Case

Open S-tube® impeller eliminates clogging at wastewater station

With a bustling population of 195,000 residents, the city of Townsville in Queensland is the largest urban centre north of Australia’s Sunshine Coast. As an industrial hub in the midst of an area of rich biodiversity, framed by the Great Barrier Reef and the dry tropics region, the city’s council acknowledges the importance of reliability in the region’s wastewater systems to avoid costly and damaging breakdowns. And in recent years, Townsville City Council emphasised the need to implement a sustainability agenda to help to facilitate sustainable growth and economic development in the region and to better serve the community.

Pictured: The previous sewage pump that frequently caused problems for the Pumping Station

The situation

At the Howitt Street Pumping Station within the Townsville wastewater system, a submersible sewage pump consistently caused problems due to repeated blockages. This meant that the council’s maintenance team were regularly called to the site to resolve issues such as removing rags and other materials which had been tangled around the shaft and behind the pump’s impeller, subsequently overworking the motor.

Removing the material was required for the pump to operate properly, while external electrical contractors were also needed to check the pump for faults as it occasionally tripped the over-load on the soft starter. But these expensive, frequent callouts contravened the city council’s sustainability agenda. It wasn’t an ideal solution.

About the Open S-tube® impeller

Open S-tube® semi-open impellers with two or more channels are highly efficient and ideal for variable speed operation and wide operating areas. They are available in Grundfos SE/SL pumps, together with a range of other hydraulic designs, including Closed S-tube® impellers and SuperVortex free-flow impellers, offering reliable and efficient operation at the highest level of performance across all wastewater applications.

The solution

Grundfos had previously worked on the Townsville wastewater system, and Townsville City Council was impressed by the reliability and efficiency of Grundfos pumping solutions to the point that around 60% of the pumps within the regional network system are Grundfos pumps. And since both the council and Grundfos consider reliability to be a major priority, Grundfos was selected to head up the project.

Members of the Grundfos team, along with director Peter Bainbrigge from local Grundfos dealer Professional Pump Service, soon visited the Howitt Street Pumping Station to conduct a comprehensive audit of the pumps in operation. Performance curves were evaluated, revealing that the existing pump was running to the left of its performance curve for the majority of the time, away from the specified duty point of 38.0 l/sec at 17.8 metres TDH. This resulted in clogging due to the recirculation caused by a lack of flow, while the increase in pressure on the impeller’s outlet led to water and debris travelling through the gaps to the low-pressure suction side of the pump.

Upon the team’s assessment and diagnostics of the pump station’s system resistance, discussions about the issue soon followed with council representatives, with the team recommending an alternative hydraulic solution to be retrofitted to the station’s current pump. Based on system curve diagnostics, an Open S-tube® impeller proved to be the best option to prevent future clogging.

The outcome

As soon as the Open S-tube® impeller was installed, the number of clogging incidents was drastically reduced, and within just four months, they were eliminated entirely. And with no cases of blockages or clogging, there have been no unplanned callouts to the Howitt Street Pumping Station.

Today, the station operates reliably. Callout costs have been completely eliminated, and the Townsville City Council has peace of mind in the knowledge that its community’s wastewater transport is functioning reliably and in line with its sustainability agenda.

The success at the Howitt Street Pumping Station has led the Townsville City Council to work even closer with Grundfos, looking to identify other wastewater sites in the region that could be improved by the Open S-tube® impeller.

“The new Grundfos Open S-tube® significantly improved wastewater handling, clogging issues and overall reliability. It also helped to overcome rag build-up behind the impeller. I am very keen to convert all existing impellers to the Open S-tube®.”

Tejaswi Laveti
Engineer in Asset Reliability, Water, and Waste Asset Management
for Townsville

Pictured: The new Open S-tube® pump