This document discusses the water treatment process of coagulation. Coagulation involves adding chemicals called coagulants to water to neutralize surface charges on particles and allow them to stick together and form larger particles that settle out via gravity. Key coagulants discussed are aluminum sulfate and ferric sulfate. The document also covers colloid stability, the coagulation process, properties of effective coagulants, and coagulant aids which add density and strength to the settling floc particles.

1. Water Treatment
Prepared by Ginger A. Amonoy BSCE-3C

2. Coagulation
 It is used to remove turbidity, color, and
bacteria from drinking waters.
 The goal of coagulation is to change the
surface charge on the particles so they can stick
together to form larger particles that will settle
by gravity.

3. Colloid Stability & Destabilization
 Colloid is a substance
microscopically dispersed
evenly throughout another
one.
 In natural waters, colloids are
stable because the surface
charge of these particles are
like-charged, and they,
therefore, repel one another.

4.  Coagulation Process
 The coagulant neutralizes the charge on the surface.
 The higher the concentration of the positive ion added, the
greater extent to which the surface charge is neutralized.

5. Coagulants
 It is a chemical added to the water to cause particles to
coagulate.
 3 key properties:
1. Trivalent cation (e.g. sodium & calcium)
2. Non-toxic
3. Insoluble in the neutral pH range
aluminum sulfate ferric sulfate

6. Aluminum Sulfate
 It can be dry or liquid alum ( Al2(SO4)3· 14H2O ).
 Using alkalinity to neutralize acid;
liquid alum alkalinity
Al2(SO4)3 · 14H2O + 6HCO3 == 2Al(OH) 3(s) + 6CO2 + 14H2O + 3SO
 No-presence of alkalinity;
liquid alum sulfuric acid
Al2(SO4)3 · 14H2O == 2Al(OH) 3(s) + 3H2SO4 + 8H2O
 pH range for alum – 5-8

7. Iron
 Ferric cations can be supplied by adding ferric sulfate
(Fe2(SO4)3 · 7H2O) or ferric chloride (FeCl3 · 7H2O).
 FeCl3 in the presence of alkalinity;
ferric chloride alkalinity
FeCl3 · 7H2O + 3HCO3 == Fe(OH)3(s) + 3CO2 + 3Cl¯ + 7H2O
 Without alkalinity;
ferric chloride
FeCl3 + 3H2O == Fe(OH)3(s) + 3H⁺ + Cl⁻
 pH range for iron – 4-9

8. Coagulant Aids
 It add density to slow-settling flocs and add toughness to
the flocs so that they will not break up during the mixing
and settling processes.
 3 basic types:
1. Activated Silica - is sodium silicate that has been
activated with sulfuric acid, alum, CO2, or chlorine.
2. Clay
3. Polymers - are man-made organic compounds made
up of a long chain of smaller molecules. Polymers can
be either cationic, anionic, or nonionic.