Removal of toluene in waste gases using a biological trickling filter

The removal of toluene from waste gas was studied in a trickling biofilter. A high level of water recirculation (4.7 m h^–1) was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting. For loads in the range from 6 to 150 g m^–3 h^–1 the maximum volumetric removal rate (elimination capacity) was 35±10 g m^–3 h^–1, corresponding to a zero order removal rate of 0.11±0.03 g m^–2 h^–1 per unit of nominal surface area. The surface removal was zero order above the liquid phase concentrations of approximately 1.0 g m^–3, corresponding to inlet gas concentrations above 0.7–0.8 g m^–3. Below this concentration the surface removal was roughly of first order. The magnitude of the first order surface removal rate constant, k_1A , was estimated to be 0.08–0.27 m h^–1 (k_1A a=24–86 h^–1). Near-equilibrium conditions existed in the gas effluent, so mass transfer from gas to liquid was obviously relatively fast compared to the biological degradation. An analytical model based on a constant liquid phase concentration through the trickling filter column predicts the effluent gas concentration and the liquid phase concentration for a first and a zero order surface removal. The experimental results were in reasonable agreement with a very simple model valid for conditions with an overall removal governed by the biological degradation and independent of the gas/liquid mass transfer. The overall liquid mass transfer coefficient, K_La, was found to be a factor 6 higher in the system with biofilm compared to the system without. The difference may be explained by: 1. Difference in the wetting of the packing material, 2. Mass transfer occurring directly from the gas phase to the biofilm, and 3. Enlarged contact area between the gas phase and the biofilm due to a rough biofilm surface.     

Nickel removal from nickel plating waste water using a biologically active moving-bed sand filter

Efficient removal of dissolved nickel was observed in a biologically active moving-bed `MERESAFIN' sand filter treating rinsing water from an electroless nickel plating plant. Although nickel is fully soluble in this waste water, its passage through the sand filter promoted rapid removal of approximately 1 mg Ni/l. The speciation of Ni in the waste water was modelled; the most probable precipitates forming under the conditions in the filter were predicted using PHREEQC. Analyses of the Ni-containing biosludge using chemical, electron microscopical and X-ray spectroscopic techniques confirmed crystallisation of nickel phosphate as arupite (Ni₃(PO₄)₂.8H₂O), together with hydroxyapatite within the bacterial biofilm on the filter sand grains. Biosorption contributed less than 1% of the overall sequestered nickel. Metabolising bacteria are essential for the process; the definitive role of specific components of the mixed population is undefined but the increase in pH promoted by metabolic activity of some microbial components is likely to promote nickel desolubilisation by others.     

Membrane bioreactor with a porous hydrophobic membrane as a gas-liquid contactor for waste gas treatment

A novel type of bioreactor for waste gas treatment has been designed. The reactor contains a microporous hydrophobic membrane to create a large interface between the waste gas and the aqueous phase. To test the new reactor, propene was chosen because of its high air/water partition coefficient, which causes a low water concentration and hampers its removal from air. Propene transfer from air to a suspension of propene-utilizing Xanthobacter Py2 cells in the membrane bioreactor proved to be controlled by mass transfer in the liquid phase. The resistance of the membrane was negligible. Simulated propene transfer rates agreed well with the experimental data. A stable biofilm of Xanthobacter Py2 developed on the membrane during prolonged operation. The propene flux into the biofilm was 1 x 10(-6) mol m(-2) s(-1) at a propene concentration of 9.3 x 10(-2) mol m(-3) in the gas phase. (c) 1995 John Wiley & Sons, Inc.     

Biofilm population dynamics in a trickle-bed bioreactor used for the biodegradation of aromatic hydrocarbons from waste gas under transient conditions

The dynamics of a multispecies biofilm population in a laboratory-scale trickle-bed bioreactor for the treatment of waste gas was examined. The model pollutant was a VOC-mixture of polyalkylated benzenes called Solvesso 100. Fluorescence in-situ hybridization (FISH) was applied in order to characterise the population composition. The bioreactor was operated under transient conditions by applying pollutant concentration shifts and a starvation phase. Only about 10% of the biofilm mass were cells, the rest consisted of extracellular polymeric substances (EPS). The average fraction of Solvesso 100-degrading cells during pollutant supply periods was less than 10%. About 60% of the cells were saprophytes and about 30% were inactive cells. During pollutant concentration shift experiments, the bioreactor performance adapted within a few hours. The biofilm population exhibited a dependency upon the direction of the shifts. The population reacted within days after a shift-down and within weeks after a shift-up. The pollutant-degraders reacted significantly faster compared to the other cells. During the long-term starvation phase, a shift of the population composition took place. However, this change of composition as well as the degree of metabolic activity was completely reversible. A direct correlation between the biodegradation rate of the bioreactor and the number of pollutant-degrading cells present in the biofilm could not be obtained due to insufficient experimental evidence.     

Verification studies of a simplified model for the removal of dichloromethane from waste gases using a biological trickling filter

The removal of dichloromethane from waste gases in a biological trickling filter was studied experimentally as well as theoretically within the concentration range of 0–10,000 ppm. A stable dichloromethane elimination performance was achieved during two years of operation, while the start-up of the system only amounted to several weeks at constant inlet concentrations. The trickling filter system was operated co-currently as well as counter-currently.However, experimental and theoretical results revealed that the relative flow direction of the mobile phases did not significantly affect the elimination performance. Moreover, it was found that the gas-liquid mass-transfer resistance in the trickling filter bed applied was negligible, which leaves the biological process inside the biofilm to be the rate limiting step.A simplified model was developed, the Uniform-Concentration-Model, which showed to predict the filter performance close to the numerical solutions of the model equations. This model gives an analytical expression for the degree of conversion and can thus be easily applied in practice.The dichloromethane eliminating performance of the trickling filter described in this paper, is reflected by a maximum dichloromethane elimination capacity EC _max=157 g/(m³ · h) and a critical liquid concentration C _lcr=45 g/m³ at a superficial liquid velocity of 3.6 m/h, inpendent of the gas velocity and temperature.List of Symbols a _s m²/m³ specific area - a _w m²/m³ specific wetted area - A m² cross-sectional area - C _g g/m³ gas phase concentration - C _go g/m³ inlet gas phase concentration - C _gocr g/m³ critical gas phase concentration - C _g ^* C_g/C_go dimensionless gas concentration - C _l g/m³ liquid concentration - C _lcr g/m³ critical liquid concentration - C _lcr ^* mC_lcr/C_go dimensionless critical concentration - c _li g/m³ substrate concentration at liquid-biofilm interface - C _l ^* mC_l/C_go dimensionless liquid concentration - C _o g/m³ oxygen concentration inside the biofilm - C _oi g/m³ oxygen concentration at liquid-biofilm interface - C_s g/m³ substrate concentration inside the biofilm - C _si g/m³ substrate concentration at liquid-biofilm interface - D _eff m²/h effective diffusion coefficient in the biofilm - D _o m²/h effective diffusion coefficient for oxygen in the biolayer - E mu_g/u_l extraction factor - E _act kJ/mol activation energy for the biological reaction - EC g/(m³· h) K _o a _w : elimination capacity, or the amount of substrate degraded per unit of reactor volume and time - EC _max g/(m³ · h) K _o a_w: maximum elimination capacity - f degree of conversion - h m coordinate in height - H m height of the packed bed - K ₀ g/(m³ · h) _maxX_b/Y zeroth order reaction defined per unit of biofilm volume - k _og m/h overall gas phase mass transfer coefficient - K ^* dimensionless constant given by Eq. (A.5) - K _l ^* dimensionless constant given by Eq. (A.6) - K ₂ ^* dimensionless constant given by Eq. (A.6) - m C _g /C_l gas liquid distribution coefficient - N g/(m² · h) liquid-biofilm interfacial flux of substrate - N _og k_oga_wH/u_g number of gas phase transfer units - N _r k_o a_w H/u_g C_go number of reaction units - OL g/(m³· h) u _g C _go /H organic load - r _s g/(m³ ·h) zeroth order substrate degradation rate given by Eq. (1) - R _s g/(g TSS ·h) specific activity - T K absolute temperature - u _g m/h superficial gas velocity - u _t m/h superficial liquid velocity - X _b g TSS/m₃ biomass concentration inside biofilm - X _s g TSS/m₃ liquid suspended biomass concentration - x m coordinate inside the biofilm - Y g TSS/(g_DCM) yield coefficient Greek Symbols dimensionless parameter given by Eq. (2) - m averaged biofilm thickness - biofilm effectiveness factor given by Eqs. (7a)–(7c) - m penetration depth of substrate into the biofilm - _max d^–1 microbiological maximum growth rate - v _o stoichiometric utilization coefficient for oxygen - v _s stoichiometric utilization coefficient for substrate - dimensionless height in the filter bed - h H/u _g superficial gas phase contact time - _o (K ₀ /DC _ii )^1/2 - _o C _o /C _oi dimensionless oxygen concentration inside the biofilm - _s C _s /C _si dimensionless substrate concentration inside the biofilm Experimental results, verifying the model presented will be discussed Part II (to be published in Vol. 6, No. 4)     

Inert filter media for the biofiltration of waste gases – characteristics and biomass control

Soil biofilters and related systems based onthe use of natural filter beds have been usedfor several years for solving specific airpollution problems. Over the past decade,significant improvements have been brought tothese original bioprocesses, among which thedevelopment and use of new inert packingmaterials. The present paper overviews the mostcommon inert packings used in biofiltration ofwaste gases and their major characteristics. Apotential problem recently encountered whenusing inert filter beds is the heterogenousdistribution of biomass on the packingmaterial, and the excessive growth andaccumulation of biomass when treating highorganic loads, eventually leading to cloggingof the biofilter and reduced efficiency.Several strategies that have been proposed forsolving such problems are described in thispaper. Technologies for controlling excessbiomass accumulation can be grouped into fourcategories based on the use of mechanicalforces, the use of specific chemicals, thereduction of microbial growth, and predation.     

净化废气的生物过滤技术及其影响因素

生物过滤方法在废气净化中具有费用低和环保的特点, 因而成为一种应用前景良好的空气污染控制技术。本文综述了不同生物过滤反应器的特点, 详细分析了应当在生物过滤过程中合理控制的关键参数, 并展望了今后的研究热点。     

废气处理生物滤器微生物生态学研究进展

废气生物处理是一项新兴的气体污染控制技术,已成为当前环境领域的研究热点.本文概述了生物滤器系统(包括生物过滤器系统和生物滴滤器系统)结构及其去除气体污染物的原理,重点阐述了生物滤器微生物的分离、鉴定及其降解特性,微生物丰度、活性与微生物群落结构多样性之间的相关性,运行条件对微生物群落的影响,微生物群落结构时空变化规律,生物膜形成机理和模型等方面的研究进展,并对今后废气处理生物滤器微生物生态学研究方向进行了展望.     

Microbial contamination in methanol biofilters inoculated with a pure strain of Pichia pastoris: A potential limitation for waste revalorization

Novel biotechnologies to valorize waste emissions are based on the use of specialized microbial groups that produce different compounds of industrial interest. On this scenario, the retention of such specific microorganisms in the system is of critical interest; however, the potential limitations of working with simplified cultures in a competitive open environment are neither fully explored nor well understood. In this work, a series of biofilters treating methanol vapors coupled with heterologous endochitinase production were used to evaluate the performance of a specialized microbial population during a typical open-to-environment operation. The biofilters were inoculated with a transformed strain of Pichia pastoris and were operated identically for about 90 days. The results showed that the biofiltration performance became diverse with time in terms of the elimination capacity (EC) shifting from a variation coefficient of 1.5% (EC = 274 ± 24, 279 ± 5, and 281.9 ± 25 g/[m³ h]) at the beginning of the operation to 33% (EC = 297 ± 9, 338 ± 7, and 341 ± 2 g/[m³ h]) at the end of operation. Epifluorescence analysis and cloning-sequencing suggested that P. pastoris remained as the dominant microorganism of methanol degradation, whereas diverse airborne bacteria, including Ochrobactrum spp. and Klebsiella oxytoca, played a secondary role possibly associated with the consumption of intermediates. Overall, this study found that low diversity systems operated under non-sterile conditions could be susceptible to contamination with external microorganisms causing a diversifying behavior at the performance and microbial community levels. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2715, 2019     

Assessing the potential of foamed clay as a biological aerated filter (BAF) medium

Materials used previously as biological aerated filter (BAF) media have not combined optimal biofilm supporting properties with optimal wear characteristics. Increasing its bentonite content decreased the attrition rate and friability of foamed clay. Although the altered medium exhibited less surface roughness, results from small-scale reactors confirmed that it had maintained its biological attributes. This suggests that surface roughness has a limited influence on biofilm formation.     

Enhancement of gas-liquid mass transfer rate of apolar pollutants in the biological waste gas treatment by a dispersed organic solvent

Dispersed water-immiscible solvents are known to enhance oxygen transfer rates in oxygen-limited aerobic fermentations. Here, this technique is applied to improve the mass transfer rate of poorly water-soluble gaseous pollutants during the biological treatment of waste gases. In a stirred-tank reactor, the enhancement of mass transfer rates was studied as a function of the pollutant solubility in water. The solvent used was FC40 (up to 10% v/v) and the model gaseous pollutants were toluene and oxygen (moderately and poorly water-soluble, respectively).

The overall volumetric mass transfer coefficient from the gas to the bulk liquid (k_la_gl) was measured under nonsteady-state conditions in the absence of micro-organisms. It was found to be essentially constant for the solvent volume fractions tested and for both toluene and oxygen. Using the values of k_la_gl and the partition coefficient gas/liquid (m_gl), the enhancement of the mass transfer rate by solvent addition could be predicted theoretically. A good agreement between the theoretical evaluation and the experimental results from experiments in the presence of biological consumption was observed. An enhancement of the mass transfer rate by a factor of 1.1 was found for toluene using a dispersion containing 10% (v/v) FC40 while the oxygen transfer rate increased by a factor of two at the same solvent volume fraction. It was further demonstrated theoretically for other gaseous compounds that the addition of solvent has a more pronounced effect on the enhancement of the transfer rate in the case of poorly water-soluble compounds compared to moderately water-soluble ones.     

Ethene removal from a synthetic waste gas using a dry biobed

A packed granular activated carbon (GAC) biobed, inoculated with the ethane-degrading strain Mycobacterium E3, was used to study ethene removal from a synthetic waste gas. Ethene, for which the dimensionless partition coefficient for an air-water system at 20 degrees C is about 7.6, was used as a model compound for poorly water soluble gaseous pollutants. In a first mode or operation, the GAC biobed was sprinkled intermittently and the waste gas influent was continuously pre-humidified, establishing relatively moist conditions (water content >40% to 45%). A volumetric ethene removal rate of 0.382 kg COD . m(-3) . d(-1) (0.112 kg ethene . m(-3) . d(-1)) was obtained for an influent concentration of 125 ppm, a superficial waste gas velocity of 3.6E-3 m . s(-1) and a pseudo residence time of 45 s. However, in the second mode of operation, omitting the pre-humidification of the waste gas influent and establishing a "dry" biobed (water content <40% to 45%), and thus obtaining better mass transfer to the biofilm, the ethene removal could be doubled for otherwise comparable operating parameters. Furthermore, under decreased wetting and for the given experimental conditions (influent concentration 125 to 816 ppm, waste gas superficial velocity 3.0E-3 m .s(-1), pseudo waste gas residence time 43 s), the ethene removal was not limited by mass transfer of ethene through the water layer covering the biofilm. (c) 1994 John Wiley & Sons, Inc.     

Field applications of a bio-trickling filter for the removal of nitrogen oxides from flue gas

A bio-trickling filter (BTF) packed with polyhedral spheres was used to remove nitrogen oxides (NOx) from the flue gas of a coal-fired power plant. The BTF system consistently removed 64–95% of the NOx after start-up and acclimation under dynamic conditions (e.g., 120–240 m³/h flue gas flow rate and inlet 300–900 mg NOx/m³). Scanning electron microscopy of the biofilms that were formed showed a shift in the predominating bacteria. Analyses by PCR-denaturing gradient gel electrophoresis showed that the naturally-selected mixed cultures in the biofilm under a flue gas environment were mainly Klebsiella sp. and Pseudomonas sp.     

Development and operation of a trickling biofilter system for continuous treatment of gas-phase trichloroethylene

A parallel trickling biofilter (TBF) system that consists of two TBFs units in parallel, one for biodegradation of trichloroethylene (TCE) and the other for reactivation of an inactivated biofilm, was developed and operated for continuous treatment of gas-phase TCE by Burkholderia cepacia G4. For inlet loadings below 8.6 mg TCE l^–1 d^–1, complete removal of TCE was achieved. The maximal TCE elimination capacity was 17 mg l^–1 d^–1.     

Biofilter performance and characterization of a biocatalyst degrading alkylbenzene gases

A biofilter treating alkylbenzene vapors was characterized for its optimal running conditions and kinetic parame-ters. Kinetics of the continuous biofilter were compared to batch kinetic data obtained with biofilm samples as well as with defined microbial consortia and with pure culture isolates from the biofilter. Both bacteria and fungi were present in the bioreactor. Five strains were isolated. Two bacteria, Bacillus and Pseudomonas, were shown to be dominant, as well as a Trichosporon strain which could, however, hardly grow on alkylbenzenes in pure culture. The remaining two strains were most often overgrown by the other three organisms in liquid phase batch cultures μ _max, K_S, K_I values and biodegradation rates were calculated and compared for the difterent mixed and pure cultures. Since filter bed acidification was observed during biofiltration studies reaching a pH of about 4, experiments were also undertaken to study the influence of pH on performance of the different cultures. Biodegradation and growth were possible in all cases, over the pH range 3.5–7.0 at appreciable rates, both with mixed cultures and with pure bacterial cultures. Under certain conditions, microbial activity was even observed in the presence of alkylbenzenes down to pH 2.5 with mixed cultures, which is quite unusual and explains the ability of the present biocatalyst to remove alkylbenzenes with high efficiency in biofilters under acidic conditions.     

废气生物处理设施排放的微生物气溶胶逸散特征、影响因素与暴露风险研究进展

生物处理技术因其具有高效、成本低廉、操作简便、清洁、无二次污染等特点,已被广泛应用于废气处理方面,但微生物气溶胶会作为二次污染物从废气处理设施排放到周围空气中。由于携带和传播有害微生物,微生物气溶胶对人体健康造成潜在危害和风险。废气生物处理设施既是微生物气溶胶的“汇”,也是微生物气溶胶的“源”。本文阐述了废气生物处理设施微生物气溶胶的逸散水平、群落结构和粒径分布特征,分析了其形成原因、主要来源、影响因素和暴露风险,为废气生物处理设施产生的微生物气溶胶的识别和控制技术研究提供科学依据和参考。     

Enhancement of ethene removal from waste gas by stimulating nitrification

The treatment of poorly water soluble waste gas compounds,such as ethene, is associated with low substrateconcentration levels in the liquid phase. This lowconcentration level might hamper the optimal development ofa microbial population. In this respect, the possible benefit ofintroducing nitrifying activity in the heterotrophic removal ofethene at moderate concentrations (< 1000 ppm) from awaste gas was investigated. Nitrifying activity is known to beassociated with (i) the production of soluble microbialproducts, which can act as (co-)substrates for heterotrophicmicro-organisms and (ii) the co-oxidation of ethene. Theused reactor configuration was a packed granular activatedcarbon biobed inoculated with the heterotrophic strain Mycobacterium E3. The nitrifying activity was introduced byregular submersion in a nitrifying medium prepared from (i)compost or (ii) activated sludge. In both cases a clearenhancement of the volumetric removal rate of ethene couldbe observed. When combined with a NH₃ dosage on adaily basis, a gradual increase of the volumetric removal rateof ethene could be observed. For a volumetric loading rateof 3 kg ethene-COD·m^-3·d^-1, the volumetric removal rate could thus be increased with a factor1.8, i.e. from 0.72 to a level of 1.26 kgethene-COD·m^-3·d^{- 1}.     

Purification of waste gas containing high concentration trimethylamine in biotrickling filter inoculated with B350 mixed microorganisms

A biotrickling filter packed with ceramic particles and seeded with B350 microorganisms was applied to remove trimethylamine (TMA) from gaseous waste. A 100% removal efficiency (RE) was obtained when the empty bed residence time (EBRT) was larger than 110 s at an inlet concentration of 0.30 mg/L. Maximum elimination capacity (EC) was 13.13 g m⁻³ h⁻¹ (RE = 64.7%) at 55 s of EBRT. TMA concentrations <0.20 mg/L at 83 s of EBRT did not affect the REs (100%). Maximum EC was 13.95 g m⁻³ h⁻¹ (RE = 78.1%) at a TMA concentration of 0.42 mg/L. Approximately 53.1% of the carbon in TMA was completely mineralized. Bacterial community analysis in the bioreactor revealed more than 21 species in a stable state. Based on all these results, biotrickling filter inoculated with B350 microorganisms is deemed highly capable of ridding waste gas of TMA.