Assessment upon heterotrophic microalgae screened from wastewater microbiota for concurrent pollutants removal and biofuel production

•Culturing native strain is a strategy to overcome wastewater sterilization problem.•20 heterotrophic microalgae were isolated from domestic wastewater microbe matrix.•Isolates worked better in untreated original domestic wastewater than autoclaved.•A selection index was proposed to assess biofuel, water treatment and settlability.•Botryococcus sp. NJD-1 was good at concurrent lipid production and C/N/P removal.

Heterotrophic microalgae, capable of converting organic carbons to biofuel, as well as assimilating nutrients, have a great prospective in wastewater treatment. Meanwhile, the knowledge about heterotrophic microalgae is still far less than the autotrophic conterpart. Hence, in this study, 20 heterotrophic microalgal strains were isolated from a domestic wastewater treatment plant, and identified according to morphology and partial 18S and 23S rRNA gene sequences. Further, their biological traits were assessed in terms of N, P, TOC removal efficiencies, growth parameters, self-settleability and lipids production, expressed through a comprehensive selection index. By such, the optimal strains were chosen and applied back to treat the real wastewater, with or without pretreatment of sterilization. An organic-adaptable strain, i.e., Botryococcus sp. NJD-1, was ultimately recommended to achieve the concurrent biofuel production (up to 61.7% lipid content) and pollutants removal (up to 64.5%, 89.8% and 67.9% for N, P and TOC) in pristine wastewater.

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