Philip D. Lusk
BioCycle November 2003, Vol. 44, No. 11, p. 55
AGRICULTURE in the U.S. produces more than 350 million tons of manure every year, and some farms have become so large that they cannot efficiently dispose of the enormous amounts of manure created. A recent USDA report states that only 18 percent of large hog farms and 23 percent of large dairy farms are applying manure on enough cropland to meet a nitrogen-based standard to protect water quality.
Current practices of disposing manure in giant open-air lagoons, and spraying liquefied manure over fields is an unacceptable option. A serious problem occurs when the crops cannot use all the nitrogen and phosphorus from the sprayfield application of untreated manures. Tremendous odor problems are often the result. Unassimilated nutrients are, in some cases, washed away into surface waters, and in other cases are leaching into groundwater, creating potential health hazards for wells and drinking water supplies because there is no place else for the nutrients to go.
There is no doubt that air pollution from untreated animal manure is associated with a number of health impacts in people living near farms. Such pollution also damages surrounding properties and lowers property values in the vicinity. Lastly, the main source of odors from livestock operations are the barns and manure storage pits. Regardless of farm size, what is needed is a manure treatment method that is both sustainable and cost-effective.
Earlier this month, an environmental advocacy group based in New York that was organized to “eliminate factory farming” issued a press release blasting anaerobic digesters as “not being an economical way to manage waste and produce energy. … They do nothing to reduce the amount of manure that must be dealt with.” According to the director of the Grace Factory Farm Project, William Weida, “it’s a red herring. Subsidizing anaerobic digesters diverts EQIP (Environmental Quality Incentives Program) funds to support a technology that will only encourage factory farms to continue producing unsustainable amounts of manure and pollution.”
However, to be a credible advocacy group, one’s entire message must always be based on facts. It is regrettable that in his rush to judgment, Dr. Weida makes several statements regarding anaerobic digestion technology that are simply in error. For example, Weida states that digesters have a high initial cost, a long payback period, a very high failure rate, and a relatively short life span. “This is why, even though digester technology is decades old, fewer than 300 digesters are in operation today in the U.S.”
SATISFACTION FROM INVESTMENT DECISIONS
Based on previous work in this area, the raw numbers are not the whole story. Farmers who have installed and continue to operate digesters are generally satisfied with their investment decisions. Many of these digesters have been operating in the 15 to 20 year range, which is not the short lifespan as alleged by Weida. Of course, farmers would have preferred to spend less money on the digesters’ design and installation, but are unsure of exactly how costs could have been cut. Most chose to install digesters for noneconomic reasons, primarily to control odors or contain excess nutrient runoff. Farmers have found that the returns provided from electricity and other coproduct sales from the digester, however limited, are preferable to the sunk cost of conventional disposal providing zero return on investment. Moreover, without the environmental benefits provided by digestion technology, some might have been forced out of livestock production. Turning a waste liability into a profit center that generates annual revenues can moderate the impacts of declining commodity prices and diversify farm income.
Why there are so few digesters operating in the U.S. today, compared to the more than 2,000 installed in Germany during the past 15 years, the 37,000 or so installed in Nepal, and the millions installed in China and India, is a complex issue of economics and public policy that is beyond the scope of this narrative. However, these referenced countries have made it an imperative that digesters be installed as shown by the respective market penetration levels.
One of the most egregious of Weida’s errors is the following statement: “Further, unless high-cost ammonia strippers are employed, digesters emit ammonia at rates that exceed industrial pollution standards, thereby increasing the amount of greenhouse gases in the atmosphere by a significant degree, as a recent study by the National Academy of Sciences confirms.”
This statement contains at least three errors. The first fact is that the use of an ammonia stripper will only remove the nitrogen contained in the liquid portion of a digester and, unless further controlled, will release ammonia directly into the atmosphere. From a nitrogen conservation perspective, this is the worst possible case. The second statement in error is that digesters emit ammonia at rates that exceed industrial pollution standards. By its inherent nature in being a closed vessel, it is impossible for a digester to emit ammonia or any other gaseous effluent. Therefore, how can a closed vessel exceed industrial pollution standards of a noncriteria pollutant? Lastly, ammonia is not now nor will it ever be considered a “greenhouse gas.” Only through the wise use of digesters will a farm be able to control ammonia emissions, which will become an issue of greater importance in the near future to all livestock operations.
CONVERSION OF AGRICULTURAL WASTES
The conversion of agricultural wastes, animal manures in particular, into a renewable energy resource has been the focus of intensive research for more than two decades. Much has been learned about how manure can be used as an energy and nutrient source. More cost-effective and easily managed manure management techniques are still needed, especially
for smaller farms, to encourage the farmer’s use of animal waste for energy and nutrients.
Only following treatment can excess nutrients be removed from animal manures. There are three basic processes by which nutrients can be removed from filtrate – biological, chemical, and physical. In addition to reducing organic solids, biological treatment processes such as digestion use microorganisms to also remove nitrogen and phosphorus.
KEY ROLE OF ELECTRIC UTILITIES
At the Anaerobic Digester Technology Applications in Animal Agriculture Summit, a major conclusion drawn from the event is that interface to the electric utilities is the limiting factor to the economic deployment of on-farm anaerobic digesters. Unless the electric utilities come to the table and offer a just rate structure to the entire renewable energy industry, and this includes wind and solar as well, there will never be an economical way to produce energy from non-traditional resources.
Not only will farmers benefit monetarily, the increased use of digesters will also help mitigate animal manure’s contribution to air, surface, and groundwater pollution. There are additional indirect benefits for sustainable rural economic development from the implicit multiplier effect resulting from the direct jobs that can be created by providing, installing, and maintaining the digester system equipment. The implicit multiplier effect of integrated agricultural production and processing can be two to three times traditional production-only values.
In summary, the necessary treatment of animal manures can only be done using aerobic or anaerobic processes. While they should never be considered a panacea to the issue of manure management, anaerobic digesters are a real solution that can be deployed today on a cost-effective basis. If spent on performance-based digestion systems, the use of the EQIP funds can become a key element in solving the environmental problems posed by the industrial quantities of manure. EQIP funds should be used to provide a balanced incentive to increase the use of well-designed anaerobic digesters, which is at the heart of EQIP’s purpose as a method to repair environmental damage.
Phil Lusk is head of Resource Development Associates in Pierre, South Dakota – who, in his words, is “an economist who spends much time pondering the costs and benefits of anaerobic digestion.”
November 1, 2003 | General
ANAEROBIC DIGESTERS IN MANURE MANAGEMENT
Philip D. Lusk