Design and operating strategies for bioreactors treating dynamically varying concentrations of gas-phase volatile organic compounds (VOCs)

The dynamically varying concentrations of volatile organic compounds (VOCs) in most waste gas streams present a challenge in design and operation of biofilters treating such off-gases. Studies described in this dissertation were directed toward development and experimental testing of two design modifications/operating strategies that have the potential to improve biofilter performance during unsteady-state loadings. In the first design modification studied, activated carbon was incorporated into biofilter packing media and a novel periodic operating strategy, Sequencing Batch Biofilter (SBB) operation, was tested under “normal” and various “shock” loading conditions treating methyl ethyl ketone contaminated air. Results demonstrate how the operational flexibility of the SBB system can lead to higher overall removal efficiency and higher minimum instantaneous removal efficiency than are achieved in a conventional continuous flow biofilter (CFB) during transient loading. Denaturing gradient gel electrophoresis of PCR-amplified genes coding for 16S rRNA was used to assess differences in bacterial community structure as a function of height in the SBB and CFB columns. Results suggest that SBB operating strategy can impart a sufficiently large selective pressure to influence microbial community structures. In the second design modification studied, an activated carbon column was placed in series before a biofilter to assess the potential of the combined system to effectively treat discontinuously loaded VOC mixtures. Abiotic fixed-bed sorption experiments and numerical modeling were conducted to assess the degree of load equalization achieved by GAC columns for gas streams containing intermittent concentrations of acetone and toluene present as single-component contaminants and as a mixture. Performance of the GAC-biofilter integrated system was experimentally evaluated in comparison to a conventional biofilter in treating a mixture of acetone and toluene at various discontinuous loadings. Results demonstrate that load dampening achieved by a passively-operated GAC buffering system can lead to more complete contaminant removal during biofilter treatment. Further, this can minimize diminished performance caused by starvation encountered in conventional biofilters under discontinuous loadings. Because of competitive adsorption, however, the degree of load equalization achieved by a passively operated GAC system for different constituents in multi-contaminant gas streams can vary markedly

A New Lab for Testing Biofiltration for Advanced Life Support

Bioregenerative systems for removal of gaseous contaminants are desired for long-term space missions to reduce the equivalent system mass of the air cleaning system. This paper describes an innovative design of a new biofiltration test lab for investigating the capability of biofiltration process for removal of ersatz multicomponent gaseous streams representative of spacecraft contaminants released during long- term space travel. The lab setup allows a total of 24 bioreactors to receive identical inlet waste streams at stable contaminant concentrations via use of permeations ovens, needle valves, precision orifices, etc. A unique set of hardware including a Fourier Transform Infrared (FTIR) spectrometer, and a data acquisition and control system using LabVIEW\sT software allows automatic, continuous, and real-time gas monitoring and data collection for the 24 bioreactors. This lab setup allows powerful factorial experimental design. In the initial phase of testing, the bioreactors will be operated in parallel to evaluate their ability to remove a complex mixture of contaminants including ammonia, carbon monoxide, methane, ethylene, acetone, and n- butanol at various operating strategies (e.g., different reactor configurations, packing medium types, gas residence time, and liquid types). Details of the experimental setup are presented herein together with pilot tests conducted to evaluate the lab setup