1502 DAFT & Dissolution Start Up SOP
Starting up the DAFT thickener involves putting the rotating surface scraper drive unit and the Dissolution system into service. Start up of the Dissolution System involves putting a dissolved air/water solution into service.
The DAFT process concentrates secondary biological sludge and scum by removing small or very light particles that settle slowly or not at all. Forced air is injected to the sludge mixture and the resulting tiny air bubbles occlude to the solids particles, rendering them lighter than the water. The solids then float to the water surface and are skimmed for pumping to the anaerobic digesters.
- To concentrate and settle out solids before the sludge is transferred to the anaerobic digesters.
- To remvoe as much water as possible before the sludge is transferred to the anaerobic digesters and to minimize digestion capactiy requirements.
- To reduce the overall volume of sludge that requires treatment in subsequent processes.
- DAFT: Dissolved Air Flotation Thickener
- A/S ratio: The ratio of pounds of air to pounds of solids. Optimization of the A/S ratio provides enhanced thickening and clarification.
Watch for open tanks and high elevations. If working on or near equipment, watch for moving parts.
- Watch for air locks in the system.
- In sufficient air flow could result in solids settlingi to the bottom of the DAFT tank. The optimal A/S ratio is approximately 0.02 pounds of air per pound of solids.
- If the speed of the rotating rake is too fast, the float thickness will be too thin. Rake speed should be such that the float thickness is approximately one half the baffle depth. If the rake speed can not be reduced sufficiently, the rake should be operated on an intermittent percentage basis.
Operator I, knowledge of thickening process and equipment controls.
- Record activity to log book.
- Monitor A/S ratio and adjust air flow if necessary to maintain optimal A/S ratio.
- Monitor thickeness of floating sludge. Adjust rake speed if necessary to maintain optimal depth.
- Record activity to log book.
- Monitor A/S ratio and adjust air flow if necessary to maintain optimal A/S ratio.
- Monitor thickeness of floating sludge. Adjust rake speed if necessary to maintain optimal depth.
1. Start DAFT Drive Unit. a. Go to the Thickener Control Building and locate the DAFT panel {tag no. 1502BKT5300}. i. Verify that DAFT Drive Unit Breaker Switch {tag no. 1502BKR5300} is in the ON position. ii. Turn hand switch {tag no. 1502HS5300B} to ON. Verify that green light {tag no. 1502YL5300} is ON. b. Go to the DAFT structure and locate the Local Switch: i. Turn DAFT drive unit {tag no. 1502MTR5300} HOA switch {tag no. 1502HS5300} to AUTO position. ii. Verify operation of DAFT drive unit {tag no. 1502VSD5300}. 2. Adjust Back Pressure Valve. a. The Back Pressure Valve is located outside the Thickener Control Building. i. Open the back pressure valve approximately 5 – 8 turns {tag no. 1505PI5687}. 3. Start DAFT Dissolution System. a. Go to the Thickener Control Building and open all of the suction valves {tag nos. 1502VLV5100 & 1502VLV5200} and discharge valves {tag nos. 1502VLV5100F, 1502VLV5200G & 1502VLV5687A}. b. Locate the Recycle Pump panel {tag no. 1502BKT5100}. i. Verify that Recycle Pump Breaker Switch {tag no. 1502BKR5100} is in the ON position. ii. Turn hand switch {tag no. 1502HS5100} to ON. iii. Bleed off air at the Recycle Pump {tag nos. 1502PMP5100 & 1502PMP5200} suction and discharge. iv. Verify flow through flow meter {tag nos. 1502FE/FIT5676}. v. Verify that air system is in operation. vi. Verity that air valves are open {tag nos. 1502FCV5673 & 1502FCV5674}. vii. Dissolution Tanks {tag nos. 1502TNK5691} 4. Adjust Back Pressure Valve. a. The Back Pressure Valve is located outside the Thickener Control Building. i. Close the back pressure valve {tag no. 1505VLV5687C} until the pressure gauge {tag no. 1505PI5687} reads approximately 55 psi.
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- Update log book.
- Update maintenance records (if applicable).
- Report any maintenance or attention that is required.
- A/S Ratio = 0.02
- Floating sludge thickness = 1/2 depth of baffle
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