After installing the Grundfos solution, the smell problem is completely gone. The hydrogen sulphide sensor in Hobro indicates zero, and the complaints have stopped.
Mariagerfjord Vand A/S is a Danish public utility company wholly owned by the Mariagerfjord county. The company operates the municipal water and sewage works and pipe networks, serving the approx. 42,000 citizens of Mariagerfjord county including the city of Hobro (population approx. 12,000). The company aims to handle wastewater in an efficient and environmental way while providing its services in a cost-effective manner.
Hydrogen sulphide causing complaints and pipe corrosion
Until recently, residents in a neighbourhood in Hobro were plagued by the smell of hydrogen sulphide. The odour problem came from manholes outside the city where a pumping main transports wastewater. The production of hydrogen sulphide in the pressurised pipes was so significant that concentrations of up to 500 ppm were measured in the manholes. In addition to the serious odour problems, hydrogen sulphide corrodes the pipes and creates a potentially hazardous working environment for the operational staff.
Hydrogen sulphide problems can be hard to predict, which makes them hard to solve. The presence of hydrogen sulphide depends on many factors, including temperature,the composition of the wastewater, and retention time in the pipes, and when and for how long the manhole pump is running. An ideal solution to hydrogen sulphide problems must be based on actual operational conditions in order to deal with this unpredictability.
The Grundfos solution
Adapting to actual conditions is precisely the approach that has led to the Grundfos Hydrogen Sulphide Solution which was installed at the Hobro pumping station in 2015. The heart of the Grundfos Hydrogen Sulphide Solution is an advanced control algorithm installed in Grundfos Remote Management (GRM). GRM receives signals from a gasphase logger installed in a manhole. The gas logger performs a measurement once every 15 seconds and sends measurements for the last 24 hours to GRM. Based on the data received, the solution automatically calculates the correct dosing amount of iron sulphate.
The Grundfos Hydrogen Sulphide Solution algorithm constantly adapts the amount of iron sulphate to the current demand in the pumping main, and the operational staff do not need to control dosing manually. GRM warns operators in case of problems, and the staff can access the internet based system at any time to view operational status and make any necessary adjustments.
The results of using the Grundfos Hydrogen Sulphide Solution so far have been very positive. ”After installing the Grundfos solution, the smell problem is completely gone. The hydrogen sulphide sensor in Hobro indicates zero, and the complaints have stopped”, says Brian Frost.
In addition to greatly improved customer satisfaction, Mariagerfjord Vand A/S has made significant financial gains. The price per cubic metre of treated wastewater has dropped to EUR 0.05 with the Grundfos Hydrogen Sulphide Solution (based on an average consumption of 590 ml of liquid iron sulphate per cubic metre of wastewater at the pumping station in 2015, and at a price of EUR 0.06 per kilo of iron sulphate). At Mariagerfjord Vand A/S, the Grundfos Hydrogen Sulphide Solution has resulted in chemical savings of around 70% in the area.
The system is designed to adjust the dosed amount of iron sulphate according to daily and seasonal variations in hydrogen sulphide amounts which have therefore dropped significantly (from up to 500 ppm to 0 with single, isolated deviations of around 50 ppm). In addition, Mariagerfjord Vand A/S staff no longer need to spend time monitoring the system and manually adjusting the chemical dose to match current demand. This reduces workload in connection with the manhole and saves staff time that can be used for handling other assignments.
As an added bonus, Mariagerfjord Vand A/S expects to be able to save money on pipe network maintenance. The greatly reduced amount of hydrogen sulphide means that pumps and pipes do not corrode as quickly as previously and therefore do not need to be replaced quite as often. “The hydrogen sulphide dissolves the lime in our concrete pipes. After installing the Grundfos solution, we expect that it will be a longer time before we need to replace them”, says Brian Frost.