There are plenty of landfills in Europe and in the rest of the world, which can pose a threat to the environment (and to us). Often, these landfills risk to produce landfill gasses (greenhouse gasses) or a highly polluted leachate. Old municipal solid waste landfills generally contain big amounts of fines (soil-type), stones, water and a big volume of plastics. Also, we can find textiles, wood, metals, paper and glass – be it in smaller quantities.
From two of my secondments; one at landfill site of Halbenrain (Austria) and another with Stadler® at the landfill of Mont-Saint Guibert (MSG) (Belgium), I was able to study the composition of two landfills in terms of quantities and qualities:
The information from these two secondments is very valuable for me as I am studying the efficiency of waste processing techniques with landfill mining material. My aim is to develop a model that can estimate the quality of the material that can be sorted, and to improve the mechanical processing, which is the main cost for landfill mining projects. If we can estimate the quality of the landfilled material, we are taking a first step to recover those resources that are waiting for us to be upcycled.
An alternative to this end-story of many materials, also called “landfills”, is the strategy contemplated in the concept of Enhanced Landfill Mining (ELFM), which we (all 15 ESR-colleagues and their supervisors) try to develop with our research. From the dirty landfill and by mechanical processing it is possible to sort out high calorific fractions (refused derived fuels, RDF) with a calorific value of approx. 22 MJ/kg dm (according to the values obtained from the RDF at the MSG landfill). This RDF can be used as a fuel in industrial processes or incinerated to recover their energy. Also, by mechanical sorting is possible to recover other materials, like inerts/soil-type and stones for construction purposes or metals for its valuable price in the market.
As it is logical, the characteristics of mined materials and the potential of landfills to be used as a source of resources depend strongly on the type of waste that was landfilled primarily. This becomes evident when we compare two types of landfills (C&D + MSW and only MSW). Looking at the material composition from MSG landfill, the inorganic fraction (stones, glass) accounts for 19%, soil-like materials approx. 46%, and combustibles (plastics, wood, textile, paper) 5%. On the other hand, MSW landfills are characterized by 10 % of inorganics (stones, glass), 20 – 30% highly calorific fraction and 50 – 60% soil-like materials (Bhatnagar et al., 2017). Regarding the metal content, in most landfill mining projects, it ranges below 5%, in the case of Halbenrain 3%. The found 1% in MSG seems low because from C&D waste more metals, especially structural steel, are expected. The low share may be due to possible metal separation before landfilling.
The sorting efficiency depends strongly on the quality/quantity of the material, e.g. dry waste is normally easier to separate (with better quality products) than wet material. Also, less amount of fines increases the quality of the products due to the reduction of the defilements attached to the surface of the particles. Thus, looking at the pictures, we can imagine that the quality of the material is not the optimum and its recovery is not an easy and economically-feasible tasks. Nevertheless, it’s not an impossible mission since the technology exists (and its being improving) and my research aims to enhance the mechanical pre-processing chain.
Thanks for reading!!
About the Author:
Cristina García is our ESR02. She comes from the sunny coast of Spain and, after being living in several countries (England, China, Finland and Poland), she stablished in Germany to study her PhD in the field of landfill mining and waste processing at the RWTH Aachen University. Her main interest is to build a model that can calculate and assess the potential of MSW landfills as a possible depot of resources, after different sorting processes. Therefore, she needs to perform several excavations in different parts of Europe in order to gain information about the quantity and the quality of the LFM waste and learn how this material can be sorted in possible marketable products. You can contact her at: Cristina.firstname.lastname@example.org