Biosorption on crosslinked starch for metal removal from industrial effluents
The surface-treatment industry consumes and discharges an important range of chemicals, in particular toxic metals and organics, that are known to be harmful to humans and the environment. Because of more and more stringent regulations, effluents polluted with heavy metals must be treated. There are a variety of treatment processes for wastewater from the surface-treatment industry. In general, conventional treatment and detoxification systems consist mainly of pH adjustments, oxidation of cyanide and reduction of chromium bearing wastewaters, followed by hydroxide precipitation, clarification, and sometimes carbon sorption. However, active carbon technology presents several problems such as rapid saturation and clogging of the reactors. Like ion-exchange resins, their widespread use is restricted due to high cost. For these reasons, most small and medium-size enterprises cannot employ such treatments. Thus, in order to overcome these problems, many attempts have been made to find inexpensive alternative sorbents, which are both effective and acceptable for industrial use. In this study, biosorption with a starch-based cross-linked adsorbent was used for the removal of heavy metals from industrial effluents. The adsorption of metals was studied as a function of contact time, adsorbent mass and pollutant load. The influence of these parameters on the adsorption efficiency was evaluated using a conventional batch method. Batch experiments showed that the material exhibited high sorption capacities toward metal ions, leading to concentrations that were below current regulatory values. Measurements of the germination rate of Lactuca sativa seeds, used as a phytotoxicity test, were carried out on discharged industrial waters before and after the finishing sorption treatment. Germination tests confirmed the ability of the sorption step to radically decrease the effluent toxicity. Both the chemical abatement and toxicity mitigation of waste water showed that biosorption onto a non-conventional sorbent may constitute an interesting additional treatment step for the detoxification of industrial wastewater.