Rotorua Wastewater Treatment Plant upgrade
Work is underway to upgrade the Rotorua Wastewater Treatment Plant and offer an alternative solution for the current discharge location and system. The upgraded Wastewater Treatment Plant will be able to handle more than 70 million litres of wastewater, which is three times more than it does today.
What is being proposed?
He aha e marohitia ana?
Rotorua Lakes Council collects and treats wastewater from the Rotorua urban area and a number of lakeside and rural communities within the district. Historically, treatment of this wastewater has been carried out at the Rotorua Wastewater Treatment Plant with the resulting effluent pumped to the Whakarewarewa forest where it was irrigated onto approximately 300 ha of plantation forest. This was done in accordance with a resource consent for the discharge of sewage effluent to land.
The resource consent for this system ends in 2021 and Rotorua Lakes Council and CNI have made a commitment to end spraying treated wastewater in Whakarewarewa Forest after successful commissioning of the upgraded Wastewater Treatment plant.
Māori knowledge (Matauranga Māori) has shaped the design of a new Water Restoration Land Contact Bed system. The design would emulate the natural water cleansing processes of Mother Nature (Papatūānuku).
Why is this project important?
He aha te tino take o te hinonga?
Rotorua’s Wastewater Treatment Plant needs to be upgraded to cater for future growth as well as ensuring we manage our waste responsibly, in a way that:
• Protects people’s health
• Is environmentally sustainable; and
• Is culturally appropriate
The objectives have been inspired by the Lakes Water Quality programme as well as aligning to the Council Vision 2030 goals of creating a vibrant and sustainable future for Rotorua and its residents.
Rotorua’s current plant has to date been the most successful initiative in reducing nitrogen going into Lake Rotorua. Our treatment plant is among the best in the country, treating wastewater to a very high standard. But it is in need of future-proofing to meet higher projected demand and to continue to reduce and maintain nutrient levels below the targets agreed under the Lakes Water Quality programme.
Discharging into Whakarewarewa Forest is no longer viable as a sustainable option for several reasons including cultural concerns. It is also resulting in ground over-saturation that’s detrimental to trees, making it an unreliable filtering system and adding to pollutants entering the Puarenga Bay.
The proposed upgrade would treat wastewater to an extremely high standard, removing pollutants like nitrogen and phosphorus and disinfect bacteria like E. Coli. The recovered water would be clean and would not pollute the lake.
Who has been part of the project development?
Nā wai te hinonga i whakarite?
A Project Steering Committee consisting of key stakeholders, Council and experts formed to identify and select alternative options for treating Rotorua’s wastewater.
After about two years of consideration of alternative options, the Project Steering Committee resolved to recommend Council proceed with a resource consent application of the preferred upgrade of the existing wastewater treatment plant and a discharge to Puarenga Bay. The Project Steering Committee also recommended that Council continues to work with interested parties to investigate alternative discharge options including the reuse of recovered water. All of the Project Steering Committee recommendations were adopted by the Rotorua Lakes Council.
Once the Steering Committee had identified options, it was worked through and shortlisted, a suite of potential discharge options identified and indicative costs estimated. The wider community was consulted and responses were fed back into the ongoing process.
The concept was designed by the Rotorua Project Steering Committee’s Cultural Assessment Sub-Committee. Council also enlisted the help of Matauranga Māori experts to refine the initial concept.
How is this being funded?
I ahu mai te pūtea i hea?
A budget of $18.6 million has been allocated to this project in Rotorua Lakes Council’s Long-term Plan. However the preferred option has a higher capital cost than the Long-term Plan estimate and will impact Council’s debt retirement programme over the 10-year period of the Plan. Once we have resource consent, a more accurate funding projection can be developed.
We are currently waiting on resource consent before progressing with this project.
Treated water leaves the wastewater treatment plant and enters the contact bed system which mimics mother nature to further purify the waiparapara/treated water leaving it just short of drinking standard.
The water enters the land contact bed system and goes through a bubbling water filtration process. This is followed by a series of rock and wetland vegetation filtering bands. A water fountain system then creates turbulence and aeration before the waiparapara moves through rills that emulate streams. The wastewater then enters a calm rock pool / pond where aquatic life is present before the water is released through a rock filtration waterfall that cascades out to Puarenga Bay
The land contact bed design has been enhanced by incorporating Māori knowledge and principles/values to address cultural concerns that were raised during consultation.
At a minimum the design aims to incorporate the following principles/values:
· Restoration of the mauri of the water
· Water is of Papatūānuku and Ranginui and is both intrinsic to life and must be able to sustain life and be life-sustaining
· Te Tūāpapa o ngā wai o Te Arawa / Te Arawa cultural framework for water
The maximum capacity of the upgraded plant will be about 70 million litres a day which will help us deal with significant weather events. If an event was to occur that makes us run at maximum capacity, it would take about five hours for the water to flow through the land contact bed (at a peak flow of about 825 litres per second). However, peak flows, caused by severe weather, usually happen in short durations and are unlikely to be sustained at this level for a full 24 hours.
Rotorua’s wastewater (sewage) is treated daily at a central Wastewater Treatment Plant on Te Ngae Road. It is sited on the eastern edge of Lake Rotorua in the Sanatorium Reserve – a reserve gifted by Ngāti Whakaue for public purposes under the 1880 Fenton Agreement. The plant uses a combination of a 5-stage Bardenpho process and Membrane Bioreactor, the first full biological nitrogen and phosphorus process that is used for municipal wastewater in New Zealand. To protect the quality of the water in Lake Rotorua, the treated effluent from the plant is currently irrigated to pass through CNI land in Whakarewarewa Forest before the groundwater discharges to Lake Rotorua.
Council suggests the provisional release location should be Te Arikiroa / Sulphur Bay. The site would be close to the newly designed Land Contact Bed on the Sanatorium Reserve.
The Project Steering Committee considered three options all incorporating a Land Contact Bed system:
• Puarenga Stream discharge
• Offshore lakebed discharge into Lake Rotorua with diffuser
• Sulphur Bay (Te Arikiroa) discharge after recovered water is infiltrated through specified aggregates within existing storage ponds
Rotorua Project Steering Committee has been exploring the options. At a 2014 Lakeswater Quality Society workshop it was suggested that Rotorua Lakes Council collaborate with the community to work together to find a suitable solution for the future, to first and foremost improve the mauri (vitality) of the treated water and make it as clean as possible before returning it to the environment. Council agreed, and with key stakeholders, including mandated hapū representatives, a Steering Committee was formed.
• Be life-sustaining and restore the mauri (vitality) of the treated water
• Meet standards consistent with the National Policy Statement for Freshwater Management
• 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
Once the Steering Committee had identified options, it was worked through and shortlisted, a suite of potential discharge options identified and indicative costs estimated. The wider community was consulted and responses were fed back into the ongoing process
Rotorua Project Steering Committee investigated numerous options including:
• Whether the Rotorua Wastewater Treatment Plant should be upgraded
• What type of system would ensure removal of pathogens and phosphorus from effluent to ensure its treated before it is disposed of
• Rotorua Project Steering Committee is unanimous on the need to upgrade the Wastewater Treatment Plant, however members did not unanimously agree on the point of effluent release
Yes. The upgrade will manage a 45% growth in population (or roughly 7,000 more households) and will also be able to deal with significant weather events that reach a peak flow of 70 million litres per day or 825 litres per second.
Yes, the current system allows for a daily flow of up to 25 million litres a day which can service an extra 7,000 households than at the moment. If we did service 7,000 more households, the flow rate though the system would take about 15 hours.
• The plant is designed to break down and treat organic material such as blood and bodily fluids
• Bacteria breaks down organic matter in to simple compounds like carbon dioxide and water, as well as important nutrients such as nitrogen and phosphorus
• Bacteria and other microorganisms grow and multiply under controlled ideal conditions in the plant
• In parts of the process they are provided with as much oxygen (air) as they need to live (for respiration) and in other parts they are starved of oxygen so they use the oxygen from the nitrate molecule and release the harmless nitrogen gas to the atmosphere
• They absorb their food from the material they live in
• Towards the end of the process they run out of food and energy (they have consumed all the organic waste from the wastewater) before they have removed all the nitrogen, so they are fed ethanol
• All the organic waste is bio-transformed into more bacteria, water and gases
• At the end of the treatment process, the wastewater also receives UV treatment to remove pathogens including viruses
• Sludge produced at the plant goes to Kawerau for vermicomposting
An independent company, Waste Management Technical Services, provide a specialised service for medical waste to our community. Medical waste is collected and taken to an Auckland plant where it is sterilised before being disposed of at their Class A landfill in Redvale, Dairy Flat.
An independent company, Waste Management Technical Services, neutralises, sterilises and dewaters hazardous chemicals. Any solid residue is taken to the landfill and the remainder goes through filtrate treatment before being treated as trade waste.
Industry waste is a form of trade waste and its disposal needs to be in line with the trade waste bylaw (link to bylaw). A trade waste officer decides the necessary treatment needed onsite before any wastewater is discharged to sewer.
Examples: Restaurants use grease traps to separate grease. Dentists separate mercury. Petrol stations have measures in place to address spills.
For most other industrial / commercial outlets, the best place for their wastewater to be treated is the Wastewater Treatment Plant. Their discharge is monitored and they are charged based on the volume and strength of their discharge.
• The Rotorua Wastewater Treatment Plant serves a population of about 60,000 people.
• It has the capacity to serve a population of 75,000
• The plant receives 20 million litres of wastewater every day
• We have the capacity to treat a daily average wastewater intake of 27million litres
• Most of Rotorua’s wastewater is generated by domestic use, while a small percentage is from industrial use
• Wastewater going into the plant includes rainwater, sediment, sewage, industrial wastewater and stormwater
Nature eventually cleans water through the water cycle, but this takes time. Treating wastewater accelerates the natural process. Wastewater has a very high number of water-borne bacteria and pathogens. Some of these are completely harmless: others are responsible for life-threatening diseases. Wastewater is also nutrient-rich. It contains high levels of nitrogen and phosphorus. In the 1980s, wastewater was a major contributor of nutrients which added to Lake Rotorua’s declining water quality problems. Council’s upgrades of the wastewater treatment plant have substantially reduced the nutrient load to Lake Rotorua. Treatment now involves biological nutrient removal with carbon dosing and land treatment.