Gore District Council employs company to stop algal blooms in wastewater plant

Thursday, 19 September 2019

The Gore District Council has employed another company to help it deal with algal blooms growing at its wastewater treatment plant.

Last week Stuff reported that Environment Southland had decided not to prosecute the council after investigating the discharge of an algal bloom from the Gore wastewater ponds into the Mataura River in December 2018, and a discharge of wastewater from the Mataura wastewater ponds the following month.

On Tuesday, council 3 Waters manager Matt Bayliss said algal blooms regularly occured in the council's ponds and were common in oxidation ponds throughout the country.

He said the removal of trees along the banks of the Mataura River had made them more visible than in the past.

**READ MORE:

* No prosecution for Gore District Council for algal bloom discharge into Mataura River

* Test results show Gore wastewater discharge was toxic algae

* Gore District Council discharges algal bloom into river**

The council had engaged the services of ERPRO, to help minimise the algal blooms from growing at the Gore plant.

The contract is for work up to $33,750.

'We are always working to optimise the performance of our treatment plants. ERPRO is currently doing pilot scale trials involving the use of two chemicals, percarbonate and potassium, to inhibit the growth of algal bloom in the ponds,' Bayliss said.

A report tabled by Bayliss at an operations committee meeting on September 3 said the focus of this work is to identify 'bridging solutions' ensuring consent compliance can be achieved in the short term. It says it is expected more significant upgrades will be required as a result of the council's discharge consent expiring in December 2023.

The council operates an Actiflow plant at Gore, which removes phosphorus and suspended solids from wastewater before it is discharged to the Mataura River.

It operates when the river level is below 60 cumecs.

'The plant has been working correctly. To optimise its performance we are installing a pH correction system.'

The council is now treating tradewaste from the Mataura Valley Milk plant at a specifically designed treatment plant, which was paid for by the company. 

It was built by the council, which now operates it.

Bayliss said the treatment of that waste was not causing algal blooms in the ponds.

He said the tradewaste mainly contained diluted milk or milk products (milk fat, protein and lactose) and cleaning compounds and sanitisers. 

It is pre-treated at MVM's plant, which removes the majority of the fats, oils and greases in the wastewater. It is then treated at the treatment plant at Gore before being discharged into the council's second oxidation pond.

Mataura Valley Milk has a consent to discharge an average of 1200 m3/day of tradewaste in this way.

Environment Southland compliance manager Simon Mapp said the Gore District Council's 2018/19 annual consent compliance report, which is lodged with Environment Southland, contained a small number of minor to moderate consent breaches.

Gore District Council also made a mistake in their sampling timing regime, he said.

None of the incidents were considered to be significant non-compliance which would trigger an investigation.