Removal of Soluble Phosphorus from Surface Water Using Iron (Fe–Fe) and Aluminum (Al–Al) Electrodes

Abstract

The removal of soluble phosphorus using iron and aluminum electrodes was studied in water samples from the Red River, a hyper-eutrophic stream in Winnipeg, Canada. Four trials were conducted: (I) mixed batch with 150-900 mA applied for 1 min to 1 L, (II) stagnant batch with 600-900 mA applied for 1 min to 1 L, and (III and IV) continuously stirred-tank reactor with 6.25-10 min hydraulic retention times and constant 900 mA. Maximum soluble phosphorus removals of 70-80% were observed in mixed batch, and there was no significant difference between aluminum and iron electrodes (P value of 0.0526-0.9487). Aluminum electrodes performed significantly worse than iron electrodes under higher hydraulic loads, with iron removing >70% soluble phosphorus and aluminum <40% (P values of 0.0035-0.0143). The estimated cost of consumables, reported per million liters of water treated, to remove 70% soluble phosphorus from eutrophic waters with 0.35 g m soluble phosphorus would include 5-17.5 USD electricity costs and material costs of 5.3-12.2 USD for iron and 39.2 USD for aluminum.

One-Step Treatment of Phosphite-Laden Wastewater: A Single Electrochemical Reactor Integrating Superoxide Radical-Induced Oxidation and Electrocoagulation

“…The in-situ release of Fe 2+ at the Fe anode is a fast step, which guarantees the availability of Fe for the subsequent formation of coagulants; the amount of Fe 2+ generated is decisively determined by the extent of the current applied to the Fe anode. The production of OH – at the stainless-steel cathode continuously supplies alkalinity, which leads to the formation of Fe­(II) hydroxides under anoxic conditions and Fe­(III) hydroxides under oxic conditions; the type of Fe hydroxides formed is highly dependent on the concentration of DO in the aqueous solution. ,, The in-situ generation of O 2 from the MMO anode significantly improves the fraction of Fe­(III) precipitates in the solid phase. More importantly, the O 2 produced in situ can react with Fe­(II), resulting in the formation of • O 2 – , a predominant reactive species that immediately leads to the oxidation of phosphite to phosphate. , Then phosphate is entrapped in the amorphous Fe­(III) precipitates by adsorption and coprecipitation .…”

“…The production of OH − at the stainless-steel cathode continuously supplies alkalinity, which leads to the formation of Fe(II) hydroxides under anoxic conditions and Fe(III) hydroxides under oxic conditions; the type of Fe hydroxides formed is highly dependent on the concentration of DO in the aqueous solution. 18,32,43 The in-situ generation of O 2 from the MMO anode significantly improves the fraction of Fe(III) precipitates in the solid phase. More importantly, the O 2 produced in situ can react with Fe(II), resulting in the formation of • O 2 − , a predominant reactive species that immediately leads to the oxidation of phosphite to phosphate.…”

Phosphorus Recovery from Eutrophic Lake Water Using Al/Fe Micro-Electrolysis

“…The products of Fe/Al electrolysis are mainly amorphous colloidal hydroxides (Figure S3), which have the potential to net small flocs and bridge them into large ones. − Moreover, dissolved P can be harvested by Fe/Al ion precipitation and adsorption on the surface of colloidal Fe/Al hydroxides. During electrolysis, Al and Fe ions were also generated from Al/Fe electrodes, which could precipitate phosphates (AlPO 4 or FePO 4 ). , Thus, the concentrations of DOP and DIP showed a remarkable decrease (Figure A). During P harvesting, an unexpected increase in PP was observed initially (Figure B), which could be attributed to the adsorption and concentration of dissolved P on the flocs by Fe/Al hydroxides.…”

“…During electrolysis, Al and Fe ions were also generated from Al/Fe electrodes, which could precipitate phosphates (AlPO 4 or FePO 4 ). 18,19 Thus, the concentrations of DOP and DIP showed a remarkable decrease (Figure 2A). During P harvesting, an unexpected increase in PP was observed initially (Figure 2B), which could be attributed to the adsorption and concentration of dissolved P on the flocs by Fe/Al hydroxides.…”

“…Iron/aluminum (Fe/Al) micro-electrolysis can generate Fe/Al ions and positively charged colloidal hydroxides, which can precipitate, adsorb, or flocculate dissolved and particulate matters. − With its advantages of low cost, high efficiency, and easy operation, Fe/Al micro-electrolysis has been widely applied to concentrate and harvest high-value resources from wastewater. − For instance, Fe micro-electrolysis was used to recover rare-earth elements from wastewater . In eutrophic lake water, P exists in both dissolved and particulate forms after uptaking by microalgae or absorption by particles .…”