Blending targets and goals

California’s Kern County Public Works celebrated the opening of its Shafter-Wasco Compost Facility in October—a project 10 years in the making.

The county began designing the facility in 2016, says Dave Lee, public works manager for Kern County’s waste diversion and transfer station programs. Facility construction began in April 2024 and was completed this September.

The goal of the decade-long project was to develop a composting facility that would be able accept 100,000 tons of organic waste, Lee says, which the facility is expected to divert annually from landfill. This aligns with Kern County’s procurement goals while helping the county and its incorporated cities meet their S.B. 1383 organic waste recovery targets.

“Really, we were looking for a technology and a system that helped us comply with our state regulations for S.B. 1383 and could be designed and built per the state water board requirements,” Lee says. “And our air district has very stringent composting rules, so we were looking for a technology, a system and a build that would help us comply 100 percent with those regulations.”

The facility is expected to produce 40,000 tons of compost each year using 32 composting bunkers, each capable of holding up to 600 tons of material. The bunkers use Sustainable Generation’s Covered Aerated Static Pile (CASP) technology with Gore covers, which control oxygen using positive aeration, temperature, air flow and moisture retention, reducing odors and emissions.

Kern County was awarded a $10 million grant from CalRecycle’s Organics Grant Program in 2024 to offset the facility’s construction costs, which totaled nearly $21 million. The rest of the money came from county funds.

“It was a competitive grant,” Lee says. “There was limited funding, with a limited amount of people that were going to be successful in receiving the grant. We, fortunately, had everything in our grant application. We had all the permitting completed and all the documentation.”

S.B. 1383 regulations

California S.B. 1383 requires jurisdictions to provide organic waste collection services to all businesses and residents, according to CalRecycle. Its goal is to reduce organics waste landfill disposal by 75 percent from 2014 levels by 2025.

“S.B. 1383 was first floated out there in 2016 by a state senator,” Lee says. “The regulations really went into effect in 2020, with some new benchmarks from 2022 and 2024. The regulation hasn’t significantly changed from the passage in 2020, but there’s been some ‘cleanup bills’ here and there.”

Lee says the changes to S.B.1383 didn’t affect the county’s plans for its facility because it already knew 100,000 tons of organic material were going to landfill.

“That material was going to be taken out anyway,” he says.

“S.B. 1383 at its core is a climate change bill. It’s not really a recycling bill, and I think that’s a little nuance that isn’t always particularly shared.”

The bill is about reducing methane and short-lived climate pollutants, he says, which result from organic material decomposing in landfills.

“It definitely forced the recycling and waste industry to change a lot of its perspective,” he says.

S.B. 1383 has targets that require the county to procure or buy a certain amount of mulch or compost produced from the diverted organics for each person who lives in Kern County. Lee says the recovered organics must be used for beneficial reuse, slope stabilization, fire remediation, fire protection or other approved purposes.

He continues, “What S.B. 1383 and this facility allowed us to do was have the option to produce our own compost and then to meet our own procurement targets without having to buy it from a third party.”

Cities in the county can bring organic material to the Shafter-Wasco facility for composting. They also can procure compost from the site to meet their targets.

“It was kind of this whole cyclical approach. ‘You bring us the material, we’ll compost and we’ll give you back finished compost to meet your 1383 goals,’” he says. “We had letters of support from each one of our cities saying, ‘This is something we want to do.”’

Facility processes

The facility accepts both residential and commercial feedstock, including green waste, agricultural materials, manure, food waste and food-soiled paper.

The composting process at the facility is managed in three phases. The first phase, which the facility started in early November, is called active composting, where the feedstock is placed in covered bunkers for three to four weeks.

Phase two is where partially composted material is moved to covered bunkers, furthering the composting process and stabilizing the material. This phase takes two to three weeks, Lee says.

In the final phase, the material is moved to uncovered bunkers to mature into finished, ready-to-use product, taking about two weeks.

“Anywhere from 10-12 weeks is when we’re expecting to have finished compost,” Lee says. “So, we will probably see at the start of next year some finished compost.”

The compost will be available to the cities within Kern County and their residents at no fee, while agricultural and landscaping businesses can purchase the product from the county.

“We’ve been working on connecting with some local growers and farmers as well, just trying to make sure that they’re getting the finished compost that they’re looking for,” he says. “We plan to use it throughout the local agricultural market, support county properties and enrich community landscapes.”

Almost one month after the site’s grand opening, Lee says the facility has been operating well, having recently built the facility’s sixth bunker.

“We are learning the ins and outs of composting, how to get the right mixture of feedstocks, making sure we have the moisture content correctly implemented and learning how the technology works,” Lee says.

The facility is expected to produce 40,000 tons of compost annually, he says, as it expects the incoming material to have a 40 percent yield.

“We expect to have as much of that 100,000 tons in that facility annually as we possibly can to reach that 40,000 tons per year,” Lee says.

Technology and equipment

With Sustainable Generation as the facility’s equipment and software provider, Lee says it can access a software link that shows real-time data, including what the temperature is, what the oxygen levels are and how long the material is within the system.

“We can adjust the blowers, the timing—we can monitor all that stuff,” he says. “The operation is going really good,” with several operators having been trained on how to use the equipment.

Lee says part of what makes the new facility innovative is a combination of Sustainable Generation’s CASP technology and Gore covers, which are advanced membrane fabrics that keep heat and moisture in and stormwater away from the composting feedstocks.

“One thing I personally really like is that we have the in-ground aeration system,” he says. “In these bunkers, we have basically a leachate collection in an aeration system. It’s like a two-in-one system that’s in there; we can turn it on and off and monitor that.”

He says the whole system helps to reduce odors and emissions associated with composting as the cover doesn’t allow volatile organic compounds to be released into the air. Using modern composting technology has helped the facility achieve its innovation goals.

Lee says the site’s six bunkers can hold 3,600 tons of material, and employees are trying to move as fast as they can to get it into the system.

Kern County acquired various types of processing and screening equipment several years ago, Lee says, including horizontal grinders. He says the facility uses 6800 and 5800 model diesel-powered grinders from Terex brand Continental Biomass Industries (CBI) of Newton, New Hampshire, to process brush, trimmings and wood waste.

The facility also uses an L3 star screening machine from Komptech, based in Austria, to process and screen green waste and a Komptech L4 to screen finished compost.

“We’re using a combination of the grinders, the Komptech and a couple other pieces of equipment to blend and get the feedstock in the right percentages with the right carbon nitrate ratios,” he says.

Other equipment used at the facility includes Caterpillar 938 and 966 loaders and a stacker and conveyor manufactured by Rotochopper of Minnesota.

Sustainable results

Building a facility that improves regional air quality was an important factor for Kern County. Lee says the area historically has had poor air quality and many industries are working toward improving it.

“With the combination of our Gore covers and the way we operate and test, we’re really going to see some improved regional air quality by reducing those volatile organic compounds but also methane emissions coming from the landfill,” he says.

“The ultimate long-term goal is to consistently provide a really good, finished compost that helps Kern County as a whole, with its agricultural community and its overall carbon sequestration throughout the county,” Lee adds.

As new operators of a compost facility, he says the county is learning how to improve its production of high-quality compost, to better prep material and to get the right moisture content.

Lee says, on a personal level, he wants to dial in the facility’s front-end screening capabilities with the addition of more equipment and staff to ensure the feedstock is as clean as possible. Future plans for the facility’s equipment include an electrically powered CBI 6800 and the 1220 Feed Mixer from Roto-Mix of Dodge City, Kansas.

“That’s the trick, to get the material as clean as possible. Get it clean on the front end rather than trying to fix it on the back end,” he says. “We’re looking at buying different types of equipment, some mixers and some other screening applications to really make that dialed in.”

The author is the Recycling Today Media Group’s assistant editor and can be contacted at atrevarthan@gie.net.