Sydney Water – North Head WWTP Primary Sediment Tank No.2 Overhaul

The Primary Sedimentation Tanks at North Head Waste Water Treatment Plant have had mechanical breakdown and corrective maintenance has become excessively frequent in recent years.  Consequently the system had to be upgraded to ensure optimal operation in future.  The works included the travelling bridges and associated equipment.

By overhauling this equipment there was a significant cost saving in maintenance of the equipment.  This saving is not be limited to the saving in equipment repair but also a saving in plant down time and the planning & coordination involved in bypassing the failed equipment. The works completed also reduced the risk of personal injury while maintaining items of plant and reduced the risk of damage caused by plant failure.

4 tanks out of the 6 total required overhauling and had to be completed one at a time to ensure that there were always four in operation with one reserve. The process for each tank was the same:

Phase 1 – Emptying the tank

The tank was deemed a confined space work and precautions had to be taken to ensure safe entry once the tank was emptied

The tank was then cleaned out and all inorganic material was removed and disposed of.

Phase 2 – Travelling Bridge Works

The following parts were replaced like for like:

• Energy chain
• Drive rack
• Drive sprocket wheel
• Drive rail  
• Scraper ropes
• Scraper wheels
• Scraper and skimmer squeegees
• Scum beach ladders
• Overhaul of drive motor and gear box
• Repair and alignment of scraper arm
• Repair of access and maintenance platforms
• Clean and paint all bridge equipment
• Replacement of electrical components & equipment

Phase 3 – Associated Works

• PST concrete remediation including engineering inspection and repair of grooves in tank’s concrete floor from scraper wheels
• Replacement of damaged Penstock fibreglass covers 
• Update electrical equipment 
• Replacement of PST aerial lighting poles and lights
• Replacement of PST sludge, scum & drain valves including 316SS pipework
• Replacement of air lines and supports with installation of isolation points.
• Develop test plans
• Complete testing of and check off
• Dry run and test
• Wet run and test
• Handover tank

 Phase 4 – Commissioning

• Develop test plans
• Complete testing of and check off
• Dry run and test
• Wet run and test
• Handover tank