Sorption Efficiency of Potentially Toxic Elements onto Low-Cost Materials: Peat and Compost

Abstract

Anthropogenic activities can lead to elevated concentrations of potentially toxic elements (PTEs) in soil and water. Thus, the search for low-cost, ecofriendly and innovative sorbents is a global necessity. The present investigation addresses the performance of peat and compost derived from the organic fraction of municipal solid waste (OFMSW) as a sorbent of zinc (Zn), lead (Pb) and cadmium (Cd). The physicochemical features and effects of the initial concentration (equilibrium) and contact time (kinetic) were systematically analyzed by batch experiments. In addition, human bioaccessibility tests were conducted to compare the human health risk of these PTEs postsorption. The results showed that the sorption capacities followed the order: compost(Pb) > peat(Pb) > compost(Cd) > compost(Zn) > peat(Cd) > peat(Zn), indicating that compost had a better sorption potential. Kinetic data were well-fitted to the pseudo-first-order (PSO), pseudo-second-order (PFO), and Elovich equation models. The external diffusion model proposed by Mathews and Weber (M&W) indicated the contribution of diffusion as a sorption mechanism, mainly in the sorption of Zn, Pb and Cd onto compost and Pb onto peat. The bioaccessible fractions in the first stage (stomach conditions) were greater than those in the second phase (intestinal simulation). Pb has higher sorption capacities (10.511 and 7.778 mg g−1 for compost and peat, respectively) and lowers fraction bioaccessible (35 to 70%). These findings demonstrate that utilizing these low-cost sorbents seems promising for the remediation of PTE soils and contaminated waters. However, more experiments should be conducted, including desorption and multielement solutions, as well as field-tests to prove the long-term effects of application in large-scale and real conditions.