This document discusses research into incorporating short-term temperature variations into automated measurements of sludge volume index (SVI). Batch tests showed SVI values varied significantly based on whether samples were in sunlight or shade, changing sample temperatures. On-line monitoring found SVI correlated better to both mixed liquor suspended solids concentration and sample temperature. A regression model for SVI had improved correlation considering both factors. The research concludes sample temperature impacts SVI and should be standardized or accounted for in testing and modeling.

1. AUTOMATED SVI MEASUREMENTS
INCORPORATING SHORT-TERM
TEMPERATURE VARIATIONS
Werner Rössle
Jurie Terblanchè
ERWAT
WISA
April 2010
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2. CONTENT
• Background
• Experimental
• Results
– Batch tests conventional SVI
– On-line tests automated on-line SVI monitoring at full-
scale reactor
– Modelling SVI combined with both MLSS
concentration and sample temperature
from on-line data
• Conclusions
• Project summary
• Acknowledgements
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3. BACKGROUND
Sludge Volume Index (SVI) test
• Developed 1934, procedure simple, fast, widely used, data
• SVI of < 100 to 150 ml/g indicates a well-settling sludge
• Temperature dependency generally not considered, and
compensation methods usually not implemented
Standard methods (APHA, 1998) SVI test procedure
• Sample of known MLSS concentration, 1 litre cylinder,
stirred, 30 minute settling
• Settled sludge volume read off cylinder wall
• SVI = settled sludge volume (ml/l) / MLSS concentration (g/l)
• Sample temperature kept constant at reactor (basin)
temperature during SVI settling test – no procedure
provided 3

4. EXPERIMENTAL(1) BATCH TEST
Basic sludge settling test in cylinders
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5. EXPERIMENTAL(2) BATCH TEST
SVI test method
• reactor and ambient temperatures
• MLSS concentration
• reactor sludge sample, remix
• sludge in 1 or 2 litre cylinder(s), remix
• cylinder in shade or sunshine (assess location)
• sample temperature
• start sludge settling test immediately
• 30 minutes settling to obtain settled volume
• sample temperature again (probe of thermometer in
same position inside cylinder during all measurements)
• calculate SVI
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6. EXPERIMENTAL(3) ON-LINE METER
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• Settler• Settler

7. EXPERIMENTAL(4) ON-LINE
METER
Automated on-line SVI meter
– Mobile (220V and water supply) in an enclosure
– 2 ℓ Perspex settling cylinder (84.0 mm diameter and
360.9 mm height), removable for cleaning
– On-line Tr, Tc, Ta, MLSS concentration
– Moving infrared light scanner
– 6-line graphic recorder, data storage, retrieval
– Automated sample filling, settling, draining, and
washing stages
– Sludge sample transfer vacuum based, no mechanical
pumping
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8. RESULTS(1) BATCH TEST
Cylinder Place
MLSS conc. [mg/l]
Tr [°C]
Ta [°C]
5830
20.5
30.1
5870
20.8
31.5
Average
1 ℓ Shade
SVI[ml/g] 118 107 113
Tc30 [°C ] 25.3 24.4 24.9
1 ℓ Sun
SVI[ml/g] 89 80 85
Tc30 [°C ] 26.2 27.9 27.1
2 ℓ Shade
SVI[ml/g] 130 126 128
Tc30 [°C ] 24.3 23.3 23.8
2 ℓ Sun
SVI[ml/g] 93 82 88
Tc30 [°C ] 25.6 26.6 26.1
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9. RESULTS(2) BATCH TEST ILLUSTRATION
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START OF SETTLING TEST 1, 15/10
MLSS = 5830 mg/l
Tr = 20.5°C
Ta = 30.1°C
Tc = 20.6°C
Samples in sun or shade - change Tc
END OF SETTLING TEST:
Sample handling:
1l sun, 1l shade, 2l shade, 2l sun
Sample temperature Tc30
26.2, 25.3, 25.6, 24.3
4 SVI from one reactor sample:
89,118, 130, 93
89 118 130 93

10. RESULTS(3) BATCH TEST ILLUSTRATION
10
START OF SETTLING TEST 2, 16/10
MLSS = 5870 mg/l
Tr = 20.8°C
Ta = 31.5°C
Tc = about 22°C
Samples in sun or shade - change Tc
END OF SETTLING TEST:
Sample handling:
2l sun, 1l sun, 2l shade, 1l shade
Sample temperature Tc30
26.6, 27.9, 23.3, 24.4
4 SVI from one reactor sample:
82, 80, 126, 107
82 80 126 107

11. RESULTS(4) DIURNAL ON-LINE SVI
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Graph of 44 on-line 30-minute settling curves, MLSS concentration,
temperature and calculated SVI trends over a diurnal period

12. RESULTS(5) SETTLING CURVES & SVI
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Graph of 2 on-line 30-minute settling curves, MLSS concentration,
temperature and calculated SVI trends

13. RESULTS(6) SVI vs. MLSS CONC.
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Data scatter, R2
= 0.47

14. RESULTS(7) SVI vs. TEMPERATURE
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Data scatter, R2
= 0.69

15. RESULTS(8) SVI vs. MLSS CONC. & TEMP.
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R2
= 0.84

16. RESULTS(9) BASIC MODEL
• Commercial statistical software package
• Basic regression model for easy use:
• R2
improvement about 0.3 with one case study
• Significant parameters affecting SVI:
– MLSS concentration
– Sample temperature
• 8 ml/g SVI change (average) per 1°C on-line
sample temperature change with one case study
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17. CONCLUSIONS
1. Batch settling test: substantial temperature
change
– Test cylinder environment has an influence on sample
temperature and SVI
1. On-line settling test: automated diurnal trends
– Short time delay between sampling and test reduces
sample temperature variations, improved SVI
– Incorporates reactor temperature variations in SVI trend
1. Modelling: correlations for general and design use
– Improved SVI correlations with both temperature and
MLSS concentration
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18. PROJECT SUMMARY
• Include temperature in sludge settling analysis
– reactor, ambient, sample temperatures, or at least
stabilised sample and room temperatures
• Use a consistent reference basis of experimental
conditions is a basic requirement
– impact of cylinder handling and temperature on results
used for plant process control or design or modelling
• Do not extrapolate any results from a case study
– develop correlations for each plant or reactor
• On-line automated sludge settling monitoring
– benefits relate to automated sampling and testing
methods and on-line data generation 18

19. ACKNOWLEDGEMENTS
• ERWAT provided facilities and research resources
• ERWAT Research and Development Forum, Board
of Directors and Executive Management provided
support
• ERWAT operational personnel assisted during
batch settling tests
• Mr G. George made key contributions during the
development, construction and upgrading of the
on-line SVI meter
• WRC provided initial project finance on a related
activated sludge settling project
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20. Thank you
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