Performance and enhancement mechanism of corncob guiding chromium (VI) bioreduction.

Chromium-contaminated groundwater has drawn extensive attention due to its high toxicity and wide application. Although bioremediation is considered to be an effective approach for Cr(VI) removal, a better method is still urgently needed. In this study, corncob-guided Cr(VI) reduction achieved the highest removal efficiency due to the highest amount of total carbon and available carbon emissions. After verifying the sustainability and operational feasibility of this approach, the broad-spectrum applicability of corncob to guide Cr(VI) bioreduction was further explored under various operating conditions. In addition, it suggested that the carrier effect, nutrient element release and electron shuttle effect were the main mechanisms enhancing the reduction process, with approximate contribution rates of 12.5%, 7.5% and 75%, respectively. Microbiological analysis demonstrated that the addition of solid-phase carbon sources increased the abundance of microbes related to carbon metabolism and promoted the expression of glycolytic metabolic pathway. Furthermore, the addition of corncob led to an elevation of expression level of the electron transport pathway, which is consistent with the function of the electron shuttle. This study provides theoretical and technical support for the practical application of corncob-mediated Cr(VI) bioreduction.