Browsing by Author "Sabalowsky, Andrew R."

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Trichloroethene and cis-1,2-dichloroethene concentration-dependent toxicity model simulates anaerobic dechlorination at high concentrations: I. batch-fed reactors
(2010-04) Sabalowsky, Andrew R.; Semprini, Lewis
A model was developed to describe toxicity from high concentrations of chlorinated aliphatic hydrocarbons (CAHs) on reductively dechlorinating cultures under batch-growth conditions.A reductively dechlorinating anaerobic Evanite subculture (EV-cDCE) was fed trichloroethene (TCE) and excess electron donor to accumulate cis -1,2-dichloroethene (cDCE) in batch-fed reactors. A second Point Mugu (PM) culture was also studied in the cDCE accumulating batch-fed experiment, as well as in a time- and concentration-dependent cDCE exposure experiment. Both cultures accumulated cDCE to concentrations ranging from 9,000 to 12,000 Î¼M before cDCE production from TCE ceased. Exposure to approximately 3,000 and 6,000mM cDCE concentrations for 5 days during continuous TCE dechlorination exhibited greater loss in activity proportional to both time and concentration of exposure than simple endogenous decay.Various inhibition models were analyzed for the two cultures, including the previously proposed Haldane inhibition model and a maximum threshold inhibition model, but neither adequately fit all experimental observations. A concentration-dependent toxicity model is proposed, which simulated all the experimental observations well. The toxicity model incorporates CAH toxicity terms that directly increase the cell decay coefficient in proportion with CAH concentrations. We also consider previously proposed models relating toxicity to partitioning in the cell wall (KM/B), proportional to octanolâ€“ water partitioning (KOW) coefficients. A reanalysis of previously reported modeling of batch tests using the Haldane model of Yu and Semprini, could be fit equally well using the toxicity model presented here, combined with toxicity proportioned to cell wall partitioning. A companion paper extends the experimental analysis and our modeling approach to a completely mixed reactor and a fixed film reactor.
Trichloroethene and cis-1,2-dichloroethene concentration-dependent toxicity model simulates anaerobic dechlorination at high concentrations: II: continuous flow and attached growth reactors
(2010-06) Sabalowsky, Andrew R.; Semprini, Lewis
A model that was used to describe toxicity from high concentrations of chlorinated aliphatic hydrocarbons (CAHs) on reductively dechlorinating cultures in batch reactors (Sabalowsky and Semprini [in press]) was extended here to simulate observations in continuous flow suspended and attached growth reactors.The reductively dechlorinating anaerobic Evanite subculture (EV-cDCE) was fed trichloroethene (TCE) and excess electron donor to accumulate cis-1,2-dichloroethene (cDCE) in a continuous flow stirred tank reactor (CFSTR); and an attached growth recirculating packed column (RPC). A concentration-dependent toxicity model used to simulate the results of batch reactors in part I (Sabalowsky and Semprini [in press, Biotechnol Bioeng]) also simulated well the observations for the CFSTR and RPC growth modes. The toxicity model incorporates cDCE and TCE toxicity coefficients that directly increase the cell decay coefficient in proportion with cDCE and TCE concentrations.Simulated estimates of the cDCE and TCE toxicity coefficients indicate reductively dechlorinating cells are most sensitive to high concentrations of cDCE and TCE in batch-fed growth, followed by CFSTR, with attached growth being least sensitive. The greater toxicity of TCE than cDCE, and ratio of the modeled toxicity coefficients, agrees with previously proposed models relating toxicity to partitioning in the cell wall (KM/B), proportional to octanol-water partitioning (KOW) coefficients.