Bedding down to treat leachate from landfill

In 2002, the EU Landfill Directive came into force in the UK as the Landfill Regulations. These regulations cover the management of existing sites as well as the introduction of new sites. The directive aims “to prevent or reduce as far as possible negative effects on the environment, in particular the pollution of surface water, groundwater … from the landfilling of waste, during the whole life cycle of the landfill”.

This means that landowners and local authorities with responsibility for landfill sites – whether active or inactive – must now prevent or reduce the pollution of surface water and groundwater by leachate from the landfill. This is especially important as local authorities look to create public parks on the land or sell the sites to private developers. While the usage of the land may have changed, the landowner must still take responsibility for impacts on the environment for the whole life cycle of the landfill.

Treating historic sites

In 2005, the Environment Agency and SEPA recorded 1,342 licensed landfill sites in England, 73 in Wales and 231 in Scotland. There were 20,736 historic sites recorded across England and Wales. Many of these sites are subject to the Landfill Directive and, as such, will need some form of ongoing treatment by the landowner. Even those historic sites that may not have been subject to such tight regulation when in operation may now be classed as contaminated land and require some form of treatment.

Landfill sites are open to the elements. Rain falling on the site, or water entering from surface streams, permeates through the layers of waste. This, combined with the resulting liquid from the decomposition process, produces a leachate. This leachate is typically difficult to treat as its composition can vary greatly from site to site. Factors such as the age of the landfill site, type of waste, size of the site, and treatment already in operation can all impact on the leachate composition.

Leachates have the potential to contaminate land and surface water or groundwater around the site. Landfill leachate is a high-strength wastewater, which is characterised by high concentrations of organics and ammonia as well as the potential for toxic levels of arsenic, and other metals such as iron.

The Landfill Directive requires that all new landfill sites are lined. These liners can be both mineral and synthetic, and they allow the leachate to be collected before being treated as required and discharged to sewer or watercourse. Some older sites do not have this protection in place but it is still possible to treat the leachate. One treatment method, which has proven effective over the past 20 years, is the use of reed beds. The leachate is collected and then directed towards storage lagoons before being distributed through a reed bed treatment system.

The use of reed beds to treat dirty water is not a new idea. In fact, records indicate their use for this purpose 2,000 years ago in China. But it is only relatively recently that their application has been considered more scientifically. Work began back in the 1960s in Germany to better understand and formalise these systems to treat effluent to a specific standard.

The volume and nature of the leachate produced will determine how the reed bed is engineered. There are different types of reed bed, which are selected on the basis of the specific treatment requirements – but the principle of how they work is the same. In essence, the wastewater is filtered through a soil or gravel matrix in which the reeds are planted. Bacteria thrive in the matrix and break down the contaminants.

A tested solution

ARM, a supplier of natural wastewater treatment systems, constructed its first horizontal reed bed system in 1985 to trial the suitability of the technology to treat agricultural effluents. After years of research and development, including affiliations with several universities, reed bed treatment systems are applied to a wide range of effluents and industries, and used to remove contaminants such as organic waste, hydrocarbons and heavy metals.

The first reed bed constructed for the treatment of landfill leachate was at Howden Clough in 2001. This trial system – in which horizontal and vertical flow reed beds were used – was soon followed by a bed at Hell Hole in Warwickshire. More recently, ARM has designed and installed a reed bed at a landfill site in Essex engineered specifically for the removal of iron from the landfill leachate. The gravel pit was used as a landfill for domestic rubbish for more than ten years in the 1960s and 1970s. More than £1M was invested by the local council to clear up the site in 2007. The works undertaken included underground barriers and drains to control the flow of water leaching through the refuse.

This leachate is then treated by a horizontal surface-flow reed bed. The bed is planted with typha latifolia reeds, which have been shown to be particularly effective in the treatment of metals, in this case reducing the level of iron in the treated water to less than 20mg/l.

Landfill sites continue to produce a leachate for many years after deactivation, which has a significant environmental impact. Reed bed treatment systems provide a sustainable and cost-comparable way of preventing groundwater contamination that is both low energy and low maintenance.

Patrick Hawes is sales manager at ARM