Performance evaluation of a water/silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove volatile organic compounds from gaseous effluents

BACKGROUND: In the framework of biological processes used for waste gas treatment, the impact of the inoculum size on the start‐up performance needs to be better evaluated. Moreover, only a few studies have investigated the behaviour of elimination capacity and biomass viability in a two‐phase partitioning bioreactor (TPPB) used for waste gas treatment. Lastly, the impact of ethanol as a co‐substrate remains misunderstood. RESULTS: Firstly, no benefit of inoculation with a high cellular density (>1.5 g L^?1) was observed in terms of start‐up performance. Secondly, the TPPB was monitored for 38 days to characterise its behaviour under several operational conditions. The removal efficiency remained above 63% for an inlet concentration of 7 g isopropylbenzene (IPB) m^?3 and at some time points reached 92% during an intermittent loading phase (10 h day^?1), corresponding to a mean elimination capacity of 4 × 10^?3 g L^?1 min^?1 (240 g m^?3 h^?1) for a mean IPB inlet load of 6.19 × 10^?3 g L^?1 min^?1 (390 g m^?3 h^?1). Under continuous IPB loading, the performance of the TPPB declined, but the period of biomass acclimatisation to this operational condition was shorter than 5 days. The biomass grew to approximately 10 g L^?1 but the cellular viability changed greatly during the experiment, suggesting an endorespiration phenomenon in the bioreactor. It was also shown that simultaneous degradation of IPB and ethanol occurred, suggesting that ethanol improves the biodegradation process without causing oxygen depletion. CONCLUSION: A water/silicone oil TPPB with ethanol as co‐substrate allowed the removal of a high inlet load of IPB during an experiment lasting 38 days. Copyright © 2008 Society of Chemical Industry     

Biofiltration of toluene in the absence and the presence of ethyl acetate under continuous and intermittent loading

BACKGROUND: Two peat biofilters were used for the removal of toluene from air for one year. One biofilter was fed with pure toluene and the other received 1:1 (by weight) ethyl acetate:toluene mixture. RESULTS: The biofilters were operated under continuous loading: the toluene inlet load (IL) at which 80% removal occurred was 116 g m^?3 h^?1 at 57 s gas residence time. Maximum elimination capacity of 360 g m^?3 h^?1 was obtained at an IL of 745 g m^?3 h^?1. The elimination of toluene was inhibited by the presence of ethyl acetate. Intermittent loading, with pollutants supplied for 16 h/day, 5 days/week, did not significantly affect the removal efficiency (RE). Biomass was fully activated in 2 h after night closures, but 6 h were required to recover RE after weekend closures. Live cell density remained relatively constant over the operational period, while the dead cell fraction increased. Finally, a 15 day starvation period was applied and operation then re‐started. Performance was restored with similar re‐acclimatization period to that after weekend closures, and a reduction in dead cell fraction was observed. CONCLUSION: This study demonstrates the capacity of the system to handle intermittent loading conditions that are common in industrial practices, including long‐term starvation. Copyright © 2008 Society of Chemical Industry     

Oxidation of ethanol vapors in a spiral bioreactor

A fixed film spiral bioreactor containing immobilized activated sludge microorganisms has been used to degrade ethanol vapors. The effect of air flow rate, and ethanol feed concentration on elimination capacity has been investigated. Air flow rate is varied in the range from 2?34 to 40?0 dm³ min^?1. Ethanol feed concentration is varied in the range from 600 to 7000 ppmv. In the concentration range studied, the elimination capacity increased proportionately with an increase in feed concentration. However, the elimination capacity decreased significantly at flow rates greater than 20 dm³ min^?1 owing to insulfficient residence time. The maximum elimination capacity observed was 185 g ethanol h^?1 m^?3 of reactor volume. Critical ethanol loading, defined as the maximum loading to achieve greater than 99% elimination at various residence times have been determined. These data are extremely useful in designing bioreactor for large scale applications.     

Removal of monochlorobenzene from air in a trickling biofilter at high loading rates

BACKGROUND: In this study, the biofiltration of air streams laden with monochlorobenzene (MCB) vapours was investigated using a trickling biofilter operated co‐currently. The device was filled with ceramic material and inoculated with an acclimated microbial culture. A neutralization process was carried out in a separate unit using crushed oyster shells. Long‐term biofilter performance was evaluated over a 10‐month period of continuous experiments under different influent pollutant concentrations from 0.10 to 1.75 g m^?3, sequentially stepped up through three different apparent air residence times of 60, 30, and 15 s. RESULTS: Pollutant removal was shown to be complete at influent concentrations up to 1.25, 0.75 and 0.20 g m^?3, and apparent air residence times of 60, 30, and 15 s, respectively. The maximum elimination capacity was found to be 95.0 g m_PM^?3 h^?1 for an influent concentration of 1.0 g m^?3 and an apparent air residence time of 30 s, corresponding to a loading rate of 120.0 g m_PM^?3 h^?1. Monochlorobenzene and biomass concentration profiles along the biofilter evidenced the dependence of microbial concentration distribution on the pollutant loading rate and the existence of a linear relationship between biomass concentration and specific pollutant removal rate, regardless of the operating conditions applied. A macrokinetic analysis shows that the MCB removal rate is zeroth order for low values of MCB concentration. A critical value of MCB concentration exists at all superficial air velocity at which the biomass growth is inhibited. A simple kinetic model is developed which is able to describe the inhibition behaviour under any operating conditions. CONCLUSION: The experimental results indicated that the system was effective and stable under various working conditions and over a long operating period, provided that the loading conditions corresponding to substrate inhibition of microbial growth are not exceeded. Copyright © 2012 Society of Chemical Industry     

Effect of pre‐treatments based on UV photocatalysis and photo‐oxidation on toluene biofiltration performance

BACKGROUND: The integration of UV photocatalysis and biofiltration seems to be a promising combination of technologies for the removal of hydrophobic and poorly biodegradable air pollutants. The influence of pre‐treatments based on UV_{254 nm} photocatalysis and photo‐oxidation on the biofiltration of toluene as a target compound was evaluated in a controlled long‐term experimental study using different system configurations: a standalone biofilter, a combined UV photocatalytic reactor‐biofilter, and a combined UV photo‐oxidation reactor (without catalyst)‐biofilter. RESULTS: Under the operational conditions used (residence time of 2.7 s and toluene concentrations 600–1200 mg C m^?3), relatively low removal efficiencies (6–3%) were reached in the photocatalytic reactor and no degradation of toluene was found when the photo‐oxidation reactor was operated without catalyst. A noticeable improvement in the performance of the biofilter combined with a photocatalytic reactor was observed, and the elimination capacity of the biological process increased by more than 12 g C h^?1 m^?3 at the inlet loads studied of 50–100 g C h^?1 m^?3. No positive effect on toluene removal was observed for the combination of UV photoreactor and biofilter. CONCLUSIONS: Biofilter pre‐treatment based on UV_{254 nm} photocatalysis showed promising results for the removal of hydrophobic and recalcitrant air pollutants, providing synergistic improvement in the removal of toluene. Copyright © 2011 Society of Chemical Industry     

An attempt to compare the performance of bioscrubbers and biotrickling filters for degradation of ethyl acetate in gas streams

This study presents a comparison of the efficiency of a bioscrubber and a biotrickling filter (BTF) for the removal of ethyl acetate (EA) vapour from a waste gas stream, under the same operating conditions. The maximum EA elimination capacity achieved in the bioscrubber was 550 g m^?3 h^?1 with removal efficiency higher than 96%. For higher EA loadings the bioscrubber was oxygen limited, which caused incomplete EA biodegradation. When pure oxygen was fed to the bioscrubber at a rate of 0.02 L min^?1, the bioscrubber recovered and could treat higher EA loadings without any oxygen limitation. The BTF achieved EA elimination capacity of 600 g m^?3 h^?1 with removal efficiency higher than 97% and the dissolved oxygen concentration remained substantially higher than in the bioscrubber. However, severe channelling and blockage of the spray nozzle occurred due to the excessive biomass growth. Overall, the bioscrubber system was easier to operate and control than the BTF, while an enhancement of the oxygen mass transfer in the bioscrubber could potentially increase its performance by up to three times. Copyright © 2005 Society of Chemical Industry     

Influence of nitrogen on the degradation of toluene in a compost‐based biofilter

Two identical laboratory‐scale bioreactors were operated simultaneously, each treating an input air flow rate of 1 m³ h^?1. The biofilters consisted of multi‐stage columns, each stage packed with a compost‐based filtering material, which was not previously inoculated. The toluene inlet concentration was fixed at 1.5 g m^?3 of air. Apart from the necessary carbon, the elements nitrogen, phosphorus, sulfur, potassium and other micro‐elements are also essential for microbial metabolism. These were distributed throughout the filter bed material by periodic ‘irrigations’ with various test nutrient solutions. The performance of each biofilter was quantified by determining its toluene removal efficiency, and elimination capacity. Nutrient solution nitrogen levels were varied from 0 to 6.0 g dm^?3, which led to elimination capacities of up to 50 g m^?3 h^?1 being obtained for a toluene inlet load of 80 g m^?3 h^?1. A theoretical analysis also confirmed that the optimum nitrogen solution concentration lays in the range 4.0–6.0 g dm^?3. Validation of the irrigation mode was achieved by watering each biofilter stage individually. Vertical stage‐by‐stage stratification of the biofilter performance was not detected, ie each filter bed section removed the same amount of pollutant, the elimination capacity per stage being about 16 g m^?3 h^?1 per section of column. © 2001 Society of Chemical Industry     

A Study of the Biofiltration of High‐Loads of Toluene in Air: Carbon and Water Balances,Temperature Changes and Nitrogen Effect

Biodegradable atmospheric pollutants, released at low to moderate concentrations, can be removed by biofiltration. In this work, a laboratory‐scale compost‐based biofilter has been evaluated for the removal of high levels of toluene in air (～ 4.0 g.m^?3). By applying a variable nitrogen input in the irrigation solution, it was shown that the biodegradation extent can be controlled through the nutrient supply. The maximum elimination capacity achieved was 135 g.m^?3.h^?1, for a N‐concentration of 3.0 g of N.L^?1. A quantitative analysis of the bioreaction aspects (stoichiometry, temperature) led to the determination of the water flow rates associated with the toluene oxidation. Thus, it was estimated that some 530 to 800 g of water.day^?1 were lost at the bioreactor outlet, but were balanced by the irrigation system.     

Biotrickling filtration of air contaminated with ethanol

A biotrickling filter (BTF) for treating high ethanol loads was operated for one year and the effect of operating conditions was studied. The BTF was operated in a range of ethanol inlet concentrations of 0.2–15.0 g m^?3 and at three different residence times (30, 65 and 130 s). The experiments show that removal efficiency decreased with increasing ethanol inlet concentration and decreasing air residence time. Removal efficiency varied in the range of 60–100%. A maximum elimination capacity of 970 g m^?3 h^?1 was obtained for an inlet load of 1610 g m^?3 h^?1. At a constant residence time, the carbon dioxide (CO₂) production rate varied with ethanol inlet concentration. BTF presented the maximum CO₂ production rate in the range of inlet concentration of 3.0–7.0 g m^?3. Two strategies for controlling biomass accumulation were applied: one consisted in periodical washing; the other combined periodical washing with nutrient starvation by consuming less water and energy. Both strategies led to maintaining the BTF stable, with high adaptability and reproducibility. Copyright © 2007 Society of Chemical Industry     

Comparison of biological reactors (biofilter,biotrickling filter and modified RBC) for treating dichloromethane vapors

BACKGROUND: Bioreactors used for waste gas and odor treatment have gained acceptance in recent years to treat volatile organic compounds (VOCs). Different types of bioreactors (biofilter, biotrickling filter and rotating biological reactor) have been used for waste gas treatment. Most studies reported in the literature have used one of these systems to treat several types of inorganic and organic gases either individually or in mixtures. Each of these reactors has some advantages and some limitations. Though biodegradation is the main process for the removal of pollutants, the mechanisms of removal and the microbial communities may differ among these bioreactors. Consequently their performance or removal efficiency may also be different. RESULTS: At low loading rate (<35 g m^?3 h^?1), all three bioreactors showed comparable removal efficiencies and elimination capacity, but at higher loading rates, rotating biological contactors (RBC) showed a better performance with higher removal efficiency (40–50%) than both the biofilter and biotrickling filter (20–40%). The biofilter showed a sharp drop in removal efficiency and elimination capacity at high loading rates. CONCLUSIONS: The modified RBC had no clogging problems and no increase in pressure drop when compared with the other bioreactors. It can thus handle pollutant load for a longer period of time. This is the first study attempting to compare the performance of three different bioreactors for removal of the same VOC under different conditions. Copyright © 2010 Society of Chemical Industry     

Removal of toluene from air streams using a gas–liquid–solid three‐phase airlift loop bioreactor containing immobilized cells

Toluene, a kind of volatile organic compound (VOC), is widely used as a solvent (paints and coatings, gums, resins, rubber) as well as a reagent (medicines, dyes, perfumes) and is one of the components of gasoline. Over the more recent decades, many studies have led to the development of biological methods to treat toluene. This paper presents the results of a study on the treatment of airborne toluene using a laboratory‐scale gas–liquid–solid three‐phase airlift loop bioreactor containing immobilized cells. Based on the optimum operating conditions such as the temperature of 28–30 °C, pH of 7.0–7.2, and an empty bed residence time (EBRT) of 39.6 s, a continuous bioprocess showed that this immobilized airlift loop bioreactor had a steady‐state performance within 15 days, the outlet concentrations of toluene were lower than the national emission standard in China (GB 16297‐1996), and the chemical oxygen demand and NH₄⁺‐N of the effluent also satisfied the primary discharge standard in China (GB 8978‐1996). In addition, this immobilized airlift loop bioreactor had a good ability to tolerate shock loads, while the maximum elimination capacity of toluene was 168 g m^?3 h^?1 which was higher than those not only in biofilters and biotrickling filters but also in the airlift bioreactor with free microorganisms. Copyright © 2005 Society of Chemical Industry     

Bio‐oxidation of ferrous ions by Acidithioobacillus ferrooxidans in a monolithic bioreactor

BACKGROUND: The bio‐oxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron and the removal of H₂S in combustible gases. Bio‐oxidation of ferrous iron may be an alternative method of producing ferric sulfate, which is a reagent used for removal of H₂S from biogas, tail gas and in the pulp and paper industry. For practical use of this process, this study evaluated the optimal pH and initial ferric concentration. pH control looks like a key factor as it acts both on growth rate and on solubility of materials in the system. RESULTS: Process variables such as pH and amount of initial ferrous ions on oxidation by A. ferrooxidans and the effects of process variables dilution rate, initial concentrations of ferrous on oxidation of ferrous sulfate in the packed bed bioreactor were investigated. The optimum range of pH for the maximum growth of cells and effective bio‐oxidation of ferrous sulfate varied from 1.4 to 1.8. The maximum bio‐oxidation rate achieved was 0.3 g L^?1 h^?1 in a culture initially containing 19.5 g L^?1 Fe²⁺ in the batch system. A maximum Fe²⁺ oxidation rate of 6.7 g L^?1 h^?1 was achieved at the dilution rate of 2 h^?1, while no obvious precipitate was detected in the bioreactor. All experiments were carried out in shake flasks at 30 °C. CONCLUSION: The monolithic particles investigated in this study were found to be very suitable material for A. ferrooxidans immobilization for ferrous oxidation mainly because of its advantages over other commonly used substrates. In the monolithic bioreactor, the bio‐oxidation rate was 6.7 g L^?1 h^?1 and 7 g L^?1 h^?1 for 3.5 g L^?1 and 6 g L^?1 of initial ferrous concentration, respectively. For higher initial concentrations 16 g L^?1 and 21.3 g L^?1, bio‐oxidation rate were 0.9 g L^?1 h^?1 and 0.55 g L^?1 h^?1, respectively. Copyright © 2008 Society of Chemical Industry     

Elimination of chlorobenzene vapors from air in a compost‐based biofilter

In this work, the removal of monochlorobenzene (CB) vapors from air was studied, for the first time, in a non‐inoculated, laboratory‐scale, aerobic biofilter. The influence of three parameters on the bioprocess has been evaluated: the rate of nitrogen supplied to the bed, the inlet concentration of CB, and the flow rate. The CB inlet concentration was varied between 0.3 and 3.2 g m^?3, at a constant flow rate of 1.0 m³ h^?1. Removal rates of greater than 90% were achieved for CB inlet concentrations of up to 1.2 g m^?3. Then the flow rate was varied from 0.5 to 3.0 m³ h^?1 with a constant inlet concentration (1.2 g m^?3). Maximum elimination capacities (70 g m^?3 h^?1) were reached for contact times of greater than 60 s. The study of varying flow rates also permitted evaluation of a first order macrokinetic constant (1.1 × 10^?2 s^?1) for the CB biodegradation. Finally, the optimum nitrogen input value was found to lie between 0.3 and 0.4 g N h^?1 and gave rise to elimination capacities as high as 70 g m^?3 h^?1 for an inlet load of near 80 g m^?3 h^?1. Copyright © 2003 Society of Chemical Industry     

Thermophilic biotrickling filtration of a mixture of isobutyraldehyde and 2‐pentanone

In this study, the possibility of the removal of isobutyraldehyde and 2‐pentanone was investigated in biotrickling filters (BTFs) at higher temperature (52–65 °C). First, the biodegradation of isobutyraldehyde and 2‐pentanone in activated sludge was proven by batch experiments at 52 and 62 °C. In batch experiments isobutyraldehyde was also degraded up to a temperature of 72 °C. Thereafter two bioreactors were operated in parallel, one at ambient temperature (BTF25), and one at 52 °C (BTF52). Maximum elimination capacities of 97 and 139 g m^?3 h^?1 were observed in BTF25 and BTF52, respectively, for isobutyraldehyde. Maximum elimination capacities of 53 and 63 g m^?3 h^?1 were obtained for 2‐pentanone in BTF25 and BTF52, respectively. A significant difference was observed in the operational stability of the two reactors. In the reactor at ambient temperature, operational problems such as foam formation, higher biomass accumulation and organic acid production were observed. In the thermophilic reactor these problems did not occur or were less severe. Copyright © 2007 Society of Chemical Industry     

A trickling fibrous-bed bioreactor for biofiltration of benzene in air

A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C_gi) was 0·37 g m⁻³, the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1·8 m³ m⁻² h⁻¹. In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was ∽11·5 g m⁻³ h⁻¹ when the inlet benzene concentration was 1·7 g m⁻³ and the superficial air flow rate was 3·62 m³ m⁻² h⁻¹. A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K_l in this model was found to be linearly related to the inlet benzene concentration (K_l=4·64−1·38 C_gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to ∽30 g m⁻³ h⁻¹. Using this model, the maximum elimination capacity for the biofilter was estimated to be 12·3 g m⁻³ h⁻¹, and the critical loading capacity was found to be 14 g m⁻³ h⁻¹. The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m⁻¹ at a high superficial air flow rate of 7·21 m³ m⁻² h⁻¹, indicating a good potential for further scale up for industrial applications. © 1998 Society of Chemical Industry     

Design and performance of biofilters for the removal of alkylbenzene vapors

Three identical biofilters, run under the same conditions but inoculated with different mixed cultures, were fed a mixture of toluene, ethylbenzene, and o-xylene (TEX) gases. Inert porous perlite was used as support material, in contrast to the more conventional biofiltration systems where natural supports are used. Biodegradation started in all three biofilters a few hours after inoculation, without previous adaptation of the inocula to the toxic mixture. Despite acidification of the systems to pH values below 4·5, the elimination capacities reached were fully satisfactory. The best performing biofilter, in which bacteria were dominant, showed an elimination capacity of 70 g TEX m⁻³ h⁻¹ with a near complete removal of the mixture up to an influent concentration of 1200 mg TEX m⁻³ at a gas residence time of 57 s. Most of the ingoing carbon was recovered as carbon dioxide in the outgoing gas. In the other biofilters fungi dominated and performance was slightly worse. With single substrates, the elimination capacity was higher for toluene and ethylbenzene than for the TEX mixture, whereas o-xylene removal was slowest in all cases. Also when feeding the mixture to the biofilters, o-xylene was removed most slowly.     

Treatment performance of volatile organic sulfide compounds by the immobilized microorganisms of B350 group in a biotrickling filter

BACKGROUND: In this work, the feasibility of biodegradation and the removal performance of sole and mixed odorous vapors, such as dimethyl disulfide (DMDS), methyl phenyl sulfide (MPS), and ethanethiol (EtSH) in an EtSH‐acclimated biotrickling filter seeded with commercially available B350 microorganisms, were investigated. RESULTS: Removal efficiencies (REs) for DMDS as a sole substrate were evaluated under different inlet concentrations and empty bed residence times (EBRT), 100% RE was achieved at concentration below 0.4 g m^?3 at EBRT 110 s. In addition, 100% RE was obtained for binary EtSH and DMDS (3:2) at the same EBRT. According to the Michaelis–Menten type kinetic equation, the maximum removal rates (V_max) were calculated as 28.7 and 13.9 g m^?3 h^?1 for DMDS and MPS as sole substrate, respectively, while V_max was 22.1 and 10.1 g m^?3 h^?1 for DMDS and MPS in the presence of EtSH and EtSH‐DMDS mixture, respectively. After 5 and 20 days starvation, the re‐acclimation times were only 2 and 8 days, respectively, for the binary system. An EtSH:DMDS:MPS (3:2:1) ternary mixture was removed efficiently by the rebooted system after starvation. CONCLUSION: The proposed system can be applied to cost‐effectively decompose a mixture of volatile organic sulfide compounds at pilot scale. Copyright © 2011 Society of Chemical Industry     

Biofiltration of volatile organic compound using two packing materials: Kinetics and modelling

The performance of two laboratory scale biofilters, packed with pressmud (BF1) and sugarcane bagasse (BF2), was evaluated for gas phase ethylacetate removal under various operating conditions. Biofilters were inoculated with mixed culture obtained from pharmaceutical wastewater sludge. Experiments were carried out at different flow rates (0.03, 0.06, 0.09 and 0.12 m³ h^?1) and inlet ethylacetate concentrations (0.2, 0.4, 0.6 and 1.2 gm^?3). Maximum removal efficiency (RE) of 100% and 98% was achieved at an inlet concentration of 0.2 gm^?3 and gas flow rate of 0.03 m³ h^?1 in BF1 and BF2, respectively. A maximum elimination capacity (EC) of 66.6 gm^?3 h^?1 and 64.1 gm^?3 h^?1 was obtained in BF1 and BF2, respectively, at an inlet concentration of 0.8 gm^?3 and a gas flow rate of 0.12 m³ h^?1. The kinetics of biofiltration of ethylacetate was studied by using Ottengraf and van den Oever model. The kinetic modelling gives an insight into the mechanism of biofiltration. The modified Ottengraf model, which was also tested, demonstrated good agreement between calculated and experimental data.     

Performance of a fluidized‐bed bioreactor with hydrogel biomass carrier under extremely low‐nitrogen availability and effect of nitrogen amendments

BACKGROUND: Because of the lower fluidization energy required and the protection against shock loading and starvation due to their sorption capacity, light adsorbents such as hydrogels could be used as biofilm carrier media in fluidized bed bioreactors for wastewater processing. This work explores the feasibility of a cyclodextrin hydrogel as biomass support to degrade phenol under extremely low‐nitrogen availability and under nitrogen amendments. RESULTS: Phenol removal capacity was low (mean 0.589 kg m^?3 day^?1) under extreme nitrogen‐limited conditions (mean C:N ratio 3830). A pulsed nitrogen amendment increased the elimination capacity (up to 1.97 kg m^?3 day^?1) controlling the biofilm thickness. An 8‐h nitrogen pulse had a highly efficient long‐term effect removing 93.5 mg‐C mg^?1‐N in 300 h. The continuous nitrogen amendment enhanced the elimination capacity (up to 5.84 kg m^?3 day^?1) although rapidly increasing the biomass growth. The inhibiting phenol concentration was smaller during the nitrogen‐limited period (below 100 mg L^?1) than in the nitrogen‐amendment periods (140 mg L^?1). Low liquid velocities were needed to fluidize the bioparticles (less than 3.1 mm s^?1) during the entire experimentation. CONCLUSION: This work shows that a fluidized‐bed bioreactor with mixed culture on cyclodextrin‐based particles can be operated for long periods at extreme nitrogen limitation, and that a limited nitrogen supply with periodic pulsed amendments would be adequate for controlling the biofilm thickness. Copyright © 2011 Society of Chemical Industry     

Biological treatment of a contaminated gaseous emission from a paint and varnish plant—from laboratory studies to pilot‐scale operation

A Vapour‐Phase Bioreactor (VPB), namely a biotrickling filter, was scaled‐up and operated in‐situ for the treatment of gaseous emissions from a paint and varnish industrial plant. A microbial culture able to degrade the target compounds was enriched and a laboratory‐scale VPB was established in order to evaluate the treatment's performance. The VPB presented removal efficiencies higher than 90% when exposed to Organic Loads (OL) of ca 50 g h^?1 m^?3 of reactor. The VPB was exposed to dynamic conditions often found in‐situ (eg night and weekend shutdown periods) and showed a fast capacity to recover, with and without mineral medium recirculation. After a prolonged interruption period (10 months), the VPB was not able to cope with OL of ca 25 g h^?1 m^?3 of reactor and re‐inoculation was required in order to recover the treatment performance. The VPB also showed limited treatment when exposed to higher OL (ca 500 g h^?1 m^?3 of reactor). The VPB was then scaled‐up and a 3 m³ VPB was operated in‐situ, showing removal efficiencies higher than 50% when exposed to an OL of c 5 g h^?1 m^?3 of reactor, thus complying with current legal demands. The addition of a maintenance feed was shown to be a useful tool for VPB pilot‐scale operation when shutdown periods occurred. A factorial design of experiments was carried out, which allowed reduction to one‐tenth of the initial supply of the main mineral medium constituents, namely phosphate buffer, ammonium and magnesium salts, and also elimination of the metal supplement. Overall, the VPBs were shown to be robust equipment, being able to respond actively to dynamic treatment scenarios, particularly night and weekend shutdown periods. Copyright © 2003 Society of Chemical Industry