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Biofiltration of Toluene Vapor Under Steady-State and Transient Conditions: Theory and Experimental Results
Abstract
Removal of toluene vapor from airstreams was studied in a vapor phase biological reactor known as a biofilter. The reactor was packed with a mixture of peal and perlite particles on which a mixed microbial population (consortium) was immobilized and formed a biolayer. The reactor was operated over a period of 11 months under various inlet-airstream toluene concentrations and flow rates of the contaminated airstream. Except at start-up, no supplemental nutrients were provided to the column, which remained active and never exhibited any significant pressure drop build-up. The process was modeled with general mass balance equations which take into account reaction, mass transfer, and adsorption of the pollutant onto the packing material. The model equations were solved numerically and the predicted concentration profiles agreed very well with the experimental data, for both steady-state and transient operation. Predicted concentration profiles for the biofilm indicate that toluene gets depleted before oxygen in a thin layer of the order of 35 μm. This finding is opposite to what has been reported for hydrophilic solvents where oxygen is depleted before the contaminant in the biolayer. The model equations have been used in parameter sensitivity studies that have revealed the parameters which need to be accurately known for predicting the performance of a biofilter.
... While modelling of biological filtration has been widely studied (Heidari et al., 2019;Hodge and Devinny, 1995;Ottengraf and van den Oever, 1983;Shareefdeen and Baltzis, 1994), very few studies are found in the literature which address the problem of modelling a biofilter with a botanical compartment. ...
... A number of assumptions can be made to reduce the complexity of the model when the process is applied under the operating conditions of the current application (Amanullah et al., 1999;Shareefdeen and Baltzis, 1994): ...
... We addressed this point by computing bootstrapping-based confidence limits (Efron and Tibshirani, 1994). Shareefdeen and Baltzis (1994) with the results predicted by the present model. ...
Botanical filtration is a biological-based treatment method suitable for removing hazardous volatile organic compounds (VOCs) from air streams, based on forcing an air flow through a porous substrate and foliage of a living botanical compartment. The pathways and removal mechanisms during VOC bioremediation have been largely investigated; however, their mathematical representation is well established only for the non-botanical components of the system. In this study, we evaluated the applicability of such a modelling scheme to systems which include a botanical compartment. We implemented a one-dimensional numerical model and performed a global sensitivity analysis to measure the input parameters influence on the transient and steady biofilter responses. We found that the most sensitive parameters on the transient-state behaviour were the mass transfer coefficient between gas and solid surfaces, and the fraction of solid surfaces covered by the biofilm; the steady-state response was primarily influenced by the biofilm specific surface area and the fraction of surfaces covered by the biofilm. We calibrated the identified set of parameters and successfully validated the model against data from a pilot-scale installation. The results showed that the application of the model to systems with a botanical compartment is feasible, although under a strict set of assumptions.
... In addition to these endeavors, some researchers endeavor to elucidate the fundamental principles governing BTF operation. Shareefdeen and Baltzis (1994) studied the biodynamics of BTF, and established a dynamic model to study the impact of biofilm accumulation on the hydrodynamics in BTF. The utilization of mathematical modeling provides an alternative approach for investigating BTF. ...
... Lebrero et al. (2012) developed a simple and reliable model to describe the mass transfer in BTF for the removal of toluene to optimize the design and operation of BTF. Shareefdeen and Baltzis (1994) introduced a mathematical model for numerical solution to the steady-state and transient BTF experiments on the removal of toluene vapor, and found that the steady-state and transient data were in good agreement with the experimental data. Masic et al. (2010) evaluated the oxygen distribution above the biofilm through a mathematical model, and at the same time used micro-electrode measurements to increase the accuracy of the model's prediction results. ...
Organic pollutants in the air have serious consequences on both human health and the environment. Among the various methods for removing organic pollution gas, biotrickling filters (BTFs) are becoming more and more popular due to their cost-effective advantages. BTF can effectively degrade organic pollutants without producing secondary pollutants. In the current research on the removal of organic pollutants by BTF, improving the performance of BTF has always been a research hotspot. Researchers have conducted studies from different aspects to improve the removal performance of BTF for organic pollutants. Including research on the performance of BTF using different packing materials, research on the removal of various mixed pollutant gases by BTF, research on microbial communities in BTF, and other studies that can improve the performance of BTF. Moreover, computational fluid dynamics (CFD) was introduced to study the microscopic process of BTF removal of organic pollutants. CFD is a simulation tool widely used in aerospace, automotive, and industrial production. In the study of BTF removal of organic pollutants, CFD can simulate the fluid movement, mass transfer process, and biodegradation process in BTF in a visual way. This review will summarize the development of BTFs from four aspects: packing materials, mixed gases, micro-organisms, and CFD, in order to provide a reference and direction for the future optimization of BTFs.
... Rene et al. [42] examined the effectiveness of biological methods for removing a mixture of benzene pollutants and compared the conditions required for achieving optimal removal under various influencing factors. Shareefdeen et al. [43] conducted a parameter sensitivity study using a model and validated the feasibility of the model through experiments on the removal of toluene vapor by gas-phase biofilters. ...
The emission of volatile organic compounds (VOCs) has resulted in increasingly severe harm to the environment and human health. In recent years, biological methods have become the preferred technology for VOC removal due to their environmental friendliness and economic advantages. Based on the theory of bibliometrics, this study analyzed research articles and reviews on biological methods for VOC removal published in the Web of Science Core Collection (WOSCC) database from 1966 to 2021. The knowledge map visualization software CiteSpace was utilized to analyze research progress in different countries, co-citation clustering, co-citation bursts, and keyword clustering in the literature data. The results indicated that early research on VOC biological treatment focused on the removal of odorous gases and single components of volatile organic waste gases. Subsequently, benzene contents (BTEX), hydrophobic VOCs, and multi-component VOCs have gradually become the focus of research. In recent years, improving VOC removal efficiency by studying packing materials and microbial communities has become an important research topic both domestically and internationally. Future research should focus on continuously improving the performance of reactors, developing novel reactors, and investigating technologies for treating complex and recalcitrant VOCs.
... The development of biofiltration models was directly connected to results from the progress of knowledge and understanding of complex phenomena occurring during the biofiltration process. The first mathematical model of biofiltration was proposed by Ottengraf and van den Oever [110]. This model served as the basis for many models of biofiltration, and the following assumptions are undertaken in this model: ...
Biotrickling filtration is a well-established technology for the treatment of air polluted with odorous and volatile organic compounds (VOCs). Besides dozens of successful industrial applications of this technology, there are still gaps in a full understanding and description of the mechanisms of biotrickling filtration. This review focuses on recent research results on biotrickling filtration of air polluted with single and multiple VOCs, as well as process modeling. The modeling offers optimization of a process design and performance, as well as allows deeper understanding of process mechanisms. An overview of the developments of models describing biotrickling filtration and conventional biofiltration, as primarily developed and in many aspects through similar processes, is presented in this paper.
... There are a plenty of studies available on biofilter applications [14][15][16]; however, the studies on practical transient models that can be used by industry are still limited. Shareefdeen and Baltzis [3] later presented a detailed transient biofilter model and validated the model with the toluene biofilter performance data. The main improvement was going from steady-state conditions to transient conditions, but still with a single compound, namely toluene. ...
Biofilters are biological air-phase packed-bed reactors used for the removal of industrial air pollutants such as volatile organic compounds (VOCs) and odors. Because of the economic and environmental benefits, biofilter technology is preferred in applications such as wastewater treatment plants, waste recycling facilities, and several chemical industries over conventional treatment methods such as adsorption, absorption, and thermal oxidation processes. In order to predict the performance of biofilters, mathematical models under steady-state and transient conditions are needed. The transient biofilter models for gas-phase bioreactors are highly complex, as they involve several parameters that are not easily determined for industrial applications. In this work, a practical transient biofilter model is developed and an analytical solution for the transient model is obtained. When this model is compared with the published but more complex model, this new transient model produces almost the same level of prediction with equal comparisons of experimental data for VOCs, benzene, and toluene. This simple model has fewer parameters and will be very useful and practical for industrial applications for the analysis of transient biofilter performance.
... Furthermore, the principles of other technologies for VOCs treatment often include adsorption and absorption. For example, the theories of biodegradation for treating exhaust gases are absorption-biofilm theory and adsorption-biofilm theory (Shareefdeen and Baltzis, 1994;Studer and Rudolf Von Rohr, 2008), i.e., biodegradation itself has processes that will be accompanied by absorption and adsorption (Ou et al., 2019). Therefore, adsorption and absorption are central to all other technologies. ...
Volatile organic compounds (VOCs) pollution is a great challenge for air environment management. However, macro quantitative research on VOC control technologies (VOCTs) evolution and global knowledge transfer is still lacking. Therefore, we analyzed the 6,636 global patents for VOCTs from 1961 to 2020 in the Derwent Innovation Index database to give a quantitative study, by using patent analysis methods such as text mining and technology life cycle analysis. The results showed that global patents surged from 2014 to 2018, and China held the most patents, followed by the US. Chinese 2013–2017 intensive atmospheric environment governance policy was the main possible reason for the sharp increase of VOC patents. However, very few Chinese patents were transferred. On the contrary, the US was the most important source country for transferred patents, and its main overseas markets were Europe, followed by China. Up to now, absorption and adsorption were the most mature technologies, accounting for 51% of the end-of-pipe patent. Biodegradation and membrane separation patents were active in transfer, indicating their high demand in the global market, so they may be promising technologies in the future. These findings enrich the literature on the evolution and transnational diffusion of VOCTs, and help policy-makers, scholars, and company managers better understand future research directions and the demands of the international market.
... The assumption of quasi-steady state was also approved by Zarook et al., who gave a lot of attention to the modeling of transient biofiltration in the removal of volatile organic compounds mixtures. 51,56,57 They solved the transient biofilter model by approximate and general approaches. Although the approximate Industrial & Engineering Chemistry Research pubs.acs.org/IECR ...
In this study, a multiscale computational fluid dynamics (CFD) coupled model comprising a macroscopic fluid flow model and microscopic mass transfer-biodegradation kinetics model is developed to obtain a comprehensive understanding of the mass transfer-biodegradation process of H2S in biofilms and biotrickling filters (BTFs). The developed CFD coupled model is calibrated and validated using the experimental data of H2S concentration profiles in a pilot-scale BTF. Using the proposed model, the dynamic removal process of H2S is investigated. A sensitivity analysis of the model parameters is then performed, and mass transfer and biodegradation kinetics characteristics are obtained. The validated model is applied to explore the effects of biofilm thickness and area on macroscopic deodorization performance. A widespread application of the established CFD coupled model can consequently be expected to optimize the design of industrial-scale BTFs.
... In biolters, Bacteria and fungi are certainly the two dominant microorganism groups [7] and there grow high and slow respectively. Toluene has been used in many industries and there are more capable than elimination capacities of bacteria and fungi in biolter [8,9,10,11,12]. Recently, dynamic Biolter model applied to control the toluene and it is more suitable for duration [13,14,15]. From the biolteration model of mathematical model, develop the partial dierential equation of mass balance equation taking into the account the chemical and physical phenomena. ...
The aim of the present work is to find the solution for concentration of pollutant in the biofilm phase using HPM with complex inversion method. The obtained results are validated and illustrate the efficiency of future technique from the figure. Furthermore, the reported analytical result is useful in future modification of mathematical modeling of the biofilter.
... Among the first models for fixed bed biofilters, Ottengraf and Van Den Oever (1983) considered steady-state operation, axial plug flow, diffusion of the pollutant in the biofilm and zero or first-order kinetics. Shareefdeen and Baltzis (1994) developed an unsteady-state model of a biofilter treating toluene vapors in air considering mass balances in the bacterial biofilm, gas phase and solid support. The reactions performed by the bacteria in the biofilm were mathematically described using Monod kinetics. ...
Volatile organic compounds (VOCs) are ubiquitous contaminants that can be found both in outdoor and indoor air, posing risks to human health and the ecosystems. The treatment of air contaminated with VOCs in low concentrations can be effectively performed using biofiltration, especially when VOCs are hydrophilic. However, the performance of biofilters inoculated with bacteria has been found to be low with sparsely water soluble molecules when compared to biofilters where fungi develop. Using conceptual and mathematical models, this review presents an overview of the physical, chemical and biological mechanisms that explain the differences in the performance of fungal and bacterial biofilters. Moreover, future research needs are proposed, with an emphasis on integrated models describing the biological and chemical reactions with the mass transfer using high-resolution descriptions of the packing material.
... Biofilters were originally developed for odor pollution control due to their high efficiency, low energy consumption, low operating costs, and environmental-friendliness [1] and have recently been proven to be a promising technology for the treatment of volatile organic compounds (VOCs) at moderately high flow rates and low concentrations (<1000 ppm) [2][3]. Biofilters have been successfully applied to treat hydrophilic VOCs, such as styrene [4] , eth- anol [5], methanol [6], xylene isomers [7], hexane [8], toluene [9], phenol [10], methylamine [11], triethylamine [12], dimethylsulfide [13], and dichloromethane [14]. However, the low mass transfer of hydrophobic VOCs from the gas phase to the biofilm phase, which limits the supply of substrates to the microorganisms, results in low biodegradation rates of these compounds. ...
To improve biofilter performance, the microbial community of a biofilter must be clearly defined. In this study, the performance of a lab-scale polyurethane biofilter for treating waste gas with low loads of nitrobenzene (NB) (< 20 g m⁻³ h⁻¹) was investigated when using different empty bed residence times (EBRT) (64, 55.4 and 34 s, respectively). In addition, the variations of the bacterial community in the biofilm on the longitudinal distribution of the biofilters were analysed by using Illumina MiSeq high-throughput sequencing. The results showed that NB waste gas was successfully degraded in the biofilter. High-throughput sequencing data suggested that the phylum Actinobacteria and genus Rhodococcus played important roles in the degradation of NB. The variations of the microbial community were attributed to the different intermediate degradation products of NB in each layer. The strains identified in this study were potential candidates for purifying waste gas effluents containing NB.
... Oxygen is also subject to diffusional resistance due to growth and replication of microorganisms. The adsorption of the pollutants is possible either after diffusion through the whole thickness of biofilms as modeled by Deshusses et al. (1995) or directly occurring on the pore of packing material (Shareefdeen and Baltzis, 1994 ). Metabolite will be produced as a result of VOC biodegradation occurring in the biofilm, and it undergoes the same processes of simultaneous diffusion, biodegradation and adsorption. ...
... Ockeloen et al. (1996) developed an extension to Diks and Ottengraf's model by including Monod kinetics. In the dynamic models of Deshusses et al. (1995), Shareefdeen and Baltzis (1995) and Zarook et al. (1997), biomass growth was not considered and a constant biofilm thickness was assumed. Unlike these models, the dynamic trickle bed biofilter model presented by Allonso et al. (1997) includes biomass growth and a variable biofilm thickness along the reactor. ...
... En la figura 3 se muestran los perfiles teóricos de concentración con respecto al tiempo en la fase de gas y la fase sólido-líquido a la salida del reactor, desafortunadamente no se encontraron trabajos experimentales que nos den información de lo que ocurre en la fase sólido-liquido, en este gráfico se tiene una mejor apreciación de la curva de ruptura esperada, en la cual al inicio de la dinámica la capa inferior de medio filtrante, entra en contacto con el efluente contaminado, y este adsorbe y metaboliza el compuesto en cuestión, provocando que el efluente a la salida este prácticamente limpio, posteriormente el soporte se satura y el biofiltro reduce su eficiencia hasta alcanzar el estado estable (Ottengraf et al., 1986;Shareefdeen et al., 1993;Deshusses et al., 1996, 1997, Hodge y Devinny, 1994, Zarook y Baltzis, 1994. ...
Se presenta la modelación matemática de un biofiltro para el tratamiento de corrientes gaseosas mediante las ecuaciones teóricas de transferencia de masa en estado dinámico. Las ecuaciones se resolvieron por medio de discretización espacial por diferencias finitas de segundo orden e integración implícita para el tiempo empleando un código en lenguaje FORTRAN, la fiabilidad del modelo fue comprobada mediante comparación con datos experimentales de un caso de biofiltración de etanol presentado por Hodge y Devinny (1995), dando una buena aproximación de las predicciones del modelo respecto a los valores reportados.
... Following this study, many models for biofilters have been reported in the literature, adding new phenomena, such as adsorption in the packing material and the inhibition kinetics of microbial growth, among others [11]. As an example, Shareefdeen et al. [12] included both oxygen and substrate inhibition effects; this model was improved by assuming the partial coverage of the support particles by biofilm and by modelling the adsorption on the uncovered particles by using the Freundlich isotherm [13]. Most mathematical models of BTFs and trickle bed biofilters are based on mechanisms that have been used to describe biofilter behavior. ...
A mathematical model for the simulation of the removal of hydrophilic compounds using biotrickling filtration was developed. The model takes into account that biotrickling filters operate by using an intermittent spraying pattern. During spraying periods, a mobile liquid phase was considered, while during non-spraying periods, a stagnant liquid phase was considered. The model was calibrated and validated with data from laboratory- and industrial-scale biotrickling filters. The laboratory experiments exhibited peaks of pollutants in the outlet of the biotrickling filter during spraying periods, while during non-spraying periods, near complete removal of the pollutant was achieved. The gaseous outlet emissions in the industrial biotrickling filter showed a buffered pattern; no peaks associated with spraying or with instantaneous variations of the flow rate or inlet emissions were observed. The model, which includes the prediction of the dissolved carbon in the water tank, has been proven as a very useful tool in identifying the governing processes of biotrickling filtration.
... Shareefdeen et al. [121] developed a steady-state model with oxygen limitation and substrate inhibition. Further, Shareefdeen and Baltzis [122] used a transient model, which considered adsorption at the gas/solid interface with only oxygen limitation and validated steady-state as well transient models by using a peat-moss perlite biofilter. Similarly, a dynamic model, which includes sorption and cross-inhibition between two pollutants was suggested by Deshusses et al. [123] in which both biofilm thickness and biomass density were assumed to be constant during the operation. ...
The rapidly increasing industrialization has adversely affected the environment due to deterioration of water and air quality. The continuous addition of hazardous chemicals, gaseous contaminants, and particulate materials to our environment imposed the life-threatening challenges for flora and fauna. There is an urgent need to adopt the sustainable technologies to reduce the contamination occurring in air and water resources. To cope up with various types of contaminants abatement techniques have been employed. In the recent decade the biofiltration-based methods have been emerged as promising abatement techniques to remove the hazardous contaminants from wastewater or polluted air. The biofiltration exploits the potentials of microbial systems (bacteria and fungi) to degrade the wide range of chemicals and volatile organic components (VOCs). In this chapter emphasis has been given on the basic concepts and mechanism of biofiltration along with its application for treatment of wastewater and polluted air. The details about the removals of hazardous heavy metals, cationic-anionic dyes, xenobiotics, organic contaminants, and assimilable organic carbon from water has been discussed. The removal of VOC, malodorous compounds, and sulfurous compound from air have been discussed. The chapter also gives the light about pros and cons of biofiltration.
Volatile organic compounds (VOCs) are hazardous and carcinogenic air toxicants that have widespread adverse implications on the environment and human health, mitigation of which has become one of the dreaded challenges for mankind. Biofiltration provides a promising way for the elimination of such noxious wastes. In this method, a stream of polluted air containing VOCs is channeled to flow through a medium on which microorganisms are immobilized. The pollutants are adsorbed on the medium surface and are metabolized to innocuous products by the immobilized microorganisms. Biofiltration outweighs other conventional waste air treatment methods in terms of cost-effectiveness, eco-friendliness, user-friendliness, and reliability. In this chapter, we present a brief insight into the application of biofilters for mitigation of VOCs, their types, design considerations, mechanism of biofiltration, the influence of operational factors, challenges and limitations, and current state of research and implementation, research gaps, and future prospects.
The application of rhamnolipids in a fungal-cultured biotrickling filter (BTF) has a significant impact on toluene removal. Two BTFs were used; BTF-A, a control bed, and BTF-B fed with rhamnolipids. The effect of empty bed residence times (EBRTs) on toluene bioavailability was investigated. Removal of toluene was carried out at EBRTs of 30 and 60 s and inlet loading rates (LRs) of 23–184 g m⁻³ h⁻¹. At 30 s EBRT, when inlet LR was increased from 23 to 184 g m⁻³ h⁻¹, the removal efficiency (RE) decreased from 93% to 50% for the control bed, and from 94% to 87% for BTF-B. Increasing the EBRT simultaneously with inlet LRs, confirms that BTF-A was diffusion-limited by registering a RE of 62% for toluene inlet LR of 184 g m⁻³ h⁻¹, whereas BTF-B, achieved RE > 96%, confirming a significant improvement in toluene biodegradability. Overall, the best performance was observed at 60 s EBRT and inlet LR of 184 g m⁻³ h⁻¹, providing a maximum elimination capacity (EC) of 176.8 g m⁻³ h⁻¹ under steady-state conditions. While a maximum EC of 114 g m⁻³ h⁻¹ was observed under the same conditions in the absence of rhamnolipids (BTF-A). Measurements of critical micelle concentration showed that 150 mg L⁻¹ of rhamnolipids demonstrated the lowest aqueous surface tension and maximum formation of micelles, while 175 mg L⁻¹ was the optimum dose for fungal growth. Production rate of carbon dioxide, and dissolved oxygen contents highlighted the positive influence of rhamnolipids on adhesive forces, improved toluene mineralization, and promotion of microbial motility over mobility.
The use of biological reactors to remove volatile organic compounds (VOCs) from waste gas streams has proven to be a cost-effective and sustainable technique. However, hydrophobic VOCs exhibit low removal, mainly due to their limited bioavailability for the microorganisms. Different strategies to enhance their removal in bio(trickling)filters have been developed with promising results. In this review, two strategies, i.e. the use of surfactants and hydrophilic compounds, for enhancing the removal of hydrophobic VOCs in bio(trickling)filters are discussed. The complexity of the processes and mechanisms behind both strategies are addressed to fully understand and exploit their potential and rapid implementation at full-scale. Mass transfer and biological aspects are discussed for each strategy, and an in-depth comparison between studies carried out over the last two decades has been performed. This review identifies additional strategies to further improve the application of (bio)surfactants and/or hydrophilic VOCs, and it provides recommendations for future studies in this field.
Mathematical models of the process of air purification from hydrophobic (styrene) or hydrophilic (vinyl acetate, VA) compounds carried out in a co‐current trickle‐bed bioreactor (TBB) were presented. These models were marked as TSM (two‐substrate model), OSM (one‐substrate model) and AOSM (approximate one‐substrate model). The experimental database was exploited to validate the two‐substrate model (TSM) which approximated very well the experimental data; the mean percentage error of RE prediction did not exceed 3% for styrene and 4.1% for VA. For the tested systems, TSM was only sensitive to the changes in biomass dry density Xb and effective diffusion coefficient Dj,ef values. The percentage relative error of the state variable Y1v computed using OSM/AOSM in relation to the Y1v value obtained from TSM was the quantitative criterion for comparison of the results obtained using different mathematical models of the process. It was shown that the simplified models describe the process investigated with satisfactory accuracy. This article is protected by copyright. All rights reserved.
Selection of sustainable and environmental friendly technologies is very important in meeting strict environmental regulations on industrial emissions of volatile organic compounds and greenhouse gases. Many of the industrial volatile organic compounds are toxic and carcinogenic, and they are regulated under Clean Air Act for hazardous air pollutants. Similarly, global environmental agreements such as European Union’s 2015 Paris Agreement and Kyoto Protocol restrict carbon emission, which is responsible for global warming, sea-level rise, flooding, and ecological imbalance. It is essential that industries choose suitable technologies that reduce not only toxic volatile organic compounds in the air but also greenhouse gas emissions. In this communication, biotechnological methods are discussed and compared with conventional processes, which are used for control of volatile organic compounds. The readers may find this article useful in the selection of an appropriate technology for their application while minimizing the greenhouse gas emissions.
Mathematical modeling of biofiltration systems improves our understanding and design of such complex systems. This study focused on the theoretical and technical aspects of the modeling of xylene biofiltration in the absence and presence of a nonionic surfactant. In this regard, a mathematical model was developed based on mass balance principles in gas and biofilm phases. The developed model was calibrated and validated using the experimental data obtained from a lab‐scale scoria‐compost biofilter, which operated for 151 days in the absence and presence of Tween‐20, a nonionic surfactant. First, the model was calibrated using the experimental data obtained at empty bed retention time (EBRT) of 90 s and then validated with the data obtained at two other EBRTs. The biofilter provided maximum elimination capacities (ECmax) of 97.5 and 93.6 g m⁻³ hr⁻¹, respectively, in the absence and presence of the surfactant at EBRT of 90 s. The corresponding predicted ECmax values were 99.9 and 95.7 g m⁻³ hr⁻¹, respectively. Both model output and experimental data revealed that the nonionic surfactant improved the performance of the biofilter at moderate inlet loading rates. Various statistical measures, including fractional bias, average absolute relative error, and coefficient of determination (R²), showed good agreement between experimental data and estimated model predictions. Sensitivity analysis of the model showed that the specific surface area and bioreactor length affected strongly the results of the model. In general, the results of this study would in turn form the design basis for engineering purposes.
Due to increasingly stringent legal regulations as well as increasing social awareness, the removal of odorous volatile organic compounds (VOCs) from air is gaining importance. This paper presents the strategy to compare selected biological methods intended for the removal of different air pollutants, especially of odorous character. Biofiltration, biotrickling filtration and bioscrubbing technologies are evaluated in terms of their suitability for the effective removal of either hydrophilic or hydrophobic VOCs as well as typical inorganic odorous compounds. A pairwise comparison model was used to assess the performance of selected biological processes of air treatment. Process efficiency, economic, technical and environmental aspects of the treatment methods are taken into consideration. The results of the calculations reveal that biotrickling filtration is the most efficient method for the removal of hydrophilic VOCs while biofilters enable the most efficient removal of hydrophobic VOCs. Additionally, a simple approach for preliminary method selection based on a decision tree is proposed. The presented evaluation strategies may be especially helpful when considering the treatment strategy for air polluted with various types of odorous compounds.
The present work explores and discusses the derivation and application of a generic mathematical model (Multiple Continuum Interacting Model, MCIM) in the prediction of the effectiveness dynamics for a trickling biofilter treating toluene. A computational solution strategy is presented, including the proper validation study case. Then, numerical studies for dimensionless Péclet and Sherwood numbers (Pe and Sh) are discussed; the effect of these over the efficiency biofilter behavior is shown. For Two Interacting Continuum phases (TIC), three sophistication levels are compared, concluding that the growth phenomenon (including the inoculation process) is crucial for designing and modelling of biofiltrations systems by MIMC’s. Achieving with MDC 2 an ER< 8% being the approach that comes closest to the experimental data reported in literature.
BACKGROUND
The studies on the removal of styrene from airstreams carried out in pilot‐scale biotrickling filter (BTF) are still scarce thus making difficult its industrial application. Moreover, it seems necessary to develop a comprehensive description of the phenomena occurring in the bioreactor that could be used as a tool for BTF design and performance prediction.
RESULTS
The removal of styrene from airstreams in the pilot‐scale biotrickling filter (BTF) inoculated with Pseudomonas sp. E‐93486 bacteria was investigated (operational parameters: = 100 ‐150 m³h‐1, = 8 m³h‐1, = 0.2‐1 gm‐3, EBRTs = 41‐62 s, T=303 K). The experiments performed during the period of more than 120 days confirmed high effectiveness of the examined process; RE=78‐94.2% was obtained for all the sets of operational parameters.
The experimental data‐base was exploited to validate every of the three mathematical models of the process. All the tested models approximate very well experimental data; the mean percentage error of the RE value prediction did not exceed 3%.
CONCLUSION
The formulated approximate Simple One‐Substrate Model (SOSM) described the investigated process with excellent accuracy (eY = 2.72%) and was numerically relatively simple. Therefore, this model was recommended as a useful tool for modelling the biodegradation processes of moderately hydrophobic compounds carried out in BTF.
Biofiltration is an emerging and attractive air pollution control technology for controlling odors, VOCs, and air toxics. It has numerous advantages over conventional air pollution control methods. Biofiltration units are microbial systems incorporating microorganisms grown on a porous solid media like compost, peat, soil, or mixture of these materials. The filter media and the microbial culture are surrounded by a thin film of water called biofilm. Waste gases containing biodegradable VOCs and inorganic air toxics are vented through this material, where soluble contaminants partition into the liquid film and are biodegraded by the microorganisms in the biofilm. The technology has been applied to a wide range of industrial and public sector sources for the abatement of odors, VOCs, and air toxics, with removal efficiency of more than 90%. Because of its economic benefit over the traditional air pollution control alternatives coupled with environmental advantages, biofiltration is becoming more popular in meeting the statutory emission regulations. Biofiltration harness the natural degrading abilities of microorganisms to biochemically oxidize waste gas contaminants into environmentally benign end products like carbon dioxide, water, and mineral salts. Conventional air pollution control technologies like carbon adsorption, incineration, etc. can treat a wide variety of pollutants at higher concentrations; however, for treating waste air with low pollutant concentrations, these approaches become economically prohibitive. In comparison, biofiltration is more cost-effective particularly for treatment of large volumes of waste air with low concentrations of biodegradable contaminants. The low cost of biofiltration is associated with its use of natural sorbents and microbial oxidation. However, one must accept the trade-off in terms of longer residence time that is partially compensated by lower operating cost. The acceptance of biofiltration has followed from advances in biotechnology that provide thorough knowledge about the system and how the process can be optimized, not only to achieve high removal efficiencies with low energy consumption but to achieve these elimination efficiencies over long periods with minimal maintenance. Further research is needed to develop good understanding of the metabolic degradation pathways for single and multiple contaminant waste gas streams, effective mass transfer from gas to liquid phase, and improved modeling techniques incorporating better kinetic data.
This study evaluated the efficiency of a laboratory scale biofilter packed with a mixture of scoria-bagasse-compost to treat unsymmetrical 1,1-dimethyl hydrazine (UDMH) from the air. Effect of different inlet loadings (0.44–2.68 gm⁻³h⁻¹), various EBRTs (30, 60 and 90s), bed height, and non-ionic surfactants Tween 80 on biofilter efficiency were evaluated during a long-term period (126 days). The average of removal efficiency (RE) and elimination capacity (EC) were 88% and 0.72 g m⁻³ h⁻¹ respectively. Over 60% of the total average of RE was related to section 1 of biofilter, where the average of bacterial population (6.74 log CFU/g) and fungi population (4.95 log CFU g⁻¹) was significantly more than in the other sections. Although the effect of surfactant on the removal efficiency was negligible, the removal efficiency of was significantly increased by increase of EBRT and reduction of inlet loading. Dominant species of bacteria in the biofilter bed included Pseudomonas, Acinetobacter, and Proteus spp; fungi species were Aspergillus and Fusarium spp. regarding to the rapid adaptation period (9 days), suitable RE and EC, low pressure drop, and negligible compactness of media, this point is inferable that the biofilter system can be a suitable method to remove UDMH from the polluted airflow.
This paper aims at providing a practical iterative learning control (ILC) scheme for a wide class of heat transfer systems in the sense that it avoids high-gain learning of ILC, thus a potential non-monotonic convergence issue, and the risk of violating the hardware limitation of input profile in implementation. Meanwhile, the ILC scheme guarantees the identical initial condition of heat process. As a result, the output tracking precision may be improved while not reducing the anticipatory step size as in . All the benefits of the proposed ILC scheme are achieved by applying a heuristic selection algorithm for the anticipatory step size and rectifying the output reference simultaneously. © 2016 Chinese Automatic Control Society and John Wiley & Sons Australia, Ltd.
People living in or near a kraft pulp mill often complain of the odor nuisance associated with the mill’s operations. These complaints are directly related to the production of odorous compounds during the cooking of wood chips with white liquor and subsequent points of gaseous release to the atmosphere. Even when pure sodium hydroxide is used to treat wood and straw, odors are produced. The cause of these odors is to be found in the residual sulfurcontaining protoplasm which reacts with the alkali to form mercaptans and organic sulfides during the digestion phase. It was found that the mercaptans are formed by the saponification of lignin methoxyl groups by sulfide ions.
Odour treatment is a significant portion of the marketplace. Biofiltration is capable of biodegrading a wide variety of air contaminants. Current research and application of biofiltration has been focused on the removal of volatile organic compounds and air toxics from the industrial exhausts of chemical and other processes. Biofiltration of hydrogen sulphide has been studied extensively, because it is one of the most frequently produced odourous compounds in industrial processes such as petroleum refining, rendering, wastewater treatment, food processing and paper and pulp manufacturing. Removal of reduced sulphur (RS) compounds (either singly or as part of a mixture), and odourous volatile organic compounds, ammonia and hazardous air pollutants are presented in this chapter.
Microbial dynamics during aerobic biodegradation of an alternating mixture of organic compounds was investigated experimentally in a continuous stirred tank bioreactor (CSTB). A mathematical model describing this system was developed and tested using the experimental results. A model microbial culture consisting of Pseudomonas sp. JS150, a monochlorobenzene (MCB) degrader, and Xanthobacter autotraphicus GJ10, a 1,2-dichloroethane (DCE) degrader, each with exclusive degradation capabilities, was used. The CSTB was inoculated with both microbial strains and exposed to an alternating sequence of the two compounds at noninhibitory concentrations. Concentrations of each microbial strain, of each organic compound, and of degradation product evolved, as well as specific microbial activities via oxygen uptake tests, were monitored. Reduction of the residual DCE discharged from the bioreactor after an MCB to DCE transition was successfully achieved by continuously feeding a low flow of a concentrated solution of both compounds. (C) 2000 John Wiley & Sons, Inc.
This article presents the development of a MATLAB® computer program to simulate the performance of biotrickling filters. Since these filters behave differently during spraying and nonspraying cycles, the presented simulation tool is built on top of a mathematical description of each situation. The resulting variable-structure model is then used as the basis for simulation experiments. The model presented herein represents the first attempt to take into account the variable spraying pattern usually found in industrial installations. Overall, the software is flexible and easy to use, allowing the user to specify the emission concentration pattern, the gas concentration pattern, as well as the spraying cycle periods for up to two different emission patterns per day. The model is able to predict experimental data from a biotrickling filter treating isopropanol under intermittent conditions of loading and spraying. Simulation examples are then provided to study the effect of variable inlet concentrations and gas flow rates.
A commercially competitive on the world market and nature-preserving technology of microbiological purification of waste gases from toxic volatile organic compounds (VOC) was developed. This technology employs a biocatalyst consisting of a consortium of microorganisms immobilized on a fibrous carrier; the microorganisms were specially selected and adapted for highly efficient degradation of various VOC. The biocatalyst is located in a Bioreactor, a specially designed apparatus that uses original techniques. The technology developed has advantages over existing technologies in its technical parameters, capitsl investment, and operating costs. Theoretical bases of this technology were developed. Facilities for experimental work were created. The gas purifying units were tested under industrial conditions, and small-scale production of these units was organized. Marketing efforts made the Bioreactor technology gained international recognition. The technology was implemented under a license by the English company Waterlink Sutcliffe Croftshaw, which started installation of industrial Bioreactors in 1997. The work of these units for more than one year showed their high effectiveness and reliability.
In the work reported here, the removal of methyl ethyl ketone from waste gases in a novel bioreactor type was studied experimentally within the pollutant loading range of 0.35 to 16.2 kg mr-3 d-1. The solvent eliminating performance of the bioreactor described in this paper is reflected by a maximum methyl ethyl ketone elimination capacity ECmax = 4.2 kg mr-3 d-1. The effect of the pH was studied. A nutritive medium with pH=7.3 appeared to give better system performances than a solution with pH = 6.8. Moreover, the effects of air and liquid flow rates were studied. The reduction of either the gas or liquid flow rates led to a significant improvement of the degradative capacity of the system suggesting mass transfer limitation. Finally, selected aspects of the dynamic behavior of the dry tubular bioreactor have been investigated.
To Modeling Biological treatment of contaminated air in bio filters and bio trickling filters involves a complex combination of physical, chemical, and biological processes. This makes it very difficult to mentally understand and integrate the subtle details of the phenomena occurring during treatment. Even simple exercises, such as to predict the behavior of bio filters and bio trickling filters under a different set of conditions, can be challenging. Fortunately, computers and mathematical models can track a multitude of complex relationships much better than the human mind. Therefore, mathematical models can be very useful tools in research and for design. Mathematical models help in the development of a fundamental understanding of the process, and to accomplish engineering tasks such as reactor design and scale up, or process optimization. There are many advantages to modeling and simulation, including: • The ability to gain insight into a given process. • The possibility to obtain quantitative information on a variable that is difficult or impossible to measure (e.g., concentration of contaminant in the bio film). • The low cost and rapidity of performing "virtual experiments". • The ability to evaluate conditions that may not be possible to test. • The possible use in experimental design in order to maximize outcome and representative ness of the experimental data. • The ability to automatically perform numerous simulations to support process optimization. At the same time, one has to acknowledge the many limitations of mathematical modeling: • Models will only be as good as the basic concept and the assumptions that were made during model development. • In many instances, model parameters will be unknown, and it will require significant experimentation to determine these model parameters. • The fact that simply because a model fits the experimental data does not mean that the model or the concept on which the model is based are correct. • Application of a model and extrapolation of modeling data outside the range for which the model has been validated, or application of a model for a completely different system involve risks, as uncertainties and discrepancies may be multiplied. Models may be classified depending on their features and structures. In this chapter, the focus was placed on models that make attempts to describe the actual phenomena occurring during a biological treatment. These are often called structured or conceptual models. A number of other models, ranging from simple multi-parameter correlations to lumped parameter models, exist but these are not discussed in great detail here.
Biopurification Technology of volatile organic compounds (VOCs) has the advantages of mild reaction conditions, low operating costs, less pollution. The paper reviews the current study on the packing characteristics, and long-running biofilm blockage, and kinetic model, and microorganism domestication and cultivation of high efficient degradation bacteria, and safety evaluation in the research of domestic and foreign scholars. Through the above analysis, the paper puts forward the existing problems using biological purification technology and future development trends. The aim is to improve the removal ability of the equipment unit volume and resistance to impact load capacity, and to prolong the service life of equipment, in order to drive the biological treatment technology in the practical application and industrialization.
In the work the biofiltration research results of the selected systems were analysed: • methyl ethyl ketone (MEK) natural peat bed, • methyl ethyl ketone (MEK) fractionated pine tree bark, • butanol fractionated pine tree bark, • butanol partly deacidified peat, • triethylamine partly deacidified peat, • triethylamine wooden pieces, • triethylamine compost bed. Biofiltration tests were carried out at 8-hour cycles for stabilized work, after 4 to 8 weeks of exploitation in a column 0.175 m in inner diameter and active bed heights of 0.45 and 0.225 m. A range of contaminant concentration was 1-100 mg/m 3 while gas flow rates - 2-10 m 3/hr. Concentrations in the inlet and outlet of the column were determined chromatographically, gas entering the column was wetted to 80%, and it had temperature of about 20°C. On basis of experimental data, gas spatial residence time in the column, pollutants' loading of the bed, process efficiency, biodegradation rate and reaction constants under assumption of first and zero reaction order were calculated, according to Ottengraf and van den Oever's proposal. It was stated that the model quite well described a course of biofiltration. The values of pollutants' concentrations for which a change of biofiltration kinetics in tested systems were determined. It was proved that the transition from first order to zero order kinetics decided about a proper selection of the bed for specific organic contaminant. Analyzed data indicated that all pollutants were removed from gases, however different systems were characterized by different concentrations for which process kinetics changed. The highest value was found for MEK - fractionated pine tree bark system (over 100 mg/m 3), the lowest triethylamine - wooden pieces and triethylamine - compost bed systems (below 3 mg/m 3). Nevertheless these values should be treated as some kind of approximation. Although the data obtained are not sufficient for biofiltration modelling, they provide information about course of the process and first of all indicate that the simple Ottengraf and van den Oever model can be used in process description.
A review with 42 refs. covering a modified Monod equation and its use to describe the rate of assimilation of VOCs by microflora. The biofilter operates in the dynamic and in the static regions where process efficiency falls and remains const., resp. The region extent is affected by contaminant concn. and linear gas flow velocity in the biofilter, nature of VOC, type of bed, temp., humidity of gas, bed porosity, etc. After the parameters have been detd. In individual studies (e.g., adsorption, bed hydraulics, lab.-scale deodorization), the process can be modeled. Comparison of simulated with exptl. data showed the model equation to describe well the dynamic and the static steps of the process.
Mathematical modeling in the biofiltration of volatile organic compounds is a valuable tool for performance prediction and in scaling up. Majority of the published models include parameters obtained from fitting experimental data, thus masking their real influence as they are lumped generally. The present work aims to evaluate experimentally some of the most relevant parameters including kinetic constant, partition coefficient in the biofilm, biofilm thickness, superficial area, and effective diffusivity. For the fungal biofilm, all the parameters mentioned above were obtained experimentally; and for the bacterial biofilm, the biofilm thickness and some intrinsic parameters used to obtain the first-order kinetic constant were taken from the literature. These parameters were then incorporated in a mathematical model to describe the steady-state degradation of hexane in bacterial and fungal biofilters operating under continuous mode. Experimentally, the dimensionless partition coefficients (mG) indicated that hexane was 4 and 35 times more soluble in the bacterial (mG = 9·14) and fungal (mG = 0·88) biofilters, respectively, than in water (mG = 30·4). Comparison of model estimates with experimental concentration profiles of the pollutant along the height of the biofilters proves that the first-order limited by reaction model was appropriate to interpret the experimental results with a small error of ∼1%.
The detrimental impact of many air pollutants to human health, vegetation, human property, or the global environment is evident from various studies conducted over many years. Inorganic air pollutants are among those that require special attention because of their significant environmental impacts as well as their lack of response to many physical air pollution control techniques(e.g., filters, vapor capture, and condensation). Many of these inorganic air pollutants (such as hydrogen cyanide and hydrogen sulfide) can be associated with severe and acute health impacts following industrial accidents. However, most of the interest in air pollution and health is directed at long-term and low concentration exposure to harmful air contaminants. With the compelling evidence on the long-term impacts of inorganic air pollutants, many researchers have focused on developing and optimizing novel and cost-effective air pollution control strategies that can meet the increasingly stringent regulations on the emissions of these chemicals (e.g., Barnes et al. 1995; Chung et al. 2000;Philip and Deshusses 2003).
Most of the recent literature dealing with biological waste gas treatment indicates that it is not really a new technology, which is indeed basically correct, taking into account that biofiltration has been applied for several decades, though at small scale and with low flow rates, mainly for the removal of volatile pollutants emitted from waste water treatment plants and composting processes (Pomeroy, 1957; Ottengraf and Diks, 1992). Biofiltration was initially mainly exclusively used for the removal of odours by means of soil biofilters designed and set up according to empirical considerations. Applications have recently been extended to a much wider range of compounds, mainly volatile organic compounds, over the last two decades. Development of scientific studies, engineering concepts and non-empirical design of biofilters is also quite recent, as well as the search for new support media and new bioreactor configurations, as will also be described in following chapters.
Flax for centuries has provided important industrial products such as textiles, oilseed, and paper/pulp. Fibers are obtained from flax stems by the process of retting. Two methods employed for retting flax at commercial levels using pectinolytic microorganisms are water- and dew-retting. Water-retting traditionally depends upon anaerobic bacteria, such as Clostridium spp., that live in lakes, rivers, ponds, and vats to produce pectinases and other enzymes to ret flax. The stench from anaerobic fermentation of the plants, extensive pollution of waterways, high drying costs, and putrid odor of resulting fibers resulted in a move away from anaerobic water-retting in the mid-twentieth century to dew-retting. Dew-retting is the result of colonization and partial plant degradation by plant-degrading, aerobic fungi of flax stems, which are harvested and laid out in swaths in fields. The highest quality linen fibers are produced using dew-retting, but concern exists within this industry about low and inconsistent quality. Enzymes have the potential to provide an improved method to ret flax for textile fibers. Enzymatic-retting produces high and consistent quality fibers of staple length for blending with cotton and other fibers. Enzymatic-retting is faster and more reproducible than traditional methods and may provide the spinners with a better quality product.
Biofiltration is an emerging and attractive air pollution control technology for controlling odors, volatile organic carbons (VOCs), and air toxics. It has numerous advantages over conventional air pollution control methods. Biofiltration units are microbial systems incorporating microorganisms grown on a porous solid media such as compost, peat, soil, or a mixture of these materials. The filter media and the microbial culture are surrounded by a thin film of water called biofilm. Waste gases containing biodegradable VOCs and inorganic air toxics are vented through this material, where soluble contaminants partition into the liquid film and are biodegraded by the microorganisms in the biofilm. The technology has been applied to a wide range of industrial and public sector sources for the abatement of odors, VOCs and air toxics, with removal efficiency of more than 90%. Because of its economic benefit over the traditional air pollution control alternatives coupled with environmental advantages, biofiltration is becoming more popular in meeting the statutory emission regulations. Biofiltration harnesses the natural degrading abilities of microorganisms to biochemically oxidize waste gas contaminants into environmentally benign end products such as carbon dioxide, water, and mineral salts. Conventional air pollution control technologies such as carbon adsorption, incineration, etc., can treat a wide variety of pollutants at higher concentrations, however, for treating waste air with low pollutant concentrations these approaches become economically prohibitive. In comparison, biofiltration is more cost-effective particularly for treatment of large volumes of waste air with low concentrations of biodegradable contaminants. The low cost of biofiltration is associated with its use of natural sorbents and microbial oxidation. However, one must accept the trade-off in terms of longer residence time that is partially compensated by lower operating cost. The acceptance of biofiltration has followed from advances in biotechnology that provide thorough knowledge about the system and how the process can be optimized, not only to achieve high removal efficiencies with low energy consumption, but to achieve these elimination efficiencies over long periods with minimal maintenance. Further research is needed to develop good understanding of the metabolic degradation pathways for single and multiple contaminant waste gas streams, effective mass transfer from gas to liquid phase, and improved modeling techniques incorporating better kinetic data.
This work describes the growth of filamentous fungi in biofilters for the degradation of hydrophobic VOCs. The study system was n-hexane and the fungus Fusarium solani B1. The system is mathematically described and the main physical, kinetic data and morphological parameters of aerial hyphae were obtained by independent experiments for model validation. The model proposed in this study describes the increase in the transport area by the growth of the filamentous cylindrical mycelia and its relation with n-hexane elimination in quasi-stationary state in a biofilter. The model describing fungal growth includes Monod-Haldane kinetic and hyphal elongation and ramification. The reduction in the permeability caused by mycelial growth was further related to pressure drop by Darcy's equation. The model was verified with biofiltration experiments using perlite as support and gaseous n-hexane as substrate.
The transient behavior of hybrid system composed of a photo-catalytic reactor and a biofilter was observed at the height of each sampling port to treat waste-air containing hydrogen sulfide highly concentrated up to 1000 ppmv with high loading. The biofilter packed with mixed media (of granular activated carbon and compost) was inoculated with a pure culture of Thiobacillus sp. IW, while the photo-catalytic reactor was composed of 15 W UV-A lamps and annular pyrex tubes packed with glass beads coated with TiO2 sol before calcination. The maximum elimination capacity of a biofilter-only process was 95 g/m3/h. On the other hand, the maximum elimination capacity of a hybrid system was observed to be 140 g/m3/h. The contribution of the photo-catalytic process to the increment of the elimination capacity of the applied hybrid system was composed of the direct contribution of photo-catalytic process and its indirect contribution to the increment of the elimination capacity of subsequent process, a biofilter. The contributions of the photo-catalytic process to the hybrid system-elimination capacity turned out to consist of a direct (37–55%) one and an indirect (45–63%) one for the removal of highly concentrated hydrogen sulfide with high loading of 232 g/m3/h. However, the indirect contribution of the photocatalytic process could not be estimated for the stages of lowly-loaded hybrid system run. Consequently, the percent-fraction of the indirect contribution of photo-catalytic process for the removal of hydrogen sulfide is reported to be smaller than that for the removal of VOCs.
Removal of mono-chlorobenzene (m-CB) vapor from airstreams was studied in a biotrickling filter (BTF) operating under counter-current flow of the air and liquid streams. Experiments were performed under various values of inlet m-CB concentration, air and/or liquid volumetric flow rates, and pH of the recirculating liquid. Conversion of m-CB was never below 70% and at low concentrations exceeded 90%. A maximum removal rate of about 60 gm−3-reactor h−1 was observed. Conversion of m-CB was found to increase as the values of liquid and air flow rate increase and decrease, respectively. The effects of pH and frequency of medium replenishment on BTF performance were also investigated. The process was successfully described with a detailed mathematical model, which accounts for mass transfer and kinetic effects based on m-CB and oxygen availability. Solution of the model equations yielded m-CB and oxygen concentration profiles in all three phases (airstream, liquid, biofilm). It is predicted that oxygen has a controling effect on the process at high inlet m-CB concentrations. From independent, suspended culture, experiments it was found that m-CB biodegradation follows Andrews inhibitory kinetics. The kinetic constants were found to remain practically unchanged after the culture was used in BTF experiments for 8 months. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:328–343, 1998.
The immobilization of whole cells involves the retention of catalytically active cells within a restricted region of a bioreactor. Techniques which have been used to immobilize whole cells include adsorption, aggregation, confinement and entrapment. These techniques can be applied to essentially all of the viable or non-viable whole cell systems of potential interest: microorganisms, animal and plant cells. The fact that immobilized cells may be living leads to unique effects in this form of heterogeneous catalysis. These include the impact of immobilization on cell physiology and cell mobility, physical interactions of immobilized cells with the support, and the creation of a microenvironment. The theory of mass-transfer and reaction in these types of systems is well understood, but schemes capable of predicting substrate and product diffusivities and the intrinsic kinetics in the aggregate must still be developed. New experimental approaches are being used to elucidate the basic mechanisms that determine these physical and metabolic properties of immobilized cells. Several reactor configurations have been successfully used with immobilized cells, and many more have been proposed. The choice of a particular design for a given process depends on the requirements for mass-transfer, the growth behaviour of the cells, and the structural properties of the aggregate.
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. However, experimental and theoretical results revealed that the relative flow direction of the mobile phases did not significantly affect the elimination performance. Moreover, it was found that the gas-liquid mass-transfer resistance in the trickling filter bed applied was negligible, which leaves the biological process inside the biofilm to be the rate limiting step. A simplified model was developed, the 'Uniform-Concentration-Model', which showed to predict the filter performance close to the numerical solutions of the model equations. This model gives an analytical expression for the degree of conversion and can thus be easily applied in practice. The dichloromethane eliminating performance of the trickling filter described in this paper, is reflected by a maximum dichloromethane elimination capacity (EC(max) = 157 g/(m3·h) and a critical liquid concentration C(lcr) = 45 g/m3 at a superficial liquid velocity of 3.6 m/h, independent of the gas velocity and temperature.
For various industrial solvent vapors, biofiltration promises to offer a cost-effective emission control technology. Exploiting the full potential of this technology will help attain the goals of the Clean Air Act Amendments of 1990. Concentrating on large volumes of volatile industrial solvents, stable multicomponent microbial enrichments capable of growing a mineral medium with solvent vapors as their only source of carbon and energy were obtained from soil and sewage sludge. These consortia were immobilized on an optimized porous solid support (ground peat moss and perlite). The biofilter material was packed in glass columns connected to an array of pumps and flow meters that allowed the independent variation of superficial velocity and solvent vapor concentrations. In various experiments, single solvents, such as methanol, butanol, acetonitrile, hexane and nitrobenzene, and solvent mixtures, such as benzene-toluene-xylene (BTX) and chlorobenzene-o-dichlorobenzene (CB/DCB) were biofiltered with rates ranging from 15 to334 g solvent removed per m[sup 3] filter volume /h. Pressure drops were low to moderate (0-10 mmHg/m) and with periodic replacement of moisture, the biofiltration activity could be maintained for a period of several months. The experimental data on methanol biofiltration were subjected to mathematical analysis and modeling by the group of Dr. Baltzis at NJIT for a better understanding and a possible scale up of solvent vapor biofilters. In the case of chlorobenzenes and nitrobenzene, the biofilter columns had to be operated with water recirculation in a trickling filter mode. To prevent inactivation of the trickling filter by acidity during CB/DCB removal, pH control was necessary, and the removal rate of CB/DCB was strongly influenced by the flow rate of the recyling water. Nitrobenzene removal in a trickling filter did not require pH control, since the nitro group was reduced and volatilized as ammonia.
One of the most formidable challenges posed by the Clean Air Act Amendments of 1990 (CAAA) is the search for efficient and economical control strategies for volatile organic compounds (VOCs). VOCs are precursors to ground-level ozone, a major component in the formation of smog. Under the CAAA, thousands of currently unregulated sources will be required to reduce or eliminate VOC emissions. In addition, sources that are currently regulated may seek to evaluate alternative VOC control strategies to meet stricter regulatory requirements such as the maximum achievable control technology (MACT) requirements in Title III of the CAAA. Because of the increasing attention being given to VOC control, the American Institute of Chemical Engineers' (AIChE) Center for Waste Reduction Technologies (CWRT) initiated a study of VOC control technologies and regulatory initiatives. A key objective of the project was to identify and describe existing VOC control technologies and air regulations, as well as emerging technologies and forthcoming regulations. That work is the basis for this article.
A mathematical model is presented for both batch and continuous cultures of microorganisms utilizing inhibitory substrates. The key feature of the model is the use of a inhibition function to relate substrate concentration and specific growth rate. Simulation studies show that the primary result of inhibition by substrate in a batch culture is an increase in the lag time whereas in continuous culture inhibition by substrate may result in process instability. The model should be of value in investigations of the stability of biological processes used for the treatment of certain industrial wastes such as those containing phenols, thiocyanates, nitrates, ammonia, volatile acids, etc., which are known to be inhibitory to many of the organisms metabolizing them.
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.
However, experimental and theoretical results revealed that the relative flow direction of the mobile phases did not significantly affect the elimination performance. Moreover, it was found that the gas-liquid mass-transfer resistance in the trickling filter bed applied was negligible, which leaves the biological process inside the biofilm to be the rate limiting step.
A simplified model was developed, the “Uniform-Concentration-Model”, which showed to predict the filter performance close to the numerical solutions of the model equations. This model gives an analytical expression for the degree of conversion and can thus be easily applied in practice.
The dichloromethane eliminating performance of the trickling filter described in this paper, is reflected by a maximum dichloromethane elimination capacity EC
max=157 g/(m3 · h) and a critical liquid concentration C
lcr=45 g/m3 at a superficial liquid velocity of 3.6 m/h, inpendent of the gas velocity and temperature.
Biofiltration is a relatively recent air pollution control (APC) technology in which off-gases containing biodegradable volatile organic compounds (VOC) or inorganic air toxics are vented through a biologically active material. This technology has been successfully applied in Germany and The Netherlands in many full-scale applications to control odors, VOC and air toxic emissions from a wide range of industrial and public sector sources. Control efficiencies of more than 90 percent have been achieved for many common air pollutants. Due to lower operating costs, biofiltration can provide significant economic advantages over other APC technologies if applied to off-gases that contain readily biodegradable pollutants in low concentrations. Environmental benefits include low energy requirements and the avoidance of cross media transfer of pollutants. This paper reviews the history and current status of biofiltration, outlines its underlying scientific and engineering principles, and discusses the applicability of biofilters for a wide range of specific emission sources.
In order to eliminate organic pollutants in waste gases, a biological filter bed technique has been developed, with a high self-regenerating capacity and a low pressure drop. The bed consists of an appropriate filling material (mainly peat compost), in order to let the microorganisms grow on the solid surface and to supply them with inorganic nutrients. Most organic compounds are oxidized to carbon dioxide and water. The compositions of the solid phase and the viable organisms present are such that aging is prevented, as a result of which a relatively high activity can be maintained during a long period of time (years). Experiments have been carried out in laboratory-scale columns with composite gas mixtures at varied concentrations and superficial gas velocities. The (macro) kinetics of the elimination processes have been studied, which enables the prediction of the elimination capacity of the filter bed.
Concentration multiplicity in a two-phase or three-phase draft tube fluidized-bed bioreactor containing biofloc particles is studied. The kinetics of biological reactions considered involve two limiting substrates. The necessary and sufficient conditions for concentration multiplicity in both the biofilm and bioreactor are examined in terms of effectiveness factor, inlet and bulk concentration of substrates, and liquid flow rate. Hysteresis behavior in both the biofilm and bioreactor and multiplicity of concentration profiles in the biofilm are also discussed.
Diffusion of phenol through a biofilm attached to activated carbon particles was investigated. The biofilm was grown on activated carbon particles in a draft-tube three-phase fluidized-bed bioreactor operating in a fed-batch mode. It was found that phenol did not adsorb on the biofilm and that the diffusion coefficient of phenol within the biofilm varied from 13 to 39% of its corresponding value in water. The diffusion coefficient of phenol within the biofilm was reduced by increasing the biofilm density. An extensive literature review of diffusion of substrates through biofilms indicated that this conclusion could be extended to biofilms grown on flat surfaces, rotating cylinders, and even bioflocs.
A phenomenological model has been developed to describe biomass distribution and substrate depletion in porous diatomaceous earth (DE) pellets colonized by Pseudomonas aeruginosa. The essential features of the model are diffusion, attachment and detachment to/from pore walls of the biomass, diffusion of substrate within the pellet, and external mass transfer of both substrate and biomass in the bulk fluid of a packed bed containing the pellets. A bench-scale reactor filled with DE pellets was inoculated with P. aeruginosa and operated in plug flow without recycle using a feed containing glucose as the limiting nutrient. Steady-state effluent glucose concentrations were measured at various residence times, and biomass distribution within the pellet was measured at the lowest residence time. In the model, microorganism/substrate kinetics and mass transfer characteristics were predicted from the literature. Only the attachment and detachment parameters were treated as unknowns, and were determined by fitting biomass distribution data within the pellets to the mathematical model. The rate-limiting step in substrate conversion was determined to be internal mass transfer resistance; external mass transfer resistance and microbial kinetic limitations were found to be nearly negligible. Only the outer 5% of the pellets contributed to substrate conversion.
The purpose of this study is to investigate the feasibility of biologically removing phenol from waste gases by means of a biofilter using a Pseudomonas putida strain. Two series of both batch and continuous tests have been performed in order to ascertain the microbial degradation of phenol. For the preliminary batch tests, carried out in order to test the effective feasibility of the process and to investigate their kinetic behavior, two different microbial cultures belonging to the Pseudomonas genus have been employed, a heterogeneous culture and a pure strain of P. putida. The results of these comparative investigation showed that the pure culture is more efficient than the mixed one, even when the latter has undergone three successive acclimatization tests. The continuous experiments have been conducted during a period of about 1 year in a laboratory-scale column, packed with a mixture of peat and glass beads, and utilizing the pure culture of P. putida as microflora and varying the inlet phenol concentration from 50 up to 2000 mg m(-3). The results obtained show that high degrees of conversion can be obtained (0.93/0.996) operating at a residence time of 54 s.
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.
Recherches sur la Croissance des Cultures Bacteriennes VOC control: current practices and future trends Biofiltration of solvent vapors from air
- J Monod
- Hermann
- Paris Cie
- E C Moretti
- N Mukhopadhyay
Monod, J., 1942, Recherches sur la Croissance des Cultures Bacteriennes. Hermann et Cie, Paris. Moretti, E. C. and Mukhopadhyay, N., 1993, VOC control: current practices and future trends. Chem. Engng Progress 89(7), 20. Oh, Y.-S., 1993, Biofiltration of solvent vapors from air. Ph.D. thesis, Rutgers University, New Brunswick, NJ.
Kinetics of double-substrate limited growth, in Microbial Population Dynamics (Edited by M Modeling and preliminary design criteria for packed-bed biofilters
- H Androutsopoulou
- Nj Baider
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Kinetics of double-substrate limited growth
- Baider
A study of the biofiltration process under shock-loading conditions
- Androutsopoulou
Modeling and preliminary design criteria for packed-bed biofilters
- Baltzis
Engineering analysis of a packed-bed biofilter for removal of volatile organic compound (VOC) emissions
- Shareefdeen