Aqueous natural organic matter removal by quaternary-ammonium-compound-modified iron-oxide-coated sand

In this study, modification of iron-oxide-coated sand (IOCS) with three quaternary ammonium compounds (QACs) was tested as a means to improve the removal of aqueous natural organic matter (NOM) by IOCS. The assessment was conducted in batch, isotherm setup with changes in types and concentrations of QACs, modification pH, additions of H₂O₂ during modification, and adsorption pH. IOCS modification with long chain QACs, including hexadecyltrimethylammonium bromide (HDTMA) and hexadecylbenzyldimethylammonium chloride (HDBDMA) significantly increased the adsorption of NOM, while coating IOCS with short chain QAC, tetrapropylammonium chloride (TPA) had no positive effect. The enhancement increased with increasing pH and increasing QAC concentration used during modification. Co-additions of long chain QACs with H₂O₂ during modification could further improve NOM adsorption. Modification of IOCS with 10.0 mM HDTMA at pH 9.9 with the 0.2% H₂O₂ addition doubled NOM adsorption capacity on IOCS at pH 9.1. The results presented here suggest that the modification of IOCS using long chain QACs can enhance NOM removal by IOCS during drinking water treatment.