Very simply, wastewater treatment technology speeds up nature's own process of oxidation and bacterial decomposition of organic materials. A treatment plant accomplishes in a few hours what would take place over a period of days or weeks if the wastewater was discharged directly into the river, thus preserving the ecosystem of the river.
Treatment begins when the wastewater flows from the mainline sewer through a bar screen which prevents large pieces of material from clogging or damaging the plant equipment. Pumps lift the sewage into a grit chamber, in which sand, gravel, and other objects settle out of the flow.
From the grit chamber wastewater passes into primary clarifiers, where gravity settling separates the solid materials from the water. Floatable solids (scum) are also removed at this time.
- Sewer mains
- Bar screen
- Lift pumps
- Grit chamber
- Primary clarifier
- Solids screening
- Dissolved air flotation thickening
- Solids digester and heater
- Gas, solids below
- Chemicals introduced
- Biosolids storage
- Belt filter presses
- Final disposal on agricultural land
- Trickling filter
- Secondary clarifier
- Activated sludge basins
- Waste water
- Solids
- Final clarification
- Disinfection
- Oxycharger
- Final discharge to river
- Secondary Treatment
- Primary Treatment
Wastewater which has received primary treatment at Plant #1 flows by gravity through a line 66 inches in diameter to Plant #2 for secondary treatment.
The solid, settled material, called sludge, and floatable scum is screened and pumped to a dissolved air floatation thickener where it is blended and then pumped into anaerobic digesters. The solids remain in the digesters 50 to 60 days, during which time anaerobic bacterial action converts approximately one half of it to methane gas, carbon dioxide and water. Part of the gas produced is used for heating the digesters to a constant temperature of 98 degrees Fahrenheit, and the remainder is destroyed by flaring to the atmosphere. Digested biosolids are then pumped to belt filter presses where excess water is pressed out. Chemicals added at the beginning of the process assist the separation action.
The dewatered biosolids are then trucked to a storage facility where they are stored prior to being applied to agricultural land as a soil supplement.
Secondary treatment depends on the action of bacteria to remove dissolved organic matter from the water. Wastewater enters twelve large units called trickling filters. These filters consist of rock beds 200 feet in diameter and 7 feet deep. The wastewater trickles over the rocks, and a biological growth that thinly covers their surfaces consumes the dissolved organic material. As the organisms consume the pollutants, they grow until the growth becomes so thick on the rocks that pieces break off and enter the water flowing to seganic matter from the water. Solids which settle out in the secondary clarifiers return by gravity to the beginning of the treatment process.
The secondary effluent is then pumped to activated sludge basins where micro organisms and bacteria further reduce the organic pollutants and ammonia.
Following final clarification the treated wastewater is disinfected using chlorine gas. After disinfection the treated wastewater is de-chlorinated using sulfur dioxide, aerated again and then discharged to the Arkansas River. At this point, 95% of the pollutants have been removed.
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