Published: 14. Apr 2021

Egaa WWTP produces more electricity than it uses


Total energy renovation of the treatment plant at Egaa, just outside Aarhus, means that Aarhus Vand is setting new standards for developing treatment plants from energy guzzlers into energy producers.

A large number of wastewater treatment plants, in Denmark and abroad, must be transformed from energy guzzlers to energy producers. This will be through entirely new technologies that exploit the green energy production potential in wastewater. Total energy renovation of the treatment plant at Egaa, just outside Aarhus, means that Aarhus Vand is setting new standards for turning treatment plants into energy producers.

This is no less than a milestone in the technological development of treatment plants towards becoming energy producers. Not only in Denmark, but throughout the world. When the treatment plant at Egaa is fully developed, the goal is to be producing 50 percent more electricity than it consumes.

This achievement marks the conclusion of a long and exciting process of innovation, in which there were originally 63 ideas from Denmark and abroad for how to establish ‘the energy producing treatment plant of the future’. The new plant at Egaa will be completed on the basis of this innovative approach to developing new water technology and it is the fine result of unique and fruitful collaboration between two companies, Envidan and Aarsleff, and Aarhus Vand.

How we will transform Egaa WWTP from an energy consumer to an energy provider

First of all we have built an anaerobic digester at Egaa WWTP. The presence of an anaerobic digester is a prerequisite for turning a waste water treatment plant into a net energy producing plant. However, the digester alone will not be sufficient. It will also require optimization of both the energy producing process taking place in the anaerobic digester and the energy consuming process taking place in the activated sludge tanks - without jeopardizing the effluent water quality. Further, the optimization cannot be seen as two independent tasks as the energy production and energy consumption are closely linked through the mutual carbon source available in the raw wastewater flowing to the treatment plant.

Through development of innovative processes we wish to demonstrate that Egaa WWTP can generate 50 percent more electricity than it uses for daily operation. This will be achieved by incorporating several technologies in a “150 percent concept", including a short-cut nitrogene removal process in the main process tanks, sludge liquor treatment, a new carbon harvest (micro filtration as new primary treatment technology), an optimized control system and an ORC (Organic Rankine Cycle) process.

Optimal control of the interaction between the different systems results in an overall reduction in energy consumption and an increase in energy production. Optimizing the distribution of the carbon source between the energy production and the energy consumption means to minimize the demand for carbon source in the aerobic treatment in the activated sludge tanks in order to maximize the carbon source available for anaerobic treatment in the digester.

The overall success criteria of the project is to develop and demonstrate that the new technologies can work individually and in interaction with each other, as well as with well proven energy technologies such as combined heat and power generation from extracted gas.

A demonstration plant to showcase the newest technological advances

Aarhus Vand’s strategy is to be energy-neutral and CO2-neutral by 2030 at the latest throughout the whole water circle. Already today both Egaa and Marselisborg Wastewater Treatment Plants are supplying green energy to the electricity and heat grids at competitive prices.

The plant acts as a demonstration plant to showcase the latest technological advances to Danish and foreign experts and decision-makers with an interest in energy optimisation and energy production.