Effects of Packed Layer Structure and Submerged Zone on Nutrient Removal in Bioretention Systems with Sand, Soil and Fly Ash

Both sand and fly ash were found to be promising for phosphorus removal in bioretention systems. However, nutrient removal in bioretention systems with sand, soil and fly ash was still uncertain due to a lack of data about the influence of layer structure and submerged zone. In this study, a mixture with sand, soil and fly ash (1:1:1) was selected as the base in bioretention systems with different packed layer structures and heights of submerged zone. The comparison of multi-layered structure with mixed structure implied that the used bioretention system with multi-layered structure was superior to that with mixed structure for nitrogen and phosphorus removal. The investigation of the influence of submerged zones on nutrient removal indicated that the submerged zone could significantly improve nitrate removal efficiency with 67.52%-86.32%, while sharply reduce the removal of ammonia nitrogen (from 95.15% to 51.81%) and TP (from 88.66% to 44.50%). Overall evaluation of the effect of packed layer structures and submerged zones suggested that the bioretention system with multi-layered structure at the height of submerged zone at 20-40cm was the most satisfactory, due to its microbial environment.

Equilibrium acoustic velocity in vapor-liquid mixture in layer of spherical particles

Theoretical and experimental study of acoustic velocity in vapor-liquid mixture that contained close-packed layer of spherical particles was performed with respect to nonstationary heat transfer between mixture and particles in compression half-wave. Theoretical model allows to explain the decay of equilibrium acoustic velocity compared to its adiabatic value in case of increasing of void fraction in the mixture. Calculated results are in agreement with experimental data, obtained in vertical channel with vapor-liquid filtration with close-packed layer of spherical particles of borosilicate glass, steel and lead.

Exploring Research on Raschig Rings/Ceramic Double-Packed BAF

A BAF double packed with Raschig rings/ceramic media was developed to determine its pollutants removal efficiency with less frequent backwashing as compared with ordinary BAF. Results showed that a stable operation was achieved during the entire test period and the backwashing cycle time could be extended as well. The COD and SS removals of 57% and 52%, respectively, could be achieved by the Raschig rings packed layer. Nitrifying bacteria accounted for as much as 95% in the ceramic packed layer and ensured high nitrification efficiency with a removal rate of 40.2 gNH4+-N/h•m3. With wastewater pretreatment and backwashing of the packed Raschig rings, the operation cycle of double-packed BAF could be extended to 16 days. In addition, the recovery of treatment performance was fairly rapid after backwashing.

Extended Validation of a Model of Segregating Fluidization of Homogeneous Two-Solid Beds

In the industrial processes that employ the fluidized bed technology (gasification of coal or biomasses, polymerization, etc.), solids of various kinds are simultaneously subjected to fluidization. Due to the fact that solids that differ in density and/or size differently react to the frictional force exerted by the gas stream, mixtures of two solids tend to form, when fluidized, segregated layers rich in either of their components. A peculiar case, in this frame, is that of homogeneous mixtures whose denser component is also the smaller one and achieves the fluidized state at the bottom of the column, while the other solid, bigger and lighter, forms a packed layer on top of it.With reference to this special type of binary systems, several series of experiments are presented that provide their initial and final fluidization velocities at varying composition. Following what done in a recent study on beds of two solids differing in density or size, it is shown that the theoretical equations for calculating uif and uff keep their validity even when applied to mixtures that exhibit an unusual fluidization pattern. Calculated values of the initial and final fluidization velocities are characterized by a low error level, fully comparable with that encountered with other types of binary beds.