Central Otago District Council (CODC) has awarded a contract for vital maintenance work at the Ranfurly Wastewater Treatment Plant, with desludging of the oxidation pond and wetlands set to begin this month. 

Glasgow Contractors will carry out the work, which is expected to run from December through to June. 

In a statement, the council said the project involves removing a “significant” build-up of sludge identified during a recent survey.  

The council said the work is essential to restore the pond’s capacity, improve treatment performance and support the long-term operation of the wastewater system. 

“It’s not just about clearing material; it's about restoring the plant's capacity and efficiency,” CODC capital projects programme manager Patrick Keenan said.  

“By removing the sludge, we ensure the oxidation pond can perform its role optimally, securing the long-term effectiveness of the Ranfurly wastewater treatment system for the community.” 

Sludge removal increases the volume of water the pond can hold, extending retention time and improving biological treatment processes within the system. 

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The Ranfurly desludging is part of the council’s wider programme to bring its wastewater treatment plants into compliance following abatement notices issued after a 2023 audit by Otago Regional

Council. 

Since that audit, abatement notices have been lifted for Alexandra, Cromwell and Naseby. 

Notices remain in place at Ranfurly and Roxburgh, although council has previously reported encouraging compliance results at Roxburgh following earlier desludging and aeration upgrades. 

On its website, Auckland-based Glasgow Contractors says it has experience in dredging and desludging oxidation wastewater treatment ponds across the country.

Read more: Sludge-busting works set to start in Ranfurly