Coagulation polyelectrolytes

By calibrating the column or column set with a set of standards, a calibration curve of retention versus the logarithm of molar mass is constructed so that molar mass averages may be calculated for unknown polymers. Figure 6.10 is an example chromatogram of a separation of a polyDADMAC coagulant polyelectrolyte. The molar mass distribution, see Figure 6.11, is relative to the calibration standards used, polyethylene oxide in this example. 

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

Polyelectrolytes refers to all water-soluble organic polymers used for clarification, whether they function as coagulants or flocculants. Water-soluble polymers may be classified as follows ... 

Coagulation involves the addition of chemicals to alter the physical state of dissolved and suspended solids. This facilitates their removal by sedimentation and filtration. The most common primary coagulants are alum ferric sulfate and ferric chloride. Additional chemicals that may be added to enhance coagulation include activate silica, a complex silicate made from sodium silicate, and charged organic molecules called polyelectrolytes, which include large-molecular-weight polyacrylamides, dimethyl-diallylammonium chloride, polyamines, and starch. 

Polymer A chemical formed by the union of many monomers (a molecule of low molecular weight). Polymers are used with other chemical coagulants to aid in binding small suspended particles to form larger chemical floes for easier removal from water. All polyelectrolytes are polymers, but not all polymers are polyelectrolytes. 

These condensed tannins and their derivatives, all of high molecular weight, function as anionic polyelectrolyte sludge conditioners, tending to sequester hardness salts and hinder their precipitation as crystalline scales. In addition, when precipitation does occur, the condensed tannins coagulate the particles, resulting in a mobile sludge that can be easily blown down. 

The first step in the precipitator is the addition of polyelectrolyte solution in the flash mix tank [T-98], surge tank [T-99], and then into the slow mix unit [T-100] containing a variable speed mixing paddle. The purpose of this unit is to coagulate and flocculate53 the metal hydroxide precipitates. 

This plant produces 130 m2/h of enameled steel and operates 3500 h/yr. It uses 0.0036 m3 water/m2 of product to coat the steel. Average process water flow is 0.144 m3/h for coating operations and 0.734 m3/h for metal preparation. The primary treatment in-place for process wastewater is clarification and settling. Other water treatment practices employed are pH adjustment with lime or acid, sludge applied to landfill, polyelectrolyte coagulation, and inorganic coagulation. 

This facility produces 360 m2/h of porcelain enameled aluminum for 4000 h/yr, and uses 0.038 m3 of process water/m2 of product coated. The mixed wastewater stream is treated by equalization (settling), pH adjustment (lime or acid), polyelectrolyte coagulation, clarification, and contractor removal of the resulting sludge prior to discharge to a surface stream. Process water flow for this production consists of 8.12 m3/h and 4.37 m3/h for surface preparation and coating operations, respectively.3 5... 

Method Chemical precipitation of dissolved and complexed metals by reaction with lime and subsequent removal of the precipitated solids by gravity settling in a clarifier. Alum and polyelectrolyte are added for coagulation and flocculation. 

In steric stabilization the colloids are covered with a polymer sheath stabilizing the sol against coagulation by electrolytes. In sensitization or adsorption flocculation, the addition of very small concentrations of polymers or polyelectrolytes leads to destabilization (Lyklema, 1985). 

The presence of polymers or polyelectrolytes have important effects on the Van der Waal interaction and on the electrostatic interaction. Bacterial adhesion, as discussed in Chapter 7.9 may be interpreted in terms of DLVO theory. Since the interaction in bacterial adhesion occurs at larger distances, this interaction may be looked at as occurring in the secondary minimum of the net interaction energy (Fig. 7.4). Particle Size. The DLVO theory predicts an increase of the total interaction energy with an increase in particle size. This effect cannot be verified in coagulation studies. 

Coagulants/ Flocculants Ferric chloride, ferric sulphate, polyelectrolytes... 

Coagulants are used to bind together particulate and colloidal matter so they may be filtered from the feed before the membrane process. Coagulants can be either inorganic (such as ferric salts) or organic polyelectrolytes. The correct dosage and... 

Repulsive forces between Fe oxide particles can be established by adsorption of suitable polymers such as proteins (Johnson and Matijevic, 1992), starches, non-ionic detergents and polyelectrolytes. Adsorption of such polymers stabilizes the particles at electrolyte concentrations otherwise high enough for coagulation to occur. Such stabilization is termed protective action or steric stabilization. It arises when particles approach each other closely enough for repulsive forces to develop. This repulsion has two sources. 1) The volume restriction effect where the ends of the polymer chains interpenetrate as the particles approach and lose some of their available conformations. This leads to a decrease in the free energy of the system which may be sufficient to produce a large repulsive force between particles. 2) The osmotic effect where the polymer chains from two particles overlap and produce a repulsion which prevents closer approach of the particles. 

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