PMo12 as a redox mediator for bio-reduction of Cr(VI): promotor or inhibitor?

As an efficient redox mediator, how phosphomolybdic acid (PMo12) affected bio-reduction of Cr(VI) was worthy of exploration. In this study, short-term and long-term effects of PMo12 on Cr(VI) reduction were investigated to reveal the relevant mechanism. The results showed that 0.50 mM PMo12 was optimum to improve the Cr(VI) reduction rate by 16.3% and microbial electron transport system activity (ETSA) by 43.0% in short-term (22 h) batch experiments. By contrast, in long-term (28 days) experiments, 0.50 mM PMo12 exhibited serious inhibition on Cr(VI) bio-reduction. The cumulative toxicity of PMo12, strong oxidative stress, the inhibition of extracellular polymeric substances production and the reduction of microbial activity were proved to be the main inhibition mechanism.