Pilot-Scale Removal of Metals from Iron-Rich Contaminated Groundwater Using Phosphorylated Lignocellulosic Fibers

The performance of the phosphorylated lignocellulosic fiber (PLF) was assessed for metal removal in an acidic mine drainage (AMD) influent at pilot scale and at laboratory scale with synthetic water. Substrate showed strong potential for sorption with a cation exchange capacity (CEC) of 540 meq 100g-1, a point of zero charge (PZC) of 7.3, and a limited amount of organic carbon released. Average concentrations (mg L-1) of Ca, Mg, Fe, Mn, and Zn in the influent were 427, 289, 1,420, 18.3, and 19.2, respectively. Retention of 1635 mg g-1 of Fe, 23.1 mg g-1 of Mn, and 18.1 mg g-1 of Zn was achieved by the PLFs at pilot scale. The pump and treat system was in function for a total of 852 h over a 9-week period and allowed the treatment of 4806 L of Fe-rich contaminated water from an abandoned mining site in Quebec (Canada). This medium-term experiment allowed to assess some of the key uncertainties that limit biosorption applications at large scale, namely organic carbon release and longevity and degradation of biosorbents. The substrate was subject to degradation, but it was found that acidic water reaching the PLF was mainly responsible for its dissolution. Hence, the PLF is a good candidate for long-term treatment when the influent pH is higher than 6. Metal removal was about 10 times higher during the field experiments compared with laboratory-scale equilibrium experiment, suggesting that many sorption reactions took place in the field and not in the laboratory. Differences between the laboratory and pilot experiments are the scale (0.45 L vs 4806 L) and water characteristics (continuous feed of various metals in the field).