Critical and sustainable fluxes: theory, experiments and applications

Over the last ten years, numerous membrane filtration data have been viewed in the light of the concept of critical flux. This concept, used in a number of different ways often without explicit redefinition, is here clarified both from a theoretical and from an experimental viewpoint. Also, a link is make with the sustainable fluxes. Also covered are the various methods of measurement and the influence of membrane and suspension properties on the critical flux. Over the same period of time, models have been developed to explain the observed behaviour. Those for stable colloidal suspensions are based on the existence of repulsive interactions between soft matter constituents. The assumptions and usefulness of various models are discussed. The concept of a critical concentration for phase transition is introduced into the theoretical discussion. For theoreticians and experimentalist, this and the clarified concept of a small set of critical fluxes will continue to provide a valuable framework. For membrane users dealing with most industrial process streams (mixtures and complex fluid) the concept of a sustainable flux (shown as being derived from critical flux) is of a great utility; above a certain key flux (dependent on hydrodynamics, feed conditions and process time) the rate of fouling is economically and environmentally unsustainable. For many, knowledge of the point below which no major irreversible fouling occurs (the critical flux) in a membrane separation will always be of greatest utility

Exploring the differences between forward osmosis and reverse osmosis fouling

A comparison of alginate fouling in forward osmosis (FO) with that in reverse osmosis (RO) was made. A key experimental finding, corroborated by membrane autopsies, was that FO is essentially more prone to fouling than RO, which is opposite to a common claim in the literature where deductions on fouling are often based solely on the water flux profiles. Our theoretical analysis shows that, due to a decrease in the intensity of internal concentration polarization (ICP), and thus an increase in the effective osmotic driving force during FO fouling tests, the similarity of experimental water flux profiles for FO and RO is in accordance with there being greater fouling in FO than RO. The specific foulant resistance for FO was also found to be greater than that for RO. Possible explanations are discussed and these include the influence of reverse solute diffusion from draw solution. Whilst this explanation regarding specific foulant resistance is dependent on the draw solution properties, the finding of greater overall foulant accumulation in FO is considered to be a general finding. Additionally, the present study did not find evidence that hydraulic pressure in RO plays a critical role in foulant layer compaction. Overall this study demonstrated that although FO has higher fouling propensity, it offers superior water flux stability against fouling. For certain practical applications this resilience may be important

A Ligand Field Theory View Of The Electronic Structure Of Cax (x=f, Cl, Br, I, And O)

The CaX family of diatomic molecules illustrates concepts developed by inorganic chemists to rationalize the properties of metal-centered complexes. The basic idea is that an atom or an atomic-ion is surrounded by ligands, and that the electronic properties of the complexes are dealt with in a model in which the central metal atom and the ligands are treated as retaining their separated atom or molecule properties perturbed by identifiable and quantifiable metal-ligand interactions. Ligand Field Theory is \textit{semi-empirical} in the sense that it is a framework for building a systematic understanding of the properties of families of complexes from spectroscopic measurements of the properties of the separated species and the interactions between them. The electronic structures of the CaX molecules are described by atomic-ions-in-molecule ligand field models. The Ca atom is treated as Ca$^{+}$ with a single electron in the 4s$\sigma$ , 4p$\sigma$ or $\pi$, or 3d$\sigma$,$\pi$, or $\delta$ orbital For X=F, Cl, Br, and I, the ligand is a closed-shell halide ion. For X=O, the ligand is an open-shell O$^{-}$ ion with a single hole in the p$\pi$ ($\pi$$^{-1}$) or $p\sigma$ ($\sigma$$^{-1}$) orbital. The building blocks of the electronic structure model are known by different names in the inorganic chemistry, small-molecule spectroscopy, and quantum chemistry communities. Fine structure (spin-orbit, spin-spin, spin-rotation, and lambda-doubling) and spectroscopic perturbation matrix elements (spin-orbit and L-uncoupling) report on the CaX electronic structure

Financial reporting in the extractive industries; Accounting research study no. 11

https://egrove.olemiss.edu/aicpa_guides/1142/thumbnail.jp

The control of escape behaviour in, and the histopathology of, the Norway lobster, Nephrops norvegicus (L.)

Nephrops norvegicus, like other lobsters and crayfish, react to threatening stimuli by producing of the tail-flip escape response. This response, which is important in both predator avoidance and capture by trawling, takes the form of repeated flexions and extensions of the abdomen, produced by the deep abdominal flexor and extensor muscles. Much research has been concentrated on both the metabolic and neuronal factors controlling and limiting the tail-flip swimming of decapod Crustacea, but little attention has been focused upon the interactions between these two areas. This study has examined the tail-flip swimming of N.norvegicus in terms of both metabolic and neuronal limitations. Results have indicated that prolonged swimming and its recovery are limited neither by the availability of energy (from direct, stored sources - endogenous muscle ATP; or from indirect sources - by glycolytic production of ATP from D-glucose),nor by alteration of inter- or intra-cellular conditions by the build up of the glycolytic end product L-lactate. However, the part played by phospho-L-arginine (another short-term energy reserve in muscle) in the limitation of tail-flipping has not been unequivocally defined, and the possibility remains that there may be some metabolic influence in determining the endurance and recovery of swimming. Despite the lack of definitive evidence against any metabolic limitation of escape swimming, the results of further experiments suggest that neuronal factors play a major role in the limitation of tail-flipping. These experiments were designed to assess the importance and site of action of neuronal factors, in particular habituation, in swimming. Furthermore, the waning of tail-flipping in response to repeated stimulation appears to represent true habituation. By the use of both histochemical and morphological techniques, the roles of the muscles of the thoraco-abdominal joint in both tail-flipping and postural control have been partially elucidated. These results suggest both bracing and steering functions for the larger muscles of the two groups examined (thoraco-abdominal extensors and abdominal abductors) and postural roles for the smaller muscles. These investigations also identify suitable areas for further research, not least an examination of the innervation and recruitment of these muscle groups during tail-flipping in order to determine unequivocally their bracing and steering functions