Grantee Research Project Results
Final Report: Innovations in Vapor Phase Bioreactor Design
EPA Grant Number: R826168Title: Innovations in Vapor Phase Bioreactor Design
Investigators: Kinney, Kerry A.
Institution: The University of Texas at Austin
EPA Project Officer: Hahn, Intaek
Project Period: December 1, 1997 through November 30, 2000
Project Amount: $293,809
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
Vapor-phase bioreactors (VPBs) have the potential to treat air streams contaminated with volatile organic compounds (VOCs) in a cost-effective and efficient manner. However, conventional bioreactor systems do not adequately control several important operating parameters such as biomass distribution, biomass activity, and nutrient/moisture levels within the biofilm. These simple systems work acceptably during short-term tests in the laboratory, but fail to ensure reliable performance in the field where process variables fluctuate widely. Typically, these systems are analyzed using a black box approach over short periods of operation, and the activity of the biomass responsible for pollutant degradation remains uncharacterized. The overall goals of this research project were to develop an innovative VPB that operates reliably over long periods of operation, and to characterize the temporal and spatial distribution of active biomass in the systems.
In this research project, three design features were tested for their ability to overcome several problems that inhibit reliable bioreactor performance over long periods of operation: (1) directionally switching (DS) operation (to improve biomass distribution and prevent clogging); (2) slip stream feed (to maintain high biomass activities even during periods of little or no contaminant feed); and (3) aerosol delivery system (to efficiently deliver nutrients and moisture to the biofilm).
More specifically, the DS feature was examined to determine the optimal switching frequency needed to control biomass accumulation, and the effect of contaminant-loading rate and gas residence time on biomass activity and composition. The slip stream feed was studied to assess the contaminant mass flow rate required to maintain high biomass activities, and the length of time that a slip stream feed could maintain acceptable pollutant-degrading microbial activities. Specific issues that were addressed for the aerosol delivery system include: (1) the capture efficiency of the aerosol as it passed through the packed bed; and (2) the effect of nitrogen utilization on biofilter performance.
Summary/Accomplishments (Outputs/Outcomes):
Bioreactor column studies reveal that DS operation promotes a more even distribution of active biomass along the column and yields more stable performance than unidirectional operation. These results indicate that DS operation is a feasible bioreactor control method that can be implemented easily without a significant change in conventional bioreactor design. Of the three switching frequencies (1-, 3-, and 7-day cycles) tested in this research project, the 3-day switching frequency yielded the most efficient bioreactor performance by balancing reacclimation requirements with biodegradation activity losses. Although DS operation can substantially extend bioreactor life, biomass continuously accumulates in the mixed-culture biofilm of the DS bioreactor, and pollutant-degrading microbial activity declines with increasing operation time and toluene loading rate, regardless of operating conditions. As a result, a supplemental control method to remove the excess biomass should be considered along with DS operation to guarantee reliable VPB operation for extended periods.
A slip feed system can maintain the pollutant-degrading microbial activity in a VPB during starvation or shutdown periods. By maintaining microbial activity in the carbon-deprived zones of the bioreactor, the slip feed system improves the biodegradation capacity in the carbon-deprived zones and increases the overall pollutant degradation capacity of the bioreactor during spike loads. The main benefit of the slip feed system is a reduction in the reacclimation period required following a shutdown period. It can reduce the reacclimation time required to achieve 90-percent removal by 65 percent after a 3-day shutdown period, and by 70 percent after a 7-day shutdown period. Trace levels of pollutant provided by the slip feed stream may prevent the biomass from completely shutting down their pollutant degradation pathways; as a result, the initial removal efficiency is higher in the bioreactor after restart. This greatly reduces the total mass of pollutant that is emitted following restart of the bioreactor.
The aerosol system proved to be an effective method for delivering nutrients and moisture to biofilters packed with either natural compost media or synthetic pelletized media. The aerosol system required a minimal amount of water to deliver the nutrients, and had little impact on the pressure drop across the biofilter column. The aerosol was delivered throughout the length of the biofilter column; however, more aerosol was captured in the front half of the column. This skewed distribution of the aerosol delivery was acceptable, because more nutrients are required in the front half of the column where most of the contaminant biodegradation takes place.
Bioreactor performance is a strong function of the nitrogen concentration available in the packing media. Reductions in media nitrogen concentration led to declines in VOC elimination capacity, implying that a threshold amount of nitrogen should be supplied to maintain bioreactor performance. A soluble nitrogen concentration of 200 mg N/kgmedia was suggested as a threshold in this study. In addition, recycling of soluble nitrogen occurs in the media as nitrogen taken up by microbial cells is mineralized to ammonia when the cells die and lyse. The nitrogen recycling process appears to become more efficient as the nitrogen levels in the media decrease. As a result, both the nitrogen recycle efficiency and the media nitrogen levels should be considered to improve bioreactor performance.
The experimental results of this research project indicate that changes in biofilm characteristics with respect to biomass distribution, activity, and composition strongly reflect overall VPB performance. In spite of the significance of these changes in evaluating bioreactor performance, most VPB studies conducted to date have focused on overall pollutant-degrading capacity at a certain point in time. These simple "black box" approaches have substantially limited not only our understanding of VPB processes, but also our capability to predict VPB performance over extended periods. Continuous monitoring of bioreactor performance with respect to biomass quantity and pollutant-degrading activity is required to better predict the fate of VPB.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 15 publications | 4 publications in selected types | All 4 journal articles |
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Park J, Kinney KA. Evaluation of slip feed system for vapor-phase bioreactors. Journal of Environmental Engineering - ASCE 2001;127(11):979-985. |
R826168 (Final) |
not available |
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Song J, Kinney KA. Effect of vapor-phase bioreactor operation on biomass accumulation, distribution, and activity: linking biofilm properties to bioreactor performance. Biotechnology and Bioengineering 2000;68(5):508-516. |
R826168 (1999) R826168 (Final) R826128 (Final) |
Exit |
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Song J, Kinney KA. Effect of directional switching frequency on toluene degradation in a vapor-phase bioreactor. Applied Microbiology and Biotechnology 2001;56(1-2):108-113. |
R826168 (1999) R826168 (Final) |
Exit |
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Song J, Kinney KA. Microbial response and elimination capacity in biofilters subjected to high toluene loadings. Applied Microbiology And Biotechnology. 2005;68(4):554-559. |
R826168 (Final) |
not available |
Supplemental Keywords:
air, volatile organic compound, VOC, environmental biotechnology, vapor-phase bioreactor, VPB, directionally switching, DS, slip feed system, nutrient aerosol delivery, biomass accumulation, pollutant-degrading activity., Scientific Discipline, Air, Environmental Chemistry, air toxics, Engineering, Chemistry, & Physics, Environmental Engineering, airborne suspension, atmospheric particles, chemical treatment, emission control technologies, VOCs, air sampling, biomass, vapor phase bioreactors, environmental contaminants, directionally-switching parameters, treatment, biofilms, biofiltration systems, cost effective, innovative technologiesRelevant Websites:
http://www.ce.utexas.edu/prof/kinney/ Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.