Effect of Batch Discharges on Extant Biodegradation Kinetics in Activated-Sludge Systems
Abstract:The biodegradation kinetics of several toxic organic compounds were determined during the operation of two sequencing batch reactor activated-sludge systems to evaluate the effect of specific operational changes on the degradative ability of the biomass. The length of the fill period had a dramatic effect on the measured kinetic parameters for phenol, 4-chlorophenol, acetic acid, and monochloroacetic acid. The shortest fill period (0.08 hours) corresponding to an instantaneous food-to-microorganism (F:M) ratio of 106.6 kg chemical oxygen demand (COD)/kg biomass·d resulted in the greatest degradative ability with respect to the maximum specific growth rate, μ but resulted in the lowest substrate affinity (highest half-saturation coefficient, Ks value). Longer fill periods (1.5 and 3 hours, corresponding to instantaneous F:M of 5.68 and 2.84 kg COD/kg biomass'd, respectively) resulted in monotonically decreasing μ and Ks values. In separate tests when phenol was excluded from the feed for a IS-day period, the degradative ability of phenol was partially maintained but at a lower rate and increased affinity (lower Ks ). Removing phenol from the feed also had an effect on the 4-chlorophenol biodegradation kinetics, although no changes were made to the concentration of 4-chlorophenol in the feed. In addition, when both phenol and 4-chlorophenol were excluded from the feed, the degrading activity of both compounds decreased, but at different degrees. These results suggest that the way that a treatment system is operated with respect to batch discharges of toxic organic compounds can have a significant effect on measured biodegradation kinetics and consequently will affect design and operation of these systems to achieve specific effluent limits.
Document Type: Research Article
Publication date: May 1, 1999
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