Eastern Selwyn Sewerage Scheme

The towns of Prebbleton, Lincoln, and Rolleston in Selwyn, on New Zealand’s south island, had commissioned the Eastern Selwyn Sewerage Scheme (ESSS) to help them cope with a continuing increase in population. Our team was brought in to develop the ESSS to convey and treat wastewater flows for the projected population. However, after the devastating Canterbury earthquakes in 2010 and 2011 resulted in more population spikes (as people moved away from the affected areas), we also needed to fast-track the project.

To overcome the large operating cost in handling and disposing of sludge, our team developed its most innovative feature yet—the design of solar, air-drying halls to manage sludge biosolids. As the first municipal waste biosolids drying facility of this scale in New Zealand, the redesigned plant now converts sludge to 70% dry solids using a natural process. Disposal of sludge is far less frequent than before, and alongside treatment efficiencies, that means significant ongoing cost savings.

Not only did our team keep the existing system operational while the expansion took place, but by reusing existing infrastructure, costs were kept low which avoided burdening ratepayers and ensured that past investments were not put to waste. Now, these communities can rest easy knowing that even as the population grows, their wastewater system can rise to the challenge.