Title

15 Gravity Thickener Start Up

Starting up the Gravity Thickener involves putting the collector drive into service and adding Elutrient Water to the Gravity Thickener Tank. Once the system has been started up, the operator monitors DO in the Gravity Thickener by obtaining grab and composite samples for analysis. Elutrient water valves are manipulated in order to maintain optimal DO levels in the Gravity Thickener. Thickened sludge is transferred from the Gravity Thickener via an automated pumping system.

SOP Identification Number
SOP Identification Number:
1501_Start Up
Purpose and scope
Purpose and scope:

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. 
Health & Safety Warnings
Health & Safety Warnings:

Watch for open tanks and high elevations. If working on or near equipment, watch for rotating parts.

Cautions
Cautions:
  • 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. 
Potential Interferences
Potential Interferences:
  • 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.
Personnel Qualifications
Personnel Qualifications:

Operator I, knowledge of thickening process and equipment controls.

Quality Control/Quality Assurance Activities for the Procedure
Quality Control/Quality Assurance Activities for the Procedure:
  • 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. 
Data & Records Management, Calculations, Forms, Reports
Data & Records Management, Calculations, Forms, Reports:
  • Update log book.
  • Update maintenance records (if applicable).
  • Report any maintenance or attention that is required.
Limits/Criteria for Data/Results
Limits/Criteria for Data/Results:
  • Consistent DO levels in overflow.
  • 6 hour (minimum) detention time.
  • 7% solids concentration achieved through gravity thickening.
Corrective Action Plan
Corrective Action Plan:

  • 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.

ID
Maintenance Connect