Molendinar Clarifiers Refurbishment

About the project

The two clarifiers at the Molendinar WTP were installed when the plant was first built in 1983. The aging assets had deteriorated and risked the reliability of the plant.


Molendinar, Queensland

Client & Duration

December 2018 — September 2019

Project Scope

  • Coating all structural components, above and below water, to comply with WSA201 and AS4020 standards
  • Major refurbishment of mechanical elements including mixer and rake gearboxes
  • Replacement of rotating elements including sprockets, pinion and spur gears, bearings, bushes and chains
  • Replacement of DN900 inlet pipe and installation of isolation inlet valve
  • Reinstatement of all ancillary services following major refurbishment, to enable operation of clarifiers
  • Commissioning and testing


  • Clarifier one was to be completed within a 9 week plant shut down, whilst coordinating multiple subcontractors and deliveries
  • Refurbishment works were completed offsite which involved disassembling the structure, transporting all components for refurbishment and reinstalling once returned to site
  • Transportation permits were required to remove a 15t, 34m bridge structure. Access was challenging and care was to be taken to avoid damaging the bridge
  • Works and materials used for the refurbishment were to be AS4020 compliant, meeting Drinking Water Quality requirements


  • Extensive planning and risk assessments were completed prior to the shutdown, ensuring risks were identified and contingency plans in place
  • Successfully coordinated multiple stakeholders, including plant operators, suppliers, subcontractors and work teams
  • Proactive, early identification of non-compliant clarifier components reduced costs and avoided delays
  • 3D scanning and modelling was used for the replacement of the inlet pipework, to achieve an exact connection and avoid delays
  • The bridge structure was successfully lifted in one piece, as a result of an effective lift study and structural assessments
  • Works for both clarifiers delivered on time and commissioning completed without disruption to plant operations

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