Web Release Date: June 21,
Removal of Antibiotics in Wastewater: Effect of Hydraulic and Solid Retention Times on the Fate of Tetracycline in the Activated Sludge Process
and
Department of Civil, Structural, and Environmental Engineering, State University of New York at Buffalo, 207 Jarvis Hall, Buffalo, New York 14260, and Department of Chemistry, State University of New York at Buffalo, 611 Natural Science Complex, Buffalo, New York 14260
Received for review January 2, 2005
Revised manuscript received May 7, 2005
Accepted May 10, 2005
Abstract:
A study was conducted to examine the influence of
hydraulic retention time (HRT) and solid retention time
(SRT) on the removal of tetracycline in the activated sludge
processes. Two lab-scale sequencing batch reactors
(SBRs) were operated to simulate the activated sludge
process. One SBR was spiked with 250 
g/L tetracycline,
while the other SBR was evaluated at tetracycline
concentrations found in the influent of the wastewater
treatment plant (WWTP) where the activated sludge was
obtained. The concentrations of tetracyclines in the influent
of the WWTP ranged from 0.1 to 0.6 g/L. Three different
operating conditions were applied during the study
(phase 1-HRT: 24 h and SRT: 10 days; phase 2-HRT:
7.4 h and SRT: 10 days; and phase 3-HRT: 7.4 h and SRT:
3 days). The removal efficiency of tetracycline in phase
3 (78.4 ± 7.1%) was significantly lower than that observed
in phase 1 (86.4 ± 8.7%) and phase 2 (85.1 ± 5.4%) at
the 95% confidence level. The reduction of SRT in phase
3 while maintaining a constant HRT decreased tetracycline
removal efficiency. Sorption kinetics reached equilibrium
within 24 h. Batch equilibrium experiments yielded an
adsorption coefficient (Kads) of 8400 ± 500 mL/g and a
desorption coefficient (Kdes) of 22 600 ± 2200 mL/g. No
evidence of biodegradation for tetracycline was observed
during the biodegradability test, and sorption was found
to be the principal removal mechanism of tetracycline in
activated sludge.
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