January 16, 2007
AMES, Iowa - Researchers in Iowa State University's College of Agriculture continue to look for ways to reduce odor and gas emissions from livestock and poultry operations. A manure additive is one avenue being considered. A team of agricultural engineers and chemists recently conducted laboratory studies that found adding zeolites to poultry manure reduces odors and the release of ammonia and some volatile organic compounds (VOCs). Zeolites, which are minerals that have a micro-porous structure, can be mined from abundant low-cost deposits. The Iowa State researchers used a novel sampling and sample preparation technique to evaluate the effectiveness of zeolite as a manure additive. In this approach, researchers simultaneously analyze gases and the resulting odor. Once compounds are isolated, an instrument is used that can identify different substances within a test sample. The instrument also is equipped with special software and a sniff port, used by panelists who have been trained to evaluate odors associated with each compound. "The software records odors caused by each chemical and records information about the odor intensity associated with each compound," said Jacek Koziel, assistant professor in Iowa State's agricultural and biosystems engineering department, who conducted the study. "The analysis allows olfactory responses from panelists to be measured compound-by-compound at the same time chemical compositions are evaluated." In two trials, zeolite was topically applied on fresh laying-hen manure at three rates, with a top rate of 10 percent. In a third trial, zeolite was applied at a 5 percent rate with each addition of fresh manure into the storage vessel simulating periodic 'layered' application of zeolite. More than 90 volatile compounds were identified as emitted from the manure. Among those, only a few chemical groups contributed to the offensive odor. Topical application of zeolite showed the potential for reducing emissions of several compounds from manure storage, with the effectiveness of treatment proportional to the zeolite application rate. The 10 percent zeolite application rate was the most effective. "One sniff is better than a thousand words," said Koziel. "With this simultaneous chemical-olfactometry analysis, we are finding links between specific chemicals released by manure and the overall offensive odor. That makes it possible to focus odor mitigation on compounds that really matter." The study was funded by the Midwest Poultry Research Program and a Special USDA-CSREES Air Quality Research Grant. Results from the study are published in the January-February 2007 issue of the Journal of Environmental Quality.