From Alga to Consortium: Advancing Petroleum Refinery Wastewater Biotreatment with Picocystis

Petroleum refinery stripped wastewater (SWW) is characterized by high concentrations of organic matter, hydrocarbons, and polyphenols, making its treatment challenging. Microalgae and microalgae-bacteria consortia represent sustainable alternatives to conventional physicochemical approaches, offering the combined benefits of pollutant removal and biofuel feedstock generation. In this study, the capacity of Picocystis sp. (Pico) alone and in consortium with aerobic bacteria (Pico-Bac) to remediate SWW was assessed in 2-L photobioreactors. Both systems supported algal growth in 10% and 25% SWW, with enhanced chlorophyll a content relative to controls. Notably, lipid accumulation in Picocystis biomass reached 55 mg/g dry weight after six days in 25% SWW, compared with only 9.5 mg/g in the control. Pollutant removal efficiency varied with treatment: Pico-Bac achieved maximum COD and polyphenol reductions of 72% and 96.4%, respectively, at 10% SWW, while hydrocarbon removal was highest (80.4%) at 25% SWW. In contrast, the greatest oil and grease removal (62.2%) occurred in the Pico monoculture at 25% SWW. Phytotoxicity assays of lipid- using Lepidium sativum seeds confirmed detoxification, as treated 25% SWW not only supported germination but also stimulated root elongation. To the best of our knowledge, this study provides the first evidence of the combined application of Picocystis sp. and an activated sludge bacterial consortium sourced from a municipal wastewater treatment plant for the remediation of refinery stripped wastewater (SWW). The results highlight a dual advantage: efficient pollutant reduction and production rich biomass, underscoring the potential of this eco-biotechnological process as an innovative route for sustainable wastewater management and biodiesel production.