Wastewater-based microalgal cultivation enables coupling environmental remediation with the production of sustainable, value-added biomass. In this study, Euglena gracilis was cultivated under non-axenic conditions in a 2% anaerobically digested livestock wastewater (LSWW)-based medium to enhance biomass accumulation, paramylon storage, and biodiesel precursor production, while simultaneously removing residual nitrogen and phosphorus. The LSWW medium was strongly phosphate-limited relative to ammoniacal nitrogen (N:P mass ratio ~39:1), which constrained growth. Adjustment of the N:P ratio to ~10:1 by NaH2PO4 supplementation, together with MgSO4·7H2O addition, significantly enhanced biomass production, whereas trace metals and CaCl2 provided minimal benefit. Cultivation at an initial pH of 3 resulted in substantially higher biomass accumulation than at pH 7 under xenic conditions. Under these optimized conditions, total phosphate and ammonia were efficiently removed, decreasing from 5.27 to 0.009 mg/L (99.8%) and from 57.40 to 2.11 mg/L (96.3%), respectively. Although paramylon accumulation was low in LSWW alone (~4% dry weight), short-term ethanol supplementation (0.095%, v/v, 24 h) enhanced paramylon content to ~20% dry weight. Subsequent anaerobic treatment further enhanced lipid conversion, increasing fatty acid methyl ester (FAME) content to ~45% dry weight. Collectively, low-pH non-axenic cultivation of E. gracilis in LSWW, combined with minimal nutrient supplementation, provides an integrated platform for enhanced biomass, paramylon, and biodiesel precursor production with efficient nutrient removal.
Kang et al. (Tue,) studied this question.