Whanganui's wastewater treatment plant has had a first year without major technical problems, senior wastewater engineer Tony Hooper says. Photo / Bevan Conley
Whanganui's wastewater treatment plant has had a first year without major technical problems, senior wastewater engineer Tony Hooper says. Photo / Bevan Conley
Whanganui's wastewater treatment plant is in full operation but the sludge it produces still has too much chromium, which is limiting disposal options.
However, the technical manager at Tasman Tanning, the source of wastewater with a high chromium content, says a chromium extraction process will be fully operational by October.
At present three to five truckloads of chromium-laced sludge are trucked to Bonny Glen Landfill for disposal every day, Whanganui District Council senior wastewater engineer Tony Hooper said.
The rest of the plant's dried sludge is stored in an empty pond near its site in Airport Rd.
The wastewater treatment plant, commissioned in mid-April last year, has had only minor operational problems since. It takes in 24,000 to 35,000 cubic metres of wastewater a day for treatment.
Some have said the plant is unnecessarily large - and Hooper said it was big enough to cater for the organic load of a town of 200,000.
But water from the toilets, showers and sinks of Whanganui residents only makes up about 50 to 60 per cent of the total. Another 30 per cent comes from the town's wet industries and they contribute most of the organic load - 70 tp 80 per cent.
The big five are Affco Imlay's meatworks, Mars Petcare, Tasman Tanning, Land Meat and Open Country Dairy. Affco is probably the biggest contributor of water, Hooper said, while Tasman Tanning contributes about 25 per cent of the organic load of solids - animal remnants from the tanning process.
"I struggle to see how you could do this job with less."
Dried sludge from the Whanganui wastewater treatment plant still contains too much chromium for safe disposal to land. Photo / Bevan Conley
It was hoped that dried sludge from the treatment process could be a saleable product, for application to land as fertiliser. That's not possible at the moment, Hooper said, because it has 80 per cent more chromium than permitted.
Tasman Tanning only provides 5 per cent of the water treated, but it includes chromium, a heavy metal used in the tanning process. Chromium content in the dried sludge is too high to make it a safe fertiliser.
Tasman Tanning technical manager Craig Thiele said the factory's new chromium extraction plant has had some infrastructure issues and it has only been working for trial periods for the past year. It should be going fulltime when the new hide season begins in October.
"We have given a commitment to be fully operational this coming season. We believe it's within the capability of the plant to capture more than 80 per cent of the chromium."
In the meantime some of the sludge is being trucked to Bonny Glen Landfill, near Marton, and the rest is dumped in a lined pond that is a remnant from Whanganui's previous failed wastewater treatment plant, which shut down in 2012.
Putting it there saves transporting the sludge, which would be a cost even if disposal at the end point was free, Hooper said. But the pond won't last forever as a storage place - it will be full in two to four years.
Tasman Tanning technical manager Craig Thiele holds chrome-laced tanning liquid and the clear fluid he hoped would result from a chromium extraction process. Photo file / Stuart Munro
The council has tabled its concerns about the way chromium limits disposal options with Tasman Tanning. It is waiting to see whether the $1.8 million chromium filter plant at Tasman can do the job.
Whanganui's wastewater treatment has a troubled past. The last plant never reached resource consent and stopped operating in 2012 because it wasn't working well and was wafting sickening smells over Whanganui town. After that all our wastewater was screened then pumped out to sea until the new plant started taking it in 2018.
Occasional bad smells were a concern last year, Hooper said, but they were sorted out on Christmas eve. The plant covers and contains its ponds and drier, to stop odour escaping.
"The place is designed to control the smells. In some ways that makes it hard for us as operators, because there are things we can't see because there are covers on things."
The smell enclosed in the drier building is pungent. Chronicle photographer Bevan Conley compared it to a woolshed, and Hooper called it "musty" - then said his nose may be desensitised, because he spends so much time at the plant.
"There are some funny smells, but nothing really bad happening."
When smooth running is securely established more options can be looked at, Hooper said.
When there is less chromium in the sludge other uses could be found for it. And the methane that bubbles up under the cover of the anaerobic pond could be used as a fuel - at present it is flared off.
