Expanded Bed Research Articles

Expanded Bed Treatment of Complete Recycle Aquaculture Systems

The popular dietary shift to fish and the limits on natural fish populations have caused rapid growth in fish farming and aquaculture. Optimized aquaculture systems are attempting to use as complete recycle as possible to obtain maximum control over the fish populations, and limit water and energy requirements. Closed systems aquaculture is severely limited by water quality since pollutants accumulate in the system. This study examined the possibility of simultaneous BOD5 reduction, SS removal, nitrification and denitrification with an expanded bed in complete recycle growth systems with Atlantic salmon and brook trout. The fish rearing tank volume was 10 m3 and the expanded bed volume was 2.6 m3. The total duration of the study was 180 days. The expanded bed developed a film capable of nitrification and denitrification within 40 days. After this time, the SS and BOD were maintained at less than 6 mg/l. Ammonia, nitrates, and nitrites were below detectable levels, thus confirming the simultaneous one-stage removal potentials. Maximum nitrogen removal rates of 40 mg per liter of AFEB per day are similar to the higher removal rates predicted for maximum removal efficiencies at bulk solution ammonia-nitrogen concentrations of 0.5 mg/l. Dissolved oxygen concentrations in the expanded bed appear to be the most sensitive control parameter for these simultaneous reactions. This one-stage pollution control process for complete recycle aquaculture would be useful in both freshwater and seawater applications. The system is easily modularized for fish rearing tank capacities of 1,000 to more than 10,000 kg. The treatment system volume would be less than half the rearing volumes at low fish densities and low ammonia concentrations (less than 0.5 mg/l of ammonia nitrogen).

Effects of Particle Shape and Size Distribution on Sorption and Flow Performance in Electrically Stabilized Expanded Beds

Use of the electrically stabilized expanded bed is an approach to the improvement of the performance of processes in beds of solid sorbents. Particle motion in a fluidized bed of nonconducting particles such as molecular sieves is halted when the bed is frozen by a strong electric field imposed across the bed. This allows sorption performance to approach that of fixed beds while maintaining the low pressure drops which are characteristic of fluidized beds. Beds with axial and radial electrode geometries function equally well in the sorption of carbon dioxide (CO/sub 2/) from nitrogen (N/sub 2/). The effects of particle shape and particle size distribution on bed stabilization are presented. Particle shape was varied from spherical to the irregular forms that are characteristic of crushed particles. The sorption performance was not appreciably different with particles having various shapes. Particles with a size range from 200 to approximately 1200 ..mu..m were blended from individual spherical fractions to create mixtures with peak distributions at both ends of this range. To a first approximation, the distribution of particle sizes did not affect sorption performance. These results demonstrate that both irregularly shaped particles and multiple-sized particles can be stabilized in electric fields, and themore » stabilized beds behave much like fixed beds of the same materials except that the pressure drops across the beds can be significantly less than those for fixed beds. However, the rate of adsorption in the system used for this study is controlled by diffusion within the particles (actually within the micropores of crystals); so the study did not address the effects of electric stabilization on the gas-film resistance.« less

Behaviour of an anaerobic expanded bed reactor in non-steady state conditions

This paper presents a series of experimental data on an expanded bed anaerobic reactor operating at high organic loading rates in non-steady state conditions. The first four experiments were conducted in start-up periods after shut-downs. In the section dedicated to behaviour in the face of fluctuations, two experiments with overloading, two with decrease in temperature and one with air inflow, have been included. In all cases, the reactor demonstrated great stability with short recovery periods.

Electrically Stabilized Expanded Beds for Sorption Separations

Abstract Recent studies have shown that when high electric fields are imposed on expanded fluidized beds, motion of the particles can cease. This provides the potential for fixed bed operations with the void fraction sufficiently large that only moderate pressure drops are required, even with small particles. This paper explores the dielectric forces that inhibit particle motion in alternating-current electric fields and the potential and limitations of the concept for adsorption operations. The dielectric constants of the particles and the fluid, the size of the particles, the density and viscosity of the fluid, and the imposed electric field gradient are the variables of most importance to bed stabilization. In adsorption tests, the expanded-stabilized beds perform essentially as well as densely packed fixed beds but with only a fraction of the pressure drop.

Studies with an anaerobic expanded bed reactor comparing the performances achieved with synthetic waste and domestic sewage

The performance of an anaerobic expanded bed reactor has been examined during the treatment of a synthetic low strength waste whose consistency and composition were constant. The organic loading rates used were in the range 0.2–5 kg total organic carbon m −3 day −1 and the removal efficiencies varied from 89 to 52%. Comparing these results with those obtained previously for the treatment of domestic sewage, whose strength and composition was very variable, showed that not only can higher removal efficiencies be achieved with the synthetic waste but also that a significantly better ( R 2 > 0.85, as opposed to <0.5) correlation between data could be obtained. This indicates the potential danger of using synthetic feedstocks for the prediction of reactor performance under real conditions.

Microbial attachment in anaerobic expanded bed reactors

Abstract The examination of the rate of bacterial attachment to the sand support medium in an anaerobic expanded bed reactor showed that the greatest biofilm thickness developed at the top of the bed. After 80 days the amount of biofilm on sand taken from this point corresponded to an increase in particle diameter of 92 μm. In the same period, support media taken from the middle of the bed increased by only 25 μm.

Fluidized breccias: A record of brittle transitions during ductile deformation

Unusual breccias, of Caledonian age, are described in relation to the tectonic and metamorphic history of their greywacke sandstone and siltstone parent rocks. The variety of field and textural relationships displayed by the breccias indicate a combination of dilational and non-dilational components in a fluidized system of breccia development. The velocity of the escaping fluid phase and the viscosity of the fluidized suspension are strongly influenced by competency controls. Due to their finer grained nature, the pelite-based breccias allow a greater mobility of the fluid phase and locally record a turbulent expanded bed stage of the fluidized system. However the sandstone-based breccias, lacking the intricate flow patterns, retain a replacive non-dilational fracture network. The breccias occur in a zone of intense D 2 deformation. The age relationships of the breccias indicate a repeated pattern of brecciation with syntectonic temporal and partly genetic affinities to the S 2 cleavage development. The syntectonic dilational elements, involving boudinage and hydraulic fracture, are coupled with intense pressure solution and conjugate cleavage development. Metamorphism to lower greenschist facies is synchronous with deformation and brecciation. A focussing of the metamorphic fluid phase within the breccia zones is indicated, contributing the non-dilational components of the brecciation process. A simple shear model of the D 2 deformation within this zone is proposed. The orientation of the breccia zones suggests that their localization is determined by tensional components within the overall D 2 stress field. The cyclical pattern of the brecciation during the D 2 deformation is considered to represent rapid brittle transitions during the ductile deformation. Stratigraphie controls on the generation of the increased fluid pressures are identified. The presence of an impermeable barrier facilitating the necessary conditions for the excess fluid pressures to accumulate is indicated. It is suggested that the brecciation process is fundamentally controlled by a seismic pumping phenomenon following periodic shear failure on a major basement fault at depth.

The use of aim anaerobic expanded bed reactor for the treatment of domestic sewage

Abstract The performance of an anaerobic expanded bed reactor treating settled domestic sewage at 37 C has been evaluated over a period of some eight months. The organic strength of the sewage varied from day to day, as it would in a practical treatment plant. With these unsteady‐state conditions prevailing, the results showed that the process was unlikely to give the type of performance (in terms of the removal of organic matter and gas productivity) that would make it a serious competitor to existing methods of treating domestic sewage. This is contrary to the interpretation of other workers who used steady‐state conditions.

Alternative Modes of Processing SRC in an Expanded Bed LC-Finer to Produce Low Nitrogen Distillates

Alternative Modes of Processing SRC in an Expanded Bed LC-Finer to Produce Low Nitrogen Distillates

The effect of particle size and bed height on the expansion of mixed phase (gas—liquid) fluidized beds

The expansion of gas—liquid fluidized beds has been measured for beds of glass ballotini fluidized by air/water. Particle diameters varied from 0.28 to 2.2 mm, and settled bed heights from 14–107 cm. The flow rates of air and water were varied independently. The expansion of a liquid fluidized bed is often reduced when a swarm of gas bubbles is injected into the bed. This bed contraction is largest for beds of small particles; a contraction of 48 per cent has been observed in a highly expanded bed of 0.28 mm ballotini. For small particles the largest contraction was observed in beds of high height to diameter ratio. For larger particles the contraction is less pronounced, and no significant effect of the ratio between bed height and diameter was observed.

Cyanosis After Surgical Closure Under Direct Vision of Atrial Septal Defects

Three patients with atrial septal defects are reported in whom postoperative cardiac catheterization revealed the elimination of left-to-right shunt and the first appearance of peripheral artery desaturation. This was already apparent at the pulmonary venous level and cyanosis was therefore not sustained by intracardiac right-to-left shunts. In two of these, pulmonary vascular thrombosis was invoked as a cause of pulmonary vein desaturation, the mechanism presumably being a postoperative discrepancy between expanded pulmonary bed and decreased blood flow, conducive to stasis and stagnant thrombosis. There was no apparent explanation in the third patient. It is felt that detailed pre- and postoperative investigation of the respiratory function, in particular of the diffusing capacity of the lungs, might help in the understanding of the reported unusual behavior.