Rotorua WWTP sidesteam MBR upgrade

The Rotorua District Council (RDC) as part of the Rotorua Lakeside Communities Sewerage Scheme Programme identified the need for improvement to allow greater treatment capacity in Rotorua, securing growth for the next 30 years within the existing infrastructure & allowing for the potential connection of new communities through population growth.

The decision was made to proceed with the installation of MBR (Membrane Bio Reactor) technology, the detailed design was awarded to AWT Water with GE Water & Process Technologies being the nominated membrane supplier & Downer New Zealand were appointed as principal Contractor for the execution of the project.

The upgrade was introduced as a Sidestream to run parallel with the existing Biological Nitrogen Removal (BNR) plant, providing greater flexibility by having two nutrient removal processes running concurrently. An existing, decommissioned clarifier was identified to house the new installation, with 4 new tanks being constructed to house the membrane filters.

RDC decided to procure all major equipment through NZS:4911, with the installation standard at NZS:3910, thus free issuing these items to Downer for installation, this approach whilst being commercially beneficial to RDC was not without challenge, chiefly with the management of risk & liability of equipment, however the exercise was a complete success, further enhancing the collaborative nature of the project between client (RDC), Designer (AWT) & Contractor (Downer).

Further challenges to the installation were the geothermal activity associated with Rotorua & the high water table within the area however due to swift preventative action, Downer New Zealand& RDC were able to identify and deal with potential seepage enabling the eventual successful application of the protective membrane coating contractually required by GE to protect the integrity of the concrete tank from chemicals used during membrane cleans.

This paper outlines information which led to the successful conclusion of this project:

• First hollow fibre submerged ZW MBR on wastewater application in New Zealand.
• Excellent example of collaborative effort by RDC, Downer New Zealand, AWT & GE.
• Membrane Technology for high specification treatment.
• Highly competent design & build capabilities & methodologies.