A Simpler Approach for Determining Biodegradation of SOCs in Wastewater Treatment

1
A Simpler Approach for Determining Biodegradation
of SOCs in Wastewater Treatment

• Tim Ellis
• Associate Professor
• Dept. of Civil and Construction Engineering
• Iowa State University

2
Objective

• To evaluate technique to determine the
  biodegradation of specific organic compounds in
  wastewater treatment systems
• To use the measured biodegradation rate
  parameters to predict the performance of
  full-scale activated sludge plants

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Background

• Technique originally developed at Clemson
  University under direction of Les Grady
• Several assumptions in the technique
• How the test is performed affects results
• Using a low substrate to biomass ratio has least
  affect on measured rate constants
• Measured dissolved oxygen concentration can be
  correlated to compound concentration

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Basis of Technique

• Sample of mixed liquor obtained from operating
  wastewater treatment plant
• Sample is placed in a respirometer vessel and
  aerated with O2
• Respirometer is sealed and DO concentration is
  continuously measured and recorded

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Typical Response
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Biodegradation Model

• Based on substrate and biomass mass balances at
  steady-state
• Monod kinetic relationship adequate
• Requires knowledge of concentration of biomass
  degrading the target compound (competent fraction)

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Biodegradation Model
(h-1)
S (mg/L as COD)
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Experimental Set-up
D.O. Meter
Injection Port
Data Acquisition
CMAS
D.O. Probe
Water Bath
Biomass Sample
Respirometric Vessel
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Respirometric Response
Raw Data
Normalized Response
1
4
.
0
0
B
A
1
2
.
0
0
DO Conc. (mg/L)
1
0
.
0
0
8
.
0
0
6
.
0
0
4
.
0
0
0
2
0
0
4
0
0
6
0
0
8
0
0
1
0
0
0
0
2
0
0
0
4
0
0
8
0
0
1
2
0
0
Time (s)
Time (s)
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Participating Plants
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Acetone
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Ethylene Glycol
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Furfural
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Furfural Respirometric Response
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Furfural and Furoic Acid
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Furfural
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Furoic Acid
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Two-step model
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Field Results - variability
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Competent Biomass

• Assumption that COD fraction is a good estimate
  not always accurate
• Required an alternative method to evaluate
  competent biomass when COD fraction not adequate
• Proposed using a model calibration period

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Model Calibration
Steady-state mass balance equation for effluent
concentration
Rearranged gives
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Acetone Competent Fraction
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Furfural, furoic acid
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