TOXIC LANDFILL SITES! … Perhaps not

Man has the capacity to generate vast quantities of waste; practically everything that is bought comes in a packet or container of some sort. In normal middle class households there is approximately 4-5 pounds or 2kgs of waste generated per person per day (not recycling households). If you had to work this out for your household you would realize just how quickly this adds up.

So, what happens to all your rubbish? Well, you leave your trash bags outside your gate once a week and they get whisked off and you don’t need to worry about them again. I’m sure we all know that the garbage gets thrown on a big pile and when it is big enough it is covered with soil and that is the end of that.

It would be pretty easy to comprehend that the pile of garbage would soon become fairly toxic, and that is usually the case. As the garbage decomposes and gets rained on a toxic liquid called leachate is brought into existence. This cloudy, yellow brown liquid contains some lethal ingredients such as alcohols, sulphates, chlorides, iron, aluminium, zinc, ammonia, heavy metals and more. Leachate is often responsible for the pollution of surface and underground water.

The Durban eThekwini Municipality in South Africa have created an ecosystem restoration landfill, it is in fact a landfill conservancy (a conservancy is a protected area to be left in its natural state). It is the first landfill internationally to be registered National Conservancy.

Through careful planning and ingenious foresight the Marionhill landfill has been designed in such a manner as to operate as a close loop system, meaning that all the components of the waste process are fully harvested before re-entry into the ecosystem. The system works roughly as follows:

• At the start of construction all the vegetation in the landfill site was removed and placed in a nearby nursery aptly named PRUNIT (Plant Rescue Unit). Here plants are propagated and used to re-establish the landfill site once a cell has been filled as well as the rehabilitation of other areas.
• The site is divided into a number of different cells. Each cell is lined by a geomembrane, this consists of a thick plastic liner which isolates it from the environment and prevents contamination of the surrounding area. A layer of rock and sand is then placed over the plastic liner to allow drainage of accumulate liquids.
• Garbage arrives and where possible all recyclable material is recovered from the load.
• The recyclable material that is recovered is sent off to appropriate recycling facilities.
• The remaining waste is placed into the operating cell and compacted by bulldozers reducing the volume of waste and making it more stable.
• At the end of each day the waste is covered with a layer of sand reduce the odour as well as accumulation of flies and rodents. The sand cover also promotes the anaerobic process ie. the biodegradation of the waste material by microorganisms.
• The anaerobic process creates two main by-products, Landfill gas (LFG) made up mainly of methane and carbon dioxide, and leachate.
• The LFG is channelled through pipes constructed into the landfill. The methane gas collected is used to power engines, thus creating electricity. Making the landfill project sustainable and may even generate income from electricity sales. Extracting the methane from the landfill also speeds up the degrading reaction.
• The leachate in most normal landfill sites becomes very toxic, this is aggravated by the length of time it is left to ‘brew’. At the Marionhill landfill the leachate is collected in a huge reservoir called a Sequence Batching Reactor. This ‘young’, less toxic leachate is treated through a process of aeration and settlement, so that both anaerobic and aerobic cycles can further break down the biological components in it. The cleaned leachate is then drained off and passed through a reedbed which acts as a ‘polishing treatment’.
• The fully treated leachate is used for irrigation within the conservancy including Prunit.

And thus a closed loop system is created. Every element produced is treated and utilized to create a healthy, toxin free environment. The Marionhill landfill conservancy is an exceptional example of how we can face the ecological challenges of waste management in urban environments.

Research by Shannon Hagemann

For more information:

http://www.durban.gov.za/durban/services/cleansing/gastoelec/fill