Sacramento, Calif., Anaerobic Digester Goes Back to the Drawing Board

A Sacramento, Calif., anaerobic digestion plant that was making transportation fuel from municipal solid waste has hit a roadblock, and its new owner, alternative energy investment group Incline Clean Energy, is trying to get back on track.

There have been three main challenges: odor, identifying the best feedstocks and identifying the best processing technology approaches, says David Schroeder, a consultant for ES Engineering and the onsite manager.

“This facility was taking organics since 2014, at first 50 tons per day and eventually increased to 100 tons per day [making it one of the largest commercial high-solids food waste digesters in the U.S.],” says Ini Ghidirmic, an attorney for Incline. “There were operational challenges by virtue of expanding capacity, like volatile organic compounds and other byproducts generated through the anaerobic digestion process. We are now trying to identify the materials that work from an economic returns perspective while providing environmental benefits and following the rules and regulations.” Created for this project, Incline has affiliated entities that have worked in solar and other alternative energies.

Food waste was coming into the facility in many types and packaged. Depackaging was labor-intensive as was identifying the right mix of organics that could be digested for proper outflow as materials interact differently.

The anaerobic digester started receiving organics in 2014, when it was owned by technology company CleanWorld. Incline acquired majority interest at the end of 2015, once the capacity was in the process of expanding.   

Initially, Incline thought it could reduce emissions and the possibility for odor by taking liquid food waste only, but even this typically somewhat less problematic material proved challenging. The company stopped processing solid food waste in spring 2017, and it stopped accepting liquid in early 2018. Now, it’s working to address leaks around tank lids.

“Our goal is to be in production toward the end of summer 2018. We expect to receive liquid by then in the form of fats, oils and greases,” says Schroeder. “We are still evaluating feedstock options. I do foresee solid organic waste as part of the picture, but we are currently evaluating what percentage will be solid and what percentage will be liquid.”

Refuel, a subsidiary of Atlas Disposal, is a strategic partner of Incline and was supplying municipal solid waste as feedstock at one time.

“Atlas originally collaborated with CleanWorld to develop a digestion system before Incline bought the facility,” says Dave Sikich, Atlas president. “The plan was to develop an energy conversion project that turned food waste into transportation fuel for the Sacramento County region. We were going to be equity partners but decided Atlas would own the fueling station.”

The refuse company anticipates supplying feedstock once the plant is running again, and, for now, Incline is evaluating feedstock categories.

“Depending on what we find in those categories, we may need to do additional onsite preprocessing,” says Ghidirmic. “Whatever material is being discarded affects the outcome. Materials with more liquid are typically easier to dispose, while those of a high solid content may require different and more costly post-processing before they are discarded. It’s not just finding a technical solution; it’s trying to identify the best business decision from a financial perspective.”

Solar is a less complex investment type, but the company plans to stay with this new venture and anticipates taking its work in this new space further.

“Solar might not be as hard to pursue because inputs are readily available, and there are less regulatory concerns,” says Ghidirmic. With anaerobic digestion, operating systems are more challenging from a regulatory standpoint. Both the waste steam and the emissions that get produced are tightly regulated. But will we do more projects like this? Absolutely. As soon as this facility is firing on all pistons, we will look to duplicate them throughout California.”