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Professors study more efficient way to generate renewable energy from waste

Two New Mexico State University professors say they may have a partial solution to the tons of solid waste generated in the United States every year -- turn much of it into a renewable source of energy for electric power plants.

New Mexico State University civil engineering professor Zohrab Samani is developing a process for producing usable natural gas for electric power from solid waste. Samani is working with civil engineering professor Adrian Hanson on the project. (NMSU p..

in landfills, much solid waste lies undegraded for decades, but a process being developed by New Mexico State civil engineers Z.A. Samani and Adrian Hanson can digest even such tough substances as paper, generating high quality natural gas and leaving usable compost as a residue, Samani said.

Called a "two-phase bio-fermentation process," the method entails the use of two separate containers. Solid waste is mixed with cattle manure and placed in the first container. Water is applied through a sprinkler system, then circulated through the container while bacteria convert solids in the waste to volatile fatty acids. Once the desired concentration of acids has been leached into it, the water is piped into the second container, where a different type of bacteria turn the acids into methane, Semani said.

Converting the acids to methane takes less than a day and results in a gas with a 70 to 80 percent concentration of methane, with the remainder being carbon dioxide. The gas can be used locally or transported for use in gas-fired electric power plants and the solids eventually are reduced by the process to a usable compost, he added.

Many waste treatment facilities, including those in Albuquerque and Las Cruces, now extract methane from waste and use it to provide at least part of the fuel for their electric generators. But they use a single-phase anaerobic process that is less efficient and uses a slurry composed of 80 percent water. The two-phase process is cleaner, doesn't use as much water and produces a higher concentration of methane, Semani said.

In a 2001 feasibility study done for the city of Albuquerque's wastewater utility division, Hanson and Samani put a sample composed of 70 percent paper, 20 percent food scraps and 10 percent lawn clippings -- approximately the composition of Albuquerque's solid waste stream - through their fermentation process. They found they had reduced the volume of the sample by 80 percent and its weight by 90 percent, while at the same time generating 180 cubic meters of natural gas per ton of waste, Samani said.

Steven Glass, technical programs manager for Albuquerque's wastewater utility division, said the results were extremely encouraging. He said he hopes eventually to build a demonstration plant using the process near Albuquerque's landfill.

"We project that with the 31,000 tons of solid organic waste we collect each year, just from commercial sources and from our parks department, we could generate 93 billion BTUs of energy a year," he said.

Semani said he first learned of the two-phase process in 1995, when he worked as a summer intern for Samuel Ghosh, a University of Utah engineering professor who developed the process. The use of cow manure in the mixture is his and Hanson's innovation, he said.

Cellulase bacteria, which break down grass in the stomachs of cows and other ungulates, also break down paper and other materials in the methane production process. Use of the manure in a methane production process could provide a market for waste from dairies and feed lots.

Samani is looking into combining manure and other waste materials to produce energy. With a $50,000 grant from the U.S. Department of Agriculture and the Cooperative Extension Service, he is researching combining cow manure and cotton gin waste in the two-stage process.

"Manure and cotton gin waste work well together. The cotton gin waste has a good carbon content, but doesn't have a good nitrogen content or a source of bacteria. On the other hand, the potential energy value of manure is considerably lower than cotton gin waste. Combined, they result in an excellent biofuel source," he said.

Hanson noted that in July 2001 he and Semani were invited to present a paper on their process, co-authored with New Mexico State biology professor Geoffrey Smith and civil engineering graduate student Hui Wei Yu, at a symposium in Chicago co-sponsored by the Environmental Protection Agency and the Water Environmental Federation. They've been invited to discuss it again in May of this year at a joint EPA/WEF symposium in Washington, D.C., and in June at the annual meeting of the New Mexico Recycling Coalition.

Photo is available at http://ucommphoto.nmsu.edu/newsphoto/samani_zohrab.jpg.
CUTLINE: New Mexico State University civil engineering professor Zohrab Samani is developing a process for producing usable natural gas for electric power from solid waste. Samani is working with civil engineering professor Adrian Hanson on the project. (NMSU photo by Darren Phillips)

Jack King
Feb. 12, 2002