LEACHATE TREATMENT PLANT DESIGN
It is only 20 years since Aspinwall (now Enviros) designed and commissioned the first fully engineered Sequencing Batch Reactor (SBR) leachate treatment plant at a landfill site high on a mountain in mid-Wales, UK.
That plant is still pre-treating leachate before discharge to sewer, but has been joined by more than 50 other UK plants using the same process, nearly half of which are required to meet stringent standards, which allow them to discharge treated effluent safely into surface watercourses.
Some of these plants are extremely sophisticated, treating strong and difficult leachates (e.g. Robinson et al, 2002; 2003). However, the most common requirement at UK landfills is the reliable, robust, automated and cost-effective treatment of everyday leachates, where the main contaminants are ammoniacal-N, and organic compounds measured in total as COD and BOD5.
State-of-the-art technology has moved on significantly, even since 1999 when a detailed review paper was published (Robinson, 1999).
Demand for simple, automated and reliable leachate treatment systems, suitable for operation on remote rural sites, has grown rapidly during even the last 5 years. An increasing number of plants is now being required to discharge high quality effluents, directly into surface watercourses.
This trend is certain to continue – primarily driven by the requirements of Integrated Pollution Prevention and Control (IPPC), for the application of Best Available Techniques of treatment.
At some sites where local sewerage networks are able to accept raw leachate for co-treatment with domestic sewage in Water plc works, often the only pre-treatment required is removal of dissolved methane from the leachate, to avoid generation of explosive atmospheres within the sewer system itself. This involves careful process design – reliable removal of 99% dissolved methane can often be needed to achieve the widely-adopted discharge standard of 0.14 mg/l.
Detailed design guidance has been published to allow adequate systems to be provided (see Robinson, 2001 and Robinson et. al., 1999), and as explained in another of our web sites (www.methane-stripping.com).
The largest growth, however, is in demand for medium-sized leachate treatment plants (typically to treat 100-200 m3 of leachate per day) in aerobic biological treatment systems, often with reed bed effluent polishing.
These systems are built to allow discharge of high quality effluents into surface watercourses. Although other biological processes are entering the field (eg Biological Aerated Filters (BAFs), Membrane Bioreactors (MBRs), the SBR process probably accounts for more than 90 percent of biological treatment schemes designed for leachate, during the last ten years in the UK.
For Case Study examples visit our main Leachate Management web site here.
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