PDP assisted Waipā District Council to investigate options for a new wastewater treatment plant (WWTP) to service the growing Cambridge population and significantly improve the quality of discharge to the Waikato River. We shortlisted advanced process options to achieve the required discharge standard and evaluated these using a multi-criteria analysis. Assessment criteria included minimising greenhouse gas (GHG) emissions, electricity and chemical demand, waste sludge production and whole-of-life costs.
We undertook detailed biological process simulations to quantify operational parameters for each option and applied the WaterNZ (2021) and IPCC (2019) guidelines to assess Scope 1 (direct plant CO2, CH4 and N2O), Scope 2 (purchased electricity) and Scope 3 (Indirect) emissions.
Our preferred option reduced GHG emissions by 90% compared to emissions generated from the existing lagoon based WWTP system. Our detailed design incorporated various energy and GHG reduction design features, including 5.5 m deep aeration basins and fine bubble diffuser grids to provide a very high oxygen transfer efficiency, energy efficient rotary screw blower technology, low-head through-wall propeller pumps for efficient recycle transfer, and low energy screw-press solids dewatering technology in lieu of traditional centrifuge dewatering. To further reduce emissions a 1.5 ha solar farm is proposed for the site, which will completely power the WWTP during summer day-light periods.
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