Comparison of the environmental effects of manure- and crop-based agricultural biogas plants using life cycle analysis

The environmental effects of anaerobic digestion (AD) plants have not, to date, been thoroughly analysed. The technology of biogas production has developed enormously in the last 10 years, with equipment functioning at ever-improving efficiency. In the present study, we aimed to examine the environmental effects of biogas plants that operate with the same power production capacity, but use different raw materials during the full life cycle. In addition, the environmental effects that occur during the establishment of AD plants were defined and contrasted against emissions during the full life cycle. In life cycle analysis (LCA), the greenhouse gas (GHG) emission effect of biogas production was measured as kg CO2 eq/kWhe, the acidification potential as kg SO2 eq/kWhe, and the eutrophication potential as kg PO4 eq/kWhe. The calculations proved that an AD plant that processes only energy crops as raw materials can be regarded as a CO2 absorber (−188 g/kWhe). The CO2 emission of all three examined plants was below the average emission of electrical power currently produced in a conventional manner. The AD plant that processes low-energy-density agricultural wastes produced 7.7% of its full-life-cycle CO2 emissions during its construction phase, compared with a 0.9% ratio for the AD plant processing only energy crops. However, the manure-based AD plant contributed the most to the decline in environmental acidification.