Anaerobic microbial cocktail of lignocellulolytic fungi and bacteria with methanogens for boosting methane production from unpretreated rice straw

Rice straw (RS) has been recognized as a sustainable renewable energy resource for converting into sugars and volatile fatty acids (acetate, propionate, and butyrate) and subsequently to produce biogas. Enhanced production of these intermediates from RS by the different combinations of two consortia was investigated. Anaerobic microbial cocktails of fungi, bacteria, and methanogens were evaluated for performance and stability in the anaerobic digestion of untreated RS. The best-defined anaerobic microbial cocktail for high RS degradation and methane production, consisting of anaerobic bacteria (mainly Proteiniphilum acetatigenes, Pyramidobacter piscolens, and Mesotoga prima) and anaerobic lignocellulolytic/fermentative fungi (uncultured Neocallimastigales, Orpinomyces, Anaeromyces, and Feramyces sp.) at a copy number ratio of 10³–10⁵ copies/mL, including hydrogenotrophic and acetoclastic methanogens (Methanosarcina mazei, Methanoculleus marisnigri, Methanofollis liminatans, Methanoculleus bourgensis, and Methanosaeta harundinacea) concentration of 10⁶ copies/mL, was successfully constructed. The system performance was 80% VS (volatile solids) RS degradation, 34 mL/day methane production rate, 318 mL/g VS_added methane yield, and a pH range of 6.90–7.70 within a short time of 14 days. A defined microbial cocktail has been proven as a potential alternative process for lignocellulose hydrolysis and methane production.