Garbage In, Global Warming Out: Can We Disrupt the Flow?

By Al Sattler

Did you know that when you are discarding food waste into the trash, you are contributing to global warming?  Here in Los Angeles County, our residential garbage is buried in “sanitary landfills,” a.k.a. dumps. Once it is buried, isolated from air, bacteria decompose it, producing methane, a potent greenhouse gas. Food waste is one component of garbage that decays most rapidly. Operators of landfills capture some of the methane by putting a dirt cap on top and pipes to suck it out, but much of the methane escapes before it can be captured, so landfills are a significant source of methane in the atmosphere, contributing about 21% of methane emissions. To address this issue, the California legislature passed a law, SB 1383, to greatly reduce the amount of organic* waste, including food waste that is dumped in landfills. Cities must divert 50% of their organic waste from landfills by 2020 (this goal will not be met), and 75% by 2025.

4,000 tons per day of food waste is produced in Los Angeles County. SB 1383 sets a goal that at least 20 percent of edible food that is currently disposed of be recovered for human consumption by 2025. SaveTheFood offers hints on food storage and other ways to reduce your personal food waste. There is also an Ugly Fruit and Vegetable campaign, to encourage people to buy less-than-perfect produce. Business Insider reviewed Imperfect Foods, one company that delivers homely produce. The Center for Food Loss and Waste Solutions at has significant information resources. The Angeles Chapter’s newsletter “The Southern Sierran” also has an article this month by Palos Verdes-South Bay member Simone Kuhfal, “Food Waste, Food Insecurity, Climate and Equity,” that includes tips on reducing your food waste.

It is a shame that a huge amount of food waste is discarded while so many people are hungry, but much of this is spoiled and inedible. Recently, the Sanitation Districts of Los Angeles County presented a virtual tour of their installation at the Joint Water Pollution Control Plant in Carson to process some of this food waste. The video is available to watch. Food waste from restaurants and grocery stores is collected by garbage haulers and delivered to outlying facilities where it is ground up, and the slurry pumped into tanker trucks to be delivered to Carson. Currently, 300 tons per day of slurry is delivered to Carson. (That’s less than 8 percent of the total food waste produced in the county.) The food waste slurry is pumped into existing anaerobic digesters, commingling with sewage sludge. The digestion produces digester gas “biogas” which contains methane and carbon dioxide, most of which is sent to existing gas turbines, which generate electricity to power the plant. There are plans to expand the system to take up to 600 tons per day, which will produce more gas than needed for the turbines, so they are cleaning up the gas and selling it at an existing compressed natural gas fueling station for vehicles that run on compressed natural gas, like some large trucks. I asked why they don’t build more gas turbines to generate more electricity to sell on the grid. It turns out that electricity from wind and solar is priced at 2-3 cents per kilowatt-hour, and electricity from additional gas turbines would not be cost-competitive. 

After 15-16 days in the digester, the remaining sludge is dewatered in large centrifuges (like the spin cycle of a washing machine), and transported to several distant facilities where it is composted, then used as soil amendment. Unfortunately, the food waste is mixed with the sewage sludge, so the resulting compost is not suitable to use directly on many food crops. 

The county sanitation district should be commended for taking some steps to manage the greenhouse gas emissions of food waste, but there is still a long way to go. It would certainly be preferable to compost decently clean food waste or digest it separately from sewage. Using the digester gas to fuel vehicles, perpetuating use of fossil fuels for vehicles, is a step backward. A new solution is needed to first, reduce the amount of food waste produced, and second, to scale up the recycling of the waste in a productive way.   Collecting food waste from individual homes would be much more difficult than collecting food waste from large commercial sources. For now, the food waste you put into your garbage will still go to a landfill, and will still contribute to global warming. So minimize your personal food waste, and compost if you can.

*”Organic” here means derived from living matter; it does not refer to “organic farming.”

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