Elsevier

Chemical Engineering Journal

Volume 357, 1 February 2019, Pages 633-640
Chemical Engineering Journal

Electrostimulated bio-dechlorination of trichloroethene by potential regulation: Kinetics, microbial community structure and function

https://doi.org/10.1016/j.cej.2018.09.191Get rights and content

Highlights

  • Microbial community structure and function varied with cathodic potentials.

  • Highest trichloroethylene dechlorination rate was observed at potential of −0.26 V.

  • Cis-1,2-dichloroethene and ethene were major and minor metabolites, respectively.

  • Dehalorespiring electroactive genera were highly enriched as potential decreasing.

  • Promoted expression of functional genes by suitable potential regulation.

Abstract

Bioelectrochemical system with biocatalyzed cathode is regarded as a promising approach for the enhanced bio-dechlorination of chlorinated aliphatic hydrocarbons (CAHs). However, the microbial community structure variation law and the corresponding function in the cathodic biofilm in response to the different cathode potentials remain poorly understood. In this study, biocathode systems were established for trichloroethene dechlorination under four cathode potentials (−0.06, −0.26, −0.46 and −0.66 V vs standard hydrogen electrode). About 2.6–4.3 times higher dechlorination rates were obtained in biocathodes than opened circuit, verifying the efficient electrostimulated bio-dechlorination. The highest trichloroethene dechlorination rate (1.01 mmol/L·d) was observed at −0.26 V, while higher (−0.06 V) or lower potentials (−0.46/−0.66 V) resulted in the 7.2–48.9% lower dechlorination rates. Under the different cathode potentials, the similar TCE dechlorination pathway was observed with cis-1,2-dichloroethene and ethene as the major and minor dechlorination products, respectively. The correlation and sharing network analysis of bacterial community illustrated that the negative potentials facilitated the enrichment of cathode-utilizing and dechlorination populations. The highest abundance of electroactive and dechlorinating bacteria (Lactococcus, Bacillus and Pseudomonas) and the highest expression of reductive dehalogenase (pceA and tceA) were observed at −0.26 V. The expression of extracellular electron transfer related gene omcX was promoted as the potential decreased. The decreased dechlorination capacity at potentials of −0.46 and −0.66 V could possibly be attributed to the lack of H2-utilizing dechlorinators and the low expressed pceA. This study offers insights into the molecular mechanism involved in the electrostimulated bio-dechlorination of CAHs by potential regulation.

Introduction

Trichloroethene (TCE), a typical representative of chlorinated aliphatic hydrocarbons (CAHs), is among the most ubiquitous and persistent organic pollutants found in groundwater and aquifers [1]. TCE is carcinogenic to humans by all routes of exposure and poses a potential human health hazard for noncancer toxicity [2]. Bioremediation via anaerobic dechlorination is regarded as an economic and environmental-friendly approach for the treatment of groundwater contaminated CAHs [3]. The approach relies on organohalide-respiring bacteria, which use CAHs as a terminal electron acceptor for respiration and metabolism, with less/none halogenated hydrocarbons sequentially generated as end products [4]. For either ex situ bioreactors or in situ bioremediation sites, the mostly applied electron donors are organic substrates which release H2 upon fermentation [5], [6]. However, a number of drawbacks were frequently emerged, including the competition of electrons between dechlorination and competing metabolisms, accumulation of undesirable toxic by-products, and the poor control of dechlorination process [7].

Recently, bioelectrochemical systems (BESs) have been developed for the accelerated reduction of various refractory organic pollutants including nitroaromatics, halogenated aromatics, azo dyes and etc. [8], [9], [10], [11]. As far, several biocathode BESs have been established for CAHs dechlorination by acclimating Geobacter, Dehalococcoides or the highly enriched dechlorination consortia [12], [13], [14], [15], [16], [17], [18]. In view of application perspective, it is very difficult to consider dechlorinating isolates or consortia since most of them possess either narrow ecological niches or strict nutrients/redox potential demands [4], [19], [20]. In principle, biocathode systems can manipulate the redox potential to create the favorable environment for biodechlorination either through the direct electron transfer from electrode surface or via the intermediate electrolytic generation of H2 [21]. It has been demonstrated that electron transfer pathway between electrode and microorganism partially relied on the applied cathode potential [22], [23], [24]. The rate and extent of CAH dechlorination, as well as the competition for available electrons, are also highly dependent on the set cathode potential [17], [22], [25]. Aulenta et al. revealed about 3.7 times higher TCE dechlorination rate was obtained as cathode potential decreased from −0.25 to −0.45 V, however, over 60% of electric current would be consumed for the other microbial metabolisms (like methanogenesis) with the potential of −0.45 V [22]. Sáez et al. found a current density under 4 mA cm−2 was sufficient enough for the reasonable PCE conversion rate (>85%) and degradation efficiency (>65%) on the lead-made cathode [25]. These studies demonstrated that the regulation of cathode potential was as an essential element for optimizing the electrostimulated CAHs dechlorination. It is known that the formation of an effective cathode biofilm is vital for the dechlorination performance of a biocathode [14], [23], [26]. By supplying the different negative potentials during the acclimation of anaerobic sludge, the microbial community structure and composition in the cathodic biofilm would vary and further influence the dechlorination capacities and characteristics. However, as far, the microbial community structure variation laws and the cooperative relationship of functional populations in response to the different cathode potential settings, as well as the related dechlorination functions and characteristics (efficiency, kinetics and metabolites) remain poorly understood.

In this study, biocathode systems were established for TCE dechlorination through acclimatization with anaerobic sludge given four different constant cathode potential settings (−0.06 V, −0.26 V, −0.46 V and −0.66 V vs standard hydrogen electrode, SHE). The dechlorination feasibility, characteristics and functional communities were investigated thoroughly under the different cathode potentials. Objectives of this study were to reveal whether and how potential regulation affects microbial community structure and function in cathodic biofilm as well as the influence law on TCE dechlorination rate and metabolic pathway, through a comprehensive microbial analysis conducted at molecular and genetic expression levels.

Section snippets

System construction

A schematic diagram of the bioelectrochemical reactors employed in this study is shown in Fig. S1. The reactors consisted of two equally sized cylindrical borosilicate glass chambers (4 cm in diameter and 8 cm in length with an effective volume of 80 mL) and separated by cation exchange membranes (CEM, Ultrex CMI-7000, Membranes International, Ringwood, NJ, U.S.). The two chambers were fixed together with an aluminum clamp and rubber seal, ensuring airtightness. Graphite fiber brushes (both

Cathode potential regulated dechlorination activities

After inoculation with anaerobic sludge for approximately 60 days, taking conditions with a set potential of −0.26 V as an example, the E24h for TCE approached over 90% in the seven successive cycles (Fig. S2); correspondingly, currents underwent the similar trends in different cycles, starting at the relatively high levels (0.16–0.16 mA) and dropping to less than 0.05 mA after 24 h. The similar current variation trend and the efficient TCE dechlorination capacity were observed under the

Conclusions

The variation of cathodic potential settings gave rise to the significant change in bacterial community structure and trichloroethene dechlorination function in constructed biocathodes. The optimal trichloroethene dechlorination capacity was found at a cathode potential of −0.26 V (dechlorination rate of 1.01 mmol/L·d), which was about 4.3 times higher than the opened circuit. The higher (−0.06 V) or lower potentials (−0.46 and −0.66 V) resulted in the decreased dechlorination capacities, but

Acknowledgments

This research was supported by National Natural Science Foundation of China (No. 31400104, No. 21577162), by Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (No. ES201806), by Special Financial Grant from China Postdoctoral Science Foundation (2015T80359), by Natural Science Foundation of Heilongjiang Province China (No. C2018035).

References (51)

  • M. Rosenbaum et al.

    Cathodes as electron donors for microbial metabolism: which extracellular electron transfer mechanisms are involved ?

    Bioresour. Technol.

    (2011)
  • A. Di Battista et al.

    CARD-FISH analysis of a TCE-dechlorinating biocathode operated at different set potentials

    New Biotech.

    (2012)
  • H. Wang et al.

    Bioelectrochemical system platform for sustainable environmental remediation and energy generation

    Biotechnol. Adv.

    (2015)
  • Z. Li et al.

    Mass balance and kinetic analysis of anaerobic microbial dechlorination of pentachlorophenol in a continuous flow column

    J. Biosci. Bioeng.

    (2010)
  • F. Chen et al.

    Henry’s law constants of chlorinated solvents at elevated temperatures

    Chemosphere

    (2012)
  • F. Chen et al.

    Effects of different carbon substrates on performance, microbiome community structure and function for bioelectrochemical-stimulated dechlorination of tetrachloroethylene

    Chem. Eng. J.

    (2018)
  • V. Sáez et al.

    Electrochemical degradation of perchloroethylene in aqueous media: an approach to different strategies

    Water Res.

    (2009)
  • J. Ding et al.

    Electroreduction of nitrate in water: role of cathode and cell configuration

    Chem. Eng. J.

    (2015)
  • D. Kong et al.

    Electrochemical degradation of nitrofurans furazolidone by cathode: characterization, pathway and antibacterial activity analysis

    Chem. Eng. J.

    (2015)
  • B. Liang et al.

    Microbial community structure and function of nitrobenzene reduction biocathode in response to carbon source switchover

    Water Res.

    (2014)
  • P.J. Haest et al.

    Dechlorination kinetics of TCE at toxic TCE concentrations: assessment of different models

    Water Res.

    (2010)
  • S. Freguia et al.

    Lactococcus lactis catalyses electricity generation at microbial fuel cell anodes via excretion of a soluble quinone

    Bioelectrochemistry

    (2009)
  • H. Hassan et al.

    Chemical impact of catholytes on Bacillus subtilis-catalysed microbial fuel cell performance for degrading 2,4-dichlorophenol

    Chem. Eng. J.

    (2016)
  • Y.-C. Yong et al.

    Bioelectricity enhancement via overexpression of quorum sensing system in Pseudomonas aeruginosa-inoculated microbial fuel cells

    Biosens. Bioelectron.

    (2011)
  • O. Scialdone et al.

    Abatement of 1,1,2,2-tetrachloroethane in water by reduction at silver cathode and oxidation at boron doped diamond anode in micro reactors

    Chem. Eng. J.

    (2012)
  • Cited by (53)

    View all citing articles on Scopus
    View full text