Bacteria-based biological system treats leachate
An increasingly important area of landfill management is the treatment of leachate, including the application of bacteria-based biological systems featured in this report from the West of Scotland sites operated by Barr Environmental Ltd, where Andrews Sykes played a key role
Using bacteria-based biological systems to treat leachate in purposely-created lagoons is common practice at many landfill sites across the UK and Europe. But when the landfill sites are located in Western Scotland, the ambient temperature often falls low enough to render the bacteria ineffective. To overcome this temporary difficulty pending the delivery of permanent heat exchange units, waste management company Barr Environmental Ltd required the capability to heat the lagoons. The company turned to Andrews Sykes for the hire of a 500kW Hotmobil boiler, a 2.40MW heat exchanger and a 2,800 litre fuel tank.
Most landfills are lined with an impermeable membrane to prevent the escape of leachate into the surrounding geology where it could possibly inflict ecological damage to rivers and streams resulting in the potential loss of water resources. However, lined landfill sites means the inevitable accumulation of leachate, which then has to be extracted and treated before it can be dispersed in a safe manner. To overcome the problem, Barr Environmental Ltd pumps leachate into specially constructed lined lagoons, where it is biologically treated. However, elevated ambient temperature is key to the success of the process, as, when the temperate dips below 10°C, the bacteria, used to break down the toxicity of the leachate, dies. Also, as leachate production is dependent on the amount of rainfall delivered, Scotland is susceptible to accumulation thanks to its receipt of above average quantities, especially in winter months. The critical situation needed resolving, which is why Andrews Sykes was invited to consult, particularly as the company had successfully completed a similar scheme at Levenseat landfill, also in Scotland.
It was clear that a temporary heating system would provide the answer. The simple option would be to use a boiler, however, due to the presence of sediment in the leachate, engineers at Barr and Andrews Sykes decided a straightforward boiler solution was not suitable for transferring the fluid directly around its primary circuit. It was apparent that a secondary system had to be installed in order to create a safe alternative.
Andrews Sykes proposed a separate heat exchanger that featured large bore passages and a filter to reduce any potential effects of clogging. The primary circuit on the boiler fed the primary side of the heat exchanger and returned the water back to the boiler for reheating. The secondary side of the heat exchanger was fed by the customer's own pumps from the lagoon, from where the fluid was returned to the lagoon as heated water. This ensured a temperature in excess of the minimum requirement was constantly maintained, thus allowing the biological treatment of leachate to continue, unaffected by the ambient temperature.
Barr Environmental ordered two identical systems from Andrews Sykes, one for Auchencarroch near Dumbarton and one for Garlaff near Ayr.
The hired equipment remained on site until Barr was able to install and commission its own permanent leachate heating systems.
"When we were suffering with the cold weather, we phoned around to see who could help us out," explains Barr's Environment Manager, Colin Peebles, "and it was Andrews Sykes that came up with the best response. The proposed solution was installed and up and running within a week, ensuring that overall the project was extremely successful."
Barr Environmental Ltd is a company with assets of 6.5 million cubic metres of consented landfill.
It is a wholly owned subsidiary of Barr Ltd, which carries out design and construction works across the UK and incorporates its own pre-cast concrete, steel fabrication and quarries division.