The TWTP is designed to treat the wide range in water quality provided by the city’s multiple source waters. The raw water intake area is designed to allow for isolation or blending of the raw water sources before the water is sent to the pretreatment processes that reduce turbidity caused by smaller particles and condition the water for filtration.
Flash mixing, the first component of the pretreatment stage, involves injection of chemicals via a nozzle within the raw water pipeline to destabilize particles suspended within the water. From there, the water moves to the flocculation stage, a mixing process with three zones of decreasing intensity, allowing the destabilized particles to combine and form larger particles to more easily settle to the bottom.
Next, the water moves into a sedimentation zone with stainless steel plate settlers designed to separate solids via gravity. The plate settlers are designed with an incline to increase the settling rate for optimal separation. After flowing through the plates, the water is then ready for ozone injection in an intermediate treatment stage.
The ozone injection process addresses MIB and geosmin, naturally occurring compounds that are the primary cause of taste and odor within the raw water supply. The ozone oxidizes these and other organics as well as pharmaceutical compounds and algal toxins. Additionally, ozone provides disinfection that reduces the formation of chlorinated disinfection byproducts, if they are present.
Following the ozone injection, the water moves to a biological filtration stage consisting of granular media filters without chlorination or other compounds that could deter growth of the microscopic beneficial bacteria. Functioning similarly to conventional granular media filters, biological filtration is an additional treatment stage that typically is used within wastewater treatment facilities as a way of removing remaining impurities.
The final treatment stage is a chlorine disinfection process to remove Giardia lamblia, a microorganism that can cause intestinal distress if present in larger amounts, as well as viruses. The entire treatment process produces drinking water that exceeds existing state and federal water quality standards.