Comparing Different Strategies for Cr(VI) Bioremediation: Bioaugmentation, Biostimulation, and Bioenhancement

Unchecked releases of industrial waste, including chromium smelting slag (CSS), have resulted in disastrous effects on the environment for human use. Considering the problems of environment, efficiency, and sustainability, the present research was designed to evaluate the potential feasibility of Cr(VI) bioremediation by different strategies of natural attenuation (NA), bioaugmentation (BA), biostimulation (BS), and bioenhancement (BE). Results showed the BE was the best strategy for Cr(VI) removal and reached 86.2% in 84 days, followed by the BA, BS, and NA. The variation of Eh values indicated all systems translated the oxidation state into reduction continuously except for NA and BS during the bioremediation process. After bioremediation, the Tessier sequential extraction analyzed in the BE showed stable chromium levels up to 97%, followed by BA (89~93%), BS (75~78%), and NA (68%), respectively. Moreover, High-throughput sequencing was also used to assist in revealing the differences in microbial community structure between the different strategies. Stenotrophomonas, Ochrobactrum, and Azomonas, as the bioremediation microbes, were enriched in the BE in comparison with the others. This provided a new enhancement strategy for bioremediation microbes colonized in a new environment to achieve sustainable removal of Cr(VI).