12 Air Balancing
Air flow to the aeration basin grid system is distributed via a common airline that is equipped with isolation valves. The Operator adjusts dissolved oxygen (DO) levels in the aeration basins by adjusting air flow via the position of the Rotork isolation valves. The aeration basin DO, air flow, and Rotork valve position can be viewed from the SCADA screen.
To provide oxygen at levels required for the activated sludge process.
- DO: Dissolved Oxygen
- Ladder safety
- Ensure that DO sensors and transmitters are calibrated and properly installed.
- Ensure that aeration diffusers are operational and air flow is uniform thought out basin(s). Observe water surface during daily rounds.
- Adjustments to air flow at one aeration basin may effect air flow at another aeration basin. DO levels in all aeration basins must be monitored while making adjustments.
Operator 1, knowledge of air flow system and equipment controls.
- Ladder (to access Rotork handwheels located approximately 6' above the floor)
- Record activity to log book.
1. Adjust Rotork valve air flow : The Rotork valves are typically adjusted via electronic control, as described below. The valves can also be adjusted manually be turning the handwheel for that valve. The Rotork controls are located approximately 6 ft from the floor in the air piping corridor of the Secondary Process Building basement. a. Determine which Rotork valve must be manipulated in order to adjust air flow to the target aeration basin {tag nos. 1202VLV2237(aeration basins #1 & #2), 1202VLV2239 (aeration basins #3 & #4), 1202VLV2241 (aeration basin #5)}. b. Use a ladder to access the local Rotork controls. Place the selector switch into the HAND control mode. c. Adjust the valve position by turning the black knob and viewing the position display on the screen. The valve position is typically displayed as a percentage open. d. Place the selector switch into the STOP position. e. Monitor DO levels {tag nos.1202AE/AIT2481, 1202AE/AIT2482, 1202AE/AIT2483, 1202AE/AIT2484, 1202AE/AIT2485} and air flow rates {tag nos. 1202FE/FIT2238 (aeration basins #1 & #2), 1202FE/FIT2240 (aeration basins #3 & #4), 1202FE/FIT2442 (aeration basin #5)}at the SCADA screen. Make further adjustments as required to reach the target DO levels. |
DO ranges should normally range between 1.0 - 3.0 mg/l, with 1.0 mg/l being a minimum value.
Adjusting and correcting DO levels in the aerations basins is an iterative process.
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