Utilization of tofu wastewater and Nannochloropsis oceanica for eutrophication mitigation and eicosapentaenoic acid valorization: Advancing carbon neutrality and resource recycling

Abstract

Seeking environmentally-friendly and resource-recycling strategies for tofu wastewater (TFW) treatment could effectively mitigate harsh ecological impacts and resource wastage caused by direct discharge. This study investigated the feasibility on the utilization of Nannochloropsis oceanica (N. oceanica) for TFW eutrophication mitigation and eicosapentaenoic acid valorization. The findings demonstrated that employing N. oceanica resulted in significant removal rates for total phosphorus, total nitrogen, ammonia nitrogen, and chemical oxygen demand by 88.60 %, 97.02 %, 94.22 %, and 98.02 % under fed-batch treatment mode. Such nutrients removal efficiency met discharge permit standards while accomplished a superior biomass at 26.37 g/L and EPA yield at 43.5 mg/g by N. oceanica, representing 2.61- and 2.52-fold more than that of batch treatment mode. Furthermore, TFW feeding enhanced the cytomembrane fluidity of N. oceanica and promoted TFW nutrients uptake into cells consequently boosted the nutrients removal efficiency. Simultaneously, TFW feeding upregulated enzymes such as antioxidases, desaturases and elongases responsible for EPA biosynthesis in N. oceanica to collectively protect EPA from oxidation stress and stimulate proactive accumulation. EPA derived from TFW-fed N. oceanica exhibited promising in vitro antihyperlipidaemia efficacy in constructed hyperlipopyte HepG-2 cells. Further, the molecular docking indicated that the hypolipidemic activity partly contributed to that EPA inhibited PPARα signaling to trigger fatty acids β-oxidation and cholesterol transport suppression. The outcomes present a viable route that utilization of microalgae for TFW eutrophication mitigation and EPA valorization to advance carbon neutrality and resource recycling.