氫能，而且也可以同時處理廢棄物，極具資源再生的意義。而生物產氫主要是藉由行光合反應或醱酵作用的微生物來進行產氫，其中又以梭菌屬（Clostridium sp.）在厭氧醱酵過程中的高產氫能力最受矚目。Clostridium sp.是具有孢子的微生物，於一般堆肥熟成過程中，經由高溫菌作用的堆肥土溫度可高達60℃，所以在已熟成堆肥之中含有大量具有孢子的微生物，所以本研究也選用堆肥土作為植種材料之來源。 厭氧醱酵過程中除了可以解決固體廢棄物處理的問題外，其代謝過程中所產生的氫氣總能源效益也比甲烷高，而氫氣在厭氧醱酵過程中是一種中間產物。於厭氧醱酵代謝路徑中是進入產氫、產酸或者是產醇之階段即受許多因素的影響，包括植種材料前處理、環境因子中的pH值、溫度、營養鹽中鐵鹽、磷、有機氮之濃度等等，當改變其環境因子時也將可以改變氫氣的產率。 本研究主要為探討環境對有機廢棄物氫醱酵的影響，並以營養鹽中鐵鹽濃度、磷濃度和有機氮濃度為主要探討之環境因子。本研究先以前實驗（pre-test）之批次式厭氧產氫實驗，找出鐵鹽、磷、有機氮濃度之較適範圍為，當鐵鹽濃度為81 mg/L、磷濃度為1625 mg/L、有機氮濃度為563 mg/L時，在遲滯期（l）、產氫潛勢（Ps）、比產氫速率（Rs）有較佳的值產生。經由前實驗所找出的濃度條件以中心因子實驗設計（Full Factorial Central Composite Design）進行三者之實驗參數規劃，並再進行批次式厭氧產氫實驗。此時經過鐵鹽、磷、有機氮三者不同濃度變化之交互做作用後，根據實驗設計法及應答曲面法的歸納，當鐵鹽濃度為144 mg/L、磷濃度為1875 mg/L、有機氮濃度為625 mg/L時其產氫參數值為：遲滯期（l）為14小時、產氫潛勢（Ps）為75 mL/gTVS、比產氫速率（Rs）為450 mL/gTVS/day。由上述所找出之最適化條件，再經由重複試驗的再現性可得知實驗數據的可靠性；另外，當培養時間為14小時左右，pH值則急速下降，而氫的累積生成呈現急速上升之趨勢，相對的酸及醇的產生也漸漸同時形成。[[abstract]]Renewable energy is the energy extracted from the sources that can be regenerated or grown in nature. Due to higher prices and unpopularity, renewable energy sources are unable to replace conventional resources such as crude oil and coal. Renewable energy still worth of researching and development because it causes less pollution and emits less green house gases. Hydrogen is a clean form of alternative energy. After burning, it only produces clean water. Using fuel cell, electricity can be easily converted and readily utilized without going through conventional combustion-electricity generation process. Therefore, hydrogen has a great potential to replace conventional fuels and is expected to emerge into commercial energy market in 2020. Hydrogen can be produced by a great many ways. Among those, the microbial hydrogen production receives greatest attention. The microbial process is to use microorganisms to convert organic substrate into hydrogen gas. The process not only produces cleaner fuel-hydrogen, but also recovers and reduces organic fractions in the waste. Thus, it is a process of energy generation and resource recovery. Biohydrogen can be produced through photosynthesis and anaerobic digestion. In principle, photosynthesis produces more hydrogen, but anaerobic digestion has better potential to be commercialized because of simpler and inexpensive reactor design. Among many anaerobic hydrogen producing microorganisms, Clostridium sp. has the greatest potential. Because Clostridium sp. have spores, those bacteria can survive in the temperature of 60 o C and above such as those in the compost while most other bacteria cannot. Therefore, the cured compost contains a significant number of Clostridium sp. and can be used as the seeding materials. In this study, the compost is also used as the seeding material. Anaerobic digestion is an old waste treatment process that has been used in treating municipal, agricultural and industrial wastewaters. In the anaerobic digestion process, hydrogen is an intermediate product during the metabolism of bacteria. Many environmental factors such as pretreatment of seeding material, pH, temperature, concentrations of iron, phosphate and organic nitrogen affects the directions of the metabolic pathways toward the productions of hydrogen, acids or alcohols. The purpose of this study is to investigate the effects of nutrient concentrations to the hydrogen producing potential from the anaerobic digestion of organic waste. At first, the optimal concentrations of iron, phosphate and organic nitrogen were obtained independently from the batch experiment; then the optimal concentrations of 81 mg/L, 1625 mg/L and 563 mg/L were used as the references for the Full Factorial Central Composite Design to find the global optimal conditions. By using the methods of factorial design and response surface design, the optimal concentrations of iron, phosphate and organic nitrogen were found to be 144 mg/L, 1875 mg/L, and 625 mg/L respectively. The corresponding lag-phase time (l), specific hydrogen producing potential (Ps), specific hydrogen producing rate (Rs) were 14 hours, 75 mL/gTVS, and 450 mL/gTVS/day, respectively. When the lag-phase time reached 14 hours, hydrogen production increased rapidly, the pH value dropped drastically, and both the acids and alcohols began to increase