Development of a hollow fiber membrane bioreactor for cometabolic degradation of chlorinated solvents

The purpose of this research was to develop the hollow fiber membrane (HFM) bioreactor system for treatment of chlorinated solvents in waste mixtures. This new technology employs a hollow fiber membrane reactor to separate chlorinated solvents from water or air with subsequent cometabolic biodegradation using a mutant methanotrophic microorganism, Methylosinus trichosporium OB3b PP358. Research objectives included demonstrating successful performance of the HFM bioreactor system for the treatment of trichloroethylene (TCE) contaminated water and air, increasing process efficiency for cost competitiveness with conventional technologies, extending HFM bioreactor studies to chlorinated solvent mixtures, and developing a system design strategy.; HFM bioreactor demonstration experiments evaluated various process configurations, flow rates, and influent TCE concentrations. In TCE contaminated water experiments, mass transfer coefficients as large as 2.7 × 10−2 cm/min were estimated and the system was able to sustain an average first-order degradation rate constant of 0.57 L mg TSS−1 d −1 for 500 hours. While configuring the system with chlorinated solvents flowing through the HFM lumen and microorganisms flowing through the HFM shell was preferred for aqueous experiments, air treatment experiments required switching the flows because water vapor mass transfer resulted in water clogged fiber lumen.; Following the demonstration experiments, shorter HFM hydraulic residence times between 0.16 and 0.57 minutes were investigated. A tradeoff between providing sufficient oxygenation and methanol stripping in the chemostat was observed. A new process decision variable, specific transformation was defined and values as large as 38.5 μg TCE/mg TSS were sustainable for TCE treatment. In HFM bioreactor experiments with a mixture of TCE and chloroform (CF), large TCE first-order degradation rate constants between 0.75 L mg TSS−1 d−1 and 1.08 L mg TSS−1 d−1 indicated that the addition of CF did not affect TCE degradation. CF mass transfer coefficients were approximately 10% less than TCE coefficients and the average CF degradation rate constant was 0.32 that of TCE. Computer models of mass transfer and biodegradation in the system were constructed and validated with experimental data. A modeling analysis was then conducted on the important decision variables and parameters and the results were used to develop a system design strategy.