ESTIMATION OF KINETIC RATE CONSTANTS FOR BIODEGRADATION OF CHEMICALS IN ACTIVATED-SLUDGE WASTE-WATER TREATMENT PLANTS USING SHORT-TERM BATCH EXPERIMENTS AND MU-G L RANGE SPIKED CONCENTRATIONS/

Biodegradation rate constants that are believed to be predictive for a ctivated sludge sewage treatment plants have been determined at mu g/L concentration levels using short term (hours) laboratory scale batch experiments with activated sludge. Rate constants were estimated for f our model chemicals with widely different biodegradability characteris tics, and experiments were conducted with sludges of various origin an d treatment. Test substances were applied at concentrations ranging fr om a few mu g/L for deriving first order rate constants and up to seve ral mg/L for full investigation of the kinetics. Model substances were acetate, aniline, 4-chloroaniline and pentachlorophenol and their bio degradation was assessed by means of C-14 tracer technique. Some exper iments included test concentrations equal to those prescribed in stand ard biodegradability tests (20 mg DOC/L). Sludge types investigated in cluded adapted and non-adapted sludge from laboratory scale semicontin uous reactors as well as sludges collected from a pilot scale sewage t reatment plant loaded with predominantly domestic sewage. At low chemi cal concentrations (< approx. 100 mu g/L) first order degradation rate constants were reasonably constant and varied only little with the ap plied concentration. With aniline, however, elimination rates increase d at concentrations below about 20 mu g/L, probably because transient sorption became significant. At higher concentrations absolute (linear ) degradation rates could be described by saturation kinetics, and for aniline a half saturation constant, K-s, was estimated at 3 mg/L. ''B est estimates'' of average first order rate constants in the low conce ntration regime measured with 3 g SS/L and at 22 degrees C were: aceta te, 8 h(-1); aniline, 0.8 h(-1), 4-chloroaniline, 0.15 h(-1), and pent achlorophenol, 0.01 h(-1) (non adapted sludge) or 0.02 h(-1) (adapted sludge). These figures seem to agree well with standard or default bio degradation rate constants for sewage treatment plants suggested in a European Union technical guidance document for chemical risk assessmen t, which is currently under preparation. Copyright (C) 1996 Elsevier S cience Ltd