Cannons at the ready to tackle any Shotover sewage stink

Brace yourselves Queenstown, a poo pond at the Shotover Wastewater Treatment Plant is set to be drained.

However contractors have a few tricks up their sleeves to limit odour, and the Queenstown Lakes District Council is optimistic the whiff will be able to be controlled.

At the ready are aerosol cannons and lime, which will work to neutralise any sludge that remains at the bottom of the pond after the water goes.

Crews have this week finished dredging the pond - pays not to think for too long about what's being removed - before they pull the plug on Tuesday.

The pond is expected to take four to five weeks to empty, but any considerable amount of rain could drag that out.

A bit like when you empty a bathtub after the kids have had a particularly messy day in the Central Otago dirt, it is expected that some sludge will be left behind.

And it will be left to dry out before being collected and removed too.

"We don’t expect this remaining sludge will smell as it will be older and low in organic content – lovely stuff right – but there’s still the possibility it will create some odour in the area around the facility," a council spokesperson says in a social media post updating on the works.

This particular pond will be repurposed and used for improved stormwater management on site, with a section of it also reserved to act as a 'calamity' pond if something goes wrong with the treatment plant.

It means the facility will be better able to handle heavy rain.

Two other oxidation ponds - poo ponds is just the more colloquial word for them - are still doing their thing at the plant, and will do for a wee bit longer yet.

The work is part of wider upgrades happening at the facility to increase capacity as more people choose to call the Whakatipu home.

It is budgeted to cost $37.5 million, and a spokesperson for the council tells Crux the project is running within budget.

The plant is transitioning to a treatment system that relies on two Modified Ludzack-Ettinger reactors.

No idea what that means? We didn't know either, but the council has plenty of details about it here.

"The Modified Ludzack-Ettinger process sees raw sewage screened to remove the bulk of the non-degradable solids before it’s pumped through a series of tanks," the council says.

"The first tank starves the bacteria of oxygen, causing them to begin to break down elements in the wastewater in order to produce the oxygen they need to survive.

"The second tank then feeds the wastewater with an oversupply of oxygen, causing further biological processes that complete the stabilization of the organic matter, reducing the nitrogen concentration in the end product.

"The material is then pumped into a settling tank that further separates and clarifies the resulting liquid.

"The processed clear water is then UV treated and pumped out of the system.

"Some of the remaining solids are then pumped back to the start of the process to begin it all over again, while the rest is pumped into a dewatering plant where it is dried out and removed, to be disposed of at an approved off-site location."

The first of the reactors was built in 2016 and is operational, while the second is due to switch on by the end of next year. Once that happens, the plan is for the final two poo ponds to be drained and repurposed too.

The Shotover Wastewater Treatment Plant currently services Queenstown, Arthurs Point, Frankton, Kelvin Heights, Quail Rise, Shotover Country, Lake Hayes Estate, Lake Hayes, and Arrowtown.

The upgrades will allow the plant to also receive additional wastewater flows from Jacks Point Village, Hanley Farm, Ladies Mile and an extension of the Quail Rise residential development area.

Arrowtown-Kawarau councillor Lisa Guy is asking people to get their heads around the bigger picture before "kicking up more stink" in light of the latest phase of work.

In October, members of the public did 'kick up a stink' after enduring an unpleasant odour while work to decommission another poo pond at the plant was underway.

Weeks later, a series of faults resulted in a lingering small so bad the Otago Regional Council's pollution monitoring team was required to step in.

Main image (QLDC): The Shotover Wastewater Treatment Plant.

Watch: Lead contractor McDonnell Dowell provides an update in May on the upgrade works.