The aim of this work is to evaluate an efective fltration technique for residual organic pollutants and heavy metals removal using two types of sand rich in iron oxide as a massive flter (sieved and gross sand). X-ray difraction, X-ray fuorescence (XRF), scanning electron microscopy, energy dispersive spectroscopy (EDS) and specifc surface area BET were investigated to characterize the sand. Experimental results showed that the BOD5 removal was found to be 93% for gross sand (GS) and 96% for sieved sand (SS). The COD removal was equal to 98.9 and 99.7% for GS and SS, respectively. The hydrogen bonding, complexation/precipitation process, ions exchanges and electrostatic interactions are the main phenomena proposed to describe residual organic pollutants removal. For heavy metals adsorption, results show a great efciency removal between 90 and 100% for both cases. The adsorption mechanism was proposed based on zero-point charge, FTIR analysis, fuorescence (XRF) and EDS. The fxation of heavy metals onto the sand could be referred to hydrogen bonding, electrostatic interaction, ion exchange and electron donor–acceptors.

Introduction

Increased urbanization and population growth have resulted in an increase in water requirements, which has resulted in excessive use of water resources with a large volume of pollutants. Moreover, wastewater becomes an important source of pollution and a major human health problem (Chaves et al. 2016; Ellis and Butler 2015; Miao et al. 2015). In recent years, several environmental problems were observed as a result of water contamination by organic and inorganic pollutants characterized by their persistence, toxicity and bioaccumulation capacity. Therefore, they must be removed before being discharged into a receiver medium (Albishri and Mahmoud 2013; Ji et al. 2012; Gebru and Das 2017; Karnib et al. 2014; Tunali et al. 2006; Liu et al. 2013; Shannon et al. 2008). Heavy metals are the most common environmental water pollutants and pose a potentially carcinogenic risk to humans, such as anemia, nervous system deterioration, failure of kidneys, and DNA-protein cross-linkage leading to cancer of the kidneys, liver and gastric tract (An et al. 2001; Chaudhry et al. 2016a, 2017a; Yan and Viraraghavan 2003; Inglezakis et al. 2002). Unlike organic pollutant waste, heavy metals are characterized by a long-term persistence and high non-biodegradability (O’Carroll et al. 2013; Jiang et al. 2010; Hongjie et al. 2009; Zhong et al. 2014). For these reasons, efective elimination of organic pollutants and inorganic pollutants has become an important issue today (Gaikwad 2004; Uzun and Güzel 2000). Today, innovative and cost-efective solutions to wastewater treatment and wastewater reutilization with new materials and techniques become a priority (Ding et al. 2014). Iron oxide sand fltration can be an efective innovative technique to solve these problems. A number of papers have used diferent types of sand rich in iron oxide such as sand coated with iron oxide modifed with sulfate (Vaishya and Gupta 2005), iron impregnated quartz sand (IIS) (Vaishya and Gupta 2003), Ce(IV) doped iron oxide (Zhang et al. 2003), silica-containing iron(III) oxide (Zeng 2003), iron-oxide-coated polymeric materials (Katsoyiannis and Zouboulis 2002) and iron oxide coated sand (Gupta et al. 2005), iron-zirconium oxide-coated sand (Chaudhry et al. 2017b; Chaudhry and Khan 2017), iron oxide activated red mud (Khan et al. 2015), and zirconium oxide-coated marine sand (Khan et al. 2013). Various techniques have been explored to remove heavy metals and organic pollutants from wastewater such as electrocoagulation (Adhoum et al. 2004; Hanay and Hasar 2011; Heidmann and Calmano 2008; Kabdasli et al. 2009), ion exchange (Sapari et al. 1996), precipitation, adsorption (Chen and Wang 2000; Siddiqui and Chaudhry 2017), and ion exchange-assisted membrane separation (Dzyazko and Belyakov 2004; Vasilyuk et al. 2004). Among these techniques, fltration using sand is an innovative method for treating water contaminated by toxic pollutants. The simplicity, low energy consumption and relatively low operational costs make sand fltration one of the most common pretreatments currently used in large installations (Bar-Zeev et al. 2012).