Sewage does the business

A ground-breaking trial to turn treated sewage into top quality compost has the potential to save Coromandel ratepayers money.

The Thames Coromandel District Council trial involves mixing treated sewage, or biosolids, from the new Pauanui wastewater treatment plant with green waste from the Tairua transfer station.

It is the first time in New Zealand a revolving vessel has been used to mix biosolids and green waste such as lawn clippings enabling operators to maintain the required temperature to kill pathogens in the compost.

After 15 days in the vessel, the compost is tested before being spread on the ground for another 20 days.

Council spokesman John Whittle said the new process had the potential to save ratepayers a lot of money. The new plants operated differently to the old pond system sewerage plants. One of the major differences was the production of highly treated wastewater and biosolids as by-products.

"While the old plants would store treated waste for years over time eventually creating significant and increasing costs and environmental risks the new plants produce potentially beneficial resources on a daily basis," he said. "We were faced with sending this nutrient-rich biosolid matter to landfills outside the district at significant cost both environmentally and financially, so decided to see how we could use it to the benefit of our ratepayers and environment."

In the off-peak season, peninsula residents and visitors produced about 1.5 tonnes of biosolids a day from each of the three new treatment plants in Pauanui, Whitianga and Whangamata.

Sending that material to a landfill at Tirohia, near Paeroa, would cost between $1100 and $1400 per dry tonne.

Those costs were expected to increase as oil prices rose, available landfill volumes diminished and environmental controls became more stringent, Mr Whittle said.

Although the unit cost of the compost has been raised by extra controls imposed by Environment Waikato, the district council hoped to save additional money by no longer having to dispose of green waste or buy in high quality compost for its parks and reserves.

"We see this trial as a real win-win."

Mr Whittle urged residents to visit the monitoring sites and observe the benefits of the compost on plant growth. The sites, at the Tairua Cemetery and the south end of Pauanui Beach Reserve, will be signposted when the compost is delivered. They will be monitored for six months.

- © Fairfax NZ News