A circular economy strategy for valorizing industrial saline wastewaters: Techno-economics and environmental impacts

Mussels cooking wastewater (MCW) and fish processing wastewater (FPW) were utilized as feedstocks for the production of polyhydroxyalkanoates (PHA) and triacylglycerides (TAG) at the laboratory scale. This study presents a comparison of the techno-economic and environmental performance of ten circular economy-based and innovative processes, in which PHA/TAG are produced using Mixed Microbial Cultures (MMC), with benchmark wastewater treatments for MCW and FPW. The innovative systems were modeled based on the upscaling of lab-scale data using mass balances, and a centralized downstream processing (DSP) plant was proposed for PHA/TAG extraction. This study is the first to conduct a techno-economic and environmental analysis of a system with a centralized DSP. Consequently, the most favorable operational options were selected based on the techno-economic and environmental performance of the ten proposed scenarios. The techno-economic evaluations demonstrate that treatment costs for MCW and FPW could be reduced by 10% and 40%, respectively, compared to the benchmark treatment. Furthermore, environmental impacts could be significantly reduced (e.g., 10–70% for global warming potential) compared to the baseline scenario by implementing a system expansion approach. Regarding the centralized DSP, the production cost of PHA from MCW falls within a competitive market threshold, ranging from 0.95 to 1.18 €/kg. However, the production costs of PHA and TAG from FPW (1.40–2.21 €/kg PHA and 0.51–0.69 €/kg TAG) are hindered by the lower biomass concentration achieved. Hence, this study demonstrates, for the first time, the potential feasibility of circular economy-based strategies for valorizing saline industrial wastewaters through a centralized DSP approach.