Wastewater is made up of human and household wastes from toilets, sinks, baths and drains. It also consists of chemicals and other wastes from factories, food-service operations, airports, shopping centers and many other businesses. The wastewater generated in Bowling Green and parts of Warren County flows to the wastewater treatment plant via sewer lines. Bar screens let the water pass, but not trash. The trash is collected and discarded. A grit chamber (large tank) slows down the flow of water. This allows sand, grit and other heavy solids to settle to the bottom to be removed. The sand and grit is removed so that it does not damage pumps and other equipment. A primary sedimentation tank lets smaller particles settle. Scrapers or other devices collect the solid matter that remains (primary sludge) plus scum or grease floating on top of the tank. Secondary treatment completes the cleaning process so that a minimum of 85 –90% of the pollutants are removed. An activated biofilter provides a means of aeration to a mixture of wastewater, bacteria and other microorganisms. Oxygen in the air speeds the growth of helpful microorganisms, which consume harmful organic matter in the wastewater. A secondary sedimentation tank allows the microorganisms and solid wastes to form clumps and settle. Some of this mixture, called “activated sludge,” can be mixed with air again and reused in the biofilter. Any activated sludge that is not used is wasted back to the beginning of the process to be mixed with the primary sludge. Primary sludge is then de-watered and sent to the landfill. Chlorine, a disinfectant, is added to the wastewater before it leaves the treatment plant to kill disease-causing organisms in the water. Before the disinfected water is discharged, it must be treated to remove the chlorine so that fish and other organisms in the receiving stream are not adversely affected. After treatment, the water is returned to the Barren River.