The critical utilization of active heterotrophic microalgae for bioremoval of Cr(VI) in organics co-contaminated wastewater

Considering the importance of removing toxic Cr(VI) from practical wastewater containing complex pollutants, this study presented for the first time the utilization of the live heterotrophic microalgae (Botryocossuss sp. NJD-1) to achieve a concurrent abatement of Cr(VI), TOC, NO3-N and PO4-P, through a comprehensive biochemical process. The experimental results showed that the Cr(VI) removal efficiencies in the culture with different types of organic descended in the order of sodium acetate, ethanol and methanol. The highest removal efficiencies were achieved as 94.2%, 98.2%, 66.9% and 99.2% for Cr(VI), TOC, NO3-N and PO4-P, respectively, in the culture with 5 mg L−1 Cr(VI) and sodium acetate of equivalent to 2.92 g C L−1. Through mass balance calculation and characterization, the fate of Cr(VI) and Cr(III) was tracked and quantified in the culture system, which indicates that 87.17% of initial Cr(VI) were reduced to Cr(III) and then adsorbed in algal biomass for the optimal removal case. Consequently, the mechanism demonstrating the correlation among the removal process of Cr(VI), the biological activity of microalgae and the effect of organic compounds was proposed. [Display omitted] •Heterotrophic microalgae was applicable towards Cr(VI) removal in org-C wastewater.•Org-C type and concentration affected Cr(VI) removal and microalgae growth.•Simultaneous removal of Cr(VI), TOC, N, P were up to 94.2%, 98.2%, 66.9%, 99.2%.•Fate of Cr(VI) was assessed after mass balance calculation and characterization.•Mechanism to remove Cr(VI) and org-C by live heterotrophic microalgae was proposed.