Grantee Research Project Results
1998 Progress Report: Innovative Biomass Control Technology for Biotrickling Filters for Waste Air Treatment
EPA Grant Number: R825392Title: Innovative Biomass Control Technology for Biotrickling Filters for Waste Air Treatment
Investigators: Deshusses, Marc , Wistrom, Anders O.
Institution: University of California - Riverside
EPA Project Officer: Hahn, Intaek
Project Period: November 1, 1996 through October 31, 1998
Project Period Covered by this Report: November 1, 1997 through October 31, 1998
Project Amount: $186,270
RFA: Exploratory Research - Air Engineering (1996) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Air , Safer Chemicals
Objective:
The original objective of this proposal was to develop a general strategy to control biomass growth in biotrickling filters for waste air treatment by engineering predation of the bacterial process culture by protozoa. A detailed description of the original objectives is available in the 1997 report. In light of the first year's results, the objectives have been broadened to include a more general understanding of the factors that influence biomass growth and pollutant elimination in biotrickling filters so that better biomass control strategies can be developed.
Progress Summary:
The first year experiments in shake flasks with the protozoa Tetrahymena pyriformis fed on toluene vapors degrading bacterial cultures were continued. T. pyriformis effectively grazed on the toluene-degrading bacteria and, in the presence of protozoa, biomass yields were strongly reduced (up to three orders of magnitude). Toluene gas phase concentrations affected the predation rate of toluene-degrading bacteria by
T. pyriformis only at high toluene concentrations (2?3 gm-3), which is higher than usually encountered in biotrickling filters. This shows promise as far as future implementation of protozoa as a means for biomass control. Mathematical modeling of the predator-prey relationships was performed but was only partially successful because the variations between the experiments did not allow a good fitting of all experiments with a single set of parameters.
The results of bench-scale biotrickling filter reactors operated in parallel, one with protozoa and one without, show that clogging of bench-scale biotrickling filters could be slowed down with the use of protozoa. The presence of protozoa resulted in a lower pressure drop across the column, a lower biomass buildup, and an increase in pollutant mineralization as compared with the control biotrickling filter. The reactor with protozoa eventually clogged, which led us to consider higher organisms for the control of biomass in biotrickling filters and also motivated us to initiate a series of experiments on the use of chemicals for removal of excess biomass.
It was later fortuitously found that one biotrickling filter reactor had achieved constant weight and that another had actually lost biomass with no detrimental effect on the pollutant elimination. Further experiments were conducted to find the causes of these phenomena, and fly larvae were noticed in the biofilm while flies colonized the headspace of the reactor. These were identified as belonging to the species Colbodia fuscipes and seemed to be the origin of the observed phenomena. A number of experiments were conducted to quantify the larvae in the reactors and possibly link the presence of the larvae to the low biomass yield. The difficulty is that larvae go through a cycle (fly eggs larvae pupae flies) and that it was unknown what factors affected the cycle and what form of the insect could have an effect on biofilms. In one experiment, larvae were taken out of the reactor and were fed biofilms, but results were not conclusive. Other experiments tried to eradicate the larvae and the fly using a potent organophosphate insecticide from one bioreactor while monitoring the reactor weight, but the results were inconclusive. To date, it could not be firmly demonstrated that a cause-and-effect relationship existed between the presence of the fly larvae and the low biomass yield. Biotrickling filters are very complex systems that include bacteria, fungi, protozoa, rotifers, nematodes, and insects in a subtle equilibrium. Further research, particularly in a multidisciplinary context, will be needed to explain the observed phenomena and fully understand the microecology of the process.
One obstacle throughout this research was the difficulty in distinguishing between biofilm growth, biofilm detachment due to shear, biofilm detachment due to higher organisms tunneling, biomass consumption by predators, and link biofilm phenomena to pollutant degradation. In addition, in a three-phase (biofilm, gas, liquid) system, some pollutant degradation is achieved in the biofilm and some is achieved by suspended microorganisms. For these reasons, we have looked further into the question of how much of the pollutant was actually degraded in the biofilm and how much was degraded in the recycle liquid (suspended organisms). Using two different methods, it was demonstrated that up to 25 percent of the pollutant degraded in biotrickling filter could be degraded in the recycle liquid, and we showed that the average specific activity of the suspended cells was up to 20?30 times higher than the specific activity of the immobilized cells. This may have important implications for future reactor design, as reactors based on suspended biomass (biowasher type) do not have clogging problems and may be able to achieve much higher pollutant removal.
Finally, an original setup with 20 small lab-scale biotrickling filters that allowed us to investigate a number of parameters in parallel was constructed. Biotrickling filtration experiments with various mineral nutrient concentrations (nitrate, ammonia, urea, and other mineral nutrient limitation) were performed, and the influence on biomass growth and on the efficiency of pollutant elimination was determined. It was found that biomass yield and pollutant elimination do not vary linearly from one another. This has profound implications as far as the selection of a method for the control of biomass is concerned. A mathematical model was developed that considered nutrient supply as a key parameter limiting pollutant removal rate and biomass accumulation. Integration of the experimental results in a general treatment cost model showed that there was an optimum nutrient loading that minimized the overall treatment costs. Interestingly, the major part of the treatment costs were capital cost and the cost for controlling biomass. This confirmed that biomass control is a very important problem and that cost-effective solutions are needed to reduce treatment costs.
Overall, significant progress has been made since the project initiation. Biotrickling filters for air pollution control are very complex systems and the present understanding of these reactors is still relatively incomplete. It is our opinion that this EPA funded research has contributed to a significant improvement of the general understanding of biotricklying filters.
Future Activities:
Future modeling effort will include a comparison of previously published biomass control strategies and those developed within this project.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
Other project views: | All 20 publications | 8 publications in selected types | All 8 journal articles |
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Cox HHJ, Deshusses MA. Biological waste air treatment in biotrickling filters. Current Opinion in Biotechnology 1998;9(3):256-262. |
R825392 (1998) R825392 (Final) |
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Cox HHJ, Nguyen TT, Deshusses MA. Predation of bacteria by the protozoa Tetrahymena pyriformis in toluene-degrading cultures. Biotechnology Letters 1999;21(3):235-239. |
R825392 (1998) R825392 (Final) |
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Cox HHJ, Deshusses MA. Innovative experimental setup for the parallel operation of multiple bench scale biotrickling filters for waste air treatment. Environmental Technology 2000;21(4):427-435. |
R825392 (1998) R825392 (Final) |
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Cox HHJ, Deshusses MA. Biomass control in waste air biotrickling filters by protozoan predation. Biotechnology and Bioengineering 1999;62(2):216-224. |
R825392 (1998) R825392 (Final) |
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Cox HHJ, Deshusses MA. Chemical removal of biomass from waste air biotrickling filters: screening chemicals of potential interest. Water Research 1999;33(10):2383-2391. |
R825392 (1998) R825392 (Final) |
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Supplemental Keywords:
Future modeling effort will include a comparison of previously published biomass control strategies and those developed within this project., Scientific Discipline, Air, Environmental Chemistry, Engineering, Engineering, Chemistry, & Physics, bacteria filtration, protozoa, biomass, biofilms, waste air treatment, pollutant degrading bacteria, mathematical formulationsRelevant Websites:
http://engr.ucr.edu/~mdeshuss 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.