Biomethane production using goat manure and cheese whey: statistical analysis of the effect of mixture composition

Abstract

Lignocellulosic biomass and agricultural residues rich in carbohydrates, lipids, and proteins are promising sources for renewable energy production, particularly in the field of biofuel. Goat manure (GM) is a suitable raw material for the anaerobic digestion process owing to its high total nitrogen content, besides providing stability to fermentation. However, its utilization results in a relatively low biogas production yield. This yield can be significantly increased by co-digesting animal manure with co-substrates such as cheese whey (CW). Therefore, this study applied the Simplex Lattice experimental design to verify the biomethane production through different mixture concentrations of goat manure and cheese whey using bench reactors in batch mode. The volumetric compositions (CW₁₀₀/GM₀, CW₇₅/GM₂₅, CW₅₀/GM₅₀, CW₂₅/GM₇₅, CW₀/GM₁₀₀) were evaluated by adjusting linear and quadratic models. The results presented COD removal efficiencies between 40.07 and 63.73% and total volatile solids removal between 22.87 and 58.99%. According to the statistical analysis of the Simplex Lattice design, co-digestion showed favorability for methane production compared to goat manure alone. Furthermore, the maximum methane production yield (MY_COD) was 319.89 mL-CH₄/gCOD, with a productivity rate (MYPR) of 3.39 mL-CH₄/gCOD.d. These maximum values were observed in the CW₇₅/GM₂₅ condition. The quadratic model exhibited the best fit for the design adopted.