The Royal New Zealand Navy need to waterblast their ships above and below the waterline in order to recoat them. This water is then collected into a sump and pumped to a treatment plant. Recent tightening of their trade waste consent necessitated a plant upgrade.
Due to the dry dock servicing different types of ships, from navy vessels through to privately owned commercial ships, there is no way of accurately predicting the type of paint, or concentration that is required to be treated. On top of this the salt water that is being pumped through the system creates a highly corrosive environment for mechanical equipment.
Since Filtration Technology was dealing with an existing process, their engineers had to utilise as much of the existing equipment as possible, meaning refurbishing, where possible, rather then replacement.
Water enters the equalisation tank where it is dosed with PACl, based on the combined suspended solids and flow measurement, from here is it decanted, dosed with Poly and sent to a Lamella Clarifier and rapid Gravity Sand Filter before being polished at 1 micron and pumped into the sewer.
It depends on the results of jar tests from each ship’s wastewater to determine the type and amount of Poly that will be dosed into the Conditioning Tank.
The solids that settle within the equalisation tank are put through a Macerator and sent to a sump, from here they are pumped up to a Conditioning Tank, mixed with Poly and allowed to settle before being pumped to a press. Cakes from the press are fed by an auger to awaiting drums. |
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| Contractors waterblasting a RNZN ship in drydock at the Devonport Naval Base. |
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| Views of the treatment plant at the RNZN drydock. |
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