Closing the Circle: Enhanced Landfill Mining

Waste-to-Energy

Closing the Circle: Enhanced Landfill Mining

Landfill mining has been touted as a way to recover valuable materials discarded over the years. So how does Enhanced Landfill mining differ? The Flanders-based Enhanced Landfill Mining Consortium addresses the difference with a case study outlining the REMO landfill site in Belgium and potential energy recovery.

Over the last 50 years, waste management has undergone significant paradigm shifts. The first shift was the phasing out of uncontrolled landfilling. Since the 1980s, all landfills must comply with several regulations. A major drawback is that the aftercare period for a closed landfill is limited, and landfills also occupy enormous amounts of land. The next step in waste management policy, therefore, consisted of combining landfill (landfill mining) practices with a Waste to Energy (WtE) approach.

Under the Enhanced Waste Management (EWM) concept, prevention and re-use/recycling become even more important, while the idea of landfilling as ‘a final solution’ is discarded. Landfills can become part of EWM, provided they are considered as ‘temporary storage places awaiting further treatment’.

Waste brought to new storage facilities must be mined after a fixed time, and the storage operation will be performed to make mining and valorisation as efficient as possible. The non-recyclable fraction at that particular moment in time must be stored so that future mining is possible.

Enhanced landfill mining (ELFM) is also applicable to old landfills to deal with the waste legacy of the past. Billions of tonnes of waste has already been stored in landfills worldwide. As recycling and energy technologies have rapidly improved (and continue to do so), and as prices of commodities and carbon emissions are steadily climbing, new opportunities are arising to reclaim the value stored in old landfills.

This integrated approach makes ELFM part of the transition towards a fully closed loop material system. It must be clarified that the presented ELFM approach clearly differs from traditional landfill mining, where the mining is often limited to reclaiming methane, land and a few valuable metals.

The Closing the Circle project

The REMO landfill site in Houthalen-Helchteren (Belgium) currently contains more than 16 million tonnes of waste, which consists of roughly equal quantities of household and industrial waste. The amount, type and location of the various waste streams has been closely documented, suggesting that excavating and separating various recyclable fractions could be performed in a controlled, efficient and effective manor.

It has been estimated that about 45% of the waste could be recycled as Waste to Materials (WtM), either directly or after a controlled treatment process. The remaining fractions have enough caloric value for use in energy generation after pre-treatment. A large fraction of the recycling residue is organic-biological and a highly efficient energy conversion plasma plant could enable a maximum energy yield, while minimising emissions and final residue fractions.

The study’s proposed process starts with the capture and valorisation of the landfill gas, and the processing of the leachate to provide clean water to the site and its environment. After the landfill is re-opened, waste would be mined and fed to the material recuperation process.

Recovery: Enhanced landfill mining can be applied to old landfills to deal with the waste legacy of the past

A decision tool to determine whether a recuperated fraction goes towards the WtM or the WtE process has been developed. WtM targets glass, ceramics, ferrous and non-ferrous metals, plastics, paper, wood, textiles, aggregate fractions and fines; these last two elements would be processed to ELFM building materials through a combination of processes. WtE valorises recycling residue from the material recuperation process, the so-called Refuse Derived Fuel (RDF), containing mostly organics.

The WtM and WtE plants will operate for 20 years to achieve total valorisation of the stored waste, and are due to become operational by the end of 2013. Over that period the landfill site will be developed into a sustainable nature park. The project requires an investment of well over €230 million and will fire a 75 MW to 100 MW electrical power plant based on plasma technology.

Carbon dioxide from the WtE plant is intended to be captured through various carbon sequestration methods. A very limited amount of the waste, for which no valorisation potential is yet identified, will have to be restored to a state-of-the-art landfill. This renewed storage will only be temporary, as it is envisaged that further development of recycling and energy technologies will enable the restored waste to be valorised in the future. Hence, Closing the Circle becomes part of closed materials loop, albeit over a long period.

Character of the landfilled waste

The goal of the characterisation study was to test several assumptions about the landfilled waste against available landfill inventory and associated data: type, amount and location of the landfilled waste; potential for material recuperation; potential for energetic valorisation.

The analysis had three primary objectives: to establish the reliability of existing reports of the waste inventory, to establish more accurately the potential of the different waste streams for material recuperation or use in generation, and to define routes for research to elaborate on or improve the valorisation potential of certain waste streams.

Characterisation is based on trial excavations and the examination of the waste samples and a study corroborated the accuracy of the inventory, allowing it to be used as the basis for the conceptual analysis of the material and energy recuperation potential. The valorisation potential of the available fractions, for both material recuperation and thermal valorisation, was established more precisely and was still in line with the former estimates.

Material recuperation

The material mined from the landfill consisted of a batch of municipal waste and a batch of industrial waste, and originates from the same zones where the samples for the characterisation study were taken. Batches of waste were processed separately in a commercial facility, which implemented the required process steps, including screening, wind shifters, washing, dense medium separators, magnets, eddy currents and shredders.

The results from the material recuperation on the industrial waste were compared with the results of a mass balance of the characterisation study of the landfilled waste. The results show that the fraction designated for thermal valorisation had well matched characteristics.

Energy recuperation

A theoretical analysis and testing programme has been undertaken to assess if Advanced Plasma Power’s Gasplasma™ technology is an appropriate candidate for the thermal valorisation technology. A theoretical model was developed to assess the behaviour of the system on the recycling residue of the mined waste, allowing the construction of a full mass and energy balance.

This approach differs from traditional landfill mining, which is often limited to reclaiming methane

To validate and verify this theoretical model, a set of tests was developed for the recycling residue (RDF) from the material recuperation test on municipal waste and industrial waste. The characteristics of the RDF were representative of the fraction intended for thermal valorisation. A full-scale theoretical model predicted a net electrical efficiency ranging from 25% to 30%. Even higher energy conversion efficiencies are expected to be possible in future plasma converter designs currently being elaborated.

From the analysis of the vitrified slag, it can be concluded that the material is a proper candidate for use as building aggregate or gravel replacement for the construction industry.

Biodiversity and Enhanced Landfill Mining

The impact of ELFM on the environment and biodiversity can have positive knock on effects, such as land reclamation and site restoration as well as a reduction in the use of fossil fuels. On the other hand, the various operational aspects of the ELFM process can impact biodiversity, through indirect and off-site effects as well as direct ones.

Methodologies such as Environmental Impact Assessment (EIA) can tend to focus on direct and local effects. Nevertheless, the positive trade-offs are often global or off-site and must be weighed against temporary negative effects on biodiversity.

Analysis of soil samples from the cover layer of different landfill zones revealed that the current top layer has the potential to restore the required habitat types in the mined landfills. After a temporary loss of habitat, the ecotope balance can be secured, resulting in a net improvement at the end of the project from the current situation.

Carbon footprint

The goal of the carbon footprint study was to quantitatively investigate if the Closing the Circle project would have a significant net CO2 benefit, compared to a ‘do-nothing scenario’. This was done using the Bilan Carbone approach, which is designed to estimate the greenhouse gases linked to the physical processes necessary. The final conclusion of the study is that, to produce the same amount of energy and materials, the total level of greenhouse gas emissions from the Closing the Circle scenario is significantly lower than the alternative of taking no action – 5.3 million tonnes CO2e compared with 6.3 million tonnes CO2e, a 15% reduction in GHG emissions.

Future research

The results of the studies that were undertaken confirmed the conceptual assumptions to establish the feasibility of the Closing the Circle project. But more research is still required, to address:

  • A robust treatment scheme for aged and heterogeneous waste streams
  • Innovative methodologies to convert waste streams into high-value building materials
  • Energetic valorisation of the recycling residue using plasma technology, which focuses on the integrated optimisation of energy valorisation and material recuperation
  • A decision tool scheme to decide if a material stream should be directed to a WtE or a WtM conversion process.
  • This required research was incorporated in an IWT R&D proposal, with a total budget of over €6 million, scheduled to kick off early this year. In parallel, the Closing the Circle project will progress with:
  • Conceptual, planning and detailed engineering
  • Going through the process to obtain the required permits and trying to overcome non-technical barriers using a multi-actor approach.

Through collaboration with strategic knowledge partners and research institutes, the Closing the Circle project could be developed into a competence centre for Enhanced Landfill Mining and Enhanced Waste Management.

This could help generate a major shift in both waste management technologies and national and European waste management visions, contributing to the transition from linear to circular economies.