Synthesis and Characterization of Crosslinked Chitosan Beads for Removal of Nitrate Nitrogen from Drinking Water

Introduction:  Filtration has been an accepted technology to remove nitrate nitrogen from drinking water which is usually originated from fertilizers or composts. Interactions between positively charged chitosan and negatively charged nitrate nitrogen lead to the ionic removal of nitrate nitrogen. However, chitosan beads are needed to improve physical strength because they show low aqueous stability such as crosslinking of chitosan molecules formed as bead may be technically feasible to remove nitrate nitrogen from drinking water.

Purpose:  The purpose of this research was to develop chitosan beads to remove nitrate nitrogen from drinking water by using chitosan. In detail, nitrate nitrogen was removed by ionic coupling with the chitosan beads. Sodium-tripolyphosphate (STPP) crosslinking was used to improve the physical strength and swelling capacity of the chitosan beads.

Methods:  For crosslinked chitosan bead (CLCB) preparation, chitosan solution was prepared by dissolving 3.0 g of chitosan flakes in 60 ml of 5% acetic acid solution. Under stirring 0.5 M NaOH solution, the chitosan solution was added dropwise in the NaOH solution. Then, STPP was added to trigger crosslinking reaction at 30°C for 12 h. The adsorption kinetics of CLCB was investigated with respect to nitrate nitrogen concentration, temperature, and pH.

Results: The CLCB fabricated possessed porous surface (porosity 84.5%). The nitrate nitrogen adsorption capacity was 1.8 - 2.4 g nitrate nitrogen adsorption /kg CLCB at pH 5.5, 25°C and 100 rpm for 15 min. A diffusion model was used to interpret the kinetic data of nitrate nitrogen adsorption test and subsequently determined the removal rate constants of CLCB. The adsorption capacity increased largely with decreasing solution pH or with increasing collecting time.

Significance:  The CLCB can be used as a positively charged filtering material for the drinking water filtration.