The role of biochar in the psychrophilic anaerobic digestion: Effects on kinetics, acids metabolism, and microbial population

This study investigated the effect of biochar in the psychrophilic anaerobic co-digestion regarding biomethane production potential (BMP), metabolic efficiencies, and microbial population. BMP tests of cheese whey and cattle manure as substrates were conducted at different gasified pine wood biochar concentrations (Bc) (10 g/L, 30 g/L, 50 g/L); and particle sizes (Ps) (~0.15 mm, ~0.575 mm, ~1 mm). The most favourable conditions of Ps = 0.575 mm and Bc of 30 g/L, allowed BMP values to go from 0.23 m3 CH4/kg VSadd to 0.34 m3 CH4/kg VSadd. The study of metabolic stages showed how the biochar modulates hydrolysis and methanogenesis and favours the acetoclastic metabolism to improve methane yield even at 15 °C. The biochar's positive effect is reinforced by its addition boosting the growth of methanogen psychrotrophs populations up to 520 % compared with a BMP with no biochar added at 15 °C. The study showed that psychrophilic AD + biochar might overcome mesophilia's energy needs by improving yields with no extra energetic requirements. [Display omitted] •Adding biochar from gasified pine wood (PWBc) accelerates anaerobic kinetics at 15 °C.•Adding biochar modulates the formation of acetic acid favouring the acetoclastic route.•PWBc (30 g/L) boosts psychrophilic CH4 yield, reaching 70 % of the obtained at 35 °C.•Biochar facilitates the growth of methanogens represented in 500 % more archaea.