Microbiology of municipal solid waste landfills: a review of microbial dynamics and ecological influences in waste bioprocessing

Municipal solid waste landfills are widely used as a waste management tool and landfill microbiology is at the core of waste degradation in these ecosystems. This review investigates the microbiology of municipal solid waste landfills, focusing on the current state of knowledge pertaining to microbial diversity and functions facilitating in situ waste bioprocessing, as well as ecological factors influencing microbial dynamics in landfills. Bioprocessing of waste in municipal landfills emanates from substrate metabolism and co-metabolism by several syntrophic microorganisms, resulting in partial transformation of complex substrates into simpler polymeric compounds and complete mineralisation into inorganic salts, water and gases including the biofuel gas methane. The substrate decomposition is characterised by evolution and interactions of different bacterial, archaeal and fungal groups due to prevailing biotic and abiotic conditions in the landfills, allowing for hydrolytic, fermentative, acetogenic and methanogenic processes to occur. Application of metagenomics studies based on high throughput Next Generation Sequencing technique has advanced research on profiling of the microbial communities in municipal solid waste landfills. However, functional diversity and bioprocess dynamics, as well as key factors influencing the in situ bioprocesses involved in landfill waste degradation; the very elements that are key in determining the efficiency of municipal landfills as tools of waste management, remain ambiguous. Such gaps also hinder progressive understanding of fundamentals that underlie technology development based on waste biodegradation, and exploration of municipal waste as a bioresource.