In the United States, landfills are #3 on the methane list, behind those cute cows and our natural gas systems. (2)
But our relatively urban area has few cattle, little natural gas production, and lots of people (and their trash), so landfills are an easy #1 for us.
Why so much methane from landfills? They are oxygen-free environments packed with organic material like paper, yard waste, and food. As you may remember from an earlier blog post, that is a perfect recipe for methane! 16% of the anthropogenic methane emissions in the US come from landfills. Incredibly, that is down 40%(!) since 1990. Partly that is because we are recycling and composting more, taking organics out of the landfill. (3) And partly it is because (fewer, larger) landfills are doing a better job of capturing methane gas. But our improvements are tapering off. With only 9% of food waste being composted nationally (see the EPA’s chart below), we need to continue to find ways to keep organics out of our landfills. (4)
Are we faring better locally, in our cities? Yes! Palo Alto and Mountain View are diverting an impressive 80% or so of waste from landfills, compared to the national average of 52%. (5) But despite that, so much of what heads to the landfill is compostable. Here is what is found in Palo Alto’s “single family residence” trash bins:
We are great at composting our yard waste and compostable plastics. But food? Paper? Not so much.
Of the top items found in our trash bins, most should be in the green bin:
Fortunately for us, the SMART station in Sunnyvale sorts through the trash from Palo Alto and Mountain View. They do a good job pulling out food scraps, but even so, nearly 40% of what remains after sorting (all of which goes to landfill) is compostable. These are the top items sent to landfill after sorting, from a mix of residential and commercial trash:
It’s true in Menlo Park and Mountain View as well -- around half of the trash from single family residences is compostable material. (5)
You may be thinking -- but won’t the landfills capture the gas for us? At best, just some of it. A perfectly operating landfill will emit methane from the portions that are unsealed or only temporarily sealed. (6) And inoperative landfills need to handle methane emissions for decades after they are closed. If the gas collection system is overdrawn, gas can leak out or, worse, subsurface fires can start and be very difficult to put out. Mistakes happen. For example, shortly after Shoreline Amphitheater opened in the mid-80’s atop Mountain View’s closed landfill, concert-goers lighting up on the grass ignited “great balls of fire”, due to methane leaks from the underlying landfill. Yikes. (7) Landfills can be pretty dangerous places. Composting makes them safer, not only by reducing methane, but also by stabilizing landfill loads and killing pathogens in our waste.
Palo Alto continues to monitor and manage methane at the old landfill at Byxbee Park nearly a decade after the final portion was closed. (8) Back in the 80’s, when the landfill was still open, a cogeneration facility produced electricity from the methane and sold it back to the grid. More recently, with a smaller methane supply making that financially infeasible, the methane was piped over to the water treatment facility where it was used to process sewage, saving an estimated $250,000 annually versus using natural gas. (9) Below you can see the blowers that draw the methane in from the landfill (pipe to the left), and the pipe in back that sent gas over to the water treatment facility.
Now that Palo Alto no longer incinerates its sewage (yay!), the methane is simply flared (burned) on site, turning it into carbon dioxide, which is a much less potent greenhouse gas. You can see the chimney where it is burned in the picture below.
Many thanks to Elise Sbarbori, of Palo Alto’s Public Works Department, for showing me around these facilities, and for her work helping to maintain our safe and environmentally-friendly landfill.
In the next blog, we’ll see what happens to the food and yard waste you are putting into the green bins…
Notes and References
1. You can find out more about Bay Area methane emissions here (60-page pdf).
2. The EPA’s inventory of greenhouse gases through 2017 (executive summary) is here (29-page pdf). The entire inventory, consisting of multiple chapter pdf’s, is here.
3. Much of our progress with recycling and composting can be traced back to California’s AB 939, sponsored by Palo Alto’s own Byron Sher. PBS has an interesting discussion of things other states are trying to reduce food waste and bypass the landfill, and some of the challenges they face.
4. The EPA’s 2017 inventory of greenhouse gases coming from waste is here (39-page pdf).
5. Palo Alto’s thorough and interesting waste characterization from early 2018 can be found here (92-page pdf), along with some zero waste plans at the end of this 2018 Earth Day report. Menlo Park’s 2017 zero waste plan (and current status) can be found here (65-page pdf). Mountain View has some information available here, with a new waste composition analysis coming soon.
6. A 2011 EPA document reviews where and when methane is emitted from landfills, and outlines ways to reduce methane emissions.
7. An interesting but brief overview of methane leaks at Shoreline Amphitheater can be found in the fourth case study listed at the bottom of this CalRecycle page.
8. A timeline of waste management in Palo Alto can be found here. Interesting fact: In the early 1900’s, Palo Alto used to incinerate its garbage, right near where the fire station is today at Embarcadero and Newell. Ironically, the incinerator burned down after about 20 years, and trash disposal was moved to the Baylands.
9. The EPA maintains a registry of projects that produce energy from landfill methane. This is a brief writeup on Palo Alto’s usage of landfill methane for water treatment.
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