ANHEUSER-BUSCH, owner of 12 large breweries in the U.S., has committed to reduce its greenhouse gas emissions 5 percent from 2005 levels by 2010. The company is well positioned to adopt new technologies and tap into employees’ creativity to reach its climate goals. Pollution prevention approaches have already led to recycling 99 percent of its solid waste. And Anheuser-Busch (A-B) is continuously improving its use of water and energy through innovations in technology and processes. At the intersection of waste, water and energy is anaerobic digestion (AD).
The primary driver behind adopting AD is wastewater treatment. A-B has been using AD since the late 1980s. The company completed work on it tenth system in the fall of 2008 and is working on designing the eleventh. Its Bio-Energy Recovery System (BERS) removes a large portion of the waste material in the leftover brewing process water and produces a more stable and easy-to-treat waste stream.
Figure 1 illustrates a typical process flow of the BERS system. Fine screens with 1 mm apertures are used to remove solids that could cause biomass to wash out of the AD process. Smaller solids like flocculated proteins from the grain, yeast and the filter media pass through these screens as well as any grain husk that squeezes through the 1 mm screen. These solids often are beneficially reused through land application. In some facilities, there is a clarifier to settle out the solids so they can be processed separately. The majority of large grain husks that make it down the drain are collected in the brewery for cattle feed.
The next step is the equalization tank where the wastewater is retained for 6 to 8 hours to prepare for anaerobic digestion. Variability in wastewater strength is reduced and the temperature and pH are balanced, as necessary. A-B typically uses high rate anaerobic digestion, where the hydraulic retention time is a matter of hours instead of days, as in some higher solids digesters. This approach is typical for industrial-strength, soluble flows. It optimizes the decomposition of wastes and the recovery of biogas to be used in the brewery process, and minimizes the amount of space it uses.
After digestion, treated wastewater flows to a postaeration tank where any residual CH4 is “stripped out” to reduce the Lower Explosive Limit (LEL) in the headspace above the wastewater. Some additional degradation takes place to further reduce BOD. Effluent can be discharged to a public treatment facility. At one brewery, the effluent is aerobically treated and discharged directly to a river. At another, the effluent is used to irrigate energy and forage crops.
ENERGY AND SOLIDS RECOVERY
Biogas is scrubbed and sent to boilers to be used for brewing process heat. The gas recovery accounts for 10 to15 percent of the total fuel needs at each brewery. Some facilities have heat recovery steam generators that can be used to cogenerate electricity.
At some breweries, the equalization tank at the beginning of the BERS systems is preceded by a clarifier, where solids are settled so that they can be processed separately from the wastewater stream. At facilities without the clarifier, solids pass through the system (due to the short retention time) and are used differently at different locations. One facility treats the solids aerobically. They are dewatered through a belt press and sold for land reclamation to grow willow trees, which are then used as a fuel (see sidebar). Two other facilities apply the solids as a liquid organic fertilizer. The solids, which are sprayable, are between 0.5 and 3 percent. Two additional facilities run their solids through a press and produce a fertilizer with a “soil-like” consistency. It is applied as a soil amendment for growing energy crops.
A-B manages the levels of anaerobic bacteria in its reactors by removing and selling granules of the bacteria to other industries for AD system start-ups or to plants that need to recover from a process upset. Systems that can utilize the granules include upward flow anaerobic sludge blanket, expanded granular sludge bed (EGSB) or internal circulation systems.
A-B adopted anaerobic digestion as a cost-effective way to treat its wastewater. The primary economic drivers are cost-avoidance for both wastewater treatment fees and fossil fuel purchases. “Our payback thresholds are normally between three and five years, which vary due to varying sewer and other site-specific costs,” says Greg Kellerman, A-B’s Director of Utilities and Wastewater Operations.
Breweries with AD facilities are located in Baldwinsville, New York (near Syracuse); Cartersville, Georgia (near Atlanta); Columbus, Ohio; Fairfield, California (between San Francisco and Sacramento); Houston; Jacksonville, Florida; Los Angeles; Merrimack, New Hampshire; Newark, New Jersey and St. Louis. The eleventh installation is planned for the brewery in Williamsburg, Virginia.
Best practices are communicated between the 10 facilities, with technical support and corporate initiatives coming out of A-B’s St. Louis headquarters. Benchmarking biogas flaring is a case in point. The amount of biogas that did not make it to the boiler was monitored as a key performance indicator. This indicator was reviewed weekly by corporate and the breweries at every level, leading to improved coordination between the wastewater treatment operators and boiler operators. A best practice recommendation around boiler control logic was developed. Biogas utilization has increased to over 99 percent, yielding economic and environmental benefits.
The company is in continuous collaboration with industry partners. To date, A-B has worked with three AD vendors: Biothane, Paques and Global Water Engineering. Its approach, says Kellerman, is for the vendor to supply the AD process — everything “in the box” — and for A-B to provide everything “out of the box” (e.g., loading data for design, utilities, power supply, treated flow to municipal plant, etc.). The suppliers provide a design/construction package for the “in the box” portion.
A-B also collaborates with a team of researchers originally based out of Washington University in St. Louis and now at Cornell University. One study, headed by Lars Angenent, of Cornell (formerly with Washington University) concluded that A-B could increase energy output an additional 8 percent (minimum) if the secondary residuals from the AD system were further digested over a longer period of time (e.g., 15-day hydraulic retention time). A-B is evaluating this technology, which has the potential to reduce total solids output and increase energy output.
Utilization of microbial fuel cells is also under discussion. “This is research that a PhD candidate at Washington University is doing to determine effectiveness of a microbial fuel cell as an alternative to an AD system converting organic waste to electrical energy rather than heat energy,” says Kellerman. “He has been working with a synthetic waste stream in the lab designed to imitate our wastewater, and plans to then bring his pilot unit onsite to test it on a slip stream of wastewater from our St. Louis brewery.”
REDUCING CARBON FOOTPRINT
Along with AD to treat brewery wastes, A-B has implemented a number of cost-effective measures to reduce its carbon footprint. These include brewing and powerhouse heat recovery systems, energy efficient lighting, improving refrigeration systems, and reducing the number of aeration units. The company also has a formal process where employees can submit ideas and they are then rewarded based on the level of energy and cost savings achieved.
As the nation evolves towards creating more local renewable energy sources, so too does Anheuser-Busch. They are in agreements with other entities to use local landfill gas and solar power, and are also busy looking into the use of wind, and other forms of biomass energy at their facilities.m
Katherine Gekas is a consultant based in Newton, Massachusetts, with 18 years of experience in the alternative energy industry.
Effluent For Energy Crops
AT both its Fort Collins, Colorado and Jacksonville, Florida breweries, Anheuser-Busch (A-B) is permitted to use effluent from the wastewater treatment system as irrigation water on energy and forage crops. Currently, both locations are growing forage crops, due to the lower price of energy. Last year, Fort Collins — because of higher demand (and prices) for energy crops and proximity to biofuel manufacturers — grew corn for ethanol, and canola and camelina for biodiesel.
In addition, A-B is in experimental stages of growing willow near its Baldwinsville (NY) facility. “The longer-term plan,” says Greg Kellerman, “could be to grow willows, chop them up, and use them as solid fuel in a steam generation facility.”