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In this work, we report experimental studies on the disinfection of irrigation water using a flow cell assembled with low-cost graphite plates as both anode and cathode. Natural irrigation waters collected from two irrigation locations (Reservoir 225 and Bott Well Pond) in Hawaii were used, and synthetic irrigation waters were prepared based on the chemical analysis of natural irrigation waters. The concentration of chloride was 10.2 mg/L in the synthetic Reservoir 225 water and 6.9 mg/L in the synthetic Bott Well pond water. Escherichia coli K12 ER2738 was selected as a model bacterium to evaluate the disinfection capability of the flow cell. Experiments performed in the synthetic irrigation waters showed that E. coli was inactivated by free chlorine species electro-generated from oxidation of chloride ions at the graphite anode. Complete removal of E. coli was achieved within 10 min in the synthetic irrigation waters. The disinfection of the natural irrigation waters took about four times longer than the disinfection of the synthetic irrigation waters. This result is most likely due to the presence of organic matter (and possibly other oxidizable species) in the natural irrigation waters. © 2020 Water Environment Federation • Practitioner points • Electrochemical flow cell disinfects to 99.9% with commercial graphite electrodes. • E. coli is removed in 10 min from synthetic irrigation water by a flow cell. • E. coli removal takes 4× longer in natural irrigation water. • A minimum current density of ≥1 mA/cm 2 is required for disinfection. • The primary disinfection mechanism is through chlorine generated from chloride ions.

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Bimetallic nanoparticles comprised of iron (Fe) and nickel (Ni) were investigated for the removal of an azo dye contaminant in water. Morphology (core shell and alloy) and metal molar ratio (Ni2Fe10, Ni5Fe10, and Ni10Fe10) were tested as key nanoparticle properties. The shelf life of the nanoparticles was tested over a 3-week period, and the effect of initial nanoparticle concentration on dye removal was evaluated. The highest initial nanoparticle concentration (1000 mg/L) showed consistent Orange G removal and the greatest extent of dye removal, as compared to the other tested concentrations (i.e., 750 mg/L, 500 mg/L, and 250 mg/L) for the same nanoparticle morphology and metal molar ratio. The metal molar ratio significantly affected the performance of the core shell morphology, where overall dye removal was found to be 66%, 89%, and 98% with an increasing molar ratio (Ni2Fe10 → Ni5Fe10 → Ni10Fe10). In contrast, the overall removal of the dye for all molar ratios of the alloy nanoparticles only resulted in a variability of ±0.005%. When stored in water for 3 weeks, core shell nanoparticles lost reactivity with an average>17% loss in removal with each passing week. However, the alloy nanoparticles were able to continually remove Orange G from solution after 3 weeks of storage to ~97% when used at a starting nanoparticle concentration of 1000 mg/L. Overall, the Ni2Fe10, Ni5Fe10, and Ni10Fe10 alloy nanoparticles with a starting nanoparticle concentration of 1000 mg/L resulted in the greatest dye removal of 97%, 99%, and 98%, respectively. Kinetic rate models were used to analyze dye removal rate constants as a function of nanoparticle properties. Kinetic rate models were seen to differ from core shell (first-order kinetics) to alloy morphology (second-order kinetics). Alloy nanoparticles resulted in as high as X kinetic rate constant, and core shell nanoparticles resulted in as high as XX kinetic rate constant. Metal leaching from the nanoparticles was investigated; alloy nanoparticles resulted in leaching of 3% Fe and 5% Ni which is similar to core shell leaching of 3.2% Fe and 4.3% Ni from the Fe10Ni10 nanoparticles.