Biological Treatment of Mining Impacted Groundwater and Streams – an Option to Meet European Legal Standards?
Weber, Anne (1); Bilek, Felix (1); Lünich, Kathleen (2)
1: Dresdner Grundwasserforschungszentrum e.V. (DGFZ), Germany; 2: Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie, Germany
Mining has a tradition in Saxony (Germany) since centuries. According to the standards of the European Water Framework Directive most rivers and groundwater bodies in Saxony are in a poor chemical or ecological status. Mining impact being one reason among others is reflected in lowered pH-value, elevated concentrations of sulphate, iron, further metals and arsenic. In Saxony mine water is typically treated physico-chemically at discrete discharge points. Aim of this study was to evaluate the potential for (micro‑)biological treatment to achieve a good quality status for water bodies in Saxony.
The study was founded by the European Union and comprised the following tasks: 1) Delineation and visualization of the state of Saxony's surface water bodies and groundwater bodies with respect to mining related contamination. 2) Deriving characteristic mining induced contaminants. 3) Surveying literature for established biological treatment methods of these contaminants involving practical experiences in Saxony. 4) Evaluation of applicable biological treatment methods for their potential benefit to remediate mining impacted groundwater and streams in Saxony including economic limitations.
Mining influenced surface and groundwater bodies were grouped by their contamination characteristics, reflecting the association to the lignite open pit mining and the former ore mining regions. Mapping the pollution revealed that about one third of the groundwater and one sixth of the streams do not meet legal standards due to the mining impact. Suitable biological treatment methods for mining impacted waters were classified in engineered ecosystems, technical reactors and subsurface in-situ technologies. These utilize either iron oxidation or sulphate reduction as the core microbial process inducing a network of additional mitigation reactions (e. g. sorption, coprecipitation). Some technologies have numerous applications worldwide whereas others still have pilot status. With respect to Saxony all recent efforts to install biologically driven mine water treatment plants ceased at the pilot scale due to economic reasons or insufficient purification effect.
Whereas biological treatment of mine water has potential to improve water quality at discrete discharge points or hotspots of groundwater plumes its large scale application to mitigate the long-lasting and widespread mining impact in Saxony seems limited. Some of the obstacles delineated are: Low reaction rates in cold season; the sheer amount of carbon source necessary to stimulate sulphate reduction at the affected scale; long term instability of sulphides in per se aerobic systems; too low iron concentration to utilize iron oxidation as core process.