Think twice before you recycle another plastic bag.

That was a major takeaway from a citizen tour of Waste Management's single-sort recycling facility in Northeast Minneapolis last week. The midday session, hosted by council member Lisa Goodman, garnered a crowd of about 50 people.

In a bid to increase resident recycling, Minneapolis started rolling out a new single-sort system across the city last fall. Eventually all residents will be able to toss all of their recyclables into one bin, rather than separate them.

But some wondered: "How does all the material get sorted?"

That's what brought Goodman's constituents to Waste Management's single-stream plant, where the city's recyclables are now being processed. It's the company's second largest facility in the country, handling trash from much of the upper Midwest.

Plant Manager John Saladis explained the process, which relies heavily on gravity and spinning rubber wheels of varying sizes to sort the paper, plastic, metal and glass.

Stage by stage, the wheels grind the trash so only certain material is left on the surface. Everything else drops through to the next level, where it meets a smaller rubber disc.

Those spinning discs are the reason Waste Management wants residents to take plastic bags back to the grocery store. They become wound around the spindles, which need to be cleaned several times a day.

"If we could pick one thing to take out, it would be plastic bags," Saladis told the room. They also have problems with needles and electronics.

Other aspects of the sorting are much more high tech. One machine uses split-second photographs and air jets to separate different colored plastic. Another uses a rare earth magnet to separate aluminum items. Yet another one uses a "paper magnet" to catch paper.

About 97 percent of what the plant takes in can be recycled. The three percent that cannot be is picked out manually by plant workers.

Questions from the crowd ranged from the proper disposal of batteries (take them to a county hazardous waste site) and whether recycled items should be put in bags (it makes no difference, as long as the bags are not plastic).

The single-sort "blue bins" are being rolled out to different neighborhoods in phases between 2012 and 2013. Click here to see when your area will get single-sort recycling.

Here's a taste of what this all looks like at a similar plant in Philadephia: