Rotorua District Council (RDC) is now reducing nutrients such as phosphorous and nitrogen previously causing algae blooms in New Zealand’s lake Rotorua through membrane bioreactor technology (MBR).
A NZ$8.5 (US$6.7) million upgrade to its 20,000 m3/day wastewater treatment plant includes the commissioning of the MBR system, the first time a New Zealand city has used the technology on this scale.
The city’s wastewater plant had historically treated sewage with treated effluent being used for irrigating parts of the Whakarewarewa Forest. However, RDC said achieving the desired limits for nutrient nitrogen entering Lake Rotorua via the Puarenga Stream had always been challenging due to a number of natural factors.
RDC utilities operations manager Eric Cawte said: “With membrane filtration technology we’re able to remove very minute particles containing nitrogen and phosphorus, on top of the already successful biological removal process. About a third of the sewage is treated in this way, enabling the current process to operate to its maximum efficiency without flow fluctuations.”
The upgraded treatment plant had been undergoing testing and is now fully operational after being fine-tuned to achieve high levels of nutrient removal.
The district council is now in the process of preparing an application to the Bay of Plenty Regional Council to amend resource consent conditions. The council is also in the process of undertaking a full review of the forest irrigation system and assessing a number of alternatives for discharging highly-treated process water.
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