Project at a Glance
Title: Emissions characteristics of cooling towers using reclaimed wastewater in California
Principal Investigator / Author(s): Rogozen, Michael B
Contractor: Science Applications, Inc.
Contract Number: A8-126-31
Research Program Area: Emissions Monitoring & Control
Topic Areas: Stationary Sources
Present and planned use of reclaimed municipal wastewater, industrial process water, and geothermal condensate as makeup to cooling towers have raised questions about the potential for atmospheric emissions of pathogenic microorganisms, organic compounds, heavy metals, and other wastewater constituents. In this study, the makeup and circulating water of six towers were sampled and analyzed for indicator bacteria and virus, volatile and nonvolatile organic compounds, metals, and other components of potential concern. Further water sampling and exhaust air emission tests were then conducted on four of the towers; for the microbiological emissions tests, a special isokinetic sampling device was developed.
Toxic trace metal emissions resulting from wastewater use were insignificant. A simple modeling exercise showed that ambient metal concentrations around a typical plant would at most be two to three orders of magnitude below levels of human health concern. However, there is a potential for significant chromium emissions if that metal is added to a tower's circulating water as a corrosion inhibitor.
Both water sampling and stack emission data are consistent with the premise that all volatile organic compounds present in the makeup water are emitted to the atmosphere, perhaps before thorough mixing with circulating water. Towers also act as conduits, emitting organic components of the inlet air. Some evidence for generation of halogenated methane compounds in the tower was found. Total net emissions of both volatile and nonvolatile organic compounds are very small compared to those of other stationary sources.
Cooling towers using municipal wastewater provide good environments for bacterial growth. Indicator and bacterial virus particles were found in the exhaust from one tower. Emissions of hydrogen sulfide and mercury from the geothermal tower tested were consistent with previous researchers' findings, while measured ammonia emissions were higher than expected. A survey of California cooling tower users identified 407 towers associated with manufacturing plants, and 56 towers used by electric utilities. The number of towers in the state is probably between 900 and 1,900. Almost half of the towers are used by wineries, fruit and vegetables canneries, and industrial organic chemical plants. The largest towers are those associated with power plants and the industrial gas, petroleum refining and organic fiber and synthetic rubber industries. Most cooling towers in California are in Southern California. The use of asbestos in construction and chromium in water treatment chemicals is declining. Technology for controlling drift emissions from cooling towers is well advanced. Considerable research in means to abate hydrogen sulfide emissions from geothermal cooling towers is underway. Finally, while techniques for removing volatile organics from wastewater are available, it is questionable whether the very low concentrations of these compounds in makeup water can or need to be removed.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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