Vejle Spildevand A/S implements advanced dosing control as an efficient mitigation solution

To manage operations more efficiently, the water utility Vejle Spildevand A/S centralised its wastewater treatment. However, this resulted in increased and severe hydrogen sulphide (H₂S) production in the sewer network, leading to negative consequences such as odour problems, sewer system degradation and health and safety concerns for workers and the public. By implementing automated chemical dosing, Vejle Spildevand A/S is now able to adequately deal with H₂S-related issues, streamline operations and contribute to positive environmental outcomes.

Challenge

Sewer network length, transport time of wastewater and industry types in the catchment were identified as the main causes for H₂S formation. H₂S can have numerous negative consequences:

• Odour issues: H₂S has a characteristic unpleasant smell which can spread to nearby areas, affecting residents, businesses and public spaces
• Degradation of the sewer: H₂S is a corrosive gas that can react with metal components, leading to the degradation of pipes, manholes and other infrastructure, resulting in leaks, failures and costly maintenance
• Health and safety concerns: H₂S is toxic and poses health and safety risks. At low concentrations, H₂S can cause respiratory irritation, headaches and other health issues. At higher concentrations, it can cause unconsciousness and is highly explosive.

To mitigate H₂S issues, Vejle Spildevand A/S originally implemented chemical dosing in selected pumping stations and manually up- or down-regulated dosing at irregular intervals. This approach resulted in time-consuming manual regulation and over- or under-dosing, as wastewater composition can vary significantly over time.

Solution

Vejle Spildevand A/S desired an automated solution for efficient regulation of chemical dosing for H₂S management. Preferably, a cost-efficient solution which could be integrated into their existing management platform. They found the answer in DHI.

Data from the H₂S sensors were integrated into DIMS.CORE, DHI’s data repository and real-time data management platform. Together with existing data from pumping stations, the sensor data provide real-time information on H₂S concentrations in selected parts of the sewer network. This is instrumental for understanding the dynamics of H₂S formation and regulating chemical dosing. Next, DHI developed and customised the controller logic in the sewer network to dynamically adjust dosing rates based on hydraulic retention time and the H₂S concentrations measured upstream.

This solution integrated data from sensors, pumping stations and the customised controller logic into the utility’s DIMS.CORE management system. This enabled Vejle Spildevand A/S to optimise chemical dosing strategies and suppress H₂S with efficient chemical use. The combination of real-time data and customised controller logic empowers Vejle Spildevand A/S to make automated proactive decisions, and the system responds promptly to changing conditions while minimising the impact of H₂S-related problems. 

Vejle Spildevand A/S uses DIMS.CORE for numerous other operations, including aeration control, sludge recirculation control and quantification of combined sewer overflows (CSO). Furthermore, DIMS.CORE is used for data collection and transfer to applications such as ‘Badevandsudsigten’ and ‘PULS’. Incorporating the advanced H₂S controller in DIMS.CORE was a more efficient solution as compared to implementing a new system.