Wastewater treatment with particulate biofilm reactors

▪ Abstract Gravity-driven bubbly flows are a specific class of flows, where all action is provided by gravity. An industrial example is formed by the so-called bubble column: a vertical cylinder filled with liquid through which bubbles flow that are introduced at the bottom of the cylinder. On the bubble scale, gravity gives rise to buoyancy of individual bubbles. On larger scales, gravity acts on nonuniformities in the spatial bubble distribution present in the bubbly mixture. The gravity-induced flow and flow structures can increase the inhomogeneity of the bubble distribution, leading to a turbulent flow. In this flow, specific scales are identified: a large-scale circulation with the liquid flowing upward in the center of the column and downward close to the wall. On the intermediate scale there are vortical structures; eddies of liquid, with a size on the order of the diameter of the column, that stir the liquid and radially transport the bubbles. On the small scale there is the local stirring of the...

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Gravity-driven bubbly flows

https://core.ac.uk/download/pdf/138479.pdf

Biomass effects on oxygen transfer in membrane bioreactors.

https://repositorium.sdum.uminho.pt/bitstream/1822/55039/1/document_47543_1.pdf

Bioreactor design for enzymatic hydrolysis of biomass under the biorefinery concept

The principle of the air-lift reactor is finding wide application in the fields of both chemical technology and biotechnology because it offers simple and effective mixing in three-phase processes involving gases, liquids and solids. The air-lift principle offers advantages of no moving parts, high gas absorption efficiency, good heat transfer characteristics and rapid mixing which are applicable in a range of industrial processes. This review considers specific aspects of air-lift reactors emphasizing their function and relevance to particular applications. The two main groups of air-lift reactor, baffled vessels and external loop reactors, have four main component parts in common, the riser, the downcomer, the base and the gas separator, all of which have distinct characteristics. The performance of these four components with respect to flow configurations, fluidization of suspended solids and mass transfer are discussed together with methods of evaluating mass transfer coefficients.

Air-lift reactors in chemical and biological technology

The effects of column dimensions, gas velocity and properties of the liquid and the solid particles on the gas holdup eG and the volumetric liquid-phase mass transfer coefficient kLa in a solid suspended bubble column with a draught tube and a conical bottom were studied experimentally in a liquid-solid batch operation. The presence of suspended solid particles in the column reduces the values of eG and kLa, and their reduction due to the addition of solid particles to the column increases with increasing solid concentration and terminal velocity of a single particle. Based on these observations, empirical equations for eG and kLa are proposed which are applicable to columns with diameter of 0.1-0.3 m.

Gas holdup and volumetric liquid-phase mass transfer coefficient in solid-suspended bubble column with draught tube

The critical gas velocity required for complete suspension of solid particles was studied experimentally in a solid-suspended bubble column with a draught tube It was shown that the critical gas velocity increases with increasing terminal velocity of a single particle, solid concentration, liquid surface tension, diameter of gas distributor and density difference between solid and liquid, and decreases with increasing column diameter and liquid viscosity Based on these observations, an empirical equation for critical gas velocity is proposed that is applicable to columns with diameters of 01-03 m

Critical gas velocity required for complete suspension of solid particles in solid-suspended bubble column with draught tube

The flow rate QL of circulating liquid was measured by the heat-pulse method. It was found that QL increased with increasing liquid viscosity. In a h''quid where bubble coalescence was not hindered, the gas holdup in the annulus decreased and therefore QL increased. Empirical equations for gas holdups in the draught tube and the pressure drop due to flow reversals, necessary for estimating QL, were proposed.

Hirokazu Kawabata

Papers

Gas holdup and volumetric liquid-phase mass transfer coefficient in solid-suspended bubble column with draught tube

Critical gas velocity required for complete suspension of solid particles in solid-suspended bubble column with draught tube

Liquid circulation in bubble column with draught tube

Observing the impact force and low-speed droplet behavior of wet surfaces with very-thin liquid films