Project Description

A potential game-changer for odor and corrosion management in the sewer networks in Aarhus

Like many other cities around the world, Aarhus is facing the challenge of increasing levels of hydrogen sulfide in the sewer networks. In collaboration with Unisense and Danva’s Hydrogen Sulfide Network, Aarhus Water Utility has tested the SulfiLoggerTM sensor in Trankær south of Aarhus to explore how to minimize the consequences of hydrogen sulfide presence such as corrosion of the pipelines and odor issues in the future.

Measuring H2S directly in wastewater shows extraordinary potential

In a city where the number of citizens grows every year and where wastewater treatment is moved to larger centralized treatment facilities, problems with H2S levels are bound to increase unless measures are taken to handle the situation. In the Trankær case the goal was to identify where H2S occurred in the sewage network.

“Up until now we have only been able to measure levels of H2S in the gas phase and carry out location specific measurements often based on complaints from citizens about odor nuisances. We are lacking a complete 24/7 overview of the H2S levels and how they develop,” says Ole Pedersen, Operations Manager at Aarhus Water Utility, and continues “The SulfiLoggerTM sensor gives us the possibility to measure H2S directly in the wastewater, which can really make a difference for us because we can get the measurements directly and see how H2S develops in the sewers.”

In the Trankær case both gas sensors and the Unisenses sensor, which is designed to measure directly in wastewater where used to measure hydrogen sulfide.

“The results showed that the gas sensors in many cases measured lower levels than the sensors inserted directly into the wastewater. The SulfiLoggerTM sensor gave a very precise picture of the H2S levels and location,” says Karsten Egebjerg, Project Manager at EnviDan and member of Danvas Hydrogen Sulfide Network.

Improved asset management due to detailed knowledge of H2S levels

In the coming years two of Aarhus’ wastewater treatment plants are closing and treatment is centralized at a new and larger plant. Therefore, the wastewater will be transported over much longer distances, which can cause an increase in the levels of hydrogen sulfide. At Aarhus Water Utility this causes concerns about how the increased formation of H2S in the sewer network can cause not only odor challenges for the citizens but also how future infrastructure investments can be lost due to corrosion.

“The SulfiLoggerTM sensor shows great potential for identifying exactly where H2S is formed in the sewers, and consequently we can determine when certain parts of the pipes need to be replaced. This gives us a unique opportunity to plan our asset management and budgets accordingly,” says Ole Pedersen “Additionally, the sensor can help us to control the dosage of chemicals used for H2S removal.”

The SulfiLoggerTM sensor opens up exciting possibilities for learning more about H2S in the future

Making it possible to measure levels of H2S directly in wastewater changes the possibilities for working with and minimizing the damaging effects of hydrogen sulfide in sewage networks. Aarhus Water Utility, Danvas Hydrogen Sulfide Network and Unisense continue to work together towards finding even more answers about the impact of H2S in sewage networks.

“There are still many things about H2S that we don’t know, but with the ability to measure directly in wastewater, we’ve have taken a large step in the right direction. H2S is as mentioned before a significant problem in many wastewater systems and if we can monitor the level online and in real time we have a new and comprehensive foundation for our work with hydrogen sulfide,” says Jan Egelund, Project manager at Krüger and member of Danvas Hydrogen Sulfide Network.

The SulfiLoggerTM sensors monitor dissolved hydrogen sulfide in liquids. Measuring in the liquid instead of in the head space gives us the ability to get the full picture of sulfide in our sewer instead of just seeing the tip of the iceberg from our gas loggers. The sensors react instantly to changes in the wastewater composition. Correlating the sulfide concentrations with hydraulic data and temperature readings from our SCADA system has given us new insights into the sources of odor in our system.

“It is easy and quick to install the SulfiLoggerTM sensor and there is no need for large trial setups. It is possible to calibrate in the lab and then install it right away.” Karsten Egebjerg, Project Manager at EnviDan and member of Danva’s Hydrogen Sulfide Network.