On-line screening of soil VOCs exchange responses to moisture, temperature and root presence

The exchanges of volatile organic compounds (VOCs) between soils and the atmosphere are poorly known. We investigated VOC exchange rates and how they were influenced by soil moisture, temperature and the presence of plant roots in a Mediterranean forest soil. We measured VOC exchange rates along a soil moisture gradient (5%–12.5%–20%–27.5% v/v) and a temperature gradient (10°C–15°C–25°C–35°C) using PTR-MS. Monoterpenes were identified with GC-MS. Soils were a sink rather than a source of VOCs in both soil moisture and temperature treatments (−2.16 ± 0.35 nmol m⁻² s⁻¹ and −4.90 ± 1.24 nmol m⁻² s⁻¹ respectively). Most compounds observed were oxygenated VOCs like alcohols, aldehydes and ketones and aromatic hydrocarbons. Other volatiles such as acetic acid and ethyl acetate were also observed. All those compounds had very low exchange rates (maximum uptake rates from −0.8 nmol m⁻² s⁻¹ to −0.6 nmol m⁻² s⁻¹ for methanol and acetic acid). Monoterpene exchange ranged only from −0.004 nmol m⁻² s⁻¹ to 0.004 nmol m⁻² s⁻¹ and limonene and α-pinene were the most abundant compounds. Increasing soil moisture resulted in higher soil sink activity possibly due to increases in microbial VOCs uptake activity. No general pattern of response was found in the temperature gradient for total VOCs. Roots decreased the emission of many compounds under increasing soil moisture and under increasing soil temperature. While our results showed that emission of some soil VOCs might be enhanced by the increases in soil temperature and that the uptake of most soil VOCs uptake might be reduced by the decreases of soil water availability, the low exchange rates measured indicated that soil-atmosphere VOC exchange in this system are unlikely to play an important role in atmospheric chemistry. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Biodegradation of BTEX vapors in a silicone membrane bioreactor system

The biotreatment of complex mixtures of volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylene isomers (BTEX) has been investigated by many workers. However, the majority of the work has dealt with the treatment of aqueous or soil phase contamination. The biological treatment of gas and vapor phase sources of VOC wastes has recently received attention with increased usage of biofilters and bioscrubbers. Although these systems are relatively inexpensive, performance problems associated with biomass plugging, gas channeling, and support media acidification have limited their adoption. In this report we describe the development and evaluation of an alternative biotreatment system that allows rapid diffusion of both BTEX and oxygen through a silicone membrane to an active biofilm. The bioreactor system has a rapid liquid recycle, which facilitates nutrient medium mixing over the biofilm and allows for removal of sloughing cell mass. The system removed BTEX at rates up to 30 μg h⁻¹ cm⁻² of membrane area. BTEX removal efficiencies ranged from 75% to 99% depending on the BTEX concentration and vapor flowrate. Consequently, the system can be used for continuous removal and destruction of BTEX and other potential target VOCs in vapor phase streams. Journal of Industrial Microbiology & Biotechnology (2001) 26, 316–325. Received 14 August 2000/ Accepted in revised form 28 February 2001     

Toluene vapour removal in a laboratory-scale biofilter

A bench-scale biofilter with a 0.5-m high filter bed, inoculated with a toluene-degrading strain of Acinetobacter sp. NCIMB 9689, was used to study toluene removal from a synthetic waste air stream. Different sets of continuous tests were conducted at influent toluene concentrations ranging over 0.1–4.0 g m⁻³ and at superficial gas velocities ranging over 17.8–255 m h⁻¹. The maximum volumetric toluene removal rate for the biofilter (242 g m⁻³ h⁻¹) was obtained at a superficial gas velocity of 127.5 m h⁻¹ (corresponding to a residence time of 28 s) and a toluene inlet concentration of 4.0 g m⁻³. Under these operating conditions, toluene removal efficiency was only 0.238, which suggested that effective operation required higher residence times. Removal efficiencies higher than 0.9 were achieved at organic loads less than 113.7 g m⁻³ h⁻¹. A macro-kinetic study, performed using concentration profiles along the bioreactor, revealed this process was limited by diffusion at organic loads less than 100 g m⁻³ h⁻¹ and by biological reaction beyond this threshold. Received: 10 October 1999 / Received revision: 15 February 2000 / Accepted: 18 February 2000     

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     

Performance of a biotrickling filter in the removal of waste gases containing low concentrations of mixed VOCs from a paint and coating plant

The performance of a field-scale biotrickling filter (BTF) in the removal of waste gases containing low concentrations of mixed volatile organic compounds was evaluated. Results showed that acetone and methyl ethyl ketone (MEK) were more easily removed than toluene and styrene. The removal efficiency for acetone and MEK reached over 99% on days 28 and 25 of the operation, whereas those for toluene and styrene were 80 and 63% on day 38. The maximum individual elimination capacities for styrene, toluene, acetone, and MEK were 10.2, 2.7, 4.7, and 8.4 g/m³ h, respectively. These values were achieved at inlet loading rates of 13.9, 3.3, 4.8, and 8.5 g/m³ h, respectively, at an empty bed retention time of 14 s. the removal efficiency for styrene and toluene rapidly increased from 67% and 83% to 86% and over 99%, respectively, when the concentration of ammonia nitrogen (N–NH₄ ⁺) and phosphates (P) in the nutrients increased from 350 to 840 mg/l and 76 to 186 mg/l. When the BTF was restarted after a four-day shutdown, the removal efficiency for toluene was restored to over 99% within a week. However, that for styrene was not restored to its previous level before the shutdown. No noticeable adverse effect on acetone and MEK removal was observed. Denaturing gradient gel electrophoresis results for the bacterial community in the BTF during VOC removal showed that proteobacterial phylum was dominant, and the changes of nutrient concentration and shutdown periods may have played a role in the community structure differences.     

Effect of operational cycle time length on nitrogen removal in an alternating oxidation ditch system

This paper refers to nitrogen removal optimization of an alternating oxidation ditch system through the use of a mathematical model and pilot testing. The pilot system where measurements have been made has a total volume of 120 m³ and consists of two ditches operating in four phases during one cycle and performs carbon oxidation, nitrification, denitrification and settling. The mathematical model consists of one-dimensional mass balance (convection–dispersion) equations based on the IAWPRC ASM 1 model. After the calibration and verification of the model, simulation system performance was made. Optimization is achieved by testing operational cycles and phases with different time lengths. The limits of EU directive 91/271 for nitrogen removal have been used for comparison. The findings show that operational cycles with smaller time lengths can achieve higher nitrogen removals and that an “equilibrium” between phase time percentages in the whole cycle, for a given inflow, must be achieved.     

Immobilization materials mixed with activated sludge as column biofilters for the treatment of gaseous stream containing benzene and toluene

Activated sludge has been utilized for the treatment of volatile organic compounds (VOCs) which are emitted from industrial processes. Nevertheless, activated sludge systems often suffer from the problem caused by concentration gradients as well as pressure drops. Channeling is also a major problem in the treatment process. As the bed height of the packed activated sludge system increases, the pressure drop increases accordingly. To solve these problems, we proposed immobilized activated sludge column reactors for treating VOCs in air. The immobilization material used to mix with activated sludge was properly selected in this work. Elemental compositions of these materials were analyzed. In this study, we also proposed a VOC feed system so that more stable inlet concentrations could be achieved. Hence, the equipment and operating costs were reduced and the problem of VOCs leaking from peristaltic pumps was avoided. The moisture content of the system was well maintained and better VOC removal efficiency was achieved. With an operation condition of progressive VOC inlet concentrations, better removal efficiency of benzene and toluene was then obtained. In conclusion, by the utilization of immobilization materials selected from wastes as well as immobilized activated sludge column reactors, significant removal efficiency for both benzene and toluene was demonstrated.     

Transpiration and whole-tree conductance in ponderosa pine trees of different heights

Changes in leaf physiology with tree age and size could alter forest growth, water yield, and carbon fluxes. We measured tree water flux (Q) for 14 ponderosa pine trees in two size classes (12 m tall and ∼40 years old, and 36 m tall and ∼ 290 years old) to determine if transpiration (E) and whole-tree conductance (g _t) differed between the two sizes of trees. For both size classes, E was approximately equal to Q measured 2 m above the ground: Q was most highly correlated with current, not lagged, water vapor pressure deficit, and night Q was <12% of total daily flux. E for days 165–195 and 240–260 averaged 0.97 mmol m^–2 (leaf area, projected) s^–1 for the 12-m trees and 0.57 mmol m^–2 (leaf area) s^–1 for the 36-m trees. When photosynthetically active radiation (I _P) exceeded the light saturation for photosynthesis in ponderosa pine (900 μmol m^–2 (ground) s^–1), differences in E were more pronounced: 2.4 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 1.2 mmol m^–2 s^–1 for the 36-m trees, yielding g _t of 140 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 72 mmol m^–2 s^–1 for the 36-m trees. Extrapolated to forests with leaf area index =1, the 36-m trees would transpire 117 mm between 1 June and 31 August compared to 170 mm for the 12-m trees, a difference of 15% of average annual precipitation. Lower g _t in the taller trees also likely lowers photosynthesis during the growing season. Received: 19 April 1999 / Accepted: 23 March 2000     

Expression and substrate specificity of the toluene dioxygenase of Pseudomonas putida NCIMB 11767

 Pseudomonas putida NCIMB 11767 oxidized phenol, monochlorophenols, several dichlorophenols and a range of alkylbenzenes (C₁–C₆) via an inducible toluene dioxygenase enzyme system. Biphenyl and naphthalene were also oxidized by this enzyme. Growth on toluene and phenol induced the meta-ring-fission enzyme, catechol 2,3-oxygenase, whereas growth on benzoate, which did not require expression of toluene dioxygenase, induced the ortho-ringcleavage enzyme, catechol 1,2-oxygenase. Monochlorobenzoate isomers and 2,3,5-trichlorophenol were gratuitous inducers of toluene dioxygenase, whereas 3,4-dichlorophenol was a fortuitous oxidation substrate of the enzyme. The organism also grew on 2,4- and 2,5-dichloro isomers of both phenol and benzoate, on 2,3,4-trichlorophenol and on 1-phenylheptane. During growth on toluene in nitrogen-limited chemostat culture, expression of both toluene dioxygenase and catechol 2,3-oxygenase was positively correlated with increase in specific growth rate (0.11–0.74 h^-1), whereas the biomass yield coefficient decreased. At optimal dilution rates, the predicted performance of a 1-m³ bioreactor supplied with 1 g nitrogen l^-1 for removal of toluene was 57 g day^-1 and for removal of trichloroethylene was 3.4 g day^-1. The work highlights the oxidative versatility of this bacterium with respect to substituted hydrocarbons and shows how growth rate influences the production of competent cells for potential use as bioremediation catalysts. Received: 26 June 1995 / Received revision: 4 September 1995 / Accepted: 20 September 1995     

BTEX catabolism interactions in a toluene-acclimatized biofilter

BTEX substrate interactions for a toluene-acclimatized biofilter consortium were investigated. Benzene, ethylbenzene, o-xylene, m-xylene and p-xylene removal efficiencies were determined at a loading rate of 18.07 g m⁻³h⁻¹ and retention times of 0.5–3.0 min. This was also repeated for toluene in a 1:1 (m/m) ratio mixture (toluene: benzene, ethylbenzene, or xylene ) with each of the other compounds individually to obtain a final total loading of 18.07 g m⁻³h⁻¹. The results obtained were modelled using Michaelis–Menten kinetics and an explicit finite difference scheme to generate v _max and K _m parameters. The v _max/K _m ratio (a measure of the catalytic efficiency, or biodegradation capacity, of the reactor) was used to quantify substrate interactions occurring within the biofilter reactor without the need for free-cell suspended and monoculture experimentation. Toluene was found to enhance the catalytic efficiency of the reactor for p-xylene, while catabolism of all the other compounds was inhibited competitively by the presence of toluene. The toluene-acclimatized biofilter was also able to degrade all of the other BTEX compounds, even in the absence of toluene. The catalytic efficiency of the reactor for compounds other than toluene was in the order: ethylbenzene>benzene>o-xylene>m-xylene>p-xylene. The catalytic efficiency for toluene was reduced by the presence of all other tested BTEX compounds, with the greatest inhibitory effect being caused by the presence of benzene, while o-xylene and p-xylene caused the least inhibitory effect. This work illustrated that substrate interactions can be determined directly from biofilter reactor results without the need for free-cell and monoculture experimentation. Received: 13 April 2000 / Received revision: 20 July 2000 / Accepted: 27 July 2000     

Kinetics of biodegradation of gasoline and its hydrocarbon constituents

Aerobic biodegradation of gasoline and its constituents, benzene, toluene and ethylbenzene were studied by an enrichment from soil indigenous microbial population. The enrichment culture completely degraded 16.1–660 mg/l gasoline in 2.5–16 days respectively, without accumulation of any by-products. The kinetics of gasoline as well as benzene, toluene and ethylbenzene biodegradation was investigated with initial gasoline concentrations of 16.1–62.6 mg/l. The maximum specific rates of biodegradation of benzene, toluene and ethylbenzene were 0.12, 0.38 and 0.19 mg mg biomass⁻¹ day⁻¹ respectively. When benzene and toluene were used as sole substrate, the maximum specific rates of their biodegradation were 62.9 and 16.4 times greater than the corresponding values for a mixture (gasoline). The microbial culture was able to mineralize up to 200 mg/l pure toluene and benzene. Maximum mineralization efficiencies of benzene and toluene were 76.7 ± 5.1% and 76.8 ± 1.3% respectively. Self-inhibition and competitive inhibition patterns were observed during the biodegradation of benzene and toluene alone and in the mixture respectively. The observed kinetics was modeled according to Andrews' inhibition model. Received: 6 August 1997 / Received revision: 18 November 1997 / Accepted: 29 November 1997     

A novel method for characterisation of microbial growth kinetics on volatile organic compounds

A novel method for the determination of microbial growth kinetics on hydrophobic volatile organic compounds (VOC) has been developed. A stirred tank reactor was operated as a fed-batch system to which the VOC was continuously fed via the gas phase, assuring a constant VOC concentration in the mineral medium. A flow of air was saturated with the VOC, and then mixed with a further flow of air, to obtain a predetermined VOC concentration. Thus, different VOC concentrations in the mineral medium could be obtained by altering the VOC concentration in the feed gas. The growth kinetics of Xanthobacter autotrophicus GJ10 on 1,2-dichloroethane (DCE) and of Pseudomonas sp. strain JS150 on MonoChloroBenzene (MCB) were assessed using this method. The growth of strain JS150 was strongly inhibited at MCB concentrations higher than 160 mg l⁻¹, and the results were fitted using a piecewise function. The growth kinetics of strain GJ10 were described by the Luong model where maximum growth rate μ_max = 0.12 h⁻¹, substrate saturation constant K _S = 7.8 mg l⁻¹, and maximum substrate concentration S _m (above which growth is completely inhibited) = 1080 mg l⁻¹. Varying nitrogen and oxygen flows enabled the effect of oxygen concentration on the growth kinetics of Pseudomonas JS150 to be determined. Received: 30 November 1998 / Received revision: 19 March 1999 / Accepted: 20 March 1999     

Biofiltration of toluene-contaminated air using an agro by-product-based filter bed

An innovative, coir-pith-based, filter bed for degrading vapor phase toluene in a gas biofilter over 160 days without any external nutrient supply is reported in this study. Indigenous microflora present in the coir pith as well as in the aerobic sludge added at the start-up stage metabolized the toluene, and correspondingly, CO₂ was produced in the biofilter. Inlet toluene concentration in the range of 0.75 to 2.63 g/m³ was supplied to the biofilter in short acclimation periods. The maximum elimination capacity achieved was 96.75 g/m³·h at 120.72 g/m³·h loading where around 60% was recovered as CO₂. The filter bed maintained a stable low-pressure drop (0–4 mm H₂O), neutral pH range (6.5–7.5), and moisture content of 60–80% (w/w) throughout the period. In addition to toluene-degrading microbial community, a grazing fauna including rotifer, bacteriovoric nematode, tardigrade, and fly larvae were also present in the filter bed. The overall performance of the biofilter bed in pollutant removal and sustainability was analyzed in this study.     

Methanol and other VOC fluxes from a Danish beech forest during late springtime

In-canopy mixing ratio gradients and above-canopy fluxes of several volatile organic compounds (VOCs) were measured using a commercial proton transfer reaction mass spectrometer (PTR-MS) in a European beech (Fagus sylvatica) forest in Denmark. Fluxes of methanol were bidirectional: Emission occurred during both day and night with highest fluxes (0.2 mg C m⁻² h⁻¹) during a warm period; deposition occurred dominantly at daytime. Confirming previous branch-level measurements on beech, the forest’s monoterpene emissions (0–0.5 mg C m⁻² h⁻¹), and in-canopy mixing ratios showed a diurnal cycle consistent with light-dependent emissions; a result contrasting temperature-only driven emissions of most conifer species. Also emitted was acetone, but only at ambient temperatures exceeding 20°C. Slow deposition dominated at lower temperatures. Our in-canopy gradient measurements contrast with earlier results from tropical and pine forest ecosystems in that they did not show this beech ecosystem to be a strong sink for oxygenated VOCs (OVOCs). Instead, their gradients were flat and only small deposition velocities (<0.2 cm s⁻¹) were observed to the onsite soil. However, as methanol soil uptake was consistent and possibly related to soil moisture, more measurements are needed to evaluate its soil sink strength. In turn, as canopy scale fluxes are net fluxes with stomatal emissions from photosynthesizing leaves potentially affecting non-stomatal oxygenated VOC uptake, only independent, controlled laboratory experiments may be successful in separating gross fluxes.     

Impacts of Urbanization on Ecosystem Goods and Services in the U.S. Corn Belt

In this study, three cities located in the U.S. Corn Belt are evaluated for impacts of past (1992–2001) and projected (2001–2030) urban expansion on ecosystem goods and services, with a specific focus on changes in energy balance, hydrology, and productivity. Scenarios for high-, medium- and low-density urban areas are simulated using a dynamic agro-ecosystem model (Agro-IBIS), by incorporating new parameterizations for impervious surfaces and turf grass. Moderate Resolution Imaging Spectroradiometer (MODIS) 500-m albedo data and remote sensing-derived 30-m resolution maps from the U.S. National Land Cover Database are used as model input to simulate biogeochemical, thermodynamic, and hydrological cycles for a range of land-cover types in each region. The results show that the expanding urban areas have a significant impact on each city’s capacity to regulate climate and flooding. High-density urban areas, for instance, have soil surface temperatures up to 6°C higher than soils within natural and managed ecosystems. Expansion of turf grass in residential areas could require an additional 8–105 million m³ of water use annually, which increases runoff by 15–48% and reduces the capacity to respond/adapt to flooding. Finally, the analysis shows that net primary productivity (NPP) decreases as expected due to the removal of cropland, forests, and grasslands in favor of development, but increased urban turf grass provides an annual offset of 40–210 g C m⁻². Urban expansion through 2030 is estimated to lower total annual crop production by 8.1, 8.6, and 16.7% for the Madison, Peoria, and Indianapolis regions, respectively. Given current projections for city growth to exceed 2–3% per year in the north-central U.S., urban expansion across a nine-state region in the Corn Belt could potentially take an additional 210,000–310,000 ha of farmland out of production annually at a time when demand for food, fuel, and fiber is increasing. Because conversion of cropland to urban uses is nearly always unidirectional, any changes to ecosystem goods and services due to urbanization are likely to be permanent and irreversible.     

Performance and Microbial Diversity of a Trickle‐Bed Air Biofilter under Interchanging Contaminants

A trickle‐bed air biofilter (TBAB) was evaluated under conditions of interchanging the feed volatile organic compounds (VOCs) in the sequence methyl ethyl ketone (MEK), toluene, methyl isobutyl ketone (MIBK), styrene, and then back to MEK. The obtained performance results revealed that the biofilter provided high removal efficiency within the critical loading of each VOC, which was previously defined in the non‐interchanging VOC fed biofilter. The biofilter easily acclimated to the oxygenated compounds (MEK and MIBK), but re‐acclimation was delayed for the aromatic compounds (toluene and styrene). Ratios of the molar mass of CO₂ produced per molar mass of VOC removed were investigated. It has been found that the ratios for the aromatic compounds closely resembled the theoretical complete chemical oxidation based ratios while larger differences were encountered with the oxygenated compounds. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes was used to assess the impact of interchanging VOCs on the bacterial community structure in the biofilter. The results from denaturing gradient gel electrophoresis (DGGE) showed that the structure of the microbial community in the biofilter was different after each interchange of VOCs.     

Influence of gaseous VOC concentration on the diversity and biodegradation performance of microbial communities

In this work, the influence of toluene gas concentration on the isolation of toluene degrading microbial communities from activated sludge was studied. Toluene biodegradation at gas phase concentration of 10?g?m^?3 (R1) resulted in process instability with removal efficiencies (RE) lesser than 33?%, while operation at toluene gas phase concentrations of 300?mg?m^?3 (R2) and 11?mg?m^?3 (R3) was stable with RE ranging from 74 to 94?%. The consortium isolated in R1 exhibited the highest tolerance toward toluene but the lowest biodegradation performance at trace level VOC concentrations. Despite R2 and R3 showed a similar sensitivity toward toluene toxicity, the microbial community from R2 supported the most efficient toluene biodegradation at trace level VOC concentrations. The Shannon-Wiener index showed an initial biodiversity decrease from 3.2 to 2.0, 1.9 and 2.7 in R1, R2 and R3, respectively. However, while R2 and R3 were able to recover their initial diversity levels by day 48, this loss in diversity was permanent in R1. These results showed that traditional inoculum isolation/acclimation techniques based on the exposure of the inoculum to high VOC concentrations, where toxicity tolerance plays a key role, may result in a poor abatement performance when the off-gas stream is diluted.     

Occurrence of the benthic trachymedusa Ptychogastria polaris Allman, 1878 (Cnidaria: Hydrozoa) off Northeast Greenland and in the northern Barents Sea

The trachymedusa Ptychogastria polaris Allman, 1878 has been identified in seabed photographs from high-Arctic shelves and upper continental slopes off Northeast Greenland and in the northern Barents Sea. It was found to be a common epifaunal element, being present at 34 of 57 stations in 40- to 495-m depth and at 7 of 11 stations in 70- to 330-m depth, respectively. All specimens recorded in the photographs either sat directly at, or hovered very closely (≤ about 1 cm) over, the sea bed, indicating a primarily epibenthic life style of this hydrozoan species. The small-scale (i.e. within-station) distribution of medusae was rather patchy, with frequencies along photographic transects – consisting of 35–73 pictures distributed over seabed strips of 150- to 300-m length – varying from 1 to 58% off Northeast Greenland and from 1 to 34% in the Barents Sea. Absolute maximum density was 6 ind m⁻², and station mean abundances ranged from 0.01 to 0.91 ind m⁻² and from 0.01 to 0.52 ind m⁻², respectively. Values tended to decrease with water depth, albeit significantly only off Northeast Greenland. Otherwise, no clear relationships to environmental conditions, such as geomorphology or near-bottom water hydrography, were detected. Circumstantial evidence suggests that seabed granulometry and potential food supply are important distribution determinants. However, further investigations are required to identify more stringently the key factors controlling the distribution of P. polaris. Received: 8 September 1997 / Accepted: 12 September 1997     

Microbial treatment of a styrene-contaminated air stream in a biofilter with high elimination capacities

A styrene-utilizing mixed microbial culture was isolated and utilized in a biofilter for the biological treatment of a contaminated air stream. Biofilter media consisted of composted wood bark and yard waste. The biofilters were acclimated at 120 s residence time and further evaluated at 60 and 30 s gas residence times. The biofilters received organic loading rates of up to 350 g/m³ h. The styrene volumetric removal rate was a function of the organic loading rate and increased with increasing loading rates. Average volumetric removal rates of 69–118 g/m³ h observed in our studies were higher than reported values for styrene biofilters. Average styrene removal efficiencies ranged from 65% to 75% (maximum 100%). Axial analysis of styrene concentration along the column indicated that the bulk of the styrene removal occurred in the first section of the biofilter. Analyses of the media indicated that the moisture content of the first section (50–55% w/w) was significantly lower than in the second and third sections (65–70% w/w). The pressure drops across the biofilter were low due to the high concentration of large media particles. The total pressure drops were 1–3, 4–6, and 10–16 mm for the 120-, 60-, and 30-s residence time periods, respectively. Journal of Industrial Microbiology & Biotechnology (2001) 26, 196–202. Received 04 March 2000/ Accepted in revised form 25 January 2001     

Mathematical modeling of Fe(II), Cu(II), Ni(II) and Zn(II) removal in a horizontal rotating tubular bioreactor

Industrial wastewaters polluted with toxic heavy metals are serious ecological and environmental problem. Therefore, in this study multi-heavy metals (Fe²⁺, Cu²⁺, Ni²⁺ and Zn²⁺) removal process with mixed microbial culture was examined in the horizontal rotating tubular bioreactor (HRTB) by different combinations of process parameters. Hydrodynamic conditions and biomass sorption capacity have main impact on the removal efficiency of heavy metals: Fe²⁺ 95.5–79.0%, Ni²⁺ 92.7–54.8%, Cu²⁺ 87.7–54.9% and Zn²⁺ 81.8–38.1%, respectively. On the basis of experimental results, integral mathematical model of removal heavy metals in the HRTB was established. It combines hydrodynamics (mixing), mass transfer and kinetics to define bioprocess conduction in the HRTB. Mixing in the HRTB was described by structured cascade model and metal ion removal by two combined diffusion–adsorption models, respectively. For Langmuir model, average variances between experimental and simulated concentrations of metal ions were in the range of 1.22–10.99 × 10⁻³ and for the Freundlich model 0.12–3.98 × 10⁻³, respectively. On the basis of previous facts, it is clear that developed integral bioprocess model with Freundlich model is more efficient in the prediction of concentration of metal ions in the HRTB. Furthermore, the results obtained also pointed out that the established model is at the same time accurate and robust and therefore it has great potential for use in the scale-up procedure.