What do a banana peel, an empty soda can and that essay you never picked up last semester have in common? They’re all trash, and in San Francisco, they have an increasingly small chance of ending up in a landfill.

San Francisco has reached a milestone by diverting 80 percent of its garbage into recycling, composting and reuse programs, signifying another step toward the city’s goal of zero waste by 2020.

The SF Environment department and its waste hauler, Recology, now have eight years to eliminate the remaining 20 percent of landfill garbage from the waste stream to reach the goal set by the city’s Board of Supervisors.

Zero waste is “a vigorous goal, and a very high standard,” said assistant professor Jennifer Blecha, who teaches a class on the geography of garbage in the geography and human environmental studies department. “Nobody has reached it, but it’s pretty inspiring. San Francisco is doing a great job.”

Half of the approximately 440,000 tons of rubbish San Francisco still sends to landfills every year is missorted and could be recycled or composted, according to Recology and SF Environment. The final 10 percent is made up of materials not currently recyclable or compostable by Recology.

“We’ve picked all the low-hanging fruit, so it is getting harder and harder,” Jack Macy, SF Environment commercial zero waste coordinator, said.

Even more important than diversion for achieving zero waste is reducing what gets discarded in the first place, Macy said. Ten years ago, San Franciscans threw about 880,000 tons of trash into landfills. Now the city discards about 440,000 tons, the lowest amount on record, Macy said.

Reducing what gets thrown into landfills will mitigate several strains on the environment, according to Blecha.

Toxins buried in dumps have a tendency to mix with rainwater and create a poisonous mixture called leachate, which can pollute the water table. Landfills are also some of the biggest producers of the greenhouse gasses carbon dioxide and methane.

“If we can capture 40 percent of the municipal solid waste that is organic material and put it back on the land — what a waste to have it go into a hole in the ground,” she said. “We should stop calling it waste and start calling it our resources. We think it’s normal to put ‘waste’ in a hole in the ground.”

The city’s recent ban on plastic shopping bags could remove thousands of tons of nettlesome “plastic film” from the waste stream that clogs recycling sorting machines. Macy said it might only add up to a fraction of a percent of the 1.6 million tons of recyclables, compost and trash Recology handles every year.

“How do you meet a challenge? You bring a combination of solutions,” Recology spokesman Reed said. “It’s kind of like cooking dinner — you’ve got a recipe and a list of like nine ingredients.”

SF State microbiology major Ren Newman said the zero waste goal seemed like a positive thing, depending on its cost. He said it would be hard to get people to sort their discarded materials.

“On campus, it’s nice because they have all the cans next to each other with pictures telling you what goes in which place,” he said. “It almost makes you feel like a bad person not to (recycle correctly).”

Reed emphasized the importance of source sorting, an industry term for residents sorting trash, compost and recyclables. He said once people learn about the huge positive impact composting has on the environment, they are more likely to participate in sorting.

For example, San Francisco compost is used to nurture ground-cover crops between the rows of traditional agriculture on local farms, Reed said. The plants pull carbon dioxide out of the atmosphere.

“It’s been estimated that if every city in the U.S. replicated this program, we could offset 20 percent of America’s carbon impact,” Reed said.

Macy knows his department can’t depend on 100 percent source sorting to achieve zero waste. That’s why the department is planning a “futuristic zero-waste facility” with the technology to mechanically separate recyclables from the mixed garbage that makes up what experts call municipal solid waste, Macy said. Reed described an optical laser system already in place in San Francisco’s main recycling plant that can recognize and sort different types of plastic.

SF Environment aims to fire up the new facility before the 2020 zero waste deadline and keep San Francisco a leading city for waste diversion.

“The number of different types of recycling programs we provide is more than any other city in North America,” Reed said. “Because garbage is different depending on where you go.”