With its ability to expand production restricted by BOD discharge limits, Vermont brewer directs its wastewater, spent yeast and grain waste to anaerobic digestion.
The Magic Hat Brewing Company, a craft brewery located in South Burlington, Vermont, produces 165,000 barrels of beer annually, including three year-round beers, four seasonal beers, four IPAs in a series and a variety of one-batch specialty beers. Magic Hat began brewing beer in 1994 in Burlington, and moved to its current location in 1997. The company purchased Pyramid Breweries in 2008. In 2010, Magic Hat was acquired by North American Breweries of Rochester, New York.
The brewing process yields 21 tons of grain waste, 30,000 gallons of waste-water and 10,000 gallons of spent yeast a day. The wastewater is discharged to the local treatment plant, for which the brewery was paying a significant surcharge. The spent yeast was trucked to farms and stored in manure pits before being land applied. The grain waste was used by farms as an animal feed supplement. The ability to expand brewing production was restricted by the BOD (biochemical oxygen demand) discharge limits set by the city’s wastewater treatment plant.
About four years ago, Magic Hat was approached by Purpose Energy, a Massachusetts digester company, with a solution to reduce the BOD in the brewery’s wastewater and generate energy. The two companies executed an agreement in March 2008. “Magic Hat Brewing Company contracted with Purpose Energy to lower our BOD costs and the environmental impacts to the city,” says John Patrick Williams, the brewery’s plant manager. “As we were rapidly growing to the brewery we have now, so was our effluent that needed to go somewhere.”
Now the effluent and spent grain is pumped to a 492,000-gallon digester in a parking lot behind the brewery. (Solids content ranges anywhere from 0.3% to 25%, depending on the feedstocks.) A combined heat and power (CHP) unit produces heat and electricity from the biogas. Magic Hat has the option of using biogas in its natural gas fired steam boiler that heats the water for the brewing process. It takes about 100 cubic feet of gas per minute to fire this boiler.
Purpose Energy built, owns and operates the digester and subleases the land behind the Magic Hat brewery on which it was built. To date, $2.7 million has been invested in the project, including loans from Pizzagalli (the project’s general contractor) and the Clean Energy Development Fund (a Vermont state agency), equity investors and a grant from Green Mountain Power.
The permitting process included obtaining pretreatment discharge permits from the State of Vermont and City of South Burlington, wastewater permits from the Department of Environmental Conservation and an Act 248 Certificate of Public Good from the state. Construction of the approximately 5,000-square-foot digester facility began in November 2009 and was completed in July 2010.
Discharge and Energy Savings
The CHP unit was custom-built by Martin Machinery of Latham, Missouri and has the capacity to produce 1.6 million BTUs/hour and 330 kW of electricity. The heat is used to control the temperature of the digester. All electricity produced is sold to Green Mountain Power (GMP), a local electric utility, at the market rate. GMP in turn sells electricity to Magic Hat. “Purpose Energy can’t sell the electricity directly to Magic Hat because we are not a regulated utility,” explains Eric Fitch of Purpose Energy.
The City of South Burlington limits the amount of BOD that the brewery can discharge to 600 pounds a day. Before the digester began operating, the brewery was paying $1/lb of BOD, or $600 a day. If the BOD level drops below a certain threshold, the City of South Burlington will treat the effluent as domestic waste, which does not have a surcharge. “Magic Hat wanted to not only lessen our impacts on the environment, but also lower BOD to the point where city fees are eliminated,” says Williams. “The digester has already made our BOD come down a couple of hundred pounds a day. As we grow, so does our BOD level, so we could see a couple thousand a month in savings at that point.” The digester also eliminates Magic Hat’s pull fees for the effluent to be trucked off site. But, notes Williams, “the real savings will be from the purchase of the biogas for the boiler.”
The digester system operated for five months before being shut down for improvements when the brewery closed for the holidays in December 2010. Diaphragm pumps were replaced with progressive cavity pumps because the diaphragm pumps had a tendency to clog. Another issue was the biogas piping. “The pipes were designed to carry natural gas, not biogas,” says Fitch. “The big problem was humidity. Biogas is super-saturated and when it hit the stainless steel pipes, it caused condensation. There were five gallons or more of condensate in the pipes each day.” To correct the problem, the pipes were insulated and automatic drips were installed to remove the condensation.
The digester came back on line in June 2011, and has been operating continuously since then. In late September 2011, dissolved air floatation (DAF) equipment manufactured by EcoLab in Dalton, Massachusetts was installed to remove phosphorus from the brewery’s wastewater before it is discharged. “Iron salt binds with the phosphorus and becomes a solid, iron phosphate, which is then removed from the wastewater,” explains Fitch. “The solid material can be used as a fertilizer.”
The digester currently generates 15 cubic feet of biogas per minute. With the new equipment, Fitch predicts that the digester will be producing 100 cubic feet of biogas per minute by the end of 2011, enough for almost all of Magic Hat’s natural gas needs.
Molly Farrell Tucker is a Contributing Editor to BioCycle.