BioCycle January 2009, Vol. 50, No. 1, p. 42
A three-fold increase in sewer fees led Sierra Nevada Brewery to install an upflow anaerobic sludge blanket digester. In 2005, fuel cells powered by biogas were brought on line.
AS breweries experience increased energy and waste treatment costs, they are turning to solutions that allow them to reduce expenses and simultaneously improve the environment. One of these solutions, among others, is anaerobic treatment of the wastewater from the brewing process.
The Sierra Nevada Brewery, in Chico, California (pop. 80,000), built its current brewery in 1989. However, it wasn’t until 2002 that the brewery set out to construct an ecofriendly wastewater treatment system on site. Sierra Nevada’s production had expanded significantly (and is currently at 750,000 barrels/year), leading the local wastewater treatment plant to more than triple the brewery’s rates from about $1.80/ccf to more than $6.00/ccf.
While its motives didn’t start out with the environment, but with economics, the brewery became determined to close the loop on its production system and become one of the most environmentally friendly breweries in the U.S. The goal was to ensure that all “waste” products were turned into resources, and all resources were being used efficiently. Having looked at a number of treatment systems, Sierra Nevada decided to go with a combination of anaerobic and aerobic treatment for brewery process effulent water.
Anaerobic treatment – biological treatment of wastewater through anaerobic microbes – results in reduction of COD and total solids and the production of biogas and reduced sludge disposal costs. Anaerobic treatment has been increasing popular in the food processing beverage industry, where COD sewer charges can be high, and organics hard to remove from the waste stream.
The wastewater treatment train at Sierra Nevada starts with a rotary screen that removes the larger solids. These solids go to a local composter. The influent flows to an equalization tank, where it is adjusted for pH and temperature. Next, the influent is pumped into the upflow anaerobic sludge blanket (UASB) digester supplied by Biothane, where it mixes with the anaerobic microbes in the tank. Sierra Nevada installed a 125,000 gallon tank.
The UASB technology is often used in industrial applications because of its small footprint and quick retention time for the amount of COD and total suspended solids (TSS) reduced. One of the reasons the process is faster is that the granules in the system provide increased surface area for the microbes to live on. Retention time in the digester is 10 to 12 hours. The digester operates at mesophilic temperatures. The average COD of the influent is 4,200 going in, and about 400 after digestion; TSS is 765 going in and is reduced to about 730.
The effluent is pumped out the top of the tank; biogas is piped out the top to a biogas clean-up skid. An aerobic digester, using a fine bubble diffuser, aerates the remaining effluent to further reduce COD and TSS before it is discharged to a clarifier, which settles out any solids still remaining in the effluent. These solids are applied on the hops fields adjacent to the plant. The treated effluent is still discharged to Chico’s wastewater treatment plant, but Sierra Nevada just received the go ahead to irrigate its 9 acres of hops fields with the treated water starting in the spring of 2009. This also helps the company close the loop on its manufacturing process and reduces water demand for the local watershed.
Operation and maintenance of the wastewater treatment process are handled internally by one full-time and two part-time staff. They take care of operations of all parts of the system, including lab testing.
Ken Grossman, owner of Sierra Nevada, always intended to use the biogas as a fuel and not flare it, as was done when the digester first began operating. After initial research and a few meetings with the local school community, Grossman decided that fuel cells were the way to go due to their high efficiency and ultraclean emissions. In 2005, Sierra Nevada installed four Fuel Cell Energy 250-kW units. Those were upgraded to four 300-kW fuel cells in 2006.
The biogas clean-up skid ahead of the fuel cells has an activated carbon filter and a sulfatreat filtration vessel that remove hydrogen sulfide, water vapor, carbon dioxide and siloxanes. After cleaning, the biogas is roughly 75 to 78 percent methane.
Sierra Nevada received a total of about $3.4 million in funds for the fuel cell installation from two different sources – the Department of Defense and Pacific Gas and Electric Co. The project also receives a tax credit as part of the Federal Investment Tax Credit program. Combined with the 1.9 MW of solar electricity arrays installed on the Sierra Nevada campus, the brewery produces enough electrical power to provide 100 percent of its power needed during peak times of the year and about 80 to 85 percent of the power needed all year long.
The bulk of the cleaned biogas goes to the fuel cells, with the remainder going to the brewery’s boilers. While a typical fuel cell installation runs on 100 percent of a certain kind of gas, e.g., natural gas or biogas from a landfill or digester, Sierra Nevada has been blending two different gases – the cleaned biogas and natural gas. “This has posed a large learning curve for our particular installation,” says Cheri Chastain, Sierra Nevada’s Sustainability Coordinator. “The problem with the biogas for us is not its quality or the ability of the fuel cells to accept it, it is the blending and availability of the biogas that has posed some problems that require creative solutions. We have been, in a sense, a guinea pig for the process and both Sierra Nevada and Fuel Cell Energy have learned a lot with our installation. We think we have some solutions to improve the utilization of biogas into the fuel cells.”
The biogas utilization system is being optimized for maximum usage. One adjustment is adding a small volume of gas storage. The production of biogas fluctuates with the beer production, and in order to even out the fluctuations, a small amount of gas storage is needed.
One cited benefit of the fuel cell technology is its low emissions, which is a factor as states adopt more stringent air quality rules. For example, California’s Air Resources Board will phase in lower emissions requirements (Table 1) for distributed generation in 2013. These standards apply to reciprocating gas engines and other on-site generators used by many anaerobic digester and landfill gas recovery installations to supply electricity.
“As cleaner technologies are needed in ‘nonattainment’ areas, more and more biogas generators are going to be looking at using fuel cells as a way to meet those requirements,” says Joe Heinzmann, Regional Director of Business Development for Fuel Cell Energy. Nonattainment areas are regions where the air pollution levels exceed U.S. EPA standards. Chastain explains that the basic reason fuel cells can meet nonattainment area requirements is that nothing is being combusted, therefore there are no NOx (nitrous oxide) or SOx (sulfur oxide) emissions. “The only emission from fuel cells is CO2 and water – very clean compared to other forms of electricity generation,” she says.
Sierra Nevada has an operating agreement with Fuel Cell Energy for full maintenance of the system. This includes remote monitoring, dispatches of field technicians and full replacement of fuel cells every 45,000 hours of run-time. The current run-time of the system is about 92 percent. Sierra Nevada staff are responsible for maintaining the heat recovery units attached to each cell. These units capture the fuel cell exhaust (~700°F) and run it through a heat exchanger to produce steam that is sent back into the plant for reuse. The heat recovery units add roughly 15 percent efficiency to the installation.
Several engineering and equipment providers worked with Sierra Nevada on this project: Biothane, an engineering and construction firm with proprietary treatment technologies, designed and partially constructed the wastewater treatment system; Symbiont, an engineering firm unaffiliated with a specific technology, assisted Sierra Nevada with a biogas utilization study, preliminary design of the gas clean-up system and the bubble diffuser system upgrade; Fuel Cell Energy provided the fuel cells for the 1.2-MW system; and General Electric provided the electrical switchgear for the grid interconnection.
Both Dr. Daniel Zitomer of Marquette University, who tracks wastewater treatment systems for food processors, and Jeff VanVoorhis, Project Manager at Symbiont, point out that breweries have been using anaerobic treatment as a cost-effective pretreatment measure for years now, as it is very effective at reducing high municipal treatment charges, and creating renewable energy that can be used on site. With incentives to generate more renewable energy on site and energy costs rising over the long-term, much of that biogas that was once flared is now being viewed as more of a resource than ever before.
Katherine Gekas (firstname.lastname@example.org) is founder of Neighborhood Power, LLC, founded in 2004 to provide services to site owners interested in investigating anaerobic digestion as an option for creating renewable natural gas. Visit www.neighborhoodpower.com for details.