A $2.5 million upgrade for the Rakaia wastewater treatment plant has been approved by Councillors and the money will be used to construct drying beds for wastewater sludge.

From 31 January Council must stop discharging sludge that results from the treatment process on land at the Acton Road site. Once the new facility is constructed, the sludge will instead be dried and carted to landfill.

The Rakaia treatment site was commissioned in 1999 but has faced compliance challenges in recent years around how the sludge was applied to land.

Human sludge is different to farm sludge or manure because it contains pathogens, excessive nitrogen, heavy metals, organic matter and detergents; there are strict rules about how municipal waste can be discharged.

Group Manager of Infrastructure and Open Spaces Neil McCann said 12 sludge drying beds would be constructed to take all sludge from the treatment process.

“The beds will use a combination of evaporation and gravity drainage to dewater the sludge, which will be left to dry and eventually taken to landfill. The 12 beds will be used in rotation and given the volume of waste produced by Rakaia town, two beds will need to be cleaned around every two weeks.”

The drying beds will be 100 square metres each.

Officers have looked at a range of options to deal with the sludge, and have presented them to councillors over the past few months. The issue became urgent when Environment Canterbury issued an abatement notice and fined Council $1,000 for non-compliance.

In light of the upgrade commitment, Council has written to ECan seeking the abatement be cancelled or amended so that Council is not forced to transport liquid sludge from the site to the Ashburton scheme while the new facility is constructed.

The $2.5m upgrade will be funded by the district’s urban wastewater group (all those on Council wastewater schemes) and will take priority over a $3.14m grit chamber pipeline renewal on the Ashburton scheme, which has been reprogrammed to 2024-25.