Kristian L. Dubrawski

In-situ identification of iron electrocoagulation speciation and application for natural organic matter (NOM) removal.

In this work, iron speciation in electrocoagulation (EC) was studied to determine the impact of operating parameters on natural organic matter (NOM) removal from natural water. Two electrochemical EC parameters, current density (i) and charge loading rate (CLR), were investigated. Variation of these parameters led to a near unity current efficiency (φ = 0.957 ± 0.03), at any combination of i in a range of 1-25 mA/cm(2) and CLR in a range of 12-300 C/L/min. Higher i and CLR led to a higher bulk pH and limited the amount of dissolved oxygen (DO) reduced at the cathode surface due to mass transfer limitations. A low i (1 mA/cm(2)) and intermediate CLR (60 C/L/min) resulted in low bulk DO (<2.5 mg/L), where green rust (GR) was identified by in-situ Raman spectroscopy as the primary crystalline electrochemical product. Longer electrolysis times at higher i led to magnetite (Fe3O4) formation. Both higher (300 C/L/min) and lower (12 C/L/min) CLR values led to increased DO and/or increased pH, with lepidocrocite (γ-FeOOH) as the only crystalline species observed. The NOM removal of the three identified species was compared, with conditions leading to GR formation showing the greatest dissolved organic carbon removal, and highest removal of the low apparent molecular weight (<550 Da) chromophoric NOM fraction, determined by high performance size exclusion chromatography.

Production and transformation of mixed-valent nanoparticles generated by Fe(0) electrocoagulation.

Mixed-valent iron nanoparticles (NP) generated electrochemically by Fe(0) electrocoagulation (EC) show promise for on-demand industrial and drinking water treatment in engineered systems. This work applies multiple characterization techniques (in situ Raman spectroscopy, XRD, SEM, and cryo-TEM) to investigate the formation and persistence of magnetite and green rust (GR) NP phases produced via the Fe(0) EC process. Current density and background electrolyte composition were examined in a controlled anaerobic system to determine the initial Fe phases generated as well as transformation products with aging. Fe phases were characterized in an aerobic EC system with both simple model electrolytes and real groundwater to investigate the formation and aging of Fe phases produced in a system representing treatment of arsenic-contaminated ground waters in South Asia. Two central pathways for magnetite production via Fe(0) EC were identified: (i) as a primary product (formation within seconds when DO absent, no intermediates detected) and (ii) as a transformation product of GR (from minutes to days depending on pH, electrolyte composition, and aging conditions). This study provides a better understanding of the formation conditions of magnetite, GR, and ferric (oxyhydr)oxides in Fe EC, which is essential for process optimization for varying source waters.

Metal type and natural organic matter source for direct filtration electrocoagulation of drinking water.

Electrocoagulation (EC) was combined with immediate microfiltration as direct filtration electrocoagulation (DFEC) for dissolved organic carbon (DOC) removal in drinking water from synthetic and natural highly natural organic matter (NOM) impacted waters from three different sources: Suwannee River (Georgia, USA DOC(0)=13.79 mg/L), Nordic Reservoir (Vallsjøen, Norway DOC(0)=9.03 mg/L), and a natural source (Lost Lagoon, Vancouver, Canada DOC(0)=13.31 mg/L). Three anode materials were investigated: iron, aluminum, and zinc, in a batch EC process without rapid mixing, flocculation, or settling. Fifteen seconds of process time with the iron electrode (36 mg Fe/L) led to DOC removal of 44%. After 1 min of process time, DOC reduction was 65% (zinc)-73 (iron)%, with ~ 85% reduction (all metals) in UV-abs-254 (UV-abs-254 final=0.06 cm(-1)) for Suwannee NOM. Specific UV absorbance (SUVA-L/mgm) values decreased from 3.1 to 4.2 to under 2.0, indicating removal of high MW fractions of NOM. High performance size exclusion chromatography (HPSEC) fractionation supported SUVA results, showing reductions from 76% of DOC>1450 Da to approximately 40% after EC for all metals and Suwannee NOM. EC performed equally well for two different initial DOC concentrations of 13.79 and 21.59 mg/L DOC, showing 75% DOC and 89% UV-abs-254 reductions.