Wastewater Plant Process Overview
Influent Pumping
Raw wastewater enters the Moccasin Bend Wastewater Treatment Plant influent pump station wet well through bar screens. The screens remove large pieces of paper, rags, leaves, plastic bottles, and tin cans. After screening, the wastewater is pumped to the grit removal system and more screening.
Grit Removal and Fine Screens
Detritors are used to remove grit, rock, sand, and gravel from the raw wastewater before it passes through fine screens. The screens remove cigarette filters and other pieces of debris smaller than 0.25 inches in size.
Primary Clarification System
Flow leaves the grit removal system and enters the primary settling basins. Raw sludge and floating scum are collected in the primary system. Raw sludge is pumped to the gravity sludge thickeners and floating scum is removed, screened, and dewatered through rotating basket-type screens.
Flow Equalization System
The treated primary wastewater next enters the equalization basins before secondary treatment. The equalization basins are used to store water during high flow conditions and to create a constant flow rate to the secondary treatment system. Blowers provide air to the equalization basins to keep the solids suspended and prevent the wastewater from going septic. Equalization pumps pump the wastewater from the basins to the activated sludge process.
Secondary Treatment Process
The secondary treatment process is a biological activated sludge high purity oxygen process. Microorganisms are used to convert suspended and dissolved solids to settleable solids. High purity oxygen is supplied for the microorganisms in the activated sludge system by an on-site, cryogenic air separation plant.
Secondary Clarification System
Wastewater called mixed liquor flows from the activated sludge system to secondary clarifiers. Sludge collected in the secondary clarifiers flows by gravity to a return sludge pump station. The (RAS) pumps return a portion of the sludge back to the activated sludge system to keep the food chain going for the microorganisms in the secondary influent wastewater. A portion of the (RAS) flow, called waste activated sludge (WAS), is pumped to thickeners to be thickened before dewatering.
Additional Information:
Disinfection System
The cleaned wastewater leaves the secondary clarifiers and enters a chlorine contact tank. Sodium hypochlorite is injected into the water to disinfect the treated plant effluent.
Dechlorination System
Liquid sodium bisulfite is injected in the plant effluent after chlorination to remove the chlorine before it is released to the Tennessee River.
Wet Weather Pumping/Screening
When the flow coming to the plant exceeds the capacity of the influent pump station, the wet weather system is activated. Wet weather flow enters the influent relief pump station through fine screens. A mechanical bar screen is available for backup in case the fine screen malfunctions.
Wet Weather Grit Removal
Wet weather flow leaving the influent relief pump station is routed to vortex type grit separators to remove the grit, rock, and sand from the wastewater.
Wet Weather Primary Treatment
The next phase of the wet weather treatment process is primary treatment. Aluminum sulfate or polymer is added in the effluent line of the wet weather grit removal system to enhance solids separation in the wet weather primary clarifiers. The sludge is collected and pumped to gravity thickeners.
Wet Weather Disinfection
After primary treatment, the wet weather flow is disinfected with sodium hypochlorite and dechlorinated with sodium bisulfite before being combined with the secondary effluent flow. The combined flow has to meet the same NPDES limits as the plant effluent flow during dry weather flow.
Solids Handling System
There are two types of solids produced by the wastewater treatment processes, both of which receive further treatment resulting in the production of a biosolids fertilizer product suitable for land application.
All solids from the sludge holding tank are then dewatered and further conditioned and stabilized by either the centrifuge process or the filter press process.
Centrifuge System
The Centrifuge Building operates with two Flottweg Model Z-73 high G centrifuges. These units are rated at 60 dry tons per day per machine. The dewatered biosolids cake from the machines ranges from 20-25%. Dewatered biosolids are post-lime stabilized using lime-kiln dust. Class B biosolids are produced with material that ranges 27-32% solids.
Wastewater Operator's Creed
We, the members of the Professional Wastewater Operations Division, are dedicated to the task of conserving a healthy environment for terrestrial and aquatic life.
We are obligated by duty, conscience, and personal power to meet at a minimum permit limits as set forth by this state, province, or country.
We, as operations professionals, will fulfill our responsibility to protect the interest and investment in the facility by maintaining safe, attractive, economical, and efficient wastewater treatment facilities to the best of our ability.
We will endeavor to increase our knowledge and skills in modern technology in the science of water pollution control to advance to the point of returning water back to its natural state upon which all forms of life depend.
Created by Casey Hall 1983
Adopted by the WEF 1992