July 14, 2010 | General

Pioneering Partnership Optimizes Power Production

BioCycle July 2010, Vol. 51, No. 7, p. 50
Central Contra Costa Solid Waste Authority successfully piloted collection and preparation of commercial food discards for anaerobic digestion by keeping the material clean at the source. A full-scale roll out is underway.
Stefanie Pruegel

LOCATED in the San Francisco East Bay, the Central Contra Costa Solid Waste Authority (CCCSWA) manages the franchise agreements to provide solid waste and recycling services for 132,000 residents and 3,000 commercial customers. The CCCSWA already offers its constituents an impressive array of waste reduction programs, but continually works to identify additional opportunities that can help the agency fulfill and exceed California’s ambitious landfill diversion requirements.
“It’s not an easy task because the low hanging fruit is gone,” comments CCCSWA Board Chair Victoria Smith. “Our challenge now is to expand existing diversion programs and design new ones, yet keep services cost-effective for our constituents.”
The agency’s most recent target is commercial food discards. Legislative pressure is mounting to reduce greenhouse gas emissions and increase diversion of food discards from landfills – particularly in California. “Available composting capacity in our area is very limited, and the facilities that do exist are a long drive from the communities that generate most of the material,” explains Paul Morsen, CCCSWA’s Executive Director. Currently, the composting operations closest to the agency’s service area are one- or two-hour drives away.
Looking for an alternative to commercial composting of food discards, Morsen took interest in the area’s wastewater treatment plant, located only a few miles away in Oakland. Owned and operated by the East Bay Municipal Utility District (EBMUD), the facility uses anaerobic digestion to treat municipal wastewater and generate power with three gas engines. About one-third of the digested solids are land applied on nonfood crops and about two-thirds are used for alternative daily cover.
Currently, EBMUD has significant excess digestion capacity. “When the facility came online in 1951, we had to treat the wastewater of dozens of food processing plants in the area, along with municipal sewage,” says Dave Williams, Director of Wastewater at EBMUD. “Today, with not a single cannery left in Oakland, we are operating at less than capacity and have the ability to utilize our excess capacity to the benefit of our ratepayers and the environment.”
However, that situation is changing rapidly. Since 2004, EBMUD has been experimenting with full-scale anaerobic digestion of food discards, and making the necessary modifications to the existing system. “We are processing 100 to 200 tons of food discards per week along with municipal wastewater solids, generating 90 percent of the electricity needed to run our facility,” calculates Williams. EBMUD is permitted to receive food waste under a Local Enforcement Authority “notification tier.”
Food discards are the perfect feedstock for anaerobic digestion because they degrade rapidly in the absence of oxygen. Typically rich in energy content, food discards produce on average 376 m3 of biogas per ton – over three times more than biosolids from municipal wastewater. Over the next year, EBMUD plans to increase the amount of food discards processed five times. This will produce enough energy not only to power the plant fully, but also put as much as 2 MW of electricity back into the grid.
The primary challenge is getting food discards that are pure enough so that they don’t clog EBMUD’s complex system of grinders, screens, pumps and other equipment necessary to prepare the material for the digester. “Food discards for anaerobic digestion have to be quite a bit cleaner than what a commercial composting facility can accept,” says Sophia Skoda, an engineer working with EBMUD’s food digestion program. Ideally, material entering the digester should be ground to particles two inches in diameter or smaller, and be free of plastics, utensils and other contaminants. To meet these requirements, most of the food discards currently collected from various sources for anaerobic digestion at the EBMUD plant have to undergo a labor-intensive and costly cleanup process before they are delivered to the facility.

In 2007, determined to avoid paying for a facility to clean up food discards to an acceptable quality, Morsen proposed to pilot a new approach. “Instead of expensive preprocessing before the food discards go to EBMUD, we were going to innovate a program that keeps the material clean at the source,” he explains. This meant that generators – such as restaurants, cafeterias, grocery stores and institutional kitchens – would have to separate the material from solid waste diligently before it was picked up and further processed, in order to meet EBMUD’s specifications.
“I know I was asking our Board for a lot of trust in the team, and to take risk,” Morsen recalls. “Most people in the industry thought it was simply impossible to deliver quality material without a processing facility.”
In addition to the Board’s support, Morsen needed a strong partnership between all players involved: the CCCSWA, their contracted waste hauler, Allied Waste Services of Contra Costa County, EBMUD, and most of all, the food discards generators themselves. Allied Waste was on board right away. “Like the Authority, I’m always interested in improving the ways we handle waste,” says Tim Argenti, Allied Waste of Contra Costa County’s General Manager. “Besides, the CCCSWA and my company have a track record of successful collaboration.”
In close cooperation with Allied and EBMUD, CCCSWA designed a pilot program for approximately 100 commercial food discards generators in the Authority’s service area. Participating businesses were recruited in several phases, starting in 2008. The goal was to get organics out of the garbage and into EBMUD’s digester, without an additional post-collection sorting process. The approach involved careful selection of participants, intensive training, a high level of quality control at the points of generation and collection, and an effective grinding operation. The program accepts pre and postconsumer food discards and some paper such as napkins and towels, and paper bags (fiber products that can easily be slurried). No corrugated or other heavy paper packaging is accepted.

Recruiting and setting up the pilot participants was a critical step. Environmental Science Associates (ESA), the consultant hired for this task, had ample experience providing technical assistance for commercial organics programs that collect materials for composting in San Francisco, Alameda and San Mateo counties. However, CCCSWA’s program presented new challenges. “The tolerance for contamination is extremely low,” recalls Judith Silver, ESA Senior Associate. “At first I was skeptical if businesses would comply with the program requirements.”
Working from a list of commercial businesses, her team first approached those with ample discards of organics, including restaurants, cafes, hotels, grocery stores, country clubs, an elementary school and assisted living facilities. Clustering businesses into routes and finding businesses with sufficient space to accommodate extra bins were also determining factors for the pilot. Many had wanted food discards collection for a while, knowing it was available in other Bay Area locations.
Once signed up, each business received prominently labeled indoor “Slim Jim”-style containers to collect the food discards, and 64-gallon wheeled carts or a 2-yard dumpster to consolidate the material for pick-up. Participation in the program was offered at no additional charge, and could possibly lower a business’ disposal costs, if – along with avid recycling of other materials – it resulted in reduced regular garbage service. This approach simplified the recruitment process. ESA staff worked with kitchen staff to modify the collection and flow of discards, and suggested sharing of food discards dumpsters by two or more restaurants, when space was a concern. When possible, ESA staff identified traditional recycling opportunities as well to further reduce disposal.
The on-site training visits were the most critical step. Scheduling was done to ensure that all staff – from executive chef to dishwasher – were engaged in the program. “Sometimes this meant scheduling trainings at odd times, or coming back to reach out to the late shift workers,” relates Silver. She also made sure that management was fully on board with the program and present at the training, and that a clear chain of command was established among staff.
“During everyday operations, it has to be clear whose job it is to empty the indoor containers into the carts, and you want somebody designated by management to enforce the program,” Silver asserts. During the training visits, the ESA team explained in detail which materials were accepted in the program. Recognizing the cultural diversity among workers – especially in the food service industry – all of ESA’s trainers were bilingual in Spanish. Bilingual Russian and Mandarin speakers were sent out as needed. In addition, durable, image-based signs were posted in strategic locations throughout the food handling areas.
A unique aspect of the training was a phased approach. At first only food discards generated by “back-of-house” staff (preconsumer) were captured. This helped keep the process simple and, therefore, the risk of contamination low. Once those practices were well established at a pilot business – usually after a month – the training began to include plate scrapings (postconsumer), involving additional staff like bussers and waiters.
“We are really happy with the program,” says Alex Robles, Director of Purchasing at Lafayette Park Hotel in Lafayette, who was among the first to sign up for the pilot. With two full-service restaurants, room service and a catering business, the hotel generates a significant amount of food discards – 1,000 to 1,500 pounds/week. “On top of that, we were able to reduce our regular garbage service to one pickup per week, saving us some $7,000 each year,” calculates Robles. At first he was concerned separating food discards was “just one more thing for our kitchen staff to do,” but he now reports that “everybody got on board and is doing a great job.”

Allied Waste collects the food discards from the pilot route one to three times a week, depending on each customer’s needs. Material pick-up is also an important part of quality control. Pilot participants are instructed to place the food discards in clear bags, so that Allied’s specially trained route drivers can assess the cleanliness of the material before collecting it. If the driver finds contamination that can’t easily be removed, the bag is left behind with a note to the customer. In addition, the driver immediately notifies Allied’s dispatch – transmitting a digital photo of the rejected food discards, if needed – so that a regular garbage pick-up can be arranged and the business contacted by a service representative. “We can’t afford to have food discards sitting on the street,” explains Argenti. “Of equal importance, we make sure we touch base with the business right away to get them back on track.”
An innovation Argenti contributed to the pilot was the custom-built collection truck used exclusively on the pilot route. Since both 64-gallon carts and two-yard dumpsters have to be serviced on the same route, none of the standard collection trucks were suitable. “It took several attempts, but we didn’t let that problem stop us,” he recalls. Working with an industrial machine and welding specialist, Allied essentially created a custom vehicle with forks to pick up dumpsters and a hydraulically driven, reinforced grabber to pick up the heavy food discards carts.
Ongoing monitoring and as-needed support have been essential to keeping the pilot businesses’ motivation up and maintaining the high quality of material collected. As with other aspects of the project, CCCSWA, Allied and EBMUD share this responsibility. The collaboration is paying off: Pilot participants have been overwhelmingly positive, and the quality of food discards remains high.

The next stop for the collected material is the grinding operation, temporarily located at Allied’s Newby Island Facility in Milpitas, California, about 40 miles south of CCCSWA’s jurisdiction. Because EBMUD’s processing system ahead of the digester is capable of removing plastic, CCCSWA was not required to separate the bags out prior to grinding.
A Morbark 900 tub grinder was selected for the program. Originally designed to process wood and plant debris, it has proven suitable to chop food discards into particles of two inches or less, as required for EBMUD’s digestion process. A previously chosen grinder model failed to produce the desired results and got jammed by the plastic bags containing the food discards. This put the partnership to a test, as all three parties – CCCSWA, Allied and EBMUD – had to agree to move forward with the pilot and pitch in financially for a new grinder. “It takes commitment to work through these issues,” acknowledges Skoda. “If any of us had said no, it would have been the end of the project.”
Bags of food discards are loaded into the grinder. Ground material is about 50 to 60 percent wet weight. It is conveyed directly from the grinder into a rolloff bin and trucked to the EBMUD facility in Oakland. The paddle finisher on EBMUD’s processing line removes the plastic film. (See “Green Energy From Food Wastes At Wastewater Treatment Plant,” January 2008 for a complete description of the EBMUD system.)
Currently the pilot delivers approximately 30 tons/week. EBMUD has been pleased with the quality of the material. “The staff loves the project,” says Joe Augustine, EBMUD shift supervisor, who is in charge of handling the food discards from CCCSWA. “We’re looking forward to seeing the program expand.”


Starting in fall 2010, the food discards collection program will be available to all commercial customers in CCCSWA’s jurisdiction that produce significant volumes of food discards. Like the pilot, participation will be on a voluntary basis and will not cost customers more than regular garbage service. “Our customers are already paying for the program because the cost is blended into the rates,” explains Morsen. “If a business can reduce garbage service as a result of its participation in our diversion programs, that’s an extra bonus.” Based on the number of restaurants and other major food discards producers in the jurisdiction, he expects the current count of participants to quadruple.
Allied is ready for the additional food discards accounts. Just in time for the full roll-out, the grinding will move from the Newby Island facility to Allied’s Contra Costa Transfer and Recovery Station (CCTRS) in Martinez, reducing the distance the material has to travel from approximately 40 miles, to just over 10 miles. Allied has applied to Contra Costa Environmental Health for a solid waste facility permit revision to allow for recovery and processing of up to 60 tons per day to occur at the CCTRS.
“The challenge now is to keep the quality as high as it was during the pilot phase,” says Argenti. He has hired a new full-time staff member, dedicated exclusively to assisting the new and existing food discards customers. CCCSWA, EBMUD and ESA staff will continue to outreach as well. “The partnership is dedicated to providing the same thorough training, monitoring and ongoing support as we have done so far,” adds Argenti.
The project appears to be a win for everybody involved. CCCSWA projects that the commercial food discards program will make a significant contribution to helping the jurisdiction reach, and even exceed, its mandated diversion goals. When transport is factored in, the cost per ton of the digestion ($45) is lower than that of commercial composting. Meanwhile, the limited capacity of local composting operations can be reserved to process mixed plant debris and food discards collected from residents – a feedstock currently not suitable for digestion.
Allied Waste is planning to replicate the new program with their other franchises in the area and beyond. Allied’s parent company, Republic Services, has signaled interest to promote the service nationwide.
At EBMUD’s wastewater treatment facility, the capacity to digest food discards is far from exhausted. “Even with our plan to process 200 tons each day, we will still have significant available capacity,” projects Skoda. Currently EBMUD collects $45/ton for food discards delivered to the facility, as well as revenue from the sale of any excess electricity generated. Other wastewater treatment facilities in California have similar potential. According to an EBMUD report, 137 wastewater treatment plants in the state have anaerobic digesters and an average of 15 to 30 percent excess capacity.
CCCSWA and its partners take pride in the fact that they have led the way in this emerging resource recovery area, but they’re not resting on their laurels. The Authority plans to continue to highlight the food discards diversion potential of a well-executed anaerobic digestion program, in the hope that many more communities will make the most of their organics.

Stefanie Pruegel is with Gigantic Idea Studio in Oakland, California. This article was written in collaboration with the Central Contra Costa Solid Waste Authority (, the East Bay Municipal Utility District ( and Allied Waste Services of Contra Costa County (

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