Grantee Research Project Results
1997 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, 1996 through October 31, 1997
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 main objective of this proposal is 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. The main advantage associated with the proposed technique is that long term stability can be obtained without reducing reactor performance. This is not the case for other techniques that are currently in their early phases of investigation. The supporting objectives for reaching this goal are: 1) quantification of predator-prey relationships between protozoa and pollutant degrading bacteria, 2) development of strategies to enhance and control grazing of biofilms in biotrickling filters, and 3) demonstration and optimization of the developed strategies in bench-scale biotrickling filters. Experiments will be performed with shake flasks, biological contactors containing both suspended and immobilized bacteria, and bench-scale waste air biotrickling filters. Mathematical modeling of the process will be performed to better understand the observed phenomena.Progress Summary:
A number of analytical methods for the quantification of bacteria and protozoa are being developed. While direct counting of bacteria and protozoa using light microscopy turned out to be the most simple technique, the Coulter Counter has been successfully applied to accurately quantifying bacteria and protozoa in various types of samples. Sequential counting of bacteria and protozoa was necessary due to their differences in size, but the technique has proved to be robust and reliable. Mild sonication and the addition of a surfactant, Tween 80, to the culture samples worked reasonably well to prevent large aggregates of biomass to clog the aperture tube during counting. In many instances, direct counting was preferred, because it allowed to simultaneously count and identify protozoa.
Initially, selection of protozoa was made based on their motility and their reported grazing activity. Pure cultures were obtained from the ATCC collection and, in parallel, a mixed culture of protozoa was enriched using activated sludge as inoculum. Shake flasks experiments were conducted with the protozoa Tetrahymena pyriformis fed on bacterial culture. Most experiment were performed in quadruplicate due to the difficulty to obtain reproducible results in the presence of protozoa. Shake flasks were used first to investigate the influence of various parameters such as pH, sodium chloride, and toluene concentration on the protozoan cultures. Next, experiments were performed with flasks continuously aerated with air contaminated with toluene. The influence of various concentrations of toluene and of nitrogen concentration in the liquid medium on the growth of both the bacterial and protozoan culture was further investigated. These results provide the baseline information on grazing rates, on optimum grazing conditions and means to control protozoan activity. Mathematical modeling of the observed predator-prey relationships will be started soon and will extend into the second year. It was shown (for the first time) that T. pyriformis could effectively graze on VOC (toluene) degrading bacteria, and that in the presence of protozoa, biomass yields were strongly reduced. Toluene gas phase concentrations commonly encountered in industrial waste gases did not significantly affect the predation rate of toluene degrading bacteria by T. pyriformis. Reducing the nitrate content of the liquid media had a strong influence on the metabolism of the cells and the predator-prey relationships. Of particular interest is that cultures with protozoa became extremely viscous, probably as a result of some polymer or protein formation. This was more pronounced when the nitrate content of the medium was reduced. Although this is not within the direct scope of this project, efforts will be placed in identifying this new phenomena and attempt to identify the product(s) formed.
At the time the project was awarded by US EPA, experiments were undergoing with two bench-scale reactors in parallel: one was operated with protozoa and one without. The intend of this -at that time unfunded- experiment, was to jump start these investigations to demonstrate the soundness of using protozoa as a control for biotrickling filters. These investigations continued for a few months after the award was made and the results are reported in the proceedings of the 1997 Annual Meeting of the Air & Waste Management Association. In summary, it was shown that clogging of bench-scale biotrickling filters could be slowed down with the use of protozoa which was evidenced by a lower pressure drop across the column, a lower biomass build-up, and an increase in pollutant mineralization in the reactor with protozoa as compared to the control. Interestingly, it was found that the reactor with protozoa had a shorter start-up time, possibly because of bacterial growth factors secreted by the protozoa. This will be investigated further as it may prove to shorten the startup phase of biotrickling filters. Also, it was observed that inoculated pure cultures of protozoa had a reduced survival in the biotrickling filter, whereas other strains of protozoa became dominant as the result of natural selection. As a whole, the results of these experiments were very encouraging because they confirmed our hypothesis that protozoa could be used to control biomass in waste air biotrickling filters. Eventually, the biotrickling filter with protozoa clogged as well, but as the conditions for grazing were not optimized, we expect that significant improvements can be made. Clearly, protozoan activity needs to be stimulated, enrichment of protozoa grazing on biofilms needs to be performed, and factors influencing the grazing kinetics of protozoa on biofilms need to be better understood. This is a major research focus for coming months and for the second year of this project.
To better understand protozoa grazing on biofilms, a series of experiments were performed with small scale (16 cm diameter) rotating disk contactors (RDCs) where the sole carbon source was toluene provided via the gas phase. The liquid phase was inoculated with various sources of protozoa: cow manure, pond sediment, aqueous phase or biofilm from laboratory biotrickling filters, activated sludge, a blank not inoculated, and a control containing cycloheximide, a common protozoa inhibitor. The reactors were operated for over 5 weeks and selected parameters pertaining to the liquid phase and to the biofilm were monitored. In summary, these experiments showed that protozoa had a significant effect on the structure of the biofilm. The cycloheximide control compartment had a very firm, high carbon content biofilm, while those biofilms attached on disks inoculated with protozoa were much less dense and had a lower carbon content. Further, it was observed that biofilms had a marked tendency to detach by large patches in compartments where protozoa were present. Hence, it was hypothesized that the benefits of protozoa in biofilm systems was not so much direct reduction of biomass by grazing, but biomass removal by triggering detachment. These experiments also showed that significant cross-contamination occurred between the compartments over time, and that certain protozoa species developed resistance to cycloheximide which is unreported to date. One manuscript is in preparation relating these experiments.
The experiment with the biotrickling filters resulted in bioreactors completely clogged with biomass. Hence, this provided an opportunity to develop a rapid protocol to test the usefulness of various chemicals to remove biomass in the event of a clogging. Two papers are in preparation and one disclosure of invention has been filed.
A very efficient bacterial phage (T7) was tested for its ability to lyse toluene mixed bacterial culture from the biotrickling filter in shake flasks. This would have offered a drastic treatment option, to biologically remove biomass. The results were negative.
Research in the second year
As it appeared that protozoa might not be the ideal predator to maintain a absolute zero balance of biomass in waste air biotrickling filters, we thought about other predators, higher up in the food chain. We recently made a fortuitous observation in our reactors: a small fly larvae, tentatively identified as belonging to the species Colbodia fuscipes seemed to be the origin of the loss of 10 kg of biomass out of initially 13 kg in a 23 L reactor within two months. Future efforts will be directed towards means to exploit the ability of Colbodia fuscipes larvae to feed on biomass in waste air biotrickling filters.
Finally, an original setup with 10 small lab-scale biotrickling filters allowing to investigate a number of parameters in parallel will be constructed. Biotrickling filtration experiments with various mineral nutrient concentrations, with protozoa, with fly larvae including appropriate controls will be performed and the influence on biomass growth and on the efficiency of pollutant elimination will be assessed. If appropriate, the optimized strategy will be demonstrated in a full-scale biotrickling filter recently constructed by the PI in the context of other research projects.
Disclosure of invention
Improved removal of excess biomass from waste-air biological trickling filters (Disclosure of invention filed with the University of California, http://www.ucop.edu/ott/ncd/ott.98-003-0.00.html) Exit
Journal Articles:
No journal articles submitted with this report: View all 20 publications for this projectSupplemental Keywords:
Scientific Discipline, Air, Environmental Chemistry, Engineering, Engineering, Chemistry, & Physics, bacteria filtration, protozoa, biomass, biofilms, waste air treatment, pollutant degrading bacteria, mathematical formulationsProgress 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.