Repaired oxidation pond aerators are being installed

Contractors are working hard to repair and reinstall the five disc aerators on oxidation Pond 1, and this work is on track to be completed by Friday 9 June.

Three of the disc aerators were repaired and brought back into operation last week, with the fourth reinstated today. The fifth and final aerator will be installed on Friday. These aerators help circulate the wastewater on oxidation Pond 1.

Given that we're now in the cooler months and the biological health of the ponds naturally reduces, it's still too early to tell how much difference the replaced aerators will make to the dissolved oxygen and biological oxygen demand of the ponds.

While we hope to have more information in next week's e-newsletter, we're also updating our website daily (click the link  below) with news and information as it comes to hand.

Latest hydrogen sulphide monitor results

We have strategically set up hydrogen sulphide (H₂S) monitors at locations around the oxidation ponds and nearby community. These have been in place since July last year and the results are published on the webpage below.

While the monitors recently recorded an increase in H₂S activity that coincided with the aerators being out of commission, we suspect the Rudds Rd monitor might be displaying faulty readings: the H₂S levels don't correspond with the wind direction that carries odour from the ponds to this location. We're looking into this as a matter of priority.

Our monitor at South Brighton School has also experienced technical difficulties and has now been replaced. We expect to have a reading from 1 June later this week and will update the graph then.

The next steps

Once the reinstallation of the five disc aerators is complete, we hope to see a decrease in the intermittent odours as the oxygenated wastewater is again circulated around the entire pond.

If the odours don’t decrease, we’re looking at a range of other options, such as adding hydrogen peroxide – a compound that naturally breaks down into water and oxygen – and a coagulant to potentially settle the sludge in Pond 1.

To further optimise the sludge process, we're considering what we can do with trade waste, looking at tweaking the flow distribution and level control on the oxidation ponds, and increasing our internal and external odour monitoring programme. 

However, there is still a risk that odours could persist over the winter months. Last year we saw the ponds begin to recover and perform well from September onwards, as the warmer weather and longer daylight hours improved the biological health of the ponds.

Where to get help

If you need health support, we have information available on our website. This includes information on Pegasus Health's Partnership Community Workers and contact numbers for Healthline and counselling services.

Stay updated

We want everyone to be able to stay updated on our response and recovery from the treatment plant fire, and we regularly post new information and reports on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

If you have any questions, or would like further information on the project, please call us on 03 941 8999 or 0800 800 169 or email wastewater@ccc.govt.nz  

Thanks for your patience and understanding. We’ll be in touch again soon.