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.     

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.     

Biomass accumulation and clogging in biotrickling filters for waste gas treatment. Evaluation of a dynamic model using dichloromethane as a model pollutant

A dynamic model is developed that describes the degradation of volatile acidifying pollutants in biotrickling filters (BTFs) for waste gas purification. Dynamic modelling enables the engineer to predict the clogging rate of a filter bed and the time it takes the BTF to adapt to changes in its inlet concentration. The most important mechanisms that govern the behaviour of the BTF are incorporated in the model. The time scale of the accumulation of biomass in a filter is investigated, and an approach is presented that can be used to estimate how long a BTF can be operated before its packing has to be cleaned. A three-month experiment was carried out to validate the model, using dichloromethane (DCM) as a model acidifying pollutant. Valuable experimental data about biomass accumulation and liquid hold-up in the reactor were obtained with an experimental set-up that allows the continuous registration of the weight of the BTF. The results show that in BTFs eliminating DCM from a waste gas, clogging is not to be expected up to concentrations of several g/m3. Model calculations based on the measurements also suggest that the maximum carbon load that can safely be applied per unit void packing volume should not exceed 0.5-1.6 C mol/(m3. h), depending on the density of the biofilm formed. The model is a good predictor of the elimination of the pollutant in the system, the axial gas and liquid concentration profiles, the axial biomass distribution, and the response of the system upon a stepwise increase in the DCM inlet concentration. The influence of the buffer concentrations in the liquid phase upon the performance of the BTF is investigated.     

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.     

Kinetics of microbial growth and biodegradation of methanol and toluene in biofilters and an analysis of the energetic indicators

The kinetics of microbial growth and the biodegradation of methanol and toluene in (a) biofilters (BFs), and (b) biotrickling filters (BTFs), packed with inert materials, has been studied and analyzed. The specific growth rate, mu, for the treatment of methanol was 0.037h(-1) for a wide range of operating conditions. In the BF, mu was found to be a function of the methanol and toluene concentrations in the biofilm. In the BF used for treating methanol, mu was found to be affected by (1) the nitrogen concentration present in the nutrient solution, and (2) the kind of packing material employed. The kinetics of the methanol and toluene biodegradations were also analyzed using "mixed order" models. A Michaelis-Menten model type provided a good fit for the elimination capacity (EC) of the BTF treating methanol, while a Haldane model type provided a good fit to the EC of the BF treating methanol and toluene. The carbon dioxide production rate was related to the packed bed temperature and the content of the volatile solids within the biofilm. For the BF, the ratio of temperature/carbon dioxide production rate (PCO(2)) was 0.024 degrees C per unit of PCO(2), and for the BTF it was 0.15 degrees C per unit of PCO(2).     

Dictyostelium Myosin Bipolar Thick Filament Formation: Importance of Charge and Specific Domains of the Myosin Rod

Myosin-II thick filament formation in Dictyostelium is an excellent system for investigating the phenomenon of self-assembly, as the myosin molecule itself contains all the information required to form a structure of defined size. Phosphorylation of only three threonine residues can dramatically change the assembly state of myosin-II. We show here that the C-terminal 68 kDa of the myosin-II tail (termed AD-Cterm) assembles in a regulated manner similar to full-length myosin-II and forms bipolar thick filament (BTF) structures when a green fluorescent protein (GFP) “head” is added to the N terminus. The localization of this GFP-AD-Cterm to the cleavage furrow of dividing Dictyostelium cells depends on assembly state, similar to full-length myosin-II. This tail fragment therefore represents a good model system for the regulated formation and localization of BTFs. By reducing regulated BTF assembly to a more manageable model system, we were able to explore determinants of myosin-II self-assembly. Our data support a model in which a globular head limits the size of a BTF, and the large-scale charge character of the AD-Cterm region is important for BTF formation. Truncation analysis of AD-Cterm tail fragments shows that assembly is delicately balanced, resulting in assembled myosin-II molecules that are poised to disassemble due to the phosphorylation of only three threonines.     

Minimising biomass accumulation in biotrickling filters

Various approaches can minimize biomass accumulation in biotricking filters (BTF), which can be classified as: (1) physical, (2) chemical and (3) biological. Other approaches include (4) improvement of the bioreactor design and (5) modification of the mode and operational parameters. All of these methods involve either reduction in biomass growth or removal of excess biomass and each method has unique advantages and disadvantages as far as biomass reduction capability, sustainability and ease of integration to the system are concerned, which are compared and contrasted in this review. A careful comparison and analysis of these methods is a requisite to an optimum operation of a BTF system.     

Dictyostelium myosin bipolar thick filament formation: importance of charge and specific domains of the myosin rod

Myosin-II thick filament formation in Dictyostelium is an excellent system for investigating the phenomenon of self-assembly, as the myosin molecule itself contains all the information required to form a structure of defined size. Phosphorylation of only three threonine residues can dramatically change the assembly state of myosin-II. We show here that the C-terminal 68 kDa of the myosin-II tail (termed AD-Cterm) assembles in a regulated manner similar to full-length myosin-II and forms bipolar thick filament (BTF) structures when a green fluorescent protein (GFP) “head” is added to the N terminus. The localization of this GFP-AD-Cterm to the cleavage furrow of dividing Dictyostelium cells depends on assembly state, similar to full-length myosin-II. This tail fragment therefore represents a good model system for the regulated formation and localization of BTFs. By reducing regulated BTF assembly to a more manageable model system, we were able to explore determinants of myosin-II self-assembly. Our data support a model in which a globular head limits the size of a BTF, and the large-scale charge character of the AD-Cterm region is important for BTF formation. Truncation analysis of AD-Cterm tail fragments shows that assembly is delicately balanced, resulting in assembled myosin-II molecules that are poised to disassemble due to the phosphorylation of only three threonines.     

Abatement of odorant compounds in one- and two-phase biotrickling filters under steady and transient conditions

The removal of hydrophobic volatile organic compounds (VOCs) still remains the main restriction in the biological treatment of odorous emissions due to mass transfer limitations. The addition of a non-aqueous phase to conventional biotrickling filters (BTF) may overcome this limitation by enhancing VOCs transport from the gas to the microorganisms. This study compared the long-term and transient performance of a one- (1P) and two-liquid phase (2P; with silicone oil as non-aqueous phase) BTFs for the removal of four VOCs (butanone, toluene, alpha-pinene, and hexane) at empty bed residence times (EBRT) ranging from 47 to 6 s. Removal efficiencies (RE) >96 % were obtained for butanone, toluene, and alpha-pinene in both bioreactors regardless of the EBRT, while higher hexane REs were recorded in the 2P-BTF (81–92 %) compared to the 1P-BTF (60–97 %). The two-phase system always showed a more consistent performance, being able to better withstand step VOC concentration increases and starvation periods, although it was more affected by liquid recycling shutdowns due to a reduced VOC mass transfer. The analysis of the microbial communities showed a high biodiversity and richness despite the low C source spectrum and high community evenness and richness. In this context, the presence of silicone oil mediated the development of a highly different phylogenetic composition of the communities.     

Clogging in horizontal subsurface flow constructed wetlands: influencing factors,research methods and remediation techniques

The treatment of wastewater in constructed wetlands (CW) has been increasingly applied throughout the world, as it is an efficient technique for the removal of pollutants and presents low construction and operational costs. However, a major operational problem of these systems is clogging of the porous medium. Clogging of CW has therefore attracted the attention in several studies, but there are several gaps in the understanding of this phenomenon, especially with regards to its genesis. In order to evaluate the contribution of the influencing factors and to facilitate remediation, it is important to have methods that favor characterization of the real conditions of CW. In this review, the objective was to gather information on the main factors interfering in the clogging process of horizontal subsurface flow constructed wetlands, the available and the new methods for characterizing the degree of obstruction of the porous medium and the techniques/strategies for unclogging these systems.     

Biodegradation of gas-phase styrene in a high-performance biotrickling filter using porous polyurethane foam as a packing medium

A biotrickling filter (BTF) packed with porous polyurethane (PU) foam sheets was developed and operated for removal of gas-phase styrene. The specific surface area and void fraction of the PU foam sheet were determined to be 497 m²/m³ and 0.92, respectively, by using mathematical modeling and experimental measurement. The effects of gas flow direction (co-current and counter-current), styrene loading rate and empty bed residence time on the efficiency of the BTF were analyzed. The BTF achieved a high elimination capacity of 4.0 ∼ 5.0 kg styrene/m³ day due to the high specific surface area of the PU foam. The BTF could be operated repeatedly when excessively-grown biomass was periodically removed, using circulating NaOH solution for 2 h every four days.     

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.     

High-temperature biotrickling filtration of hydrogen sulphide

Biofiltration of malodorous reduced sulphur compounds such as hydrogen sulphide has been confined to emissions that are at temperatures below 40°C despite the fact that there are many industrial emissions (e.g. in the pulp and paper industry) at temperatures well above 40°C. This paper describes our study on the successful treatment of hydrogen sulphide gas at temperatures of 40, 50, 60 and 70°C using a microbial community obtained from a hot spring. Three biotrickling filter (BTF) systems were set up in parallel for a continuous run of 9 months to operate at three different temperatures, one of which was always at 40°C as a mesophilic control and the other two were for exploring high-temperature operation up to 70°C. The continuous experiment and a series of batch experiments in glass bottles (250 ml) showed that addition of glucose and monosodium glutamate enhanced thermophilic biofiltration of hydrogen sulphide gas and a removal rate of 40 g m⁻³ h⁻¹ was achieved at 70°C. We suggest that the glucose is acting as a carbon source for the existing microbial community in the BTFs, whereas glutamate is acting as a compatible solute. The use of such organic compounds to enhance biodegradation of hydrogen sulphide, particularly at high temperatures, has not been demonstrated to our knowledge and, hence, has opened up a range of possibilities for applying biofiltration to hot gas effluent.     

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.     

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.     

微生物胞外活性氧的产生及其促进有机污染物降解的研究进展

生物法处理是环境中有机污染物去除的主要途径,具有费用低、环境影响小等特点,其不足之处在于所需处理时间长,尤其当有机污染物难降解时,处理时间长达数十年甚至数百年.胞外活性氧(extracellular reactive oxygen species,EROS)是微生物代谢时产生的一类含氧活性基团,对难降解有机物的生物降解...     

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.     

Enzymatic reactors for the removal of recalcitrant compounds in wastewater

Abstract

Enzymatic treatments based on oxidative enzymes, such as peroxidases, laccases and tyrosinases, have been proposed as an alternative to conventional methods to remove a broad range of contaminants present in wastewater. The aim of this study is to discuss existing technologies for the removal of pollutants based on the use of oxidative enzymes, including a discussion on the most important factors affecting the efficiency of the proposed systems. Factors involved in the catalytic cycle of the enzyme (biocatalyst, substrates and mediators), the addition of certain components to the reaction medium (additives, surfactants or solvents) as well as operational parameters (temperature, pH or agitation) will be discussed. Finally, two types of reactors: one-stage and two-stage enzymatic membrane reactors, especially designed for the treatment of micropollutants present in secondary effluents, will be described in detail.     

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.     

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.