A look at anerobic digesters

With everyone going green these days, farmers with large herds of cattle or hogs are pondering the benefits of investing in an anaerobic digester, an industrial system that collects manure and treats it using a natural decomposition process, which in turn produces a biogas that can be used to power electricity generators and produce a material that improves the soil.
Increasing environmental pressures on waste disposal have increased the use of AD as a process for reducing waste volumes and generating useful byproducts. It is a fairly simple process that can greatly reduce the amount of organic matter that might otherwise end up in landfills or waste incinerators.
Essentially, a large box-like digester heats the manure while an auger mechanism breaks down the waste to produce methane. The excess solids are removed from the manure and used as bacteria-free bedding for livestock and weed-free fertilizer. Use of the digester also reduces the smell associated with handling cow manure. Several times a day, manure is added and digested by the equipment.
Leading most lists of advantages is the electricity generation. Other benefits touted to a lesser degree include:
– Quality bedding without composting
– Excess heat for farm use
– Odor reduction
– Increased fertilizer value
– Pathogen reduction
– Weed seed reduction
– Low maintenance
– Proven technology
– Low operation costs
– Fly and vector control
Like many dairy farmers before him, Doug Scheider of Scheidairy Farms in Freeport, Ill., liked what he read about the benefits of such a system. “Before I knew much about it, I thought that generating electricity would be the reason for doing it,” he says. “As we got more involved in it, I realized that wouldn’t be the case.”
Scheider did his homework and when he learned that he could get grants to fund 50 percent of the $1 million project, he decided to get on board. He received two grants: one from the Illinois Department of Commerce and Economic Opportunity and another through the Environmental Quality Incentives Program from the National Resources Conservation Services.
He retained Freeport Builders out of Lena, Ill., which had built Scheider’s 650-cow dairy set up in 2002, to construct the building to house the equipment and GHD, Inc., a Wisconsin-based company that specializes in farm-related environmental engineering, to design the anaerobic system.
Construction of the building, which was approximately 30×100 feet, was relatively simple, consisting of three parts: the generator building, which houses a diesel generator and the system controls that supply the power for the entire system; the separator room, which is home to auger equipment; and then the front part, which stores the resulting material that has been purified and partially dried as bedding material.
Since the building was in Illinois, the section containing the material that exits out of the processing tank was built within the guidelines of the Livestock Management Facilities Act. The room was three-sided and had to be built with concrete 4-foot walls. No wooden poles could be exposed; they all had to be encased in concrete. Steel picked up where the concrete walls left off and was covered with insulation to protect it from any fumes that would come off the system.
The two other rooms were built using post-frame construction and overhead doors. “It was a typical post-frame building with columns in the ground, treated plank at the bottom, liners, and insulation,” says Jim Peters of Freeport Builders. “We had to draw plans that had to go through the State of Illinois Environmental Protection Agency in order to qualify for the state grant. These things can’t be done in an unsupported manner.”
The construction challenge, according to Peters, was in trying to coordinate the project and build it alongside a 14-foot-deep pit where other workers were digging and working around the pipes that went in and out of the building. The building was completed in 2004 but start-up of the anaerobic digester was delayed until July 2005, when all the paperwork was finally in order.

Advantages
“It is a real win-win system. You’re getting rid of the manure, which there are problems disposing of, and creating useful dollars. The result is from a 600-plus cow dairy herd there is enough electricity generated to power about 80 homes, plus the electrical needs for his dairy operation, which is substantial,” says Peters.
Bedding The electricity may be substantial, but as an advantage, it does not top Scheider’s list of reasons to put in the system. “The biggest return is that it creates bedding for our cows. We were paying about $52,000 per year for bedding and that cost has gone up since. That cost is now eliminated because partially dried manure is a by-product of the system and we can sell what we don’t use to others,” he says.
Lower nutrient load The second biggest advantage, according to Scheider, is the fact that the system lowers the nutrient load of the manure. “We have a limited number of acres close to the dairy so when we go to apply the manure to the fields we can now apply all of those nutrients to the field that are close to the dairy. Before, we had the added expense of hauling the manure to further fields. The hauling expense was greater than the value of the nutrients we were hauling.”
Electricity Third on Scheider’s list of advantages is the creation of electricity. “That is a little disappointing to us because in other parts of the country people with these systems can get retail rate for their electricity directly,” Scheider says. “In some cases, the states have a green program where consumers can elect to purchase power from a green system. Here, Commonwealth Edison doesn’t have such a program, so return on electrical sales isn’t as great as it should be. If the system was built for the retail of electricity alone, it could never have been built.”
Scheider does use the electricity it generates to power the parasitic load of the digester and a small amount goes to the dairy, but that doesn’t offset the demand charge that is a constant whether Scheider used Commonwealth Edison’s power or not. “It would not have been cost effective to buy all the complicated switching systems to feed the dairy first. So what we produce is put out on Commonwealth Edison’s lines and we buy it back from them with the exception of what we use directly to power the parasitic load of the digester and what we send to the dairy.”
Improved health of the herd Finally, one of the advantages Scheider finds hardest to quantify is the improved health of the herd. The bedding by-product is very soft and Scheider believes it has reduced his cull rate, the percentage of cows that have to be sold for various reasons. “The sawdust we were using previously had some negative health issues for the cows and this material is definitely more cow-friendly.”

Disadvantages
Cost Topping the list of disadvantages is the disappointment with the electricity issue. The next big disadvantage, according to Scheider, is the cost of the system. “Without the availability of the grants, it would not be feasible to build the digester with the number of animals we have.”
Maintenance It is a system that has to be managed and while Scheider says most days it only requires about 20 minutes of maintenance, some days it requires far more. “It is a living system that needs to be monitored to make sure the environment is as it should be for the bugs to do their work.”

Return on investment
Despite some of its negatives, Scheider is happy he installed the system and the payback has been faster than anticipated. He financed nearly 100 percent of his share of the bill over 10 years. “It is returning at a rate faster than what we had projected and that is without considering any of the health issues,” he says. “When I try to do a rough calculation, I think the return may very well be half of the original time or five years.”
Another source of revenue is the money he is receiving selling carbon credits on the Chicago Climate Exchange and he is accumulating credits every day. The Chicago Climate Exchange is an exchange like the Chicago Board of Trade, but it sells energy credits for reducing various emissions. Companies that take steps to improve the environment without being asked can earn credits. The methane gas that is created from manure without a digester has been proven to be more harmful than carbon dioxide, so Scheider’s proactive move to install a digester without being forced to do so earns him credits based on the number of kilowatts of electricity he generates.

Do your homework
Scheider suggests that anyone looking to put in an anaerobic digester do their homework and find someone with proven experience in designing these systems. “There are fewer than 10 companies in the U.S. who do this. Some are foreign,” he says. “There are those selling systems that, quite frankly, have failed. Some have extreme parasitic loads. They purport to get more electricity out of the system, more kilowatts per cow and they haven’t lived up to that. I have visited two different systems on two different farms that were not working. One has shut down completely; the other one was running on propane gas.”
Scheider, whose system has been running well now for a year and a half, cautions against using a designer who wants to do something custom. “I think there is something to be said for those systems that aren’t the most complex because there is that much more to fail and shut the system down.”
Despite the obstacles, Scheider believes that anaerobic digesters will continue to be installed as more and more farmers and builders learn about the technology. “There is quite a bit of interest in it but the biggest challenge is the upfront cost. There are dairies with twice as many cows as we have and if they don’t have the grant opportunities we had, they can’t move forward with it.”
Nevertheless, the future looks good for the technology even as it competes with trendier agri-fuels like ethanol. “It won’t be pushed into the background,” Scheider predicts. “If anything, it will become placed more in the foreground. I know of one dairy in Indiana with four different sites. They installed digesters at each of the four dairies. Then, they were told by the local zoning people that if they were going to build another dairy, they would have to put in a methane digester there, too. There’s also a lot of interest in California for methane digesters.
“Our vendor, GHD, was installing two of these a year but they put in six in 2006. As livestock facilities become larger, there will be an even greater need for these systems.”

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