Sustainable Minewater Systems
Sustainable Minewater Systems
Reedbeds are the most ecologically friendly way of treating what is a serious problem – Mine water. The reedbeds provide a visually attractive solution to the mine water problem brought about by years of coal mining and more recently the cessation of dewatering of such mines which allowed many watercourses in Britain to become polluted with Iron Ochre, lowering their ecological diversity drastically and in some cases completely.
The constructed wetlands form a concentrated habitat for insects and birds which can also be used as a public amenity with some of the Authority’s mine water treatment schemes incorporating picnic areas, paths, benches and viewing points.
However, there is a scientific side of reedbeds. Reedbeds serve two main purposes in mine water treatment these are:
1. Filtration – Filtration occurs both within the soil and subsoil of the reedbed and through the roots of the reeds themselves. As the water makes the journet through the reedbed, the particles of Ferric Hydroxide become caught and remain within the natural filter whilst the rest of the mixture progresses. A successful treatment scheme is one where the reedbeds are of a sufficient size that all of the particles are removed before the water re-enters the watercourse
2. Settlement – Settlement occurs once filtration has taken place. Most of the Authority’s reedbeds have a design life (storage capacity) of in excess of 15 years. Settlement is the process by which the particles are formed during filtration collect together and fall to the base of the reedbed.
At present we allow approximately 10mg/l to enter the reedbeds at all our schemes with less than 1mg/l entering the watercourses at the end of the reedbed process.
• The Authority inherited a number of existing operations from British Coal where minewater pumping took place to control rising minewater and prevent future uncontrolled discharges. Iron exists in the ferrous form within the country’s mine workings.
• Upon exposure to the surface, the Ferrous Iron oxidises to become ferric iron – a hydrolysis reaction which causes the precipitation of ferric hydroxide – these particles fall fromt he solution and join together to form a thick substance that coats the river bed, It is this substance that causes effected watercourses to appear a red/orange colour.
Over time the iron ochre builds up in the treatment lagoons and periodic de-sludging is required to maintain the efficient operation of the process. The ochre sludge is pumped out as a liquid sludge before undergoing a process of dewatering and/or drying (e.g. centrifuge, plate filter press or drying bed). These processes result in the production of a solid ochre material which can be either safely land filles as an inert waste, or put to beneficial reuse.
The beneficial re-use of ochre is being actively pursued by the Authority. Ochre has a number of valuable properties: from use as a pigment in building materials; to absorption of phosphate in waste-water and agriculture; to treatment of metals/arsenic contaminated soils. Sustainable Water has supported the Authority in the development of the longevity of the existing systems and provides the conditional report which supports them in exposing the limitations of the wetlands and as and when they require maintenance as part of a program.
The system of Maintenance consists of prevention of Surcharging, Analysis of the content of ochre present and the expected lifecycle before such activities are required to be employed to extend the lifecycle and longevity of the treatment scheme.
We have successfully achieved maintenance objectives which have now proven to be the most cost effective solution extending the life expectancy indefinitely.