Lead bioremoval by cork residues as biosorbent

The intensification of industrial activity during the last few years has greatly contributed to the increase of heavy metals in the environment, mainly in the aquatic systems [1]. Conventional technologies traditionally used for the removal of heavy metals from aqueous solutions are expensive and inefficient at low metal concentrations [2]. Biosorption, which is a property of different types of biomass (biosorbents) to bind and concentrate heavy metals from even very dilute aqueous solutions, is one of the most promising technologies that can be used for this purpose [3]. The goal of this work was to study the bioremoval process of Pb(II) ions from aqueous dilute solutions by cork granulates (1-2 mm) from a Portuguese cork processing company. The effect of physico-chemical parameters such as initial metal solution, pH, biomass cork pre-treatments and initial metal and biosorbent concentrations on the metal removal efficiency were investigated. The maximum Pb(II) uptake capacity (Qmax) of cork biomass was also determined from the Langmuir isotherm. The results obtained showed that the optimum initial pH for Pb(II) removal was in the range 3-4, leading to removal yields of about 90-100% for initial metal concentrations of 10-100 mg/L. Cork biomass without treatment provided a higher removal yield (93%) than the biomass submitted to previous extraction with deionised water (80%), ethyl acetate (83%) and ethanol (88 %). The Langmuir model showed a very good correlation with experimental results (r2=0.995) and the Qmax was determined as being 5.3 mg Pb(II)/g cork. The optimisation of continuous bioremoval of Pb(II) (10 mg/L) from 25 L of influent, regarding metal uptake yield and volume of effluent containing a Pb(II) concentration 1 mg/L (MAV), was carried out by the factorial design methodology, leading to the establishment of the best operating conditions. In these conditions, two fixed bed-reactors (operational liquid volume of each reactor containing 20g of biosorbent=138 mL) running in sequential mode (feed flow rate - 590 mL/h) were more efficient (effluent volume with [Pb(II)] 1 mg/L=10 L) than one reactor alone (effluent volume with [Pb(II)] 1 mg/L=5 L). Finally, the chemical characterization in terms of CQO, TOC and phenolic compounds of the effluent before discharge showed that all values were lower than the ones allowed by environmental legislation