Monday, May 7, 2007

What happens to all that stuff we put in the green bins?

Last week our Soils class took a trip to Jepson Prairie Organics way out in Vacaville. Jepson Prairie is a landfill where the people in charge decided that there must be something else they could do with all the food waste they saw going into the landfill. They started an innovative composting program and are today the largest food waste compost facility in the country.
So what happens to all the food that gets thrown into those green bins? The majority of the bulk comes from restaurants in San Francisco, then from homes, and they get some from Oakland and a prison that is near Vacaville. It is trucked to Jepson Prairie, then it has to be sorted out. The biggest problem to their operation is the amount of trash- specifically plastic bags and film, that gets dumped into those bins. It has to be removed, and a big part of it is done by hand.
Here's one big stinky pile of waste from our kitchens and restaurants... and let me tell you, it is smelly, disgusting and nauseating. Let's just say we all owe a huge debt of gratitude to the folks who can do this work!

It goes into this Trommel Screen, in which everything less than 4" falls through and the rest is conveyed to a platform where 4-8 human beings pull out anything plastic, glass or otherwise non-compostable. It's a gross job, for sure, but the workers get a decent pay, sick time and are fully covered for their families health care, which is a real bonus out here where most the unskilled jobs are working the farms, and we all know those jobs don't provide any sort of health care benefits.

At the ends of the process there is always a pile of trash which then gets put into the landfill. This is their biggest headache. There's no way to filter out 100% of the plastic and glass, so until people stop putting trash into their green bins, it will be a problem.

Here is a big pile of green waste (yard trimmings). Green waste and food waste are composted differently. Food waste is super high in energy, gives off volatile organic compounds (VOC's) that make methane gas. It also has to be raised to high temperatures to kill contaminants and bacteria.

So it all gets loaded into these Ag-bags, where it cooks up for 30 days, I believe. The bad thing about these bags is that the VOC's really build up and when they are opened it releases into the environment. So they have developed a Gortex tarp that works to raise the temperature to the required levels, but allow the VOC's to escape as they are produced.

Then the tarps are removed and the rows are left open to the air to finish composting for another 30 days. These are called windrows and must be turned (aerated) every 3 days.

This is the big machine that turns the windrows. That's all steam coming from the compost. These piles produce very high temperatures as the decompose. The piles have to kept under 12 feet or fires start up. They keep a night watchman there to watch for these fires, which typically start up around 3:00 AM, for some reason. The way they stop the fire is to drive bulldozers into the piles to release the gases and lower the temperature.

Here we are by a pile of finished product, which is finely textured and does not smell at all. they sell the compost to farmers, vineyards and if you want, you can drive up there and load up a bag for free.

They make 3 or four grades of compost. They also make custom blends, according to the soil analysis, but this is for large scale buyers only. The folks here at Jepson Prairie Organics dream of a future where food waste is decomposed at a facility near San Francisco, where the VOC's are used to produce methane gas which in turn is harnessed and used to power generators. Oakland is already doing this on an experimental scale. then the solids, minus the 70% water, can be transported to the landfill and composted cleanly, without all that methane being released uselessly into the environment. It a growing field, a promising future and beneficial for our environment.
Kudos and sincere gratitude to the men and women who do this work!


chuck b. said...

I guess I'm glad I didn't go to this! Pee-euuh!

I thought it was particularly interesting to hear that if San Francisco did the primary decomposition here, we could send just 4 trucks to Vacaville instead of 18. That's a lot of water and CO2! It's hard to fathom that.

anile said...

Yeah it is amazing! When you think about it, an apple, for example, is mostly water and air, so you can see that food contains a lot of it in general, plus so much energy. It did stink really badly, but over all I'm glad I saw it.

chuck b. said...

I posted a link to this story on GardenRant here:


anile said...

Wow! Thanks Chuck! I better double check for typos ;)

Anonymous said...


Do you ever like...... sleep?


anile said...

Heehee.. not much! But school's over in 2 weeks so... YAAAAAYYYYY!!!!!!!
Thanks for reading me Ginger!

shibumi said...

I really enjoy knowing how they compost at Jepson. I always wondered what those windrows were along Hwy 101, north of Santa Rosa ... must be individual farmers doing their own. Thanks, Anile!