Biosolids trial another step in sustainability 14 April 2009

A ground-breaking trial to turn treated sewage known as biosolids into top quality compost that could save ratepayers substantial amounts has begun in Tairua.

The compost trial by Thames-Coromandel District Council has drawn interest from private firms as well as local residents keen to see how a resource previously considered to be waste can be turned into a potential money-saver for the Council.

Biosolids compost is a mix of green waste gathered at Refuse Transfer Stations and highly treated human waste from the Council’s new ES3 wastewater treatment plants in Pauanui, Whitianga and Whangamata. The finished product is no different to any other commercially available compost and is being rigorously tested prior to application at two ground trial sites in Pauanui and Tairua where it will be monitored for six months.

TCDC Group Manager Service Delivery, John Whittle, says the new plants operate differently in many ways to the old pond system sewerage plants and one of the major differences is 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.

“We were faced with sending this nutrient-rich biosolid matter to landfills outside the district at significant cost – both environmentally and financially - and so decided to see how we could use it to the benefit of our ratepayers and environment.”

In the off-peak season, Coromandel Peninsula residents and visitors produce approximately 1.5 tonnes of biosolids per day from each of the three new treatment plants. All of this sludge goes to landfill in Tirohia, near Paeroa. The rising costs of oil makes transporting this biosolid material increasingly costly, while dumping into landfills is also expensive and only set to rise in the future.

In addition to meeting the strict Grade Aa composting guidelines, at the request of the regional council Environment Waikato this natural material is also tested for estrogen at a cost of $15,000.

This and other rigorous testing required for the trial has raised the initial unit cost of the compost.

However the current price of trucking biosolids to landfill is between $1,100 and $1,400 per dry tonne and expected to spiral as available landfill volumes diminish and environmental controls become more stringent.

The Council hopes to save additional costs by no longer having to dispose of green waste, and being able to use its own high quality compost rather than buying it in for parks and reserves.

“We see this trial as a real win-win,” says Mr Whittle. “We’re expecting potentially substantial savings to the ratepayers, in the long-term, if the Council succeed in composting biosolids.”

The compost facility, located at the Tairua Refuse Transfer Station, is operated by TCDC’s Composter Operator with advice from the composter manufacturer (Andar Limited) and support by Smart Environmental Limited, which will transport biosolids daily from Pauanui Wastewater Treatment Plant.

TCDC is inviting residents to visit the monitoring sites and observe the benefits of the compost on plant growth. These sites will be signposted when the compost is delivered and are at the Tairua Cemetery and south end of Pauanui Beach Reserve.