A systematic study on adsorptive removal of arsenic using low cost adsorbents with or without the presence of NOM

Abstract

Arsenic is a toxic and bio-accumulating element in water bodies, especially in drinking water sources.One of the methods used to remove arsenic from drinking water is adsorption. NOM (natural organic matter), which is ubiquitous in natural aquatic environments, can inhibit arsenic adsorption by competing with arsenic for adsorbent surface sites. The main objectives of this study were to investigate the competitive adsorption between NOM and arsenic using low-cost adsorbents. For this purpose, batch adsorption experiments were carried out in synthetic and natural water using pumice, steel slag and red mud as low cost adsorbents.The highest arsenic removal efficiencies obtained with steel slag, pumice and red mud were 95, 95 and 50 %, respectively without the presence of NOM. The results showed that the presence of NOM caused a significant reduction in arsenic adsorption for all tested adsorbents and 20-30% less arsenic removal efficiency was obtained in natural water compared to the removal efficiencies obtained in synthetic water. The maximum adsorption capacities obtained in synthetic water with all tested adsorbents vary between 1.6 -3.05 mgAs/g, while the maximum adsorption capacities obtained in natural water vary between 0.9-1.2 mgAs/g. All these findings indicate that NOM can hinder the uptake of arsenic by all tested adsorbents. Moreover, the arsenic adsorption in natural water were modelled by Langmuir, Freundlich and modified Freundlich. The results showed that the arsenic adsorption data were well fitted by modified Freundlich isotherm with R2 values between 0.87 and 0.90.