Twelve new sludge-drying beds at the Rakaia wastewater treatment plant will soon be in use.

The beds will ensure Council complies with Environment Canterbury consents to operate the wastewater plant.

Infrastructure and Open Spaces Group Manager Neil McCann said the $1.23 million project was on time and commissioning of the beds would begin next week.

“We’re really pleased with the job done by Grant Hood Contracting, as there were some unique design and specification features of this project.”

The beds use a combination of evaporation and gravity drainage through sand-lined concrete bunkers to dewater sludge from Rakaia’s wastewater. Once dried, the sludge will be removed to landfill.

Mr McCann said the 12 concrete drying beds were each about 100m2 in area.

“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. Removing it regularly means there is less risk of odour and Council will be meeting the strict rules about managing municipal wastewater.”

Once sludge is deposited into the drying bed, the liquid drains through a filter of three layers of sand and gravel; the sludge remains on top to dry and is scraped off by a digger when it reaches about 20cm deep, and sent to landfill.

The filtered liquid is pumped back to the wastewater plant’s clarifier where it will be treated before being sprayed onto adjacent land.

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

The drying beds should be incorporated into the treatment process by early December, and will be operated by Council’s maintenance contractor, Ashburton Contracting Limited.