Raven's Settleometer is the smallest size possible without affecting the
natural settling behavior of activated sludge. Why pay more for large
settleometers that are cumbersome to handle?
Brightly marked Settleometer scale with 0% to 100% and 0 to 1000 SSV.
Snap-on lid keeps liquid from splashing if transporting from the aerator to the shop.
"The ability to observe
and measure the rate and characteristics of solids separation is
essential to control biological treatment processes that produce
sludge."
Activated Sludge Manual of Practice OM-9
The
Settleometer shows the solids liquid separation capability in the
secondary clarifier. Sludge must separate from the liquid for settling
to occur. Settling of sludge in the clarifier is a critical part of the
activated sludge process. Poorly settling sludge is a strong
indication of process problems and solids loss in final effluent.
The
scale printed on the Settleometer measures how far a sample has
settled. “SSV” is the abbreviation for Settled Sludge Volume. “%”
shows the settled sludge volume as a percentage of the entire sample.
The sample to the right has a SSV of 350 which is also 35% of the total
sample volume.
Observe Settling Characteristics
Normal sludge forms a floc and gently squeezes the
water out of the blanket forming on the bottom. Settles between 800 and
700 in five minutes. If there are excess solids in the final effluent
with Normal sludge, a clarifier mechanical problem may exist.
Rapid sludge settles like dark grains of sand leaving behind a turbid
supernatant with suspended solids. Settles to 700 or less in five
minutes.
Slow sludge appears to be stuck in the settling process with little or
no progress but with very clear supernatant. Does not settle to 800 in
five minutes. Perform the Multi-Dilution test to determine if slow
settling is caused by density or concentration.
Troubleshooting Slow Sludge
Slow settling sludge can be caused by high density sludge or high
concentrations of sludge. The Multi-Dilution Test is performed with two
Settleometers.
- Density Issue -
If the sludge in the diluted Settleometer settles the same as the sludge
in the pure Settlometer, this indicates a density issue. Density is
related to quantity. Reducing the pure sample by 50% allowed the sludge
to settle further. In other words, the sludge was simply piling up in
the pure sample.
- Concentration Issue -
If the sludge in the diluted Settleometer settles significantly more
than the sludge in the pure Settleometer, this indicates a concentration
issue. Concentration is related to sludge character. Reducing the
pure sample by 50% did not affect the settling characteristic. In other
words, the amount of sludge in the sample did not affect the settling. A
density issue should be tested further with microscopic evaluation to
determine if filamentous sludge is a problem.
Application to Process Control
The Settleometer is used in wastewater plants for primarily four applications:
1. Settling characteristics – Rapid, Normal or Slow settling.
2. SSV is used in calculating return sludge flow rates.
3. Troubleshooting settling problems to determine a density or a concentration issue.
4. Timing when denitrification occurs and sludge rises to surface of Settleometer.