Removal of Cr, Cu and Zn from liquid effluents using the fine component of granitic residual soils

Abstract

The practice of reuse of treated wastewater (TWW) is seen as a strategy for water conservation in regions where water scarcity is a natural reality and in those where population growth and/or climate change foresee this scarcity. In situations of lower water scarcity, reuse is practiced by imperatives of environmental protection of the receiving media, reducing the discharge of effiuents from wastewater treatment plants. The artificial recharge of aquifers (RAQ) with TWW is a very common practice at the international level, but little considered in Portugal. However, residual waste from TWW (e.g heavy metals), when deposited in soil or water, can cause significant environmental impacts on its uses, and cause serious health problems in several animal species due to their bioaccumulation in food chains. The present study intends to show that the granitic residual soils of the Quinta de Gonçalo Martins (Guarda), in the Beira Interior region of Portugal, present physical-chemical and mineralogical characteristics favorable to the infiltration of TWW into RAQ. The results of the batch sorption tests indicate that the soil has a reactive capacity to remove the Cu and Zn residual load at TWW at high efficiencies by adsorption and ion exchange mechanisms. The pseudo-first order model explained the reaction kinetics for the three heavy metals removal and when the sorption equilibrium state was reached, the removal of these metals was explained by the Freundlich isotherm.