This paper presents fundamental and theoretical aspects of biological waste gas treatment technologies as well as examples of applications to di†erent compounds. The three most widely used technologies are described, namely bio- -ltration, bioscrubbing and trickling bio-ltration, focusing more extensively on bio-ltration which is the most studied and most extensively used process. A description of the di†erent technologies from technological and economic points of view, including an analysis of models used in waste gas biotreatment is given. Results presented in the literature concerning the removal of aliphatic, aromatic and mixtures of contaminants are reviewed. Carrier materials, inocula selected and alternatives proposed for regulating moisture content, pH values or for con- trolling pressure drop are considered. New technologies and reactor design studied at laboratory-scale are mentioned. 1998 SCI ( J. Chem. T echnol. Biotechnol. 72, 303E319 (1998)

Review: Waste gas biotreatment technology

This paper gives an overview of present biological techniques for the treatment of off-gases and the techniques that are being developed at the moment. The characteristics, advantages, disadvantages, costs and application area are discussed and compared. Biological off-gas treatment is based on the absorption of volatile contaminants in an aqueous phase or biofilm followed by oxidation by the action of microorganisms. Biofilters, bioscrubbers and biotrickling filters are used for elimination of odour and bioconvertable volatile organic and inorganic compounds and are enjoying increasing popularity. This popularity is a result of the low investment and operational costs involved compared to physico-chemical techniques and the elimination efficiencies that can be obtained. The operational envelop is still extending to higher concentrations and gas flow rates (exceeding 200,000 m3 h−1) and a broader spectrum of degradable compounds. Research and development on the use of membranes and the addition of activated carbon or a second liquid phase to the biological systems may lead to a more efficient elimination of hydrophobic compounds and buffering of fluctuating loads. Shorter adaptation periods can be obtained by inoculation with specialized microorganisms. Improved design and operation are made possible by the growing insights in the kinetics and microbiology and supported by the development of models describing biological off-gas treatment. In conclusion, biotechniques are efficient and cost effective in treating off-gases with concentrations of biodegradable contaminants up to 1–5 g/m3. They could play a justified and important role in air pollution control in the coming years.

Biotechniques for air pollution control

Biofiltration of solvent and fuel vapors may offer a cost-effective way to comply with increasingly strict air emission standards. An important step in the development of this technology is to derive and validate mathematical models of the biofiltration process for predictive and scaleup calculations. For the study of methanol vapor biofiltration, an 8-membered bacterial consortium was obtained from methanol-exposed soil. The bacteria were immobilized on solid support and packed into a 5-cm-diameter, 60-cm-high column provided with appropriate flowmeters and sampling ports. The solid support was prepared by mixing two volumes of peat with three volumes of perlite particles (i.e., peat-perlite volume ratio 2:3). Two series of experiments were performed. In the first, the inlet methanol concentration was kept constant while the superficial air velocity was varied from run to run. In the second series, the air flow rate (velocity) was kept constant while the inlet methanol concentration was varied. The unit proved effective in removing methanol at rates up to 112.8 g h(-1) m(-3) packing. A mathematical model has been derived and validated. The model described and predicted experimental results closely. Both experimental data and model predictions suggest that the methanol biofiltration process was limited by oxygen diffusion and methanol degradation kinetics.

Biofiltration of methanol vapor.

Biofiltration is a biological air pollution control technology for volatile organic compounds (VOCs). This paper summarizes the fundamentals, design and operation, and application of the process. Biofiltration has been demonstrated to be an effective technology for VOCs from many industries. Large and full-scale systems are in use in Europe and the United States. With proper design and operation, VOC removal efficiencies of 95–99% have been achieved. Important parameters for design and performance are empty-bed contact time, gas surface loading, mass loading, elimination capacity, and removal efficiency. Key design and operation factors include chemical and media properties, moisture, pH, temperature, nutrient availability, gas pretreatment, and variations in loading.

Biofiltration: Fundamentals, design and operations principles and applications

The removal of dichloromethane from waste gases in a biological trickling filter was studied experimentally as well as theoretically within the concentration range of 0–10,000 ppm. A stable dichloromethane elimination performance was achieved during two years of operation, while the start-up of the system only amounted to several weeks at constant inlet concentrations. The trickling filter system was operated co-currently as well as counter-currently.

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Verification studies of a simplified model for the removal of dichloromethane from waste gases using a biological trickling filter (part II)

Biofiltration is a technique which is frequently applied for the odour abatement of waste gases. This technique is based on the ability of microorganisms (generally bacteria, and to a small extent moulds and yeasts) to degrade several organic as well as inorganic compounds to mineral end-products, like water and carbon dioxide. In the case of biofiltration, microorganisms are attached to suited packing materials in the filter, which contain the inorganic nutrients necessary for microbial growth. In order to make biofiltration applicable on a larger scale in process industry, it is necessary to find microorganisms able to eliminate compounds which are strange to life, the so-called xenobiotics. At the Eindhoven University of Technology microorganisms were isolated for the elimination of a number of xenobiotics, e.g. aromatic compounds and chlorinated hydrocarbons.

A. H. C. van den Oever

Papers

Biological elimination of volatile xenobiotic compounds in biofilters