15 Gravity Thickener Equipment Start Up
Typically, the Gravity Thickener drive unit operates continuously. If power to the equipment is shutoff, an alarm is signaled by SCADA.
Gravity thickening uses gravity forces to separate solids from the mixed liquor. Solids that are heavier than the water settle to the bottom of the thickener by virtue of gravity and are then compacted by the weight of the overlaying solids.
- To concentrate and settle out solids before the sludge is transferred to the anaerobic digesters.
- To remove as much water as possible before the sludge is transferred to the anaerobic digesters and to minimize digestion capacity requirements.
- To reduce the overall volume of sludge that requires treatment in subsequent processes.
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- Flow rates into the Gravity Thickener should provide for a minimum detention time of 6 hours.
- Monitoring and maintenance of overflow DO levels is ongoing during operation.
- Too low DO levels in the overflow could indicate septic conditions in the tank.
- Too low primary sludge flow rates will not maintain the minimum 6 hour detention time.
Operator I, knowledge of thickening process and equipment controls.
- Record activity to log book.
- Monitor DO levels at overflow via sampling system program.
- Monitor primary sludge flow to the Gravity Thickener (optimal flow rate = 213 gpm). Add Elutrient Water if influent flow rate falls below optimal rate.
1. Start GT Drive Unit.
a. Go to the Thickener Control Building and locate the GT panel {tag no. 1501BKT5100}.
i. Verify that GT Drive Unit Breaker Switch {tag no. 1501BKR5100} is in the ON position.
ii. Turn hand switch {tag no. 1501HS5100A} to ON.
b. Go to the GT structure and locate the Local Switch:
i. Turn GT drive unit {tag no. 1501MTR5100} HOA switch {tag no. 1501HS5100C} to START. Verify that green indicator light {tag no. 1501YL5100} is ON.
ii. Verify operation of GT drive unit {tag no. 1502VDLN5100/1501GBX5100}.
- Update log book.
- Update maintenance records (if applicable).
- Report any maintenance or attention that is required.
- Consistent DO levels in overflow.
- 6 hour (minimum) detention time.
- 7% solids concentration achieved through gravity thickening.
- If flow rates to the Gravity Thickener are too low to maintain a 6 hour detention time, Elutrient Water is added to the influent to "make up" the flow rate.
- If the contents of the Gravity Thickener turn septic, add Elutrient Water so that measureable quantities of DO are present in the overflow.
Refer to the Solids\Troubleshooting\Gravity Thickener Troubleshooting pages for more information.
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