Life cycle assessment of large-scale and household biogas plants in northwest China

Abstract

Abstract In northwest China, large-scale (modern) and household biogas production (conventional) plants are the two main methods of biogas fermentation, a promising means of livestock waste disposal and effective agricultural recycling. Differences in the operating mechanisms of the two systems result in differences in their environmental performance. In this study, detailed life cycle assessments of large-scale and household biogas production were conducted to compare their environmental performance in terms of energy use and environmental impact potential per function unit (2136 tonne/yr of manure flowing into the biogas plant). Data were collected over a two-year period (2014–2016). The results showed that the total biogas output from the large-scale digester was 1.88 times that of the household digester. Net energy output did not differ much between the two systems, due to the high energy consumption of the large-scale plant during production. The energy-use efficiency of the large-scale plant was 1.29 times that of the household plant due to the use of co-products. Higher carbon dioxide and volatile organic compound emissions from the burning of biogas in the large-scale plant caused a higher potential for global warming and photochemical oxidation. However, higher ammonia and sulfur dioxide emissions occurred in the household plant, resulting in a higher potential for eutrophication, acidification and human toxicity. In conclusion, the waste of extra biogas for heat in large-scale biogas production, and undeveloped management, emissions through poor air-tightness and lack of technical biogas purification in household biogas production are the main hotspots to improve the environmental performance.