You’re speaking at the World Water-Tech North America summit on the panel debate “Energy and Resource Recovery; A New Paradigm for Utilities”. Could you please tell us more about the pioneering Marselisborg Wastewater Treatment Plant and how Aarhus Vand is positioning itself as energy self-sufficient?

Claus Moller Pederson

Aarhus Vand’s (Aarhus Water) vision is to become not only the leading water utility in Denmark, but also one of the leading water utilities in the world by developing and building the world´s most resource effective wastewater treatment plant by 2026. To us, being a leading water utility means that we are energy self-sufficient – or even better, that we are an energy net producer.

In 2016 the Marselisborg Wastewater Treatment Plant and the wastewater transportation to the plant had a total energy consumption of 3,9 GWh, while the energy production at the plant was 7,4 GWh. In this way, the energy self-sufficiency (power + heat) for the wastewater transportation and treatment was 190%. The industrial loading contribute with about 10% of the total organic loading. There is no co-digestion of organic waste.

If we look at the entire water circle (drinking water treatment and distribution and wastewater transport and treatment) in the catchment area of Marselisborg, the total energy consumption was 7,5 GWh, while the energy production was still 7,4 GWh. Our goal is to have total energy production at the same level at least as the total energy consumption.

Marselisborg WWTP was extended with biological and chemical treatment in the early 1990’s to include sludge treatment and biogas utilization. Our current status has been achieved by, among other things, daily optimization and innovation of new biological process controls (side-stream deammonification and nitrite shunt in main process) through strategic collaboration with leading water utilities, companies, universities and organizations in Denmark and abroad since the early 1990’s.

What were the drivers behind the utility’s decision to invest in the technology and infrastructure to convert its wastewater into energy?

When Marselisborg WWTP was extended in the early 1990’s, we wanted to make sludge treatment more efficient. This was achieved by reducing the amount of sludge from the plant and increasing the reuse of biosolids in agriculture. At the same time, we wanted to make an operating income to produce electricity from biogas.

In 2007, the Aarhus city council decided that the municipality should actively participate in efforts to reduce CO2 emissions and set a target for CO2 neutrality by 2030. In order to back up this mission, Aarhus Water decided to work towards becoming energy and CO2 neutral.

In this respect, the desire to optimize sludge treatment, generate operating income from electricity production and achieve energy and CO2 neutrality have been the primary drivers behind the decision to invest in the technology and infrastructure to convert wastewater into energy.

What were the key challenges in getting this project off the ground?

The main challenge perhaps is in the mind-sets of ourselves – to believe that it is possible to be energy self-sufficient – or even better to become an energy net producer.

Another key challenge is the Danish legislation. On January 1, 2010, Danish water and wastewater utilities became utility companies, typically with the municipalities as sole owner of the new water companies. As a result, new legislation was introduced regarding the regulation of new water companies. This new legislation was problematic as it spurred a number of inefficiencies in energy production and did not offer the right incentives for energy production.

How do the project economics work? What are the specific conditions that have made this viable in Aarhus?

Return on Investment (ROI) was the key incentive behind the decision to reduce energy consumption and increase energy production. As a rule of thumb, the project will have to be repaid within a 10-year period. In special cases where, for example, the project has been able to achieve a relatively large CO2 reduction, the repayment period of projects could be up to 15 years.

What would be your advice to utilities around the world that are looking to make advancements in energy recovery and neutrality?

It’s important to get started. You have to put a vision for where you want to go, and then start where you can gain quick successes. Think big, but start small!

We had the benefit of drawing up an energy map (energy management) at our facility as a basis for initiating the projects portfolio. The concrete projects must be profitable so you have to decide which payback times you want to work with.

Where do you see the greatest potential for technological innovation? What is missing from the industry?

The greatest potential for technological innovation lies in the reduction of energy consumption and CO2 emissions, and solutions which increase energy production and the absorption of CO2 such as:
• Advanced control and steering strategies and systems for both drinking water and wastewater systems to optimize the function of these systems
• New processes to clean the wastewater – processes that demand less energy
• Energy efficiency in all technology solutions, such as membranes
• Increased carbon utilization of the highly degradable proportion
• Increased carbon harvesting for biogas production
• Smart Grid, including exploiting synergies between energy produced by wind turbines and biogas
• Solutions for heating pumps in wastewater systems
• Upgrading of biogas to fuel in the heavy transport sector (buses, lorries, etc.)

And finally, what’s next for Aarhus Vand as we advance towards an energy optimised future?

The next goal is to expand our energy self-sufficient capabilities – or even better, become an energy net producer – across the whole water cycle and other catchment areas in our utility. We want to achieve this by centralizing our wastewater treatment into two plants – Egå and the new Marselisborg WWTPs.

The plant in Egå has just been expanded to include a new, energy producing biogas production and utilization plant. The main idea is to reduce the energy consumption across the entire plant and in other parts of the water and wastewater system. This will be combined with our wish to increase energy production by directing as much carbon to anaerobic digestion as possible. We have introduced the Anammox processes in the plant, as well as hot Anammox in the side stream, and we will proceed with introducing the nitrite shunt into the main stream during Autumn 2017. The plant has a capacity of 120.000 PE. The objective of this plant is enable the catchment area of Egå to be energy self-sufficient across the entire water cycle.

We have just started the master plans for a new plant, Marselisborg ReWater, which will centralize three existing wastewater treatment plants in Åby, Viby and Marselisborg. Aarhus Vand’s ambition is to establish Marselisborg ReWater as a “resource and recovery plant”, enabling the purification of wastewater, in addition to the production and recovery of energy and nutrients from wastewater. What Marselisborg ReWater will look like when build it in 2026, we do not know. But what we know is that our goals cannot be achieved by current technologies and knowledge. We have therefor presented an innovation strategy for the development of Marselisborg ReWater building on innovation principles formulated around 15 innovation challenges to be addressed and solved in the
coming years. We invite all interested water utilities, companies, universities and organizations in Denmark and abroad to partake, gain insight and form new business alliances from this development.

See more about Marselisborg ReWater: