The Biorefinery Concept Applied to Bioethanol and Biomethane Production from Manure

Production of biofuels from farm animal waste represents a promising approach to diversifying green energy production and reducing competition for cultivable lands between fuel and food-oriented crops. This work was aimed to define the technical feasibility and the specific suitability of cattle, swine and poultry manure to integrating bioethanol and biomethane production, using the biorefinery concept. Saccharification obtained by dilute acid pretreatment (3.5% H₂SO₄, 121 °C, 30 min) followed by enzymatic hydrolysis resulted in total sugar recovery of 230.16, 160.40, and 98.40 mg g⁻¹ (of dry matter) for cattle, pig, and poultry manure respectively. The sugar was then fermented using free yeast co-cultures. The ethanol obtained was 56.32 mg g⁻¹ of dry matter for cattle (about 52.59% of the theoretical ethanol yield); 27.98 mg g⁻¹ for swine (about 88.66% of the theoretical ethanol yield); 12.69 mg g⁻¹ for poultry (about 31.32% of the theoretical ethanol yield). Methane production from distillation waste was 72.95 mg g⁻¹ from dry raw faeces for cattle, 126.48 mg g⁻¹ for swine and 119.03 mg g⁻¹ for poultry. Cattle manure showed the best energy balance in terms of ethanol production with about 824.16 kJ kg⁻¹ of dry faeces, but the two integrated processes generated a net energy balance of 1.28 MJ kg⁻¹ for cattle, 4.57 MJ kg⁻¹ for swine and 4.79 MJ kg⁻¹ for poultry.