Process

Particles finer than 0.1 µm (10^-7m) in water remain continuously in motion due to electrostatic charge (often negative) which causes them to repel each other. Once their electrostatic charge is neutralized by the use of coagulant chemical, the finer particles start to collide and agglomerate (combine together) under the influence of Van der Waals

Van der Waals force

In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...

's forces. These larger and heavier particles are called flocs.

Flocculants, or flocculating agents (also known as flocking agents), are chemicals that promote flocculation by causing colloid

Colloid

A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...

s and other suspended particles in liquids to aggregate, forming a floc. Flocculants are used in water treatment processes to improve the sedimentation or filterability of small particles. For example, a flocculant may be used in swimming pool

Swimming pool

A swimming pool, swimming bath, wading pool, or simply a pool, is a container filled with water intended for swimming or water-based recreation. There are many standard sizes; the largest is the Olympic-size swimming pool...

 or drinking water

Drinking water

Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

 filtration to aid removal of microscopic particles which would otherwise cause the water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 to be turbid

Turbidity

Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....

 (cloudy) and which would be difficult or impossible to remove by filtration alone.

Many flocculants are multivalent cations such as aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 or magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

. These positively charged molecules interact with negatively charged particles and molecules to reduce the barriers to aggregation. In addition, many of these chemicals, under appropriate pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 and other conditions such as temperature and salinity

Salinity

Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

, react with water to form insoluble hydroxide

Hydroxide

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

s which, upon precipitating, link together to form long chains or meshes, physically trapping small particles into the larger floc.

Long-chain polymer flocculants, such as modified polyacrylamide

Polyacrylamide

Polyacrylamide is a polymer formed from acrylamide subunits. It can be synthesized as a simple linear-chain structure or cross-linked, typically using N,N-methylenebisacrylamide. Polyacrylamide is not toxic...

s, are manufactured and sold by the flocculant producing business. These can be supplied in dry or liquid form for use in the flocculation process. The most common liquid polyacrylamide is supplied as an emulsion with 10-40% actives and the rest is a carrier fluid, surfactants and latex

Latex

Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...

. Emulsion polymers require activation to invert the emulsion and allow the electrolyte groups to be exposed.

Agents

• alum
  Alum
  Alum is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated potassium aluminium sulfate with the formula KAl2.12H2O. The wider class of compounds known as alums have the related empirical formula, AB2.12H2O.-Chemical properties:Alums are...
  
  
• aluminium chlorohydrate
  Aluminium chlorohydrate
  Aluminium chlorohydrate is a group of specific aluminium salts having the general formula AlnClm. It is used in deodorants and antiperspirants and as a coagulant in water purification....
  
  
• aluminium sulfate
  Aluminium sulfate
  Aluminium sulfate, alternatively spelt aluminum sulfate, aluminium sulphate, or aluminum sulphate; is a chemical compound with the formula Al23...
  
  
• calcium oxide
  Calcium oxide
  Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
  
  
• calcium hydroxide
  Calcium hydroxide
  Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
  
  
• iron(II) sulfate
  Iron(II) sulfate
  Iron sulfate or ferrous sulfate is the chemical compound with the formula FeSO4. Known since ancient times as copperas and as green vitriol, the blue-green heptahydrate is the most common form of this material...
  
  
• iron(III) chloride
  Iron(III) chloride
  Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3. The colour of iron chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red...
  
  
• polyacrylamide
  Polyacrylamide
  Polyacrylamide is a polymer formed from acrylamide subunits. It can be synthesized as a simple linear-chain structure or cross-linked, typically using N,N-methylenebisacrylamide. Polyacrylamide is not toxic...
  
  
• polyDADMAC
  PolyDADMAC
  Polydiallyldimethylammonium chloride, or shortened polyDADMAC is a homopolymer of diallyldimethylammonium chloride . The molecular weight of polyDADMAC is typically in the range of hundreds of thousands of grams per mole, and even up to a million for some products. PolyDADMAC is usually delivered...
  
  
• sodium aluminate
  Sodium aluminate
  Sodium aluminate is an important commercial inorganic chemical. It works as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate is a white crystalline solid having a formula variously given as NaAlO2, NaAl4 , Na2O·Al2O3, or Na2Al2O4...
  
  
• sodium silicate
  Sodium silicate
  Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles...
  
  

The following natural products are used as flocculants:

• Chitosan
  Chitosan
  Chitosan is a linear polysaccharide composed of randomly distributed β--linked D-glucosamine and N-acetyl-D-glucosamine...
  
  
• Isinglass
  Isinglass
  Isinglass is a substance obtained from the dried swim bladders of fish. It is a form of collagen used mainly for the clarification of wine and beer. It can also be cooked into a paste for specialized gluing purposes....
  
  
• Moringa oleifera
  Moringa oleifera
  Moringa oleifera, the word Moringa probably came from dravidian language Tamil and commonly referred to as "Shojne" in Bengali, "Munagakaya" in Telugu,"Shenano" in Rajasthani,...
  
   seeds (Horseradish Tree)
• Gelatin
  Gelatin
  Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
  
  
• Strychnos
  Strychnos
  Strychnos is a genus of flowering plants, belonging to family Loganiaceae . The genus includes about 190 species of trees and lianas, distributed around the world's tropics....
  
   potatorum seeds (Nirmali nut tree)
• Guar gum
  Guar gum
  Guar gum, also called guaran, is a galactomannan. It is primarily the ground endosperm of guar beans. The guar seeds are dehusked, milled and screened to obtain the guar gum. It is typically produced as a free-flowing, pale, off-white-colored, coarse to fine ground powder.-Production:Guar gum is an...
  
  
• Alginates (brown seaweed extracts)