Heavy metal pollution has become one of the most serious environmental problems nowadays. The removal of heavy metals from wastewaters has attracted a considerable attention because of their adverse efects on public health and ecosystems. The main objective of this work was to investigate the efciency of the coupling of infltration-percolation process with adsorption on activated carbon in the removal of heavy metals contained in urban wastewater efuents. The adsorption of heavy metals on a commercial sample of activated carbon was studied in a static mode. Several laboratory experiments made it possible to distinguish the optimum quantity of powdered activated carbon necessary to remove a large range of heavy metals. Results showed that the equilibrium of the adsorption was reached very quickly for cadmium (Cd2+), i.e., after 15 min of contact with the activated carbon. On the other hand, the equilibrium of zinc (Zn2+), lead (Pb2+) and copper (Cu2+) was achieved after 45 min. The withdrawal rates were 70.77% for Zn2+, 64.75% for Pb2+, 67.07% for Cu2+ and 78.42% for Cd2+. The adsorption isotherms determined for Zn2+, Pb2+, Cu2+ were of type I, while the shape of the Cd2+ curve showed a type II isotherm. These isotherms confrm the capacity of the powdered activated carbon to adsorb cadmium better than the other studied heavy metals.

Introduction

Heavy metals are dangerous species which induce various environmental and health problems (Göde et al. 2017). Most industries unload wastewater and efuent containing toxic materials, mainly heavy metals, into aquatic systems without treatment, which is a major environmental problem. The excessive release of these pollutants presents a particular problem because they are not biodegradable (Boussahel 2001). These pollutants do not all have the same risks to the environment (Houas et al. 1999) and to health because of their diferent physicochemical properties. Efuents are still treated at wastewater treatment plants (WWTPs), apart from exceptional cases of storm spills, and thus the future of the toxic pollutants contained in wastewater will very much depend on the purifcation efciency of these stations (Varrault 2011). This author has shown that during the treatment, a small quantity of metallic trace elements is not eradicated and will, therefore, pass into the aquatic environment. Furthermore, the uppermost proportion of metals is trapped in the sewage sludge and can, therefore, be transferred either to unloading stations or to agriculture which receives this type of sludge. Heavy metals can reach concentrations that threaten the survival of certain populations and pose dangers. Indeed, heavy metals in water are absorbed by plants and animals. When the amount of these elements exceeds the norms, they can accumulate in the organisms of the food chain (Lacoue-Labarthe 2007). There are several methods for heavy metal detection including inductively coupled plasma-mass spectrometry (Liao and Jiang 1999), spectrophotometry (Jankiewicz et al. 2000), fame-atomic absorption spectrometry (Bortoleto et al. 2004) or electrochemical methods that include ion-selective electrodes, polarography and other modifed electrodes (Yola et al. 2012; Gupta et al. 2013a, b; Yola et al. 2014; Göde et al. 2017).