Adsorptive Removal of Nitrate and Phosphate from Water by a Purolite Ion Exchange Resin and Hydrous Ferric Oxide Columns in Series

Abstract

Elevated concentrations of nitrate and phosphate in surface and ground waters can lead to eutrophication, and nitrate can also cause health hazards to humans. The adsorption process is generally considered to be an efficient technique in removing these ions provided that the adsorbent is highly selective for these ions. Removal of nitrate and phosphate from a synthetic water (50 mg N/L as nitrate, 15 mg P/L as phosphate) and a wastewater (12.9 mg N/L as nitrate, 5.9 mg P/L as phosphate) using a Purolite A500P anion exchange resin and a hydrous ferric oxide (HFO) columns (60 cm height, 2 cm diameter, flow rate 1 m/h) in series containing 1–10% (w/w) of these adsorbents and the remainder anthracite (90–99%) were studied. Data from batch adsorption experiment at various concentrations of adsorbents satisfactorily fitted to Langmuir adsorption isotherm for nitrate and phosphate on Purolite with adsorption maxima of 64 mg N/g and 7 mg P/g and only for phosphate on HFO with adsorption maxima of 14 mg P/g. Both batch and column experiments showed that Purolite selectively removed nitrate and HFO selectively removed phosphate. The Purolite column BTC time was greater for nitrate than for phosphate. At the highest percentage by weight of Purolite almost all nitrate was removed in batch study and up to 1000 min in column study, but it was not able to remove a comparatively high percentage of phosphate. However, when the effluent from the Purolite column was passed through the HFO column almost all phosphate was removed. The two columns when set up in series also removed almost all nitrate and phosphate from the wastewater.