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
