Heavy metals removal by flax fibers to a further use in urban runoff management systems

Abstract

Water pollution has long been considered a major problem causing environmental and public health issues. A range of contaminants are encountered in wastewater, industrial effluents and also road runoff, they include total suspended solids, nutrients, hydrocarbons and heavy metals. These latter have been found very toxic and hazardous, either for human health, or fauna and flora. In recent decades, studies have demonstrated a good removal efficiency of heavy metals by adsorption technique, and especially biosorption. Numerous biosorbents have been investigated, mainly lignocellulosic materials which have shown high adsorption capacity. Within this context, this study aims to investigate flax fibers capacity of zinc, copper and lead ions removal from aqueous solutions, in order to examine the best conditions to test a full-scale device designed to treat stormwater runoff. The choice of flax is related to its high availability, low cost and local economy reasons. The device consists of sand and layers of flax fibers geotextiles. It will be placed on a parking at the entrance of a retention basin in Le Havre. For this purpose, batch experiments were carried out with ternary and mono-metal solutions of zinc, copper and lead ions at room temperature with molar concentrations of 0.04 mmol.l^-1, at pH around 6.4. Biosorption kinetics and biosorption equilibrium were performed and analyzed. The results showed a favorable adsorption for the three metals in the order Pb > Cu > Zn for both types of solutions, with adsorption rates of 94%, 75% and 62% respectively in the ternary metal solution and 94%, 81% and 82% in the mono-metal solutions. The effect of competition was important for zinc, barely visible for copper, and non-existent for lead.

Keywords: Biosorption, heavy metals, pollutants, stormwater management systems.