Wastewater Treatment Table of Contents: (1.) Wastewater Treatment Basics (2.) Activity: Wastewater Treatment Plant Virtual Tour Wastewater Treatment Basics When you think about the variety of materials that enter the wastewater system from a typical home, the list is diverse and extensive: wastes from toilets; soap, detergents, and cleaning products from drains and washing machines; food items from garbage disposals - all along with large quantities of water. How is this material removed so that the water may be safely returned to the environment and, possibly, utilized again by other people downstream? The answer depends on where you live. If your home is not serviced by a public sewer system, your wastes are undoubtedly treated with a septic system. In this system, wastes are shuttled from the home into an underground storage tank. Sludge in the wastewater sinks to the bottom of the tank, oils float, and the water in between the two layers is dispersed into the surrounding soil through a network of pipes. The tank must be emptied on a regular basis, and the system properly maintained to ensure proper operation over time. If your home is serviced by a public sewer system, the process is roughly the same but on a larger scale. Wastewater leaves your residence and is piped to a wastewater treatment facility, where it is run through a series of steps to clean the water prior to release into a creek, river, lake, or ocean. The first steps are collectively known as preliminary treatment, in which large objects are removed from the water stream with screens and large particles settle out as the flow rate of the water is reduced. In primary treatment, the wastewater is funneled into large holding tanks (sedimentation tanks) and left undisturbed to allow heavy particles to sink out, and greases and oils to rise to the surface. The material on the top and bottom of the tanks is skimmed away, and the water proceeds on to secondary treatment. In this stage, bacteria are introduced and they begin consuming the small particles of organic matter that remain in the water. To facilitate this, oxygen is pumped into the water to allow the bacteria to feed continuously, as low oxygen levels cause feeding rates to slow. The water then flows into another set of settling tanks, where most of the bacteria settle out and are pumped back into the aeration tanks. The water is then chlorinated or exposed to ultraviolet light to kill any remaining bacteria. On average, this process removes over 90% of the impurities that were in the water as it entered the plant. Wastewater Treatment 1The material below describes the processes of wastewater treatment and septic tank operation in detail, and provides graphics to aid in understanding. Review this material before proceeding to the virtual tours below. Wastewater Treatment for Youngsters (Ages 8 to 80) Slide show of wastewater treatment process Metropolitan Council, St. Paul, MNhttp://www.metrocouncil.org/environment/Kids/01.htm What Can You Do to Protect Local Waterways? (PDF) (427 KB) Overview of wastewater treatment, suggestions for improving water quality United States Environmental Protection Agency http://www.epa.gov/npdes/pubs/centralized_brochure.pdf What Happens After the Flush (PDF) (2,377 KB) Wastewater treatment process in septic tanks and treatment plants United States Environmental Protection Agency, The Family Handyman Magazine http://www.epa.gov/npdes/pubs/what_happens_after_the_flush.pdf ListenTitle: Waste Water Snow Date: March 18, 1998 Summary: Noah talks with David Keith, the Superintendent of the Carrabassett Valley Sanitary District in Carrabassett Valley, Maine. He supervises the process used by the district that turns waste water into snow. He describes this process for Noah, detailing how it's used near the Sugarloaf USA ski resort in Maine. The process eliminates the need to build additional storage facilities to accommodate increased water use during tourist season. (http://www.npr.org). (3:59) Link: http://discover.npr.org/features/feature.jhtml?wfId=1036074 Requires RealPlayer Activity: Wastewater Treatment Plant Virtual Tours To truly appreciate the process of wastewater treatment and the magnitude of the job, one must visit a wastewater treatment plant in person. Seeing the processes firsthand is ideal but not always logistically practical, so we have provided two interactive, engaging “virtual tours” of wastewater treatment facilities for your use. In the Blue Plains Tour, you control the direction of the tour by selecting steps using the aerial view of the plant. Follow the numbered steps, clicking on the thumbnail images to enlarge and reading the associated text as you progress. In the West Point Treatment Plant Tour, click the “Continue” button when it appears to navigate through the plant. Be sure to examine both the Wastewater Treatment and Solids Treatment tours. Obtain a copy of the activity sheet for this exercise and answer the questions as you proceed through the tours. Wastewater Treatment 2Blue Plains Virtual TourInteractive tour of Advanced Wastewater Treatment Plant in Washington, DC District of Columbia Water and Sewer Authorityhttp://www.dcwasa.com/about/tour_flash.cfm Requires Macromedia Flash Player Tour Mirrored on ESA21site with permission West Point Treatment Plant TourInteractive tour of Wastewater Treatment Plant in King County, WA King County Wastewater Treatment Divisionhttp://dnr.metrokc.gov/wtd/wtd/westpt/Flash_splash1.htm Requires Macromedia Flash Player Tour Mirrored on ESA21site with permission Wastewater Treatment 3ESA 21: Environmental Science Activities Activity Sheet Wastewater Treatment Name: Instructor: Wastewater Treatment: Sequence of Events Based on the background material and provided virtual tours, place numbers next to each of the steps in the wastewater treatment process listed below to show the order in which they occur. Order in Process Step in Wastewater Treatment __________ Air is mixed vigorously into tanks with wastewater effluent __________ Chlorine or bleach is added to the wastewater effluent __________ Sand and grit are removed from the wastewater effluent __________ Bacteria are settled out of wastewater effluent __________ Oils and greases float to surface of wastewater effluent Anything you flush down the toilet will eventually show up at the wastewater treatment plant (albeit not always in its original