Have you ever wondered where the water goes after you flush?
In College Station, that wastewater will go to either the Carter's Creek Wastewater Treatment Plant, or the Lick Creek Wastewater Treatment Plant, depending on where you live. Each of these award-winning plants is designed to remove organic matter, trash, and disease-causing microorganisms so that the effluent, or treated wastewater, may be safely discharged into the environment. All water leaving College Station's wastewater treatment facilities must meet regulatory limits set by the Texas Commission on Environmental Quality (TCEQ) and Environmental Protection Agency (EPA) in the permits for each wastewater treatment facility. Wastewater in College Station is treated using screening and grit removal (to remove grease, grit, and large objects), aeration, clarification, biosolids digestion and dewatering, and disinfection.
PRIMARY TREATMENT
The wastewater treatment process begins at the Headworks, where floating material, oils and greases, sand and silt and trash are removed from the raw wastewater for disposal at the landfill. Screw lift pumps at the Headworks lift raw wastewater up a steep slope so that the wastewater travels through the rest of treatment process by gravity flow.
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SECONDARY TREATMENT
College Station uses biological processes rather than harsh chemicals to remove organic matter present in the wastewater before discharging the clean effluent into the receiving water body. Through an "activated sludge" process, bacteria, protozoa, and macro invertebrates feed on the pathogenic organisms and organic matter entering from raw sewage eventually cleaning the colloidal matter from the raw wastewater.
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SOLIDS HANDLING AND DISPOSAL
Biosolids are a by-product of the wastewater treatment process. During wastewater treatment, solids are removed from the aeration basins and clarifiers. Some of these solids are then treated in a process known as Autothermal Thermophilic Aerobic Digestion (ATAD), which uses very high temperatures to kill any disease-causing organisms that may be present in the solids. The ATAD process results in what is known as "Class A" biosolids. The biosolids are then de-watered in a centrifuge, a process that works similar to the "spin" cycle in a washing machine.
In some areas, biosolids are composted with wood chips and yard waste, or sold as commercial fertilizer. Biosolids produced at College Station's wastewater treatment plants are applied to agricultural land in College Station. Using biosolids for land application benefits both the City of College Station and the landowner: the City of College Station has a reliable end-use for the biosolids and the landowner gets a valuable soil amendment.
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DISINFECTION
The final step before treated wastewater can be released back to the environment is disinfection. Disinfection is needed to inactivate harmful microorganisms and protect both public health and the healt of the receiving stream.
The decision about which disinfectant to use must take into account several factors, including treatment goals, regulatory requirements and cost. Many wastewater treatment plants still use chlorine for disinfection, followed up with additional treatment to remove the chlorine before the effluent is returned to the environment. College Station's wastewater is disinfected with ultraviolet (UV) light, because we have found that UV light treatment is safer and less expensive for our operators to use than chlorine. The UV light disrupts the genetic material of disease-causing organisms, preventing the organisms from reproducing and spreading disease. Wastewater effluent disinfected with UV light can be safely discharged directly into the receiving stream with no further treatment.
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WORKING WITH NATURE TO PRODUCE CLEAN WATER
College Station's Wastewater Treatment plants utilize biological processes to remove organic matter present in the sewage before discharge into the receiving water body. Through careful analysis of microorganisms, proper aeration, and meticulous balance of solids (food and microbes), what was once a potentially dangerous waste product, raw sewage, has been transformed into clean water and a valuable soil amendment.
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