Influence of anaerobic mesophilic and thermophilic digestion on cytotoxicity of swine wastewaters

Recycling wastewater from animal production for fertilizers using anaerobic digestion (AD) is common to recover the nutrients in the digestate. However, the digestate toxicity is not well understood because AD is designed for chemical oxygen demand (COD) reduction. This study determined the toxicity during AD and the controlling factors with the goal to improve digestate safety during farmer handling to reuse the nutrients. Thermophilic and mesophilic AD of two swine wastewater sources were studied. Mammalian cell cytotoxicity revealed that the effluent after thermophilic digestion was at least 69% more toxic than the mesophilic effluent, owing to higher ammonia and total organic carbon in the former. Ammonia accounted for > 55% total cytotoxicity, and the organics of thermophilic digestate were twice more toxic than those in the mesophilic digestate. Despite less toxicity contribution than ammonia, the organics did demonstrate significant adverse effects on the thiol-mediated cellular protection mechanis...