Recovery technologies for materials in landfills

Europe hosts more than 500,000 landfills of which 90% are non-sanitary and around 80% essentially contain Urban Solid Waste (https://www.eurelco.org/infographic). Urban landfills (UL) and extractive (mining and metallurgical) industry residues (EIR) are potential sources of materials that, if recovered, can contribute to the circularity of economy. Among other factors, technology plays one essential role in the viability of landfill mining projects (Krook, et al, 2012). The methods for mapping landfills, sampling and characterizing waste, the readiness of technologies, the optimization of technologies and their combination in treatment and recovery schemes, their applicability, costs and environmental impacts effect the valorization of waste from landfills. This report addresses Deliverable 1.1 “Recovery technologies for materials in landfills” developed by Working Group 2 of COST Action “Mining the European Anthroposphere” (MINEA). MINEA aims to quantify and assess the material resources and reserves in the Anthroposphere and consolidate existing knowledge related to the exploration, evaluation, classification and recovery of materials in anthropogenic deposits and waste flows. This report integrates the activities of the MINEA WG2 in the 1st Grant Period (May 2016 to April 2017). The following documents were developed: (1) Literature Review Report on practices and technologies for waste valorization from landfills (Calvo, 2016) and (2) MINEA WG2 Workshop on technologies in the landfill-mining sector, which resulted in an overview on landfill mining projects and on state-of-the-art as well as enhanced recovery technologies (Workshop on “Technologies for material recovery from landfills and mining residues”, Book of abstracts, 2016). This report also profits from the non published report on “Science and technology in enhanced landfill mining” (EURELCO, 2016), which has been developed by the Working Group II of the European Enhanced Landfill Mining Consortium (EURELCO). Both activities examine current practices, knowledge transfer and recovery technologies across European countries, research fields and disciplines. This information is essential to assess the availability of secondary material from landfills and the viability of landfill mining projects in the context of circular economy

Three-dimensional behaviour of a prototype radioactive waste repository in fractured granitic rock

An investigation of the three-dimensional coupled thermohydromechanical behaviour of a prototype repository in fractured granitic rock is presented. The pre-placement behaviour of the repository is first considered, making use of a full three-dimensional simulation of the problem. An effective continuum approach, augmented with discrete features with a high hydraulic conductivity, is employed. The method adopted is found to be able to simulate accurately the highly anisotropic flow regime observed at the pre-placement phase. The major features of the full repository experiment under applied heating conditions were then successfully simulated. The range of buffer hydration rates, the thermal response of the repository, and the associated mechanical response were successfully simulated. Approaches to capture both the transient microstructural behaviour of the compacted bentonite (MX-80 type) and a MX-80 pellet material are incorporated. The repository behaviour was shown to be strongly influenced by complex coupled processes, including interactions between the system components. The adoption of a three-dimensional modelling approach proved to be essential to realistically simulate the behaviour of a repository incorporating anisotropic flow behaviour. Finally, potential impacts of the processes considered on performance of the barrier system and in safety assessment are considered

Modelling thermal fluxes at the soil surface

This paper investigates the impact that various representations of thermal fluxes at the soil surface have on the estimation of seasonal variations of temperature and stored thermal energy in the soil close to the surface. Three theoretical formulations representing; turbulent, nonturbulent and vegetation-covered soil surface conditions are considered. The influence of shading from nearby objects (e.g. vegetation) has also been investigated. Numerical predictions of soil temperature and stored thermal energy are compared with experimental results from a large scale field test (performed by others). The results of both 1D and 2D simulations are shown capable of representing specific aspects of field behaviour. Various sources of meteorological data have been used to define surface boundary conditions. In particular, simulations were performed using; i) data measured in-situ, ii) data obtained from The British Atmospheric Data Centre, and iii) data generated using analytical expressions found in the literature. It is found that the correct representation of the heat transfer processes occurring at the soil surface is of critical importance. In particular, it is shown that the use of publicly available sources of data, or mathematical/analytical expressions for meteorological data, may be adequate when in-situ measurements are not available

Factors influencing collection performance of near surface interseasonal ground energy collection and storage systems

The influence of surface boundary conditions, varying climatic conditions and engineering material parameters on the collection performance of near surface interseasonal ground energy collection and storage systems are investigated. In particular, the performance of a proposed design of an interseasonal heat storage system which has also been investigated by others as part of a full scale demonstration project is considered. A numerical model is developed and validated against field data. It is then applied to undertake a series of simulations with varying system parameters. It is found that (i) higher values of thermal conductivity of the storage layer result in increased storage of thermal energy and lower peak temperatures, (ii) system heat losses are strongly influenced by the performance of insulation layers, (iii) warmer climatic conditions provide more thermal energy available to be stored; however, changes in the amplitude of seasonal air temperature variations have an effect on the rate of collection of thermal energy and (iv) the use of correct surface boundary conditions is critical in modelling the dynamics of these systems

Altered chemical evolution in landfill leachate post implementation of biodegradable waste diversion

Within the UK implementation of the European Union Landfill Directive (1999) has led to the diversion of biodegradable waste (BW) from municipal solid wastes away from landfills. It has been widely anticipated, but thus far not verified, that the diversion of BW and consequent reduction in BW reaching landfill would lead to a change in the degradation processes occurring within landfills and that this would be reflected in an altered evolution in leachate chemistry compared to pre-Directive landfills. This paper provides evidence based on leachate chemistry from two operational landfills together with calculations of the reduced BW content, that demonstrate the acetogenic phase that characterised pre-Directive landfill leachates is missing and is now more typical of methanogenic phase leachate. The paper demonstrates how data from national datasets and detailed landfill records can be used to constrain likely and upper estimates of the amount of BW going into post-Directive landfills, and the observed change in the evolution of leachate chemistry which has resulted from a decrease in BW content from typical values of BW (pre-Landfill Directive) of 22% to an inferred 12% in the case-study landfills. Data provided here add to the growing literature that estimates the amount of BW in recent post-Directive landfills which importantly allow the quantitative linkage between a decrease in landfilled BW and observed changes in leachate chemistry to be established such that future landfill operators can increase confidence in the effect of Directive implementation on landfill operational parameters

Analytical Solutions for Contaminant Diffusion in Double-layered Porous Media

Analytical solutions for conservative solute diffusion in one-dimensional double-layered porous media are presented in this paper. These solutions are applicable to various combinations of fixed solute concentration and zero-flux boundary conditions (BC) applied at each end of a finite one-dimensional domain and can consider arbitrary initial solute concentration distributions throughout the media. Several analytical solutions based on several initial and BCs are presented based on typical contaminant transport problems found in geoenvironmental engineering including (1) leachate diffusion in a compacted clay liner (CCL) and an underlying stratum; (2) contaminant removal from soil layers; and (3) contaminant diffusion in a capping layer and underlying contaminated sediments. The analytical solutions are verified against numerical solutions from a finite-element method based model. Problems related to leachate transport in a CCL and an underlying stratum of a landfill and contaminant transport through a capping layer over contaminated sediments are then investigated, and the suitable definition of the average degree of diffusion is considered