A comprehensive review on recent biological innovations to improve biogas production, Part 1: upstream strategies

This study reviews the innovations and optimizations in biogas production from the biological perspective reported by recently published patents and research works. The proposed biological strategies can be categorized into three different groups, i.e., upstream, mainstream, and downstream approaches. In the first part of this review, upstream strategies, including pretreatments by fungal, microbial consortium, and enzymatic as well as some other biological methods including microaeration, composting, ensiling, and genetic and metabolic engineering are discussed in detail. The impacts of upstream strategies on biogas production as well as their potentials in further improving the biogas industry are comprehensively scrutinized. Despite their promising impacts on biogas production, such biological innovations are time-consuming and require extra equipment and facilities that should be addressed in future studies. Overall, most information on biogas production has been generated through lab-scale investigations and not by commercial plants, undermining the commercial value of these data for the right decision-making. Pilot data would be necessary for techno-economic analyses with acceptable accuracies. Therefore, the future efforts should be directed toward providing the missing data for re-engineering designs, calculations, and life cycle assessment (LCA) of the newly designed biogas plants.