Environmental impacts concerning the addition of trace metals in the process of biogas production from anaerobic digestion of slurry O. Hijazi a, * , E. Abdelsalam b , M. Samer c, ** , B.M.A. Amer c , I.H. Yacoub d , M.A. Moselhy e , Y.A. Attia b , H. Bernhardt f a Chair of Wood Science, Technical University of Munich, 85354, Freising, Germany b National Institute of Laser Enhanced Sciences (NILES), Cairo University, 12613, Giza, Egypt c Department of Agricultural Engineering, Faculty of Agriculture, Cairo University, 12613, Giza, Egypt d Department of Agronomy, Faculty of Agriculture, Cairo University,12613, Giza, Egypt e Department of Microbiology, Faculty of Agriculture, Cairo University,12613, Giza, Egypt f Chair of Agricultural Systems Engineering, Technical University of Munich, 85354, Freising, Germany article info Article history: Received 12 August 2018 Received in revised form 23 September 2019 Accepted 24 September 2019 Available online 25 September 2019 Handling editor; Prof. Jiri Jaromir Kleme s Keywords: Environmental impact assessment Trace metals Biogas production Greenhouse gases Manure abstract 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 (CoCl 2 ) causes the lowest greenhouse gas emissions among all other evaluated trace metals which were calculated on the basis of CO 2 -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. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction Life Cycle Assessment (LCA) is a methodology to carry out a cradle-to-grave investigation in to analyze and assess the energetic requirements and the negative environmental effects associated to all the stages of the lifespan of manufactured goods starting from the mining of raw materials through the processing, fabrication, handling, distribution, utilization, maintenance, repair, disposal, and recycling. Entrepreneurs deploy this methodology to support the evaluation of products. LCA is one of the thorough and exem- plary means implemented for analyzing the negative environ- mental effects of novel techniques, technologies and products. LCA can be deployed as a technique for quantifying the greenhouse gas (GHG) emissions of the different processes in an industry (Nasution et al., 2018). The technology of biogas is an effective method to process an- imal manure to generate biogas as a fuel (Samer, 2010) and bio- logical fertilizer during the anaerobic digestion (AD) of organic materials (Samer, 2012). The implementation of anaerobic diges- tion is a powerful emissions mitigation strategy to minimize the negative impacts of cattle slurry on the environment (Samer, 2016). Compared to other techniques such as field application of manure and composting, anaerobic digestion holds substantial advantages such as generating energy, recycling slurry, and producing biolog- ical fertilizer (Wang et al., 2018). A life cycle analysis should be conducted to analyze the negative environmental effects and en- ergy balance of biogas production (Ramírez-Arpide et al., 2018). Numerous studies carried out life cycle analysis in the area of biogas technology to accomplish diverse objectives: (1) Analysis for specifying the correct period to install biogas technologies (Nikkhah et al., 2018), (2) Analysis of diverse sizes of biogas units * Corresponding author. ** Corresponding author. E-mail addresses: hijazi@hfm.tum.de (O. Hijazi), msamer@agr.cu.edu.eg (M. Samer). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro https://doi.org/10.1016/j.jclepro.2019.118593 0959-6526/© 2019 Elsevier Ltd. All rights reserved. Journal of Cleaner Production 243 (2020) 118593