Biological Air Treatment Research Articles

Removal of cyclohexane vapors from air in biotrickling filters: Effects of gas mixture composition and circular economy approach

This work presents results of investigations on biotrickling filtration of air polluted with cyclohexane co-treated in binary, ternary and quaternary volatile organic compounds (VOCs) mixtures, including vapors of hexane, toluene and ethanol. The removal of cyclohexane from a gas mixture depends on the physicochemical properties of the co-treated VOCs and the lower the hydrophobicity of the VOC, the higher the removal efficiency of cyclohexane. In this work, the performance of biotrickling filters treating VOCs mixtures is discussed based on surface tension of trickling liquid for the first time. A mixed natural – synthetic packing for biotrickling filters was utilized, showing promising performance and limited maintenance requirements. Maximum elimination capacity of about 95 g/(m 3·h) of cyclohexane was reached for the total VOCs inlet loading of about 450 g/(m 3·h). This work presents also a novel approach of combining biological air treatment with management of a spent trickling liquid in the perspective of circular economy assumptions. The waste liquid phase was applied to the plant cultivation, showing a potential for e.g. enhanced production of energetic biomass or polluted soil phytoremediation.

Research into acetone removal from air by biofiltration using a biofilter with straight structure plates

The biological air treatment method is based on the biological destruction of organic compounds using certain cultures of microorganisms. This method is simple and may be applied in many branches of industry. The main element of biological air treatment devices is a filter charge. Tests were carried out using a new-generation laboratory air purifier with a plate structure. This purifier is called biofilter. The biofilter has a special system for packing material humidification which does not require additional energy inputs. In order to extend the packing material's durability, it was composed of thermally treated birch fibre. Pollutant (acetone) biodegradation occurred on thermally treated wood fibre in this research. According to the performed tests and the received results, the process of biodestruction was highly efficient. When acetone was passed through biofilter's packing material at 0.08 m s−1 rate, the efficiency of the biofiltration process was from 70% up to 90%. The species of bacteria capable of removing acetone vapour from the air, i.e. Bacillus (B. cereus, B. subtilis), Pseudomonas (P. aeruginosa, P. putida), Stapylococcus (S. aureus) and Rhodococcus sp., was identified in this study during the process of biofiltration. Their amount in the biological packing material changed from 1.6 × 107 to 3.7 × 1011 CFU g−1.

An Investigation on the Efficiency of Air Purification Using a Biofilter with Activated Bed of Different Origin

Abstract Recent studies in the area of biological air treatment in filters have addressed fundamental key issues, such as a biofilter bed of different origin composed of natural zeolite granules, foam cubes and wood chips. When foam and zeolite are mixed with wood chips to remove volatile organic compounds from the air, not only biological but also adsorption air purification methods are accomplished. The use of complex purification technologies helps to improve the efficiency of a filter as well as the bed service life of the filter bed. Investigations revealed that microorganisms prevailing in biological purification, can also reproduce themselves in biofilter beds of inorganic and synthetic origin composed of natural zeolite and foam. By cultivating associations of spontaneous microorganisms in the filter bed the dependencies of the purification efficiency of filter on the origin, concentration and filtration time of injected pollutants were determined. The highest purification efficiency was obtained when air polluted with acetone vapour was supplied to the equipment at 0.1 m/s of superficial gas velocity. When cleaning air from volatile organic compounds (acetone, toluene and butanol), under the initial pollutant concentration of ~100 mg/m3, the filter efficiency reached 95 %.

Introduction: Special Issue on Biological Air Treatment

Introduction: Special Issue on Biological Air Treatment

Characterization techniques of packing material colonization in gas biofiltration processes

Biological air treatment is largely used for the decontamination of large air streams with low pollutant concentrations. As a result of microbial metabolism, the pollutants are degraded into carbon dioxide and water or converted into cell biomass. Three main research domains have emerged within the field of biofiltration: filter bed development, process optimization, and microbiological studies (community, nutrients, …). The objective of this paper is to focus on the microbial activities in air biofiltration processes. The nutrient contribution and the packing material effects are described. Special attention is paid to the description of techniques for the characterization and identification of the microbial population.

BIOLOGICAL AIR TREATMENT EFFICIENCY OF A STRAW BIO-CHARGE

Experimental research evaluated the possibilities of air treatment efficiency of a cylindrically shaped bio-charge, namely straw, to remove volatile organic compounds from the air. As determined during experiments, the air treatment efficiency of the straw biocharge for acetone removal reached 97.3%, while for butanol removal the efficiency was 86.0%. It has been determined that, with volatile organic compound concentrations increasing biological air treatment efficiency is decreasing as higher concentrations of organic compounds reduce the activity of microorganisms, i.e. their reproduction, respiratory and pollutant oxidation capacities. A higher efficiency of a biological air treatment device is achieved by reducing the velocity of the airflow passed through the biofilter. With airflow velocity decreasing the duration of pollutant contact with the charge is increasing, which raises the biological air treatment efficiency by 1.3 times.

INVESTIGATION INTO THE AIR TREATMENT EFFICIENCY OF BIOFILTERS OF DIFFERENT STRUCTURES

Biological air treatment devices, biofilters, of four different structures with different origin charges, composed of natural zeolite granules, foam cubes and wood chips, were used for the experimental investigation. Biological and ad‐sorptive air treatment methods are employed to clean the air from volatile organic compounds by mixing foam and zeolite with wood chips. The use of complex cleaning technologies improves the efficiency of the device and extends the useful life of a charge. The investigation showed that microorganisms predominant in the process of biocleaning could also propagate in the charges of inorganic origin composed of natural zeolite. The dependences of biofilter treatment efficiency on the nature, concentration and filtration time of the fed pollutant were determined when cultivating associations of spontaneous microorganisms in a charge. The best filtration efficiency of the charge was achieved when acetone‐polluted air was fed into the device at a speed of 0.3 m/s. The treatment efficiency of a biofilter with a humidifying chamber reached 98% when cleaning the air from acetone with an initial concentration of the pollutant of 305 mg/m3. The cleaning efficiency of the device increases when reducing the concentrations of pollutants fed into the device and increasing the time of their filtration. Santrauka Eksperimentiniams tyrimams atlikti naudota keturi skirtingu konstrukciju biologiniai oro valymo irenginiai - biofiltrai su skirtingos kilmes ikrovomis, sudarytomis iš gamtines kilmes ceolito granuliu, porolono kubeliu bei medienos skiedru. Porolona ir ceolita maišant su medienos skiedromis, lakiesiems organiniams junginiams iš oro valyti taikomi biologinis ir adsorbcinis oro valymo metodai. Irenginio valymo efektyvumas pagerinamas bei ikrovos naudojimo trukme ilgeja naudojant kompleksines valymo technologijas. Ištyrus nustatyta, kad biologinio valymo procese vyraujantys mikroorganizmai gali daugintis ir neorganines kilmes ikrovose, sudarytose iš gamtinio ceolito. Ikrovoje kultivuojant savaiminiu mikroorganizmu asociacijas nustatytos biofiltru valymo efektyvumo priklausomybes nuo i irengini tiekiamo teršalo prigimties, koncentracijos, filtracijos laiko. Geriausiai ikrova filtravo 0,3 m/s greičiu i biofiltra tiekiama acetono garais užteršta ora. Šalinant iš oro acetona, kai pradine teršalo koncentracija 305 mg/m3, biofiltro su drekinimo kamera valymo efektyvumas sieke 98 %. Mažinant i biofiltrus tiekiamu teršalu koncentracijas bei didinant ju filtracijos laika irenginiu valymo efektyvumas dideja. Резюме Для экспериментальных исследований использовались четыре устройства для биологической очистки воздуха – биофильтры разных конструкций. Загрузку биофильтров составляли гранулы естественного цеолита, поролон и древесина, которые использовались для очистки воздуха от летучих органических веществ. В случае применения для очистки воздуха поролона и цеолита в смеси с древесиной применялся биологический и адсорбционный методы. Применение комплексных технологий способствует улучшению эффективности очистки воздуха и продлению срока применения загрузки. Исследования показали, что в процессе биоочистки микроорганизмы могут размножаться и в неорганической загрузке, состоящей из природного цеолита. Культивируя в загрузке ассоциации микроорганизмов, найдены зависимости эффективности биофильтра от характера загрязнителя, его концентрации, времени фильтрации. Лучше всего загрузка фильтровала воздух, загрязненный парами ацетона и подаваемый в установку со скоростью 0,3 м/с. Эффективность очистки воздуха от ацетона при начальной концентрации загрязняющих веществ в 305 мг/м3 для биофильтра с камерой увлажнения составляла 98%. При снижении концентрации загрязняющих веществ, подаваемых в биофильтр, и повышении времени фильтрации загрязненного воздуха эффективность установки увеличивается.

Performance Validation of the First North American Shell-Based Biological Air Treatment System

Performance Validation of the First North American Shell-Based Biological Air Treatment System

Characterization techniques of packing material colonization in gas biofiltration processesThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

Biological air treatment is largely used for the decontamination of large air streams with low pollutant concentrations. As a result of microbial metabolism, the pollutants are degraded into carbon dioxide and water or converted into cell biomass. Three main research domains have emerged within the field of biofiltration: filter bed development, process optimization, and microbiological studies (community, nutrients, …). The objective of this paper is to focus on the microbial activities in air biofiltration processes. The nutrient contribution and the packing material effects are described. Special attention is paid to the description of techniques for the characterization and identification of the microbial population.

Bioscrubbing as a treatment for a complex mixture of volatile organic compounds: influence of the absorption column characteristics on performanceThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

A semi-industrial bioscrubber was developed to treat a complex mixture of volatile organic compounds (VOCs), including oxygenated, aromatic, and chlorinated compounds. Packed and atomizing columns were used for the bioscrubber. For an applied inlet load of around 850–870 g VOCs·m–3 packing material·h–1, the various performances of the bioscrubber were equivalent (around 50%), regardless of the selected absorption column. Only the removal efficiency of oxygenated compounds was found to be reasonable, close to 80%–85%. For the bioscrubber equipped with an atomizing column, a doubling of the inlet load involved a decrease in the removal efficiency of the VOC mixture (35%) and oxygenated compounds (from 80% to 55%). As the transferred compounds were biodegraded, the limits could be explained by the hydrodynamic characteristics of the atomizing column. Furthermore, these results demonstrate the necessity of optimizing the gas–liquid mass transfer step. Two-phase partitioning bioreactors seem to represent an attractive option, even though knowledge of the transfer of compounds and biodegradation mechanisms is required prior to scale-up and industrial use.

Biofiltration of methane using an inorganic filter bed: Influence of inlet load and nitrogen concentrationThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

An upflow lab-scale biofilter was operated with an inorganic filter material to control methane emissions. The influence of the inlet load on methane removal was investigated and the maximum elimination capacity obtained was 36 g/(m3·h) for an inlet load of 95 g/(m3·h). The influence of the nitrogen concentration, which was provided in the form of nitrate through a nutrient solution, was also determined. We established that the optimum nitrogen concentration required for biofilter operation decreases with the methane inlet load. In fact, it was around 0.75 g/L for inlet loads comprised between 55 and 95 g/(m3·h) and of 0.50 g/L when the inlet load was comprised between 20 and 55 g/(m3·h). During this study, a nitrogen concentration of 1.00 g/L inhibited methane removal in the biofilter. In addition, the use of a nitrogen concentration superior to its optimum level can cause, in the long-term run, severe damages to the biofilter performance.

Bioaerosols in industrial environments: a reviewThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

Air quality in workplaces is a main concern for industrial hygienists and occupational health specialists. Aerosolization of microorganisms or their by-products from contaminated material can significantly decrease the air quality and expose the workers’ health to potentially harmful effects. To identify the risks and elaborate safe exposure thresholds, the microbiology of air samples from industrial workplaces must be characterized, which means the airborne microorganisms must be identified and quantified. This review summarizes, for nonbiologist specialists, the principal sampling and analysis techniques for air sample characterization regarding microbiological contamination. A survey of the literature regarding levels of airborne bacteria, fungi, and viruses in agricultural industries, waste management plants, peat and wood processing facilities, and other industries is also provided. This review shows that very complex bioaerosol sources are present in industrial settings, and variable and hardly predictable biodiversity is expected in such environments.

Waste gas treatment in bioreactors: environmental engineering aspectsThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

This paper gives an overview of the most important bioreactor configurations used in waste gas treatment, i.e., conventional and trickling biofilters, the bioscrubber, suspended-growth bioreactors, as well as two-liquid phase systems (stirred tank bioreactor and biotrickling filter). The historical evolution, main characteristics, and recent developments are described in each case.

Mathematical modeling and simulation of hexane degradation in fungal and bacterial biofilters: effective diffusivity and partition aspectsThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

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%.

Treatment of air polluted with methanol vapours in biofilters with and without percolationThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

Air polluted with methanol vapours was treated in a biofilter and a biotrickling filter, both packed with inert materials. The effects of the nitrogen concentration present in the nutrient solution, the empty bed residence time, and the methanol inlet load, on the biofilter and biotrickling filter performance were all examined and compared. The elimination capacity, the biomass and the carbon dioxide production rates all increased with the increase of the parameters tested. The maximum elimination capacity for the biotrickling filter was 240 g·m–3·h–1 with corresponding removal efficiency of 75% and carbon dioxide production rate of 10 g·m–3·h–1, whereas the maximum elimination capacity for the biofilter was 80 g·m–3·h–1 with corresponding removal efficiency of 35% and carbon dioxide production rate of 70 g·m–3·h–1. The biomass production rate was similar for both the biofilter and the biotrickling filter. The carbon dioxide production rate was higher by a factor of 2 to 9 for the biofilter compared to the biotrickling filter.

A review of the environmental pollution originating from the piggery industry and of the available mitigation technologies: towards the simultaneous biofiltration of swine slurry and methaneThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

In Canada, the piggery industry is an essential part of the agricultural sector, but the main waste product of this industry, swine slurry, is particularly harmful to the environment. The anaerobic storage conditions and the excessive use of slurry for agricultural fertilization contribute, respectively, to the emission of greenhouse gases and to aquatic pollution. This paper provides a review of these environmental concerns and of the existing mitigation technologies. Water pollution from swine slurry is associated with the nutrients it contains, such as nitrogen and phosphorous, while the main greenhouse gases produced by the piggery industry are methane and nitrous oxide. Available technologies can valorize the slurry through agricultural fertilization, reduce greenhouse gas emissions, by limiting nutrient availability for example, or treat the effluents using solid–liquid separation, flaring or biological processes. Specific attention is paid to biofiltration due to its potential to simultaneously treat these two types of pollution.

Catalytic removal of propene and toluene in air over noble metal catalystThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

In this paper we present the study of catalytic oxidation of volatile organic compound (VOC) traces in air over Pt/γ-Al2O3 catalysts. The study was carried out using a laboratory fixed-bed catalytic reactor (FBCR) with catalytic oxidation of propene and toluene as model reactions. For better understanding of catalytic activity in a FBCR, the influence of operating parameters such as of platinum (Pt) loading, total gas flow rate, VOC concentration, and oxygen content were studied. The results showed that catalytic activity increases with increase in VOC concentration and a decrease in total gas flow rate. This displayed behaviour is instrumental to working at a low temperature region for complete oxidation of volatile organic compounds.

A model for treating polluted air streams in a continuous two liquid phase stirred tank bioreactor

Biological air treatment systems have been widely under investigation in recent years. Inclusion of non-biodegradable organic solvents to these systems is a way to improve the biotic removal capacity of the systems. In this article the process of absorption and biodegradation of a hydrophobic organic compound in a two liquid phase stirred tank bioreactor has been modeled. Using the model it has been shown that the inclusion of an organic solvent is advantageous if certain conditions are met. Some simulation examples showed that the usefulness of adding an organic solvent to the system depends on kinetic parameters of biological reactions and mass transfer coefficients of pollutants and oxygen between the air and liquid phases. Since different factors influence the process, the usefulness of including an organic solvent to the system should be checked in each special case. The simple model presented in this article can help the prediction of the effect of amending a solvent to the bioreactor under a set of given conditions.

An evaluation of biological air treatment in combination with physical adsorption as polishing

An evaluation of biological air treatment in combination with physical adsorption as polishing

Ecological assessment of waste air treatment systems in the case of biological waste treatment

In this paper, the authors present a technique aimed at increasing the efficiency of biological waste air treatment. The objective is to modify the existing biological waste air treatment systems (i.e. biofilters) to reduce the emitted substances and their potential environmental impacts. The principle of the ionization system is described, along with the first experiences of applying those methods during the rotting process. The investigated system is evaluated by means of life cycle impact assessment, with a focus on odour. It is demonstrated which of the measured substances (i.e. VOC) can potentially contribute to the odorant concentration. Further, it is shown which odour-intensive substances can be reduced by deploying ionization. Finally, the authors respond to the fact that the cleaning efficiency of ionization strongly depends on the humidity of the treated waste gas stream.