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Just a small amount of contamination of the Dunedin City Council’s glass collection for recycling could lead to loads being refused which would be costly.
The council sends the glass it collects to Visy in Auckland where it is made into bottles.
However, the company was getting strict about what it accepted for its furnace, Dunedin City Council waste and environmental solutions group manager Chris Henderson told councillors last week.
"We almost had one [load] turned back because of a couple of broken ceramic cups," Mr Henderson said.
Sending a load from Dunedin to Auckland cost thousands of dollars, he said.
A refused load would be returned at the council’s cost.
The council changed the criteria last year for the plastics it accepts for recycling and lack of adjustment from residents appears to have contributed to the broader contamination problem.
The amount of material put out for recycling, but which is diverted to the landfill because it is contaminated, has increased.
Contamination increased 15.6% between the first three months of last year and the same period this year, from about 285 tonnes to 330 tonnes.
Plastic types 1, 2 and 5 are accepted in yellow-lidded kerbside recycling bins, but types 3, 4, 6 and 7 are not.
Soft plastics are out and even the "sleeves" on containers — as well as lids, caps and spray triggers — should be removed.
Cr Carmen Houlahan said the numbers on packaging were often hard to read.
Contamination can occur if residents put dirty plastic in the recycling, such as meat trays or milk bottles that have not been rinsed.
The council asks residents not to include lids in their recycling, either for glass or plastics.
Mr Henderson said plastic lids were too light for the council’s air-jet sorting system and they ended up among paper and cardboard.
The council proposed that a new materials recovery facility be included in its 10-year plan.
This would include modern optical sorters, which would enable better sorting on conveyer belts, Mr Henderson said.
Cr Jim O’Malley said the council should consider ways to develop local capacity, to keep recyclable materials out of the landfill.
"If we are finding it difficult to move material to be processed at distant sites, then we need to consider how we will process them there."