Long term performance of biotrickling filters removing a mixture of volatile organic compounds from an artificial waste gas: dichloromethane and methylmethacrylate

Two problems still hamper the widespread industrial application of biotrickling filters (BTFs) for waste gas treatment in practice: clogging of the filters at higher carbon loads and a decrease in the elimination of a target compound when more than one compound is present in the waste gas. To investigate these phenomena three identical BTFs removing dichloromethane (DCM) from an artificial waste gas were operated counter-current wise for 12 months at a DCM load of 0.94 Cmole-DCM/(m_r³ · h). After five months of operation methylmethacrylate (MMA) was added to the waste gas. Three different MMA loads were applied: 0.5, 1.0 and 1.5 Cmole-MMA/(m_r³ · h). Although the elimination of DCM in all three BTFs decreased after the introduction of MMA to the air stream, it stabilised at a lower steady-state value than before the MMA addition. MMA was completely degraded during the applied standard conditions. In all three filters biomass accumulation eventually caused clogging of the packing. In the filter with the lowest MMA load the first signs of clogging were observed only after 7 months of stable operation, illustrating the need for long term studies to evaluate process stability. Short term experiments have provided information about the system's dynamics and showed that an accumulation of intermediates and a subsequent adaptation of the biomass in the BTF will occur upon a step increase in MMA load. To evaluate whether a stable BTF operation without clogging is possible, a novel process parameter (the rate of Carbon Conversion per unit void packing Volume) is introduced which possibilities and limitations are discussed.     

Control of methanol vapours in a biotrickling filter: performance analysis and experimental determination of partition coefficient

Methanol vapours were treated in a biotrickling filter (BTF) packed with inert polypropylene spheres. The effects of the nitrogen concentration in the nutrient solution, the empty bed residence time (EBRT) and the methanol inlet concentration, on the BTF performance, were all examined. The elimination capacity (EC), the biomass and the carbon dioxide production rates were all increased with the rising of the nitrogen concentration and the EBRT. The EC also rose with increasing methanol inlet load (IL) when the methanol inlet concentration and the EBRT were varied, from 0.3 to 37.0 g m(-3), and from 20 to 65 s, respectively. The BTF reached its maximum EC level of 2160 g m(-3) h(-1) when it was operated at an IL level of 3700 g m(-3) h(-1). The input methanol was removed through two mechanisms: biodegradation and absorption in the liquid phase. The partition coefficient for the methanol in the BTF was determined at five EBRTs and along the packed bed. It generally followed the Henry model, having an average value of 2.64 x 10(-4)[mol L(-1)](gas)/[mol L(-1)](liquid).     

Effects of pH, CO2, and flow pattern on the autotrophic degradation of hydrogen sulfide in a biotrickling filter

In this study, the effects of pH, CO(2), and flow pattern on the performance of a biotrickling filter (BTF) packed with plastic Pall rings and treating a H(2)S-polluted waste gas were investigated to establish the optimum operating conditions and design criteria. The CO(2) concentration had no effect on the biodegradation at H(2)S concentrations below 50 ppm. In the range of 50-127 ppm H(2)S, CO(2) concentrations between 865 and 1,087 ppm enhanced H(2)S removal, while higher concentrations of 1,309-4,009 ppm CO(2) slightly inhibited H(2)S removal. The co-current flow BTF presented the advantage of a more uniform H(2)S removal and biomass growth in each section than the counter-current flow BTF. Examination of the pH-effect in the range of pH 2.00-7.00 revealed optimal activity for autotrophs at pH 6.00. Under optimal conditions, the elimination capacity reached 31.12 g H(2)S/m(3)/h with a removal efficiency exceeding 97%. In the present research, autotrophic biomass was developed in the BTF, performing both a partial oxidization of H(2)S to elemental sulfur and a complete oxidization to sulfate, which is favorable from an environmental point of view. Results showed that around 60% of the sulfide concentration fed to the reactor was transformed into sulfate. Such autotrophic trickling filters may present other advantages, including the fact that they do not release any CO(2) to the atmosphere. Besides, the limited growth of autotrophs avoids potential clogging problems. Experimental performance data were compared with data from a mathematical model. Comparisons showed that the theoretical model was successful in predicting the performance of the biotrickling filter.     

Air pollution control through biotrickling filters: a review considering operational aspects and expected performance

The biological removal of pollutants, especially through biotrickling filters (BTFs), has recently become attractive for the low investment and operational costs and the low secondary pollution. This paper is intended to investigate the state of the art on BTF applications. After an overview on the biodegradation process and the typical parameters involved, this paper presents the analysis of a group of 16 literature studies chosen as the references for this sector. The reference studies differ from one another by the pollutants treated (volatile organic compounds [VOC], hydrogen sulphide, nitrogen oxides and trimethylamine), the geometry and size of the BTFs, and the procedures of the tests. The reference studies are analyzed and discussed in terms of the operational conditions and the results obtained, especially with respect to the removal efficiencies (REs) and the elimination capacities (ECs) of the pollutants considered. Empty bed residence time (EBRT), pollutant loading rate, temperature, pH, oxygen availability, trickling liquid flow rate, inoculum selection and biomass control strategies revealed to be the most important operational factors influencing the removal performance of a BTF.     

Performance of three pilot-scale immobilized-cell biotrickling filters for removal of hydrogen sulfide from a contaminated air steam

Hydrogen sulfide (H₂S) is a major malodorous compound emitted from wastewater treatment plants. In this study, the performance of three pilot-scale immobilized-cell biotrickling filters (BTFs) spacked with combinations of bamboo charcoal and ceramsite in different ratios was investigated in terms of H₂S removal. Extensive tests were performed to determine the removal characteristics, pressure drops, metabolic products, and removal kinetics of the BTFs. The BTFs were operated in continuous mode at low loading rates varying from 0.59 to 5.00 g H₂S m⁻³ h⁻¹ with an empty bed retention time (EBRT) of 25 s. The removal efficiency (RE) for each BTF was >99% in the steady-state period, and high standards were met for the exhaust gas. It was found that a multilayer BTF had a slight advantage over a perfectly mixed BTF for the removal of H₂S. Furthermore, an impressive amount >97% of the H₂S was eliminated by 10% of packing materials near the inlet of the BTF. The modified Michaelis–Menten equation was adopted to describe the characteristics of the BTF, and K_s and V_m values for the BTF with pure bamboo charcoal packing material were 3.68 ppmv and 4.26 g H₂S m⁻³ h⁻¹, respectively. Both bamboo charcoal and ceramsite demonstrated good performance as packing materials in BTFs for the removal of H₂S, and the results of this study could serve as a guide for further design and operation of industrial-scale systems.     

Modeling the removal of VOC mixtures in biotrickling filters

A mathematical model was derived for describing removal of mixed VOC vapors in biotrickling filters (BTFs). The model accounts for potential process rate limitation by the availability of oxygen as well as for potential kinetic interactions among pollutants during their biodegradation. Without using any fitted parameter, the model was found capable of predicting experimentally obtained removal rates of mono-chlorobenzene (m-CB) and ortho-dichlorobenzene (o-DCB) vapors. Experimental results reported here show that m-CB removal is better than that of o-DCB. The two compounds were known to be involved in a kinetic cross-inhibition interaction when degraded in suspended culture. However, model sensitivity studies showed that cross-inhibition does not affect BTF performance due to the low pollutant concentrations involved. For the same reason, the influence of oxygen on BTF performance was found to be minimal under the conditions tested. The model was found to predict experimentally obtained values with less than 10% error in the majority of cases. Computations with an earlier model describing VOC removal in conventional biofilters showed that, for the model mixture used in this study (m-CB/o-DCB), removal rates obtained with BTFs are one to more than two orders of magnitude higher than those obtained with conventional biofilters. This is attributed to the larger active specific biofilm surface area in BTFs, obtained through the creation of favorable growth conditions for the biomass, and better moisture control.     

Toluene-styrene secondary acclimation improved the styrene removal ability of biotrickling filter

In this work, ceramic pellets were used as packing material to establish a biotrickling filter (BTF) with acclimated sludge being inoculated on the surface of the packing to purify waste gas containing styrene. A method of toluene-styrene secondary acclimation was applied to achieve rapid formation of biological films. Results showed that the total time of start-up was 48 days and the removal efficiency (RE) of styrene reached up to 95%. The suitable empty bed residence time (EBRT) was obtained that is 57 s for higher RE of styrene with the inlet loading rates of 6.7–271.6 g/m³/h. The pH and moisture content showed small effect on styrene removal indicating that the operation of BTF was stable. Biomass accumulation was normal and its rising velocity under the condition of short EBRT was faster than that of long EBRT.     

Macrokinetic and quantitative microbial investigation on a bench-scale biofilter treating styrene-polluted gaseous streams

We performed a macrokinetic and quantitative microbial investigation of a continuously operating bench-scale biofilter treating styrene-polluted gases. The device was filled with a mixture of peat and glass beads as packing medium and inoculated with the styrene-oxidizing strain, Rhodococcus rhodochrous AL NCIMB 13259. The experimental data of styrene and microbial concentrations, obtained at different biofilter heights, were used to evaluate the pollutant concentration profiles as well as the influence of styrene loading on biomass distribution along the packing medium. Styrene and biomass concentration profiles permitted detection of a linear relationship between the amount of biomass grown in a given section of the biofilter and that of pollutant removed, regardless of the operating conditions tested. Biomass development in the bed appeared to: depend linearly on pollutant concentration at an inlet styrene concentration of <0.10 g m(-3) in the gaseous stream; achieve a maximum value (7. 10(7) colony forming units per gram of packing material) within a wide styrene concentration range (0.10 to 1.0 g m(-3)); and fall sharply beyond this inhibition threshold. The process followed zeroth-order macrokinetics with respect to styrene concentration, which is consistent with zeroth-order microkinetics with either fully active or not fully active biofilm. The maximal volumetric styrene removal rate was found to be 63 g m(packing material) (-3) h(-1) for an influent pollutant concentration of 0.80 g m(-3) and a superficial gas velocity of 245 m h(-1).     

Ammonia removal from a waste air stream using a biotrickling filter packed with polyurethane foam through the SND process

This paper presents the results of a bench-scale biotrickling filter (BTF) on the removal of ammonia gas from a waste stream using a simultaneous nitrification/denitrification (SND) process. It was found that the developed BTF could completely remove 100 ppm ammonia from a waste stream, with an empty bed retention time of 60 s and 98.4% nitrogen removal through the SND process under the tested conditions. It was elucidated that both autotrophic and heterotrophic bacteria were involved in the nitrogen removal trough the SND process in the BTF. Additionally, the elimination capacity of total nitrogen by the BTF increased from 3.5 to 18.4 g N/m³ h with an inlet load of 20.6 g N/m³ h (73.6%). The findings of this study suggest that the BTF can be operated to attain complete ammonia removal through the SND process, thereby making the treatment of ammonia-laden gas streams both short and cost-effective.     

The Rotary Trickle‐Bed Reactor – A New Reactor Concept for Biological Gas Purification

A new type of reactor employed to the biological gas purification is presented. The avoidance of clogging in the carrier packing is achieved by i) the use of a structured, rotating carrier packing, ii) a definite liquid irrigation regime during start‐up, operation and clean‐up time phases, iii) an on‐line determination and control of the fixed biofilm mass. A uniform biofilm thickness is generated by an optimized liquid irrigation of the carrier packing with spray nozzles. The detachment of the fixed biomass is accomplished by liquid shear forces generated with jet nozzles. The time‐scheduled operation regime of the reactor is founded on the on‐line quantification of the immobilized biomass, which results in a new quality of process governing of biotrickling reactors applied to gas purification. This is proved by the experimental results of pressure drop, dynamic liquid holdup as well as the volumetric degradation rates. The degradation of styrene was investigated in laboratory and field experiments showing a maximal volumetric degradation rate of 150 g m^–3 h^–1 at a pollutant load of 200 g m^–3 h^–1. The feasibility of this reactor prototype is demonstrated by employing it to the elimination of industrial waste gas.     

Steady-state and transient-state performance of a biotrickling filter treating chlorobenzene-containing waste gas

Biotrickling filter (BTF) technology was applied for the treatment of waste gas containing a mixture of chlorobenzene and 1,2-dichlorobenzene. An adapted microbial community was immobilised on a structured packing material. The strategy followed was to reach high removal efficiencies at initially low mass loading rates followed by an increase of the latter. This procedure was successful and resulted in a short start-up period of only 2 weeks. A 3-month operation under steady-state conditions showed good performance, with >95% removal efficiency at a mass loading rate of 1,800 g m^–3 day^–1. Dimensionless concentration profiles showed that the chlorobenzenes were simultaneously degraded. Low dissolved organic carbon of 15 mg l^–1 and stoichiometric chloride concentrations in the trickling liquid indicated complete mineralisation of the pollutant. Transient-state experiments with five times higher mass loading rates caused a decrease in the removal efficiency that recovered rapidly once the mass loading rate returned to its original steady-state level. A progressive increase of the mass loading rate in a long-term performance experiment showed that the removal efficiency could be kept stable between 95 and 99% at loads of up to 5,200 g m^–3 day^–1 over several days. Above this mass loading rate, the elimination capacity did not increase any further. These results demonstrated that with a well-adapted inoculum and optimal operation parameters, a BTF system with excellent performance and stability that efficiently removes a mixture of cholorobenzene vapours from air can be obtained.     

A bioactive foamed emulsion reactor for the treatment of benzene-contaminated air stream

An adapted bioactive foamed emulsion bioreactor for the treatment of benzene vapor has been developed. In this reactor, bed clogging was resolved by bioactive foam as a substitute of packing bed for interfacial contact of liquid to gaseous phase. The pollutant solubility has been increased using biocompatible organic phase in liquid phase and this reactor can be applied for higher inlet benzene concentration. Experimental results showed a benzene elimination capacity (EC) of 220 g m⁻³ h⁻¹ with removal efficiency (RE) of 85% for benzene inlet concentration of 1–1.2 g m⁻³ at 15 s gas residence time in bioreactor. Assessment of benzene concentration in liquid phase showed that a significant amount of transferred benzene mass has been biodegraded. By optimizing the operational parameters of bioreactor, continuous operation of bioreactor with high EC and RE was demonstrated. With respect to the results, this reactor has the potential to be applied instead of biofilter and biotrickling filters.     

The operating performance of a biotrickling filter with Lysinibacillus fusiformis for the removal of high-loading gaseous chlorobenzene

Removal of gaseous chlorobenzene (CB) by a biotrickling filter (BTF) filled with modified ceramics and multi-surface hollow balls during gas–liquid mass transfer at the steady state was by microbial degradation rather than dissolution in the spray liquid or emission into the atmosphere. The BTF was flexible and resistant to the acid environment of the spray liquid, with the caveat that the spray liquid should be replaced once every 6–7 days. The BTF, loaded with Lysinibacillus fusiformis, performed well for purification of high-loading CB gas. The maximum CB gas inlet loading rate, 103 g m^?3 h^?1, CB elimination capacity, 97 g m^?3 h^?1, and CB removal efficiency, 97.7 %, were reached at a spray liquid flow rate of 27.6 ml min^?1, an initial CB concentration of up to 1,300 mg m^?3, and an empty bed retention time of more than 45 s.     

An experimental and modeling study on the removal of mono-chlorobenzene vapor in biotrickling filters

Removal of mono-chlorobenzene (m-CB) vapor from airstreams was studied in a biotrickling filter (BTF) operating under counter-current flow of the air and liquid streams. Experiments were performed under various values of inlet m-CB concentration, air and/or liquid volumetric flow rates, and pH of the recirculating liquid. Conversion of m-CB was never below 70% and at low concentrations exceeded 90%. A maximum removal rate of about 60 gm-3-reactor h-1 was observed. Conversion of m-CB was found to increase as the values of liquid and air flow rate increase and decrease, respectively. The effects of pH and frequency of medium replenishment on BTF performance were also investigated. The process was successfully described with a detailed mathematical model, which accounts for mass transfer and kinetic effects based on m-CB and oxygen availability. Solution of the model equations yielded m-CB and oxygen concentration profiles in all three phases (airstream, liquid, biofilm). It is predicted that oxygen has a controling effect on the process at high inlet m-CB concentrations. From independent, suspended culture, experiments it was found that m-CB biodegradation follows Andrews inhibitory kinetics. The kinetic constants were found to remain practically unchanged after the culture was used in BTF experiments for 8 months. Copyright 1998 John Wiley & Sons, Inc.     

Biological waste gas treatment with a modified rotating biological contactor. ΙΙ. Effect of operating parameters on process performance and mathematical modeling

In the first part of this paper, we introduced a modified rotating biological contactor (RBC) for the biological treatment of waste gas, and demonstrated its feasibility by applying the process to the biodegradation of toluene in a 91-liter reactor containing 20 biofilm support discs with a diameter of 40 cm [1]. We showed that the proposed system allows the unlimited growth of the biofilm to be suppressed, hence eliminating the risk of clogging associated with other biological waste gas treatment systems. Furthermore, we observed stationary long-term performance for more than one year under typical standard operating conditions. In this part of our work, we investigate experimentally the influence of the main process parameters, i.e., gas flow rate, inlet gas concentration, and rotational speed of the biofilm supports on process performance for the same system. Experimental results indicate that the modified RBC system is mass transfer limited for toluene loadings below 150 g/m(3)h, whereas at higher inlet concentrations of the pollutant, it becomes limited by the biodegradation reaction inside the biofilm. Surprisingly, the disc rotational speed is found to have no major effect on process performance for the system under investigation. A time-independent mathematical model of the process is also presented, and predictions are compared with experimental degradation data. In the range of the investigation process parameters, good agreement between the experimental data and simulation results is obtained.     

Exhaust gas purification using biocatalysts (fixed bacteria monocultures) — the influence of biofilm diffusion rate (O2) on the overall reaction rate

Summary This paper presents results of experiments on the influence of O₂ and substrate (pollutant) concentration on the overall reaction rate of a trickle-bed reactor used for biological waste gas purification. The biocatalyst was a pollutant-specific bacterial monoculture fixed on porous glass carriers. The conversion of acetone and propionaldehyde, as model pollutants that are easily soluble in water, was measured. Under constant hydrodynamic conditions (gas and liquid flow rates) the inlet pollutant concentration was varied. The O₂ partial pressure in the model gas was increased to investigate the influence of O₂ supply on pollutant conversion. At higher pollutant concentrations (>117 mg acetone.m^-3 gas and > 150 mg propionaldehyde.m^-3 gas) higher concentrations of dissolved O₂ led to a significant rise in the maximum degradation capacity of the reactor. This maximum reaction rate was independent of the pollutant mass flow. It seems that the diffusion of O₂ in the biofilm is rate-determining. The reaction rate at lower inlet concentrations was not affected by the improved O₂ supply. Here the external mass transfer through the liquid film limits the reaction rate and the maximum separation efficiency of about 80% at a residence time of 1.2s (space velocity 3000h^-1) is achieved.     

The existence of a biological equilibrium in a trickling filter for waste gas purification

Clogging is well-known phenomenon in the application of a biological tricking filter for both waste gas and wastewater treatment. Nevertheless, no such observations or even significant changes in pressure drop have ever been recorded during the long-term processing of a waste gas containing dichloromethane (DCM) as a sole carbon source. To obtain more information about this phenomenon, a detailed investigation into the carbon balance of this system has been performed. During a period of operation of about 200 days the rate of DCM elimination and the overall rate of CO(2) production in a continuously operating filter were therefore recorded daily, thus allowing an evaluation of the overall conversion process. Furthermore pseudo-steady-state measurements were carried out on a regular basis. These experiments reveal more detailed information on the actual DCM conversion by Hyphomicrobium GJ21 within the biofilm. The combined results of the experiments described in this article show that on an overall basis a so-called biological equilibrium, i.e., a situation of no net biomass accumulation, is obtained in the course of time. It appeared that the overall rate of CO(2) production slowly increased until, after some 200 days, it finally counter-balanced the conversion rate of DCM on a molar-basis. As opposed to this result, all pseudo-steady-state experiments indicated that about 60% of the eliminated primary carbon source is converted into biomass. This is in good agreements with results from microkinetic experiments. Based on these results and evaluation of the experimental data, it is concluded that interactions between several microbial populations are involved in this biological equilibrium. These interactions include both biomass growth and biomass degradation. (c) 1994 John Wiley & Sons, Inc.     

Hydrogen sulfide removal performance of a bio-trickling filter employing Thiobacillus thiparus immobilized on polyurethane foam under various starvation regimes

In the present study a biotrickling filter (BTF) with countercurrent gas/liquid flow packed with open-pore polyurethane foam — as a carrier of Thiobacillus thioparus (DSMZ5368) — was subjected to various starvation regimes such as non-contaminant loading, idleness, and complete shutdown. During the starvation periods specific oxygen uptake rates of microorganisms (SOUR) on packing were monitored. The BTF was subjected to non-contaminant loading (up to 16 h), cyclic non-contaminant loading (for 4 days) and gas shut-off (up to 24 h), and it recovered to its pre-starvation removal efficiency within a 2 ～ 3 h period after resuming normal operating conditions. The recovery time values obtained during the runs in which these starvation regimes were imposed could be indirectly correlated with the corresponding SOUR values suggesting that the recovery time after such starvation regimes are dependent on the degree to which the aerobic biological activity has been reduced as a result of the imposed starvation regime. In the case of the complete shutdown of the BTF, the recovery time increased substantially after 1 and 2 days of complete shutdown, and after 5 days of complete shutdown the pre-starvation removal efficiency was not achieved even after 12 days of normal operation.     

Dichloromethane removal from waste gases with a trickle-bed bioreactor

A 66 dm³ trickle-bed bioreactor was constructed to assess the possibilities of eliminating dichloromethane from industrial waste gases. The trickle-bed bioreactor was filled with a randomly-stacked polypropylene packing material over which a liquid phase was circulated. The pH of the circulating liquid was externally controlled at a value of 7 and the temperature was maintained at 25 °C. The packing material was very quickly covered by a dichloromethane-degrading biofilm which thrived on the dichloromethane supplied via the gas phase. The biological system was very stable and not sensitive to fluctuations in the dichloromethane supply. Removal of dichloromethane from synthetic waste gas was possible down to concentrations well below the maximal allowable concentration of 150mg/m³ required by West-German law for gaseous emissions. At higher dichloromethane concentrations specific dichloromethane degradation rates of 200 g h^–1 m^–3 were possible. At very low inlet concentrations, dichloromethane elimination was completely mass transfer limited.The gas-phase mixing could be described by a series of 10 to 7 identical ideally-mixed tanks for superficial gas velocities ranging from 150 to 450 m/h. Dichloromethane elimination with the tricklebed bioreactor was modelled using an overall mass-transfer coefficient that was dependent on the gas and liquid velocities. Masstransfer resistance within the biofilm was also accounted for. Using the model, elimination efficiencies were predicted which were very close to the experimentally observed values.     

Mathematical model for a three-phase fluidized bed biofilm reactor in wastewater treatment

A mathematical model for a three phase fluidized bed bioreactor (TFBBR) was proposed to describe oxygen utilization rate, biomass concentration and the removal efficiency of Chemical Oxygen Demand (COD) in wastewater treatment. The model consisted of the biofilm model to describe the oxygen uptake rate and the hydraulic model to describe flow characteristics to cause the oxygen distribution in the reactor. The biofilm model represented the oxygen uptake rate by individual bioparticle and the hydrodynamics of fluids presented an axial dispersion flow with back mixing in the liquid phase and a plug flow in the gas phase. The difference of settling velocity along the column height due to the distributions of size and number of bioparticle was considered. The proposed model was able to predict the biomass concentration and the dissolved oxygen concentration along the column height. The removal efficiency of COD was calculated based on the oxygen consumption amounts that were obtained from the dissolved oxygen concentration. The predicted oxygen concentration by the proposed model agreed reasonably well with experimental measurement in a TFBBR. The effects of various operating parameters on the oxygen concentration were simulated based on the proposed model. The media size and media density affected the performance of a TFBBR. The dissolved oxygen concentration was significantly affected by the superficial liquid velocity but the removal efficiency of COD was significantly affected by the superficial gas velocity. An erratum to this article can be found online at .