A Simpler Approach for Determining Biodegradation of SOCs in Wastewater Treatment Tim Ellis Associate Professor Dept. of Civil and Construction Engineering Iowa State University

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

Background Technique originally developed at Clemson University under direction of Les Grady Technique originally developed at Clemson University under direction of Les Grady Several assumptions in the technique 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

Basis of Technique Sample of mixed liquor obtained from operating wastewater treatment plant Sample of mixed liquor obtained from operating wastewater treatment plant Sample is placed in a respirometer vessel and aerated with O 2 Sample is placed in a respirometer vessel and aerated with O 2 Respirometer is sealed and DO concentration is continuously measured and recorded Respirometer is sealed and DO concentration is continuously measured and recorded

Typical Response

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

Biodegradation Model (h -1 ) S (mg/L as COD)

Experimental Set-up CMAS D.O. Meter Data Acquisition InjectionPort WaterBathBiomassSample D.O. Probe Respirometric Vessel

Respirometric Response Raw Data Normalized Response A B DO Conc. (mg/L) Time (s)

Participating Plants

Acetone

Ethylene Glycol

Furfural

Furfural Respirometric Response

Furfural and Furoic Acid

Furfural

Furoic Acid

Two-step model

Field Results - variability

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

Model Calibration Steady-state mass balance equation for effluent concentration Rearranged gives:

Acetone Competent Fraction

Furfural, furoic acid