As trash bins shrink and recycling containers expand in San Francisco, residents might be tempted to cheat a little about what they put in the blue bin.

Obviously, no Recology worker wants to pearl-dive for aluminum cans in a toxic stew of loaded baby diapers, cat litter and leftover spaghetti. But even comparatively minor contaminants like a greasy pizza box or an overlooked clothespin can undermine the city's recycling effort.

For San Francisco's Zero Waste initiative to meet its 2020 goal of no waste to landfill or incinerator, people have to do their part. Recently, Recology and the city stepped up outreach efforts to persuade households to be careful about what they put into the recycling bin.

Basically, plastics, aluminum, paper, and glass jars and bottles can be recycled — a complete list of recyclables can be found on Recology's site — but items must be clean and dry.

Avoiding contamination has suddenly become more critical than ever because China, the primary receiver of recycled material from the United States and other countries, has abruptly barred its ports from all but the cleanest bales.

"Historically, China has accepted 4 to 5 percent impurities in bales of recycled materials," Recology spokesman Robert Reed said in an email. But in January, China announced that under its "National Sword" enforcement program, it will no longer accept bales with more than 0.5 percent impurities.

Reed said Recology is working to meet the new standard, but currently its bales still fall within the 4-5 percent impurity range.

By comparison, Sacramento County's contamination rate is 25 percent, and local officials there are considering fining residents who put the wrong items in recycling bins.

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With China out of the equation, Recology is "staging" more plastics bales than usual at its San Francisco facility before shipping them and recycled paper to other Southeast Asian cities as well as locations within the U.S. The company declined to name the cities "because recycling markets are competitive."

China used to take all of Recology's recycled cardboard, but as of February, it is only accepting 10 percent.

To make customers more aware of the importance of avoiding co-mingling recyclables with trash or compostable items, Recology workers place "cart hangers" — signs with notes explaining what was sorted incorrectly — on bins. Reed said most people comply after receiving their first hanger.

Correct sorting is a big deal for Recology, which handles between 500 and 600 tons of co-mingled recycling each day in San Francisco.

"Less contamination in recycling and composting bins gives sorters and machinery an opportunity to pull even more contaminates from the recycling stream and that translates into cleaner bales that command a higher price when sold," Reed says. "These commodities help offset the cost of collection and processing benefiting all rate payers."

The typical San Francisco single-family home pays $40.04 a month for weekly collection of all three bins (recycling, composting and trash) and includes utilizing the bulky item recycling service for large items such as an old carpet or appliance.

In October, Recology announced what it called the most significant advance of the city's three-bin system since its genesis in 2000.

"We've never been closer to eliminating our need for that black (trash) bin," Debbie Raphael, the department's director, told the Chronicle at the time.

Recology is gradually replacing the existing 32-gallon trash and recycling bins in the city with 16-gallon black containers and 64-gallon blue bins. (Those residents who have 20-gallon trash bins can keep either keep them or request a new bin.)

Reed said last week that the new program, expected to be completed in 2019, is working "really well."

"In neighborhoods where we have delivered the new bins, the amount of material residents place in their black bins is down between 10 and 15 percent," Reed said. "We have seen a corresponding increase in the material residents who have received the new carts place in their blue bins."

China's tightening of recycling policy could have one benefit, Reed said. It likely will spawn more domestic jobs within the plastics and paper recycling industries.