Trials of an innovative technology developed in Wales to tackle severe heavy metal pollution in rivers has seen the treatment’s success with raw samples showing metal removal of 87% while filtered samples confirmed 99.5% removal of metals.

The results have been described as staggering by Natural Resources Wales, the Agency responsible for tackling metal mine pollution in the country.

Long-abandoned metal mines, which once produced lead, zinc and copper, are now the source of severe pollution whose toxic discharges can have a severe impact on the water quality of the surrounding area.

Wales is home to nine of the 10 worst metal mine polluted catchments in the UK and overall has more than 1300 abandoned metal mines, which impact on over 67 water bodies containing more than 600km of river.

Natural Resources Wales has been sharing the results of two of its most successful innovation projects to tackle mine water pollution at Cwm Rheidol and Frongoch.

Once home to mines producing lead and zinc, production at Cwm Rheidol ended in the early 20th century but its effects are still being felt today.Two mine entrances discharge highly acidic, orange water which contains high levels of zinc, lead and cadmium. Over the course of a year eight tonnes of metals are discharged into the Afon Rhiedol that impacts the river for 18km.

The mine is situated in a narrow, steep sided valley which is unsuitable for traditional treatment processes which require a considerable area of land.

KP2M Limited trading as Power & Water, a Swansea company providing research led solutions to the water industry successfully tendered to run a trial using an innovative sono-electrochemical technique. The small footprint of the equipment makes it particularly suitable to rugged upland locations where traditional passive pond systems simply will not fit.

Encouraging preliminary laboratory results were followed by further independent laboratory results which confirmed the treatment’s success with raw samples showing metal removal of 87% while filtered samples confirmed 99.5% removal of metals.

A full-scale system like the pilot trial, benefitting from added filtration to reduce fine particulate matter will be expected to achieve 98% or more reduction of metal loading.

Lying to the south east of Aberystwyth is Frongoch, another former lead and zinc mine which operated between the mid-18th century and 1905.

Natural Resources Wales is also currently running a separate trial at Frongoch, the larger of the two sites, which has already been the subject of extensive remedial work. While the work has dramatically reduced metals pollution, concentrations in the run-off from the site are still high.

To combat this, trials are now underway with Elentec, a company located at Menai Bridge and who provide research-based water treatment solutions using an innovative approach involving an energy efficient portable containerised electrochemistry unit. The unit is ideal for upland terrain or adaptable for fly in fly out mine contracts abroad.

Two highly polluted sources which contribute 3.8 tonnes per year of zinc, lead and cadmium to Frongoch stream are collected and fed through the electrode chambers. Again, preliminary results are encouraging, enabling optimisation of the treatment process.

The polluting metals are then separated from the water through precipitation in a purpose built clarifying tank, allowing the treated water to be discharged.

Peter Stanley, water and contaminated land technical specialist for NRW, said:

“The success of the Cwm Rheidol and Frongoch trials have the potential to offer NRW and others interested in metal mine water remediation and the clean-up of metal mine process waters, new tools for successfully treating harmful discharges.

“And it’s not just the environment which will benefit from this technology, the Welsh economy could also receive a boost as the companies involved in this work share the technology with overseas markets.”