Chlorination

Water treatment systems don’t remove 100% bacteria from the waste water effluent. Bacteria and virus free water is obtained after disinfection. Chlorination is one of the most effective disinfection processes. Chlorine has a higher degree of persistence in water distribution systems. In Chlorination process, hypochlorous acid acts as disinfecting agent (Solsona and Mendez, 2003). Hypochlorous acids are formed when chlorine hydrolizes in water. When hypochlorous acids splits into H+ and OCl ions, bacteria and viruses are inactivated and enzymatic activities are inhibited [hydroinstrument, n.d.).

Gaseous chlorine, chlorinated lime, sodium hypochlorite and calcium hypochlorite are chlorine-related compounds for water disinfection. Chlorine gas (Cl2) is highly toxic and liquefied under pressure. Chlorinated lime (CaO.2CaCl2.O.3H2O) is corrosive dry white powder (Solsona and Mendez, 2003). Sodium hypochlorite (NaClO) is corrosive and yellowish liquid solution, commonly called “liquid bleach” (hydroinstrument, 2013), and calcium hypochlorite (Ca (ClO)2.4H2O) is corrosive inflammable powder or granules and tablets (Solsona and Mendez, 2003). Sodium hypochlorite (NaClO) produces hypochlorous acid (HClO) and hypochlorite (ClO) ions, in water which affects bacteria and viruses by inactivating and inhibiting enzymatic activities. Sodium hypochlorite affects biological functions of proteins and produces deleterious effects on DNA (Martinez-Hernandez et al., 2013).

Chlorination can be applied in drinking water operations such as treatment of ground water, industrial process water, chilling water, cooling tower systems, drip irrigation systems, swimming pools, sanitary sewage, package treatment plants, and process waste water and plating wastewater (Martinez-Hernandez et al.,2013). In the chlorination process, chlorine has two forms in water: free chlorine and combined chlorine. Sodium hypochlorite or chlorine gas produces free chlorine when added to water. When free chlorine and ammonia reacts, combine chlorine is formed which includes monochloramine and dichloramine (Rosemount analytics, 2013)

References

Hydroinstruments (n.d.) Basic Chemistry of Chlorination. [Online [Available at www.hydroinstruments.com [Accessed on 19 October 2013].

Martinez-Hernandez, S., Vazquez-Rodriguez, G.A., Beltran-Hernandez, R.I., Prieto-Garcia, F., Miranda-Lopez, J.M., Franco-Abuin, C.M., Alvarez-Hernandez, A., Iturbe, U., and Coronel-Olivares, C. (2013) Resistance and Inactivation Kinetics of Bacterial Strains Isolated from the Non-Chlorinated and Chlorinated Effluents of  a WWTP.  International Journal of Environmental Research Public Health. Vol 10, pp. 3363-3383.

Rosemount Analytical (2013) Measurement of Total Chlorine in Municipal Wastewater Effluent. [Online] Available at www. Prododownload.vetmarket.com [Accessed on 19 October 2013]

Solsona, F. and Mendez, J.P. (2003) Water Disinfection. [Online] Available at www.who.int [Accessed on 20 October 2013].

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.