Batch anaerobic digestion of five different livestock manures: Biogas productivity and fertilizer composition

Abstract

Abstract. The aim of this study was to evaluate biochemical methane potential (BMP) of five different livestock manures (dairy manure (DM), horse manure (HM), goat manure (GM), chicken manure (CM) and swine manure (SM)) and predict the BMP using manure chemical composition. Nutrients of the digested different manures were also monitored. The BMP tests were conducted under mesophilic temperatures with a manure loading rate of 3.5 g volatile solids (VS)/L and a feed to inoculum ratio (F/I) of 0.5. Single variable and multiple variable regression models were developed using manure total carbohydrate (TC), crude protein (CP), crude fat (CF), lignin (LIG) and acid detergent fiber (ADF)), and measured BMP data. The BMP for DM, HM, GM, CM and SM were measured to be 204, 155, 159, 259, and 323 mL/g VS, respectively. The effluents from the HM showed the lowest nitrogen, phosphorus and potassium concentrations. The effluents from the CM digesters showed highest nitrogen and phosphorus concentrations and digested SM showed highest potassium concentration. Based on the results of the regression analysis, the model using the variable of LIG showed the best (R2 = 0.851, p = 0.026) for BMP prediction among the single variable models, the model including variables of TC and TF showed the best prediction of BMP (R2 = 0.913, p = 0.068-0.075) comparing with other two- variable models, while the model including variables of CP, LIG and ADF performed the best in BMP prediction (R2 = 0.999, p = 0.009-0.017) if three-variable models were compared.