Batch and column studies on the evaluation of micrometer and nanometer Phragmites australis for nitrate removal

The effects of Phragmites australis anion exchanger (PHA-AE) with micrometer and nanometer scales as adsorbents for nitrate removal were investigated. Also, the effects of operating conditions including pH, contact time, adsorbent loading, initial anion concentrations, and desorption experiments were examined. The results showed that the optimum pH was equal to 6 as the equilibrium time were 3 and 2h for micrometer and nanometer PHA-AE, respectively. With the increased nitrate concentrations (5, 15, 50, 80, and 120mg/L) for micrometer and nanometer PHA-AE, q(e) (adsorption capacity) increased from 0.4 to 6.97mg/g and 0.45 to 7.7mg/g. With increase of adsorbents dose from 0.1 to 0.3g, the percentage of nitrate removal increased from 47 to 56% and 54 to 68% for microstructure and nanostructure adsorbent, respectively; however, the percentage of removal remained almost constant with the adsorbent dosage ranging from 0.3 to 1g. The adsorption of nitrate ions onto PHA-AE was described successfully by pseudo-second-order adsorption kinetic and Langmuir-Freundlich adsorption isotherm. The results of the present study indicated that PHA-AE may be used to remove nitrate ions from water treatment process. PHA-AE nanometer showed greater capability of nitrate adsorption, too, as compared to PHA-AE micrometer adsorbent.