Volatile Fatty Acid Emission During Composting of Swine Waste Amended With Sawdust as a Measure of Odor Potential

Abstract

Offensive odors which evolve during the decomposition of swine waste have resulted in complaints from neighbors in agricultural areas. This study chronologically monitored the emissions of volatile fatty acids (VFAs) during composting to quantify the release of malodorous compounds. Swine waste/sawdust mixtures and sawdust controls were placed in 208 liter reactor vessels and constantly aerated over a 21-day period. Acetic, propionic, isobutyric, butyric, isovaleric, and valeric acids were quantified in total collections of condensed water vapor and volatiles released from the vessels. Exit gasses were passed through water-cooled condensers, and condensate was collected every 12 hours. Composting conditions were shown to be adequate by measuring carbon to nitrogen ratios, pH, temperature, and moisture contents. The 21-day aerobic treatment decreased all VFAs in the swine waste mixtures by 61 to 100 percent, with a mean of 87 percent. Prior to peak gas volatilization, when the vessel contents attained peak composting temperatures, acetic acid was emitted in the greatest amounts, followed by butyric, propionic, valeric, isovaleric, and isobutyric acids in order of decreasing emissions. Following peak gas volatilization, butyric acid was released in the greatest amounts, followed by acetic, propionic, valeric, isovaleric, and isobutyric acids. The described condensation procedure was shown to be an effective method to quantify malodorous compounds emitted during the decomposition of livestock waste. In addition, aeration was an effective treatment to decrease VFAs and, therefore, odor potential resulting from their emissions.