Innovatively adapting an existing water treatment plant

Maximising the value for New Plymouth District Council was the driving force behind the innovative adaptation of its existing water treatment plant, with some great cost and performance outcomes.

With New Plymouth’s population growing, and existing facilities stretched to their limit, New Plymouth District Council needed to upgrade its water treatment plant to cope with the additional demand.

The water treatment plant upgrade resulted in expanding the existing plant capacity from 45,000 m³/d to 70,000 m³/d, as well as an upgraded performance that met the requirements of the new Drinking Water Standards New Zealand.

As the principal designer for the design / build contractor Fulton Hogan, we worked together to maximise the value that could be extracted by innovatively adapting the existing plant. Features of the upgrade include pre-lime and CO₂ prior to coagulation for improved coagulation control and reduced water corrosivity (which is important for waters in the Taranaki region); tube settlers installed in the existing clarifiers to enable a 50% increase in capacity; and existing filters fully refurbished, including new floors suitable for a simultaneous air water scour system that provides substantially improved filter washing and a filter-to-waste system.

An additional challenge was that the Council wanted the treatment plant to be fully operational while the upgrades took place. By specifically designing the upgrades and working closely with the contractor and the Council’s operations team, this was achieved.