Industrial wastewater generally contains a wide variety of substances, many of which are harmful to the environment. These range from organic compounds that take a long time to degrade, to toxic and even radioactive substances, to acids and heavy metals. To recover such toxic metals from wastewater originating, for example, from coal mines or electroplating plants, a group of scientists working on the BIOMIMIC project has developed biotechnological processes to remove metals and sulfate from mine wastewater.
To do this, the researchers studied three wastewater streams in three countries. In Germany, they looked at mine water from abandoned mining tunnels in Saxony. In Ireland, they examined leachate from the red mud storage of an alumina manufacturing plant, and in Sweden, they looked at solutions produced during the leaching of ash from a waste incineration plant.
Two German partners
On the German side, the “Impact” sub-project was coordinated by the Fraunhofer Institute for Systems and Innovation Research ISI. Here, researchers evaluated the potential benefits of the processes developed under BIOMIMIC in terms of “what contribution they can make to the EU’s security of supply of critical raw materials, how they are economically feasible, and what their ecological advantages and disadvantages are.”
G.E.O.S. Ingenieurgesellschaft mbH, the second German partner, developed a sulfate reduction process in the “Process Engineering” subproject, which was demonstrated on a small scale. With this process, water containing metals and sulfates can largely be removed from wastewater using a moving bed bioreactor. More than 90 percent of the metals can be separated as metal sulfides and over 99 percent of the toxic substances, as well as more than 60 percent of the sulfate, can be removed. A major advantage of the process in practice is that no gas supply is required so the control engineering effort is very low. Plus, the amount of residual material that cannot be recycled is one-tenth of the initial product, significantly less than in chemical treatment processes, the scientists are pleased to report.
The other eight project partners have also been able to show that processes with sulfate-reducing bacteria are very well suited to removing metals and sulfate from wastewater, thus recovering the valuable metals. Leachate from the alumina manufacturing plant in Ireland is treated in a dedicated facility for a biosorption process.
According to an impact assessment by Fraunhofer ISI, the advanced processes have the technical capability to remove metal contaminants from wastewater streams. Although the potential contribution of this treatment to EU supply security is rather small, the scientists admit, the potential for solving local environmental problems should not be underestimated.
Alternative to chemical processes
Until now, wastewater treatment has generally been carried out using chemical processes, which in turn have negative effects of their own. But according to the researchers, in order for the two processes developed within BIOMIMIC to represent a more environmentally friendly and economically feasible alternative to traditional chemical processes in the long term, they must be further optimized in terms of their ecological and economic performance. Among other things, they say, the process could be improved with sulfate-reducing bacteria by increasing energy efficiency. Waste streams could also be used to generate energy and carbon for the process. In the biosorption process, the use of biochar has environmental and economic advantages over hydrochar.
“The treatment of industrial wastewater often does not offer economic profit opportunities for companies, even if the wastewater streams contain supply-critical metals, as in the cases studied here,” explains project leader Dr. Sabine Langkau, who heads the Sustainability Innovations and Policy business unit at Fraunhofer ISI. “Therefore, legal requirements, such as the current EU Water Framework Directive, are still needed to bring wastewater treatment processes into use to solve local environmental problems. In addition, an assessment of the ecological and economic impact of the processes, taking into account the amounts of energy and chemicals used, can help optimize the processes and select the most appropriate one.”
The BIOMIMIC project involved 10 European partners working on several subprojects. They were funded within the framework of the transnational call for proposals of the ERA-Net ERA-MIN 2. The two German subprojects “Impact” and “Process Engineering” were funded by the Federal Ministry of Education and Research.