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Particles finer than 0.1 μm (10 −7 m) in water remain continuously in motion due to electrostatic charge (often negative) which causes them to repel each other. [citation needed] Once their electrostatic charge is neutralized by the use of a coagulant chemical, the finer particles start to collide and agglomerate (collect together) under the influence of Van der Waals forces.
A variety of salts may be added to adjust the pH and act as clarifying agents, depending on the water chemistry. These include sodium hydroxide , calcium hydroxide , aluminum sulfate , aluminum oxide , ferric sulfate , ferric chloride , sodium aluminate , with flocculant aids polyaluminum chloride , polyferric chloride . [ 17 ]
They are thus often used as thickeners, emulsifiers, conditioners, clarifying agents, and even drag reducers. They are used in water treatment and for oil recovery. Many soaps, shampoos, and cosmetics incorporate polyelectrolytes. Furthermore, they are added to many foods and to concrete mixtures (superplasticizer).
Before the water enters the clarifier, coagulation and flocculation reagents, such as polyelectrolytes and ferric sulfate, [4] can be added. These reagents cause finely suspended particles to clump together and form larger and denser particles, called flocs, that settle more quickly and stably.
Finings’ actions may be broadly categorized as either electrostatic, adsorbent, ionic, or enzymatic.. The electrostatic types comprise the vast majority; including all but activated carbon, fining yeast, PVPP, copper sulfate, pectinase and pectolase.
A sewage sludge thickener. Thickening is often the first step in a sludge treatment process. Sludge from primary or secondary clarifiers may be stirred (often after addition of clarifying agents) to form larger, more rapidly settling aggregates. [9]
Many substances have historically been used as fining agents, including dried blood powder. [5] There are two general types of fining agents — organic compounds and solid/mineral materials. [4] Organic compounds used as fining agents are generally animal based, a possible cause of concern to vegans. [6]
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