Denver Recycles, a division of Denver Public Works, has set a goal of raising the city’s recycling rate to match the national average of 34 percent of household waste being diverted from the landfill by 2020. But last year, about 80 percent of Denver’s household waste was trashed — suggesting a lot of people are not clear about what should or should not be going into their purple recycling bins.

Should your Starbucks cup go into the recycling bin? What about that aluminum lid from your burrito bowl that’s splattered with guacamole? That pizza box is made of high-grade cardboard so that’s a no-brainer right? Not so fast.

During a visit to Denver’s recycling facility, it quickly became clear that thousands of well-intentioned people are throwing items that are not recyclable into the city’s single-stream recycling program. Enrico Dominguez walked us through the Waste Management sorting facility on Franklin Street, which is contracted by the city of Denver to handle its recycling program.

We took the tour with an eye toward identifying the most common mistakes people make. For starters, mattresses, computers, and electronics are not recyclable in Denver’s single-stream program, but there are several businesses around town that specialize in recycling all of them.

A good percentage of the plastic, paper, cans and glass that are accepted in the program, ends up in the landfill because they get contaminated by food, liquid and other contaminants that disqualify them from going on to the secondary market. Little mistakes like leaving water in a plastic bottle can contaminate a load that would otherwise go on to have a new life.

Plastic bags are the enemy

“Plastic bags can get caught in the machinery, seize up the motors and cause a fire,” Dominguez says. The same thing goes for garden hoses, wire hangers and Christmas lights, or anything stringy. It’s a problem similar to how yarn gets caught up in your vacuum and stops the wheels from turning. Pretty soon you can smell that rancid burning aroma. It presents a potentially devastating problem at an $80 million dollar facility filled with plenty of fuel to keep a fire burning.

Plastic bags are recyclable, but not in Denver’s single-stream recycling program. Most large grocery store chains have a collection bin where you can drop off all your plastic bags.

Don’t put your recyclables into a big trash bag

Your recyclables are going straight to the landfill if you put them into a trash bag. Sorters don’t have the time to rip the bags open to see what’s inside. Closed plastic bags are also considered a safety hazard for workers since they have no way of knowing if medical needles or any other potential danger may be inside.

Pizza Boxes

Sorters have their eyes trained to look for pizza boxes. Anything soiled with grease is eliminated because grease is a contaminant. If you want to increase the odds of your pizza boxes being reincarnated, the best bet is to rip them in half so the non-greasy side can be recycled.

Water bottle caps are recyclable

We learned that at this facility the caps to plastic water bottles and soft drink bottles are recyclable, despite numerous reports to the contrary. Dominguez says plastic caps have been poo-pooed in some jurisdictions to eliminate the chance of liquids being trapped inside the bottles. Dominguez says that if you pour out the liquids and put the cap back on the bottle it will be recycled. The lid will otherwise not get recycled because it is too small to be processed at the sorting facility.

No liquids or food

Liquids are a contaminant because they leak out when the bottles get smashed. Liquids make surrounding paper products wet and cause them to stick to plastics and cans, which makes them ineligible for recycling. “If sorters catch it early then it will not be processed. If it gets by them it can continue going through our sorting process” which can contaminate a batch of another commodity, Dominguez says.

Foil bags from potato chips and other snacks are not accepted. Same goes for foil lids from yogurt containers and the like. Foil pie tins and food trays are accepted but Denver Recycles asks that food is removed as mush as possible.

Not all plastics are recyclable

Plastic items have to be able to hold a shape in order to qualify for Denver’s recycling program. Dominguez uses the example of plastic strawberry containers as an example of the thinnest type of plastic that qualifies for recycling.

To wash or not to wash?

Consumers have been trained to rinse food and debris from recyclable materials before putting them into the curbside bin. But at what point does the amount of water needed to get an item clean do more harm than good for the environment? Dominguez suggests you focus on rinsing off all the “big chunks” of food without wasting too much water. He says knowing how much water is too much is difficult to quantify.

Anything smaller than a Post-it note

Anything smaller than a Post-it note should be thrown in the trash. It can’t be picked up in the sorting process and it becomes a contaminant.

Metal

It appears this is a category in which a lot of consumers have questions. You can tell by looking at the heavy car parts, propane tanks, clothes hangers, barbecue grills, electronics and other mixed-metal materials contaminating the mounds of recyclables zipping by on the conveyor belt. Sorters pull out metal scraps and throw them into a pile that will go to the landfill.

Scrap metal does not belong in Denver’s single-stream recycling program. There are several facilities around town that pay cash for metal objects like car parts, brass hardware, tv antennas, wiring, piping, sheet metals, car fenders, filing cabinets, tables, and trash cans, just to name a few.

Paper with a shiny coating

No paper cups; that includes your Starbucks cup. Starbucks hot-serve cups, and those like them, have a layer of PET plastic that disqualifies them from recycling.The plastic lining serves as a safety barrier that needs to be peeled off before the cup can be recycled. The same goes for the Chipotle burrito and salad bowls. According to Chipotle’s website, the bowls are made from recycled newspaper, which is theoretically compostable, but the PET lining negates them from being acceptable for Denver’s single-stream recycling program.

Milk cartons with waxy coating

Do not flatten cartons. Consumers are asked to remove any caps or straws and eliminate any food or liquids before putting packaging into purple bins. Milk cartons and other three-dimensional products are sorted by hand. Those that are missed by human sorters are detected by infrared optical sorters that separate them into their own category.

Contaminants

In Denver, the biggest contaminants are plastic bags, liquids, food, garden hoses, Christmas-tree lights, wire hangers, electronics, propane tanks, and auto parts. Sorters at the facility are trained to hand pick and eliminate contaminants from the 30 tons of materials that run down the conveyor belt every hour. If a bundle of recyclables reaches a 10 percent contamination rate, the manufacturer that purchases the recyclable materials can reject the load and charge back the cost to the sorting center.

When in doubt throw it out

If you’ve ever thrown a questionable item into the recycling bin with the idea that you’re giving it a chance of a second life, Dominguez says throw it out. Anything questionable is treated as a contaminant and sent to the landfill.

Not accepted in Denver

Computers

Electronics

Mattresses

Propane tanks

Bowling balls

Car parts

Bicycles

Here’s a link to the full list of what is and isn’t accepted.