Characterization plan of Bortolotto large area and multi-technique approach for the study of the thermodynamic and sequestering properties towards some toxic metals of leachate from municipal solid waste

The production and disposal of wastes are pressing issues today because they represent the consumption of non-renewable natural resources that are not replenished or reintroduced into the production cycle, but their storage also poses a burden in terms of expenses and potential sources of contamination. It is well known that two phases are generated from the storage of waste in landfills; the first one aqueous, defined as landfill leachate, is essentially generated by the percolation of rainwater in its body and by the degradation of waste following chemical and biological degradation processes and whose composition depends on the waste product category, temperature, compaction, age, etc. Leachate is a waste that has a C.E.R. code mirror-like, that is dependent on the concentration and type of contaminants in it contained and can be a dangerous waste or not. The other phase forming in the body of the landfill is biogas which, despite being a degradation product of waste, today appropriately conveyed, can become an economic resource, as it is a gaseous mixture that contains significant quantities of methane. In any case, as a multicomponent aqueous matrix rich in inorganic and organic substances, landfill leachate is an environmental and health problem, as it acts as a carrier of contaminants through the ecosystem. This PhD project fits into this issue through two research parts such as the characterization plan of two landfills and the study of landfill leachate from both a chemical-physical and thermodynamic point of view and the determination of its sequestering capacity. The first part of this project consisted of drawing up the characterization plan of “Bortolotto” large area, a complex of two landfills, namely “Bortolotto” and “So.Ge.Ri.”, located in Castel Volturno (Caserta, Italy), in an area famously called as “terra dei fuochi”. Following the guidelines present in Annex 2 Part IV Title V of the Italian Legislative Degree 152/06, a preliminary model of the site was defined, and historical information of the site collected, in order to have an objective framework of the main issues and environmental contaminations. The data reported highlighted an exceeding of the CSC (Contamination Threshold Concentration) in the surface water and soil matrices, consistent with the evidence of environmental pollution that preceded the request for further investigations. A set of activities including the characterization of different environmental matrices (soil, groundwater, superficial water, air), waste, leachate was scheduled and approved but have not yet entered the operational phase. The second part of the project was based on the study of the thermodynamic properties of different leachates collected from a landfill of Municipal Solid Waste (MSW). Since some properties, such as transport, absorption, toxicity, bioaccumulation of the contaminants, depend on the chemical-physical composition of leachates, some samples were collected from landfill and downhill piezometers and in periods characterized by different rainfall, by using the official methods of analysis. For many metals and some organic contaminants, exceedances of the concentrations with respect to the limits established by the Italian Legislative Decree 152/2006 were observed. ATR-FT IR and SEM-EDX analyses where carried out on dried and calcinated leachates, obtained at T = 383 K and T = 923 K respectively. Acid-base properties were also investigated by means of potentiometric titrations carried out at T = 298.15 K in NaCl(aq) and applying the Polyprotic Like model. The interacting ability of leachates toward metal cations (Cd2+, Zn2+, Cu2+) was studied by potentiometric and voltammetric (only for Pb2+) techniques in NaCl (NaNO3 for Pb2+) aqueous solutions, at I = 0.15 mol dm−3 and T = 298.15 K, obtaining diverse speciation models and complexes of very different stability. By using the pL0.5 parameter, the effective sequestering ability of each leachate towards the metal cations was calculated, proving that each of them has a different strength of interaction towards the metals, that tends to increase with the pH and confirming that they behave as carriers of contaminants through the soil and towards groundwater, with the consequent problems of environmental contamination and risks for the human health.