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KAI RYSSDAL: I don't know how it works for you, but at my house anyway, it's the blue garbage can for recycling, the green one for yard trimmings and the brown one for trash. Nothing though, for leftover food. Unless you've got a composting heap in your backyard, you throw scraps right in with the regular trash, no? Not so in San Francisco. The city wants to boost its already high recycling rate by making composting mandatory. From the Marketplace Sustainability Desk, Caitlan Carroll explains.

Caitlan Carroll: The Boulevard Restaurant in San Francisco is packed on a Wednesday night. In the kitchen, cooks are juggling pans, grilling fish, and stirring sauces.

Pamela Mazzola: So here's the main line where all the cooking is done.

Executive chef Pamela Mazzola surveys the kitchen as plates of artfully arranged halibut and roasted potatoes make their way to the dining room. When the plates come back:

Mazzola: The waiters come, scrape off the plates. So all table scraps are composted.

Thousands of restaurants, apartments and homes participate in San Francisco's compost program. That's about 70 percent of all San Francisco residents. The city has one of the best recycling rates in the nation. But it's not good enough for Mayor Gavin Newsom. He's pushing a law to make San Francisco the first city to require recycling and composting. He wants to push the recycling rate to 75 percent or beyond.

It's not as easy as it sounds. To get the program started San Francisco had to work out a system with the company that picks up the city's trash. It's called Recology. Recology's CEO Mike Sangiacomo's points out, the waste industry's built on disposing trash, not re-purposing it.

Mike Sangiacomo: Collect it. Put it in the ground. And that's really where the bulk of the industry made its money.

Now Recology has figured out a way to turn food trash into cash. It sells the compost for to vineyards and farms. They're willing to pay $500 a truck load for the compost because it's packed with nutrients.

To get an idea of what a change the compost plan has made to the city's garbage haul, all you have to do is visit the local 44-acre dump. I put on my galoshes, hold my nose and waste manager Sean Davison leads the way.

Carroll: So we're heading into the organics annex?

Sean Davison: The organics annex where all of San Francisco 's food scraps end up where they're collected.

Thousands of birds feast on piles of rotting food.

Davison: You don't have a fear of birds do you?

Carroll: I don't, I don't.

Davison: They don't attack.

All this used to end up in landfills. Now the fish heads and rinds take on a second life as compost. Davison says people like the environmental payoff but they like something else more.

Davison: We would like to think that it's the right thing to do but most of it is financial. When you go to someone and you tell them you could cut your garbage bill in half, you're going to get their attention.

Businesses who recycle can cut their trash bills in half. The garbage companies also make more if they meet recycling goals. San Francisco residents don't get a break on their monthly $25 bill for trash pick up. But if they don't compost and recycle, they could get hit with a fine of $100. Businesses could pay more.

Recology doesn't want to play trash cop. So it's sending out compost and recycling starter kits. Apartment manager Linda Corso has hers.

Linda Corso: We put the posters that we got up over here so when people come down they can sort of look at it.

She likes the compost plan but worries that she could be punished if her tenants' don't cooperate.

Corso: I can't go in and force someone to compost rather than put things in the trash, and I certainly can't sit and go through every bag of trash that gets dumped.

Success will come down to making renters care. Take Michael Kellenbach. He's interested. He just doesn't know what to do.

Michael Kellenbach: I'd want to know what to put in there. I mean do you just put leaves?

Yep.

Kellenbach: Do you put dead flowers?

Sure.

Kellenbach: Do you put coffee grounds?

Yeah, those too. Plus ice cream cartons, cardboard boxes and any leftover food you find.

Other cities are watching San Francisco as the composting plan makes it way through the city government. If it becomes law, composting could become a household habit.

In San Francisco, I'm Caitlan Carroll for Marketplace.