Efficient energy from biowaste – Watt d'Or for PSI and Energie 360°

A major potential energy source slumbers in biological waste. In Switzerland, roughly 1.3 million tons of biowaste per year accumulate in municipal refuse alone; on top of that come 270,000 tons of collected green waste as well as 200,000 tons of sewage sludge from wastewater treatment. Today there are already methods with which biogas can be obtained from these kinds of waste. By way of the natural gas network, this energy makes its way back to the households, among other destinations.

Especially promising are those methods of biogas production that generate, out of the raw biogas that arises through fermentation of biological waste, methane – that is, artificial natural gas. Yet the raw biogas contains at most around 60 percent methane. The remaining 40 percent is carbon dioxide (CO₂), which up to now is being removed with great effort and with no further use.

Higher biomethane yield through PSI method

The PSI-developed and newly honoured technology avoids this last step. Instead of removing the CO₂, we introduce hydrogen and stimulate it to react with the carbon dioxide. As a result, additional methane is produced, says Serge Biollaz, under whose leadership the technology was developed. This method, known as direct methanation, raises the methane yield significantly: By the end, the raw biogas is almost entirely turned into methane. Furthermore, the biomethane produced in this way is of such high quality that it can be fed into the natural gas network without additional processing, Biollaz says.

Crucial reality check with Energie 360°

One of the biggest challenges for the practical feasibility of the method is that the composition of biowaste varies, and with it, the composition of the raw biogas varies too. To test the method under realistic conditions, PSI teamed up with the Zurich-based energy provider Energie 360°. The test facility they built together, called Cosyma, is housed in a container and can thus be transported to biogas plants and directly connected there. During the first half of 2017, the Cosyma facility passed a 1,000-hour test run at the biogas plant of Biogas Zurich AG at the Werdhölzli wastewater treatment site. The biomethane produced by Cosyma from sewage gas and fermentation gas was fed into the natural gas network of Zurich and delivered a quantity of gas sufficient to provide heating and hot water for a single-family home. With the long-term test we were able to show that our method is ready for industrial implementation, Biollaz happily concludes.

The ESI Platform at PSI

The mobile test facility Cosyma is part of PSI's Energy System Integration Platform. The ESI Platform started operating in the fall of 2016. Its goal is to study and refine different variants of Power-to-Gas technologies and energy-efficient use of biomass with a focus on their technical and commercial feasibility, in close collaboration with partners from research and industry.

About the Watt d'Or

With the Swiss energy prize Watt d'Or, the Swiss Federal Office of Energy annually recognises innovative projects in the energy field. The Watt d'Or 2018 was awarded in the four categories Energy Technologies, Renewable Energy, Energy-Efficient Mobility, and Building and Space. The award ceremony took place on 11 January 2018 in the Kursaal Bern conference center.

Text: Paul Scherrer Institute/Martina Gröschl