REGENERABLE CATIONIC HYDROGELS AS NEW ADSORBENT MATERIALS TO ELECTROSTATICALLY REMOVE NITRITES FROM WATER

1. Introduction Metastable anions as nitrites, deriving from the oxidation of ammonia by agricultural pollution, sewage, decaying protein, and other nitrogen sources, are a recognized environmental issue, due to their role in eutrophication, surface and groundwater contamination, as well as toxicity towards almost all living creatures. Anyway, while several studies report on methods to remove nitrate from water, novel methods to remove nitrite are missing. 2. Results and Discussion Two cationic resins found capable to form hydrogels (R1HG and R2HG) by dispersion in aqueous medium, and to remove anionic dyes from water by electrostatic binding, were first tested in nitrite adsorption experiments in batch, to assess their removal efficiency by contact over time. Nitrites removal from samples of water appositely contaminated and containing 118 mg/L NO2-, was monitored by UV–Vis methods, using the Griess reagent system (GRS). The removal efficiency of R1HG and R2HG (89.2 and 89.6%), their maximum adsorption (21.0 and 23.5 mg/g), as well as the adsorption kinetics and mechanisms were evaluated. R1HG- and R2HG-based columns, mimicking mini-scale decontamination systems by filtration under pressure, succeeded in rapidly and totally removing nitrites (99.5 and 100%) from volumes of nitrite solutions (NO2- = 118 mg/L) 10 times the volumes of resins used. When filtration was extended to increasing volumes of the same nitrite solution up to reach 60 times the volume of resins used, the removal efficiency of R2HG remained stable at over 89% . Interestingly, both the hydrogels were regenerable by 1% HCl washing, without a significant reduction in their original efficiency. 3. Conclusions R1HG and especially R2HG represent low-cost, up-scalable, and regenerable column-packing materials, promising for applications in the treatment of drinking water contaminated by nitrites.