Reviving the ‘mother’ load: Port Pirie’s poo plant gets its bugs back

If you’ve ever guarded a sourdough starter like a prized family heirloom, you’ll understand the dedication behind SA Water’s work at Port Pirie
.
Inside the regional city’s wastewater treatment lagoons lives a thriving colony of microscopic organisms – known in the industry as “activated sludge biomass” – working around the clock to break down and clean sewage before it’s safely returned to the environment.

But as part of a major upgrade to the Port Pirie Wastewater Treatment Plant, SA Water had to do something operators almost never want to do. They deliberately wiped out an entire bioreactor ecosystem of treatment microbes.

Thankfully, much like keeping a jar of sourdough starter alive through a kitchen renovation, crews carefully saved a portion of the original microbial “mother culture” before works began.

Now, as the upgraded bioreactors comes online, those hardy little bugs are being reintroduced to reseed the system and kickstart the treatment process all over again.

SA Water’s Senior Manager of Production and Treatment Paul Bendotti said while replacing pipes and equipment was standard infrastructure work, rebuilding an entire living treatment ecosystem was a much rarer challenge.

“Wastewater plants are essentially giant biological factories powered by billions of microorganisms,” Paul said.

“You normally try to keep those bugs alive at all costs because they’re doing the heavy lifting in the treatment process.

“In this case, we needed to temporarily shut down and clean out the bioreactors as part of the upgrade, so we carefully preserved part of the existing biomass to act as our starter culture once the new system was ready.

“It’s a bit like borrowing a scoop of sourdough starter before renovating the kitchen.”

The plant faces unique treatment challenges because wastewater in the region is naturally more saline than many other South Australian systems, influenced by local environmental conditions and industrial history.

Higher salinity can place extra stress on wastewater treatment microorganisms and infrastructure.

To help tackle those conditions, SA Water installed a new type of aeration system in the treatment reactors, designed to better distribute oxygen through the more saline wastewater.

Aerators work by pumping oxygen into sequence batch reactors – a type of system that cleans water in a single tank - so microorganisms can break down nutrients and organic matter.

SA Water has previously used aeration upgrades at other regional treatment plants to improve biological treatment performance and efficiency.

Paul said getting the revived biomass colony re-established was expected to take time as the microscopic workforce gradually rebuilds itself.

“Once those microorganisms settle back in, they multiply rapidly and rebuild the ecosystem naturally,” he said.

“It might not look exciting from the outside, but there’s an enormous amount of biology happening beneath the surface.

“We’re effectively restarting a living ecosystem that treats the community’s wastewater every single day.”

The Port Pirie Wastewater Treatment Plant safely treats an average of 4.5 million litres of wastewater each day, or around 1,643 million litres a year
.
Wastewater is screened, cleaned and treated through advanced biological processes, with lagoons providing additional storage and polishing to maintain consistent, high-quality treated wastewater. Solids are carefully managed and reused through composting.

Meanwhile, SA Water is also delivering a major wastewater rising main replacement project across Gordon Street, Broadway Road and Kitchener Terrace, installing around 3.4 kilometres of new pipe to improve the long-term reliability in Port Pirie’s wastewater network.

The works include a combination of trenching and trenchless construction methods designed to minimise disruption for the community while upgrading the infrastructure approaching the end of its service life.

This upgrade forms part of SA Water’s ongoing investment in regional wastewater infrastructure to improve operational performance and environmental outcomes for Port Pirie, and is expected to be complete in 2027.