ALGAE-INTEGRATED PROCESS FOR RESOURCE RECOVERY, METABOLITE PRODUCTION, AND RECYCLING OF REVERSE OSMOSIS REJECT

Abstract

This study unveiled the usability of reject generated from a drinking water RO plant for algal biomass and valuable metabolite production. Initially, the RO reject collected from the domestic RO unit (ROR1), and commercial RO plants (ROR2) were investigated for algae (Chlorella pyrenoidosa) cultivation. The initial assessments revealed that the addition of some amount of BG11 (0-100%) into ROR significantly enhances biomass growth and improves the biochemical composition of C. pyrenoidosa. Notably, 25% BG11 supplementation in ROR1 increased biomass by 29.52%. Additionally, lipid content in C. pyrenoidosa grown on 50% ROR1 was nearly double that of the BG11 (positive control). RORs from various locations were further examined for algal cultivation, demonstrating the robustness of the proposed approach. A diverse range of algal strains, including C. pyrenoidosa, Scenedesmus obliquus, Chlorella sorokiniana, Scenedesmus sp., and native strains, were successfully cultivated in ROR. The highest biomass productivity for S. obliquus and the native isolate was achieved in 50% ROR, while C. sorokiniana and Scenedesmus sp. exhibited the highest lipid productivities (19.37 ± 1.04 and 18.49 ± 0.0 mg L-1 d-1, respectively) in the same medium. Furthermore, the algae demonstrated efficient nutrient removal capabilities, achieving up to 77.59% nitrate, 82.71% phosphorus, and 79.69-95.89% total dissolved solids (TDS) removal from the ROR-based growth media. Species-specific responses were observed with varying bicarbonate concentrations (0-4 g L-1) in the ROR. C. pyrenoidosa exhibited the highest biomass growth (760.81±34.24 mg L-1) at 4.0 g L-1 bicarbonate, while Scenedesmus sp. showed the maximum biomass yield (1041.81±33.32 mg L-1) in ROR without bicarbonate. Interestingly, bicarbonate in ROR promoted biofuel precursor synthesis. S. obliquus and C. sorokiniana acquired maximum carbohydrate and lipid yields at 0.5 and 1.0 g L-1 bicarbonate, respectively. Fatty acid methyl ester (FAME) analysis revealed improved biodiesel quality for C. sorokiniana, while C. pyrenoidosa was found to be rich in polyunsaturated fatty acids (PUFA). Theoretical methane potential (TMP) analyses additionally indicated enhanced biogas yield in ROR supplemented with bicarbonate.