In 2007, MWH was commissioned to develop the Eastern Selwyn Sewerage Scheme (ESSS) to convey and treat wastewater flows for the projected population increases of the communities of Prebbleton, Lincoln and Rolleston which had already seen two decades of significant growth.
Following the devastating Canterbury earthquakes in 2010 and 2011, these towns experienced rapid growth, above previous projections, and there was an urgent need to bring forward and expand the programme to meet the new future requirements.
It was vital to keep the existing system operating while the expansion was undertaken to ensure continuity of services to the local community. In addition, a way had to be found to meet the need for an expanded wastewater treatment plant without high infrastructure costs burdening rate payers. This required a unique solution of innovative design and project management. Unique elements of the scheme MWH developed included:
Significant infrastructure reuse – ensuring past investment was used to benefit the wider scheme.
Balancing of wastewater flows to minimise the size of the infrastructure installed.
Staging to minimise cost, while future proofing the infrastructure to allow for expansion and projected needs.
A step-change innovative sludge solar-drying design solution, the first of its kind in New Zealand, using the natural climate to minimise the sludge to be removed from site, substantially decreasing operational costs.
After the devastating earthquakes MWH also expanded the project plans in a way which could relieve the Christchurch City Council’s damaged infrastructure should the need arise. The solution developed for the ESSS is future-proofed, cost effective and able to meet the community’s current and on-going needs.
Innovation and Creativity
Finding an innovative, cost effective and efficient solution for the disposal of sludge was one of the most significant challenges in the entire project. A large portion of the operating cost of the existing Pines WWTP was in the handling and disposal of sludge where the waste sludge was carted off from the site and disposed. To overcome this, MWH developed its most innovative feature of the entire scheme – the design of solar air drying halls to manage sludge biosolids. This was the first municipal waste biosolids drying facility of this scale in New Zealand.
MWH re-designed the original plant to expand it as a waste sludge gravity thickener and aerobic digester. Attached to this are a dewatering plant and solar air drying halls. The drying halls include a robotic sludge management system where sludge is converted to greater than 70% dry solids, using a natural process, so disposal of sludge is now far less frequent than the previously.
The innovative MWH design for the management of sludge treatment and disposal provides a cost saving of about $3-4M. This saving could be further increased if a Grade Aa biosolid standard was achieved and the biosolids disposed of on site.
This is the first municipal waste biosolids drying facility of this scale in New Zealand.
2014 Institute of Public Works Engineering Australasia, NZ Division, (IPWEA NZ) Engineering Excellence Award for the Eastern Selwyn Sewerage Scheme (Physical Works over $10 million award)
2014 New Zealand Engineering Excellence Awards – Winner of the Water, Waste and Amenities Award for the Eastern Selwyn Sewerage Scheme
Finalist – Supreme New Zealand Engineering Excellence Award 2014
Finalist – ACENZ Innovate Awards 2014
Winner – Water New Zealand Ronald Hicks Memorial Award 2015
Finalist – Global Water Awards for Wastewater Project of the Year 2016
Winner – Water New Zealand Project Award 2016
The innovative solar air drying halls Selwyn project
The completed upgrade allows for future staged expansion Selwyn project
Superstructure of the solar air drying hall Selwyn project