Biofiltration of Air: A Review

Abstract

In this paper we present a review of the existing air pollution control technologies (APCT), when used essentially for the elimination of volatile organic compounds (VOC). The biotechnologies referred to, bioscrubbers, biotrickling filters and biofilters, are also described. A more detailed review of biofiltration is proposed, presenting the most recent and latest developments achieved in the field of bioprocessing. In particular, the influence of the filter bed, the polluted air flowrates, the pollutants, the pressure drop, bed moisture content, temperature, nutrients, pH and the microorganisms are reviewed. Models of biofiltration are also presented.     

Biofiltration for treating VOCs: an overview

In this paper we present a review of Biofiltration, one of the air pollution control technologies (APCT) used to treat volatile organic compounds (VOCs) effectively. It also talks about the history of biofiltration, and also proposes few ideas for the future developments in the biofiltration research pertaining to VOC control. Moreover, the paper also discusses about various important physical, chemical and biological factors which affect the performance of a biofilter both directly and indirectly. This paper will be handier for those who are new to the field of biofiltration research for VOC treatment.     

Biofiltration eliminates nuisance chemical odors from industrial air streams

This paper focuses on recent developments of biofiltration technology used in treating nuisance chemical odors from industrial and municipal air streams. In the biofiltration process, odorous chemical constituents in the air are first transported to biofilms by diffusion, solubilization and adsorption processes. Bacteria within the biofilms oxidize odor constituents into harmless and odorless products. Through successful laboratory and pilot research on biofiltration of odorous air-stream constituents, numerous commercial biofilters have been designed and installed across North America. In this paper, case studies related to biofiltration of air emissions from meat rendering plants, municipal wastewater treatment applications, and printed circuit board production are discussed to demonstrate the robustness of this technology in eliminating a wide variety of compounds. Electronic Publication     

Biofiltration of volatile organic compounds

The removal of volatile organic compounds (VOCs) from contaminated airstreams has become a major air pollution concern. Improvement of the biofiltration process commonly used for the removal of odorous compounds has led to a better control of key parameters, enabling the application of biofiltration to be extended also to the removal of VOCs. Moreover, biofiltration, which is based on the ability of micro-organisms to degrade a large variety of compounds, proves to be economical and environmentally viable. In a biofilter, the waste gas is forced to rise through a layer of packed porous material. Thus, pollutants contained in the gaseous effluent are oxidised or converted into biomass by the action of microorganisms previously fixed on the packing material. The biofiltration process is then based on two principal phenomena: (1) transfer of contaminants from the air to the water phase or support medium, (2) bioconversion of pollutants to biomass, metabolic end-products, or carbon dioxide and water. The diversity of biofiltration mechanisms and their interaction with the microflora mean that the biofilter is defined as a complex and structured ecosystem. As a result, in addition to operating conditions, research into the microbial ecology of biofilters is required in order better to optimise the management of such biological treatment systems.     

净化废气的生物过滤技术及其影响因素

生物过滤方法在废气净化中具有费用低和环保的特点, 因而成为一种应用前景良好的空气污染控制技术。本文综述了不同生物过滤反应器的特点, 详细分析了应当在生物过滤过程中合理控制的关键参数, 并展望了今后的研究热点。     

Biofiltration of n-butyric acid for the control of odour

Odour control from pig production facilities is a significant concern due to increased public awareness and the development of more stringent legislation to control production. Although many technologies exist, biofiltration is still the most attractive due to its low maintenance and operating costs. One of the key odour components, n-butyric acid, was selected for a laboratory scale biofilter study. It was examined as a sole carbon substrate in order to investigate the effectiveness of biofiltration in reducing n-butyric acid concentration under different operating conditions using a moist enriched woodchip medium. Three superficial gas velocities; 38.2, 76.4, and 114.6 m x h(-1) were tested for n-butyric acid concentrations ranging from 0.13 to 3.1 g [n-butyric acid] m(-3) [air]. For superficial gas velocities 38.2, 76.4, and 114.6 m x h(-1), maximum elimination capacities (100% removal) of 148, 113 and 34.4 g x m(3) x h(-1), respectively, were achieved. Upon investigation of effective bed height, true elimination capacities (100% removal) of 230, 233 and 103 g x m(-3) x h(-1), respectively, were achieved at these superficial gas velocities. Averaged pressure drops for superficial gas velocities 38.2, 76.4, and 114.6 m x h(-1) were 30, 78 and 120 Pa, respectively. It was concluded that biofiltration is a viable technology for the removal of n-butyric acid from waste exhaust air, but near 100% removal efficiency is required due to the low odour detection threshold for this gaseous compound.     

Biofiltration of ethylbenzene vapours: influence of the packing material

In order to investigate suitable packing materials, a soil amendment composed of granular high mineralized peat (35% organic content) locally available has been evaluated as carrier material for biofiltration of volatile organic compounds in air by comparison with a fibrous peat (95% organic content). Both supports were tested to eliminate ethylbenzene from air streams in laboratory-scale reactors inoculated with a two-month conditioned culture. In pseudo-steady state operation, experiments at various ethylbenzene inlet loads (ILs) were carried out. Maximum elimination capacity of about 120 g m(-3) h(-1) for an IL of 135 g m(-3) h(-1) was obtained for the fibrous peat. The soil amendment reactor achieved a maximum elimination capacity of about 45 g m(-3) h(-1) for an inlet load of 55 g m(-3) h(-1). Ottengraf-van den Oever model was applied to the prediction of the performance of both biofilters. The influence of gas flow rate was also studied: the fibrous peat reactor kept near complete removal efficiency for empty bed residence times greater than 1 min. For the soil amendment reactor, an empty bed residence time greater than 2 min was needed to achieve adequate removal efficiency. Concentration profiles along the biofilter were also compared: elimination occurred in the whole fibrous peat biofilter, while in the soil amendment reactor the biodegradation only occurred in the first 65% part of the biofilter. Results indicated that soil amendment material, previously selected to increase the organic content, would have potential application as biofilter carrier to treat moderate VOC inlet loads.     

Elimination of methane generated from landfills by biofiltration: a review

The production of biogas in landfills, its composition and the problems resulting from its generation are all reviewed. Biofiltration is a promising option for the control of emissions to atmosphere of the methane contained in biogas issued from the smaller and/or older landfills. A detailed review of the methane biofiltration literature is presented. The microorganisms, mainly the methanotrophs, involved in the methane biodegradation process, and their needs in terms of oxygen and carbon dioxide utilization, are described. Moreover, the influence of nutrients such as copper, nitrogen and phosphorus, and the process operating conditions such as temperature, pH and moisture content of the biofilter bed, are also presented. Finally, the performance of various filter beds, in terms of their elimination capacities, is presented for laboratory scale biofilters and landfill covers.     

Environmental biotechnology in China: progress and prospect

Biotechnology could be widely applied in the technological development of environmental protection. This report gives a brief Chinese review on the major progress of environmental biotechnology in the following fields: Monitoring technology and treatment of dioxin-like chemicals and cyanobacterial toxins, biofiltration for air pollution control, solid waste treatment and reutilization, bioremediation of soil pollution, risk assessment and control of endocrine disturbing substances in environment, wastewater treatment, clean production and recycling economy. The effect of government policy and fund on the progress of environmental biotechnology is also discussed.     

废气处理生物滤器微生物生态学研究进展

废气生物处理是一项新兴的气体污染控制技术,已成为当前环境领域的研究热点.本文概述了生物滤器系统(包括生物过滤器系统和生物滴滤器系统)结构及其去除气体污染物的原理,重点阐述了生物滤器微生物的分离、鉴定及其降解特性,微生物丰度、活性与微生物群落结构多样性之间的相关性,运行条件对微生物群落的影响,微生物群落结构时空变化规律,生物膜形成机理和模型等方面的研究进展,并对今后废气处理生物滤器微生物生态学研究方向进行了展望.     

Biofiltration of methanol vapor

Biofiltration of solvent and fuel vapors may offer a costeffective 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. (c) 1993 John Wiley & Sons, Inc.     

Modelling the nitrification in a full-scale tertiary biological aerated filter unit

A wastewater biofiltration model is used to assess its capacity to reproduce the treatment behaviour of a plant-sized tertiary nitrifying biofilter unit. It is calibrated on two different types of datasets collected at the Seine-Aval biofiltration plant (Achères, France): grab samples at several heights inside the media bed and a long-term daily plant monitoring over a 1-year period. The model parameters are first calibrated to fit the dynamics observed in the media bed, after which the model is compared to the second dataset. Further parameter changes are then made if necessary and the model is once again compared to both datasets to ensure its ability to predict the treatment behaviour on both size scales. The calibrated model provides correct predictions for most observed nutrient variables for both datasets. An overestimation of the oxygen transfer under a summer, low ammonia load period however leads to a slight underestimation of the nitrifying efficiency of the biofilters. Statistical score computation corroborates the model accuracy as the mean error scores usually remain low. They also point to a certain weakness of the model regarding the suspended solids filtration. Both datasets are overall correctly modelled using a single parameter set. Most of this parameter set is close to or contained in value ranges found in the literature. The parameters related to aeration, however, seem to be slightly higher than what is reported elsewhere.     

Biofiltration for the removal and ‘detoxification’ of a complex mixture of volatile organic compounds

A study was performed to determine the effectiveness of using biofiltration for the removal of a complex mixture of volatile organic compounds (VOCs) air-stripped from petroleum hydrocarbons. A biofilter was constructed which contained 264 cm³ of packing material (Celite^? R-635). The unit was inoculated with a mixed culture containing a hydrocarbon-degrading Pseudomonas sp and an Alcaligenes sp. Several of the major compounds in the VOC mixture were monitored individually, along with the total VOCs, using gas chromatography. The average influent concentration of the VOC mixture was 320 ppmv and the average total VOC removal rate was over 56%, with the average removal rate of the monitored individual compounds ranging from 49–90%. After 30 days of operation the average overall removal rate was 69% and the removal of the major compounds averaged 92%. The toxicity and mutagenicity of the air stream was monitored using the Microtox and Ames assays, respectively. These data show marked decreases in toxicity and mutagenicity of the air stream as a result of the biofiltration treatment. The biofiltration system, therefore, was not only effective in removing VOCs from the air stream over an extended time-period, but was also effective in greatly reducing the toxicity and mutagenicity associated with the remaining VOCs. Received 03 July 1997/ Accepted in revised form 25 November 1997     

Fungal biocatalysts in the biofiltration of VOC-polluted air

Gas-phase biofilters used for the treatment of waste gases were originally packed with compost or other natural filter beds containing indigenous microorganisms. Over the past decade much effort has been made to develop new carrier materials, more performant biocatalysts and new types of bioreactors. Elimination capacities reached nowadays are 5 to 10 times higher than those originally reported with conventional compost biofilters. With the recently developed inert filter beds, inoculation is a prerequisite for successful start-up and operation. Either non-defined mixed cultures or pure bacterial cultures have originally been used. The search for efficient fungal biocatalysts started only a few years ago, mainly for the biofiltration of waste gases containing hydrophobic compounds, such as styrene, alpha-pinene, benzene, or alkylbenzenes. In this review, recently isolated new fungal strains able to degrade alkylbenzenes and other related volatile organic pollutants are described, as well as their major characteristics and their use as biocatalysts in gas-phase biofilters for air pollution control. In biofiltration, the most extensively studied organism belongs to the genus Exophiala, although strains of Scedosporium, Paecilomyces, Cladosporium, Cladophialophora, and white-rot fungi are all potential candidates for use in biofilters. Encouraging results were obtained in most of the cases in which some of those organisms were present in gas-phase biofilters. They allow reaching high elimination capacities and are resistant to low pH values and to reduce moisture content.     

Microbial characterization of organic carrier colonization during a model biofiltration experiment

AIMS: Dynamic microbial characterization of the colonization of organic carrier during a model biofiltration experiment using methanol as air pollutant. METHODS AND RESULTS: A model biofilter was used in order to characterize the micro-organisms involved in the colonization of a model organic carrier. The model system consisted of closed vial as biofilter, peanut shells as lignocellulosic carrier and methanol as air pollutant. The micro-organisms involved in biofiltration were identified and characterized for their lignocellulolytic and methylotrophic activities. Fungi presented a higher lignocellulolytic activity than bacteria. A steady-state was reached after 15 to 20 days. CONCLUSIONS: The consortium naturally associated to peanut shells is limited to few aerobic bacteria and lignocellulolytic fungi. This consortium was able to degrade methanol without external nutrient supply. SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first paper that focuses on carrier degradation processes and the micro-organisms involved during the start-up period of a biofiltration process.     

H2S gas biological removal efficiency and bacterial community diversity in biofilter treating wastewater odor

The objective of this study was to assess the feasibility of using a biofilter system to treat hydrogen sulfide (H2S) contaminated air and to characterize its microbial community. The biofilter system was packed with peat. During the experimental work, the peat was divided in three layers (down, middle, and up). Satisfactory removal efficiencies of H2S were proved and reached 99% for the majority of the run time at an empty bed retention time (EBRT) of 60 s. The polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method was used to uncover the changes in the microbial community between the different layers. Analysis of SSCP profiles demonstrated significant differences in community structure from a layer to another with a strong decrease in species diversity towards the up layer. It was found that the used support was suitable for microorganism growth, and may have a potential application in H2S biofiltration system.     

Biofiltration--the treatment of fluids by microorganisms immobilized into the filter bedding material: a review

Biofiltration is distinguished from other biological waste treatments by the fact that there is a separation between the microorganisms and the treated waste. In biofiltration systems the microorganisms are immobilized to the bedding material, while the treated fluid flows through it. In recent decades, a vast amount of literature has been written on single experiments involving the treatment of fluids by immobilized microorganisms. Several artificial immobilization methods have been examined and impressive results have been achieved in the treatment of fluids with one of the artificial immobilization methods the entrapment of microorganisms within polymer beads. This method, even though it needs to be improved, seems to have a future potential in commercial biofiltration systems. The methods of artificial immobilization of microorganisms within biofiltration systems have several advantages, but also suffer from several disadvantages in comparison to the treatment of fluids by naturally attached microorganisms. Understanding the mechanisms and forces responsible for the attachment of microbes to the bedding material, in attempt to improve this attachment, is of the utmost importance. Further improvement of the artificial entrapment of microorganisms within polymers will allow the exploitation of the advantages of this method in the treatment of fluids. The aim of this review essay is to introduce the main principles of two immobilization processes - the self-attachment of microorganisms to the bedding material and the artificial entrapment of microorganisms within polymer beads. Both treatments of liquids and gases with each immobilization process are discussed. The advantages and disadvantages of each immobilization process are pointed out and different aspects of the fluid treatment with the two immobilization processes are compared.     

Application of biofiltration to the degradation of hydrogen sulfide in gas effluents

A laboratory scale bioreactor has been designed and set up in order to degrade hydrogen sulfide from an air stream. The reactor is a vertical column of 7 litre capacity and 1 meter in height. It is divided into three modules and each module is filled with pellets of agricultural residues as packing bed material. The gas stream fed into the reactor through the upper inlet consists of a mixture of hydrogen sulfide and humidified air. The hydrogen sulfide content in the inlet gas stream was increased in stages until the degradation efficiency was below 90%. The parameters to be controlled in order to reach continuous and stable operation were temperature, moisture content and the percentage of the compound to be degraded at the inlet and outlet gas streams (removal or elimination efficiency). When the H₂S mass loading rate was between 10 and 40 g m^-3h^-1, the removal efficiency was greater than 90%. The support material had a good physical performance throughout operation time, which is evidence that this material is suitable for biofiltration purposes.     

The phytoremediation of indoor air pollution: a review on the technology development from the potted plant through to functional green wall biofilters

Poor indoor air quality is a health problem of escalating magnitude, as communities become increasingly urbanised and people’s behaviours change, lending to lives spent almost exclusively in indoor environments. The accumulation of, and continued exposure to, indoor air pollution has been shown to result in detrimental health outcomes. Particulate matter penetrating into the building, volatile organic compounds (VOCs) outgassing from synthetic materials and carbon dioxide from human respiration are the main contributors to these indoor air quality concerns. Whilst a range of physiochemical methods have been developed to remove contaminants from indoor air, all methods have high maintenance costs. Despite many years of study and substantial market demand, a well evidenced procedure for indoor air bioremediation for all applications is yet to be developed. This review presents the main aspects of using horticultural biotechnological tools for improving indoor air quality, and explores the history of the technology, from the humble potted plant through to active botanical biofiltration. Regarding the procedure of air purification by potted plants, many researchers and decades of work have confirmed that the plants remove CO₂ through photosynthesis, degrade VOCs through the metabolic action of rhizospheric microbes, and can sequester particulate matter through a range of physical mechanisms. These benefits notwithstanding, there are practical barriers reducing the value of potted plants as standalone air cleaning devices. Recent technological advancements have led to the development of active botanical biofilters, or functional green walls, which are becoming increasingly efficient and have the potential for the functional mitigation of indoor air pollutant concentrations.