Eliminating grit from wastewater

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High-performance inlet screening and grit removal technology suited to wastewater treatment plants (WWTP) operating in sandy environments throughout Australasia has been introduced at Ozwater by CST Wastewater Solutions.

The latest Smith and Loveless PISTA 360 technology, which removes 95 per cent of grit as small as 105 microns, featured at Ozwater in Sydney from May 16-18. PISTA 360 technology eliminates the build-up of grit in downstream aeration basins and sludge digesters of waste water treatment plants.

The technology is relevant to councils and utilities serving the more than 80 per cent of Australia’s population living within 50 km of the coast and more than 72 per cent of New Zealanders living within 10km of the coast, often in sandy areas.

It reduces damage to downstream equipment from abrasion, enhances WWTP reliability, reduces OH&S hazards involved in unclogging systems and helps to prevent environmental spills from blocked and flooded systems.

“PISTA technology has set the global benchmark for grit removal for many years. It far exceeds the established standard for grit removal, which has been 95 per cent removal at 250 microns. We are now achieving the same removal efficiency at 105 microns (140 mesh), this latest technology sets an entirely new benchmark,” said Michael Bambridge, Managing Director of CST Wastewater Solutions.

 

The latest PISTA 360 uses an integral flow chamber baffle for both the inlet and outlet of the main chamber. The baffle is designed to direct the inlet flow into the chamber in a manner that ensures the proper vortex flow and prevents short-circuiting.

The V-Force Baffle allows for a full 360 degrees rotation through the inlet and outlet, providing maximum travel of the wastewater for the most effective grit removal before proceeding to downstream treatment processes. The baffle acts as a “slice weir” to control the water level in the main chamber and in the inlet channel. A 10:1 turn down in performance is achievable with this the system.

“This innovation further enhances the world’s best grit removal system from PISTA®, which incorporates many engineering and cost saving considerations,” Mr Bambridge said.

“By increasing chamber velocity during low flow periods, the baffle extends the grit extraction path within the vortex grit chamber. This is the key, because a longer path increases the amount of grit being captured on the chamber’s flat floor.”

The PISTA 360 with V-Force Baffle permits design flexibility so that water elevations can be controlled. “Water level control is important because it upholds the proper velocities approaching the grit chamber,” he said.

“Previously, the common way to accomplish water level control was to back up the flow with a downstream submerged weir. The PISTA 360 with its preset inlet and outlet openings supplants the need for the submerged weir.

“By integrating the water elevation settings with the baffle, the outlet footprint requirements decrease by as much as half the typical size. The resulting smaller footprint provides significant construction cost savings.”

Features of the V-Force Baffle include:

  • 95 per cent grit removal efficiency down to 140 mesh particle size.
  • Construction cost savings due to decreased overall grit system footprint.
  • Increased grit chamber velocity during low-flow periods.
  • Full 360 degrees rotation in the chamber, lengthening the grit extraction path.
  • Elimination of the need for downstream level control devices.