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CONFERENCE: NZWWA 49th Annual Conference, Rotorua, New Zealand, September 2007

ABSTRACT:
The Tirau Sewage Treatment Plant, New Zealand’s first municipal Membrane Bioreactor (MBR) sewage treatment plant, was designed by Harrison Grierson for the South Waikato District Council and successfully commissioned in 2006. An advanced treatment process was required for the Tirau Plant as the effluent is discharged to the environmentally sensitive Oraka Stream, a trout fishery in the highly valued Waihou River catchment. MBR is the combination of the activated sludge treatment process and the application of advanced membrane technology. The plant design has created a highly controlled, intensive treatment environment where the population of bacteria used to stabilise the wastewater is up to 5 times higher than most other processes. Flat sheet membranes, are used to produce the treated effluent (permeate) from the wastewater being treated in the reactor. The membranes produce a disinfected effluent wh ere most viruses and practically all bacteria are removed. The project was particularly innovative in that the advanced process and technology were retrofitted to a 1970’s treatment plant. The existing plant was stripped of the original mechanical equipment and the structures were rehabilitated, modified and used in the reconfigured plant.  The South Waikato District Council took the further progressive step of appointing itself as main contractor on the project. Council engaged Harrison Grierson to construction manage four separate, concurrent contracts and commission the completed project. The majority of the work was undertaken using the resources of local general and specialist contractors.

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