Improvement of Process Stability of Microbiological Quinoline Degradation in a Three‐Phase Fluidized Bed Reactor

The biological degradation of quinoline by suspended and immobilized Comamonas acidovorans was studied under continuous and discontinuous operating conditions in a three‐phase fluidized bed reactor. C. acidovorans degrades quinoline into biomass and carbon dioxide. Quinoline and the intermediates of its metabolic pathway are found only by quinoline shockloads. The continuous degradation of quinoline by suspended biomass was only possible, if the dilution rate was less than the growth rate (μ_max =0.42 h^–1) and the concentration of a shockload was less than 1 kg/m³. A concentration greater than 1 kg/m³ led to an irreversible damage of the cells. Hence, two different carrier materials were used for immobilization by attachment, to increase the stability of the process. Using immobilization of biomass on carriers decouples the hydrodynamic retention time and the growth rate of the microorganisms. A comparison of the carrier material showed no differences with respect of activity and stability of the biofilm. The process stability of a three‐phase fluidized bed reactor was increased by immobilized biomass. The degradation of toxic shockloads was only possible with immobilized biomass. A dynamic model has been developed to describe the concentration profile of quinoline, 2‐hydroxyquinoline as metabolite and the suspended biomass. A comparison of the measured and calculated values showed good agreement.     

Denitrification Performance of Pseudomonas denitrificans in a Fluidized‐Bed Biofilm Reactor and in a Stirred Tank Reactor

Denitrification of a synthetic wastewater containing nitrates and methanol as carbon source was carried out in two systems – a fluidized‐bed biofilm reactor (FBBR) and a stirred tank reactor (STR) – using Pseudomonas denitrificans over a period of five months. Nitrogen loading was varied during operation of both reactors to assess differences in the response to transient conditions. Experimental data were analyzed to obtain a comparison of denitrification kinetics in biofilm and suspended growth reactors. The comparison showed that the volumetric degradation capacity in the FBBR (5.36 kg _N · m^–3 · d^–1) was higher than in the STR, due to higher biomass concentration (10 kg _BM · m^–3 vs 1.2 kg _BM m^–3).     

Biodegradation Kinetic Studies on Phenol in Internal Draft Tube (Inverse Fluidized Bed) Biofilm Reactor Using Pseudomonas fluorescens: Performance Evaluation of Biofilm and Biomass Characteristics

The bioremediation potential of Pseudomonas fluorescens was studied in an internal draft tube (inverse fluidized bed) biofilm reactor (IDTBR) under batch recirculation conditions using synthetic phenol of various concentrations (400, 600, 800, 1000, and 1200 mg/L). The performance of IDTBR was investigated and the characteristics of biomass and biofilm were determined by evaluating biofilm dry density and thickness, bioparticle density, suspended and attached biomass concentration, chemical oxygen demand, and phenol removal efficiency. Biodegradation kinetics had been studied for the suspended biomass culture and biofilm systems. Suspended biomass followed substrate inhibition kinetics, and the experimental data fitted well with the Haldane model. The correlation coefficient, R ², and root-mean-square error (RMSE) obtained for the Haldane model with respect to specific growth rate were .9389 and .00729, respectively, and with respect to specific phenol consumption rate were .9259 and .00972, respectively. It was also observed experimentally that biofilm overcame substrate inhibition effect and fitted the same to the Monod model (R ² = .9831, RMSE = .00884 for specific growth rate and R ² = .9686, RMSE = .00912 for specific phenol consumption rate).     

Bed expansion characteristics of liquid fluidized particles with attached microbial growth

The bed expansion behavior of liquid fluidized beds of char particles coated with attached microbial growth of denitrifying mixed bacteria was studied experimentally to obtain an expression that relates the bed expansion to the liquid velocity for liquid fluidized beds of composite particles. As for liquid beds of homogeneous spheres, the bed voidage and the liquid velocity v_z for liquid fluidized beds of biomass-coated particles were found to be related as v_z/V_i = ∈ⁿ. The correlations recommended by Richardson and Zaki for homogeneous spheres are found to be satisfactory for the estimation of the constant n, but only under certain conditions for the constant V_i.     

Organic Matter Degradation Kinetics in an Anaerobic Thermophilic Fluidised Bed Bioreactor

This paper describes the thermophilic anaerobic biodegradation of wine distillery wastewater (vinasses) in a laboratory fluidised bed reactor (AFB) with a porous support medium. The experimental protocol was defined to examine the effect of increasing organic loading rate on the efficiency of AFB and to report on its steady-state performance. Moreover, in order to evaluate treatment efficiency and to investigate fermentation kinetics in an AFB reactor, experimental data were used to estimate the ‘active biomass’ concentration using an autocatalytic kinetic model proposed in this paper, since viable biomass in AFB reactors is very difficult to measure experimentally. The AFB reactor was subjected to a program of steady-state operation over a range of hydraulic retention time (HRTs) of 2.5–0.37 days and organic loading rate (OLRs) up to 5.88 kgCOD/m³/day in order to evaluate its treatment capacity. The AFB reactor was initially operated with organic loading rate of 5.88 kgCOD/m³/day and HRT of 2.5 days. The chemical oxygen demand (COD) removal efficiency was found to be 96.5% in the reactor while the methane content of biogas produced in the digester reached 1.08 m³/m³digester/day. Over 94 days operating period, an OLR of 32 kgCOD/m³/day at a food-to-micro-organisms (F:M) ratio of 0.55 kgCOD/kgVS_att/day was achieved with 81.5% COD removal efficiency in the experimental AFB reactor. At this moment, the methane content of biogas produced in the digester reached 9.0 m³/m³digester/day. The proposed kinetic model is able to estimate kinetic constants of the biodegradation process: non-biodegradable substrate (S_nb) and active adhered biomass concentration (X_a). The parameters of the model were obtained by the curve-fitting method to the proposed kinetic model using the COD as substrate of the anaerobic process and assuming a maximum specific μ_max: 0.72 per day. The comparison of the measured concentration of volatile attached solids (VS_att) with the estimated ‘active’ biomass concentration indicated that extremely high ‘active biomass’ concentrations can be maintained in the system because biofilm thickness is limited by the liquid flow rate applied. This is due to the fact that the anaerobic fluidised bed system retains the growth support medium in suspension by drag forces exerted by upflowing wastewater, and the distribution of biomass holdup (in the form of a biofilm) is thus relatively uniform.     

Influence of synthetic packing materials on the gas dispersion and biodegradation kinetics in fungal air biofilters

The biodegradation of toluene was studied in two lab-scale air biofilters operated in parallel, packed respectively with perlite granules (PEG) and polyurethane foam cubes (PUC) and inoculated with the same toluene-degrading fungus. Differences on the material pore size, from micrometres in PEG to millimetres in PUC, were responsible for distinct biomass growth patterns. A compact biofilm was formed around PEG, being the interstitial spaces progressively filled with biomass. Microbial growth concentrated at the core of PUC and the excess of biomass was washed-off, remaining the gas pressure drop comparatively low. Air dispersion in the bed was characterised by tracer studies and modelled as a series of completely stirred tanks (CSTR). The obtained number of CSTR (n) in the PEG packing increased from 33 to 86 along with the applied gas flow (equivalent to empty bed retention times from 48 to 12 s) and with operation time (up to 6 months). In the PUC bed, n varied between 9 and 13, indicating that a stronger and steadier gas dispersion was achieved. Michaelis–Menten half saturation constant (k _m) estimates ranged 71–113 mg m⁻³, depending on the experimental conditions, but such differences were not significant at a 95% confidence interval. The maximum volumetric elimination rate (r _m) varied from 23 to 50 g m⁻³ h⁻¹. Comparison between volumetric and biomass specific biodegradation activities indicated that toluene mass transfer was slower with PEG than with PUC as a consequence of a smaller biofilm surface and to the presence of larger zones of stagnant air.     

Evaluation of biological nutrient removal from wastewater by Twin Circulating Fluidized Bed Bioreactor (TCFBBR) using a predictive fluidization model and AQUIFAS APP

A two-phase and three-phase predictive fluidization model based on the characteristics of a system such as media type and size, flow rates, and reactor cross sectional area was proposed to calculate bed expansion, solid, liquid and gas hold up and specific surface area (SSA) of the biofilm particles. The model was subsequently linked to 1d AQUIFAS APP software (Aquaregen) to model biological nutrient removal in two phase (anoxic) and three phase (aerobic) fluidized bed bioreactors. The credibility of the proposed model for biological nutrient removal was investigated using the experimental data from a Twin Circulating Fluidized Bed Bioreactors (TCFBBR) treating synthetic and municipal wastewater.The SSA of bio-particles and volume of the expanded bed were simulated as a function of operational parameters. Two-sided t-tests demonstrated that simulated SCOD, NH₄-N, NO₃-N, TN, VSS and biomass yields agreed with the experimental values at the 95% confidence level.     

Simplified Modeling of Simultaneous Reaction Kinetics of Carbon Oxidation and Nitrification in Biofilm Processes

Batch experiments with varying initial substrate concentrations and biomass volumes were performed in a three‐phase fluidized bed biofilm reactor treating simulated domestic wastewater to study the simultaneous carbon oxidation and nitrification in the biofilm process. A simplified mass balance equation for the biofilm was proposed and five different kinetic rate equations were used to match the actual data. The kinetic parameters were obtained by nonlinear regression analysis on a set of two differential equations representing the simultaneous carbon oxidation and nitrification. The competitive inhibition model incorporating the effects of total organic carbon (TOC) concentrations on nitrification rates was the best‐suited model based on the average r². In this model, oxygen concentration and its affinity constants were not included. Instead, it was assumed that the rate of carbon oxidation is independent of the NH₄⁺‐N, while nitrification is affected by TOC. The number of parameters was successfully minimized without reducing its ability to accurately predict the bulk concentration time course, which would reduce computational complexity and possibly enhance the availability for an actual wastewater treatment process.     

Maximizing the productivity of catalytic biofilms on solid supports in membrane aerated reactors

A new solid support membrane aerated biofilm reactor was designed for the synthesis of enantiopure (S)‐styrene oxide utilizing Pseudomonas sp. strain VLB120ΔC growing in a biofilm as biocatalyst. In analogy to traditional packed bed systems, maximizing the volumetric oxygen mass transfer capability (k_La) was identified as the most critical issue enabling a consistent productivity, as this parameter was shown to directly influence biofilm growth and biotransformation performance. A microporous ceramic unit was identified as an ideal microenvironment for biofilm growth and for efficient oxygen transfer. A uniform and dense biofilm developed on this matrix. Due to this dual function, the reactor configuration could be significantly simplified by eliminating additional packing materials, as used in traditional packed bed reactors. Up to now, a maximum productivity of 28 g L day^?1 was achieved by integrating an in situ substrate feed and an in situ product recovery technique based on a silicone membrane. The system was stable for more than 30 days before it was actively terminated. Biotechnol. Bioeng. 2010;106: 516–527. © 2010 Wiley Periodicals, Inc.     

Application of fluidized carrier to bacterial sulphate-reduction in industrial wastewaters purification

Summary Comparative laboratory investigation of two types bioreactors with iron as a carrier of biofilm was made. One was a packed bed reactor and the another was fluidized bed. The results showed that maximum productivity of carrier in fluidized bed bioreactor {7,97 g/m²·d} is two times higher than productivity of carrier in packed bed one {3,45 g/m²·d}.     

Biodegradation of dichloromethane in waste water using a fluidized bed bioreactor

Summary Biological treatment of a synthetic waste water containing 120 mM dichloromethane (10.2g/l) was carried out under aerobic conditions using dichloromethane-degrading bacteria as an inoculum. The bacteria were adsorbed to support particles and grown in a fluidized bed bioreactor. Charcoal and sand particles were compared as support materials with regard to abrasion, the maximum degradation rate for dichloromethane and the stability of the biological activity in the system.The use of charcoal led to the incorporation of coal dust into the biomass and to an uncontrollable thickness of the biofilm. Therefore the system became unstable and the biological activity decreased. In contrast sand as support material was indifferent to abrasion and allowed biofilm thickness to be controlled. The dichloromethane degrading capacity of the bioreactor increased during the first 30 days. It reached a steady state level of 1.6 g CH₂Cl₂/lxh. Dichloromethane concentration in the effluent was <0.01 mM (<0.85 mg/l) and consequently the degradation efficiency better than 99.99%.     

Influence of biomass accumulation on bed expansion characteristics of a down-flow anaerobic fluidized-bed reactor

This article describes the bed expansion characteristics of a down-flow anaerobic fluidized bed reactor treating a synthetic wastewater. Experiments were carried out in a 0.08 m diameter and 1 m length PVC column. The carrier used was ground perlite (an expanded volcanic rock). Particles characteristics were 0.968 mm in diameter, specific density of 213 kg x m-3 and Umf (minimal fluidization velocity): 2.3 m x h-1. Experimental data of terminal velocities and bed expansion parameters at several biofilm thicknesses were compared to different models predicting the bed expansion of up-flow and down-flow fluidized beds. Measured bed porosities at different liquid superficial velocities for the different biofilm thicknesses were in agreement with the Richardson-Zaki model, when Ut (particle terminal velocity) and n (expansion coefficient) were calculated by linear regression of the experimental data. Terminal velocities of particles at different biofilm thicknesses calculated from experimental bed expansion data, were found to be much smaller than those obtained when Cd (drag coefficient) is determined from the standard drag curve (Lapple and Sheperd, 1940) or with others' correlations (Karamanev and Nikolov, 1992a,b). This difference could be explained by the fact that free-rising particles do not obey Newton's law for free-settling, as proposed by Karamanev and Nikolov (1992a,b) and Karamanev et al. (1996). In the present study, the same free-rising behavior was observed for all particles (densities between 213 and 490 kg x m-3).     

A Model for the Biofiltration of Butyl Acetate and Xylene Mixtures by a Trickle‐Bed Air Biofilter

A mathematical model that incorporates the rates of the mass transfer process and the biofilm reaction is presented to predict the performance of a trickle‐bed air biofilter (TBAB) for treating butyl acetate and xylene mixtures. A thorough understanding of the factors that influence these rates is necessary before the practical application of a TBAB for treating many kinds of pure and mixed volatile organic compounds (VOC) in the air stream. The model presented consists of a set of mass balance equations for butyl acetate, xylene and oxygen in the bulk gas phase and within the biofilm. The butyl acetate and xylene concentration profiles of the gas phase predicted by the model were in good agreement with the measured data documented in a previous study. The most relevant parameters were evaluated in a sensitivity analysis to determine their respective effects on the model performance. Four parameters were identified to strongly influence the model performance, the surface area of the biofilm per volume unit of the packing material (A_S), the empty‐bed residence time (EBRT), the maximum specific growth rate of the microorganism (μ_m), and the microbial yield coefficient (Y). The practical application of the model to derive the performance equation is also presented and discussed. This equation makes it possible to simultaneously obtain a relatively high VOC removal efficiency and to minimize the capital cost.     

Performance of inverse anaerobic fluidized bed reactor for treating high strength organic wastewater during start-up phase

The aim of this work is to report on the physical characteristics of carrier material (perlite), biomass growth on the carrier material and the biogas production during an apparent steady state period in an inverse anaerobic fluidized bed reactor (IAFBR) for treating high strength organic wastewater. Before starting up the reactor, physical properties of the carrier material were determined. One millimeter diameter perlite particle is found to have a wet specific density of 295 kg/m(3) with specific surface area of 7.010 m(2)/g. This material has provided a good surface for biomass attachment and development. The biofilm concentration (in terms of attached volatile solids (AVS)) attached to carrier material was found to be 0.66 g(AVS)/g(solid). Most particles have been covered with a thin biofilm of uniform thickness. Once the inverse anaerobic fluidized bed system reached the steady state, the organic load was increased step wise by reducing hydraulic retention time (HRT) from 2 days to 0.16 day, while maintaining the constant feed of chemical oxygen demand (COD) concentration. This system has achieved 84% COD removal and reached the biogas production of 13.22 l/l/d at an organic loading rate (OLR) of 35 kgCOD/m(3)/d.     

A novel in vitro flat‐bed perfusion biofilm model for determining the potential antimicrobial efficacy of topical wound treatments

Aims: To develop an in vitro flat‐bed perfusion biofilm model that could be used to determine the antimicrobial efficacy of topically applied treatments. Methods and Results: Pseudomonas aeruginosa and Staphylococcus aureus biofilms were grown within continuously perfused cellulose matrices. Enumeration of the biofilm density and eluate was performed at various sampling times, enabling determination of the biofilm growth rate. Two antimicrobial wound dressings were applied to the surface of mature biofilms and periodically sampled. To enable real‐time imaging of biofilm growth and potential antimicrobial kinetics, a bioluminescent Ps. aeruginosa biofilm was monitored using low‐light photometry. Target species produced reproducible steady‐state biofilms at a density of c. 10⁷ per biofilm support matrix, after 24‐h perfusion. Test dressings elicited significant antimicrobial effects, producing differing kill kinetic profiles. There was a good correlation between photon and viable count data. Conclusions: The model enables determination of the antimicrobial profile of topically applied treatments against target species biofilms, accurately differentiating bactericidal from bacteriostatic effects. Moreover, these effects could be monitored in real time using bioluminescence. Significance and Impact of the Study: This is the first in vitro biofilm model which can assess the antimicrobial potential of topical therapies in a dynamic growth environment.     

Cellulase production by Aspergillus niger in biofilm, solid-state, and submerged fermentations

Cellulase production by Aspergillus niger was compared in three different culture systems: biofilm, solid-state, and submerged fermentation. Biofilm and solid-state fermentations were carried out on perlite as inert support, and lactose was used as a carbon source in the three culture systems. In cryo-scanning electron microscopy, biofilm and solid-state cultures gave similar morphological patterns and confirmed that both spore first attachment and hyphal adhered growth are helped by the production of an adhesive extracellular matrix. Biofilm cultures produced higher cellulase activities than those in submerged and solid-state cultures (1,768, 1,165, and 1,174 U l⁻¹, respectively). Although biofilm cultures grew less than the other cultures, they produced significantly higher cellulase yields (370, 212, and 217 U g⁻¹ lactose, respectively) and volumetric productivities (24, 16, and 16 U l⁻¹ h⁻¹, respectively). Likewise, endoglucanase and xylanase activities were higher in biofilm cultures. Under the conditions tested, it seems that fungal attached growth on perlite may favor better enzyme production. Biofilms are efficient systems for cellulase production and may replace solid-state fermentation. Biofilm fermentation holds promise for further optimization and development. The results of this work reveal that fungal biofilms may be used for the commercial production of cellulase employing the technology developed for submerged fermentation at high cell densities.     

Influence of waste water composition on biofilm development in laboratory methanogenic fluidized bed reactors

Summary The influence of the volatile fatty acid composition of waste waters on biofilm development and on the time course of reactor start-up was investigated in laboratory scale fluidized bed reactors. It was found that biofilm development proceeded in a similar way with either acetate, butyrate, propionate or a mixture of these compounds as carbon source in the waste water. Startup was retarded, however, with propionate as sole carbon source. Scanning electron microscopic examination revealed that immobilization of bacteria on the sand used as adhesive support initially occurred in crevices and that thereupon the surface of the sand particles became colonized. The composition of the newly developed biomass was determined when reactors reached steady state. Significant differences in the relative substrate spectra and in the amounts of hydrogenotrophic and acetotrophic methanogenic bacteria were measured. The differences reflected the differences in the composition of the waste waters. The results obtained emphasize the role of the structure of the carrier surface in start-up of methanogenic fluidized bed reactors.Abbreviations used Aw ash weight - COD chemical oxygen demand - EB fluidized bed - hbi vitamin B₁₂-HBI - spt sarcinapterin - UASB upflow anaerobic sludge blanket - VFA volatile fatty acid - VSS volatile suspended solids - Ww wet weight     

A new post-treatment system for anaerobic effluents containing a high Ca2+ content

A novel reactor concept has been developed that combines Ca²⁺ removal and BOD conversion under mesophilic (30 °C ) as well as under thermophilic (55 °C ) conditions. Soluble Ca²⁺, present in many industrial wastewaters, precipitates as a result of forced aeration in the aerobic bioreactor. The CaCO₃ precipitates, in turn, act as a carrier material for biofilm growth. This resulted in dense rapidly settling sludge granules covered with a biofilm on the surface. These sludge characteristics facilitate the application of hydraulic retention times of 1 h while maintaining a high biological activity in the reactor.     

Phenol and sulfide oxidation in a denitrifying biofilm reactor and its microbial community analysis

A microbial consortium attached onto a polyethylene support was used to evaluate the simultaneous oxidation of sulfide and phenol by denitrification. The phenol, sulfide and nitrate loading rates applied to an inverse fluidized bed reactor were up to 168 mg phenol–C/(l d), 37 mg S^2?/(l d) and 168 mg NO₃^?–N/(l d), respectively. Under steady state operation the consumption efficiencies of phenol, sulfide and nitrate were 100%. The N₂ yield (g N₂/g NO₃^?–N) was 0.89. The phenol was mineralized resulting in a yield of 0.82 g bicarbonate–C/g phenol–C and sulfide was completely oxidized to sulfate with a yield of 0.99 g SO₄^2?–S/g S^2?. 16S rRNA gene-based microbial community analysis of the denitrifying biofilm showed the presence of Thauera aromatica, Thiobacillus denitrificans, Thiobacillus sajanensis and Thiobacillus sp. This is the first work reporting the simultaneous oxidation of sulfide and phenol in a denitrifying biofilm reactor.