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member of the liquid phase to being a member of the solid phase. The final problem that arises is separating these two phases as efficiently and completely as possible. New Separation Technology It has come to my attention from several client companies that there is a new technology that works both in the initial and tertiary treatment of these waste streams. Several patents have been issued in this regard, and I have considered it best to address them as tangential flow separators. These devices are liquids/solids separators employing a unique principle, whereby "leaky" hoses utilize a laminar flow vector for the solid phase and a tangential flow vector for the liquid phase. The fluid path is contained within a tube (or hose, if you like), and the solid phase is forced down and out of the lumen of the tube. The liquid phase is collected by a mesh membrane of sorts and, for you chemical engineers out there, is related to a modified Frasch process minus the high pressures and temperatures. The solid phase continues down the tube where it is collected. The result is the removal of the solid phase from the liquid and the dewatering (or desolvating, depending on the solvent) of the solid phase. As it results in removal of particulates and their concentration for disposal or other applications, these may be considered as primary treat- ment devices. If the waste stream has a specific character, such as a waste stream from a plating operation, these devices could be used as such. But that's not the whole story, nor the designed intent. Tangential flow separators have, in fact, been designed as ter- tiary treatment devices to address recalcitrant waste streams with difficult-to-remove regulated and/or dangerous components. This is the result of a "package" of coagulants/flocculents designed specifically to address these situations. A not uncommon method of addressing these problems involves the oxidation of offending ionic species (such as Cu++, Cd++, Pb++, and others), as well as sequestering those anions (PO 4 ≡) that form insoluble precipitates and/or complex ions, and then utilizing the principle of ion- exchange to remove other offending anions (NO 3 - ). This involves a clay (usually a montmorillonite), an inorganic coagulant (alum or ferric ion compound), and a specially formulated polymer (usually a cationic polymer) to complete the removal process. The big advantage of this tangential flow separator technology is that it lowers the cost by controlling the cost of the polymers necessary (though not eliminating their usage) and by allowing the use of zeolites (specifically, clinoptilolites) to both remove and bind a variety of offending ionic species. Clinoptilolites are zeolites that function as scavengers for both anions and cations become highly charged and are readily removed as larger particulates from the liquid phase. Considerations Regarding Flocculants It is incumbent upon one wishing to separate solid and liquid phases to have them clearly delineated. The more completely they are delineated, the more effective the results. To this end, different coagulants/flocculants are employed depending on the waste stream that is encountered. Included among these are natural flocculants such as the montmorillonite clays (Bentonite, for example), as well as various volcanic clays including the various forms of zeolites (clinoptilolite, for example). Either mixtures of these coagulants/flocculants are used, or possibly those with additions of processing chemicals including various inorganic salts and polymer ion-exchange moieties, in order to effect an acceptable separation for particular waste streams. In any waste stream, there are both suspended and dissolved solids. The separation technology, whatever it is, is efficacious only insofar as it is capable of aggregating or precipitating these differing physical forms. So, both a physical and chemical reaction are usually necessary. Dissolved solids are precipitated, suspended solids are unsuspended, and both of these components are then collectively aggregated and removed via the tangential flow separation technology. How this separation occurs in any system is essential to understanding the functioning of the system and the rationale for its design. How And Why It Works Dissolved solids are the first to be considered. There are two ways to remove them: First, solubility may be altered by chemi- cal means. To this end, the addition of various salts may affect their solubility and result in the formation of an insoluble pre- cipitate. Secondly, these dissolved solids may be sequestered as solids in various complexes, which themselves are insoluble. By these means, virtually any dissolved solid can be removed. All one has to do is find an agent that will precipitate or sequester it. Bentonite is an economical and effective choice as a carrier, especially if it is treated to effect a particular separation. The suspended solids are next on the agenda for particular waste streams. These are a bit more complex as they vary widely in chemical structure and even in the mechanism of their suspension. Some are suspended as a result of their size (either very large or very small). Those that are very large depend, for the most part, on the velocity of the waste stream and its temperature. Smaller ones usually depend on surface charge. In removal, large ones are mostly an annoyance, but small ones can be a real problem, as surface phenomena are wateronline.com ■ Water Innovations Forward progress: Tangential flow separators can be small and transportable, as shown, or scaled up for large flows. TERTIARYTREATMENT 24