Disposable coffee cups and used nappies are items commonly put out for recycling that have to be sent to landfill, but the number one culprit is plastic bags.

Plastic bags, disposable coffee cups and used nappies are in the almost 16,000 tonnes of rubbish put out in recycling bins that had to be diverted to landfill, at a cost to Auckland ratepayers of $1 million in the most recent financial year.

Of a total 130,000 tonnes of recycling, 15,740 tonnes, or 12 per cent, were non-recyclables that had to be sent to Auckland landfills between 1 July 2016 and 1 July 2017.

"Contamination is measured by weight, but that does not necessarily reflect the most common contaminants by number and volume, which are plastic bags," Auckland Council's general manager waste solutions Parul Sood said.

STUFF The number one recycling contaminant is plastic bags, and these jam recycling plant machinery,Auckland Council waste planning manager Parul Sood says .

Plastic bags and soft plastics are particularly dangerous at the recycling plant, because they get caught up in machines and jam them.

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The most common items are soft plastics, clothing, food and garden waste, nappies and sanitary products, wrong plastics and glass, metal and hazardous items.

Supplied The cost of removing contaminants, $1 million in the past financial year, is covered by the council's contract with Visy, Councillor Penny Hulse says.

Bottles need to be rinsed, especially as people are going through the conveyor belt and removing items by hand, councillor Penny Hulse, chair of the environment and community committee, said.

Some items are serious hazards for workers on rubbish trucks and at sorting stations, especially broken glass, but also batteries and gas canisters, which people have to pay to dispose of.

The cost of $1m to remove contaminants in the most recent financial year was met by recycling provider Visy, as part of its contract.

SUPPLIED Most Aucklanders are good at recycling, but, where there are hot spots, bin inspectors audit bins and red-sticker the worst.

Over the past few years, an average of 18,000 tonnes of recycling waste has been sent to landfill, a figure the council wants to reduce to 5 per cent, as part of its goal of becoming a zero-waste city by 2040.

This programme saw Auckland winning top city in international sustainability awards last year, with a Cities4ZeroWaste award.

While most Aucklanders are good at recycling, there are "hot spots", Sood said.

123rf.com Organic rubbish collection has been piloted on the North Shore and will be introduced in Papakura this year.

Auckland Council recently introduced bin inspectors and, in the first half of 2017, they inspected 100,000 bins and red-stickered 2200, which meant they wouldn't be collected.

The council has been trialling organic waste collection in 2000 homes on Auckland's North Shore and will roll out an organic collection to Papakura in South Auckland this year.

Around half of general household waste is currently food or other organic matter.

The council is still working on finding outlets for organic waste, which could include composting or one idea would be harnessing biogas, such as methane, for energy, as has been done overseas, Hulse said.

However, the council's wider aim is to encourage waste reduction through home composting, and, in Stockholm, as waste reduced, there wasn't enough to feed the biogas plant, Sood said.

See Auckland Council's website for what you can put in recycling and how to dispose of unwanted items.