畜殖場固體廢棄物厭氧消化生成沼氣之研究

Abstract

摘要 台灣養豬場處理廢水時可分離出大量豬糞固體，固體廢棄物成分中含有大量有機物，現今固體廢棄物經堆肥脫碳後製作為氮肥，將有機物轉化為二氧化碳釋放，因此本研究是將固體廢棄物利用厭氧醱酵轉化成沼氣，取代堆肥脫碳作用，使固體廢棄物轉換為能源使用。本論文探討不同厭氧反應參數對固體廢棄物產沼氣的影響，並建立實驗室規模之厭氧反應系統。 豬糞固體廢棄物含有纖維素與半纖維素比例為77%，具有高比例有機物可轉化為沼氣，批次厭氧醱酵實驗中，證實固體廢棄物與活性汙泥最佳混合比例(Substrate/Inoculum ratio, S/I ratio)為4，依此比例的固體廢棄物每公克化學需氧量可產出211毫升甲烷體積，達理論甲烷產量之60%。在連續式反應產甲烷氣實驗中，我們探討排放出流及進料體積，發現每次進料時保留80%至90%厭氧汙泥體積甲烷產量最為穩定，在8週厭氧醱酵可處理830公克固體廢棄物後生成沼氣總體積約100 L，生化甲烷潛力(Biochemical Methane Potential, BMP)變化範圍各為260-516 ml CH4/gVS及334-432 ml CH4/gVS，試程中S/I ratio變化範圍各為2.4-3.1及2.7-3.6，總固體含量變化範圍各為4.9-6.3%及4.6-5.1%。在厭氧系統內菌相定序比對出15種細菌、8種古生菌。細菌群在連續培養中變化不大，相對菌量最高之菌屬為Clostridium，其主要功能可轉化有機物為乙酸、二氧化碳與氫氣。此系統中古生菌進行甲烷化作用，在第1週僅有利用甲基化合物之甲烷菌Methanohalophilus zhilinae，在系統經長時間作用後，出現乙酸營養型甲烷菌與氫營養型甲烷菌。連續式反應系統反應前碳氮比由18降低至出流碳氮比9.7-13，此碳氮比適合用來製作肥料，故本研究建立之厭氧反應系統可有效將固體廢棄物轉化為沼氣，取代堆肥化之脫碳作用。

Abstract The excrement sewage from swine industry was separated into liquid waste and solid waste in Taiwan. The solid waste can be composted to fertilizer, and abundant organic matter is converted into carbon dioxide. In contract, anaerobic degradation of solid waste to produce biogas and remove organic matter is an alternative way. In this study, we evaluate the biochemical methane potential of solid waste in swine industry and establish a lab-scale anaerobic system for biogas production. The solid waste (SW) in swine industry was fibre-rich, which was composed of 77% cellulose and hemicellulos. This organic contents make SW with high conversion efficiency to produce biogas. Effect of substrate/inoculum ratio (S/I ratio) on biogas production of SW was performed in batch experiment. The results shown the maximum methane yields were 211ml/g CODadded at S/I ratio of 4, which was equivalent of 60% of theoretical yield. A lab-scale continuous biogas production experiment was used to investigate the optimal volume of feedstock and outflow. The result showed that conditions for keeping 80%-90% volume of sludge made the system more stable to produce biogas than others. The total biogas production of two conditions was nearly 100L in 8 weeks, and the variation of BMP was 260-516 ml CH4/gVS、334-432 ml CH4/gVS, respectively. The variation of S/I ratio and total solid of two conditions were shown at 2.4-3.1、2.7-3.6 and 4.9-6.3%、4.6-5.1%, respectively. Microbial community included 15 bacteria and 8 archaea in the anaerobic digestion system. The more popular bacterial genus was Clostridium which utilize organic matter to generate acetate、CO2 and hydrogen. In the first week, Methanohalophilus zhilinae which utilized methyl compounds was observed. The acetotrophic and hydrogenotrophic methanogen were found after long-term anaerobic digestion. After continuous anaerobic digestion, the C/N ratio in this system decreased from 18 to 10-13 which was appropriate for composition. Those results demonstrated that anaerobic system could converse SW to biogas efficiently and use to remove organic matter from SW in swine industry.