Dissertation

Gas-phase trichloroethylene degradation and mineralization using a fixed-film biofilter

Sun, Adam Kuo-Yun

1997

Overview

The objective of this research was to develop a novel fixed-film biofilter and investigate the feasibility of this biofilter for the treatment of TCE in a laboratory setup. To select the best microorganism for the remediation of TCE, batch studies using six different microorganisms were conducted to determine biokinetic parameters (the maximum TCE degradation rate, the extent of both TCE degradation and mineralization). For TCE bioremediation, B. cepacia PR1$\\sb{23}$ was chosen because it has relatively high TCE degradation rates, a high growth rate, and the advantage of expressing the TCE-degrading enzyme (TOM) constitutively (without a toxic inducer). To show TCE degradation by the microorganism resulted in complete TCE mineralization (e.g., generation of chloride ions), a novel medium was formulated where the TCE degradation activity of B. cepacia PR1$\\sb{23}$ in a biofilter was determined without removing the fixed biomass in the biofilter. To confirm the presence of B. cepacia PR1$\\sb{23}$ and expression of its TCE-degrading enzyme (TOM), a plate assay with indole was developed. An aerobic, single-pass, fixed-film biofilter with a pure culture of B. cepacia PR1$\\sb{23}$ was designed for the continuous degradation and mineralization of gas-phase trichloroethylene (using sintered glass and activated carbon as supporting materials). At gas-phase TCE concentrations ranging from 0.04 to 2.42 mg/L of air and a volumetric air flow rate of 0.1 L/min, initial maximum TCE degradation rates of 8.6 to 392.3 mg TCE/L of reactor/day were obtained. Using chloride ion generation as the indicator of TCE mineralization, the bioreactor with activated carbon mineralized an average of 6.9 to 10.3 mg TCE/L of reactor/day at 0.242 mg/L TCE concentration with 0.1 L/min of air flow for 38 to 40 days. However, TOM was inactivated at a rate which increased with increasing TCE concentration (e.g., in $\\sim$2 days at 0.242 mg/L and less than 1 day at 2.42 mg/L) although the biofilter could be operated for longer periods at lower TCE concentrations. A mathematical model was developed which includes axial dispersion, convection, film mass transfer, and biodegradation terms coupled with TCE-degrading enzyme deactivation. The numerical simulation of this model was in good agreement in most part with the experimental results; however, the agreement was not as good at early times in the experiment. The proposed model suggests the best microorganism to be considered for TCE degradation would be a microbe with high TCE-degrading enzyme activity and high transformation capacity for TCE.

• Publisher: ProQuest Dissertations & Theses
• Subject: Chemical engineering / Environmental science
• ISBN: 0591301202, 9780591301205