Disused Mineawter Treatment - UK Coal Authority Case Study

The UK Coal Authority (http://www.coal.gov.uk/) has the responsibility to manage the stock of disused coal mines within the UK. A primary responsibility is to ensure that water flowing from disused mines does not pollute the environment.

When a mine has been disused for a period of time and pumping has stopped, water levels rise in the mine and eventually flow out of the mine. This water has resided in the mine for a lengthy duration and has surrounded the iron steel works that supported the mine. Over time the iron corrodes and dissolves into the water so that the resultant outflow is iron-laden.

When that water reaches the surface and is exposed to air, there is a chemical reaction with the oxygen and ochre is formed. This settles out of the water and will usually deposit itself on a stream or river bed in the form of a thick ochre coloured film. This has two undesirable impacts, firstly it acts as a choke on the river bed so that vegetation cannot grow and other river life is deprived of food and nutrients and secondly it is aesthetically very unpleasant.

The UK Coal Authority has a particular responsibility to treat minewater discharges, in particular that this ochre does not enter into the nation’s rivers. It installs minewater treatment systems at a number of disused mines each year. A key part of this system is the oxygenation of the minewaters and the ochre settles as sludge in purpose-built lagoons and also captured in reed beds. This ochre sludge can then be removed and used for various purposes. Following treatment the clean water is then allowed to flow into the river system.

The Authority’s traditional method of aerating disused minewaters has been to install cascades that take the water as it is discharged from the mine and aerate it before it enters the lagoon. This has been found to be successful but has the disadvantage that water has to be raised 2.5m in order to transfer sufficient oxygen into the water and secondly it is a costly structure that has to be designed for each site.

Newton Industrial Group approached the Coal Authority with a solution based on the Newton Gravity Aerator. This has the primary advantage that it only requires a head of 0.5m and is cheaper to manufacture and install. The Coal Authority decided to commission a trial at its Wooley site.

Newton built an aerator and installed it into a tank at the site where accurate measurements of the oxygen transfer could be made. The Coal Authority was also concerned about ochre build up on the aerator and this was observed over a period of 3 months. The picture shows the aerator in operation and the bubbly column generated by a head of around 0.4m. This is a dual downflow arrangement that enabled the aerator to handle a flow of around 30 l/s with a footprint of 1 sq m.

This trial was successful and convinced the Coal Authority that the Gravity Aerator could supply the oxygenation needs of its minewater treatment systems. This could be achieved with a low head of 0.5m and no detrimental effect from ochre build up. Subsequently the Coal Authority has ordered the Newton Gravity Aerator to be installed at other treatment sites.