Superfund Research Program
Scientists Investigate the Properties and Structure of Biofilm Treatment Systems
Biofilm treatment systems are rapidly becoming a popular method for the bioremediation of toxic organic compounds because of their superior performance over conventional technologies. Biofilms consist of microbial cells and the extracellular biopolymer they produce. The bacteria within biofilms can break down contaminants making biofilms useful for waste water treatment and hazardous waste remediation. However, the use of biofilm technology for bioremediation has been somewhat limited because, until recently, very little was known about the basic structure of biofilms and their role in mediating treatment processes. Without a clear understanding of the mechanics of biofilm treatment systems, it has been difficult to optimize and improve the technology to one of sustained, cost-effective utility.
Scientists at the University of Cincinnati have addressed the need for a mechanistic understanding of biofilm treatment systems by closely examining the structure and properties of biofilms used in the treatment of toxic waste waters. This is being accomplished by spatially and quantitatively characterizing the microbial populations in biofilms; by evaluating transport mechanisms for contaminants, nutrients, and by-products in and out of the biofilms; and by applying the results to full-scale treatment systems.
The researchers are currently focusing on the use of biofilms to biodegrade a variety of azo dyes, which are serving as model toxic organic compounds in the studies. As a class of compounds, azo dyes range from easily biodegradable to essentially nonbiodegradable. They serve as an effective test of the ability of biofilms to degrade recalcitrant organic compounds. An organism was recently isolated and identified that is capable of aerobically converting some azo dyes into harmless end products without producing any of the toxic intermediates that usually occur. This organism, a type of Sphingomonas bacteria, is now being grown in waste water biofilm reactors and is demonstrating nearly complete biodegradation of the azo dyes in the reactor feed water. Additionally, the scientists developed a fluorescent antibody for the bacteria which is being used to determine numbers and locations of the microbe in the biofilm.
The scientists have also developed a series of microelectrodes for the measurement of chemical conditions inside biofilms. Because of their tiny tip size and rapid response time, the microelectrodes enable direct and non-destructive measurements of conditions inside the biofilms. The microelectrodes can measure dissolved oxygen, pH, redox potential profiles, ammonium, nitrate and sulfide in waste water biofilms. These measurements aid in the understanding of the internal structure of biofilms. The influence of biofilm structure on transport mechanisms and environmental conditions can also be determined by these measurements.
In order to gain a clearer understanding of the physical biofilm structure, scientists have employed a sophisticated imaging technique, known as confocal scanning laser microscopy, to reveal the fine details of biofilm structure in fixed-film waste water treatment systems. This area of research will lead to subsequent studies that identify the rate-limiting processes in bioremediation systems.
This research is significant because it provides basic mechanistic knowledge that is of great benefit to engineers who design treatment systems for waste water or groundwater. The results are being applied to real-world waste water treatment systems with the intent to extend investigations into soil bioremediation. Furthermore, researchers investigating other toxic organic compounds undergoing biofilm treatment can apply the analytical procedures to their studies.
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To learn more about this research, please refer to the following sources:
- Bishop PL. 1997. Biofilm structure and kinetics. Water Sci Technol 36:287-294.
- Coughlin MF, Tepper A, Kinkle BK, Bishop PL. 1997. Characterization of aerobic azo-dye degrading bacteria and their activity in a wastewater biofilm. Water Sci Technol 36:215-220.
- Taylor DG, Breen A, Bishop PL. 1997. Determination of phenol-degrader distribution in biofilms using gene probes. Water Res 31:119-129.
- Kudlich M, Knackmuss HJ, Stolz A, Bishop PL. 1996. Simultaneous anaerobic and aerobic degradation of the sulfonated azo dye Mordant Yellow 3 by immobilized Cells from a naphthalenesulfonate-degrading mixed culture. Appl Microbiol Biotechnol 46(5-6):597-603.
- Fu YC, Bishop PL. 1995. The evaluation of respiration rate in fixed-film systems under various organic loading rates. Water Environ Res 67:1036-1043.
- Zhang TC, Fu YC, Bishop PL. 1995. Competition for substrate and space in biofilms. Water Environ Res 67:992-1003.
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