Excessive amounts of fat are threatening the performance of the Owhanake sewage treatment plant – and the problem is being traced back to Oneroa cafés and restaurants.

Watercare’s wastewater regional manager, Jonathan Piggot says: “We’re removing approximately one cubic metre of fatty scum from the surface of the primary treatment tank every few weeks—which is really excessive given that the plant only services such a small number of local residents and businesses.”

The agency’s trade waste team will be visiting cafés and bars in the next few weeks as part of a ‘general health check’ of the wastewater network that serves about 40 Oneroa businesses and properties.

Watercare spent almost $1 million in 2016 maintaining and upgrading the treatment plant but now has real concerns that the plant will exceed its consented discharge limits over summer when visitor numbers soar.

It says the treatment plant continues to produce high quality effluent which is disinfected with UV light before discharge into a constructed wetland. From here the discharge enters a natural wetland system that flows to Matiatia Bay.

Despite the high standard of treatment, it says excessive amounts of fat are being cleared from the plant on a regular basis.

“Our trade waste team will be visiting Oneroa cafés and restaurants to make sure they are not tipping hot fats, oil and grease down the sinks and that their grease traps are being cleared regularly,” Mr Piggot says.

“Residents are also asked to dispose of fats, oils and grease responsibly and to use low phosphorous cleaners, detergents and shampoos.

“Installing water efficient devices will also help to reduce wastewater flows and reduce your wastewater charges. Composting, rather than disposal of food scraps down the drain, can also help reduce the organic load on the plant.

Contractors will inspect the pipe network using harmless smoke to look for damaged pipes and illegal connections, which may be allowing stormwater to enter and overwhelm the wastewater network during wet weather.

Next year, Watercare will begin a $2 million upgrade that will ensure the plant continues to produce wastewater of a very high quality to protect waterways and ecology.
Geoff Cumming

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