Characterization of Methane Emissions from Rice Fields in Asia. III. Mitigation Options and Future Research Needs

Methane (CH₄) emissions from rice fields were determined using automated measurement systems in China, India, Indonesia, Thailand, and the Philippines. Mitigation options were assessed separately for different baseline practices of irrigated rice, rainfed, and deepwater rice. Irrigated rice is the largest source of CH₄ and also offers the most options to modify crop management for reducing these emissions. Optimizing irrigation patterns by additional drainage periods in the field or an early timing of midseason drainage accounted for 7–80% of CH₄ emissions of the respective baseline practice. In baseline practices with high organic amendments, use of compost (58–63%), biogas residues (10–16%), and direct wet seeding (16–22%) should be considered mitigation options. In baseline practices using prilled urea as sole N source, use of ammonium sulfate could reduce CH₄ emission by 10–67%. In all rice ecosystems, CH₄ emissions can be reduced by fallow incorporation (11%) and mulching (11%) of rice straw as well as addition of phosphogypsum (9–73%). However, in rainfed and deepwater rice, mitigation options are very limited in both number and potential gains. The assessment of these crop management options includes their total factor productivity and possible adverse effects. Due to higher nitrous oxide (N₂O) emissions, changes in water regime are only recommended for rice systems with high baseline emissions of CH₄. Key objectives of future research are identifying and characterizing high-emitting rice systems, developing site-specific technology packages, ascertaining synergies with productivity, and accounting for N₂O emissions.     

Upgrading techniques for transformation of biogas to bio‐CNG: a review

Increasing consumption of fossil fuels and environmental concern has led to increased use of compressed natural gas (CNG) in the transportation sector. Keeping in view limited resources of CNG, biogas is advised as potential fuel to provide continuous supply of CNG in the form of bio‐CNG. Various technologies, that is, physical and chemical absorption (using water and amine solutions, respectively, for the absorption of carbon dioxide), pressure swing adsorption, membrane separation, and cryogenic separation, are available for purifying biogas and thus upgrading it, to bio‐CNG with about 95% methane. Among these, water scrubbing and pressure swing adsorption are the best technologies with respect to various aspects including cost; however, suitability of a technology is decided by various factors including size/quantity of biogas generation, targeted quality of biogas, site of application, and economics of process. Copyright © 2017 John Wiley & Sons, Ltd.     

生物强化技术对厌氧消化特性影响研究进展

将生物强化技术应用到厌氧消化过程中，可克服复杂底物类型或消极环境条件等不利因素，因而近年来备受研究者的青睐。本文从生物强化制剂的类型出发，阐述了细菌强化、真菌强化、古菌强化、互营微生物强化和生物酶强化对厌氧消化特性的影响，并在此基础上回顾了生物强化技术在木质纤维素类底物、受氨氮/丙酸抑制类废水和难降解有机物消化中的应用，最后讨论了附着型强化方式和多段式强化方式对生物强化技术的影响。大量研究表明生物强化技术具有显著促进厌氧消化特性的积极影响，但在部分研究中并未得到良好成效，生物强化制剂的选择是该技术的关键所在。利用互营微生物的协同代谢或提高生物酶在系统中的稳定性将稳固生物强化技术的作用。此外，选择合适的附着载体和投加策略将进一步拓展生物强化技术在废水厌氧处理中的应用。     

Upgrading biogas produced at dairy farms into renewable natural gas by methanation

Renewable natural gas can be produced from raw biogas, a product of the anaerobic decomposition of organic material, by upgrading its CO₂ content (25‐50%) via thermocatalytic hydrogenation (CO₂ methanation). The H₂ needed for this reaction can be generated by water electrolysis powered by carbon emission‐free energy sources such as renewable or nuclear power, or using surplus electricity. Herein, after briefly outlining some aspects of biogas production at dairy farms and highlighting recent developments in the design of methanation systems, a case study on the renewable natural gas generation is presented. The performance of a system for renewable natural gas generation from a 2000‐head dairy farm livestock manure is evaluated and assessed for its economic potential. The project is predicted to generate revenue through the sale of energy and carbon credits with the payback period of 5 years, with a subsidized energy price.