Jepson Prairie Organics Tour
In 2008, CUESA visited Jepson Praire Organics composting facility.
NorCal Waste Systems operates the Jepson Prairie Organics composting facility adjacent to its landfill in Vacaville. 4500 tons of organic materials are processed here each month.
Yard trimmings and food scraps from San Francisco restaurants and residences are brought in 25-ton loads to this facility, along with organic matter from UC Davis, Folsom State Prison, and the cities of Vacaville, Oakland and Berkeley.
The organic matter is screened in this machine, which has a rotating barrel with 4" holes. Particles that fall through the screen go onto the pile on the left.
Larger particles continue on a conveyer belt into this sorting shed, where four or five workers discard non-compostables into the bins below. Can you guess what non-biodegradable contaminant is most problematic? (Click "next" to find out the answer.)
Facility manager Greg Pryor says plastic bags and other film plastics are their number one challenge. The sorters fill two 35-yard boxes (pictured in previous slide) each day with contaminants, most of which are plastic bags.
Next, the organic material is ground for faster composting. Loads of yard trimmings, including those from residential green bins, are kept separate from loads of food scraps from restaurants and cafeterias. Yard debris needs additional water for optimal composting; food scraps contain too much moisture and are mixed with wood shavings.
The material is spread out into long windrows. This one contains yard trimmings; the machine is turning the row with a rototiller-like device while adding water. The rows are turned several times and temperatures are monitored to ensure they heat up sufficiently to kill pathogens and weed seeds.
Windrows of food scraps are covered to reduce emissions of volatile organic compounds (a natural byproduct of composting). After 2-3 months, the composting process is complete and the material is screened one last time.
This is the finished product. Several Ferry Plaza Farmers Market farms use this compost, including Bruins Farm, Capay Fruits & Vegetables, and Eatwell Farm.
At the time of our visit, Jepson Prairie Organics was awaiting permits to put all the material through an anaerobic digester before composting. The digester reduces gas emissions, speeds up the compost process, and produces electricity--more than enough to power the plant. They are currently operating the digester on an experimental basis in partnership with UC Davis.
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CUESA (Center for Urban Education about Sustainable Agriculture) is dedicated to cultivating a sustainable food system through the operation of farmers markets and educational programs. Learn More »