I have spent the last two days attending the US Composting Council Conference in Oakland, CA. I have learned more than I ever imagined there was to know about composting, and I have just scratched the surface. Composting food scraps and yard/plant debris can provide a world of benefits in reducing green house gases, contribute nutrients to and renew our soils, aid in flood water management, and potentially reduce or remove toxins and antimicrobials from our environment. Composting what would otherwise be waste is a truly amazing opportunity for our communities.

I took a tour of the Jepson Prairie composting facility in January, and thanks to the help of Greg Pryor (thanks, Greg!) with Norcal Waste Systems, I am able to share that tour with you here. In just 60 days, the food scraps and other compostable materials collected in San Francisco are converted (composted) into a beautiful, rich material. When food scraps go to landfill, they either do not breakdown at all or breakdown anaerobically (without oxygen), creating methane gas and contributing to global warming instead. I am SO glad SF collects food scraps. Seems like a no brainer to me!

Jepson Prairie Compost Tour

Step One – Food scraps from San Francisco are delivered in 18 wheeler trucks to Jepson Prairie every day. Food scraps from Oakland, the UC Davis food court and special events, the CA Medical Facility in Vacaville and the State Prison in Folsom are also taken there. Yard debris from Vacaville, Dixon and Vallejo are hauled to the Jepson Prairie facility in standard route trucks.

The food scraps and yard debris are kept separate due to higher levels of non-compostable material (i.e. plastics) in the food scraps. A total of 300 tons of material are processed each day: on average 200 tons of food scraps and 100 tons of yard debris.

Food Scraps

 Yard Debris (lots of Christmas trees in early January)

Step Two – The food materials and yard debris are run through a grinder to reduce the material size. Straw and other organic materials are added to the food scraps in order to get the proper carbon to nitrogen (C:N) ratio and porosity for composting. This is typically not necessary for the yard debris. After going through the grinder, the food scraps are run through a sort line to remove non-compostable contaminants.

Food scraps after grinding

Step Three – After the material is ground, it is set out in windrows or long rows. The food rows are covered as a regulatory requirement to help aid the pathogen kill process. The material used to cover the food rows is like a textile, and also helps keep small bits of plastics and other contaminants from blowing onto neighboring land. The yard windrows are left uncovered.

Food Windrows

Step Four – The food windrows are left covered for 30 days, and must achieve a temperature of 131F for three consecutive readings before the cover can be removed. After it is uncovered, the food windrows are turned five times in 15 days so the entire windrow reaches the required temperature. The yard windrows are not covered, so turning begins immediately. The yard windrows must reach and maintain a temperature of 131F for 15 consecutive days and five turns.

Windrow Turner – Straddles/drives over the windrows, and flips/stirs and reforms the rows as it moves forward. (The background in this picture is previously covered landfill.)

Step Five – The compost stays in windrows for 60 days and until the required temperature is met. It is then cleaned and screened to 3/8” pieces or smaller, and any remaining contaminants in the food compost are removed. The food and yard debris compost is marketed separately, and is available for purchase by nurseries, wineries and for other agricultural uses. Nurseries typically get a blend of the food and yard compost, while wineries take the straight food compost, which is higher in nutrients. All of the compost is tested for pathogens and heavy metals, and specific testing can be done on request. Residents from Vacaville and Dixon may pick up three yards for free.

Final Product