In LandfillsLandfills are a complex system of naturally occurring chemical and biological reactions that break the waste materials down into its basic components. The base odors are the result of these biological and chemical processes taking place in an environment of moisture, heat and pressure. In an anaerobic (low oxygen) reaction phase the biological processes release methane and carbon dioxide gases that slowly make their way to the surface of the landfill. Attached to the methane molecules, as they rise to the surface, are other odorous substances resulting from materials with varying states of decay, which can compound the odor problems. Hydrogen sulfide, mercaptans and ammonia are just some of the other odorous and toxic gases that are produced in a landfill. The most common and easily identifiable odor problems in a landfill occur at or near the surface. Materials that are moist and wet can emit substantial amounts of odors as the moisture evaporates.
In Transfer Stations & Recycling CentersOdors found in transfer stations largely come from the breakdown of the waste in its early stages of decomposition. The odor molecules are escaping from the waste on the floor and in areas where the waste is being loaded onto rail cars or on waste trucks prior to transport to the landfill.
In Contaminated SedimentsMany contaminated sediments have odors that are the result of the chemistry which has contaminated the sediments. Hydrocarbon contaminated waste may have odors of sulfur. Coal processing operations have, over the years, released lots of coal tar, pesticides, PCBTâ€™s and dense nonaqueous phase liquids which often carry a uniquely bad odor. Sediments contaminated with creosote, naphthalene, and similar hydrocarbons also have bad odors. When removing contaminated sediments, regulations may require focused ambient-air monitoring, field observations of odors at regular intervals, and focused odor testing. Odor testing can also be performed in accordance with ASTM Method E 679 (modified) due to the subjectivity of odor detection and the difficulty in quantifying odors using standard air monitoring equipment. This method utilizes a trained odor panel to evaluate air samples for odor character and average intensity.
In Wastewater Treatment Plants
A wide variety of odor-producing substances are found in municipal and industrial wastewater treatment and collection systems, usually as the result of biological activity. Most odors arise from the anaerobic (low oxygen) decomposition of organic matter containing sulfur or nitrogen. Gas produced from domestic wastewater is sometimes called sewer gas and commonly includes hydrogen sulfide, methane, ammonia, and carbon dioxide. Sewer gas may also contain build-up of wastewater solids can result in the formation of scum or sludge which can further inhibit a sufficient inward diffusion of oxygen, again resulting in anaerobic conditions which favor the production of these odor-causing chemicals.