Foam flotation for fine particles removal from water: The example of zeolites

An experimental investigation is reported of the effects of several parameters on the foam flotation of fine zeolite particles, used here also as a model of fine particles. A general discussion is given relative to the application of the process to large‐scale clarification of turbid waters. Ion exchange of zinc, a typical heavy metal, by zeolite followed by flotation was also examined, resulting in the simultaneous removal (recovery) of zeolite and of heavy metal.     

Migration effects in a stochastic multipopulation model for African bee population dynamics

The rate of northern migration of the Africanized honey bee (AHB) in the United States has recently slowed dramatically. This paper investigates the impact of migration on the equilibrium size distributions of a particular stochastic multipopulation model, namely a coupled logistic power law model. The bivariate equilibrium size distribution of the model is derived and illustrated with parameter values used to describe AHB population dynamics. In the model, the difference between the equilibrium sizes of the two populations is a measure of the effect of migration. The distribution of this difference may be approximated by a normal distribution. The mean and variance parameters for the normal are predicted accurately by a second-order regression model based on the migration rate and the maximum size of the first population. The methodology is general, and should be useful in studying the migration effect in many other applications with one-way migration.     

On the use of growth rate parameters for projecting population sizes: Application to aphids

This paper extends the application of the cumulative size based mechanistic model, which has previously been shown to describe diverse aphid population size data well. The mechanistic model is reviewed with a focus on the explanatory role of the birth and death rate formulation. An analysis of two data sets, one on the mustard aphid and the other on the pecan aphid, indicates that multiple linear regression equations based on the estimated birth and death rate parameters alone account for nearly all (R² > 0.95) of the variability in two key population attributes, namely the peak count and the cumulative density. This indicates that population size variables may be projected directly from the growth rate parameters using linear equations. Such linear relationships based on the birth and death rate parameters are shown to hold also for certain generalized mechanistic models for which the analytical solution is not available. The birth and death rate coefficients, therefore, constitute a new succinct set of variables that could be included in the predictive modeling of aphid populations, as well as other insect and animal populations with local collapse which follow similar growth dynamics.     

Population dynamics models based on cumulative density dependent feedback: A link to the logistic growth curve and a test for symmetry using aphid data

Density dependent feedback, based on cumulative population size, has been advocated to explain and mathematically characterize “boom and bust” population dynamics. Such feedback results in a bell-shaped population trajectory of the population density. Here, we note that this trajectory is mathematically described by the logistic probability density function. Consequently, the cumulative population follows a time trajectory that has the same shape as the cumulative logistic function. Thus, the Pearl–Verhulst logistic equation, widely used as a phenomenological model for density dependent population growth, can be interpreted as a model for cumulative rather than instantaneous population. We extend the cumulative density dependent differential equation model to allow skew in the bell-shaped population trajectory and present a simple statistical test for skewness. Model properties are exemplified by fitting population trajectories of the soybean aphid, Aphis glycines. The linkage between the mechanistic underpinnings of the logistic probability density function and cumulative distribution function models could open up new avenues for analyzing population data.     

Modelling the sorption of metals from aqueous solutions on goethite fixed-beds

The research on separation methods of toxic metals from wastewater streams is continuous and intensive and, among them, sorption processes are considered of particular importance, mainly due to their effectiveness. The sorption of chromate anions and zinc cations from dilute aqueous solutions using a packed-bed (column configuration) of synthesised granulated goethite was investigated in the present study. The examined parameters during this investigation were the following: (1) the initial pH value of metal-laden aqueous solution (two representative values at acidic pH, 3.5 and 5.0, were tested); (2) the quantity of sorbent in the column, corresponding to bed height; and (3) the influence of ethylene diamine tetra acetic acid (EDTA) addition, a common, strong chelating agent. The Bed Depth-Service Time model has been applied to the sorption results in order to model the column operation. The removal efficiency of Cr(VI) anions by the sorptive column was found to be higher than that of Zn(II) cations. The presence of EDTA caused a certain decrease of removal efficiency for the case of hexavalent chromium, due to competition for the same sorption sites, while the removal of divalent zinc was increased, due to variation of cation speciation.