Promotion of Para-Chlorophenol Reduction and Extracellular Electron Transfer in an Anaerobic System at the Presence of Iron-Oxides.

Xinbai Jiang,Xiuyun Sun,Changjin Ou,Xiaodong Liu,Jiansheng Li,Weiqing Han,Yuzhe Chen,Jinyou Shen,Lianjun Wang,Chen Hou

doi:10.3389/fmicb.2018.02052

Abstract

Anaerobic dechlorination of chlorophenols often subjects to their toxicity and recalcitrance, presenting low loading rate and poor degradation efficiency. In this study, in order to accelerate p-chlorophenol (p-CP) reduction and extracellular electron transfer in an anaerobic system, three iron-oxide nanoparticles, namely hematite, magnetite and ferrihydrite, were coupled into an anaerobic system, with the performance and underlying role of iron-oxide nanoparticles elucidated. The reductive dechlorination of p-CP was notably improved in the anaerobic systems coupled by hematite and magnetite, although ferrihydrite did not plays a positive role. Enhanced dechlorination of p-CP in hematite or magnetite coupled anaerobic system was linked to the obvious accumulation of acetate, lower oxidation–reduction potential and pH, which were beneficial for reductive dechlorination. Electron transfer could be enhanced by Fe2+/Fe3+ redox couple on the iron oxides surface formed through dissimilatory iron-reduction. This study demonstrated that the coupling of iron-oxide nanoparticles such as hematite and magnetite could be a promising alternative to the conventional anaerobic reduction process for the removal of CPs from wastewater.

Highlights

As one class of the most important raw materials and intermediates, chlorophenols (CPs) are widely used in many industries such as wood preservers, dyes, drugs, and herbicides (Van Aken et al, 2015)
In the biodegradation system coupled with ferrihydrite, the concentrations of residual p-CP were always higher than those in the biotic control system at all incubation time. p-CP removal was ignorable in ironoxides adsorption control groups, suggesting that p-CP removal through adsorption by hematite, magnetite, and ferrihydrite was insignificant under iron-oxide nanoparticle dosage of 100 mg/L
Less than 10% of p-CP could be removed in the biomass adsorption control group within 25 h, indicating insignificant adsorption of p-CP by biomass inoculated in the biodegradation system

Summary

Introduction

As one class of the most important raw materials and intermediates, chlorophenols (CPs) are widely used in many industries such as wood preservers, dyes, drugs, and herbicides (Van Aken et al, 2015). Improper management of industrial wastes, accidental spills, and liberal use of pesticides in crops have resulted in the prevalence of CPs in natural waters and soil (Garbou et al, 2017). There is an urgent need to remediate sites polluted by CPs, in order to prevent their further risk to ecosystems. Due to the pronounced electron-withdrawing character of chlorine substituent group, CPs harbor a highly electron deficient π-electron system on benzene ring. CPs are subject to initial reductive transformation, i.e., dechlorination,

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