Safety and nutritional evaluation of biogas residue left after the production of biogas from wastewater

We investigated the safety and nutritional value of biogas residue left after the production of biogas from wastewater. In Exp. 1, ninety-six female mice were selected for acute oral toxicity testing and randomly allocated to 4 treatment groups, which received distilled water (control) or the biogas residue solution at 1 g/mL, 5 g/mL. or 15 g/mL. Activity levels and serum biochemical parameters were measured after 24 hours. In Exp. 2, eighty mice were divided into 2 treatment groups for subacute and sub-chronic toxicity testing, which received either a control group diet or the biogas residue diet (20% biogas residue). In Exp. 3, to test the nutritional value of the biogas residue, four pigs were fed either a low casein corn starch-based diet or a semi-purified diet with biogas residue as the only source of protein, and the apparent and true digestibility of crude protein and amino acids, apparent metabolic energy, and digestible energy were measured. Group differences in serum parameters and mouse weight gain were not significant 24 hours after biogas residue solution gavage, and the viscera appeared normal. At day 30 of the observation period, changes in serum biochemical parameters were not significant, but the mean spleen index of mice treated with biogas residue was greater (P<0.05) than that of the control group. In this study, biogas residue had no significant adverse effects on the body and it was safe as a feed supplement at a 20% replacement level. The current observations showed that the biogas residue might be considered as a protein feed source for pigs.