Sewage pump improves plant performance

Operated by the Bundaberg Regional Council, Woodgate Vacuum Sewer Station is a medium-sized plant which services an area of approximately 3000 people and can grow to a population of 8000 in peak holiday times.

The sewer station incorporates a network of sewage lines that come from houses and businesses, and which all lead back to a collection point. A vacuum tank is located at the collection point and the sewage flows towards the tank with the aid of vacuum pumps.

Once full, the tank then needs to be emptied using a pump that transfers the sewage out of the tank under vacuum and into the treatment plant. To undertake this task, the station was using a positive displacement lobe-style pump.

By the end of 2009, Bundaberg Regional Council recognised that the overall efficiency of the plant was being hampered by the performance of the lobe-style pump.

“The design of the plant is such that the pump used to transfer the sewage from the tank to the treatment plant experiences a high differential between its suction and delivery side. This can cause excessive wear and tear and make the pump less efficient, and this is exactly what we started to experience,” explained Kevin Harris, Metal Trade Support Technician for Bundaberg Regional Council.

“Over time, the wear and tear on the lobe-style pump had increased and our maintenance bills were rising. The tips on the pump’s rotor were continuously wearing and it required maintenance almost monthly with major works every quarter. By the end of 2009, our bills had become enormous,” said Harris.

The increasing wear and tear on the pump also meant that the pump was becoming less efficient. As the velocity of the sewage travelling through the pipe was slowing, the council found that rags and grit were settling out and not moving through to the sewer plant. This caused higher head pressures as the pipes were starting to block.

“We were also experiencing higher power consumption and increasing electricity bills. Initially we were shifting say 20 L of sewage a second, and then as the pump became more and more inefficient we would only move 5 L per second. Much more power was now required to pump out 20 L of sewage. We were also running out of pumping time,” said Harris.

Faced with such a dilemma, Harris decided to explore alternative pumps with the aim of identifying a more efficient and robust solution.

A chance meeting at the 35th Queensland Water Industry Operations Workshop in Rockhampton, Queensland, in June 2010 brought him into contact with Hydro Innovations.

“I had already been assessing different pumps and suppliers when I came across Garry Grant from Hydro Innovations at the workshop,” said Harris.

Hydro Innovations recommended that Bundaberg Regional Council consider installing a Gormann-Rupp Ultra VS3A60-B (3″) two-stage, self-priming, centrifugal sewage pump. As a self-priming pump, it has inherently low NPSHr, making it suitable to handle the negative 80 kPa on the suction side of the pump. It is currently claimed to be the only two-stage centrifugal sewage pump on the market and provides good solids handling and increased pressure capabilities.

Thanks to an innovative transition chamber found inside the VS3A60-B, maximum pressure is said to be increased up to three times that of a traditional solids-handling, self-priming, single-stage pump to deliver greater performance. The VS3A60-B two-stage pump also provides up to 60% increased flow when compared to the industry standard.

As with other Gorman-Rupp sewage pumps, the VS3A60-B is also fitted as standard with a self-cleaning wear plate system that enables the pump to handle stringy materials and rags that would block other pumps.

A large back cover plate allows easy access to the pump’s interior. The clearance between the impeller and wear plate can be adjusted simply and quickly without the need to realign belts, couplings or other drive components. Once adjusted, the pump’s lock collar and adjusting screw maintain the clearance setting even if the cover plate is removed.

After a trial, Bundaberg Regional Council installed the pump in January 2011 and has not looked back since.

“It’s now been about 15 months since we installed the VS3A60-B and we have not even had to touch it once. It has been performing within the required parameters, maintaining a flow rate of 20 L per second and a head pressure of approximately 73 m. It has significantly improved the greater overall efficiency of the whole plant,” said Harris.

The VS3A60-B pump has also helped the council save on maintenance costs and the hassles associated with constant repairs.