Microaeration enhances methane production in anaerobic digestion: A systematic review and meta-analysis

Microaeration (MA) has emerged as a promising strategy to intensify anaerobic digestion (AD) of solid waste and wastewater. This systematic review and meta-analysis aimed to evaluate the operational parameters most frequently applied in MA and their effects on methane production in comparison to conventional AD. The Scopus, Web of Science, and PubMed databases were searched, yielding 47 studies eligible for a meta-analysis. The qualitative analysis revealed that research on this strategy has increased in recent years, with 50.0 % of the studies published between 2020 and 2025. However, most studies have been conducted at a small scale, with a predominance of batch experiments and direct application in the liquid phase, which limits extrapolation of the results to real operational conditions. Based on the meta-analysis, MA promotes a significant overall increase in methane production in batch systems, with an average gain of 9.0 % for biomass, 28.8 % for animal manure, and 18.8 % for co-digestion, particularly under mesophilic conditions and intermediate volatile solids concentrations (10-30 g L^-1). In continuous-feeding reactors, MA has a relatively limited, non-significant effect; nevertheless, it markedly increases biomass (+6.6 %). Overall, the results indicate that MA has clear potential to intensify rate-limiting steps of AD; however, its effectiveness is highly dependent on the interaction between substrate characteristics and operational conditions. Its broader implementation therefore requires greater standardisation of oxygen input and control strategies, improved data reporting, and validation at pilot and large scales under realistic treatment conditions.