Enhancing biodiesel production from urban sewage sludge: A novel industrial configuration and optimization model

In this work, a novel industrial configuration for the lipid extraction from sewage sludge was proposed. In detail, respect to conventional scheme based on direct extraction of lipids from wet sedimented sewage sludge using hexane, a preliminary centrifugation of sewage sludge prior to the extraction process was introduced. Economic and energetic balances for both configurations were evaluated using Aspen Plus simulator, including the post-treatment of exhausted sewage sludge obtained after the process. By centrifuging sewage sludge prior to the extraction process, overall costs can be reduced (27 % less), while preserving the same extraction efficiency for lipid recovery (80 %). Initial capital investments, amounts of reactants and total energy demand were sensibly reduced to achieve BEP of extracted lipids of 784 € ton-1 (vs 1.291 € ton-1 for conventional route). Finally, the economic feasibility of biodiesel production from lipids obtained from centrifuged sludge was evaluated by applying direct esterification with methanol and AlCl3·6H2O BEP of biodiesel produced of 1.186 € ton-1 was obtained with NPV of 27.5 M€ and DPP of 2.5 years. These values, show that biodiesel production from sewage sludge could be profitable considering only the proposed approach, fully unlocking the potential of waste in coherence with circular economy principles.