Or at least the energy it contains? Let’s start by defining the issue.

Wastewater generated by households contain significant amounts of energy in the form of latent heat. The heating of the wastewater comes from, among other things, everyday activities in our homes, like showering, cooking and washing. The extra heat energy greatly benefits treatment processes in the wastewater treatment plant, especially denitrification, and WWTP design in fact relies on the added heat energy for its proper function.

Property owners on the other hand are becoming increasingly aware of the energy potential of wastewater and society are calling for increased energy efficiency of buildings.

In this case there is a matter of conflicting interests, where property owners have an incentive to save money and energy by recovering heat from wastewater, while municipal WWTP need the heat to continue BAU. There are proponents for regulation and even prohibition of building-level heat recovery from wastewater as widespread adoption would incur cost increases downstream.

However, this raises a few interesting questions. Should energy efficient appliances be regulated too? Can dishwashers become too energy efficient? What about showers? There are solutions on the market that recovers 30-80% of the heat energy from shower water, either through heat exchange or recirculating the shower water. Should these be banned? Maybe we should also ban taking cold showers, since those who enjoy this strange pleasure don’t contribute their share to the common good.

Maybe a fee corresponding to the temperature deficiency of the wastewater that a property generates? How about 4 SEK per Δ°C m3 below 20°C?

Provocative questions, but what is your opinion? Who owns the energy in the wastewater? How do we resolve this conflict of interests in the most efficient way (by this I mean efficient in an overall way for society)?

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