Hydroponic effluent recycling and resource recovery using heterotrophic Chlorella microalgae: Advancing a circular bioeconomy

Abstract

Agricultural activities, particularly those involving hydroponic systems that generate untreated wastewater (nutrient-rich effluent), pose a major environmental challenge. This study investigated the potential of Chlorella sp. G049 microalgae to serve a dual purpose: recycling residual nutrients from hydroponic effluent (HE) and bio-converting them into microalgal biomass rich in valuable biochemicals. Results showed that HE was heterotrophically recycled and bio-converted into polyunsaturated fatty acid (PUFA) − rich biomass under optimized nutrient supplementation: glucose at 12.2 g/L and indole-3-acetic acid (IAA) at 15 mg/L. This yielded a biomass production of 2.80 g/L, with a lipid content of 8.29 % in the biomass and a PUFA content of 32.41 % in total fatty acids (TFA). After bioremediation, the pollutants in HE were significantly removed, with nitrate removal at 93.79 %, ammonia removal at 81.21 %, phosphate removal at 89.94 %, and COD removal at 88.74 %. Furthermore, the nutritional indices of the obtained lipid indicated its potential applications in the pharmaceutical, nutraceutical, and functional food industries. Additionally, the lipid demonstrated promise as a future alternative to biodiesel feedstocks, exhibiting exceptional fuel properties that meet global biodiesel specifications. Overall, this study highlights the potential of Chlorella sp. G049 for recycling HE and recovering resources, thereby contributing to a wastewater-based circular bioeconomy.