Estimating Dosing Rates and Energy Consumption for Electrocoagulation Using Iron and Aluminum Electrodes

Abstract

The effect of current density on dosing rates and energy requirements for iron and aluminum electrodes in a bench-scale electrocoagulation (EC) reactor have been investigated. Dissolution rates of the iron and aluminum anodes were independent of bulk solution pH values. Iron dosing rates followed Faraday's law, but aluminum dosing rates averaged 83% greater than those predicted by Faraday's law. Chemical corrosion of both the anode and cathode contributed to the extra-faradaic aluminum dosing. A method was developed to determine the faradaic power consumption as a function of the current density. An equation describing power dissipation by ohmic and faradaic mechanisms was derived and used to estimate energy consumption per unit coagulant dose for EC reactors operating over a wide range of conditions. The derived equation can be used to compare the operational costs for EC with those using chemical additives, such as alum or ferric chloride.

Arsenic removal from groundwater using iron electrocoagulation: Effect of charge dosage rate

“…The exact electricity consumption depends on the final device design, including electrode spacing, electrode plate area, resistivity of the source water, and operating current among other factors. [40] These cost estimates use the 100L reactor configuration which was shown to remediate real contaminated groundwater with initial concentrations of ~ 300µg/L As[III] to levels below the WHO-MCL. In both real and SBGW water matrices, the total cell voltage in the 100L prototype did not exceed 3.0V.…”

Laboratory and pilot testing of electrocoagulation for removing scale-forming species from industrial process waters

“…The abscissa is expressed both in terms of charge loading in Coulombs per L (C/L) and mmol/L of iron (mM-Fe). The Faradaic relationship between coagulant dose and charge loading was verified in a previous investigation (Gu et al, 2009) and can be expressed as:…”

“…NonFaradaic dosing results from chemical dissolution of the aluminum cathodes in the high pH solutions produced by reduction reactions on the cathode surface. Aluminum dosing as a function of charge loading in the bench reactor was determined in a previous investigation to be 1.8 times that given by Faraday's law (Gu et al, 2009). The Al 3+ dose in the bench unit can therefore be calculated from the charge loading using equation 1 with z = 3 mol e -per 1.8 mol Al 3+ or z=3÷1.8= 1.67.…”

“…Additionally, the overall process has a minimal impact on the solution pH value, since the acid formed by the formation and precipitation of Al(OH) 3 or Fe(OH) 3 is removed by the cathodic reactions of oxygen reduction or hydrogen gas evolution. In contrast, chemical coagulants result in the net production of H 2 SO 4 or HCl (Gu et al, 2009). EC units are mechanically simple devices, and in many common industrial applications, inexpensive to run, costing no more than a few dollars per thousand gallons of water treated (Lin et al, 2005;Gu et al, 2009).…”

“…In contrast, chemical coagulants result in the net production of H 2 SO 4 or HCl (Gu et al, 2009). EC units are mechanically simple devices, and in many common industrial applications, inexpensive to run, costing no more than a few dollars per thousand gallons of water treated (Lin et al, 2005;Gu et al, 2009). Current reviews of EC (Chen, 2004;Mollah et al, 2004;Holt et al, 2005) cover the many uses of the technology, which include the removal of organic compounds (Laridi et al, 2005;Lin et al, 2005;Can et al, 2006;Soltanali and Shams Haghani, 2008), metal ions (Adhoum et al, 2004;Kumar et al, 2004;Gao et al, 2005;Abdel-Ghani and El-Chaghaby, 2007), colloidal abrasive particles (Den and Huang, 2006), phosphate (Bektas et al, 2004;Akpor et al, 2007) and viruses (Zhu et al, 2005).…”