Pig slurry valorization by ammonia recovery, biogas upgrading and microbial protein production

The management of pig slurry is associated with environmental concerns due to its high nitrogen content and greenhouse gas emissions. This work proposes a photobiorefinery concept integrating steam explosion pretreatment, ammonia recovery via gas-permeable membranes, anaerobic digestion, and microbial protein production using purple phototrophic bacteria (PPB). Pretreatment at 145 °C for 30 min led to 57% solubilization of organic matter and 29% reduction of total solids. More than 99% of ammoniacal nitrogen was recovered from the hydrolysate in less than 3 h. Methane production increased by up to 350% after pretreatment. The recovered nitrogen was used as a nutrient for PPB growth, enabling CO₂ assimilation from biogas under photoautotrophic conditions and microbial protein production. The results demonstrate the feasibility of coupling thermal, biological, and phototrophic processes for the integrated valorization of pig slurry, with simultaneous recovery of energy and nutrients.