Simultaneous removal of ammonium and phosphate from eutrophic waters using natural calcium-rich attapulgite-based versatile adsorbent

Abstract

In this study, natural calcium-rich attapulgite (NCAP) was used to develop a versatile adsorbent for simultaneous removal of ammonium and phosphate from contaminated waters. Batch studies indicated that a combination of mixed salts and thermal treatments imparted the modified NCAP (named NCAP-NM) with the maximum nitrogen and phosphorus sorption capacity. This versatile adsorbent displayed a very fast nutrient adsorption rate and can, after 1h of adsorption, lower a solution enriched with 20mg/L of nutrients to <0.01mg P/L and 0.354mgN/L with a dosage of 30g/L. Fixed column adsorption studies indicated that sorption of phosphate was predominately affected by HCO3−, while sorption of ammonium was predominately affected by Ca2+. The result of a real-world application indicated that NCAP-NM could purify 1440 and 1000 bed volumes of water for phosphate and ammonium, respectively, in eutrophic river water treatment. While SEM-EDS and XPS analysis confirmed a dual function in the nutrient removal process utilizing NCAP-NM where phosphate was removed through precipitation by calcium, and ammonium was exchanged with magnesium and sodium in the adsorbent. These results offer a promising new method for lake eutrophication control if NCAP-NM is used as the adsorbent for nitrogen and phosphorus removal.