Activated carbon is regarded as an effective means of removing micropollutants from wastewater. But appearances are deceptive. In this interview, Dr. Reinhard Voigt sheds light on the ecological and economic disadvantages of this method and shows what sustainable alternatives are available for wastewater treatment.
Activated carbon is often proposed as a solution for removing micropollutants from wastewater. Why do you think this approach is problematic?
Dr. Reinhard Voigt: At first glance, activated carbon may seem like an effective method of removing micropollutants from wastewater. However, when we look at the ecological and economic effects, it quickly becomes clear that large-scale use in sewage treatment plants is associated with considerable disadvantages. The immense consumption of raw materials, the high energy requirement for production and the additional costs for disposal and incineration show that this approach is not sustainable.
Can you explain the figures in more detail? How high is the actual consumption of resources?
Dr. Reinhard Voigt: Let’s take an example from the ZeroTrace project: to achieve an average concentration reduction of 80 % for micropollutants, around 30 to 40 grams of powdered activated carbon (PAC) are required per cubic meter of wastewater. Extrapolated to large sewage treatment plants, this means an annual requirement of 94,000 tons of activated carbon for Germany alone. The 94,000 tons of activated carbon mentioned above would be required if all wastewater treatment plants of size classes 5 and 4 in Germany were equipped with activated carbon for the 4th purification stage.
Around 280,000 tons of hard coal or 15 times the amount of wood or coconut shells have to be processed for this. The energy required to activate the coal is around 85 gigajoules per tonne of activated carbon, which in total requires an additional 266,000 tons of coal per year. All in all, we are talking about a total requirement of 546,000 tons of coal per year – an incredible amount.
What impact does this have on the carbon footprint?
Dr. Reinhard Voigt: The figures are frightening. The production of activated carbon causes around 171,000 tons of COâ‚‚ emissions per year – just for the operation of the additional purification stage in German wastewater treatment plants of the highest size classes. This does not include transportation or disposal costs.
And what happens to the activated carbon after it has been used?
Dr. Reinhard Voigt: That is precisely another major problem. Although activated carbon binds micropollutants, it does not dissolve them. The loaded activated carbon has to be disposed of, often by incineration – which in turn causes additional costs and COâ‚‚ emissions. With the phase-out of coal-fired power generation, it is becoming increasingly difficult to find suitable incineration plants. We are therefore facing a double challenge here: high costs and no truly sustainable solution.
Are there more environmentally friendly alternatives to activated carbon?
Dr. Reinhard Voigt: Yes, there are promising approaches. One example is the use of enzymatic reactions in a cascaded membrane system. This process could specifically break down micropollutants instead of just binding and displacing them. Research into this is still ongoing, but the results so far show that this technology could represent a more efficient and resource-saving alternative.
How do you think the discussion about the fourth purification stage in sewage treatment plants should continue?
Dr. Reinhard Voigt: We need to move away from purely technical solutions that only appear to make sense at first glance, but cause high costs and environmental problems in the long term. We need a sustainable approach that is both ecologically and economically viable. Instead of investing billions in the widespread use of activated carbon, we should invest specifically in innovative processes such as enzymatic cleaning.
What do you specifically demand from politicians and authorities?
Dr. Reinhard Voigt: The current discussions about a mandatory fourth purification stage must be supplemented by a differentiated cost-benefit analysis. Instead of demanding blanket solutions, pilot projects for alternative methods should be promoted in order to develop more sustainable concepts.
Conclusion:
The large-scale use of activated carbon for wastewater treatment has considerable ecological and economic disadvantages. In view of high COâ‚‚ emissions, rising costs and unresolved disposal issues, it is high time to research and promote more sustainable alternatives such as enzymatic reactions in combination with membrane systems.
Dr. Reinhard Voigt
Head of R&D
Phone: +49 3621 73 77 922
Email: r.voigt@wta-unisol.com