Water Renewal Process
Removal of Solids
The domestic wastewater first undergoes fine screens and grit removal. The industrial wastewater which is 85% of the total flow, flows through the parallel grit chambers. Grit chambers use the force of gravity to remove smaller, heavier particles like gravel and sand by decreasing the velocity of the flow. From there the flow enters the Parshall flumes which measure the rate of flow.
The flow then enters primary treatment which consists of sever clarifiers, four industrial and three domestic which includes disinfection. Primary treatment removes the settleable and floatable solids from the wastewater.
After primary treatment, the domestic and industrial wastewater combine prior to entering a denitrification basin where bacteria convert nitrates to nitrogen gas. The flow then enters secondary treatment which is biological. In this stage, bacteria consume most of the remaining waste materials. To sustain the growth of this bacteria, oxygen is added to the wastewater in one of four sealed pure oxygen reactors. This oxygen is produced in an on-site cryogenic plant. After a few hours, the water flows into sedimentation tanks where solids settle to the bottom. This completes the secondary phase of treatment. At this point, 90 to 95% of the pollutants have been removed from the wastewater.
Throughout the wastewater treatment process, solids have been removed from the wastewater. These solids are called sludge or biosolids and require further processing. The goal in processing sludge is to take as much water out of it as possible and to return the water to the river in an environmentally safe state. To remove the water from the sludge, it is pumped into gravity thickeners. These thickeners also use the force of gravity to separate water from these solids. The sludge is placed in a holding tank at this point, followed by treatment using a dry solid centrifuge, polymer feed system, and multiple hearth incineration. Ash from the incinerator is then disposed of in an approved landfill, safely returning the materials to the environment.