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The ability of osmotically assisted reverse osmosis to draw water from concentrated brine (> 75 g/L) can be attributed to the combined effect of reducing the transmembrane osmotic pressure difference via a draw solu

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A model is presented that describes the effect of pH on the adsorption of an isomerically pure anionic surfactant species at a mineral oxide/water interface. A site-binding model, to account for effects of pH, surface heterogeneities, and counterions, is incorporated into a patchwise, phase-separation modeling approach, making it possible to predict both the surface charge and the counterion association beneath an adsorbed surfactant aggregate. Parameters for the site binding model on α-alumina are obtained from experimental surface charge measurements. The formation of both local monolayers (hemimicelles) and bilayers (admicelles) is allowed, although the isotherms studied in this paper are fit by parameter values that predict admicelle formation only. The model is able to predict experimental measurements of the adsorption of an isomerically pure, anionic surfactant species on α-alumina as a function of pH. It reproduces several previously unexplained experimental observations; in particular, it offers an explanation for the observation of significant adsorption of anionic surfactant above the point of zero charge (pzc) of a mineral oxide surface.

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The addition of water treatment chemicals has always been considered as a standard operation in water and wastewater treatment. The concentration of chemicals was usually kept to the minimum necessary to achieve a good quality of potable or otherwise treated water. A significant interruption to the status-quo occurred more than 20 years ago after a severe and highly publicized outbreak of Cryptosporidium parvum oocysts. The strategic planning after the outbreak was to shift from physical-chemical to physical treatment methods, such as membrane filtration and UV disinfection. As such, the new procedures were supposed to eliminate the threat of water contamination through a minor addition of chemicals. Such was the mistrust and disappointment with water treatment chemicals themselves.Indeed, water treatment technologies are now using novel physical treatment methods. Membranes largely replaced granular filtration, and UV is paving the way towards minimization or elimination of the use of classic disinfection chemicals, such as chlorine and its derivatives. Yet, far from the "high-tech" revolution in water treatment technologies actually reducing the use of chemicals, it has in fact been significantly increased. The "conventional" chemicals used for pre-treatment, disinfection, corrosion prevention, softening and algae bloom depression are all still in place. Furthermore, new groups of chemicals such as biocides, chelating agents and fouling cleaners are currently used to supplement them. These latter are the chemicals needed to protect the high-tech equipment, to optimize the treatment, and to clean the equipment between uses.The health effects of the new chemicals introduced into water are yet to be fully established. Typically, a higher treatment efficiency requires effective chemicals, yet those are not always environmentally friendly. It seems obvious that the "high-tech" revolution currently affects the sustainability of water resources, and certainly not in a completely positive way. In short, the adverse effects of the introduction of such a significant amount of treatment chemicals into our source water are yet to be evaluated.

An in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) technique has been developed to study the adsorption of sodium dodecyl sulfate (SDS) onto pure, colloidal hematite as a function of both concentration and pH. The absorption bands of methyl and methylene groups are most reliable for quantifying adsorption unambiguously. The infrared spectral results have been correlated with -potential studies to establish an absence of adsorption above the iso-electric point of 7.3, and to indicate that the mechanism of adsorption is physical, involving reversible electrostatic and hydrophobic forces. In the same way, there is no evidence for the existence of chemisorption. This is supported in the spectral results by the absence of shifts in relative band intensities and the absence of new adsorption bands. At low pH and high SDS concentrations, the adsorption is sufficient to cause a reversal in sign of the -potential. Spectral absorption measurements should be made under in situ conditions to obtain unambiguous results. Studies of adsorption on natural hematite indicate a high depletion of SDS from solution at low pH; the measurements are consistent with precipitation losses due to the presence of calcium and ferric ions. This precipitation leads to a drop in flotation recovery. At high pH, adsorption occurs onto mineral particles which have become coated with carbonate mineral, leading to a flat variation of recovery with pH. The results have enabled optimum flotation conditions to be defined. Recovery can be directly related to adsorption density at moderate pH below the iso-electric point. The optimum pH for flotation is 5; extremes of pH are detrimental to flotation recovery of pure mineral and should be avoided. Low pH causes surfactant precipitation, while high pH will lead to surface transformation of the mineral. A collector concentration of 0.05 times the critical micelle concentration, corresponding to partial monolayer coverage on the hematite surface, is sufficient to ensure good recovery.