Treatment thickening

The biodegradability of functional derivatives of polyethylene, particularly polyvinyl alcohol and polyacrylic acid and derivatives have received attention because of their water solubility, high-volume use, and disposal into the aqueous environment. Polyvinyl alcohol is used in a wide variety of applications, including textiles, paper, plastic films, and temporary packaging, and polyacrylic acid is widely used in detergents as a builder, super absorbent for diapers and feminine hygiene products, water treatment, thickeners, pigment dispersant, and the like. 

Inverse microemulsion polymerization is used for the production of water-soluble polymers of high molecular weight, with applications in enhanced oil recovery, as flocculants in water treatments, thickeners for coatings, and retention aids in papermaking. 

Definition Mixed ethoxylated and propoxylated monomer Properties Cl. liq. APHA color 10 m.w. 568 pH 7.7 acid value 0.17 Uses Surface modifier in water treatment thickener dispersant hydrophilic agent in aq. sol ns. and emulsion polymers Manuf./Distrib. GelesI Polysciences Trade Names Containing Silwet L-7608... 

Most carbide acetylene processes are wet processes from which hydrated lime, Ca(OH)2, is a by-product. The hydrated lime slurry is allowed to settle in a pond or tank after which the supernatant lime-water can be decanted and reused in the generator. Federal, state, and local legislation restrict the methods of storage and disposal of carbide lime hydrate and it has become increasingly important to find consumers for the by-product. The thickened hydrated lime is marketed for industrial wastewater treatment, neutrali2ation of spent pickling acids, as a soil conditioner in road constmction, and in the production of sand-lime bricks. 

The most common thickener is the circular basin type shown in Figure 7. After treatment with flocculant, the feed stream enters the central feed well which dissipates the stream s kinetic energy and disperses it gendy into the thickener. The feed finds its height in the basin where its density matches the density of the inside suspension and spreads out at that level. SoHds concentration increases downward in an operating thickener giving stabiHty to the process. 

Dissolved Air Flotation. Dissolved air flotation (DAF) is used to separate suspended soflds and oil and grease from aqueous streams and to concentrate or thicken sludges. Air bubbles carry or float these materials to the surface where they can be removed. The air bubbles are formed by pressurizing either the influent wastewater or a portion of the effluent in the presence of air. When the pressurized stream enters the flotation tank which is at atmospheric pressure, the dissolved air comes out of solution as tiny, microscopic bubbles. Dissolved air flotation is used in many wastewater treatment systems, but in the United States it is perhaps best known with respect to hazardous waste because it is associated with the Hsted waste, K048, DAF flotation soflds from petroleum refining wastewaters. Of course, the process itself is not what is hazardous, but the materials it helps to remove from refining wastewaters. 

Clarifiers typically are used in chemical precipitation and biological treatment processes to remove precipitated metal soHds and suspended biological soHds. To prevent the sludge blanket from becoming too thick or heavy, part of the sludge blanket is removed continuously or intermittently from the system and thickened prior to disposal. 

More detailea descriptions of small-scale sedimentation and filtration tests are presented in other parts of this section. Interpretation of the results and their conversion into preliminary estimates of such quantities as thickener size, centrifuge capacity, filter area, sludge density, cake diyness, and wash requirements also are discussed. Both the tests and the data treatment must be in experienced hands if error is to be avoided. 

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

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