Standardizing electrocoagulation reactor design: Iron electrodes for NOM removal

A novel systematic approach for reactor design was described for iron electrocoagulation (EC) and applied to drinking water treatment. Suwannee NOM was used as a model compound; performance was quantified by UV-abs-254 and DOC removal. Significant EC design variables were identified and examined: current density (i) (2.43–26.8 mA cm−2), coagulant or charge loading rate (CLR) (100–1000 C L−1 min−1), and flocculation methodology (“fast” and “slow”). A correlation was found between increased i and decreased current efficiency (φ), optimum NOM removal was found at i ∼10 mA cm−2. A lower CLR showed greater total DOC removal, while a higher CLR led to less reactor residence time and required either longer flocculation times or greater coagulant dose for similar NOM removal. This paper defines and describes the four general EC “classes” of operation that have implications on several important measures of success: coagulant dose, electrical consumption, process speed, volumetric footprint, and post-EC flocculation requirements. Two classes were further examined with or without pH adjustment for DOC removal, showing that a “fast” EC mode without flocculation is more appropriate for smaller applications, while a “slow” EC mode is more effective for large permanent applications, where flocculation and settling can reduce coagulant and electrical consumption. The effect of pH adjustment showed greater impact with the “fast” dosing mode than with the “slow” mode, adjustment to pH 6 with the “fast” mode gave 13.8% and 29.1% greater DOC and UV-abs-254 removal, respectively, compared to the baseline without pH adjustment.

► Natural organic matter successfully reduced >50% DOC with iron EC. ► Quantitative comparison of operating conditions led to reactor optimization. ► Defined four EC classes of operation, establishing precedent in reactor design. ► “Fast” EC appropriate for small applications, “Slow” EC for large applications.