Leachate pollution from landfills (Signal)

Landfill leachate (LFL) is the liquid that has seeped through solid waste in a landfill, extracting soluble dissolved or suspended materials in the process. When leachate escapes from landfills it can contaminate groundwater, surface waters and soil with toxic organic and inorganic pollutants; these include heavy metals and ammonia nitrogen compounds, as well as emerging pollutants such as pharmaceuticals, plasticisers and Per- and polyfluoroalkyl substances (PFAS). Therefore, ensuring adequate measures are in place to monitor, prevent and treat LFL is essential for protecting human health and the environment.

Managing LFL releases to the environment

The EU Landfill Directive 1999/31/EC sets out strict operational requirements for landfill sites, including provisions for effective sealing systems and the collection and treatment of LFL. Prior to the implementation of this directive, landfilling in the EU was not consistently regulated across Member States. The legislation has resulted in significant improvements in the way landfills (and specifically LFL) are managed. Landfilled waste decreased by 27.5%, from 173 million tonnes to 125 million tonnes between 2010 and 2020. Over the same period, the share of waste generated (excluding major mineral waste) that is being landfilled in the EU has declined from 23% to 16% as shown on the Figure. However, leachate generation remains a problem. The collection and treatment of leachate also continues to be a major management issue facing landfill operators. This issue is likely to continue for decades to come.

Brennan et al. (2016) used historic landfill data, combined with leachate characterisation data (e.g. total nitrogen, chemical oxygen demand and total metals) to determine the impacts of a number of EU Directives (Landfill Directive, Waste Framework Directive 2008/98/EC, Urban Wastewater Treatment Directive 91/271/EEC and the Water Framework Directive 2000/60/EC) on landfill leachate management, composition and treatability in Ireland. The study indicated that there was a reduction in the volume of leachate produced per tonne of waste landfilled in Ireland since the Landfill Directive was enforced, but the concentration of pollutants in leachate has increased.

Challenges in collecting and treating LFL

The collection and treatment of LFL presents technical and logistical challenges for landfill operators. As it is often not possible to treat LFL on site, it is becoming common practice to transfer leachate to wastewater treatment plants (WWTPs) and co-treat LFLs with domestic sewage. To date, there has been limited investigation into the environmental impacts of co-treatment of landfill leachate and municipal wastewater in WWTPs. Studies have been largely limited to laboratory-scale batch experiments. This lack of data is a concern for WWTP managers, as wastewater effluent is subject to increasingly stringent legislation in the EU, for example under the proposal for a revised Urban Waste Water Treatment Directive. This has raised questions regarding how LFLs will be managed going forward and the implications for future environmental and human health impacts.

Though the EU Landfill Directive mandates Member States to establish a monitoring regime for landfills, more specific requirements for monitoring the quantities and concentrations of pollutants in leachates are needed to ensure comprehensive oversight. There is a lack of regulatory requirements in the EU to monitor the volumes and/or concentrations of contaminants that are present within leachates. As a result, data on contaminants in LFL is scarce and is usually available from academic studies of specific landfill facilities for a specific time period. Therefore, there is currently no reliable way to assess the magnitude of risk posed by LFL to the environment and human health.

Possible solutions

Preventing landfill leachate is important for mitigating environmental contamination and promoting sustainable waste management practices. Waste prevention, and proactive waste diversion strategies, such as recycling, reduce the volume of waste disposed in the landfills, thereby decreasing leachate generation. In addition to the updates to Waste Framework Directive and Landfill Directive, the new Circular Economy Action Plan, also underscore the importance of reducing landfilling and promoting sustainable waste management practices, thereby indirectly targeting leachate prevention.

On the other hand, several new technologies and processes to treat LFL are being developed which can be adopted and deployed in conventional WWTPs. For example, floccular activated sludge has evolved to granular sludge processes; shortcut denitrification processes can potentially lower the oxygen and carbon requirement for nitrogen removal; membrane processes can provide higher effluent quality; more advanced aeration methods enhance energy efficiency, instrumentation and control; and automation capabilities have increased. Several projects in the EU have focused on treating landfill leachates, including the CLEANLEACHATE project, which explored a treatment system for the removal of refractory organic substances and ammonium by oxidation processes without chemical additives in LFLs; and the OXFLOC project, which aimed to reduce treatment costs of industrial wastewater in Europe and has been tested with LFL. In addition, while generally not specific to landfilling activities, the ‘Best Available Techniques Reference Documents’ (BREFs) developed to support the Industrial Emissions Directive 2010/75/EU implementation is also a useful source of available technical solutions for treating effluents. For example, the BREF on common waste water treatment techniques in the chemical sector is of particular relevance.