Nitrous oxide (N₂O), which is produced during wastewater treatment, is one of the industry’s biggest environmental offenders with an eco-footprint 300 times higher than that of CO₂. To address this problem, the water and wastewater company VCS Denmark invested in measurement technology from Unisense Environment. VCS can now measure N₂O levels directly in the wastewater treatment units and use the measured data to calculate N₂O emission and reduce this by optimized process control.

Wastewater treatment has previously been a very energy-intensive process, but in recent years the industry has focused on reducing CO₂ emissions. VCS Denmark, one of the largest and oldest water and wastewater companies in Denmark, is actively committed to resource optimization.

One of the major efforts has been on optimizing its biggest treatment plant – Ejby Mølle Renseanlæg – to produce significantly more energy than it consumes. However, in its efforts to achieve its goal, VCS Denmark encountered a problem: When you reduce energy consumption in the complex microbiological treatment process, you also potentially increase N₂O emissions. N₂O is a potent, overlooked greenhouse gas which – when emitted – has an eco-footprint 300 times that of CO₂.

Increased levels of N₂O do not sit well with VCS Denmark’s goal of reducing greenhouse gas emissions and becoming CO₂ neutral. The company therefore decided to invest in N₂O sensors from Unisense Environment.

“We wanted to measure N₂O levels in our wastewater treatment tanks, as these data enable us to optimize the operation of our treatment plants and reduce N₂O emissions. Unisense Environment had the technology we were looking for – and at a very affordable price,” explains Per Henrik Nielsen, Project Manager at VCS Denmark.

Unisense Environment’s measurement technology integrates with VCS Denmark’s monitoring system, enabling the water company to monitor N₂O concentration along with ammonium, nitrate, oxygen, and redox potential.

N₂O concentration and emission data have been scarce. Therefore, the wastewater treatment companies have based their control efforts on guesswork and lab tests from the 1990s. Armed with the new technology, however, VCS Denmark can measure N₂O concentration levels with a high degree of accuracy.

“There’s a big difference between lab tests and the real world. So it’s a huge leap forward to be able to perform stable, full-scale, online N₂O measurements in an industrial context online 365 days a year using Unisense Environment’s measurement technology,” says Per Henrik Nielsen.

The measurement technology was jointly developed by Unisense Environment and VCS Denmark with the help of DHI, and the project was funded by The Foundation for Development of Technology in the Danish Water Sector and Aarhus Water.

The development process has been so smooth that the measurement technology was developed and made implementable in record time. Per Henrik Nielsen believes this has a lot to do with Unisense Environment’s attitude and business approach.

“Unisense Environment possesses extensive theoretical background knowledge and a deep understanding of the biological processes in wastewater treatment. They have also shown a great deal of respect for how things work in practice and understand our operational needs. That’s a rare but highly desirable combination, which we value highly,” he concludes.