Pure Energy Group brings AD to urban settings with new technology

By Katie Fletcher | September 03, 2014

Anaerobic digestion (AD) facilities are increasingly found processing food waste at large, centralized facilities outside of communities or processing manure on dairy and swine farms. Now AD can be found in a less remote, urban setting. Pure Energy Group LLC designs, builds and installs high-rate AD waste-to-energy systems for various commercial and industrial companies that produce organic waste streams with their day-to-day operations. The company’s first customer and first waste-to-energy system permitted and operational in an urban setting in the U.S. is Devil's Canyon Brewery, located in San Carlos, California.

The estimated $500,000 pilot demonstration system is in its final commissioning phase. The facility will have a 6,500 gallon tank with the capacity to process 2 million pounds of spent grains per year. The facility will also include a 30 kW combined-heat-and-power (CHP) unit, which will generate approximately 230,000 kWh of electricity per year. According to Brandon Julian, CEO of PEG, the facility will produce enough power to offset about 20 homes per year, the equivalent of eliminating around 50 cars off the road or 26,000 diesel gallon equivalents (DGE).

The San Francisco Bay area has some of the strictest air quality emission, siting and permitting standards in the nation, according to Julian. This point and brewery owner, Chris Garrett’s, interest in AD brought the project together to showcase the technology. “We thought that if we could get it permitted there, we could potentially be able to permit it anywhere,” Julian said.

Breweries are only one of the operations PEG has scouted out as benefitting from their technology—food and beverage processors, cheese and dairy producers, distillers and wineries, grocers, fast food chains, fruit and vegetable packagers, meat and poultry processors, hotels, restaurants, campuses, hospitals, prisons, military bases and any large-scale institutional cafeterias make the list. The reason these sites make good candidates for a PEG system is because of the technology’s modular capabilities. Each tank or reactor can operate independently of others in the system, making it easy to expand, contract or even relocate if necessary. Renewable energy is created on-site from the organic waste stream, reducing the processing waste burden by 50 percent or more, according to Julian.  

These systems utilize technology known as Induced Bed Reactor, which represents eight combined U.S. and global patents developed at Utah State University. “The IBR is unique among competing AD systems in that it provides a smaller footprint, higher solids loading capacity, shorter processing time and higher Btu value biogas,” Julian said.

Large, centralized facilities designed to produce large volumes of material over 20 days or more sometimes have costs and logistics associated with them that make it impracticable and unaffordable for smaller or geographically challenged applications. PEG has three sizes of expandable systems that can convert from 1,200 to 40,000 tons per year of organic waste into as much as 3 MW of cogenerated heat and power.

The IBR design cuts the 20-plus day processing time to around 5 days by separating the solid’s retention times (SRT) and the hydraulic retention times (HRT). SRT is a measure of how long organic solids will remain in the digester and HRT is the length of time it takes water to pass through the system. In most AD systems, the HRT and SRT are always equal, meaning that as new hydrated waste material is pumped into the system digested material is pushed out. The uncoupling of the HRT and SRT is key to PEG’s design. The water or liquid passively moves out of the tanks, while the solids and microbes are retained in the digester. The tanks can be one-fourth to one-fifth the size of other systems, because the water is not stored all at once, according to Julian. The system can process waste streams up to 15 percent solids, and has no mixing motors, only 1 RPM passive auger.

PEG is a fairly new company to the AD scene, but as AD technology picks up in U.S. the company hopes to take part by spreading knowledge and providing a technology option in the space. Devil’s Canyon Brewery is the first application of their technology, but they are currently speaking to others in the brewing industry, as well as some grocery and fast food chains.

Julian provides the example of an Oxnard, California, onion grower and processor as the type of commercial or industrial food processing company PEG hopes to work with in the future. Gills Onions has converted up to 300,000 pounds per day of onion peels and other processing leftovers into renewable energy and cattle feed.

PEG recently became a member of the American Biogas Council, and is also affiliated with the Biogas Association of California to track California and federal legislative policies for the renewable energy business, specifically AD.

Small to medium sized waste-to-energy facilities will continue to gain traction as AD awareness and legislative support increases, Julian believes. “Our unique technology is game-changing.”