Project Scope

• The scope of work was to remove Alumina sludge from the Water Treatment Plant  from the bottom of the ponds and process it to a substance with at least 20% solids and  then transport it to the onsite landfill for drying and final placement.
• The Sludge had to be dried in the landfill to 30% before it could be finally placed; this was done by regularly working the sludge to gain strength and dryness.
• The contract commitment was to lower pond 1 and 2 to 2.6m below the weir levels and to lower pond 3 to 1m below the top of the weir. The levels were monitored by regular ‘strawing’ to ensure it was dredged to the correct depth.
• We made use of our dredging barge for a large part of the works.
• The centrifuge and associated processing plant was established on site to modify the dredged wet materials.
• To determine the solid content of the removed sludge a Sartorius Moisture Balance was used. This provided a quality check and gave valuable feedback to the processing plant operator.
• The total amount of sludge removed from the ponds is estimated to be well over 7500 dry tonnes.

Project Outcomes

• The first pond took 6 months to complete. 3500 dry tonnes were removed in that time.
• The average production rate is 28 dry tonnes per day.
• The Client’s expectations had been exceeded in all aspects of the operation.
• We are able to optimise (and therefore minimise) the amount of polymer used in the sludge processing. Frequent samples are taken and analysed by polymer-supplier Orica to enable this.
• Internal and Client site safety audits both resulted in ‘A’ pass marks. There were no lost time injuries during the execution of the works.