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An offensive and prolonged smell that significantly interferes with the enjoyment and use of the affected property is known as odor nuisance. It can cause adverse health effects such as emotional unease, eye irritation, and respiratory problems. The most significant odorous gases are volatile organic compounds, nitrogen compounds including ammonia, and sulfur compounds including hydrogen sulfide. Major sources of these pollutants are animal farms, various chemical as well as food- and feed-processing industries, waste treatment or disposal facilities, and wastewater treatment plants. As more and more countries adopt regulations that prohibit business organizations from emitting strong odors, various technologies for removal of odorous compounds from waste gases are in use. Physical and chemical processes, such as activated carbon adsorption, ozone oxidation, catalytic oxidation, and incineration, are characterized by rather high energy requirements and high treatment costs. As more sustainable processes, microbiological odor treatment methods using various types of air filtration equipment are introduced. Their advantages include absence of explosion risk, operation at near atmospheric pressure and temperature range 10–40 °C, no secondary waste generation, less energy requirements. This chapter will review microbiological odor treatment methods and summarize authors’ experience of development and applications of compact trickle-bed bioreactor for odors removal from ventilation air discharged from various industrial facilities.

A wide range of volatile organic compounds (VOCs) chemical characteristics (aromatic, sulfur-containing organics and alcohol) were selected to demonstrate a prospective potential of the biotrickling technology in practical applications through the appropriate selection and combination of biological ‘agents’. The principal objective of this study was to specify operating boundaries of parameters at which the sampled microorganisms were most effective in the biodegradation of gaseous streams containing styrene, ethanol and dimethyl sulfide mixture at dynamic variations of pollutant load. The average conversion factor for the 3-component VOCs mixture was higher than 95% at lower range of the individual pollutant load and basically fell to 80% at middle range vs. 55% at the higher contaminant loads; however, the effectiveness of ethanol biodegradation is stable at the entire investigated range of the mass load. The consequences of an unexpected pollutant overload (media clogging) and the time necessary for the subsequent regeneration of the microbial community and restoring the process stability were investigated as well.

A compact trickle-bed bioreactor (CTBB) was tested for the removal of volatile organic compounds (VOCs) and hydrogen sulphide (H2S) present in the exhaust air of a wastewater treatment plant. At gas-flow rates varying between 2.0 and 30.0 m3/h and for specific pollutant loads up to 20 g/(m3·h), removal efficiencies for H2S and VOC were >95%. The CTBB was designed for a maximum H2S concentration of ∼200 ppm and removal efficiencies >97% were noticed. VOC concentrations were in the range of 25–240 ppmv and the removal efficiency was in the range of 85–99%. Possible consequences of an excessive pollutant overload and the time required for regenerating the microbial activity and reviving stable process conditions in the CTBB were also investigated. An increase in the H2S concentration from 400 to 600 ppmv for a few hours caused bioreactor poisoning; however, when original H2S concentrations were restored, stable CTBB operation was ascertained within 3 h.

The study presents the preliminary results of research with the aim to test a Compact Trickle-Bed Bioreactor (CTBB) to the biopurification of air from VOC’s mixtures (ethyl alcohol, dimethyl sulphide, styrene). The experiments were performed using a 45 dm3 semi-industrial scale bioreactor in which gas and liquid phases flowed co-currently in downward direction through a bed made up of polyethylene rings. The bioreactor was inoculated with a co-culture of microorganisms including bacterial strains found in the wastewater and adopted to chosen pollutants. The gas-flowrate was 4.0 m3/h and VOC concentration in the gas phase was changed from 40 to 255 ppm. In the whole period of research the efficiency of pollutant removal was in the range 92-99%. The lowest result of efficiency was achieved in the 2nd day of research as a response of the highest concentration of VOC. Possible consequences of a violent pollutant overload and the time required for regenerating the microorganisms and returning to the stable process conditions were also investigated. An increase of VOC concentration to 220-255 ppm did not significantly influence the deterioration of process efficiency. After the period of adaptation of microorganism to the process condition and immobilization of microflora on the packing material, the experimental set-up has been working reliably for 21 days.

Selected results are presented of an on-going project conducted by Ekoinwentyka Ltd. with the aim to design, test and apply a compact trickle-bed bioreactor – operated in a biofiltration system with circulating salt solution – to the biodegradation of VOCs, mercaptans and H 2 S contained in the ventillation air in a copper-ore mine at a depth of 1000 m underground. The experiments were performed using a 48 dm 3 semi-industrial scale bioreactor in which gas and liquid phases flowed co-currently in downward direction through a bed made of polyethylene rings. The bioreactor was inoculated with a co-culture of microorganisms including bacterial strains found in the cooper-ore mine and adopted to chosen pollutants. In the laboratory tests, biodegradation of 4-components VOC mixture (acetone, styrene, benzene, vinyl acetate) and 8-component pollutant mixture (VOCs + xylene, H 2 S, dimethyl sulfide, dimethyl disulfide) was studied. In the gas-flowrate range 2.0 – 15.0 m 3 /h and at a specific pollutant load up to 40 g/(m 3 h), values of the efficiency of pollutant removal above 80% were measured for all mixture components except benzene which caused bioreactor poisoning at a specific load above 5 g/(m 3 h). Possible consequences of a fatal pollutant overload and the time required for regenerating the microorganisms and returning to stable process conditions were also investigated. In the copper-ore mine, it was found that pollutant concentration in the ventillation air was normally low not exceeding values attained during laboratory tests but temporary bursts of very high H 2 S concentration were also detected. An increase in H 2 S concentration to 1000 ppmv lasting for 1 h caused bioreactor poisoning but after H 2 S concentration returned to normal, stable process conditions were restored within 45 min. On the basis of experiments carried out both in the laboratory and copper-ore mine, acceptable values of parameters of the biodegradation process were determined. Despite harsh working conditions that are characteristic of the copper-ore mine 1000 m deep, the experimental set-up has been working reliably for several months and a high efficiency of pollutant removal has been achieved.

BACKGROUND: The removal of styrene from air streams in a co-current gas-liquid downflow trickle-bed bioreactor (TBB) inoculated with Pseudomonas sp. E-93486 strain was studied experimentally. The experiments were conducted to determine such parameters of the bioprocess as gas and liquid flow rates and specific styrene loading for which maximum elimination capacity was achieved. RESULT: The effect of inlet styrene concentration in gas phase on its degradation was studied in the range from 0.08 to 1.1 g m−3. The recirculation rate of the liquid medium was changed from 0.17 to 0.35 m3 h−1 whereas the gas flow rate was changed in the range from 1.2 to 6 m3 h−1. The treatment of air streams contaminated with styrene in a trickle-bed bioreactor was described with a mathematical model. The model incorporates mass transfer in both the gas and liquid phases and a biological reaction in biofilm. The rate of the partial stages of the process was determined experimentally. Microbial growth tests in the presence of styrene as the sole carbon and energy source were performed both in batch and continuous cultures. The Haldane model was used to describe Pseudomonas sp. E-93486 strain growth kinetics on styrene. CONCLUSION: The experiments conducted showed high activity of the examined bacterial strain in the styrene biodegradation process and relatively low sensitivity to inhibition of its growth at higher concentrations of styrene in the solution. The results of the experiments carried out in TBB were compared with the values obtained from a mathematical model. Satisfactory compatibility of the calculated and experimental data was obtained. Copyright © 2012 Society of Chemical Industry