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High Attenuation Recycling Materials as sustainable barriers for waste disposal sites

Periodic Reporting for period 1 - HARM (High Attenuation Recycling Materials as sustainable barriers for waste disposal sites)

Okres sprawozdawczy: 2018-03-13 do 2020-03-12

The need to minimize the amount and foster the safe treatment of waste, and thereby reduce the risk of contamination; emphasises the importance of promoting technologies which are environmentally sound with products suitable for re-use/recycling. This project establishes a laboratory experimental study to determine the performance of clay mixed with construction and biomass plant waste as materials for the enhanced attenuation of contaminants in landfill leachate. The aim is to (1) evaluate the contaminant attenuation capacity of these mixtures for different conditions, (2) develop design guidelines to construct barriers for waste containment systems and similar applications, and (3) interpret their performance using numerical modelling tools. Column experiments where landfill leachate is passed through different waste:clay mixtures will be run in a state-of-the-art centrifuge facility which simulates realistic times, pressures and temperatures of landfill field conditions. The geochemistry of the column pore water and material residues after permeation with leachate will be examined to deduce the processes responsible for pollutant removal and retention. After permeation with landfill leachate, the effects of exposure of these liners to an aggressive rainfall infiltration or rising water table will be studied. The concept will be applicable for barrier design at other waste disposal facilities. The results will provide a novel and timely improvement which addresses the problem of managing the vast amounts of construction and biomass plant waste. Instead of disposal these will be re-used/recycled as an additive in host clay for building contaminant liners, thus also conserving natural resources (clay and other man-made liner materials). It will also provide an effective and more environmentally sustainable basis to control landfill pollution risks
Landfill leachate liners built with readily available natural clays and industrial by-products without any value (i.e. residues with no current application) were tested in self-designed experiments to mimic real landfills
After the optimum compaction in test cells also specifically designed for this, 10-cm liners were permeated with a landfill leachate and 50% CO2/N2 gas using a 2-m radius geotechnical centrifuge at 25 gravities (106 rpm) for periods of 19 days
At the end of it, solid samples (liner slices with depth) and liquid samples (above and below the liner) were prepared for physicochemical analyses and based on them, the contaminant transport and attenuation mechanisms through the liners could be deduced
By running a subsequent rainwater permeation test, the potential for release of previously attenuated leachate contaminants in selected liners was also evaluated
Apart from replicating real pressures and temperature, this experimental set-up allowed to extrapolate the results from a test of weeks with a sample of centimetres, to a real scenario of yrs and meters, i.e. the prototype
12 different liners (40 incl. replicates and control samples) were studied for prototype periods of 33 yrs of landfill operation (leachate permeation) with 72 yrs of landfill closure and monitoring (rainwater permeation)
The data showed good quality with high reproducibility between replicate samples within the same and separately experiments.
Differences depending on the additive (by-product) and on the clay were due to their mineralogy and physicochemical-engineering properties, but in any case, the leachate impact was always characterized by a pH of 8-8.5 (buffer), higher than in the underlying unimpacted zone
The characteristic elements due to their high concentration (x10^3 mg/L) of landfill leachate pollution were ammonium and organic carbon; while for clays were calcium and sulphate
Heavy metals resulted in very low concentrations (10^-2 mg/L)
The liners containing until 20% additives minimised leachate migration up to 1 m depth (1) and attenuated as much as 95% of pollutants in leachate (2):
(1) The changes in permeability over 105 yrs (prototype) were insignificant, with values below the most common max. regulatory criterion [a], even when changing from leachate to rainwater
(2) Leachate pollution decreased in the pore water until background natural values even after long periods of landfill leachate exposure due to redox precipitation, sorption (esp. cation exchange), complexation
Based on the initial comprehensive characterization of the materials, the favourable properties of best liner materials for attenuating leachate pollutants could be identified
Results were exploited and disseminated through approx. 4500 people from science (62%), industry (18%), general public (17%) and policy sector (3%); via 4 conferences with 5 presentations, 2 scientific publications (plus 4 in the pipeline), 5 outreach events and other dissemination activities (press release, poster, project webpage, videos, social media)

[a]10-9 m/s, e.g. Council Directive 1999/31/EC
The project has
*characterized/identified the most relevant properties of waste and natural materials for liner design to be geotechnical stable and effective in pollutant attenuation, over long periods of time (mineralogy, shrink potential, attenuation capacity, dispersive/erosion behaviour and fluid permeability variation)
*implemented the enhanced pollutant attenuation approach within the conventional liner construction, incl. the establishment of guidelines to apply attenuation criteria in liner systems. This means the capacity to not only limit pollutant transport, but also enhance their attenuation, DOI:10.31025/2611-4135/2020.13946
*redesigned (zero-waste hierarchy) a new application for industrial by-products (currently with no other beneficial/marketable use) which has no risk of leachability of their own constituents to fresh water or soils. This decreases the waste generation by avoiding their landfilling, DOI: 10.13140/RG.2.2.13407.89761
*succeeded in representing pollutant transport through compacted liners, as the pore water within the liners was highly homogenously distributed and hydraulically connected after the centrifuge. The (1) centrifuge set-up (fluids tubing, sensors, valves, connections), (2) test cells design (sample liner container, effluent bottom collector, gas outlets) and (3) instructions on avoiding experimental errors (flow homogenization, size-mass-time relationships, gravity calculations, data collection-analysis-interpretation) to link the experimental data with the corresponding prototype are open access to anyone for their own research, DOI: 10.31223/
*proven long-term liners with constant low permeability (0.2–0.4∙10-9 m/s) and compatible under landfill leachate (pollution source) and rainwater (reversibility risk scenario) exposures
*decreased the high plasticity of the clays, and therefore their associated risk of shrinkage (which induces instability and cracks with an increase of contaminant leakage through them) by adding the by-products
Overall, the redesigned (sustainable and competitive) liners will benefit the society’s health from the protection of leachate pollution and the EU's economy from the decrease of industrial waste. The developed liners minimize leachate migration by their impermeability (slow transport) and attenuation (leachate self-cleaning) capacities and may readily be transferred to other pollution management issues, such as mine drainage management or contaminated stormwater runoff
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Summary of what we do and how you can help
The idea from which all began
New approach: what is attenuation and its benefits against pollution
These are our materials which are widely distributed