Biorefinery-based sustainability assessment of macroalgae waste valorization to polylactic acid: Exergy and exergoeconomic perspectives

This study evaluated the exergetic and exergoeconomic performance of three L-lactic acid (L-LA) production scenarios. All three scenarios produced L-LA from red macroalgae waste, Eucheuma cottonii residue (ECR) with the same species of enzymes, and lactic acid bacteria (LAB). Scenario 1 is the biorefinery process for the L-LA. Scenario 2 is the biorefinery process for the L-LA with fertilizer production and wastewater treatment. Scenario 3 is the polylactic acid (PLA) biorefinery process with fertilizer production and wastewater treatment. From the study, the total production rate for L-LA was 5194 kg/hr, with a total consumption rate of 12079 kg/hr for ECR. In addition, the production rates of organic fertilizer and reused water were 1609 and 1233 kg/hr, respectively, for scenario 2. Then, the production rate of the PLA was 4142 kg/hr for scenario 3. From the comparison, the energy consumption was increased due to the increased demand for process and equipment (from 28272.53 kW to 30296.15 kW). From the exergetic analysis aspect, the highest contributor to the exergy loss was the simultaneous saccharification and fermentation (SSF) unit, totaling 18875.62 kW. For the exergoeconomic aspect, the SSF unit also contributed the highest exergy destruction cost rate (average 70%). The study results provide theoretical guidance for exergetic and economic performance improvement in future L-LA and PLA production.