Flow regime, hydrodynamics, floc size distribution and sludge properties in activated sludge bubble column, air-lift and aerated stirred reactors

This paper presents a comparative study how reactor configuration, sludge loading and air flowrate affect flow regimes, hydrodynamics, floc size distribution and sludge solids-liquid separation properties. Three reactor configurations were studied in bench scale activated sludge bubble column reactor (BCR), air-lift reactor (ALR) and aerated stirred reactor (ASR). The ASR demonstrated the highest capacity of gas holdup and resistance, and homogeneity in flow regimes and shearing forces, resulting in producing large numbers of small and compact flocs. The fluid dynamics in the ALR created regularly directed recirculation forces to enhance the gas holdup and sludge flocculation. The BCR distributed a high turbulent flow regime and non-homogeneity in gas holdup and mixing, and generated large numbers of larger and looser flocs. The sludge size distributions, compressibility and settleability were significantly influenced by the reactor configurations associated with the flow regimes and hydrodynamics.     

The use of direct osmosis tests as complementary experiments to determine the water and salt permeabilities of reinforced cellulose acetate membranes

In this article the use of the direct osmosis test as a complementary experiment to the reverse osmosis test is described. The membranes investigated are cellulose acetate membranes reinforced with mineral fillers. In both tests the same influence of the type of fillers on the water permeability coefficients is found. The salt permeability coefficients indicate the presence of pressure sensitive defects in the reinforced membranes. The direct osmosis test is found to be a suitable test to confirm and predict the membrane properties under reverse osmosis conditions.     

Chlorinated polyethylene modification of blends derived from waste plastics Part I: Mechanical behavior

Recycling of waste plastics as a blend of generic types is attractive since a difficult separations problem is avoided. However, blends of incompatible polymers are frequently very brittle and cannot be considered for many applications. Additives which modify the blend to give it ductility may provide a solution to this problem. Chlorinated polyethylene (CPE) made by a slurry process has been suggested for this application by Schramm and Blanchard. Further documentation of the effectiveness of this approach is given here. Addition of CPE to such a blend generally increases the elongation at break and the energy to break very dramatically with ordinarily some loss in strength and modulus. This approach works most effectively in blends of high polyethylene and poly(vinyl chloride) content. Three grades of CPE were studied here which revealed that the specific structure of the CPE molecule is a factor. The effectiveness of CPE for blend modification is believed to derive from the graded molecular structure acquired during chlorination.     

Polyester–polycarbonate blends. V. Linear aliphatic polyesters

Polycarbonate blends with the linear aliphatic polyesters poly(ethylene succinate) (PES), poly(ethylene adipate) (PEA), poly(1,4-butylene adipate) (PBA), and poly(hexamethylene sebacate) (PHS) were prepared by solution casting. Blends containing PES, PEA, and PBA exhibited a single T_g by DSC and thus form a single, miscible amorphous phase with polycarbonate. However, blends containing PHS exhibited only partial miscibility. Crystallinity of the polyesters was reduced by mixing with polycarbonate; however, plasticization by the polyesters induced crystallization of the polycarbonate. Miscibility in these systems is the result of an exothermic heat of mixing stemming from an interaction of the carbonyl dipole of the ester group with the aromatic carbonate. The effect of polyester structure on miscibility with polycarbonate is interpreted by and correlated with heats of mixing obtained by direct calorimetry of low molecular weight liquid analogs of the polymers.     

Optimization of design and operating policy of an industrial two-bed co-shift reactor

The optimal operating policy for a two-bed adiabatic CO-converter is computed using the Discrete Maximum Principle. The problem is then extended to determine also the optimal design of the system. A sensitivity analysis of the optimal solutions is presented, showing the influence of the principal process parameters. Economical, chemical and physical data have been obtained from an existing CO-converter in a standard 1000 short Tons/day NH₃ plant.     

Gas and vapor sorption in polymers just below Tg

Generally, sorption isotherms for gases like CO₂ in glassy polymers are concave to the pressure axis, whereas in the rubbery state these isotherms are linear for gases or sometimes convex to the pressure axis for more condensable vapors. Examples of CO₂ isotherms are reported here that show at low pressure the curvature characteristic of glasses and then become linear at higher pressures. This is observed when the glass transition temperature T_g is not much greater than the observation temperature T, and plasticization of the polymer by sorbed CO₂ causes T_g to become equal to T within the range of pressures employed in the isotherm measurement. For the sorption of vapors in glassy polymers, this can lead to sigmoidal isotherms, as discussed using an illustration from the literature.     

Modelling formation and growth of H2SO4-H2O aerosols: Uncertainty analysis and experimental evaluation

An aerosol dynamics model, AERO2, is presented, which describes the formation of H₂SO₄-H₂O aerosol in a smog chamber. The model is used to analyse how the uncertainties on four input parameters are propagated through an aerosol dynamics model. The input parameters are: the rate of the reaction between SO₂ and OH (k₁), the ratio between the nucleation rate used in AERO2 and that derived from classical nucleation theory (t_n), the H₂SO₄ mass accommodation coefficient () and a measure of the turbulence intensity in the reactor (k_e). Uncertainties for these parameters are taken from the literature. One of the results of the analysis is that AERO2 and aerosol dynamics models in general can only predict upper bounds for the total number (N_tot) and total volume (V_tot) concentrations of the particles. The uncertainties on N_tot and V_tot are mainly due to the uncertainties on k₁, and t_n. An uncertainty factor of 20–100 still remains when the uncertainty on k₁, is reduced to ±5%. Aerosol measurements from three smog chamber experiments have therefore been used, in an attempt to reduce the uncertainty on k₁ and t_n. Values for k₁ are obtained in the reduced range 7.8 × 10⁻¹³ to 1.0 × 10⁻¹² cm³ s⁻¹, which is within the range found in the literature. For t_n, values in the range 10⁴–10⁷ are obtained, which is close to the upper bound of the range in literature. These values for t_n are in marked contrast with a recent set of experiments on nucleation in H₂SO₄-H₂O mixtures, which suggests a value for t_n of at most 10⁻⁵.     

Aryl phosphate ester fire‐retardant additive for low‐smoke vinyl applications

Additives that act as flame retardants can contribute significantly to smoke generation because they decrease the efficiency of the fuel source and, as a result, create a sooty combustion. Work on a new phosphate ester material has shown interesting results and synergies that complement both flame retardancy and low smoke generation in flexible vinyl compositions. This new proprietary aryl phosphate was examined in both neat and blended systems and compared to other typical phosphate ester fire‐retardant (FR) compounds for vinyl. Additionally, the flammability and smoke effects were measured with and without other common vinyl FR additives (zinc borate and ammonium octamolybdate). J. Vinyl Addit. Technol. 10:187–192, 2004. © 2004 Society of Plastics Engineers.     

Behavior of the western pine beetle during host colonization

After living ponderosa pines were baited with either female-infested bolts or synthetic pheromones,Dendroctonus brevicomis were caught on sticky screens throughout trapping periods of 15–46 days; however, large numbers of beetles were trapped during only a small portion (5–10 days) of these trapping periods. The most attractive portions of trees attacked contained 3–6 beetles dm², in galleries ca. 2 cm long. Catch increased following addition of males to female-infested bolts, supporting the hypothesis that male-produced frontalin is an attractive pheromone of the western pine beetle. Catch at bolts removed from trees under attack was strongly dependent upon levels of boring activity. We found no evidence of interruption of the response to attractants during host colonization.Coleoptera: Scolytidae. Trade names and commercial enterprises or products are mentioned solely for information and do not constitute endorsement by the U.S. Department of Agriculture or University of California.     

Inhomogeneous Density in Die Compaction: Experiments and Finite-Element Calculations

X-ray density measurements and two-color powder displacement observations were used to determine the reliability of the cylindrical test cell as a source of data for a plasticity model of granular materials. Calculations with such a model agree well with the experimental density distribution, for the cylindrical test cell itself and for a cylindrical die, compacted from one side by means of a profiled plunger .