Biogas engineering technology screening based on analytic hierarchy process and fuzzy comprehensive evaluation

Biogas typically refers to a gas produced by the breakdown of organic matter in the absence of oxygen. Biogas, like solar and wind energy, is a renewable energy source. Biogas is produced through anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials, usually from regionally available raw materials such as recycled waste like manure, sewage, municipal waste, green waste, plant material, and crops. Biogas is comprised primarily of methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture, and siloxanes. This energy release allows biogas to be used as a fuel. Biogas can be used as a fuel in any country for any heating purposes, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat. In China during the last year, this biogas technology has met with high growth rates, and it has become the main way to use the waste of livestock manure. Currently, a vast variety of biogas technologies and techniques are available at home and abroad. The effects of biogas technologies differ in different regions. Using scientific methods to screen out the right biogas technology for certain areas is applicable, economically viable, and environmentally friendly. Comprehensive evaluation on one certain technology in a specific area is the key issue to select and integrate the modern technology. In order to construct the comprehensive evaluation index system and method for one certain technology in China, construction on the system and method is put forward, and the comprehensive evaluation index system is established with a research method of literature analysis based on a social economic-natural compound ecosystem. In this study, based on the analysis of currently available approaches to screening technologies for biogas and methods to solve the multi-parameter problem in decision making, an AHP and fuzzy comprehensive evaluation based decision making process were applied to establish an index system for biogas technologies screening. The weights of the indices for the screening were worked out through investigation by experts in this field using AHP. Then, the biogas technologies were collated with the fuzzy comprehensive evaluation method. This decision making process was verified with the actual screening for a case of biogas technologies application site in China. The AHP and fuzzy comprehensive evaluation method combined could be used to solve the complicated multi-factor problem in decision making, thus not only overcoming the issue of subjectiveness of AHP in handling hard-to-quantify indices, but also avoiding the shortcoming of neglecting index weights with the fuzzy comprehensive evaluation method. It is, therefore, a good tool to screen biogas techniques for the recycling of agriculture waste. Comparisons of operating effects between two biogas technologies were carried out; the results from calculations based on the AHP and fuzzy comprehensive evaluation method were consistent with the facts of the real application at the two sites adopted with the two biogas technologies. Compared to completely mixed anaerobic technologies, red-sludge plastic anaerobic technology had better effects in terms of consumption of waste. In addition, red-sludge plastic anaerobic technology generated more electricity to meet the needs of a local village in Hubei on electricity expenditure, provided better solutions to the non source pollution contaminating water and soil, and even potentially helped reduce two released main gases, nitrogen dioxide and methane, that cause global climate change. All in all, the methods in this study will provide the methodology reference for assessing, selecting, integrating, and promoting biogas technology in China.