Using Biochar to Reduce Composting Odor

Large scale commercial composting facilities must deal with complaints of odor from surrounding communities and neighborhoods. The use of biochar, plant-based charcoal, is being studied as a potential compost additive and other studies have shown that biochar helps increase plant growth and yield in certain crops. This project, funded by the State of Washington Department of Ecology, was a preliminary study looking at the effects of varying percentages of biochar within compost piles on gaseous emissions of ammonia and volatile organic compounds that might cause odor. A total of twelve compost piles were made: 3 piles of each 0%, 2.5%, 5%, and 10% biochar. Piles were sampled six times over 31 days, collecting temperatures, ambient conditions, and air samples. Air samples were analyzed using gas chromatography mass spectrometry (GC-MS) to identify and quantitate compounds. There is great interest in sulfur and nitrogen containing compounds because they tend to have very low odor thresholds. Analysis indicates that piles containing biochar tend to have smaller emission rates of most sulfur and nitrogen compounds. On average, piles containing biochar emitted less than or equal to the amount of sulfur and nitrogen compounds that control piles did. This reduction most likely correlates to an overall reduction of odor in the compost.