CASE STUDY:

Hydro-Dyne Center Flow Screen Selected to Help Remove Toxic Plastic Nurdles from Australian Waters

SITUATION:

Warrnambool, Victoria is a coastal town along the scenic Great Ocean Road who’s 35,000 residents are closely connected to their maritime history, beaches, and marine environmental reserves.

 

They were unexpectedly thrust into the spotlight after large concentrations of “Nurdles” – pre-production plastic or plastic resin pellets – washed up on a beach adjacent to the Warrnambool Sewage Treatment Plant. These pellets are heated and chemically treated to mold plastic goods (Figure 1).

 

Shortly after that discovery, an operator at Wannon Region Water Corporation discovered more Nurdles in their tanks and other equipment, prompting an investigation. The Nurdles had been illegally dumped through the sewage treatment system and were being expelled into the ocean through the plant’s effluent outfall. Due to their size, hardness, and buoyancy, it was easy for them to float through the wastewater plant without being removed.

 

Huge volumes of Nurdles are produced and shipped around the world each year, and a large number is lost in marine areas due to cargo loss and spills.

Equipment: Great White Center Flow Screen

Location:     Warrnambool, VIC Australia
Date:             2020

As they sit in the environment, they absorb pollutants becoming toxic and because they never disappear completely (they only break down into smaller and smaller pieces), they are ingested by animals and are difficult to remove from the environment. It was critical that the Nurdles be eradicated as quickly as possible.
 

SOLUTION:
The solution to eliminate the Nurdles from the discharge effluent at the Warrnambool STP required a high-performance screen with the ability to remove all hard solids greater than 1mm in any two dimensions prior to plant discharge. The screen must perform to the precision of a filter while passing municipal instantaneous plant flows of 600 L/s (9510 GPM).

 

Hydro-Dyne and its local partner, Green Process, designed a solution including Hydro-Dyne’s Great White Center Flow band screen (Figure 2). The Great White was selected over alternative options due to:

  • The overall design was able to accommodate the channel geometry limitations on site, high instantaneous flow, and fine screen opening requirements without requiring modifications to the structure of the facility.
  • The moving band design seals and maintains 0.5mm tolerances, within pivoting components of the band itself and the band to the static screen body.
  • Use of 1mm mesh grid openings and industry leading screening capture ratio.

 

RESULTS:
Multiple (40+) performance tests, with zero reported failures, demonstrated 100% removal of hard solids above 1mm and a very high percentage of hard solids above 0.5mm were captured by the screen. Head losses were consistent with the projections within the hydraulic profile presented for technical review at tender stage. The operators at both Wannon and Warnambool STP have put the screen through its paces and have been very pleased with its performance – and they continue to push it to further reduce water use.

 

While removing all the Nurdles from the environment is not possible, the Hydro-Dyne screen and ongoing clean-up efforts from the community continue to result in decreased amounts washing up on Warrnambool beaches and ensure no additional Nurdles or plastics enter the pristine marine environment through the treatment plant outfall.

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