TY - JOUR
T1 - Sustaining efficient production of aqueous iron during repeated operation of Fe(0)-electrocoagulation
AU - Müller, Simon
AU - Behrends, Thilo
AU - van Genuchten, Case M.
N1 - Funding Information:
We gratefully acknowledge funding provided by a NWO Veni Grant (Project No. 14400 ) awarded to CMvG. We would like to thank Peter Kraal, Alwina Hoving and Helen King for their support in the laboratory. We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities and we would like to thank Dipanjan Banerjee for assistance at the Dutch-Belgium beamline (BM-26a).
Publisher Copyright:
© 2018 The Author(s)
PY - 2019/5/15
Y1 - 2019/5/15
N2 - Iron-electrocoagulation is a promising contaminant (e.g. arsenic) removal technology that is based on electrochemical Fe(II) production from steel electrodes and subsequent transport of Fe(II) to the bulk solution, where contaminant removal occurs. Although Fe-electrocoagulation systems have been shown to effectively remove contaminants in extended field trials, the efficiency of field systems can be lower than in laboratory studies. One hypothesis for this disparity is that the Faradaic efficiency of short-term laboratory experiments is higher than field systems operated over extended periods. The Faradaic efficiency is a pivotal performance indicator that we define as the measured Fe dosage normalized by the theoretical Fe dosage calculated by Faraday's law. In this work, we investigated the Faradaic efficiency in laboratory experiments for up to 35 operating cycles (>2 months) with varied Fe(0) anode purity, charge dosage rate, and electrolyte composition. Our results showed that the Faradaic efficiency decreased continuously during repeated operation under typical field conditions (charge dosage rate = 4 C/L/min, synthetic groundwater) regardless of the Fe(0) anode purity, leading to a Faradaic efficiency ≈ 0.6 after 2 months. By contrast, increasing the charge dosage rate to ≥15 C/L/min produced a Faradaic efficiency >0.85 over the entire experiment for both Fe(0) anode purities. Electrolyte solutions free of oxyanions also resulted in sustained Faradaic efficiency >0.85, regardless of the charge dosage rate. Our results confirm a previously proposed relationship between low Faradaic efficiency and the formation of macroscopic electrode surface layers, which consist of Fe (oxyhydr)oxides on the anode and a mixture of Fe (oxyhydr)oxides and calcite on the cathode. Based on these results, we discuss potential strategies to maintain a high Faradaic efficiency during Fe-electrocoagulation field treatment.
AB - Iron-electrocoagulation is a promising contaminant (e.g. arsenic) removal technology that is based on electrochemical Fe(II) production from steel electrodes and subsequent transport of Fe(II) to the bulk solution, where contaminant removal occurs. Although Fe-electrocoagulation systems have been shown to effectively remove contaminants in extended field trials, the efficiency of field systems can be lower than in laboratory studies. One hypothesis for this disparity is that the Faradaic efficiency of short-term laboratory experiments is higher than field systems operated over extended periods. The Faradaic efficiency is a pivotal performance indicator that we define as the measured Fe dosage normalized by the theoretical Fe dosage calculated by Faraday's law. In this work, we investigated the Faradaic efficiency in laboratory experiments for up to 35 operating cycles (>2 months) with varied Fe(0) anode purity, charge dosage rate, and electrolyte composition. Our results showed that the Faradaic efficiency decreased continuously during repeated operation under typical field conditions (charge dosage rate = 4 C/L/min, synthetic groundwater) regardless of the Fe(0) anode purity, leading to a Faradaic efficiency ≈ 0.6 after 2 months. By contrast, increasing the charge dosage rate to ≥15 C/L/min produced a Faradaic efficiency >0.85 over the entire experiment for both Fe(0) anode purities. Electrolyte solutions free of oxyanions also resulted in sustained Faradaic efficiency >0.85, regardless of the charge dosage rate. Our results confirm a previously proposed relationship between low Faradaic efficiency and the formation of macroscopic electrode surface layers, which consist of Fe (oxyhydr)oxides on the anode and a mixture of Fe (oxyhydr)oxides and calcite on the cathode. Based on these results, we discuss potential strategies to maintain a high Faradaic efficiency during Fe-electrocoagulation field treatment.
KW - Charge dosage rate
KW - Faradaic efficiency
KW - Iron oxide minerals
KW - Iron-electrocoagulation
KW - Low cost water treatment
KW - Surface layer formation
UR - http://www.scopus.com/inward/record.url?scp=85062494458&partnerID=8YFLogxK
U2 - 10.1016/j.watres.2018.11.060
DO - 10.1016/j.watres.2018.11.060
M3 - Article
C2 - 30870635
AN - SCOPUS:85062494458
SN - 0043-1354
VL - 155
SP - 455
EP - 464
JO - Water Research
JF - Water Research
ER -