Solving a gritty problem for wastewater treatment plants

CST Wastewater Solutions introduces high-performance inlet screening and grit removal technology, suitable for wastewater treatment plants (WWTPs) operating in sandy environments throughout Australasia. The Smith and Loveless PISTA 360 technology — which removes 95% of grit as small as 105 µm — eliminates the build-up of grit in downstream aeration basins and sludge digesters.

The technology is particularly relevant to councils and utilities serving the more than 80% of Australia’s population living within 50 km of the coast and more than 72% of New Zealanders living within 10 km 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,” said CST Managing Director Michael Bambridge. “It far exceeds the established standard for grit removal, which has been 95% removal at 250 µm. We are now achieving the same removal efficiency at 105 µm (140 mesh).”

The 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° rotation through the inlet and outlet, providing maximum travel of the wastewater for 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 turndown in performance is achievable with this the system.

“By increasing chamber velocity during low-flow periods, the baffle extends the grit extraction path within the vortex grit chamber,” said Bambridge. “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,” Bambridge 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.”