BioCycle September 2011, Vol. 52, No. 9, p. 29
Casebook profiles facilities in the Great Lakes region using anaerobic digestion systems to treat their high strength wastewaters.
FOOD industry facilities have been using anaerobic digestion (AD) to treat their own wastewater for decades. More recently, innovative business models and broadening options for biogas use are opening up new opportunities for making renewable energy and displacing fossil fuel use. The Energy Center of Wisconsin completed a series of 12 brief case studies of AD systems at food processing facilities in the Great Lakes region and published them in a casebook report released in March 2011 (Great Lakes Region Food Industry Biogas Casebook). This article includes observations gleaned from these cases, and provides some details on facilities profiled.
Company representatives and plant and environmental managers were asked why they chose AD for their primary treatment technology. Their answers build a strong case for AD as the most cost-effective treatment option for high strength wastewaters. The primary reason is due to energy inputs and outputs. For high strength waste streams, AD systems require much less energy to run than alternative aerobic treatment options due to the reduced need for pumping. Another benefit is digestion destroys rather than creates biosolids, meaning a smaller volume of solids require disposal. This translates into reduced vehicle fuel costs for transporting solids to their final destination (e.g., landspreading, landfill). Finally, the biogas can be substituted for, or blended with, natural gas for use on site, resulting in a lower volume of natural gas purchased and a reduced carbon footprint for the producer.
Facilities from several different sectors were analyzed, including brewing, cheese production, sugar refining, vegetable and oat processing, corn snacks production, meat processing and production of refrigerated dough products. A variety of AD system designs are being used to treat these wastewaters. Table 1 lists the companies with facilities profiled in the casebook, types of systems, and year they were installed.
Digester designs run from relatively simple to quite complex. On the simpler end of the scale are covered lagoons equipped with an impermeable cover and gas collection equipment. In northern climates like the Great Lakes region, covered lagoons will show increased effectiveness if heated, and when some form of mixing is used. Covered lagoons tend to be large and have relatively long hydraulic residence times (HRT).
The City of Monmouth, Illinois has an unheated and unmixed covered lagoon that acts as pretreatment for wastewater received from a local hog processing operation, prior to it entering the city’s main wastewater treatment plant. This system, despite being in northern Illinois, operates effectively without added heat because the wastewater they receive is already heated. It has a HRT of about seven days. Because they do not need heat for their digester, Monmouth is looking into electricity-only options for using their biogas. In contrast, Saputo Cheese in Waupun, Wisconsin, has a mixed, heated, covered lagoon used as the first stage of a multistage regimen for on-site treatment of its cheese production wastewater. This system has an HRT of five to six days. Biogas is scrubbed to remove hydrogen sulfide, then fed to a boiler to provide heat for the digester in colder months.
Complete mix and anaerobic contact process (ACP) digester designs work well with wastewaters that have high suspended solids. These systems are stirred tanks, and include solids recovery and return to the digester tank. Return of recovered solids helps maintain the population of microbes in the digester, allowing them to put more energy into digestion and less into reproduction.
JBS Green Bay, a beef producer in Green Bay, Wisconsin, has an ACP system that was installed in 1987 to pretreat production wastewater before sending it to the city wastewater treatment plant. The ACP system works well with its wastewater, which includes high amounts of fats, oils and grease. This digester has a HRT of about two days.
On the other end of the scale, one of the more complex systems is an up-flow anaerobic sludge blanket (UASB) digester. With a UASB, wastewater flows in through the bottom of the digester tank and passes through a “blanket” of granulated biota. This provides much opportunity for those organisms to have contact with the digestible materials and can provide very rapid rates of treatment. However, UASB systems require wastewater with low suspended solids for the blanket to function properly.
Both breweries examined in the casebook, Anheuser Busch in Baldwinsville, New York, and City Brewery in La Crosse, Wisconsin use UASB systems. The design hydraulic residence times for these systems is four to six hours in comparison to other designs that retain wastewater for days or even weeks.
Biogas generated by food industry digesters is typically used on site or flared – versus used directly in food production. In addition to heating the digester, biogas is used for drying residues, and providing facility or other process heat. In these roles, it allows producers to displace some natural gas purchases or to further lighten the load of residues requiring disposal elsewhere. JBS Green Bay reports saving as much as $10,000 to $13,000/week in avoided operating expenses by using biogas in a dedicated boiler.
Generating renewable electricity with biogas from these facilities is a newer application. Two of the profiled sites are using engine generator sets for combined heat and power (CHP): the Beaver Dam pretreatment facility in Beaver Dam, Wisconsin (a tour stop on November 2, 2011 as part of the BioCycle Energy Conference) and City Brewery. The Beaver Dam system is a UASB digester that was installed to pretreat cream cheese production wastewater (primarily acid whey) from the local Kraft Philadelphia Cream Cheese plant. The City of Beaver Dam was facing the prospect of a costly upgrade to the municipal treatment plant in order to meet discharge requirements. The Kraft plant is the city’s largest industrial customer and also a major employer.
After reviewing the options, Beaver Dam decided to install and own the digester to pretreat the wastewater from Kraft, allowing the city to avoid a more costly upgrade to its entire system. Kraft, which had been landspreading a portion of its whey, was able to avoid those costs and agreed to help pay for the digester through increased user fees – equivalent to what it had been paying for landspreading. The result was cost savings for both the city and Kraft, and the project was nearly cost-neutral for Beaver Dam residents. Biogas is used to run engine generator sets for CHP, electricity is sold to Alliant Energy and captured heat is used to heat influent and the digester itself.
The City Brewery UASB digesters have been working at that location since 1982 when the brewery was under different ownership. In recent years, an employee of Gundersen Lutheran, a local health care provider with strong sustainability goals, noticed the flaring biogas and the companies began talking about renewable energy options. (See “Brewery Digesters As Power Source For Healthcare Network,” December, 2009.) Gundersen offered to install a CHP generator set at City Brewery so the biogas could be utilized. The electricity is sold to Xcel Energy (offsetting what Gundersen purchases from Excel), and the captured heat is given to City Brewery for its use on site. This arrangement moved Gundersen further along in their goal to be energy independent by 2014 and resulted in a free renewable heat source for the brewery. It also saved the brewery the cost of buying new boilers if it wanted to use the biogas directly.
Anaerobic digesters have a decades-long track record of cost-effectively treating wastewater from food and other industries. New opportunities to put these seeming waste products to beneficial use are being uncovered, often to the benefit of all parties involved. Innovative partnerships such as those described in the Great Lakes Region Food Industry Biogas Casebook will continue to provide ways for food industry use of anaerobic digestion to expand and evolve.
Joe Kramer is a Senior Project Manager at the Energy Center of Wisconsin in Madison, and author of the Great Lakes Region Food Industry Biogas Casebook. A direct link to the Casebook and downloadable PDF is available at www.biocycle.net.
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Goat Cheese Producer Opts For AD
Montchevré—Betin, Inc., located in Belmont, Wisconsin, processes 50 million pounds of goat milk from 300 dairy farms throughout Wisconsin, Iowa, southern Minnesota and Missouri, producing 8 million pounds of goat cheese annually. To further its stated mission, “respect our environment by investing in renewable energy, reducing waste, and limiting our carbon footprint,” Montchevré partnered with Procorp Enterprises and Alliant Energy to install a 600,000 gallon complete mix digester to treat more than 25,000 lbs/day of COD. Montchevré had been hauling all of its wastewater – about 17 million gallons/year – off site for land application as the municipal wastewater treatment plant did not have the capacity to process the volume or the load. The hauling was getting increasingly difficult due to the volume and the concentration of chlorides in the wastewater.
The $3.5 million project was partly financed by a $550,000 low-interest loan from the State Energy Program (funded by the American Recovery and Reinvestment Act of 2009) and a $225,000 grant from the Wisconsin Focus on Energy—Renewable Energy program. Montchevré is one of the largest employers in Belmont, Wisconsin, with about 150 employees. The digester was dedicated in October 2010. Electricity produced by the 350 kWh engine is sold to Alliant Energy under a 3-year buy-back contract. Heat from the gas engine is used to warm the digester and adjacent building. – Vicki Lipinski, Procorp Enterprises
September 19, 2011 | General
Food Industry Digesters In The Great Lakes Region
BioCycle September 2011, Vol. 52, No. 9, p. 29