The power of sludge


Imagine wastewater treatment plants producing more energy than they consume. This could soon be a reality if Dr Christian Remy from the Berlin Centre of Competence for Waterbrings his plan to fruition. Remy studied environmental technology in Berlin and wrote his PhD thesis on life cycle assessment. He was attracted to and quickly convinced by the project “Carismo’s” (abbr. for “carbon is money”) positive energy balance – that more energy is gained from the wastewater than is used to clean it. An interview about sludge, special bacteria and life cycle assessment.

Sludge researcher Dr Christian Remy

Dr Remy, you would like to see wastewater treatment plants producing more energy than they consume. How would this work?

We want to increase the amount of organic material taken from wastewater by 50 per cent and turn it into biogas. The biogas can then be transformed into electricity. In contrast to conventional wastewater treatment processes, we treat the water with metallic salts and polymers. This causes the solid components to form flocs that can then be filtered out with a fine drum sieve. This way, we can remove much more organic sludge from the wastewater than was previously possible.

Will wastewater treatment plants need to be rebuilt in order to implement your idea?

Not necessarily. All we needed to do for our pilot project at a Berlin wastewater treatment plant was erect two containers. Existing digestion tanks on plant premises may not always be big enough to handle the increased amount of sludge gathered, however, in which case buildings would need to be modified.

Can you be sure that your process doesn’t affect water quality?

We think so, yes, and soon we will be able to prove it. In summer 2016, we will put our idea into practice at a small wastewater treatment plant in eastern Germany, co-financed by the EU in the POWERSTEP project.

What is the biggest challenge?

To regain as much carbon as possible from the sludge, which is what is later turned into biogas. This is also what gave rise to the project’s name “carbon is money”, or Carismo for short. However, a certain amount of carbon needs to remain in the water in order to guarantee that the cleaning process is not affected. Water also contains nitrogen that needs to be removed. Today, this is done by certain bacteria, but because they feed on carbon we have to make sure there is always enough carbon left for the special bacteria.

If you are successful, your idea is likely to be of interest to wastewater treatment plants outside Germany as well ...

Yes. Especially in countries with high energy costs, such as Canada or Denmark. The high energy costs in Germany were no doubt one reason why this project came into being here. That said, Germany is in any case well known for its wastewater treatment expertise and is a front-runner in research in this area.

Has there been international participation in Carismo during the development phase?

Our research centre is in Berlin, financing comes from the French water company Veolia and the Berlin water utility, and some of the technology is from Sweden. We’re well connected in Europe and our working language is English, of course.

The interview was conducted by Julia Illmer – muehlhausmoers.


Berlin Centre of Competence for Water

The Kompetenzzentrum Wasser Berlin (KWB – Berlin Centre of Competence for Water) is an international centre for water research and knowledge transfer. KWB links the water expertise of Berlin’s universities and research institutes, the Berlinwasser group of companies, Berlin-based SMEs, Berlin’s administrative authorities and Veolia, an international provider of environmental services.