การพัฒนาระบบการปรับปรุงก๊าซมีเทนในการผลิตก๊าซีวภาพจากต้นเทียนนาและมูลโค

Abstract

Currently, energy resources and the environment have increased interest and this study concerns alternative sources of energy. Anaerobic digestion or biogas technology is alternative energy and this biological process using biomass as the primary feedstock. This thesis investigates the potential of agricultural weed such as water primrose (Ludwigia hyssopifolia) for biogas production. The first research was carried out for 45 days of operation from anaerobic mono-digestion of water primrose in fresh and dry form by using a batch experiment. Pretreatment was applied for substrate using sodium hydroxide (NaOH) solution (w/v) at different concentrations (0, 1, 2, 3, and 4%) with 10% of total solids (TS) based on dry matter. The results showed that the treatment with 2% NaOH was the best condition for water primrose in dry form with the highest performance in biogas yield (8,072.00 mL) and methane content (64.72%). In order to examine the ability of co-digestion with other substrates, different pretreatment time (1, 2 and 3 weeks) of water primrose at 2% NaOH was mixed with cow dung at different ratios (1:1, 2:1 and 1:2 (w/w), water primrose to cow dung). Among the three mixing ratios of co-substrate tested, the best performance in this experiment was achieved at mixing ratio 2:1 for 2 weeks’ pretreatment time on water primrose, including all measurements as biogas production (8,610 mL), methane concentration (68.2%), and percentage of total solids (70.84%), volatile solids (64.76%), and chemical oxygen demand (66.55%) removal efficiency. To further support the result from laboratory-scale experiments, pilot-scale work of anaerobic digestion was implemented under more realistic conditions and facilitated future practical application. The best performance of pretreatment time of sodium hydroxide and cow dung ratio to water primrose was chosen for the pilot-scale experiment. A pilot-scale experiment was performed in 1000 L of the digester, which gave an average biogas yield of 1.7 mL/ gTS/day with the highest methane content of 68.6%, thereby, proved that the results from the lab-scale experiment is reliable. The gas produced was collected for quality upgrading by aqueous solutions of sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)2) at various concentrations of 1, 2 and 3% (w/v). Also, steel wool and sponge were employed to reduce H2S and humidity in raw biogas. Biogas purification in this study aimed to achieve high CO2 removal efficiency in biogas stream at minimal alkali consumption and that feasibility was confirmed. The method's efficiency using Ca(OH)2 solution under normal conditions was competitive to the method using NaOH. Moreover, CO2 absorption was more prospective for Ca(OH)2 absorbent when 60.33 to 64.00% CO2 removal efficiency was achieved compared to 58.38 to 62.91% for NaOH absorbent at 1% and 3% concentration, respectively. After enriched methane process, the purified biogas of 3% Ca(OH)2 improved the highest value of calorific heating value reached to 28.73%. Consequently, with a low concentration of H2S, CO2, and small operation scale, a simple biogas production and biogas upgrading model implemented in this study is feasible and would be an appropriate choice for rural areas.