Waste that cannot be reused or burned is dumped. This is not as simple as it may sound. New dumpsites need to satisfy the so-called ICM criteria for the isolation, control and monitoring of the waste material dumped there.

Isolation means preventing substances in the waste from entering the soil or contaminating the groundwater. Control means making sure that everything is well maintained during the period in which a landfill site is in use and that, for example, rainwater is collected and purified if it sinks into the landfill.

Monitoring has to do with the obligation that you are constantly keeping an eye on everything and regularly check to make sure that the landfill still meets the requirements.

None of this will stop after the dumpsite has reached its highest point. Indeed, as the administrator of the waste-processing site, Twence is responsible for the monitoring and the everlasting aftercare of the landfills.

Isolation

To prevent contaminants from ending up in the soil, the base of the disposal compartments have a double sealing liner. This consists of an impenetrable layer of sand-bentonite beneath an extremely strong layer of plastic film. Drainage pipes under this lining allow monitoring to make sure the lower seal functions properly.

Control

Above the base sealing liner there is a layer of sand with drainage pipes for the discharge of water that percolates out of the waste (leachate). This water is collected and then purified in Twence’s own purification system.

Once the landfill is full, it will be isolated with a waterproof layer on the top as well. According to the current practice, this definitive sealing consists of yet again a double sealing liner of plastic film along with a protective layer of sand bentonite. Once this has been added, the waste is then completely sealed off from the environment. The landfill can then be used for any number of purposes, for example as a golf course, ski slope or recreation area. At Twence we are also looking into other applications. An experiment with the cultivation of grapes on the south side of a landfill is one example. The landfills on the Twence sites will reach a maximum height of 25 metres.

Gas well

The decomposition of waste in the landfills produces a gas: landfill gas. About 50 to 60% of this gas consists of combustible methane. To keep this gas from spontaneously combusting, Twence collects it and uses it as a source of energy. To that end, perforated pipes are placed vertically in various places within the landfill to serve as an outlet for the gas.

The amount of gas involved here is considerable. We recover 1000 m³ of gas per hour from the landfill at Boeldershoek and 350m³ from the Elhorst Vloedbelt site. We use the gas that we extract from the Boeldershoek landfill site to generate our own electricity. The gas from Elhorst-Vloedbelt is sold to Cogas.

Woorden in diagram:

Stortheuvel : Landfill

gronddek : Ground cover

kunststof folie : Plastic film

afval : Waste

percolaat drainage : Pipes for landfill leachate drainage

Controle drainage : Pipes for monitoring drainage

zandbentoniet : Sand-bentonite layer

Ondergrond : Substratum

stortgasafvoer : Landfill-gas exhaust pipes