Bio-reduction and synchronous removal of hexavalent chromium from aqueous solutions using novel microbial cell/algal-derived biochar particles: Turning an environmental problem into an opportunity

In China, Dolichospermum flos-aquae is one of the most prevalent bloom-forming cyanobacteria and thus a major challenge for the concerned catchment area. To solve this problem and turn it into an opportunity for heavy metal remediation, we investigated the potential of D. flos-aquae for production algal biochar, and constructed a microbe-algal biochar composite. The microbe-biochar composite (biochar immobilized Proteus mirabilis PC801) showed superior hexavalent chromium removal capacity. It produced 100% Cr(VI) (150 mg/L) removal efficiency, with 87.7% total Cr immobilized in/on the particles and only 12.3% Cr(III) left in solution. Furthermore, Scanning electron microscopy-energy dispersive spectroscopy and antioxidase activity results showed that Cr(VI) reduction mainly occurred outside the cells, and the biochar can effectively protect P. mirabilis YC801 from the direct toxicity of chromium, thereby promoting the removal efficiency. Overall, this study provides a promising approach by utilizing this harmful algae for the bio-remediation of Cr(VI)-contaminated groundwater in practical application.