Senior reporter Matthew Martin finds out more about what Rotorua’s proposed new wastewater treatment plant will do
It's the Rotorua Lakes Council's largest and most expensive project since the 2007 Rotorua airport extension and will future-proof the city for expected growth in the coming years.
Plans to spend an estimated $29 million on a large-scale upgrade of Rotorua's wastewater treatment plant were approved at a council committee meeting this week.
The council's water solutions director, Andy Bell, said the new plant would be the best in the Southern Hemisphere and would combine a full membrane bioreactor with additional phosphorous removal and the addition of an ultraviolet disinfection system to produce the cleanest water, bar rainwater, entering the lake.
However, there is one contentious part of the plan, with some local hapu living on the eastern shores of Lake Rotorua concerned that highly treated effluent will flow into Lake Rotorua though an indirect earth treatment and waterfall system at Puarenga Bay.
For more than two years, the Rotorua Project Steering Committee has worked with the community to come up with the plan that took a range of viewpoints into consideration, before presenting the council with what it thought was the best option for the city.
The proposed upgrade follows the council signing a deed with CNI Iwi Holdings to end the spraying of treated wastewater in the Whakarewarewa Forest by the end of 2019. Mr Bell said other options, including finding a suitable area for land-based discharge, could have cost up to $54 million and would increase council debt by about $36 million.
"We would have had to go through a process like this anyway, regardless of having to move out of the forest.
"This was a completely community-led project. The council did not go out and say, 'Here's our plan, do you agree with it?' The steering group concentrated on a good technical solution and came back to us with what they thought was the best solution."
He said the design of the new plant was at the top end of the technology scale and offered a "double health barrier" with the membrane bioreactor and ultraviolet disinfection system being used, resulting in very high levels of public health and environmental protection.
It would also increase capacity at the plant from 19,000cu m per day to 24,000cu m, with the water going back into Lake Rotorua ending up so clean you could swim in it. In fact, it would be cleaner than any stream or river feeding into the lake.
Currently, two thirds of Rotorua's wastewater goes through a five-stage Bardenpho biological treatment process and one third through a membrane bioreactor process. The recovered water from the plant, still high in phosphorous and pathogens, is then sprayed on Whakarewarewa Forest.
Te Arawa Lakes Trust tumu rautaki taiao (environment and freshwater strategic manager) Roku Mihinui said the council's decision was expected.
"The outcome was pretty much what the cultural advisory sub-committee wanted anyway and aligns to the discussions we have had.
"We were very firm there would be no direct discharge to the lake and we were comfortable with the recommendation regarding the treatment itself.
"In terms of land-based discharge, we are pleased they will continue to look at that and that Te Tatou o Te Arawa will be engaged during that process.
"That the water quality would be better than that in the Awahou Stream was a surprise and there are still concerns from Ngati Uenukukopako, but I think they have been addressed. However, the decision still hasn't shut the door regarding those hapu concerns," Mr Mihinui said.
Benefits of the preferred treatment process:
- The recovered water is very high quality with nutrients as low as
- Additional barriers to pathogens - recovered water is safe to
return to the environment
- Well-known, proven, modern technology
- Better control of both nitrogen and phosphorous than most other
- The treatment process is streamlined, easier to operate and
carries fewer risks than other systems
- Allows for Rotorua to grow - the process capacity is not
- Lower operational costs than other options that reduce nutrients
- No increase in council targeted rate for wastewater
- Addresses iwi concerns about use of Whakarewarewa Forest land
- Addresses iwi concerns about discharge in the Puarenga Stream
- A cultural advisory sub-committee supports the plant upgrade
- Insignificant change in lake water quality and nutrient load to the
- Reduced ethanol dosing costs
- Reduced energy use and costs
- Reduced sludge production
- Rotorua Lakes Council
Steering committee goals:
- Be life-sustaining and restore the mauri of the water
- Meet standards consistent with the National Policy Statement for Freshwater
- Satisfy regulatory requirements and secure resource consents in partnership with the community and tangata whenua
- Achieve a high level of public health and environmental protection
- Be the best practicable option for Rotorua's future wastewater management