Biomedical subjects

S Uludag-Demirer

Publications and source records attributed to S Uludag-Demirer.

3 recordsLinked to original sources

PubMed2005

Control of trichloroethylene emissions from sparging systems by horizontal bio- and chemo- barriers.

The scope of this study was to develop a continuous system to clean-up a trichloroethylene (TCE) contaminated gas stream, where biotic and abiotic removal mechanisms are undertaken sequentially simulating the horizontal bio- and chemo-barriers proposed for the in-situ remediation of the contaminated sites. The bio- and chemo-barriers were simulated by using glass columns packed with granular anaerobic mixed culture and Fe(0) filings, respectively. The effect of gas residence time, which is adjusted by the gas flowrate, on the TCE removal efficiency of the reactor system was investigated. TCE removal efficiency of over 90% was achieved at gas residence times above 1hr. Furthermore, the effluent of reactor system contained only ethane and ethylene, which are non-toxic by-products of TCE reduction reactions, along with trace amounts of TCE.

Air Pollutants↗

PubMed2001

Comparison of methods for estimating carbonaceous BOD parameters.

The performance of seven different methods (Differential, Fujimoto, Thomas, Graphical, Integral, Log-Difference, and Nonlinear Regression) for estimating first-stage, carbonaceous biochemical oxygen demand (CBOD), curve parameters, namely k and L0, were compared using synthetic data generated by Monte Carlo simulation technique. The comparison of the methods was made based on their efficiency in retrieving the original values of k and L0, which were selected to generate the synthetic data. In the first part of the study, five sets of "true" data (without error substitution) with different k and L0 value pairs, (k (d(-1))-L0 (mg l(-1)): 0.23-10,000; 0.23-250; 0.23-50; 0.10-250; and 0.50-250) were used to obtain information about the effect of different k-L0 combinations and of using 5-day and 20-day CBOD data on the performance of the methods. In the second part, the same methods were used to calculate k and L0 for ten sets of synthetic data with log-normally distributed random errors at the coefficient of variation (COV) levels of 0.1, 0.2, and 0.3 for a single k-L0 value pair, (0.23 d(-1); 250 mg l(-1)). The results indicated that: (1) different combinations of k-L0 values had no significant effect on the performance of CBOD curve parameter estimation methods with the "true" data; (2) use of CBOD20 data, i.e., CBOD data collected for 20 days, provided better estimates for k and L0; (3) the Integral and Nonlinear Regression techniques were found to be the most reliable methods for the estimation of CBOD curve parameters among the other methods considered in this study.

Carbon↗

PubMed2001

Gas phase reduction of chlorinated VOCs by zero valent iron.

The removal of trichloroethylene (TCE) by reduction with elemental iron was examined in batch reactors representing three phase gaseous systems (Fe0 (solid), water vapor + TCE vapor + air mixture (gaseous), and condensed water on Fe0 surface (aqueous)) and two phase aqueous systems (Fe0 (solid), water (aqueous)) as the reaction medium. Two separate removal mechanisms were found for TCE removal in the gas phase reactors: (1) adsorption onto the Fe0 surface under low relative humidity (RH), and (2) reaction with Fe0 to form other organic compounds, such as ethylene, isomers of dichloroethylene, and vinyl chloride under 100% RH conditions in the gas phase. The adsorption of TCE vapor onto the Fe0 surface was fast initially and highest at low temperatures. The reduction reaction of TCE in the gas phase was first order with respect to the TCE concentration remaining in the gas phase under conditions of 100% RH at 15, 22, and 35 degrees C, and the observed reaction rate constant (kobs) exhibited a maximum at elevated temperatures. The estimated kobs values for the degradation of dissolved TCE in aqueous systems were the same order of magnitude with the rate constants in the gas phase and exhibited an increasing rate at higher temperatures. The results suggest that Fe0 represents an economical choice for vapor phase barriers to limit the spread of contaminants in soil gas and reduce fugitive air emissions from contaminated sites.

Absorption↗