Coagulation and Flocculation

Colloidal particle are often found suspended in drinking water. Colloids are minerals such as silt, clays, silica, hydroxides and metallic salts and organic particles such as humic and fluvic acids, color and surfactants (SNF, 2003). Safferman (n.d.) categorised colloids in drinking water into hydrophilic which have affinity for water such as soap, starch, proteins and detergents and hydrophobic which do not have affinity to water such as metal oxides and clay.

Coagulation and flocculation are effective water treatment procedures. Coagulation and flocculation are used to remove colour and particulate matter including protozoa, viruses, bacteria and iron, manganese, tastes and odours from water (MRWA, 2013). Vissotoviseth and Ahmed (2008) described chemical coagulation as effective filtration method however destabilization and removal of colloidal particles require high doses of chemicals.

Suspended solids can be filtered from water by coagulation and flocculation processes. Coagulation involves the neutralization of suspended solids by adding coagulants in the water which forms micro flocs after sticking together (Apostol et al., 2011; MWRA, 2011). Coagulation process is faster and involves high-energy mixing which neutralizes electrical charges of the particles and facilitates floc formation. SNF (2003) described coagulation as intermediate step in the physico-chemical treatment of water.

Flocculation is a slow and gentle mixing process (MWRA, 2013). The destabilized particles are agglomerated to form large visible flocs. Pinflocs and visible flocs are produced at the flocculation stage when microflocs are allowed to mix slowly. Pinflocs are filtered from water by sedimentation. Coagulants can be mineral or organic. Iron salts and aluminium salts are mineral coagulants used in water treatment and polyamines, polydadmac, dicyandiamide resins, and melamine-formaldehyde resins are organic coagulants (Apostol, et al., 2011; SNF, 2003).

References

Apostol, G., Kouachi, R. and Constantinescu, I. (2011) Optimization of Coagulation-Flocculation Process with Aluminium Sulphate Based on Response Surface Methodology. U.P.B. Science Bulletin, Series B, Vol 73(2).

Ministry of Health (2005) Draft Guidelines for Drinking-Water Quality Management for New Zealand. [Online] Available at http://www.health.govt.nz [Accessed on 29 September 2013].

MRWA (Minnesota Rural Water Association) (2013) Coagulation and Flocculation Process Fundamentals [Online] Available at http://www.mrwa.com [Accessed on 29 September 2013].

Safferman, S.I. (n.d.) Fundamentals of Coagulation and Flocculation. [Online] Available at http://www.waterworldce.com [Accessed on 29 September 2013].

SNF FLOERGER (2003) Coagulation Flocculation [Online] Available at http://www.snf.co.au [Accessed on 29 September 2013].

Visoottiviseth, P. and Ahmed, F. (2008) Technology for Remediation and Disposal of Arsenic. Reviews of Environmental Contamination and Toxicology. Volume 197. Springer. pp.77-129.

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