11. Identification of Most Affected Impact Categories of Wastewater-Based Biogas Production and Use

With the increasing deployment of renewable energy technologies, the current research tends to focus not only on ways to increase systems efficiencies but also on assessing the benefits of their use objectively, as much as the impact of their drawbacks on the environment. One of these technologies is biogas production that has been implemented and developed in many countries for a long time, while it is still starting in others. One of the factors that hinder the spread of this technology is greenhouse gas (GHG) emissions during the production and use of biogas from wastewater. Most of the existing studies consider the emissions from some processes but ignore biogas environmental impact. The diversity of the methods used to estimate emissions based on available resources and other factors also led to an important variation in the results making an overview of the state of the art of emissions from biogas from wastewater necessary for future research and practice. In this context, a systematic review was carried to identify and explain the existing research concerning the emissions from production and use of biogas from wastewater and the quantities of emissions and their impact on the environment. Scopus and Web of Science were chosen as paper search databases because of the amount and quality of papers they include and the wideness of the screening options. After several screening processes, 73 papers in English ranging from 2010 to 2021 were selected. Most of the experimental case studies were from Europe. There were reviews and theoretical studies from developing countries. Results show that most of the direct emissions (methane (CH₄) and nitrous oxide (N₂O)) result from the aerobic treatments of wastewater and anaerobic digester leakages, but those can be avoided in the case of regular maintenance. The most affected impact categories of the biogas deployment are human health, global warming, and climate change. The findings regarding this topic provide more awareness for engineers and system designers to conceive biogas systems with the least impact on the environment and give an insight into the importance of considering the options to mitigate GHG emissions in wastewater treatment plants equipped with biogas and energy generation for policy making in the countries who did not start implementing it yet.