Wastewater treatment plant improves pump performance

Saving maintenance with self-priming pump

For over 14 years, the Moe Wastewater Treatment Plant has been effectively and successfully processing sewage. Located in Gippsland, Victoria, the medium-sized plant serves an equivalent persons population of 22,000. Its average daily flow is 5 ML per day.

Starting in February 2010, the plant’s wastewater treatment engineers noticed that its two submersible pumps (one duty pump and a standby pump) at the inlet station, were blocking up with increasing regularity, making them virtually ineffectual and impacting on the efficiency of the plant.

“Between February and the start of December 2010 our submersible pumps were choking about once a fortnight,” explained Adrian Harper, Senior Engineer Wastewater Treatment Group, Moe Wastewater Treatment Plant. He said the pumps were no longer capable of effectively handling the rags and other solid material in the inflow.

To deal with the problem, the plant operator would call in their maintenance contractors to isolate the obstructed submersible pump, lift it, using a crane, and then clean it before lowering the pump back into the wet well. According to Harper, this was time consuming, inconvenient, expensive and negatively impacted on the plant’s performance.

“Between February and December 2010 we spent some $27,000 just on getting the contractors in to clean the pumps,” said Harper. The problem also created OH&S headaches as it required the continual lifting by crane and cleaning of a 700 kg submersible pump. The whole process increased the risk of accident when the plant was committed to improving its safety profile.

By about May the situation had become untenable and a permanent and effective answer to the choking pump problem was sought.

Impressed with the solutions that Hydro Innovations had exhibited at a tradeshow, Gippsland Water invited the company to assess their dilemma and provide a workable solution. After exploring the site and the needs of the plant, Hydro Innovations suggested that Gippsland Water consider installing an above-ground Gormann-Rupp self-priming pump.

To evaluate Hydro Innovation’s solution, as well as to explore the pros and cons of a self-priming pump versus a submersible pump with a cutter impeller, Gippsland Water initiated an option study. The study confirmed that a self-priming pump would be a workable solution.

“We had never used an above-ground, self-priming pump at the plant before, and although we were happy to think outside the box, and the study had confirmed that such a solution was viable, we weren’t entirely convinced. So we asked Hydro Innovations if we could trial the pump for three months, which they readily agreed to because they were certain the pump would meet our needs,” explained Harper.

Hydro Innovations provided the plant with a Gorman-Rupp T8A3S-B above-ground self-priming centrifugal pump in December 2010. By mid-December the pump was installed and in use.

According to Garry Grant, General Manager of Hydro Innovations, the Gorman-Rupp T8A3S-B self-priming centrifugal pump is a purpose-built sewage pump that is fitted with an aggressive self-cleaning wear plate.

The wear plate has been specifically designed to change the shape of solid waste and stringy material so that the pump does not clog. If choking does occur, the pump can be unclogged quickly and easily via the removable cover plate, without the need to disconnect piping. Better still, it can be done with only one operator and without the need for a lifting device.

The design of the pump allows users to adjust the clearance between the impeller and wear plate without having to pull it apart. This eliminates the need to realign belts, couplings or other drive components.

A unique collar and adjusting screw allow for incremental adjustments of the wear plate clearance. Once made, the collar locks in place maintaining the clearance setting. These features help double the life of the impeller and the wear plate while maintaining peak operating efficiency.

After the three-month trial period, Gippsland Water was impressed with the Gorman-Rupp pump’s performance and purchased the machine. By May 2011 the pump had been in operation for about five months. It did lightly block a couple of times but it kept pumping and, overall, made a positive impact on the processing efficiency of the plant. It performed well and delivered 110 L per second at 8.9 m of total head.

The design of the pump makes cleaning and maintenance quick and easy, and as it’s done above ground, there are fewer OH&S concerns.

“Another big plus with the Gorman-Rupp pump is that if you do get a malfunction occurring in the motor you can just replace the motor. This isn’t possible with submersible pumps. If there is a motor problem you have to change the entire pump,” said Harper.

Gippsland Water is now planning to replace its other submersible pump at the Moe WWTP with a self-priming pump.