Integration of biochar in psychrophilic anaerobic digestion: effects on the digestate quality

Biochar is known to enhance psychrophilic anaerobic digestion; however, its impact on the resulting digestate's quality and agronomic performance remains largely unexplored. This study aims to characterize and compare the physicochemical stability and fertilization potential of digestates obtained from the psychrophilic (23 °C) co-digestion of cheese whey and cattle manure in 5-L semi-continuous tubular biodigesters, under two operational conditions of the bioprocess: (i) a control system and (ii) a system amended with biochar (30 g/L). Biochar integration during the digestion process significantly optimized digestate stabilization, reducing soluble organic matter by 50% while concurrently increasing organic carbon and total nitrogen by 150% and 30%, respectively. Agronomic trials using Lactuca sativa L. demonstrated that the biochar-mediated digestate achieved biomass yields and photosynthetic pigment contents comparable to synthetic urea. Furthermore, its application mitigated environmental risks by curtailing ammonium and phosphate leaching by 67% and 50%, respectively. These findings identify biochar-supplemented digestate as a high-quality biofertilizer capable of mitigating nutrient losses and eutrophication in agricultural systems.