The cost for wastewater service is higher than the cost of drinking water service because the quality of effluent discharged to the Arkansas River is required to be similar to the quality of drinking water, but the water we start with in our wastewater treatment process is much dirtier. As a result, the wastewater treatment process incurs higher costs for electricity and treatment chemicals.
Wastewater contains high concentrations of organic matter and inorganic matter, as well as microorganisms that can transmit human diseases. Chemically, this mixture is termed a “complex matrix.” The wastewater treatment process is controlled by a discharge permit that sets specific numeric limits on such materials as nutrients, suspended solids, and heavy metals, as well as on surrogate measures like biochemical oxygen demand and whole effluent toxicity. The most demanding aspect of wastewater treatment is extracting dissolved organic material from water. This is done using living bacteria. Wastewater treatment entails growing different types of bacteria in large tanks, allowing the bacteria to grow by taking up various materials from the wastewater, and then removing the bacteria prior to releasing the reclaimed water. Growing the different types of bacteria requires controlling the amount of oxygen available in different stages of the process and recycling living bacteria to maintain the process. The treated water that is ready for discharge must be disinfected to kill any remaining microorganisms that might cause human disease. This is presently done using ultraviolet disinfection.
Those bacteria that are removed from the treatment process, as well as solid materials in wastewater, must be further treated by a process called anaerobic digestion to reduce the mass of the final residue, which is disposed of by landfilling. Finally, please note that wastewater flows to our facility continuously. We are required to accept and treat whatever volume is generated, rather than being able to control timing to make the process more efficient.
The process of drinking water treatment is simpler by comparison. Pueblo’s drinking water treatment plant uses water from the Pueblo Reservoir, which is fed by the upper Arkansas River. The Pueblo Reservoir acts as a very large settling tank, removing many solid materials. Natural bacteria in the reservoir also scavenge dissolved carbon from the water for their growth processes. Thus the water entering the drinking water treatment process is much cleaner than wastewater. Chemically, the mixture is termed a “simple matrix.” Drinking water treatment is a chemical process rather than a biological process. Chemicals are added to raw water that cause dissolved inorganic materials like metals and salts to clump together, and the chemical sludge is removed. The finished water is disinfected and stored until use. There is no need to remove the disinfectant chemical. Drinking water treatment facilities use historical trends in water usage to keep ahead of demand. During the summer irrigation season they supply a great deal of water daily; during the winter months they produce much less, needing only to keep pace with the needs of cooking, cleaning, and sanitary disposal.
Pueblo’s wastewater user charge has two components. There is a fixed monthly fee that funds the City’s maintenance of the wastewater system including sewer pipes, pump stations, and the Water Reclamation Facility. There is also a volume charge that accounts for the amount of wastewater generated by users. For residential households, the volume charge is based on winter water usage when outdoor uses of water are expected to be at a minimum. The residential winter water volume usage is assumed to represent the volume of water that goes to the sanitary sewer system via household drains throughout the year. It eliminates large-volume outdoor uses for irrigation, washing cars, etc. This is the most common method of assigning volume charges for wastewater throughout the nation.