Leachate Management

6.
Leachate Management

Leachate is the liquid component which filters through a waste body, and is a mixture of rainwater which has seeped through the waste, water soluble chemicals, by-products of microbial action and liquid from the waste itself. Leachate is a highly contaminating effluent and modern sanitary landfills prevent leachate from seeping into the groundwater by means of liners and drainage systems which collect the leachate. Once leachate is collected it can either be treated on site or can be pumped or tankered off to a waste-water treatment plant. Should the landfill be situated close to a waste-water treatment plant, then the latter option would be favoured eg Bellville landfill and Coastal Park landfill. The Vissershok landfill is far from the nearest wastewater treatment works (Potsdam, Athlone and Raapenberg), and for this reason it was more economical to construct a leachate treatment plant at Vissershok. This will reduce the transport costs of tankering the leachate off-site. The other benefit of treating the leachate is the fact that the treated effluent could be used for dust suppressing on the on-site roads and the area close to the working face. This prevents the operator from using potable water in a water-scarce region.

It is important to run laboratory trials first before embarking on a full-scale leachate treatment plant to assess the leachate treatability. The destination of treated effluent needs to be determined prior to process design, so that appropriate treatment can be provided. There are many different leachate treatment plants that could be designed, and the Vissershok as well as the Mariannhill landfill sites makes use of a sequencing batch reactor (SBR) system. The SBR makes use of aerobic biological primary treatment processes, followed by a secondary polishing process via a reedbed.

The objective of the SBR is to reduce two pollutants viz, the chemical oxygen demand (COD) fraction, and the ammoniacal-N fraction. The ammonia is converted to nitrates and nitrites by means of the Nitrosomonas and the Nitrobacter bacteria. This is the nitrification stage of the process. During the denitrification stage, the nitrates and nitrites are converted into free nitrogen. At the Vissershok plant only the
nitrification stage of the process is utilised, to save costs and due to the treated effluent being used for dust suppressing and not discharge into a water body. From the SBR the leachate is passed through a reedbed for final polishing. During this process further residual biodegradable COD, BOD and solids are removed through physical filtering through the root zones.

SBRs have proven to be robust systems, and are applied in many countries all over the world in varying climates. It is a relatively low-cost, easy to operate system.

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Sumber:
Core Notes for Module 6 (Elective) of the Course
“Environmental Engineering – Sustainable Development in Coastal Areas”
Cape Peninsula University of Technology (CPUT)
Cape Town, South Africa
2006
Available to Distance Learners on www.dlist-benguela.org