Biodiesel production in energy and material recovery in integrated meat and dairy facilities

Biodiesel can be an environmentally friendly alternative to fossil fuels and can be produced from animal waste oils. In this study animal waste oil was recovered from the wastewater of an integrated meat and dairy facility by installing an oil-separation pool at the wastewater mixing point of meat and dairy effluents followed by density-based separation into sludge, sludge+water and oil. This procedure yielded 63-77% usable oil which was further split by a decanter centrifuge into solid (37-49%) and liquid (14-20%) phases. For biodiesel production, 2-propanol (80°C), ethanol (75°C) and methanol (60°C) were used. Transesterification of the liquid oil (FFA 3.4%) was conducted at alcohol:oil molar ratios of 20:1, 25:1, 30:1, 35:1, and 40:1 with reaction times of 2, 4, and 6 h. According to ASTM D6751 acceptable results were obtained under all conditions; according to EN 14214 compliance was achieved for 2-propanol (20:1-6 h; 25:1-4/6 h; 30:1-4/6 h; 35-40:1-6 h), ethanol (30:1-6 h; 35-40:1-6 h) and methanol (35-40:1-6 h). Under compliant conditions unit costs were 0.97-1.00 $/L (methanol), 1.24-1.46 $/L (ethanol) and 1.78-2.80 $/L biodiesel (2-propanol). For the solid oil (FFA 9.7%) direct acid-catalyzed and two-step esterification / transesterification routes were applied. In the direct acid-catalyzed process H₂SO₄ (5%, 7%, 9%) and 48 h were used; complied with ASTM D6751 under all conditions while EN 14214 compliance was obtained at 30:1 molar ratio with 7% and 9% H₂SO₄ for all three alcohols. Corresponding unit costs were 0.95-1.01 $/L (methanol), 1.50-1.51 $/L (ethanol) and 2.56-2.58 $/L biodiesel (2-propanol). In the two-step process, the first stage conditions were 2-propanol (6 h, 3-4% H₂SO₄; 9:1-12:1), ethanol (5 h, 2-3% H₂SO₄; 9:1-12:1) and methanol (4 h, 1-1.75% H₂SO₄; 6:1); in the second stage methanol (6:1), 0.5% KOH and 2 h were applied for all cases producing biodiesel compliant with both EN 14214 and ASTM D6751. Unit costs under these compliant conditions were 0.38-0.40 $/L (methanol), 0.52-0.55 $/L (ethanol) and 0.76-0.82 $/L biodiesel (2-propanol). Overall across all compliant conditions, unit costs ranged from 0.38-1.01 $/L for methanol-based systems, 0.52-1.51 $/L for ethanol and 0.76-2.80 $/L biodiesel for 2-propanol.