Napa’s composting facility just got a major upgrade.

In January 2020, the brand new composting system, called the CASP facility, officially began operations. It can compost over 63,000 tons of material per year. That breaks down to about 315 tons a day — the same weight as 5 empty Boeing 757s.

What Is CASP?

CASP stands for covered aerated static pile. We’ll go into details below, but in a nutshell, that means it’s designed to provide optimal composting conditions through positive aeration, automatic irrigation, advanced temperature control, and a biofilter layer.

Covered: The compost is covered with a biofilter layer made of mature compost or wood chips. It captures any air emissions and controls odors. The biofilter cover also insulates and retains heat evenly across the pile. Heat is important during composting in order to help the material break down, as well as to kill weed seeds and any pathogens.

Aerated: Aeration is the process of adding air into the compost. Through CASP, air goes into the compost through 3,300 holes installed in the concrete floor. The forced aeration helps the decomposition process.

Static Pile: The compost is put into an unmoving pile during its “active” phase, where all of the automated aeration, irrigation, and hourly temperature feedback take place and ensure the decomposition process happens quickly.

How Does It Work?

1. Organic materials, including yard trimmings, food scraps, ground wood, grape pomace and agricultural waste are blended and loaded into the system.
2. The biofilter cover (mature compost or wood chips) is applied to control any odor or emissions.
3. Air and water are automatically added to the compost to ensure ideal composting conditions.
4. After 22 days in the actively controlled phase, compost is moved to another area where it can cure in the open for a minimum of 40 days.
5. After 40 days of curing, the compost is done! The finished compost is screened for quality and sold for use as a soil amendment in agriculture (vineyards, farms and orchards), landscaping and home or community gardens.

Why the Upgrade?

California state law (SB 1383) now requires food and yard waste to be composted instead of landfilled. New regulations also demand a better system for removing contaminants from the compost. Because of this, the City of Napa approved a $10.4 million upgrade at its composting facility back in 2017. Napa selected and implemented the new CASP system in less than three years.

In Napa’s old system of composting, all of the collected food scraps and yard waste went into windrows, where it was turned with front-end loaders until it finished decomposing.

The new CASP system gives operators greater control of the decomposition process, and it can process an additional 20,000 tons of material per year.

Our facility was designed by Engineered Compost Systems (ECS) – check out their website for more info and a video of the process.

And, you can read more about our facility in BioCycle.