Diagnosing Anaerobic Digesters' Function and Performance: From Meta-Omics to Integrated Meta-Omics Analyses.

Anaerobic digestion (AD) of organic wastes by microorganisms into biomethane contributes significantly towards bioenergy generation. However, the bioprocess remains challenging due to its complex microbial ecology, dynamic biochemical pathways and sensitivity to perturbations. Over the past decade, using meta-omics like metataxonomics, metagenomics, metatranscriptomics, metaproteomics and metabolomics to diagnose its functioning has become necessary and common. However, a single meta-omics method can only provide limited biological understanding of the bioprocess. This led to the use of multi-meta-omics analyses in tandem; however, most studies still examine and interpret each meta-omics separately, limiting their ability to uncover functional interactions across molecular levels. Currently, the frontier is integrated meta-omics, where multi-meta-omics and process data are systematically combined into a single and interpretable system to unlock mechanistic understanding, diagnostic and predictive control of AD. This review critically examines specific application of meta-omics in AD, discussing their strengths, limitations and distinct position in integrated meta-omics approach. Importantly, it explores the computational frameworks, methodologies and challenges of integrated meta-omics. Discovering diagnostic biomarkers with high predictive power and transferability across AD systems through cross-omics validation is highlighted. As workflows standardise and technologies mature, integrated meta-omics would significantly contribute to the advancement of AD bioprocess for bioenergy.