Factors maximizing biogas yield in anaerobic digestion of agro-industrial wastes: A systematic review (2015-2025)

Abstract

Agro-industrial waste has significant potential as a feedstock for biogas production, contributing to both energy generation and waste recovery. This study aimed to analyze the scientific literature published between 2015 and 2025 on biogas production from agro-industrial waste, identifying which co-substrate combinations, mixture proportions, and pretreatment strategies are associated with the highest biogas yields. A systematic literature review was conducted using the Science Direct, Scopus, and Web of Science databases, accessed through the Capes Journal Portal, applying boolean search operators and explicit eligibility criteria; after screening 351 records, 130 articles were retained for analysis. Results show an exponential growth in publications over the period, led by Brazil, India, and Italy. Anaerobic co-digestion of easily degradable substrates with more recalcitrant lignocellulosic residues produced the largest relative gains over mono-digestion, while a carbon-to-nitrogen ratio between 20:1 and 30:1 was consistently associated with the best performance. Physical, thermochemical, and biological pretreatments increased methane yield by 16% to 222%. It is concluded that, although anaerobic digestion is a technically mature process, critical gaps remain regarding standardization of yield units, comparability among studies, and economic feasibility indicators.