Wastewater treatment in Melbourne

Blowers stand test of time

Enough sewage to fill 16 Olympic-sized swimming pools is processed each day by Yarra Valley Water treatment plants dotted around Melbourne. And because reliability is everything when it comes to sewage, it seems strange at first that many of the 17 Hurll Nu-Way Aerzen blowers at the front line of treatment are at least 10 years old, with some nearing 30 years of service.

“Blowers have got to keep running because people don't stop going to the toilet when the sewage plant breaks down,” notes Yarra Valley Water northern area treatment plant coordinator Ray Crilly.

Yarra Valley Water's seven treatment plants operate non stop. The water company covers 4034 km² of Melbourne's northern and eastern suburbs, delivering Class A recycled water suitable for watering gardens to the city's newest housing developments as well as Class B water for golf courses, agriculture and industry.

The treatment process begins at the 5 m deep extended aeration tanks. Aerzen three-lobe positive displacement blowers blow air into the raw sewage via diffusers in three-hour cycles to sustain cleansing aerobic bacteria.

“Aeration is a very simple process that produces very good effluent at a very reasonable price,” Crilly says.

In fact, the financial figures involved in treatment plants are as impressive as the sewage volumes. A single blower of this scale is valued at well over $100,000 and maintenance costs can be high, too.

“Given their capital cost and the need for reliability, the longevity of the blowers is very important. Another brand of blowers burnt out after three to four years but there are five Aerzen ones still working perfectly after 30 years in the field and another five that are 10 years old,” he says.

“Maintenance is another factor in the lifetime cost of the blowers, with some more than double the cost of the Aerzen units to service.

“The Aerzen's triple lobes are spinning at something like 1600 rpm three hours on and three hours off, all day, every day,” he said. “With those workloads, the quality of the steel, the clearances and the bearings makes a difference. We only need to replace the Aerzen bearings about once every 10 years and the belts and oil are changed every 2000 hours.”

While Yarra Valley Water's Aerzen blowers force 1800 cubic metres of air per hour through the sewage, the Aerzen three-lobe positive displacement blowers are available in 16 sizes, ranging from 30 to 15,000 m³/h, with a differential pressure of up to 1 bar.