Work is about to begin on the construction of 12 sludge-drying beds at the Rakaia wastewater treatment plant.

Sludge is a by-product of the treatment process and it is currently being irrigated onto land at the Rakaia plant. Once the beds are built, sludge will be dried and removed to landfill.

Infrastructure and Open Spaces Group Manager Neil McCann said the Rakaia treatment facility was commissioned in 1999 but had faced compliance challenges in recent years around how sludge was applied to land.

“Environment Canterbury eventually issued an abatement notice for the discharge of sludge at the site but granted us time to investigate alternative ways of dealing with it.

“Council looked at several different systems and opted for the drying beds. A contract has now been awarded to Grant Hood Contracting for $1.23 million to build the beds and this work will get under way in early September.”

Twelve drying beds will be built, each about 100m2 in area.

Mr McCann said the new system would use a combination of evaporation and gravity drainage through sand-lined concrete beds to dewater the sludge.

“Then once dry, the sludge will be removed and taken to landfill. The 12 beds will work in rotation and we expect two beds will need to be cleaned every two weeks, given the volume of wastewater Rakaia produces.”

Operation and maintenance costs will be about $90,000 a year.

“One of the advantages of this system is that sludge removal is a regular activity so there is less opportunity for smell, and it means that Council will be meeting the strict rules about municipal wastewater and how it is managed.”

The drying beds should be operational late November, and will be operated by Council’s maintenance contractor, Ashburton Contracting Limited.