Heterogeneous biofilm activity in a segregated anaerobic fluidized bed bioreactor

Bed segregation in a fluidized bed bioreactor profoundly influenced biofilm thickness and microbial activities of the biofilm along the bed height. Bioparticles coated with a thin biofilm, observed at the bottom of the reactor, had a higher specific activity in propylene glycol and n-propanol degradation than in thick biofilms developed at the top of the reactor. Although no significant difference was observed in specific activity for propionate and acetate along the reactor flow axis, more total propionate and acetate conversion occurred in regions of thicker biofilm accumulation.     

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     

Biological phenol degradation in a gas-liquid-solid fluidized bed reactor

Biological phenol degradation was performed experimentally in a gas-liquid-solid fluidized bed bioreactor using a mixed culture of living cells immobilized on activated carbon particles. A comprehensive model was developed for this system utilizing double-substrate limiting kinetics. The model was used to simulate the effects of changing inlet phenol concentration and biofilm thickness on the rate of biodegradation for two different types of support particles. The model shows that gas-liquid mass transfer is the limiting step in the rate of phenol biodegradation when the phenol loading is high.     

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%.     

Biofilm reactors: an experimental and modeling study of wastewater denitrification in fluidized-bed reactors of activated carbon particles

A fluidized-bed biofilm reactor using activated carbon particles of 1.69 mm diameter as the support for biomass growth and molasses as the carbon source is used for wastewater denitrification.The start-up of the reactor was successfully achieved in 1 week by using a liquor from garden soil leaching as the inoculum and a superficial velocity u(0) = 5u(mf). Typical biofilm thickness is 800 mum; therefore covered activated carbon particles have 3.3 mm in diameter.Reactor hydrodynamics was studied by tracer (KCl solution) experiments. The analysis based on residence time distribution theory involved a model with axial dispersion flow and tracer diffusion with linear adsorption inside the biofilm. Peclet numbers higher than 100 were found, allowing the plug flow assumption for the reactor model.Experimental profiles of nitrate and nitrite species were explained by a kinetic model of two consecutive zero-order reactions coupled with substrate diffusion inside the biofilm. Under the operating conditons used thick biofilms were obtained working in a diffusion-controlled regime.Comparison is made with results obtained in the same reactor with sand particles as the support for biomass growth. Activated carbon as the support has the following advantages: good adsorptive characteristics, homogeneous biofilm thickness along the reactor, and easy restart-up of the reactor. (c) 1992 John Wiley & Sons, Inc.     

Preparation of fungal starter culture in liquid fluidized bed reactor

Summary Pregerminated Trichoderma reesei (Rut C-30) spores were grown on corncob particles in a liquid fluidized bed reactor (LFBR). Hyphal mass covered particles were recovered from the top of the reactor in 24 h and used as starters for solid substrate fermentation. The starter from LFBR gave better biomass production than spore or mycelial inoculum.     

Biofilm development in laboratory methanogenic fluidized bed reactors

Biofilm development on sand with different heterogeneous inocula was studied in laboratory-scale methanogenic fluidized bed reactors. Both the course of biofilm formation during reactor start-up and the bacterial composition of newly developed biofilms at steady-state were found to be similar irrespective of the type of inoculum applied. Biofilm formation proceeded according to a fixed pattern that could be subdivided in three consecutive phases, designated as the lag phase, biofilm production phase, and steady-state phase. Methanogenic activity and biomass content of the fluidized bed granules were found to be accurate parameters of the course of biofilm formation. More indirect parameters monitored did not give unambiguous results in all instances. The composition of the newly developed biomass as assessed on the basis of potential methanogenic activities on different substrates and of the concentration of specific methanogenic cofactors was consistent with electron microscopic observations.     

Simulation of growth and detachment in biofilm systems under defined hydrodynamic conditions

Detachment from biofilms was evaluated using a mixed culture biofilm grown on primary wastewater in a tube reactor. The growth of biofilms and the detachment of biomass from biofilms are strongly influenced by hydrodynamic conditions. In a long-term study, three biofilms were cultivated in a biofilm tube reactor. The conducted experiments of biofilm growth and detachment can be divided into three phases: 1) an exponential phase with a rapid increase of the biofilm thickness, 2) a quasi-steady-state with spontaneous fluctuation of the biofilm thickness between 500 and 1,200 microm in the investigated biofilm systems, and 3) a washout experiment with increased shear stress in three to four steps after several weeks of quasi-steady-state. Whereas the biofilm thickness during the homogeneous growth phase can be regarded constant throughout the reactor, it was found to be very heterogeneous during the quasi-steady-state and the washout experiments. Growth and detachment during all three phases was simulated with the same one-dimensional biofilm model. For each of the three phases, a different detachment rate model was used. During the homogeneous growth phase, detachment was modeled proportional to the biofilm growth rate. During the quasi-steady-state phase, detachment was described by random detachment events assuming a base biofilm thickness. Finally, the washout experiment was simulated with detachment being a function of the biofilm thickness before the increase of the shear stress.     

Prediction of substrate consumption rate, average biofilm density and active thickness for a thin spherical biofilm at pseudo-steady state

In this work, a new approach is proposed to evaluate substrate consumption rate, average biofilm density and active thickness of a spherical bioparticle in a completely mixed fluidized bed system. The substrate consumption rate and average biofilm density are predicted for a given biofilm surface substrate concentration and operational biofilm thickness. A diffusion and reaction model is developed with an effective diffusion coefficient that depends on the average biofilm density. This approach, a first in the literature, predicts the optimum average density of a biofilm to yield the maximum substrate consumption rate within the biofilm. A reasonable correlation was observed between the model prediction and experimental results for substrate consumption rate and average biofilm density for thin and fully active biofilms.     

Biodegradation by immobilized bacteria in an airlift-loop reactor-influence of biofilm diffusion limitation

Naphthalene-2-sulfonate was degraded by submerse growing Pseudomonads in a chemostat culture. The kinetic parameters for the Monod equation, including Pirts maintenance energy, were calculated from these experiments regarding naphthalene-2-sulfonate as substrate and oxygene as cosubstrate. By immobilizing the bacteria on sand particles, the degradation of naphthalene-2-sulfonate was carried out in a specialy designed three-phase airlift-loop reactor in a completely fluidized state. From these experiments, the influence of biofilm diffusion limitation on reaction kinetics and criteria for stable biofilm formation on sand particles were obtained.     

Kinetic model for dynamic response of three-phase fluidized bed biofilm reactor for wastewater treatment

Step changes in inlet concentration has been introduced into the completely mixed three-phase fluidized bed biofilm reactor treating simulated domestic wastewater to study the dynamic behavior of the system and to establish the suitable kinetic model from the response curve. Three identical reactors having different biomass volumes were operated in parallel. It was found that the response curves showed second-order characteristics, and thus at least two first-order differential equations are necessary to simulate the substrate and biomass response curves. Nonlinear regression analysis was performed using different types of rate equations and their corresponding kinetic parameters were used to simulate the theoretical response curve using the Runge–Kutta numerical integration method. As a result, although various types of conventional biokinetic models such as Monod, Haldane and Andrew types were examined, all the theoretical substrate response curves underestimated time constants compared to the actual substrate response plots. On the other hand, the theoretical curve of the kinetic model that incorporates adsorption term has best fit to the actual response in most of the cases. Thus, it was concluded that adsorption of substrate onto biofilm and carrier particles has significant effect on the dynamic response in biofilm processes.     

Some fluidization characteristics of biological beds

The free-fall terminal velocity of particles coated with a nitrifying biofilm was investigated. The drag force exerted by the liquid on a biocoated particle was found larger than that for an uncoated particle. A new formula for the drag coefficient was proposed. The wet density of biofilm was estimated as 1.14 g/cm(3). A proposed modification of the Zaki-Richardson method was successfully used for calculations of the porosity of a fluidized bed.     

Prediction of average biofilm density and performance of a spherical bioparticle under substrate inhibition

In this article, a model was proposed to predict the average performance and biofilm density of a spherical bioparticle under substrate inhibition in a fluidized bed system. The average biofilm density and substrate consumption rates were predicted for a definite biofilm thickness and limiting substrate concentrations. A diffusion and reaction model was developed over the bioparticle with biofilm-density dependent effective diffusion coefficients for maximum substrate consumption theory. This theory predicts the optimum density of a biofilm to yield a maximum substrate consumption rate within the biofilm, developed for the first time with this study and experimentally verified. A good correlation was observed between the model prediction and experimental results for biofilm density and substrate consumption rates. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 319-329, 1997.     

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.     

Operation of a three-phase biofilm fluidized sand bed reactor for aerobic wastewater treatment

A biofilm fluidized sand bed column reactor (14 L) has been operated in the three-phase mode on a soluble glucose-yeast hydrolysate substrate in which the biofilm-sand phase (1-2.5 L) was suspended by direct aeration of the bed. Within two weeks a tight biofilm was formed whose activity resulted in a 90% reduction, with loads of 10.7 kg TC/m(3)day. The residence time was 1 h. The biofilm remained intact during operation with high residence times (up to 23 h) over three weeks. Oxygen transfer coefficients varied with aeration rate and sand quantity between 0.02 and 0.04 s(-1) during non growth conditions; they decreased with increasing amounts of clean sand and were higher and relatively independent of the sand fraction with biofilm-covered sand. Aeration rates used in the 14 L reactor were 23-40 L/min (2.4-4.1 cm/s) and were sufficient to suspend 78-92% f the biofilm-covered sand. Clean sand was 50-75% suspended. Oxygen uptake rates varied between 15.4 and 23.1 mol/m(3) h.     

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).     

Adsorption with biodegradation for decolorization of reactive black 5 by Funalia trogii 200800 on a fly ash-chitosan medium in a fluidized bed bioreactor-kinetic model and reactor performance

A non-steady-state mathematical model system for the kinetics of adsorption and biodegradation of reactive black 5 (RB5) by Funalia trogii (F. trogii) ATCC 200800 biofilm on fly ash-chitosan bead in the fluidized bed process was derived. The mechanisms in the model system included adsorption by fly ash-chitosan beads, biodegradation by F. trogii cells and mass transport diffusion. Batch kinetic tests were independently performed to determine surface diffusivity of RB5, adsorption parameters for RB5 and biokinetic parameters of F. trogii ATCC 200800. A column test was conducted using a continuous-flow fluidized bed reactor with a recycling pump to approximate a completely-mixed flow reactor for model verification. The experimental results indicated that F. trogii biofilm bioregenerated the fly ash-chitosan beads after attached F. trogii has grown significantly. The removal efficiency of RB5 was about 95 % when RB5 concentration in the effluent was approximately 0.34 mg/L at a steady-state condition. The concentration of suspended F. trogii cells reached up to about 1.74 mg/L while the thickness of attached F. trogii cells was estimated to be 80 μm at a steady-state condition by model prediction. The comparisons of experimental data and model prediction show that the model system for adsorption and biodegradation of RB5 can predict the experimental results well. The approaches of experiments and mathematical modeling in this study can be applied to design a full-scale fluidized bed process to treat reactive dye in textile wastewater.     

Detachment of multi species biofilm in circulating fluidized bed bioreactor

In this study, the detachment rates of various microbial species from the aerobic and anoxic biofilms in a circulating fluidized bed bioreactor (CFBB) with two entirely separate aerobic and anoxic beds were investigated. Overall detachment rate coefficients for biomass, determined on the basis of volatile suspended solids (VSS), glucose and protein as well as for specific microbial groups, i.e., for nitrifiers, denitrifiers, and phosphorous accumulating organisms (PAOs), were established. Biomass detachment rates were found to increase with biomass attachment on carrier media in both beds. The detachment rate coefficients based on VSS were significantly affected by shear stress, whereas for protein, glucose and specific microbial groups, no significant effect of shear stress was observed. High detachment rates were observed for the more porous biofilm structure. The presence of nitrifiers in the anoxic biofilm and denitrifiers in the aerobic biofilm was established by the specific activity measurements. Detachment rates of PAOs in aerobic and anoxic biofilms were evaluated.     

The role of ash particles in the bed agglomeration during the fluidized bed combustion of rice straw

In this paper, the effects of fluidization velocity, bed temperature and fuel feeding rate on the defluidization time and agglomerate fraction in the fluidized bed combustion of rice straw were studied. The fuel ash, necks in agglomerates and coating layers of bed particles were studied by means of the scanning electron microscope, coupled with energy-dispersive spectroscopy (SEM/EDS). Results showed that the stickiness of bed particles induced by coating layers is the direct reason for bed defluidization. The alkali metals such as K and Na mainly exist in the outer layer of rice straw particles. During combustion the high temperature can cause the alkali species melting and coating the surfaces of ash particles. Consequently, ash particles become sticky and tend to adhere to the surfaces of bed particles. The large-sized ash particles may act as the necks in the formation of agglomerates. The small-sized ash particles may contribute to the formation of coating layers.