What Happens to Improperly Recycled Materials?

Most people assume improperly recycled materials go straight to landfill or the incinerator, but it's not quite that simple. Contamination, meaning anything in a recycling bin that shouldn't be there, is dealt with in different ways depending on what it is and how bad it is.

After collection, recycling is sorted at a material recovery facility (MRF). Each facility sorts differently, and what happens to contaminated recycling depends on the type and extent of the contamination. Heavily contaminated loads can end up in landfill or incinerated. A few basic habits prevent most of it: rinse your recyclables, keep rubbish out of the recycling bin, and put broken glass safely in general waste.

Common forms of recycling contamination

Food and liquid residue

Rinse recyclables before they go in the bin. Not a scrub, just enough to remove most of the food and liquid. Recyclables are washed during processing, but they often sit for days or weeks first, and a container still holding food can spoil everything around it. Heavily soiled containers are pulled off the sorting line and sent to landfill, and a single half-full smoothie bottle can contaminate a whole bag of otherwise good recycling.

Pizza boxes

Pizza boxes are recyclable as long as the food is removed and the cardboard isn't soaked with grease. New Zealand's standardised kerbside rules, in place since February 2024, explicitly accept them. If in doubt, rip the box in half and recycle the clean side.

Broken glass

Broken glass is generally not accepted because it's a hazard for the people who sort recycling and it can contaminate paper and cardboard, sometimes damaging machinery as well. Wrap it and put it in general waste.

General waste in recycling bins

Collectors will often refuse a recycling bin if rubbish is visible in it. One UK recycler reported finding nappies in recycling bins. If a contaminated load is collected, the whole bag is usually removed unless the waste can be separated easily and hygienically, and buildings that repeatedly send contaminated recycling can be blacklisted from collection services.

Why wish-cycling makes contamination worse

Recycling varies by location, and it's hard to get right every time. "Wish-cycling", putting a questionable item in the recycling bin and hoping for the best, adds to the problem. MRFs can remove many unrecyclable items, but each one adds cost and risk. Depending on the item, it may be redirected to the correct stream, sent to another facility, or sent to landfill.

Lookalike materials cause particular trouble. Plant-based bioplastics are hard to distinguish from PET plastic on a sorting line, so they should be commercially composted where that service exists, or put in general waste, never in the recycling bin. Size matters too: under New Zealand's standardised rules, anything smaller than a credit card, including most lids, stays out of the kerbside bin because it falls through the sorting machinery.

Common questions

Does one wrong item ruin a whole recycling bin?

Sometimes. Dry, clean contaminants can often be sorted out at the facility, but food waste, liquids and hygiene items can spoil an entire bag or load.

Should I rinse containers before recycling them?

Yes, a quick rinse is enough. You're removing the food and liquid that would otherwise spoil other materials while the recycling sits before processing.

Are greasy pizza boxes recyclable?

Only the clean parts. Remove leftover food, recycle the clean cardboard, and put heavily greased sections in general waste or a compost collection.