Inverse Fluidized Bed Reactor Research Articles

Oxygen transfer in three phase inverse fluidized bed bioreactor during biosurfactant production by Bacillus subtilis

Production of microbial biosurfactants requires development of bioreactors enabling sufficient oxygen supply and foaming control. Gas–liquid mass transfer in a three-phase inverse fluidized bed reactor designed for biosurfactant production by Bacillus subtilis was studied. The influence of main parameters on kLa was investigated in model and real fermentation conditions. Oxygen transfer increased up to 175% and up to 24% with the increase of superficial gas and liquid velocities, respectively. The oxygen transfer obtained in the TPIFB bioreactor (kLa up to 0.015s−1) was higher than in the other bioreactors used for biosurfactant production. A significant decrease of kLa (up to 27%) was measured during fermentation process. It was shown that this decrease of kLa was a result of surface tension decrease due to the production of biosurfactants. However the oxygen transfer remained important and allowed a correct oxygen supply for the aerobic B. subtilis strains. A correlation based on dimensional analysis was proposed to estimate kLa in function of the influencing parameters, integrating surface tension effects. This correlation allowed estimating correctly kLa in the presence or not of solid particles. The correlation being based on dimensionless numbers, it could help for further process control and scale-up considerations.

Methane yield and microscopic observation as monitoring biofilm behaviour parameters, during start up phase of anaerobic inverse fluidized bed reactor

Anaerobic biofilm behavior on polyethylene and Extendosphere™ supports was evaluated during start-up of an inverse fluidized bed reactor using methane yield and microscopic observation as parameter monitoring techniques. Two anaerobic inverse fluidized bed reactors were used, one filled with triturated polyethylene as solid carrier material (diameter = 380 μm, density = 926 kg/m 3 ) and the other with Extendosphere™ (diameter = 147 μm, density = 700 kg/m 3 ). Each support material was used at up to 25% of its working volume (polyethylene = 1.2 l, Extendosphere™ = 1.9 l). Both reactors were started up in sequencing batch mode, applying organic loading rates of 0.5 to 14 g COD/l.d. Both supports exhibited rapid biofilm growth during start-up. Maximum surface colonization was 46% with the polyethylene and 100% with Extendosphere™. Both supports had a methane yield of 0.298 l CH 4 /g COD at 10 and 14 g COD/l.d, respectively. Digital microscopic observation results coincided with methane yield results, confirming each to be viable for parameter monitoring of biofilm growth. Data generated by these two techniques is different and complementary, and in conjunction they constitute a highly effective monitoring method of biofilm growth. Key words: Anaerobic digestion, biofilm, inverse fluidized bed reactor, methane yield.

Effect of Carrier Materials in Inverse Anaerobic Fluidized Bed Reactor for Treating High Strength Organic Waste Water

This article explains that thermo cool, plastic beads, cork, teak wood and perlite were tried as carrier materials in the lab-scale reactor towards treating high strength organic wastewater by using inverse anaerobic fluidized bed reactor (IAFBR). Organic wastewater of great strength (molasses) is pronounced for its high chemical oxygen demand (COD) of 45,000 to 75,000 mg/l and low pH values of 4.3 to 5.3. The results of this study highlighted the selection, physical properties and performance of carrier materials on biomass retention. This study has also clearly indicated that perlite proves to be a suitable carrier material for high biomass retention and improvement of the reactor performances in a short time of operation.

Artificial Neural Network Modeling of an Inverse Fluidized Bed Bioreactor

The application of neural networks to model a laboratory scale inverse fluidized bed reactor has been studied. A Radial Basis Function neural network has been successfully employed for the modeling of the inverse fluidized bed reactor. In the proposed model, the trained neural network represents the kinetics of biological decomposition of pollutants in the reactor. The neural network has been trained with experimental data obtained from an inverse fluidized bed reactor treating the starch industrywastewater. Experiments were carried out at various initial substrate concentrations of 2250, 4475, 6730 and 8910 mg COD/L and at different hydraulic retention times (40, 32, 24, 26 and 8h). It is found thatneural network based model has been useful in predicting the system parameters with desired accuracy.

Strategies for the Startup of Methanogenic Inverse Fluidized‐Bed Reactors Using Colonized Particles

One of the inconveniences in the startup of methanogenic inverse fluidized-bed reactors (IFBRs) is the long period required for biofilm formation and stabilization of the system. Previous researchers have preferred to start up in batch mode to shorten stabilization times. Much less work has been done with continuous-mode startup for the IFBR configuration of reactors. In this study, we prepared two IFBRs with similar characteristics to compare startup times for batch- and continuous-operation modes. The reactors were inoculated with a small quantity of colonized particles and run for a period of 3 months, to establish the optimal startup strategy using synthetic media as a substrate (glucose as a source of carbon). After the startup stage, the continuous- and batch-mode reactors removed more than 80% of the chemical oxygen demand (COD) in 51 and 60 days of operation, respectively; however, at the end of the experiments, the continuous-mode reactor had more biomass attached to the support media than the batch-mode reactor. Both reactors developed fully covered support media, but only the continuous-mode reactor had methane yields close to the theoretical value that is typical of stable reactors. Then, a combined startup strategy was proposed, with industrial wastewater as the substrate, using a sequence of batch cycles followed by continuous operation, which allows stable operation at an organic loading rate of 20 g COD/L x d in 15 days. Using a fraction of colonized support as an inoculum presents advantages, with respect to previously reported strategies.

Gas–liquid mass transfer in three‐phase inverse fluidized bed reactor with Newtonian and non‐Newtonian fluids

AbstractLiquid‐phase volumetric mass transfer coefficients, kLa were determined in three‐phase inverse fluidized beds of low‐density polyethylene (LDPE) and polypropylene (PP) spheres fluidized by a countercurrent flow of air and Newtonian (water and glycerol solutions) or non‐Newtonian liquids [carboxy methyl cellulose (CMC) solutions]. The effects of liquid and gas velocities, particle size, solid loading and addition of organic additives (glycerol and CMC) on the volumetric mass transfer coefficient, kLa were determined. The superficial liquid velocity had a weak effect on the mass transfer whereas the gas flow rate affected the mass transfer positively. kLa increased with increase in particle diameter and decreased with increase in initial bed height (solid loading). kLa decreased as the concentration of glycerol (viscosity) and CMC increased. Empirical correlations are presented to predict the gas–liquid volumetric mass transfer coefficient in terms of operating variables. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

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 NO 3 −–N/(l d), respectively. Under steady state operation the consumption efficiencies of phenol, sulfide and nitrate were 100%. The N 2 yield (g N 2/g NO 3 −–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 SO 4 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.

Simultaneous sulfide and acetate oxidation under denitrifying conditions using an inverse fluidized bed reactor

AbstractBACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH3COO−/NO3− molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR).RESULTS: Three molar ratios of CH3COO−/NO3− (0.85, 0.72 and 0.62) with a constant S2−/NO3− molar ratio of 0.13 were evaluated. At a CH3COO−/NO3− molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N2 yield (g N2 g−1 NO3−‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g−1 CH3COO−‐C consumed. Sulfide was partially oxidized to S0, and 71% of the S2− consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH3COO−/NO3− molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N2 and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S0, with a yield of 0.92 g SO42−‐S g−1 S2− consumed.CONCLUSIONS: The CH3COO−/NO3− molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO2, S0 and N2 as the major end products. Copyright © 2008 Society of Chemical Industry

Evaluation of inverse anaerobic fluidized bed reactor for treating high strength organic wastewater

The aim of this work is to evaluate the feasibility of an inverse fluidized bed reactor for the anaerobic digestion of distillery effluent, with a carrier material that allows low energy requirements for fluidization, providing also a good surface for biomass attachment and development. Inverse fluidization particles having specific gravity less than one are carried out in the reactor. The carrier particles chosen for this study was perlite having specific surface area of 7.010 m 2/g and low energy requirements for fluidization. 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. It was used for the treatment of distillery waste and performance studies were carried out for 65 days. Once the down flow 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 0.19 day, while maintaining the constant feed of chemical oxygen demand (COD) concentration. Most particles have been covered with a thin biofilm of uniform thickness. This system achieved 84% COD removal at an organic loading rate (OLR) of 35 kg COD/m 3/d.

Brewery wastewater treatment using anaerobic inverse fluidized bed reactors

Two anaerobic inverse fluidized bed reactors were utilized to evaluate organic matter removal from brewery wastewater, applying different OLR and testing two support materials. Hydrodynamic tests varying liquid flow and solid concentration were developed on the supports in order to establish operational conditions. A batch colonization stage was applied using 25% active volume of extendosphere and triturated polyethylene as support materials. The reactors were subsequently operated continuously with stepwise increments in organic loading rate until limiting conditions was reached. For the supports studied, IFBR technology was suitable for organic matter removal present in brewery wastewater with COD removal efficiencies greater than 90%. The reactor with triturated polyethylene support showed an excellent COD removal with OLR values up to 10 g COD/L d, whereas the reactor with extendosphere support had an excellent hydrodynamic and biologic behavior working with OLR values up to 70 g COD/L d.

Simultaneous removal of carbon and nitrogen in an anaerobic inverse fluidized bed reactor

The evaluation of simultaneous removal of carbon and nitrogen in an anaerobic inverse fluidized bed reactor is described. Continuous and batch experiments were used, with synthetic wastewater and glucose as the carbon source with two different nitrate concentrations of 100 and 250 mg N-NO3/L. The evolution of substrates and the concentrations of intermediary products in the gas phase were followed. Results indicate that the use of the biofilm in the inverse fluidized bed reactor allows the expression of denitrification and methanization activities simultaneously without physical or time separation. The removal of nitrogen with both the feeding of 100 and 250 mgN-NO3/L was higher than 90%, while the removal of carbon was 65% on average for the feeding with 100 mgN-NO3/L and 70% on average for the feeding with 250 mg N-NO3/L. This carbon degradation is equivalent to that obtained during the operation of the reactor in the period previous to the nitrate feeding. It was found that by using high values of the COD/N ratio, the dissimilative reduction of nitrates is favoured. Denitrification and anaerobic digestion occurs simultaneously under low values of COD/N.

Modified gas‐perturbed liquid model (GPLM) for minimum fluidization velocity in a two‐phase inverse fluidized bed reactor with Newtonian and non‐Newtonian systems

AbstractIn the present investigation minimum fluidization velocity, Umf, in a two‐phase inverse fluidized bed reactor is determined using low‐density polyethylene and polypropylene particles of different diameters (4,6 and 8 mm) by measuring pressure drop. In a glycerol system Umf decreased gradually with increase in viscosity up to a value of 6.11 mPa s (60%) and on further increase there was a slight increase in Umf. In the case of the glycerol system the Umf was found to be higher when compared to water. In the non‐Newtonian system (carboxymethylcellulose), Umf decreased with increase in concentration in the range of the present study. The Umf was found to be lower when compared to water as liquid phase. The modified gas‐perturbed liquid model was used to predict the minimum fluidization liquid velocity (Ulmf) for Newtonian and non‐Newtonian systems. Copyright © 2006 Society of Chemical Industry

Minimum Fluidization Velocity in a Three Phase Inverse Fluidized Bed Reactor with Newtonian and Non-Newtonian Fluids

The influence of operational parameters and the effect of viscosity on minimum fluidization velocity, Ulmf (minimum fluidization liquid velocity) and Ugmf (minimum fluidization gas velocity) were investigated in a three-phase inverse fluidized bed reactor using low-density polyethylene (LDPE) and polypropylene (PP) particles. The Ulmf showed an increasing trend with an increase in particle diameter. The effect of superficial gas velocity, Ug on Ulmf and the effect of superficial liquid velocity, Ul on Ugmf for water, glycerol and carboxy methyl cellulose (CMC) as the liquid phase were studied. With an increase in Ug, the Ulmf decreased and with an increase in Ul, the Ugmf also decreased. With an increase in the viscosity (concentration) of glycerol and CMC, Ulmf decreased. Correlations for the prediction of Ulmf in Newtonian and non-Newtonian systems are proposed.

Anaerobic digestion of dairy wastewater by inverse fluidization: The inverse fluidized bed and the inverse turbulent bed reactors

This paper describes the application of the inverse fluidization technology to the anaerobic digestion of dairy wastewater. Two reactors were investigated: the inverse fluidized bed reactor and the inverse turbulent reactor. In these reactors, a granular floating solid is expanded by a down‐flow current of effluent or an up‐flow current of gas, respectively. The carrier particles (Extendospheres(™)) were chosen for their large specific surface area (20,000 m2m−3) and their low energy requirements for fluidization (gas velocity of 1.5 mm s−1, 5.4 m h−1). Organic load was increased stepwise by reducing hydraulic retention time from more than 60 days to 3 days, while maintaining constant the feed COD concentration. Both reactors achieved more than 90% of COD removal, at an organic loading rate of 10–12 kgCOD m−3d−1, respectively. The performances observed were similar or even higher than that of other previously tested fluidized bed technologies treating the same wastewater. It was found that the main advantages of this system are: low energy requirement, because of the low fluidization velocities required; there is no need of a settling device, because solids accumulate at the bottom of the reactor, so they can be easily drawn out and particles with high‐biomass content can be easily recovered. Lipid phosphate concentration has been revealed as a good method for biomass estimation in biofilms since it only includes living biomass.

Minimum fluidization velocity and friction factor in a liquid-solid inverse fluidized bed reactor

In the present study the hydrodynamic characteristics (bed expansion and pressure drop) of low-density polyethylene (LDPE) and polypropylene (PP) are studied in a liquid-solid inverse fluidized bed reactor as a function of particle diameter, liquid viscosity and density. The bed expansion and pressure drop data are used to determine the minimum fluidization velocity, Umf and friction factor, ƒ. It was found that the Umf increased with an increase in the particle diameter and a decrease in solid density and was independent of initial bed height (solid loading). In addition, the Umf decreased with an increase in the CMC concentration. The friction factor Reynolds number plot was found similar to that of classical fluidization. Dimensionless equations were proposed for the. prediction of the friction factor and the Umf.

Anaerobic treatment of low concentration waste water in an inverse fluidized bed reactor

Low concentration synthetic and municipal wastewaters were treated at HRT as short as 3 and 0.6 h respectively in an anaerobic inverse fluidized bed. Both bioreactors showed gas hold up due to the liquid downflow pattern of the prototype. The bioreactor operated at 3 h had a removal efficiency of 83%, specific activity of 4.5 kg CODremoved/kg IVS (d and the gas hold up varied from 23 to 55%. The reactor treating municipal wastewater had a removal efficiency of 44% when operating at 0.6 h, the specific activity was 4.2 kg CODremoved/kg IVS (d and no biogas was detected apparently because an important fraction was dissolved in the liquid phase. The biomass concentration was 13.8 and 1.1 kg IVS/m3 for synthetic and municipal wastewater and the SEM microphotographs showed a bacterial diversity for the first run and only cocci cells for the second run. The system does not remove suspended solids, so a polishing postreatment to improve water quality has to be implemented.

Hydrodynamics study of two different inverse fluidized reactors for the application of wastewater treatment

We investigated the hydrodynamic characteristics of two types of inverse fluidized bed reactors having different driving force for fluidization: aeration and centrifugal force. In the first reactor, only an upward gas flow allows floating low-density polyethylene beads to sink down into liquid phase and to be uniformly distributed over the entire column. The gas velocity at which the solid concentration is uniform throughout the bed expansion decreases with increasing particle loads. In the second reactor, the particle loads do not greatly affect the critical rotating velocity for the homogeneous distribution of solid particles while the geometry of reactor spacing and the type of impeller are more important for the distribution of particles. For the application of waste-water treatment, the inverse fluidized bed with aeration was found to be more efficient than the second type of reactor.

Influence of surface characteristics on the adhesion of Alcaligenes denitrificans to polymeric substrates

The adhesion of Alcaligenes denitrificans to several polymeric materials was investigated. As the nature of the surfaces of the micro-organisms and the substrate materials is an important factor in the adhesion process, characteristics such as the electrokinetic potential and hydrophobicity were also determined and correlated with the capacity of bacterial cells to adhere to solid surfaces. The substrates used were high-density polyethylene (HDPE), polypropylene (PP), poly(vinyl chloride) (PVC), and poly(methyl methacrylate) (PMMA). The electrokinetic potential of the cells and the substrates was determined by measurements of electrophoretic mobility and the hydrophobicity was determined by contact angle measurements. All the substrates studied as well as the bacterial strain have a negative zeta potential, which means that adhesion is not mediated by electrostatic interactions. As far as hydrophobicity is concerned, PP is the most hydrophobic material, PMMA is the least hydrophobic, whereas HDPE and PVC present an intermediate behavior. As bacteria cells are hydrophilic, adhesion is favored to PP; therefore, this substrate material seems to be the one that promotes a stronger adhesion and the development of the most stable biofilm for use as a biomass carrier in denitrifying inverse fluidized bed reactors. This was confirmed by the results of adhesion tests. In this way, adhesion seems to be dominated by hydrophobic interactions.