Green Gas in Gaasperdam: the structuring value of an SCBA

Case study: heating with Green Gas in Gaasperdam

In Amsterdam’s Gaasperdam district, residents
have taken the initiative to heat homes in an
alternative way: with green gas produced in
a high‑pressure digester using the residents’
own sewage and food waste. The initiative
also aims to create a social boost in the
neighbourhood. Residents work together to make curtains and low‑cost insulation
materials, and to organise their own collection of fruit and vegetable waste (separate from garden waste, which does not digest well). The approach also included insulating the homes and installing hybrid heat pumps. The digester was commissioned in June 2022 (click here to view AT5’s video report).

How do you assess such a complex project? And to what extent is the information from the initiators accurate? Iris van der Horst from the Municipality of Amsterdam considers the social cost‑benefit analysis (SCBA) a useful tool for structuring and valuing precisely these kinds of complex issues. She therefore asked Decisio to carry out an SCBA. We are pleased to let her share her perspective.

Iris: “It was a challenging but very interesting project, which Decisio carried out together with all stakeholders. Key questions included: does this digestion concept actually work? Is heating poorly insulated homes really the best use of green gas? How does the collection of food waste work in practice? What is the value of the social initiatives in the neighbourhood? And how does this initiative compare to other alternatives, such as a district heating network, knowing that doing nothing is not an option? And what does it mean for the costs and energy bills of residents?”

The Decisio team was able to answer most of these questions (drawing partly on technical studies and input from the municipality, Witteveen+Bos and Waternet). Iris does not consider the ratio of costs to benefits the most important outcome of the study: “The methodology of an SCBA forces you to think carefully about how the development would look without the digester. In this case, that could mean a district heating network, for example, or a much larger-scale digester. You also have to examine the different components of the project, which shows that some elements are more attractive than others, and that green gas, for instance, might be better used for other purposes than heating homes.”

Asked about the key conclusions, Iris says: “The main conclusion was that this initiative deserves further development, even though the benefit–cost ratio is not yet impressive and Gaasperdam is not the ideal scale. At the scale of Amsterdam, green gas could be an interesting direction, allowing the existing gas pipelines to be used and avoiding large-scale investment in heat networks that may not be future‑proof. One very tangible outcome of the project is the mini‑digester in Holendrecht, which will soon allow us to experiment on a small scale. The permitting process alone was incredibly instructive. We have made things so complicated for ourselves! If the Holendrecht project succeeds, we will be able to feed organic waste into the digester — especially food waste from the Holendrecht shopping centre — and convert it into green gas for the same local businesses. Moreover, these kinds of pioneers and community‑driven initiatives, and the innovation they spark, are worth their weight in gold for the city and society.”