Wastewater treatment plant
Gisborne city’s treatment plant is now operating with domestic wastewater treated to a far higher standard than previously. The plant was commissioned in late December 2010, as required by a condition of the resource consents granted in September 2007.
All domestic wastewater is processed through a new biological trickling filter system before being discharged through the existing 1.8km outfall to the sea. The trickling filter system enables fine wastewater solids to be transformed into plant-like matter in a process known as biotransformation.
The $39.5m project came in under budget and on time. The first sod was turned on council’s Banks Street site in late November 2009. Over the following 13 months, at a cost of $21m, HEB Structures constructed the new wastewater treatment plant at Banks Street and an associated industrial separation scheme. Downer EDI Works built the western industrial pipeline.
The total cost of the upgrade included land and equipment including the media for the biological trickling filter, and consultancy fees.
The consent has 2 stages. The infrastructure built in 2010 was only the first stage of the wastewater treatment upgrade as required by the consent. Council is currently deciding on what to do in order to comply with the second stage of the consent. This will include disinfection by UV. See wastewater management options
How the treatment plant works
Domestic wastewater is screened by one of 2 rotating drum screens (one is on duty, one on standby) and then passed through a vortex grit removal chamber. Two more drum screens are used for industrial wastewater.
The screenings and grit removed from these stages will have the water pressed from them before being bagged and trucked to a landfill at Paeroa.
The screened and de-gritted wastewater gravitates into a biological trickling filter pump station before being pumped up through the tank’s central column to a height of 8m, then distributed through 6 rotating arms to trickle slowly through many different channels in 10 layers of large plastic media blocks.
In so doing, very fine screened and degritted wastewater solids are transformed into plant-like matter. The resulting treated wastewater is pumped via a new outfall pump station to the existing marine outfall, 1.8km out to sea.
We're investigating how to make the wastewater cleaner and where the sludge should end up.
For more information about the wetlands trial