August 1, 2011 (Vol. 31, No. 14)

Editor’s Note

The search for alternative energy sources continues as an ongoing quest that is increasingly driven by widespread concerns over global warming. One area of focus has been the potential use of animal manure, simply because there is a lot of it. The goal is to anaerobically convert the animal waste to methane for various energy applications. Although not yet available on a commercial scale, research on poultry litter is taking place in virtually every nation around the world.

Work in the field goes back to the 1970s or even earlier. In our ongoing celebration of GEN’s 30th anniversary, we are publishing an article from the May/June 1982 issue. It discusses the development of one of the early anaerobic digestor systems for converting chicken manure into usable methane. The technology, which came from Taiwan, was being further advanced by scientists at North Carolina State University. Studies on the manure to methane conversion are still taking place at universities such as Virginia Polytechnic Institute and numerous companies including REM Engineering, Fibrowatt, Homeland Renewable Energy, and Alfagy.

—John Sterling, Editor in Chief

“As Seen in GEN—Flashback” Vol. 2, No. 3, May/June 1982

Chicken Waste to Methane: Anaerobic Trials at NC State

Dr. Jason Shih, a research scientist in the poultry science department at North Carolina State University, has developed an anaerobic digestor which economically converts chicken manure into usable methane (natural gas). Used in a commercial henhouse with 50,000 laying hens, the method could generate enough gas to heat 100 households, Dr. Shih estimates.

The unit is based on technology developed in Taiwan. Dr. Shih will deliver a paper on the system at an international seminar at Oxford University, Great Britain, this fall.

Several conferences this year have focused on newly developing anaerobic conversion techniques for producing methane from industrial and agricultural wastes. A series of new fermentations highlighted the Institute of Gas Technology’s recent conference on Energy from Biomass and Waste, in Lake Buena Vista, Fla. Corning Glass Works is reportedly building a pilot plant for sewage conversion, based on immobilized methanogenic bacteria in a reactor designed by Corning’s Dr. Ralph Messing.

Dr. Shih’s digestor was designed and constructed over the course of a four-year research project funded by the Department of Energy Appropriate Technology Program, the North Carolina Agricultural Research Service and the North Carolina Energy Institute.

The fermentation occurs in two steps. Chicken manure is flushed into an insulated plastic bag, around which hot water circulates, serving as a heat exchange. Under tightly controlled conditions, thermophilic bacteria, which occur naturally in the intestines of chickens, break down large carbon compounds into acetates and short-chain fatty acids. In a second anaerobic fermentation, several strains of methanogenic bacteria—Dr. Shih uses 10 to 18 different active strains—convert the smaller compounds into methane.

Pilot Study

The digestor was tested on a research farm near the university campus, outside Raleigh, in a 4,000-hen operation. A typical commercial egg-producing henhouse contains 50,000 layers and generates six to seven tons of manure daily. Dr. Shih told GEN his system could be scaled up to handle all of this waste, producing 10,000 cubic feet of methane per day, the equivalent of 10 million BTUs of energy. About 50 percent of this energy would have to be recycled back into the system, leaving 5 million BTUs to heat farm buildings, energy worth about $75 per day if optimally exploited, Dr. Shih estimated.

This type of digestor apparatus has been used in Dr. Shih’s native Taiwan to convert pig waste to methane for a number of years. The innovation in his system is the precision of control over fermentation conditions, Dr. Shih said.

Poultry science researchers, working with geneticists at NC State, are now attempting to characterize the bacteria involved. The university is in the process of establishing an interdisciplinary biotechnology program. One important goal, Dr. Shih said, is to identify the genes which govern the methane biosynthesis process. Preliminary studies suggest that several enzymes are involved, but no one knows which is key and virtually nothing is known about the regulator genes, Dr. Shih noted. An understanding of the genetic basis of methanogenesis might allow researchers to transfer genes for this function to the fermenting organisms involved in the initial step in the digestion, creating a one-step digestion and reducing time and expense for farmers.

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