Waste Water Treatment Plant

HOW DO TREATMENT PLANTS PROTECT OUR WATER? Wastewater treatment plants: Remove solids, everything from rags and plastics to sand and smaller particles found in wastewater; Reduce organic matter and pollutants--naturally occurring helpful bacteria and other microorganisms consume organic matter in wastewater and are then separated from the water; and, Restore oxygen--the treatment process ensures that the water put back into our rivers or lakes has enough oxygen to support life.

WHERE DOES WASTEWATER COME FROM? Homes--human and household wastes from toilets, sinks, baths, dishwashers, garbage grinders, clothes washers and drains. Industry, Schools, and Business--chemical and other wastes from factories, food-service operations, school activities, hospitals, shopping centers, etc. Storm Water Infiltration and Inflow from Runoff and Groundwater--water that enters the sanitary sewer system during a storm, as well as groundwater that enters through cracks in sewers. The City of Columbia has one set of sewers for wastewater from homes and businesses (sanitary sewers) and a separate system for storm water runoff.

Sanitary Sewers They carry wastewater from homes and businesses to the raw wastewater pumping station at the treatment plant. The wastewater flows by gravity, rather than pressurized pipe flow, in the sanitary sewer pipes. Routine cleaning and closed circuit television inspection of sanitary sewer lines helps keep the sewer collection system in good shape.

Bar Screens They let water pass, but not trash (such as rags, diapers, etc.). There are two bar screens located inside the Raw Wastewater Pump Building. The trash is collected and properly disposed of. The screened wastewater is pumped to the Primary Settling Basins.

Primary Settling Basins They allow smaller particles to settle from wastewater by gravity. This primary wastewater flows out to the next stage of treatment. Scrapers collect the solid matter that remains (called "primary sludge"). A surface skimmer collects scum or grease floating on top of the basins.

Aeration Basins They supply large amounts of air to the mixture of primary wastewater and helpful bacteria and the other microorganisms that consume the harmful organic matter. The growth of the helpful microorganisms is speeded up by vigorous mixing of air (aeration) with the concentrated microorganisms (activated sludge) and the wastewater. Adequate oxygen is supplied to support the biological process at a very active level. The ratio of food (organic matter) to organisms to oxygen is continually monitored and adjusted to meet daily variations in the wastewater.

Final Settling Basins They allow the clumps of biological mass (the microorganisms) to settle from the water by gravity % of this mixture, called "activated sludge," is returned to the aeration basins to help maintain the needed amount of microorganisms. The remaining 5-10 % is pumped to the anaerobic digester (described later).

primary sludge The "primary sludge" from the Primary Settling Basins is pumped to the Hydrocyclone Grit Separator where it is spun, thereby separating the inorganic solids (grit) from the lighter weight organic solids. The grit is disposed of in the City landfill.

primary sludge The primary sludge continues on to the gravity Sludge Thickener where the solids are concentrated and pumped to the anaerobic digesters. The liquid overflow is returned to the pump station. Waste Activated Sludge from the Final Settling Basins is pumped to a Centrifuge (image at right) for further solids processing, then pumped to the anaerobic digesters.

Digesters Primary and activated sludges are anaerobically digested (decomposed by bacteria without the presence of air) in the two-stage digesters. Stabilized sludge has little odor and conforms to the EPA requirements to further reduce harmful microorganisms Digestion at 35ºC

Digesters Methane gas is produced by this anaerobic digestion and is used as fuel for an engine- generator providing 240 kW of electrical power used in the treatment process. Waste heat from the engine is recovered for heating the treatment plant buildings and to provide heating to improve the sludge digestion process and produce more gas.

subsurface injection application of the stabilized sludge (biosolids) onto both City-owned and private farmland by subsurface injection (plowing). The biosolids are utilized in an environmentally acceptable manner as a beneficial and valuable fertilizer and soil conditioner. The biosolids applied to all sites are monitored for nutrients, metals, other compounds and fecal coliform bacteria. Soil testing is performed at all sites prior to biosolids application.

The End Thanks for your attention