Wastewater

One of the most important services we provide is the reticulation and treatment of wastewater on behalf of residents and ratepayers, before safely returning the treated water to the environment.

Currently, we service the wastewater needs of over 21,000 residential properties in the Queenstown Lakes District, and more than 2,900 non-residential properties, resulting in an average of 14,521m³ of wastewater produced each day.

This wastewater is then managed by a network made up of 551km of pipes, 65 pump stations, and four treatment plants throughout the district (located in Queenstown/Frankton, Wānaka, Hāwea, and Cardrona).

We use a range of different methods across the district to treat the wastewater we produce. As an example Project Shotover uses a Modified Ludzack-Ettinger (MLE) Activated Sludge process to treat wastewater before returning it to the environment.

Click to enlarge the treatment process image.

1. Wastewater is piped to the treatment plant and screened to remove the bulk of non-biodegradable solids in it.
2. Wastewater then flows through into a reactor tank with different treatment zones. Initially the wastewater is exposed to anoxic conditions which starves bacteria of oxygen. This bacteria then begins to break down elements in the wastewater to produce oxygen it needs to survive.
3. Wastewater then enters the aerobic tank and is fed with an oversupply of oxygen. This causes further biological processes that complete the stabilisation of organic matter, reducing nitrogen concentration in the wastewater.
4. The combination of water and biomass (the collection of microbes responsible for treatment), then flows into a clarifier. This is a settling tank that uses gravity to separate solids from the treated water, with heavier solids settling at the bottom.
5. A scraper mechanism within the clarifier collects the settled sludge and returns it to the front of the reactor tank to allow the biomass to further participate in the treatment process.
6. Clear treated wastewater from the clarifier then receives ultraviolet (UV) disinfection before it is discharged into a disposal field, where it is intended to soak through gravels and safely return to the environment (in the case of the Shotover WWTP the Shotover and Kawarau Rivers.

At the point of discharge from a facility like Shotover Wastewater Treatment Plant, treated wastewater is regularly tested to ensure it complies with consent limits set by Otago Regional Council. Typically these parameters include Biochemical Oxygen Demand (BOD), Total Nitrogen (TN), Ammoniacal Nitrogen, Total Suspended Solids (TSS) and E.coli.

Our operation teams undertake regular monitoring through onsite instrumentation, and regular analysis underaken at on-site labs and through independant lab testing.

We’ve invested heavily in wastewater management over the last decade, with the district’s major facilities moving towards modern treatment processes capable of producing high-quality treated water.

• Some significant wastewater projects in the district either underway or starting soon include:A third stage of upgrades underway at Project Shotover to introduce a second Modified Ludzack-Ettinger (MLE) reactor at the facility, which will mean the oxidation pond system (currently used as part of the treatment process for 20% of wastewater flows into the facility) can be decommissioned. More information on these upgrades can be found here.
• Upgrades to the Upper Clutha’s wastewater network starting soon, which will futureproof Hāwea’s wastewater needs, and increase the capacity and resilience of the wider Wānaka and Albert Town network. Click here for more information.

An additional $77M is allocated in the 2024-34 Long Term Plan for a new disposal solution at Project Shotover, and an additional $80.1M for further improvements to the Upper Clutha network.