Coagulation
After the pre-treatment process, water enters the first of the primary treatment processes, known as Coagulation. In this process, chemicals known as Coagulants and Polymers are added to the water in a technique called rapid mixing. Rapid mixing ensures that the chemicals are evenly dispersed throughout the water. These chemicals neutralize naturally occurring forces that keep the small dirt particles apart and form a jelly like substance, known as micro-floc, which is very important as the water enters the next process called Flocculation.
Flocculation
The micro-floc formed in the coagulation process is very sticky and Flocculation is a process that gently mixes the water for a long period of time so that tiny micro-floc and small dirt particles collide to form larger particles called floc. Gentle mixing is accomplished by rotating large submerged paddle wheels in the flocculation basins. The water then exits the flocculation basins and enters the Sedimentation Basins.
Flocculation Basin
Sedimentation
The primary function of the Sedimentation basins is to prepare the water for effective filtration. Currents and eddies are minimized in sedimentation basins to allow the floc that was formed in the flocculation process to settle by gravity. The settled floc, referred to as sludge, is removed and sent to water recovery basins in a separate process. Only very small unsettled particles remain in the water after the Sedimentation process and the next step in the treatment process is Filtration.
Sedimentation Basin
Filtration
After the Coagulation, Flocculation, and Sedimentation processes are complete, the Filtration process is essential in further reducing the concentration of unsettled particles in the water. Filtration is the process of passing water through filter media for the purpose of removing undesirable constituents. The Chalk Bluff and Glendale facilities use rapid sand filters consisting of sand and anthracite coal to complete this task. The filters are capable of reducing turbidity levels to below TMWAs in house standard of no more than 0.1 Nephelometric Turbidity Units (NTUs), a measure of the suspended matter in water. The filters are very effective, but as a filter begins to clog up and no longer filters efficiently, it is necessary to remove that filter from service and backwash it. An automated backwashing system is used at Chalk Bluff and Glendale to successfully clean and ready a filter for further efficient and effective filtration. Turbidity removal is extremely important because particles in the water can interfere with the disinfection process.
