Innovative Wastewater Treatment Systems for Extreme Alpine Environments

Dr Matt Savage (Apex Water Ltd)

Sewage treatment systems in the New Zealand alpine environment have a history of failure due to the biological systems utilised being unable to work effectively under the low temperatures and highly seasonal loads encountered.

With tightening regulatory compliance requirements, such failures are becoming less tolerable and a higher level of resilience must be engineered in to overcome these challenges.

A new treatment plant in Cardrona Valley servicing the village, Cardrona Alpine Resort Limited and a 500 house development at Mt Cardrona Station was built last year and has now worked through its first full winter.

The site is exposed to seasonal extremes in ambient temperature ranging from below -8°C to more than +30°C, resulting in wastewater temperatures too low for traditional biological treatment systems to function.

This was addressed by construction of a hybrid SBR / fixed biofilm reactor that utilised a novel thermodynamic solar heating system.

The SBR is operated at an extended sludge age to maximise nitrification and denitrification at low temperatures, and the fixed biofilm growing on bioblock media in the bottom of the reactors continues to nitrify down to a lower critical temperature than suspended growth biomass in the SBR.

After operating from July 2021 project completion through the 2021 – 2022 season, the plant was shown to successfully treat the influent to compliance with all consent parameters right down to the lowest recorded incoming sewage temperatures of 1.3°C.

Treated wastewater qualities of <4mg/L Total Nitrogen, xtagstartz5mg/L BOD5, <25mg/L Suspended Solids and <1mg/L Total Coliforms are regularly achieved by this plant, therefore providing not only an increase in treatment capacity, but a significant improvement in treatment performance from the Baxter sewage treatment plant which previously served the village alone.