The performance of Cu 2+ as dissolved cathodic electron-shuttle mediator for Cr 6+ reduction in the microbial fuel cell
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(2020) 30:19
RESEARCH
Sustainable Environment Research
Open Access
The performance of Cu2+ as dissolved cathodic electron-shuttle mediator for Cr6+ reduction in the microbial fuel cell Praveena Gangadharan1*
and Indumathi M. Nambi2
Abstract The study investigates the performance of Cu2+ as dissolved cathodic electron-shuttle mediator (dcESM) for simultaneous Cr6+ reduction and electricity generation in a microbial fuel cell (MFC) at pH 2 and 4 conditions. The dcESM behavior of Cu2+ on carbon cloth (CC) catalyzes the reduction of Cr6+ into Cr3+ at pH 2 by undergoing redox reactions. However, at pH 4, a simultaneous reduction of Cu2+ and Cr6+ was observed. Cyclic voltammetry studies were performed at pH 2 and 4 to probe the dcESM behavior of Cu2+ for Cr6+ reduction on CC electrode. Also, at pH 2, increasing the concentration of Cu2+ from 50 to 500 mg L− 1 favors the Cr6+ reduction by reducing the reaction time from 108 to 48 h and improving the current production from 3.9 to 6.2 mA m− 2, respectively. Nevertheless, at pH 4, the efficacy of Cr6+ reduction and electricity generation from MFC is decreased from 63 to 18% and 4.4 to 1.1 mA m− 2, respectively, by increasing the Cu2+ concentration from 50 to 500 mg L− 1. Furthermore, the performance of dcESM behavior of Cu2+ was explored on carbon felt (CF) and platinum (Pt) electrodes, and compare the results with CC. In MFC, at pH 2, with an initial concentration of 100 mg L− 1, the reduction of Cr6+ in 60 h is 9.6 mg L− 1 for CC, 0.2 mg L− 1 for CF, and 51.3 mg L− 1 for Pt cathodes. The reduction of Cr6+ (initial concentration of 100 mg L− 1) at pH 4 in 120 h is 44.7 mg L− 1 for CC, 32.1 mg L− 1 for CF, and 70.9 mg L− 1 for Pt cathodes. Maximum power densities of 1659, 1509, and 1284 mW m− 2 were achieved when CF, CC, and Pt, respectively were employed as cathodes in the MFC. Keywords: Microbial fuel cell (MFC), Heavy metal removal, Hexavalent chromium, Copper, Wastewater treatment, Bioelectricity generation
Introduction In recent years, hexavalent chromium (Cr6+) is exceedingly prevalent in various industrial effluents, and is often discharged from metallurgy, electroplating, leather tanning, and textile industries [1]. Cr6+ is a well-known mutagen, teratogen, and carcinogen [2]. The discharge of Cr6+ to the environment is of critical concern because: (i) of its non-biodegradable nature; (ii) it undergoes various transformations and forms toxic, carcinogenic compounds; and (iii) it is bioaccumulative [3]. The existing traditional * Correspondence: [email protected] 1 Department of Civil Engineering, Indian Institute of Technology Palakkad, Palakkad 678557, India Full list of author information is available at the end of the article
treatment techniques for the removal of Cr6+ are ion exchange, adsorption/biosorption, coagulation-flocculation, chemical precipitation, electrochemical method, biological reduction, and membrane filtration [4]. Although these techniques are highly promising, long-term applications are often hindered due to high operational/maint
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