Bioaugmentation in anaerobic digesters: a systematic review.

Bioaugmentation, the intentional introduction of specific microorganisms into anaerobic digestion (AD) systems, has shown promise in enhancing methane production and in mitigating stressful conditions, particularly in systems operating below optimal performance. This review presents a systematic literature review (SLR) of research on bioaugmentation in AD. This review identified and analysed studies meeting predefined eligibility criteria through a structured methodology involving research protocol, search, appraisal, synthesis, analysis, and reporting. A notable innovation of this review is its comprehensive critical comparison of different controls used in bioaugmentation studies, which has been inadequately addressed in previous literature. To facilitate the functional understanding, strains for bioaugmentation were grouped into the four phases of anaerobic digestion (hydrolysis, acidogenesis, acetogenesis and methanogenesis). A highly diverse set of microbes has been described for bioaugmentation, especially from the families Clostridiaceae, Pseudomonadaceae and Syntrophomonadaceae. Most works are related to hydrolysis. The few works that address acidogenesis are mostly related to dark fermentation. Several studies used methanogenic archaea as well as syntrophic acetate oxidising bacteria, despite the difficulties in culturing them. On the other hand, studies applying strains for acetogenesis were largely underrepresented. Especially works on syntrophic propionate and butyrate oxidation (SPO and SBO) were missing.