Wastewater Reuse From Concept To Plant: Recycling Auckland’s Wastewater For Non-potable and Potable Applications

Hamish Spence, Watercare Services Ltd

Caroline Solomon, Jacobs

Auckland City, like many urban centres, faces significant water management challenges due to increasing population growth, climate change, and water scarcity risk. During 2020’s drought in Auckland, water scarcity was no longer a risk, but a reality. This posed an interesting challenge for the Central Interceptor project as it geared up to begin tunnelling - a very water exhaustive activity. Given the proximity of the tunnelling to the Mangere WWTP (Auckland’s largest wastewater treatment plant) it was proposed to build a wastewater reuse plant to help address this challenge. This plant’s aim was to treat wastewater and produce a high quality non-potable water (a.k.a. the fourth water) for tunnelling activities and other construction purposes. In parallel, it was proposed to run a pilot plant to treat the water to a potable standard. Watercare’s Central Interceptor Project has funded and constructed a Reuse Water Plant (RWP) at Mangere Wastewater Treatment Plant. The RWP can produce 500 m3 /day of non-potable water for use in tunnelling operations and site activities.

There is also the capacity to produce up to 30 m3 /day of potable water as a pilot for future use. This project marks the start of New Zealand’s fourth water. The project approach divided the scope of works into 4 main packages: design (civil and process), construction, membrane supply, and MEICA (design and build). The selected treatment process comprises:
1. Chloramination followed by coagulation and screening.
2. Membrane ultrafiltration
3. Ultraviolet dosing
4. Chlorine dosing/contact to create non-potable water.

The pilot plant process design was developed with various options to allow diverse treatment capabilities. The supply water was membrane permeate from the main plant that can be treated with varying combinations of reverse osmosis, activated carbon, advanced oxidation, ultraviolet dosing, and chlorine contact. This variability allows for a greater trial and testing regime, as well as process adaptability to ascertain what is required to turn Auckland’s wastewater into potable water. As there are no current New Zealand standards for treating municipal wastewater the use of Australian QMRA exposure guidelines were used for the potable water section of the plant.

Severe droughts can be extremely challenging for water suppliers and users to respond to. The Watercare Central Interceptor team addressed this problem head on and faced the challenging prospect of going where no water supplier had gone before. Tackling water sustainability, lack of official guidelines, and roadblocks to water reuse is a significant step in the right direction for the betterment of New Zealand. Overcoming these challenges and sharing this journey with the industry will help pave a successful reuse water pathway that can be traversed by all.