Garden, food waste reused

By SIMON COLLINS

A group of North Shore City councillors took to the streets of Bayswater early on Tuesday to look into residents' rubbish bins.

In an experiment of national significance, residents such as Mike and Julie Cohen are testing receptacles for organic waste.

Some have small, 45-litre lidded bins for kitchen waste only. Others, such as the Cohens, have been given plastic benchtop bins to peel the potatoes into, plus two wheelie bins: a 120-litre one for the food and garden wastes, and a 240-litre bin for paper, plastic and other recyclables.

For the Cohens, it means the garbage disposal unit built into their kitchen bench to chew up food scraps has become redundant.

After three weeks, most people in the trial are doing well, councillors found.

"There are a few bad eggs who can spoil the lot," says Michelle Kaczor, of the council's waste minimisation team.

"Out of the 400, about 1 per cent of households are blatantly putting in rubbish.

"But in general, contamination is 6 to 8 per cent. That's not bad. If it was 20 or 30 per cent it wouldn't be practical."

The Bayswater experiment, which runs until July 29, is important for New Zealand's recycling effort because food and garden wastes make up 50 per cent of what is sent from home to the tip.

Home composting has shrunk with the size of the traditional urban section. Septic tanks have been displaced by centralised sewerage.

But gradually, collection systems are developing to find new ways to return grass clippings, food scraps - and even sewage - to the soil. Nationally, 47 per cent of garden waste is composted. In Auckland it is 53 per cent, in Christchurch 75 per cent.

Auckland company Living Earth collects and composts garden waste in Auckland and Christchurch, and mixes such waste with sewage sludge in Wellington to brew a powerful fertiliser.

Hamilton firm Perry Environmental has composting operations in Hamilton, Tauranga, Taupo and Waitakere, and worm farms to process green waste and some animal waste from abattoirs, chicken farms and fisheries in New Plymouth.

"There is demand in agriculture and horticulture areas, particularly organic farming," says Perry general manager Peter Higgs. "Even non-organic farmers realise that they have to put more than just chemicals on."

Food scraps have proved harder to recycle. The only council doing it is the Mackenzie District in South Canterbury, which collects three bags a week: one for food and green wastes, one for other recyclables and one for everything else.

Waitakere has won resource consent to process food waste in its 10 - soon to be 20 - vertical composting units at The Concourse, just off the Lincoln Rd exit from the Northwestern Motorway.

"We are working closely with North Shore City," says Waitakere solid waste manager Jon Roscoe.

Waitakere plans to start collecting its own food waste next July, and may also process North Shore's waste. "Our units are mulching 9000 tonnes a year of green waste. We can handle up to 14,000 tonnes with the new consent, but if they have 100 per cent participation on the North Shore, we probably couldn't cope," he says.

A North Shore consultancy, Waste Not, has studied options for collecting food scraps in Auckland and Manukau, and recommended composting.

The cities are tendering for more research into composting systems.

That leaves one other big source of organic waste: sewage.

The "biosolids" left after extracting the water from sewage are cooked or worm-farmed to make compost in Rodney, Te Puke, Kawerau, New Plymouth and Wellington, and are spread as fertiliser on forests near Rotorua and Christchurch.

In Auckland, the recent completion of a $450 million sewage plant, which replaced the oxidation ponds at Mangere, has created 100,000 tonnes of biosolids a year, which are being buried in landfills.

Watercare spokesman Trevor Jones says it is exploring potential uses in forestry, horticulture, pastoral farming and rehabilitating old quarries and mines.