Using forest ash to improve the water quality of pit lakes

Two studies have been conducted in a pit lake with the aim of investigating whether forest ash can be used to improve its water quality. The results are promising, but further studies are needed to understand whether the method can be used on a larger scale.

Vattenkvaliteten i dagbrottssjöar är ofta påverkad sulfidmineral där några av konsekvenserna kan vara låga pH-värden och höga metallhalter. Detta kan vara problematiskt då de bland annat kan påverka yt- och grundvatten och dagbrottssjöarna efterbehandlas därför ofta. En vanligt förekommande efterbehandlingsmetod är kalkning som höjer pH i sjöarna.

The water quality in pit lakes is often affected by sulphide minerals, where some of the consequences can be low pH values ​​and high metal contents. This can be problematic as they, among other things, can affect surface- and groundwater, and the pit lakes are therefore often remediated. A common remediation method is liming which raises the pH of the lakes.

An alternative remediation method could be to replace lime with forest ash which has been used to raise the pH and add nutrients to woodland. In addition to raising the pH, this could help stimulate algal growth in the pit lakes, which is often low due to a lack of nutrients. Algae have been shown to be able take up a number of elements and the forest ash could therefore potentially contribute to both raising the pH and reducing the metal concentrations in the lakes.

Two field experiments have been conducted at LTU where the effect of adding nutrients and different types of forest ash have been studied. The results showed that algal growth increased and that several mining-related metals were taken up by the algae. Although the results are promising, further studies are needed to understand whether the method could be used as an alternative remediation method as the experiments so far only have been conducted on a small scale.