Cost and Carbon Reductions Through Alternative PH Control

A. Wong*, D. Pernitsky†, J. McAndrew‡, J. Barnsley‡

* Stantec New Zealand

† Stantec Canada

‡ Dunedin City Council

The costs of potable water treatment chemicals in New Zealand have been increasing year on year since 2020. The cost escalation has been driven by a reduction in New Zealand’s domestic supply of chemicals, increased reliance on imported chemicals, and increased shipping costs. Carbon dioxide’s (CO2) rising costs and scarcity has affected the water treatment industry, as well as many other sectors (e.g., healthcare, food and beverage). 

For Dunedin City Council (DCC), this has resulted in an almost 6-fold increase in the annual CO2 costs at the Mount Grand Water Treatment Plant (WTP), one of its main WTPs. DCC have looked to review its chemical usage and the source of its chemicals to better understand supply chain logistics and national transport. Another key part of this review is the associated costs and carbon emissions, including potential mitigations. 

DCC engaged Stantec to review and optimise its chemical usage at the Mount Grand WTP, and consider alternatives to CO2. The Team worked collaboratively to first understand the current practice and rationale of chemical dosing. A baseline model of the Mount Grand WTP was developed using water solubility modelling software. Alternative pH control scenarios identified by DCC to reduce operational costs and embodied carbon were tested in the model. 

This paper provides an overview of the methodology, results of the baseline and alternative scenario modelling, and a proposed staged approach to implement changes over the next 2-3 years. Annual operational cost savings and emission reductions are likely to be in the order of $600,000 to $1 million and 160-200 tCO2e.