Bed fluidization offers the possibility of gaining the advantages of fixed-film biological processes without the disadvantage of pore clogging. However, the biofilm detachment rate, due to hydrodynamics and particle-to-particle attrition, is very poorly understood for fluidized-bed biofilm processes. In this work, a two-phase fluidized-bed biofilm was operated under a constant surface loading (0.09 mg total organic carbon/cm(2) day) and with a range of bed height (H), fluid velocities (U), and support-particle concentrations (C(p)). Direct measurements were made for the specific biofilm loss rate coefficient (b(s))and the total biofilm accumulation (X(f)L(f)). A hydrodynamic model allowed independent determination of the biofilm density (X(f)), biofilm thickness (L(f)), liquid shear stress (tau), and Reynolds number (Re). Multiple regression analysis of the results showed that increased particle-to-particle attrition, proportional to C(p) and increased turbulence, described by Re, caused the biofilms to be denser and thinner. The specific detachment rate coefficient (b(s)) increased as C(p) and Re increased. Almost all of the 6, values were larger than predicted by a previous model derived for smooth biofilms on a nonfluidized surface. Therefore, the turbulence and attrition of bed fluidization appear to be dominant detachment mechanisms.

A three-phase, liquid-fluidized-bed biofilm reactor was operated over wide ranges of liquid velocity, air velocity, medium concentration, and substrate surface loading. The biofilm characteristics (total colonization, polysaccharide content, density, and thickness) and the specific detachment coefficient (bs) were determined by a combination of experimental measurements and a hydrodynamic model. The results demonstrated that dense and thin biofilms were induced by the physical condition of high particle-to-particle contacts and high liquid turbulence. The biofilm's polysaccharide content was increased by increased air turbulence and a low substrate availability. The specific detachment coefficient, bs, was strongly correlated to the concentration of the medium (negatively) and the polysaccharide content (positively). Overall, the bs can be controlled significantly by the gas and liquid velocities; increasing either velocity tends to increase bs.

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Studies in Linear Dichroism. I. Quantitative Evaluation of Linear Dichroic Properties of Molecules in Stretched Polyethylene Films Sir:Linear dichroism is normally observed in molecules having a nonrandom organization. Molecules incorporated in stretched polymer films are partially oriented, and hence possess the property of linear dichroism.1

A method to measure the fraction of biofilm bacteria active in respiration was developed and applied to a three-phase fluidized-bed biofilm reactor. The substrate flux (J) and the biofilm detachment coefficient (bs) were controlled independently. The experimental results showed that the amount of biofilm per unit of carrier surface area (XfLf) was controlled by J and bs. However, the biofilm's active fraction was proportional to J, but independent of bs for these experiments with relatively large bs values. When J was increased, the biofilm had less inactive biomass, because the substrate concentration was higher and allowed the cells to maintain a higher growth rate. Accompanying the increased activity were an increase in the observed biomass yield and a decrease in the oxygen consumption. These results provide a tool to control bioparticle fluidization, oxygen consumption, and sludge production.