Design of a Fluidized Bed Bio Film Reactor for Wastewater Treatment

Fluidized Bed Biofilm Reactor is widely applied in many industries for various applications recently. It has been found promising to use fluidized bed reactor for water treatment procedures. When the conventional treatment procedures lags behind to remove recalcitrant compounds in waste water (Abbas, et. al., 2014). However, Anaerobic oxidation pond are yet not without limitations. Studies reveal that an effective contacting device system can increase the potential of advanced oxidation systems. Wastewater treatment involving physical unit operations and chemical and biological unit processes is carried out in vessels or tanks commonly known as ―reactors‖ (Burghate1 & Ingole, 2014). The principle types of reactors used for the treatment of wastewater are – batch reactor, complete mix reactor (continuous flow stirred tank reactor – CSTR), plug flow reactor, complete mix reactors in series, packed bed reactor and fluidized bed reactor (Tisa, et. al., 2014). Waste water that is generated from many industries is highly recalcitrant and is threatening to environmental ecology and human lives. Biological and chemical processes have failed to convert the contaminants fully as, biological and chemical processes and degrade up to 60% of the recalcitrant components and in addition they require larger operation area and more chemical processes to reduce the sludge (Tisa, et. al., 2014). The Fluidized Bed Biofilm Reactor (FBBR) is a recent process innovation in wastewater treatment. Main application of the fluidized bed biofilm reactor is in the field of biological treatment of wastewater. Aerobic as well as anaerobic fluidized bed biofilm reactors (FBBRs) have received increasing attention for being an effective technology to treat water and wastewater. Its most important features are - the fixation of microorganisms on the surface of small-sized particles , leading to high content of active microorganisms and large surface area available for reaction with the liquid; the high flow rate (low residence time) which can be achieved , leading to high degree of mixing (decreased external mass transfer resistances) and to large reduction in size of the plant; and the removal of risk of clogging (Burghate1 & Ingole, 2014). The basic concept of the process consists of passing wastewater up through a packed bed of particles at a velocity sufficient to impart motion to or fluidize the particles. As the flow of the wastewater passes upward through the biological bed, very dense concentrations of organisms growing on the surface of the bed particles consume the biodegradable waste contaminants in the liquid. Figure below is a schematic of the basic unit of the process, showing the entire fluidized bed reactor with the wastewater flowing upwards through the bed, fluidizing the particles in the liquid. Above the bed is a clear water zone wherein the particles separate from the liquid (Bayens, et. al., 1986).

As the waste water to be treated will be from domastic sources so it may containt the domastic waste particles, so the design has to be done in such a way that it can accumulate all the process required for its treatement. The strategy of Fig. 1 therefore sidesteps for specific consideration. The different steps are discussed hereafter. To predict the behavior of a chemical reactor requires information on the hydrodynamics, stoichiometry, thermodynamics, heat and mass transfer, reaction rates, and lastly, flow or contacting pattern of materials in the reactor (Tisa, et. al., 2014). Proposed design steps involved in the FBR design. i. Data Gathering ii. Kinetics and Themodynamics iii. Hydrodynamic iv. To Determine liquid velocity for optimum mixing v. To determine Gas velocity for dispersion / mxing

For the design of FBBR various properties of waste water has to be studied (Graham, et. al., 2006).

considered for analysis and calculation in case of designing.. The Fluidized Bed reactor design should be made according to information available in the literature. The formulas for the design parameters are to be selected from vast literature available on researches in fluidized bed reactors and the study of fluidization profiles (Chou and Huang, 1999).

Fluidization characteristics depend on the composition of the mixture of different particle size at varying composition. Therefore, the bed voidage, minimum fluidization velocity and fixed bed pressure drop have dependence on the average particle diameter and mass fraction of the fines in the mixture (Tisa, et. al., 2014). Supposing if, we have particle size of dp1, dp2 and dp3 of same density and if, the composition of the mixture is a1:a2:a3, generally the equation for mean particle diameter would be (fi indicates the fraction of ith component) (Tisa, et. al., 2014).

Sphericity is the measure of particles where, the particles are not ideal in both shape and roughness. It is the measure of a particle's non ideality in both shape and roughness. It is calculated by visualizing a sphere whose volume is equal to the particles and dividing the surface area of this sphere by the actually measured surface area of the particle (Tisa, et. al., 2014). The average sphericity for the particle mixture can be calculated by two different methods. First by the use of the correlation of Narsimhan for mono disperse particles. For binary and ternary mixtures the equation can be written as where dp,sm is the average particle diameter in feet, is thevoid fraction and φs is the spericity (Tisa, et. al., 2014). In the second method theaverage sphericity has been calculated from the sphericitydata of irregular particles of dolomite of different sizesreported by Singh. The average sphericity can be taken as the mass mean sphericity and can be calculated using the following equation.

Normal measured values for a typical granular solid range from 0.5 to 1, with 0.6 being a choice for every round shaped particle (Tisa, et. al., 2014).

Before determining the minimum fluidization velocity of the reactor the void fraction, emf of the bed particle should be calculated. In fluidization upward liquid flow will fluidize the bed particles. Our fluid bed consists of sand. We will consider the mean particle diameter and mean sand density as the solid particle density for this calculation (Tisa, et. al., 2014). This emf is the void fraction at the point of the minimum fluidization.

mf is the void fraction at minimum fluidization condition (Tisa, et. al., 2014). μ is the viscosity of the fluid. ρf is the density of fluid, ρp is the density of particle. ρc is the density of catalyst. s is the void fraction when the bed is stable. Hs is the height of bed when at stable condition. Mv is the volumetric flow rate. Df diameter of particle.

Minimum fluidization velocity is for fluidizing the bed particles from the bed. It is the velocity required to begin the fluidization at which the weight of particles from the rising gas (Tisa, et. al., 2014).

If gas or liquid velocity is increased to a sufficient limit, that the drag on every particle will surpass the gravitational force on the particles. This velocity if called Maximum fluidization velocity. Maximum fluidization is important parameter to know for avoiding particle entrainment. The operating fluidization velocity depends on the maximum fluidization velocity too (Tisa, et. al., 2014).

Conventional formula for the calculation of the volume (V) and cross sectional area (Ac) of a cylinder was used. The calculated results for our featured FBR are summarized below in Table

The research contains descriptive steps and calculation for designing this particular FBR which is a potential contribution to water treatment technologies. Calculations are self-explaining and can be followed for other specific FBR design purpose. The performance of the FBR is to be evaluated for treatment of phenolic water (<200ppm). Simulation work is on-going to predict the performance inside the reactor as well.

Abbas H. Sulaymon, Ahmed A. Mohammed, Tariq J. Al-Musawi (2014). "Predicting the Minimum Fluidization Velocity of Algal Biomass Bed"

C.-C. Su et al. (2011). ―Effect of operating parameters on decolorization and COD removal of three reactive dyes by Fenton's reagent using fluidized-bed reactor,‖ Desalination, vol. 278, no. 1-3, pp. 211-218. D.-H. Lee (2000). ―Hydrodynamic Transition from Fixed to Fully Fluidized Beds for Three-Phase Inverse Fluidization,‖ Korean J. Chem. Eng., vol. 17, no. 6, pp. 684-690. Doyce Tesoro Martinez , Tomas U. Ganiron Jr. and Harold S. Taylor "Use of Fludized Bed Technology in Solid Waste management"

G. Narsimhan (1965). ―On a generalized expression for prediction of minimum fluidization velocity,‖ vol. 11, no. 3, pp. 550–554. H. Gulsen and M. Turan (2004). ―Treatment of Sanitary Landfill Leachate Using a Combined Anaerobic Fluidized Bed Reactor and Fenton‘s Oxidation,” Environmental Engineering Science, vol. 21, no. 5. H. Jena, G. Roy, and K. Biswal (2008). ―Studies on pressure drop and minimum fluidization velocity of gas–solid fluidization of homogeneous well-mixed ternary mixtures in un-promoted and promoted square bed,‖ Chemical Engineering Journal, vol. 145, no. 1, pp. 16-24. Engineering and Processing: Process Intensification, vol. 48, no. 1, pp. 279-287. J. Bayens et al. (1986). Solids mixing Gas fluidisation technology, 1st ed., New York, U.S.A.: Jhon Wiley & Sons Ltd, 1986, pp. 97-122. J. F. Richardson and W. N. Zaki (1954). ―The sedimentation of a suspension of uniform spheres under conditions of viscous flow,‖ Chemical Engineering Science, vol. 3, no. 2, pp. 65–73. J.-P. Zhang, N. Epstein, and J. R. Grace (1998). ―Minimum fluidization velocities for gas-liquid-solid three-phase systems,” Powder Technology, pp. 113-118. K. Mooson et. al. (1992). ―Magneto fluidized G / L / S systems,” Chem. Eng. Sci., vol. 47, no.13–14, pp. 3467–3474. L. Antoni et. al. (1986). ―Improved equation for the calculation of minimum fluidization velocity,‖ Ind. Eng. Chem. Process Des. Dev, vol. 25, pp. 426-429. L. J. Graham, J. E. Atwater, and G. N. Jovanovic (2006). ―Chlorophenol dehalogenation in a magnetically stabilized fluidized bed reactor,‖ AIChE Journal, vol. 52, no. 3, pp. 1083-1093. M. de Luna et al. (2013). ―Kinetics of acetaminophen degradation by Fenton oxidation in a fluidized-bed reactor,” Chemosphere, vol. 90, no. 4, pp. 1444-1448. M. Lim et al. (2008). ―Fluidized-bed photocatalytic degradation of airborne styrene,‖ Catalysis Today, vol. 131, no. 1-4, pp. 548-552. P. Bourgeois and P. Grenier (1968). ―The ratio of terminal velocity to minimum fluidizing velocity for spherical particles,‖ pp. 325–328. R. K. Singh (1997). ―Studies on certain aspects of gas solid fluidization in non-cylindrical conduits,‖ PhD. Thesis, Dept. Chemical Eng., Sambalpur Univ., India. S. Chou and C. Huang (1999). ―Effect of Fe2+ on Catalytic oxidation in a Fluidized Bed Reactor,‖ Chemosphere, vol. 39, no. 12, pp. 1997-2000. S. Chou et al. (2004). ―Factors influencing the preparation of supported iron oxide in fluidized-bed crystallization,‖ Chemosphere, vol. 54, no. 7, pp. 859-66.

W. Liang et. al. (1996). ―Flow characteristics of the liquid–solid circulating fluidized bed,‖ Powder Technology, vol. 90, pp. 95-102. W. Nam, J. Kim, and G. Han (2001). ―Photocatalytic oxidation of methyl orange in a three-phase fluidized bed reactor,” Chemosphere, vol. 47, pp. 1019-1024. X. L.Yang, G. Wild, and J. P. Euzen (1993). ―Study of Liquid Retention in Fixed-bed Reactors with Upward Flow of Gas and Liquid,‖ Int. Chem. Eng, vol. 33, pp. 72–84. Y. J. Shih, M. T. Tsai, and Y. H. Huang (2013). ―Mineralization and defluoridation of 2,2,3,3-tetrafluoro -1-propanol (TFP) by UV oxidation in a novel three-phase fluidized bed reactor (3P-FBR),‖ Water Res, 30.

Assistant Professor, JSPM"s Imperial College of Engineering and Research, Wagholi, Pune