Biofiltration of a mixture of volatile organic emissions

Air biofiltration is now under active consideration for the removal of the volatile organic compounds (VOCs) from polluted airstreams. To optimize this emerging environmental technology and to understand compound removal mechanisms, a biofilter packed with peat was developed to treat a complex mixture of VOCs: oxygenated, aromatic, and chlorinated compounds. The removal efficiency of this process was high. The maximum elimination capacity (ECmax) obtained was approximately 120 g VOCs/m3 peat/hr. Referring to each of the mixture's components, the ECmax showed the limits in terms of biodegradability of VOCs, especially for the halogenated compounds and xylene. A stratification of biodegradation was observed in the reactor. The oxygenated compounds were metabolized before the aromatic and halogenated ones. Two assumptions are suggested. There was a competition between bacterial communities. Different communities colonized the peat-based biofilter, one specialized for the elimination of oxygenated compounds, the others more specialized for elimination of aromatic and halogenated compounds. There was also substrate competition. Bacterial communities were the same over the height of the column, but the more easily biodegradable compounds were used first for the microorganism metabolism when they were present in the gaseous effluent.     

Effect of Substrate Henry’s Constant on Biofilter Performance

Abstract

Butanol, ether, toluene, and hexane, which have Henry's constants ranging from 0.0005 to 53, were used to investigate the effects of substrate solubility or availability on the removal of volatile organic compounds (VOCs) in trickle-bed biofilters. Results from this study suggest that, although removal of a VOC generally increases with a decrease in its Henry's constant, an optimal Henry's constant range for biofiltration may exist. For the treatment of VOCs with high Henry's constant values, such as hexane and toluene, the transfer of VOCs between the vapor and liquid phases or between the vapor phase and the biofilm is a rate-determining step. However, oxygen (O₂) transfer may become a rate-limiting step in treating VOCs with low Henry's constants, such as butanol, especially at high organic loadings. The results demonstrated that in a gas-phase aerobic biofilter, nitrate can serve both as a growth-controlling nutrient and as an electron acceptor in a biofilm for the respiration of VOCs with low Henry's constants. Microbial communities within the biofilters were examined using denaturing gradient gel electrophoresis to provide a more complete picture of the effect of O₂ limitation and denitrification on biofilter performance.     

Carbon Disulfide and Hydrogen Sulfide Removal with a Peat Biofilter

ABSTRACT

Simultaneous removal of H₂S and CS₂ was studied with a peat biofilter inoculated with a Thiobacillus strain that oxidizes both compounds in an acidic environment. Both sulfurous gases at concentrations below 600 mg S/m³ were efficiently removed, and the removal efficiencies were similar, 99%, with an empty bed retention time (EBRT) of more than 60 sec. Concentrations greater than 1300-5000 mg S/m³ caused overloading of the filter material, resulting in high H₂SO₄ production, accumulation of elemental sulfur, and reduced removal efficiency. The highest sulfur removal rate achieved was 4500 g-S/day/m³ filter material. These results indicate that peat is suitable as a biofilter material for the removal of a mixture of H₂S and CS₂ when concentrations of gases to be purified are low (less than 600 mg/m³), but it is still odorous and toxic to the environment and humans.     

Control of Organic Emissions from Surface Coating Operations

ABSTRACT

Step tracer tests were carried out on lab-scale biofilters to determine the residence time distributions (RTDs) of gases passing through two types of biofilters: a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow. Results were used to define the flow patterns in the reactors. “Non-ideal flow” indicates that the flow reactors did not behave like either type of ideal reactor: the perfectly stirred reactor [often called a "continuously stirred tank reactor" (CSTR)] or the plug-flow reactor.

The horizontal biofilter with back-mixing was able to accommodate a shorter residence time without the usual requirement of greater biofilter surface area for increased biofiltration efficiency. Experimental results indicated that the first bed of the modified biofilter behaved like two CSTRs in series, while the second bed may be represented by two or three CSTRs in series. Because of the flow baffles used in the horizontal biofilter system, its performance was more similar to completely mixed systems, and hence, it could not be modeled as a plug-flow reactor. For the standard biofilter, the number of CSTRs was found to be between 2 and 9 depending on the airflow rate. In terms of NH₃ removal efficiency and elimination capacity, the standard biofilter was not as good as the modified system; moreover, the second bed of the modified biofilter exhibited greater removal efficiency than the first bed. The elimination rate increased as biofilter load increased. An opposite trend was exhibited with respect to removal efficiency.     

Biofiltration of odorous fume emitted from recycled nylon melting operations

This study aimed to develop a biofilter packed only with fern chips for the removal of odorous compounds from recycled nylon melting operations. The fern chip biofilters could avoid the shortcomings of traditional media, such as compaction, drying, and breakdown, which lead to the performance failure of the biofilters. A pilot-scale biofilter consisting of an acrylic column (14 cm²?×?120 cm height) packed with fern chips to a volume of around 19.6 L was used for the test. Experimental results indicate that oxygen- and nitrogen-containing hydrocarbons as well as paraffins were major volatile organic compounds (VOCs) emitted from thermal smelting of recycled nylon at 250 °C. With operation conditions of medium pH of 5.5–7.0, empty bed retention time (EBRT) of 6–12 sec, influent total hydrocarbon (THC) concentrations of 0.65–2.61 mg m^?3, and volumetric organic loading of 0.05–0.85 g m^?3 hr^?1, the fern-chip-packed biofilter with nutrients of milk, potassium dihydrogen phosphate, and glucose could achieve an overall THC removal efficiency of around 80%. Burnt odor emitted from the smelting of the recycled nylon could be eliminated by the biofilter.

Implications: Biotreatment of contaminants in air streams offers an inexpensive and efficient alternative to conventional technologies. Biofiltration have a great potential for the degradation of gas-borne odorous compounds. THC removal efficiency of around 80% can be achieved. Burnt odor emitted from the smelting of the recycled nylon could be eliminated by the biofilter. This study provides an experimentally verified model for the design and operation of such biotreatment systems.     

Treatment of 1,3-Butadiene in an Air Stream by a Biotrickling Filter and a Biofilter

ABSTRACT

This paper presents results obtained from a performance study on the biotreatment of 1,3-butadiene in an air stream using a reactor that consisted of a two-stage, in-series biotrickling filter connected with a three-stage, in-series biofilter. Slags and pig manure-based media were used as packing materials for the biotrickling filter and the biofilter, respectively. Experimental results indicated that, for the biotrickling filter portion, the butadiene elimination capacities were below 5 g/m³/hr for loadings of less than 25 g/m³/hr, and the butadiene removal efficiency was only around 17%. For the biofilter portion, the elimination capacities ranged from 10 to 107 g/m³/hr for loadings of less than 148 g/m³/hr. The average butadiene removal efficiency was 75–84% for superficial gas velocities of 53–142 m/hr and a loading range of 10–120 g/m³/hr. The elimination capacity approached a maximum of 108 g/m³/hr for a loading of 150 g/m³/hr. The elimination rates of butadiene in both the biotrickling filter and biofilter were mass-transfer controlled for influent butadiene concentrations below about 600 ppm for superficial gas velocities of 29–142 m/hr. The elimination capacity was significantly higher in the biofilter than in the biotrickling filter. This discrepancy may be attributed to the higher mass-transfer coefficient and gas-solid interfacial area offered for transferring the gaseous butadiene in the biofilter.     

Carbonyl Sulfide Removal with Compost and Wood Chip Biofilters,and in the Presence of Hydrogen Sulfide

Abstract

Carbonyl sulfide (COS) is an odor-causing compound and hazardous air pollutant emitted frequently from wastewater treatment facilities and chemical and primary metals industries. This study examined the effectiveness of biofiltration in removing COS. Specific objectives were to compare COS removal efficiency for various biofilter media; to determine whether hydrogen sulfide (H₂S), which is frequently produced along with COS under anaerobic conditions, adversely impacts COS removal; and to determine the maximum elimination capacity of COS for use in biofilter design. Three laboratory-scale polyvinyl chlo-ride biofilter columns were filled with up to 28 in. of biofilter media (aged compost, fresh compost, wood chips, or a compost/wood chip mixture). Inlet COS ranged from 5 to 46 parts per million (ppm) (0.10–9.0 g/m³fihr). Compost and the compost/wood chip mixture produced higher COS removal efficiencies than wood chips alone. The compost and compost/wood chip mixture had a shorter stabilization times compared with wood chips alone. Fresh versus aged compost did not impact COS removal efficiency. The presence of H₂S did not adversely impact COS removal for the concentration ratios tested. The maximum elimination capacity is at least 9 g/m³·hr for COS with compost media.     

Quantitative analysis of volatile organic compounds (VOCs) in atmospheric particles

There are a number of difficulties associated with the quantitative analysis of volatile organic compounds (VOCs) in atmospheric particles. Therefore, majority of the previous studies on VOCs associated with particles have been qualitative. Air samples were collected in Izmir, Turkey to determine ambient particle and gas phase concentrations of several aromatic, oxygenated and halogenated VOCs. Samples were quantitatively analyzed using thermal desorption–gas chromatography/mass spectrometry. Gas-phase concentrations ranged between 0.02 (bromoform) and 4.65 μg m⁻³ (toluene) and were similar to those previously measured at the same site. Particle-phase concentrations ranged from 1 (1,3-dichlorobenzene) to 933 pg m⁻³ (butanol). VOCs were mostly found in gas-phase (99.9±0.25%). However, the particulate VOCs had comparable concentrations to those reported previously for semivolatile organic compounds. The distribution of particle-phase VOCs between fine (d_p<2.5 μm) and coarse (2.5 μm<d_p<10 μm) fractions was also investigated. It was found that VOCs were mostly associated with fine particles.     

Design and Performance Characterization Strategy Using Modeling for Biofiltration Control of Odorous Hydrogen Sulfide

Abstract

Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H₂S). Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures. Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration. Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H₂S emissions below a minimum value, no matter how large the biofilter or how long the residence time. However, a higher biofilter temperature results in lower effluent H₂S concentrations. Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered. This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.     

Sorption and Biodegradation of Vapor-Phase Organic Compounds with Wastewater Sludge and Food Waste Compost

ABSTRACT

To test the possible use of composted food waste and wastewater sludge as biofilters to treat gas-phase volatile organic compounds (VOCs), batch experiments were conducted with an isolated strain that could degrade aromatic compounds under aerobic conditions. A benzene and trichloroethylene (TCE) mixture was used as the gas-phase pollutant in experiments with composted food waste, sludge, and soil. Under aerobic conditions, benzene was degraded as a primary substrate and TCE was degraded cometabolically, with water contents varying from 6 to 60% (volume of water added/volume of solid). Optimal water content for VOC removal was 12% for the soil, 36% for the composted food waste, and 48% for the sludge.

The extent of VOC sorption and biodegradation at the optimal water content was different for each material. With the same initial VOC concentration, more VOCs were removed by sorption onto the composted food waste and the sludge, while less VOCs were biodegraded in comparison with the results using soil. The reason the biodegradation in the soil was greater may be partly attributed to the fact that, due to less sorption, the aqueous-phase concentration of VOCs, which microorganisms could utilize as a carbon source or cometabolize, was higher. We also speculate that the distribution of microorganisms in each medium affects the rate of biodegradation. A large number of microorganisms were attached to the composted food waste and sludge. Mass transfer of VOCs and oxygen to these microorganisms, which appear to have been heterogeneously distributed in clusters, may have been limited, resulting in hindered biodegradation.     

A hybrid biological process of indoor air treatment for toluene removal

Bioprocesses, such as biofiltration, are commonly used to treat industrial effluents containing volatile organic compounds (VOCs) at low concentrations. Nevertheless, the use of biofiltration for indoor air pollution (IAP) treatment requires adjustments depending on specific indoor environments. Therefore, this study focuses on the convenience of a hybrid biological process for IAP treatment. A biofiltration reactor using a green waste compost was combined with an adsorption column filled with activated carbon (AC). This system treated a toluene-micropolluted effluent (concentration between 17 and 52 µg/m³), exhibiting concentration peaks close to 733 µg/m³ for a few hours per day. High removal efficiency was obtained despite changes in toluene inlet load (from 4.2 × 10^?3 to 0.20 g/m³/hr), which proves the hybrid system’s effectiveness. In fact, during unexpected concentration changes, the efficiency of the biofilter is greatly decreased, but the adsorption column maintains the high efficiency of the entire process (removal efficiency [RE] close to 100%). Moreover, the adsorption column after biofiltration is able to deal with the problem of the emission of particles and/or microorganisms from the biofilter.

ImplicationsIndoor air pollution is nowadays recognized as a major environmental and health issue. This original study investigates the performance of a hybrid biological process combining a biofilter and an adsorption column for removal of indoor VOCs, specifically toluene.     

Evaluation of Trickle Bed Air Biofilter Performance as a Function of Inlet VOC Concentration and Loading,and Biomass Control

ABSTRACT

The 1990 Amendments to the Clean Air Act have stimulated strong interest in the use of biofiltration for the economical, engineered control of volatile organic compounds (VOCs) in effluent air streams. Trickle bed air biofilters (TBABs) are especially applicable for treating VOCs at high loadings. For long-term, stable operation of highly loaded TBABs, removal of excess accumulated bio-mass is essential. Our previous research demonstrated that suitable biomass control for TBABs was achievable by periodic backwashing of the biofilter medium. Backwashing was performed by fluidizing the pelletized biological attachment medium with warm water to about a 40% bed expansion. This paper presents an evaluation of the impact of backwashing on the performance of four such TBABs highly loaded with toluene. The inlet VOC concentrations studied were 250 and 500 ppmv toluene, and the loadings were 4.1 and 6.2 kg COD/m³ day (55 and 83 g toluene/m³ hr). Loading is defined as kg of chemical oxygen demand per cubic meter of medium per day. Performance deterioration at the higher loading was apparently due to a reduction of the specific surface of the attached biofilm resulting from the accumulation of excess biomass. For a toluene loading of 4.1 kg COD/m³ day, it was demonstrated that the long-term performance of biofilters with either inlet concentration could be maintained at over 99.9% VOC removal by employing a backwashing strategy consisting of a frequency of every other day and a duration of 1 hr.     

Development and Demonstration of an Explicit Lumped-Parameter Biofilter Model and Design Equation Incorporating Monod Kinetics

Abstract

Biofiltration is an economical air pollution control (APC) technology, particularly suitable for the treatment of air-streams having high flow rates and low concentrations of volatile organic compounds (VOCs). This technology utilizes enzymatic catalysis at ambient conditions to mineralize such pollutants to CO₂, H₂O, and salts. A pilot-scale study conducted for more than 4 years investigated the development of a new biofiltration technology employing trickle bed air biofilters (TBABs). Following the completion of this experimental study, additional data analysis was performed to develop a simple lumped-parameter biofilter model, assuming first-order kinetics. This model related the observed biofilter performance to the principle independent physical, thermodynamic, and biochemical parameters. The initial model has subsequently been expanded to incorporate Monod kinetics. In this paper, the development and use of the final explicit lumped-parameter biofilter model and design equation, incorporating Monod kinetics, are presented. To facilitate the application of this model, practical procedures are also presented for the determination of VOC solubility, VOC biokinetic Monod parameters, and the maximum practical biofilter inlet VOC concentration.     

Effect of substrate Henry's constant on biofilter performance

Butanol, ether, toluene, and hexane, which have Henry's constants ranging from 0.0005 to 53, were used to investigate the effects of substrate solubility or availability on the removal of volatile organic compounds (VOCs) in trickle-bed biofilters. Results from this study suggest that, although removal of a VOC generally increases with a decrease in its Henry's constant, an optimal Henry's constant range for biofiltration may exist. For the treatment of VOCs with high Henry's constant values, such as hexane and toluene, the transfer of VOCs between the vapor and liquid phases or between the vapor phase and the biofilm is a rate-determining step. However, oxygen (O2) transfer may become a rate-limiting step in treating VOCs with low Henry's constants, such as butanol, especially at high organic loadings. The results demonstrated that in a gas-phase aerobic biofilter, nitrate can serve both as a growth-controlling nutrient and as an electron acceptor in a biofilm for the respiration of VOCs with low Henry's constants. Microbial communities within the biofilters were examined using denaturing gradient gel electrophoresis to provide a more complete picture of the effect of O2 limitation and denitrification on biofilter performance.     

Biofiltration Kinetics of a Gaseous Aldehyde Mixture Using a Synthetic Matrix

Abstract

Although aldehydes contribute to ozone and particulate matter formation, there has been little research on the biofiltration of these volatile organic compounds (VOCs), especially as mixtures. Biofiltration degradation kinetics of an aldehyde mixture containing hexanal, 2-methylbutanal (2-MB), and 3-methylbutanal (3-MB) was investigated using a bench-scale, synthetic, media-based biofilter. The adsorption capacity of the synthetic media for a model VOC, 3-methylbutanal, was 10 times that of compost. Periodic residence time distribution analysis (over the course of 1 yr) via a tracer study (84–99% recovery), indicated plug flow without channeling in the synthetic media and lack of compaction in the reactor. Simple first-order and zero-order kinetic models both equally fit the experimental data, yet analysis of the measured rate constants versus fractional conversion suggested an overall first-order model was more appropriate. Kinetic analysis indicated that hexanal had a significantly higher reaction rate (k = 0.09 ± 0.005 1/sec; 23 ± 1.3 ppmv) compared with the branched aldehydes (k = 0.04 ± 0.0036 1/sec; 31 ± 1.6 ppmv for 2-MB and 0.03 ± 0.0051 1/sec; 22 ± 1.3 ppmv for 3-MB). After 3 months of operation, all three compounds reached 100% removal (50 sec residence time, 18–46 ppmv inlet). Media samples withdrawn from the biofilter and observed under scanning electron microscopy analysis indicated microbial growth, suggesting removal of the aldehydes could be attributed to biodegradation.     

An Apparent Effect of the Oil Embargo on Total Suspended Participate Matter and Vanadium in New York City Air

ABSTRACT

Treatment of ethanol vapor in a peat biofilter with various initial water contents (70%, 59%, 49%, and 35%) was studied. For water contents ranging from 49% to 70%, elimination capacity was about 30 g/m³/h. For a water content of 35%, elimination capacity decreased to 4 g/m³/h. A low mean CO₂ yield coefficient (0.35 g CO₂ produced per g ethanol consumed) was found for all of the initial water contents. The value was only 20% of the yield coefficient (1.91 g/g) predicted by stoichiometry. When the packing material was dried from 70% to 59% water content during the biofiltration process, elimination capacity dropped from 27 g/m³/h to 4 g/m³/h. After 24 hours of drying, the biofiltration experiment was restarted and run for two more weeks. During this period, the biofilter did not recover. At 59% water content, the rate of water evaporation was estimated at 59.6 g/m³/h. A simplified mass balance permitted calculation of the biological water production rate, approximately 22.1 g/m³/h.     

Ethylbenzene Removal in a Multiple-Stage Biofilter

ABSTRACT

In practice, biofilters are often conceived as entire, single-unit systems. However, the activity of a biofilter varies greatly over its depth. For a given period, each stage of the biofilter dominates ethylbenzene removal. Ethylbenzene was continuously removed in a mixed-medium biofilter. The overall removal efficiency of the ethylbenzene ranged from 70% to greater than 99%. In the upflow biofilter, the most dominant ethylbenzene degrading stage shifted consecutively from the bottom to the top of the reactor. Average water content throughout the biofilter media was relatively consistent. However, the water content of each stage fluctuated dramatically and was correlated with the ethylbenzene removal rate. Without any water addition, the biofilter was operated for 62 days above the target removal efficiency of 80%. A 9-month slow-release fertilizer, mixed with composting media, was an effective way to eliminate the nutrient deficiency in the biofilter operation.     

Degradation Kinetics of Biofilter Media Treating Reduced Sulfur Odors and VOCs

ABSTRACT

A lab-scale study was conducted to determine the rate and extent of decomposition of three biofilter media materials—compost, hog fuel, and a mixture of the two in 1:1 ratio—used in biofiltration applied to removal of reduced sulfur odorous compounds from pulp mill air emissions. The rate of carbon mineralization, as a measure of biofilter media degradation, was determined by monitoring respiratory CO₂ evolution and measuring the changes in carbon and nitrogen fractions of the biofilter materials over a period of 127 days. Both ambient air and air containing reduced sulfur (RS) compounds were used, and the results were compared. After 127 days of incubation with ambient air, about 17% of the media carbon was evolved as CO₂ from compost as compared to 6 and 12% from hog fuel and the mixture, respectively. The decomposition showed sequential breakdown of carbon moieties, and three distinct stages were observed for each of the biofilter media. First-order rate kinetics were used to describe the decomposition stages. Decomposition rates in the initial stages were at least twice those of the following stages. Carbon mineralization showed close dependence on the C/N ratio of the biofilter material. Media decomposition was enhanced in the presence of RS gases as a result of increased bioactivity by sulfur-oxidizing bacteria and other microorganisms, thus reducing the media half-life by more than 50%. At higher concentrations of RS gases, the CO₂ evolution rates were proportionally lower than those at the low concentrations because of the limited acid buffering capacity of the biofilter materials.     

Exceedances of the National Ambient Air Quality Standard for Ozone Occurring at a “Pristine” Area Site

Abstract

This paper presents a comparative study of the biodegradation of three aromatic volatile compounds in a compost-based biofilter: toluene, xylene, and 1,2,4-trimethyl-benzene, used in the course of this work for the first time in the field of biofiltration. Hence, three identical biofiltration units have been operated at the laboratory scale. During the experiments, nitrogen (as urea) was supplied at various concentrations to each reactor, via irrigated nutrient solutions. A comparative analysis of the results showed that the biodegradability scale followed the degree of substitution around the aromatic ring: toluene > xylene > trimethylbenzene, with 95, 80, and 70% maximum conversions, respectively. In addition, and despite the different removal levels achieved in the three biore-actors, it was established that from a reaction viewpoint, the degradation of the three compounds seemed to follow similar metabolic pathways involving methylcatechol isomers. Finally, by varying the nitrogen input concentrations in the three reactors, three degradation regimes have been highlighted: an N-limitation regime and an N-optimum regime, common to the three solvents, and an N-excess regime, favorable to the colonization of the filter beds by nitrifying species, which particularly affected the xylene and trimethylbenzene biodegradation.     

Wet Scrubber Analysis of Volatile Organic Compound Removal in the Rendering Industry

Abstract

The promulgation of odor control rules, increasing public concerns, and U.S. Environmental Protection Agency (EPA) air regulations in nonattainment zones necessitates the remediation of a wide range of volatile organic compounds (VOCs) generated by the rendering industry. Currently, wet scrubbers with oxidizing chemicals are used to treat VOCs; however, little information is available on scrubber efficiency for many of the VOCs generated within the rendering process. Portable gas chromatography/mass spectrometry (GC/MS) units were used to rapidly identify key VOCs on-site in process streams at two poultry byproduct rendering plants. On-site analysis was found to be important, given the significant reduction in peak areas if samples were held for 24 hr before analysis. Major compounds consistently identified in the emissions from the plant included dimethyl disulfide, methanethiol, octane, hexanal, 2-methylbutanal, and 3-methylbutanal. The two branched aldehydes, 2-methylbutanal and 3-methylbutanal, were by far the most consistent, appearing in every sample and typically the largest fraction of the VOC mixture.

A chlorinated hydrocarbon, methanesulfonyl chloride, was identified in the outlet of a high-intensity wet scrubber, and several VOCs and chlorinated compounds were identified in the scrubbing solution, but not on a consistent basis. Total VOC concentrations in noncondensable gas streams ranged from 4 to 91 ppmv. At the two plants, the odor-causing compound methanethiol ranged from 25 to 33% and 9.6% of the total VOCs (v/v). In one plant, wet scrubber analysis using chlorine dioxide (ClO2) as the oxidizing agent indicated that close to 100% of the methanethiol was removed from the gas phase, but removal efficiencies ranged from 20 to 80% for the aldehydes and hydrocarbons and from 23 to 64% for total VOCs. In the second plant, conversion efficiencies were much lower in a packed-bed wet scrubber, with a measurable removal of only dimethyl sulfide (20–100%).