Bioreactor for Air Pollution Control 1.0 Introduction
Bioreactor use a natural process to survive in terms of it must have a source of energy (food) and water (moisture). In air bioreactor, moist air is passed through solid media having been previously with specific micro-bacteria that metabolizes in pollutant in the gas into useful products or less toxic substances. Same like water biofiltration, the biofilm / biomass layer that forms on the media serves as a biochemical reaction site where a mass exchange of the gaseous pollutant is converted into a non-odorous or nontoxic gaseous product. Recently, plastic based air biofilter media has been developed for odor control application (Deshusses, et al. 2004). Many of these plactic, shaped materials have low surfaces surfaces areas resulting resulting in the formation formation of flow bacterial bacterial surface populations populations per unit volume. They are also costly, voluminous and are inefficient in their bioconversion.
In air pollution, bioreaction is simply the use of microbes to consume pollutants form a contaminated air stream. Almost any substance, with the help of microbes, will decompose (decay) given the proper environment. Certain microbes also can consume inorganic inorganic compounds such as hydrogen sulfide and nitrogen nitrogen oxides.Bioreac oxides.Bioreactor tor use only small amounts amounts of electrical electrical power to drive two or small motors. motors. Bioreactors Bioreactors also do not require full-time labor and the only operating supplies needed are small quantities of macronutrients. Most common of bioreactor type, biofilter usually used beds ( media where microbes lives) made from naturally occuring organic material that are slowly consumed consumed by the biomass biomass for example microbes. These beds can supply supply macronutri macronutrients ents needed to sustain the biomass.
Although bioreactor do the work, the microbes are picky in what they will eat. Microbes need all the biotic factors such as right pollution concentration, temperature, humidity and pH.
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2.0 Objectives
To know what is bioreactor
To know what microorganism that been used in this process
To know what the advantages and disadvantages when used this process
3.0 Task 3.1 Process Principle
Microbes have a simply life cycle such as born, eat, grow, reproduce and die. Their food based on carbon-based compound such as water and oxygen for aerobic reactions and also macronutrients. Microbes be used by bioreactors to remove pollutant from emission by consume the pollutants. Its simple concept but can be quite complicated. About hundreds years ago, bioreactors be used to treat sewage and other odoriferous, water-borne waste. Europeans started using bioreactors since sixty years ago to treat contaminated air or odors, especially emission from sewage treatments plants and rendering plants. The initial process used device usually a rectangular box contains an enclosed plenum on the bottom, a support racks above the plenum and several feet of media (bed) on top of the support rack. This device was called biofilter.
Figure 3.1.1 Basic biofilter
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Oyster shells and fertilizer sometimes used to mix with bed media. The support racks used to allow air from the plenum to move into the bed media to contact microbes that live in the bed. The supports racks are perforated also permit excess, condensed moisture to drain out of the bed to the plenum. To collect contaminated air from a building or process, it used fan. Pre-treat used to contaminated air stream to obtain optimums conditions before introducing it into bioreactor if the air is too hot, too cold, too dry, or too dirty with suspended solids. When the emission flows through the bed media, the pollutants are absorbed by moisture on the bed media and come into contact with microbes.
Pollutions concentrations will be reduced by consuming and metabolizing pollutants. The will be done by the microbes. Enzymes in the microbes convert compound into energy, CO2 and water during the digestion process. The material that indigestible is left over and become residue.
Figure 3.1.2: Biofilter with emission recycle
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3.2 Biochemical reaction(s)
Organic Pollutant + O2 CO2 + H2O + Heat + Biomass 3.3 Function of microorganisms in the process
In air pollution, bioreactor use microbes to consume pollutants from a contaminated air stream. Almost any substance, with the help of microbes, pollution will decompose and give the proper environment. This is especially true for organic compounds. But certain microbes also can consume inorganic compounds such as hydrogen sulfide and nitrogen oxides. 3.4 Biotic / abiotic factors that affect these organisms
Temperature
The most important variable affecting bioreactor operations is temperature. A blast of hot air can totally kill a biomass faster than any other accident. Most microbes can survive and flourish in a temperature range of 30 to 41/C.
Moisture
Microbes need moisture to survive and moisture creates the bio-film that removes pollutants from an air stream so that they can be assimilated by microbes. Low moisture problems can be corrected by passing emissions through a humidifier. Having emissions close to saturation 100 % relative humidity will solve most dry bed problems. Humidifiers need not be fancy, store-bought, stainless steel process vessels.
Microbe Population
The strains that flourish on pollutants in an emission stream will eventually dominate the bed environment. The natural method will take a little longer to acclimate to optimum efficiency, but, because of the diversity of the strains of microbes, will be more adaptable in the long run. Specific microbes that are developed in the lab are more susceptible to changes in the environment than naturally generated microbes.
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3.5 List of advantages and disadvantages of the bioreactor process
Advantages of Biofiltration:
Lower capita costs, lower operating costs, low chemical usage, and no combustion source.
Can be designed to physically fit into any industrial setting.
Biofiltration is versatile enough to treat odors, toxic compounds, and VOCs.
Different media, microbes and operating conditions can be used to tailor a biofilter system for many emission points.
Disadvantages of Biofiltration:
Large land requirement for traditional design.
No continuous internal liquid flow in which to adjust bed pH or to add nutrients.
Traditional design does not have a covered top, making it difficult to obtain representative samples of exhaust emission and to determine DREs.
Natural bed media used in biofilters must be replaced every 2 to 5 years.
4.0 Conclusions
Bioreactor use microbes to consume pollutants form a contaminated air stream. When use living cultures, they are affected by many variables such as temperature, moisture content and microbe population. All this variables will determine the effect of performance of all bioreactor. These are crucial variables for which optimum conditions must be determined, controlled and maintained. Bioreactor is a viable, low cost option in some circumstances, for the facilities that have emissions that qualify for this technology. Bioreactor also far less expensive than traditional control technologies and easily to achieved efficiencies than the traditional control technologies.
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5.0 References
1. Q. Zhang et al, "Odor Production, Evaluation and Control", Department of Biosystems Engineering, University of Manitoba, October 2002. 2. Peter L. Voigt; "Biofiltation for Odor and VOC Control"; Clean TeQ Publication, Dandeneng, Victoria, Australia, 3175. 3. Air Compliance Advisor, U.S. EPA, OAQPS/ISEG, 2000. 4. Marc A. Deshesses and Huub H. J. Cox, “Biotrickling Filter Air Pollution Control”, Department of Chemical & Environmental Engineering, University of California, Riverside, CA, 2000.
6.0 Appendixes
Experiment Non-Use Period Humidification Toluene Benzened
Test 1 (days)
Test 2 (days)
Test 3 (days)
Test 4 (days)
Test 5 (days)
Initial Start-up NO 4 7.25
1.67
3.73
3.73
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NO 0.46 0.17
NO 1 0.21
YES 0.39 0.21
YES 1.8 2.75
Table 6.1: Bioreactor Re-Acclimation Times after Periods of Non-Use
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