Oxygen systems meet the landfill challenge
Landfill leachate has long been one of the most challenging aspects of wastewater management and treatment but advanced technology now exists to prevent this kind of diffuse pollution as Peter Barratt, Manager in European Environmental & Clean Technology, Air Products, explains
Landfill sites are typically located in areas that have impermeable strata, such as clay extraction sites, where pollution of the environment is less likely and where the fill itself can be more easily contained. Despite this, all landfill produces a leachate, or liquid waste by-product, which requires treatment before it can be safely released into the water environment.
The number of licensed landfill sites in the UK has fallen rapidly in the last 10 years and those that remain are larger and manage higher volumes of either household and industrial waste or designated hazardous waste. Most of these sites already have leachate management and treatment systems, designed to collect and treat pollutants that would otherwise be discharged, along with natural rainfall, into the water environment.
However, in some cases, these systems are becoming inadequate to meet peaks in demand - the higher volumes of leachate being produced combined with seasonal peaks in demand, caused by bursts of heavy rainfall, means discharge limits are becoming increasingly difficult to achieve.
In response, an increasing number of landfill sites are now looking to upgrade their existing systems to oxygen aerated systems to help them achieve discharge limits and manage seasonal peaks in demand. In doing so, they are also looking for ways to enhance the sustainability of the site and provide a long term solution.
The most advanced oxygen aerated systems have been designed so they can be installed easily to upgrade an existing aerated system. They work by extracting oxygen from the atmosphere, to be used as part of the treatment process. This means the system is not only highly efficient, bringing a significant increase in capacity, but also more sustainable and there is no need to store oxygen supplies on site.
Traditional aerated wastewater treatment systems work by reducing the oxygen demand of the wastewater by dissolving as much as possible of the oxygen found in the air, so encouraging the growth of natural microbes or bacteria that cleanse the water and remove organic and other contaminants. The innovative oxygen systems work in the same way but use high purity oxygen in place of air to aerate the wastewater, providing increased capacity because of the faster rate of oxygen dissolution. Depending on the capacity of the oxygen aerated system installed, it is possible to reduce oxygen demand by as little as 250 kg per day, or as much as five tonnes a day, using a compact, modular unit.
These innovative oxygen systems give the landfill manager much greater flexibility to achieve discharge limits, consistently, regardless of the climatic conditions. By increasing the flow of oxygen, it is possible to meet a surge in demand, for example, when the amount of leachate requiring treatment increases following a heavy downpour of rain.
These systems are also flexible to the additional demands created by exceptionally cold or hot temperatures. For example, during very cold weather, discharge levels of some contaminants, such as ammonia, can increase, and by using pure oxygen to aerate the system it is possible to increase the process temperature slightly, so helping to reduce emissions by keeping the key bacteria within their temperature comfort-zone. Similarly, during very hot weather, oxygen dissolution will be impaired and traditional aerated systems may provide insufficient oxygen to meet demand. The high purity oxygen used in oxygen aerated systems is less susceptible to temperature variations and can be adjusted to increase the flow of oxygen to meet any change in demand.
One of Wales' larger landfill sites, Bryn Posteg at Llandiloes, owned and operated by Potters Waste Management, has recently invested in an oxygen aerated wastewater treatment system, provided by Air Products. The new system, known as the OXY-DEP® VSA system, is capable of reducing the oxygen demand of the wastewater by as much as 875kg a day. It replaces a traditional aerated system and will provide a long term solution capable of meeting the increasing demand for the management and treatment of leachate. The system is also more efficient and sustainable.
Achieving discharge limits is not the only driver for landfill sites to review their leachate treatment and management systems. The Water Framework Directive is also entering a crucial phase and a deadline has been set for all surface and groundwater across the EU to achieve good ecological status by 2015. This deadline has been recently underlined by Patrick Murphy, head of the water protection unit at the European Commission.
Impact of legislation
Rather than wait for clarity on the precise requirements of the legislation, many forward-thinking waste management companies are taking action now to ensure wastewater treatment and management systems are designed for optimum efficiency.
This legislative change combined with the increased demands on landfill sites, is encouraging many waste management companies to find technological partners. Oxygen systems are not only proving they are more flexible, they also provide a more robust, long term solution.
Landfill managers can assess the efficiency of their current wastewater treatment system, using an online risk assessment tool at www.airproducts.com/wastewater.