Enhanced removal of p-fluoronitrobenzene using bioelectrochemical system

• Significantly Enhanced p-FNB removal was achieved in a bioelectrochemical system.
• Bioelectrocatalysis reduced the critical voltage for defluorination.
• Bioelectrocatalytic mechanisms for p-FNB degradation and defluorination were discussed.

p-Fluoronitrobenzene (p-FNB) tends to accumulate in industrial effluents because of its recalcitrant properties. Approaches to the removal of p-FNB always encounter conflicts between treatment efficiency and economic efficiency. A bioelectrochemical system (BES) was established to facilitate the removal and mineralization of p-FNB. The treatment cost was reduced by using inexpensive electrode materials and reducing the electrical energy used. p-FNB was effectively removed using the BES, and the reaction rate was higher than the sum of the rates of two control systems, i.e., a biological system (BS) and an electrocatalytic system (ECS), by a maximum of 62.9% under a voltage of 1.4 V. The voltage is a crucial kinetic factor for the BES performance; as the voltage increased from 0 to 1.4 V, the reaction rate constants for p-FNB removal and defluorination increased from 0.0520 to 0.1811 h−1 and 0 to 0.0107 h−1. The synergistic effect of multistrains gave a TOC removal efficiency in the BES of about 34.05%, yet the removal efficiencies were low for the two control. The defluorination reaction rate was significantly slower than the p-FNB removal rate, which indicated that defluorination lagged p-FNB removal, and p-FNB transformation to p-fluoroaniline (p-FA) was the fastest step. The electrochemical assistance provided electrons and accelerated the electron transfer rate in the microbial reduction of p-FNB to p-FA. In this study, the critical voltage for defluorination in the BES was 0.8 V, which was approximately 0.2 V lower than that in the ECS. The decrease in the critical voltage for defluorination was based on the production of p-FA, which is more electrocatalytically activated. These results demonstrate the mechanism of efficient p-FNB removal and mineralization in a BES.

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