Solar-powered mobile dosing trailer is first of its kind

The Coal Authority has invested in a unique mobile chemical dosing trailer to help in its work to protect and enhance the environment.

The off-grid system, which can be monitored and operated remotely, will be used while we carry out essential work at our 76 mine water treatment schemes across the UK.

For most of the year the innovative unit will be powered entirely by its 4 solar panels, but in poor weather conditions the 5.12kW lithium-ion battery will require supplementary charging every 2 to 3 days by a small, portable, petrol-powered generator. However, this charge cycle only takes 1 to 2 hours, so manual intervention is minimal.

Andrew Hargreaves, our operations contract service manager, said:

Most of our schemes are working principally to remove dissolved iron from the mine water. They are ‘passive’, which means they use natural means such as aeration cascades to oxidise the iron – converting ferrous iron to ferric iron – and then settling lagoons and reed beds to remove the particulate ferric iron.

To ensure they continue to operate as efficiently as possible, routine maintenance such as cutting back the reeds or removing ‘ochre’ iron deposits is critical. However, while this work is carried out it can temporarily reduce their capacity to clean the water.

As a short-term solution we sometimes need to bring in chemical dosing, or ‘active’ treatment, adding hydrogen peroxide to ensure we continue to meet discharge consents. In the past we have used mobile dosing units, but these are typically based in shipping containers which also require generators and fuel bowsers to power them.

By their very nature, our mine water treatment sites can be very remote and inaccessible, so we’ve developed this small, mobile system, with specialists Leada Engineering Ltd and our contractor Severn Trent Services, to enable us to dose whenever and wherever needed. The unit has on-board chemical storage as well, sufficient for 7 days’ dosing at average dose rates.

This trailer also gives us the ability to make an emergency response to an acid-flush event, which is where an existing mine water discharge suddenly and unpredictably exhibits a rapid and significant decrease in pH, which can be sustained for weeks or even months.

These situations require the addition of an alkaline chemical to increase the pH and restore treatment, so the system has been designed to be multifunctional and – following appropriate safety procedures for chemical changeover – it can also dose sodium hydroxide.