Biological denitrification in a fluidized bed

A fluidized bed biofilm reactor using sand as the carrier particle was employed to study the effects of superficial velocity on the removal of nitrates as well as on the growth of the biofilm. Velocity was found to affect significantly both nitrate removal and biofilm growth. An analysis based on heterogenous catalysis was used to describe the denitrification process. There is good agreement between analysis and experimental measurements for startup and steady-state operating conditions.     

Torrefaction of sawdust in a fluidized bed reactor

In the present work, stable fluidization of sawdust was achieved in a bench fluidized bed with an inclined orifice distributor without inert bed materials. A solids circulation pattern was established in the bed without the presence of slugging and channeling. The effects of treatment severity and weight loss on the solid product properties were identified. The decomposition of hemicelluloses was found to be responsible for the significant changes of chemical, physical and mechanical properties of the torrefied sawdust, including energy content, particle size distribution and moisture absorption capacity. The hydrophobicity of the torrefied sawdust was improved over the raw sawdust with a reduction of around 40 wt.% in saturated water uptake rate, and enhanced with increasing the treatment severity due to the decomposition of hemicelluloses which are rich in hydroxyl groups. The results in this study provided the basis for torrefaction in fluidized bed reactors.     

An experimental study on biomass air-steam gasification in a fluidized bed

The characteristics of biomass air-steam gasification in a fluidized bed are studied in this paper. A series of experiments have been performed to investigate the effects of reactor temperature, steam to biomass ratio (S/B), equivalence ratio (ER) and biomass particle size on gas composition, gas yield, steam decomposition, low heating value (LHV) and carbon conversion efficiency. Over the ranges of the experimental conditions used, the fuel gas yield varied between 1.43 and 2.57 Nm3/kg biomass and the LHV of the fuel gas was between 6741 and 9143 kJ/Nm3. The results showed that higher temperature contributed to more hydrogen production, but too high a temperature lowered gas heating value. The LHV of fuel gas decreased with ER. Compared with biomass air gasification, the introduction of steam improved gas quality. However, excessive steam would lower gasification temperature and so degrade fuel gas quality. It was also shown that a smaller particle was more favorable for higher gas LHV and yield.     

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.     

Biotreatment of s-triazine-containing wastewater in a fluidized bed reactor

Mixed cultures of microorganisms immobilized on sand were used to degrade s-triazine-containing industrial wastewater in a fluidized bed reactor. Immobilized cell concentrations of up to 18 g/L volatile suspended solids could be achieved with the s-triazines as sole nitrogen source for growth and carbon sources added at a C--N ratio of about 12. Maximal removal efficiencies of 80% of the s-triazines could be maintained only if (a) the bio-film thickness was limited to avoid oxygen deficiency and (b) the carbon source and complete wastewater (/=20-25 h.     

Hydrolysis of cellulose in a cellulase-bead fluidized bed reactor

Cellulase was immobilized in a collagen fibril matrix, and no leakage of cellulase from the collagen fibril matrix was observed. The immobilized cellulase was more stable than the native cellulase. The substrate cellulose was hydrolyzed quantitatively with immobilized cellulase. The final reaction product was identified as glucose. Immobilized cellulase was used in a fluidized bed reactor where the pressure drop of the fluidized bed reactor was low and constant. Cellulose was hydrolyzed to glucose by the cellulase-bead fluidized bed reactor. The minimum flow velocity (U_mf) was 0.5 cm/sec and the optimum flow velocity of the cellulose hydrolysis was 1 cm/sec.     

Mathematical description of bikaverin production in a fluidized bed bioreactor

Summary  Growth of Gibberella fujikuroi in submerged cultures occurs as micelles or filamentous hyphae dispersed in fluid and pellets or stable, spherical agglomerations. Gibberella fujikuroi growth, substrate consumption and bikaverin production kinetics obtained from submerged batch fermentation were fitted to three different sigmoid models: two and three-parameter Gompertz models and one Logistic model. Growth fitting was used to compare between models and select the best one by means of an F test. The best model for describing growth was the two-parameter Gompertz model and was used for glucose consumption and bikaverin production fitting. Data from eight different schemes of fermentations were analysed and parameter estimation was carried out by means of minimization of residual sum of squares. Some characteristic values obtained with the two-parameter Gompertz model fit are: μ=0.028 h⁻¹, Y_x/s=0.1089 g substrate/g biomass, α =0.1384 g product/g biomass.     

Phenol degradation in a three-phase biofilm fluidized sand bed reactor

A previous three phase fluidized sand bed reactor design was improved by adding a draft tube to improve fluidization and submerged effluent tubes for sand separation. The changes had little influence on the oxygen transfer coefficients(K _L a), but greatly reduced the aeration rate required for sand suspension. The resulting 12.5 dm³ reactor was operated with 1 h liquid residence time, 10.2dm³/min aeration rate, and 1.7–2.3 kg sand (0.25–0.35 mm diameter) for the degradation of phenol as sole carbon source. The K _La of 0.015 s^–1 gave more than adequate oxygen transfer to support rates of 180g phenol/h · m³ and 216 g oxygen/h · m³. The biomass-sand ratios of 20–35 mg volatiles/g gave estimated biomass concentrations of 3–6 g volatiles/dm³. Offline kinetic measurements showed weak inhibition kinetics with constants ofK _s=0.2 mg phenol/dm³, K _o2=0.5 mg oxygen/dm³ and KinI= 122.5 mg phenol/dm³. Very small biofilm diffusion effects were observed. Dynamic experiments demonstrated rapid response of dissolved oxygen to phenol changes below the inhibition level. Experimentally simulated continuous stagewise operation required three stages, each with 1 h residence time, for complete degradation of 300 mg phenol/dm³ · h.     

Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor

Abstract Until now, oxidation of ammonium has only been known to proceed under aerobic conditions. Recently, we observed that NH₄⁺ was disappearing from a denitrifying fluidized bed reactor treating effluent from a methanogenic reactor. Both nitrate and ammonium consumption increased with concomitant gas production. A maximum ammonium removal rate of 0.4 kg N · m⁻³ · d⁻¹ (1.2 mM/h) was observed. The evidence for this anaerobic ammonium oxidation was based on nitrogen and redox balances in continuous-flow experiments. It was shown that for the oxidation of 5 mol ammonium, 3 mol nitrate were required, resulting in the formation of 4 mol dinitrogen gas. Subsequent batch experiments confirmed that the NH₄⁺ conversion was nitrate dependent. It was concluded that anaerobic ammonium oxidation is a new process in which ammonium is oxidized with nitrate serving as the electron acceptor under anaerobic conditions, producing dinitrogen gas. This biological process has been given the name ‘Anammox” (anaerobic ammonium oxidation), and has been patented.     

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.     

Use of a tapered fluidized bed as a Continuous bioreactor

Reactor systems based on tapered fluidized beds are being developed for aqueous bioprocesses in which adhering microorganisms or immobilized active biological fractions are used. The use of a fluidized bed prevents biomass buildup, accommodates particulates in the feed stream, is compatible with gas sparging, and allows easy removal or addition of the active materials. The tapered reactor tends to stabilize the fluidized bed, thus allowing a much wider range of operating conditions. Preliminary experimental results and an empirical mathematical model of the tapered bed indicate that bed stability is associated with a decreasing velocity and void-fraction profile up the bed and the pressure drop across the bed decreases with increasing flow rates. The tapered fluidized bed bioreactor is being evaluated for use in the enzymatic production of hydrogen, microbiological denitrification, and microbiological degradation of coal conversion aqueous waste streams. The enzyme catalyzed conversion of lactose to glucose and galactose was used in the evaluation of the reactor concept.     

Hydrodynamics and performance in fluidized bed adsorption

The performance of fluidized bed adsorption is strongly influenced by the hydrodynamics of the fluidization process. Especially axial mixing in the liquid and solid phase may lead to reduced capacity and resolution. In this article axial mixing in the liquid phase of a classified fluidized bed based on porous glass granules is presented. Axial mixing was analyzed by measurements of residence time distributions in a fluidized bed, showing a reduction of mixing at increased ratio of bed height to diameter as well as at increased linear velocity of the liquid stream. These results were transferred to two real adsorption systems on two different scales: In a bench scale (up to 15 mL of adsorbent) the purification of monoclonal antibodies from hybridoma supernatant was performed with a cation exchanger, in a larger scale (up to 750 mL of matrix) the adsorption of bovine serum albumin (BSA) on the same matrix was investigated. The results showed an increase of capacity at increased bed height-to-diameter ratio; with regard to linear velocity a broad range of only slightly changed capacity was found. A shift from dispersion controlled to diffusion controlled adsorption at intermediate linear velocity was proposed by isolating the effect of pore diffusion from the effect of dispersion. (c) 1995 John Wiley & Sons, Inc.     

Overloading responses of a glucose-fed anaerobic fluidized bed reactor

The responses of a glucose-fed anaerobic fluidized bed (AFB) reactor towards single- and multiple-pulse overloadings are evaluated. Under the conditions tested (i.e., pulse magnitude: 3-fold, pulse frequencies: 1 and 3; and pulse durations: up to 60 h), the AFB reactor is capable of sustaining good total organic carbon (TOC) removal (i.e., >89%) during overloading periods and achieving quick recoveries (i.e., <1 week) without displaying any detrimental symptoms. This performance is a result of using porous media particles for biomass retention, which enhances the process stability by minimizing excessive washout of bacterial cells during overloading periods when biogas production intensifies. The completely mixed conditions maintained in the liquid phase also help to mitigate the overloading impacts. However, the experimental data suggest that the glucose-fed AFB reactor is more susceptible towards multiple-pulse overloadings.     

Antibiotics production in a fluidized bed reactor utilizing a transverse magnetic field

A mathematical model is developed to describe the performance of a three-phase fluidized bed reactor utilizing a transverse magnetic field. The model is based on the axially dispersed plug flow model for the bulk of liquid phase and on the Michaelis-Menten kinetics. The model equations are solved by the explicit finite difference method from transient to steady state conditions. The results of the numerical simulation indicate that the magnetic field increases the degree of bioconversion. The mathematical model is experimentally verified in a three-phase fluidized bed reactor with Penicillium chrysogenum immobilized on magnetic beads. The experimental results are well described by the developed model when the reactor operates in the stabilized regime. At low and relatively high magnetic field intensities certain discrepancy in the model solution is observed when the model over estimates the product concentration.     

Modeling of experiments on biofilm penetration effects in a fluidized bed nitrification reactor

A four-component, diffusion-reaction model with double Michaelis-Menten kinetics was used to describe the experimental data obtained from a laboratory biofilm, fluidized-bed nitrification reactor. Theory and experiment demonstrated that the stoichiometric ratio (3.5 mg O(2)/mg NH(4) (+)-N) can be employed as a criterion to determine whether the limiting substrate is oxygen or ammonia. For the present work, in the range of concentrations where limitation occurred, 4 mg/L NH(4) (+)-N and 14 mg/L O(2), the ratio of oxygen to ammonia in the bulk liquid determined which substrate was penetration-limiting-O(2) if <3.5 and NH(4) (+) if > 3.5. Halforder kinetics with respect to the limiting substrate described the apparent overall rates. Simulations provided biofilm concentration profiles which demonstrated the role of the oxygen-ammonia ratio. Experiments indicated that, generally, high NO(2) (-) concentrations can be expected. These depend on the residence time, biofilm area, and oxygen concentration. This dependency was investigated with the model, as was the parametric sensitivity with respect to the saturation constants. Particularly important for the NO(2) (-) levels were the ratios of the saturation constants for oxygen.