Mining in the Ore Mountains still leaves traces in the environment for decades after its end. Suffered waters loaded with metals flow from the heaps into surrounding waters. Now researchers have developed a sewage treatment plant that can clean these seepage waters from the pollutants. Initial tests with the pilot plant were promising. In the future, the procedure could be used EU or worldwide.
Various ores and minerals were dismantled and processed in the so-called Freiburg area in the Easter Mountains for centuries- from the 12th century to 1969. Lead, silver and zinc and various trace metals were among the funded and controlled noble and metal metals. With the rain, which flowed through the poured heaps and tips, the metals also got into the so -called seepage water and from there into the surrounding waters. This still happens today, decades after the mines were closed.
“The seepage waters with whom we work here are still strongly contaminated by aluminum, cadmium, zinc, manganese and other metals,” explains Sabrina Hedrich from the TU Bergakademie Freiberg. “They are also contaminated by low pH values and high sulfate concentrations.” For humans, these contamination is not a danger, but for living things in nature, however. Many of the metals are poisonous for the environment.
Detoxification in three stages
Researchers around Hedrich have therefore developed a new sewage treatment plant to clean such seepage waters. Your natural -based pilot balance has been in operation on the Hammerberg flush dorm on the eastern outskirts of Freiberg since July 2024. The first results are promising: “We were able to show that our procedure is able to efficiently remove pollutants from the water,” says Hedrich. The cascade-like treatment system cleans the contaminated seepage water in three stages through a combination (micro) biological and chemical process.
In the first level of treatment, the acid water is directed and neutralized via a limestone filter. The pH value of around 4.9 is increased to values between 6.5 and 7.0. As a result, the aluminum dissolved in the water fails as aluminum hydroxide and can be collected. In the second stage, the water flows through a bioreactor, which is filled with a biomix made of limestone, wood chips, straw and compost. Under these conditions, bacteria thrive that the sulfate convert into hydrogen sulfide in seepage water. This sulfide in turn ensures that the other metal pollutants fail as metal sulfides and remain in the Biomix. In the last cleaning level, the water is led by a pelvis with plants that serve as a natural sewage treatment plant and filter out the remaining malicural and suspended matter.
Is the system also suitable for other mining areas?
The current that the sewage treatment plant needs for your pumps comes from a connected small photovoltaic system including battery storage. Water treatment itself is passive, requires no electricity and hardly requires maintenance. “Therefore, the process is inexpensive and can of course also be integrated into renovation landscapes as a large system. This makes it interesting not only for our region, but also for mining landscapes worldwide,” says Hedrich.
The procedure developed in Freiberg could also help to comply with the prescribed guidelines in the EU. Because, according to the EU Water Framework Directive, all European waters are said to have reached a “good ecological and chemical state” by 2027. So far, this goal has been missed in many regions of Europe. “In Saxony alone, over 1300 kilometers of streams and rivers, the good condition fail due to the mining and sometimes very high metal pollution, which are transported further downstairs downstream,” explains Christine Stevens from the Saxon State Office for the Environment, Agriculture and Geology. “The catchment areas of the Freiberger and Zwickau Mulde are particularly affected.” Sustainable water treatment technology such as the Freiberg sewage treatment plant could significantly reduce the environmental damage of the mining.
Source: Technical University of Bergakademie Freiberg, Project Mindmontan