Title

12 Poor Settling - Bulking

This SOP discusses steps to take when bulking sludge is affecting effluent quality.

SOP Identification Number
SOP Identification Number:
1201 Bulking
Purpose and scope
Purpose and scope:

When filamentous organisms grow in large amounts, sludge settling and compaction can be hindered. Bulking takes place when filamentous organisms interfere with the formation and compaction of activated sludge floc.

Definitions
Definitions:


A bulking sludge settles and compacts slowly. From an operational perspective, a bulking sludge has a sludge volume index (SVI) greater than 150 mL/g, although lower SVI values can still result in sludge bulking.

Sludge Volume Index (SVI) is the volume occupied by one gram of mixed liquor suspended solids (MLSS) after 30 minutes of settling.

Cautions
Cautions:

It is imperative that bulking sludge be controlled as quickly as possible, as it can lead to possible Permit violations. In severe cases, bulking sludge can result in a loss of the solids inventory, leading to a loss of the plants ability to treat waste and a failure of the treatment process.

Potential Interferences
Potential Interferences:

Poor clarifier performance, such as short-circuiting, can result in a bulking sludge. Hydraulic overload of the secondary clarifier is another cause of bulking sludge.

Procedure
Procedure:

  1. Monitor the occurrence and abundance of filamentous organisms at least weekly using a microscope.
  2. Establish that a bulking problem is due to sludge quality (filaments) and not sludge quantity by performing a dilute settleability test.
  3. Identify the causative filament to determine the appropriate remedial action.
  4. Short term solutions involve treating the symptoms (changing influent feed points, changing RAS rates, adding settling aids, and chlorinating.)
  5. Long term solutions involve treating the cause (controlling pH, controlling influent septicity, adding nutrients, changing aeration rates, and changing the F:M ratio.)
  6. Evaluate the effectiveness of the remedial action on the types and abundance of the filaments.
  7. Depending on the type of filament, closely monitor and adjust the following: dissolved oxygen concentration, organic loading, septic wastes, nutrient deficiency (not typical), and pH.
ID
Maintenance Connect