The Wastewater Treatment Process

The wastewater starts its journey through the treatment process from the moment it is flushed or poured down a drain. The wastewater goes from the structure by way of a lateral line (the property of the owner) to the collector line where it becomes the responsibility of the city. The wastewater proceeds to a trunk line and then to a main line. On its route to the treatment plant it is moved by gravity most of the way, however, at some point in its journey it may go through a lift station to gain height so that gravity can once again take effect.

The wastewater must maintain a speed of at least one and one half feet of travel per second to keep solid materials in suspension. If the wastewater slows below this point, the suspended solid material will settle out and can become septic. The collections section is responsible for maintaining the proper flow rate by removing roots, rocks or any other obstructions that will impede the flow of wastewater to the treatment plant. During the travel to the treatment plant, the raw sewage is aerated and the solid materials are reduced in size physically.

The raw sewage reaches the treatment plant through the thirty inch main line. The raw sewage must pass through the headworks prior to entering the main treatment process. In the headworks, the effluent first passes through the rock removal chamber where large inorganic materials are settled out. The influent travels through a grinder that shreds the larger pieces. The influent then passes through a screening devise that removes particles larger than a quarter of an inch in size. The influent then proceeds through the grit separator where inorganic particles are removed and thence into the wet well.

The influent is pumped from the wet well into the sequential batch reactors where the main treatment process is performed. In the reactors, the fresh influent is mixed into the “mixed liquor” of older influent which contains the microorganisms that consume the volatile organic materials. In the course of this treatment process, the mixed liquor is aerated and mixed to ensure the maximum efficiency of the biological treatment process.

After the reactor contents have been aerated and mixed to allow the treatment process to function, the reactor is ready to start on the wasting and decant stage. The reactor is allowed to become quiescent allowing the solid materials to settle to the bottom of the unit. Once the solids have settled out, they are “wasted” to the sludge holding tanks. Upon completion of the wasting cycle, the clear water (supernatant) is decanted through the equalization basin to the UV units.

The disinfection of the SBR effluent is the final stage in the treatment process for the water. The water flows past a set of ultraviolet lights which disinfects the water. The pathogenic organisms die due to the disruption of their RNA which stops them from reproducing. The water is not sterilized as not all organisms are killed. The water is then sent either to Garrison Creek or lagoon #2 for the irrigation system.

The wasted solids are stored under aeration until the dewatering process is begun. The solids are pumped to the belt press building where polymer is introduced prior to the actual dewatering process. The solids/polymer mixture is run through the belt press where the solids concentration is increased from 1% to 20%. The dewatered sludge is removed to the drying beds where it is processed further to meet DOE and EPA standards prior to application to our croplands.

The treatment process is controlled in most instances by computers. The treatment parameters are determined by plant staff based on the results of laboratory testing. The goal of the treatment process is to remain in compliance with our operating permit and all state and federal laws and regulations.