Environmental impacts concerning the addition of trace metals in the process of biogas production from anaerobic digestion of slurry

The use of trace metals as additives to the biogas production process to increase the biogas yield has been identified as a very common approach. Such additives can biostimulate the methanogenic bacteria to increase the biogas and methane production from the anaerobic digestion (AD) of livestock manure. The environmental impact of using the trace elements as manure additives still not evaluated. The objective of this paper is to conduct a comparative environmental impact evaluation of manure treatment with different trace elements for biogas production. The trace metals under evaluation were in the form of the chlorides of nickel (Ni), cobalt (Co) and iron (Fe) which were used as additives to the anaerobic digestion of livestock manure. The results were shown in the form of the specific impacts on global warming and greenhouse gas (GHG) emissions mitigation of producing and utilizing biogas as a bioenergy source. The results of this investigation show that the use of 1 g/m(3) cobalt chloride (CoCl2) causes the lowest greenhouse gas emissions among all other evaluated trace metals which were calculated on the basis of CO2-equivalent. An important observation is that the greenhouse gas emissions from the electricity generated using biogas produced without any additives, i.e. without trace metals, were the highest among all other variants/scenarios. (C) 2019 Elsevier Ltd. All rights reserved.