Enhancing nitrate removal efficiency of micro-sized zero-valent iron by chitosan gel balls encapsulating

Abstract

The activity of micro-sized zero-valent iron (MZVI) material for nitrate removal in neutral pH and low C/N ratios water needs to be improved. In this study, micro-sized zero-valent iron@chitosan (MZVI@CS) material was synthesized through embedding MZVI particles into chitosan (CS) gel by sol-gel method, and was used for deep removal of NO3−-N in the absence of organic carbon sources and neutral pH. The NO3−-N removal rate of MZVI@CS was 0.37 mg-N·L−1·d−1 (dosage of 1%, initial pH = 7, 25 °C, initial nitrate concentration = 15 mg-N·L−1), which was 11.33 times higher than that of MZVI. The apparent activation energy (Ea) of MZVI@CS with nitrate was 38.23 kJ·mol−1. MZVI@CS can remove nitrate effectively at a low concentration (15 mg-N·L−1). A stable denitration rate (0.37–2.28 mg-N·L−1·d−1) could be maintained under weak acidic, neutral and alkaline conditions (pH = 5–9). More than 80% of reduced nitrate was converted to N2, and only a small amount was converted to NH4+ or NO2−. The gel structure of MZVI@CS eliminated the agglomeration between MZVI particles while the forming of Fe-CS chelates reduced the formation of iron oxide and solved the problems of passivation, hence successfully strengthened the NO3−-N removal efficiency of MZVI. Therefore MZVI@CS has great application potential in NO3−-N deep removal of water bodies with neutral pH and low C/N ratios.