Transcript A New Twist on an Old Test for Activated

A New Twist on an Old Test
for Activated Sludge Process
Control
Estes Park PWO Seminar
October 22, 2004
Greg Farmer – Littleton / Englewood WWTP
L/E WWTP Process
Schematic
Aerial View
Phase 2 Construction
Project
Phase 2 Construction
Project
TF/SC
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40 – 70% of SBOD and 25 – 50% of
CBOD is removed in the trickle filter
Aeration basins provide remaining
BOD removal and flocculation
SRT < 2 days
SVI around 100
Not intended for nutrient removal
Typical Activated Sludge
Control Methods
Control MLSS Inventory
 Dissolved oxygen concentration
 And RAS/clarifier blankets
To produce a sludge that:
 Flocculates
 Settles
 Compacts
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Traditional Performance
Indicators
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Secondary clarifier
effluent TSS and
BOD
Final effluent TSS
and BOD
SVI / Settleometer
SRT
F/M
But, what if……..
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What if your secondary clarifiers do not
function properly due to hydraulic and/or
flocculation deficiencies
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Too shallow
Short circuiting
RAS return problems
Poor sampling location
Thermal Currents
Floc shear
Final Effluent TSS
Secondary Clarifier TSS
Temperature
Temperature plays a major role:
 Biological activity decreases by 50%
for every 10° C drop in temperature
 Clarifier thermal currents are created
with as little as a 0.5° C temperature
difference
Final Effluent TSS
Secondary Clarifier TSS
Aeration Basin
Temperature Swing
Thermal Currents
What Tools Are Available?
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Does a tool exist that can be used to
predict or forecast the correct MLSS
inventory to maintain a healthy
biomass?
This tool must not look at deficiencies
in the secondary clarifiers
Enter the Wally Meter
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Developed by Dr. Eric Wahlberg as the
Wahlometer
Consider it a “flocculated settleometer”
Determines the “health” of an
activated sludge
Negates the influence of secondary
clarifier inefficiencies on process
control decisions
Wally Meter in Action
Wally Meter
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Collect a MLSS grab sample 2 times/day
Pour into square Phipps and Bird
flocculation jar or authentic “Wahlometer”
Mix at 50 rpm for 30 minutes
Record the 5 minute SSV5 reading
Settle for 30 minutes and record the 30
minutes SSV30 reading to calculate SVI
Sample subnatant for TSS and/or NTU
Wally Meter Terms
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ESS – Effluent Suspended Solids
FSS – Flocculated Suspended Solids,
SS that remain in the subnatant after
30 minutes of settling preceded by 30
minutes of flocculation
Clarifier ESS vs.
Wally Meter FSS
How to Use the Data
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The Wally Meter TSS value is the
lowest possible TSS value that can be
attained in a perfect environment
Adjust MLSS to maintain low Wally
Meter TSS
Adjust seasonally for temperature
changes
The Equation
Inventory =
(21,000lbs MLSS + ((Avg Wally Meter TSS – 6) * 500))
+(21.5 C – Avg Basin temp.) * Lbs MLSS Inventory * .1)
- (5-minute Wally Meter reading – 400) * 20
The Equation
Predictive Chart
Spreadsheet
Last 45 Days
Final Effluent
Applicability
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Will the equation work for an activated
sludge plant? A BNR plant?
Collect data for a period of time
Experiment with equation values to
attain a fit