Environmental Engineering 343

1. Philadelphia University Faculty of Engineering Department of Civil Engineering First Semester, 2013/2014 Environmental Engineering 343 Lecture 8: Water Treatment 2

7. Selection of Treatment Processes Selection of the set of Treatment Processes will be based on : • Sources of water intake • Characteristic of water Detailed raw water quality analysis for a minimum of one year, or longer, at periods of high, low and medium flows. The parameters to be looked at all those listed in the legislative standards • Cost • Suitability of the processes for removing particulate impurities. Example: • Turbidity; suitable process might be coagulation , sedimentation or filtration • For pathogen, pre or post chlorination, UV, ozone, or chloramines

9. Coagulation & Flocculation Effective removal of particles < 50um is difficult in normal settling operations. Colloidal particles are difficult to separate from water because they do not settle by gravity and are so small that they pass through the pores of filtration media. To be removed, the individual colloids must aggregate and grow in size. The objective of coagulation (and subsequent flocculation) is to turn small particles into larger particles called flocs. The flocs are readily removed in subsequent processes such as settling, filtration or other methods. Coagulation means the addition of one or more chemicals to condition the small particles for subsequent processing by flocculation Flocculation is the process of aggregation of the destabilized particles and precipitation products.

10. Water treatment -Coagulation • Colloids possess a negative charges that repels other colloidal particles before they colloid with one another . • In order to destabilize the colloids, we must neutralize the charge by addition of an ions of the opposite charge for the colloids • Positive ions is added to water to reduce the surface charge to the point where the colloids are not repelled from each other. • Coagulants tend to be positively charged.  Due to their positive charge, they are attracted to the negative particles in the water • The combination of positive and negative charge results in a neutral , or lack of charge

12. Filtration Filtration is a process for separating suspended or colloidal impurities from water by passing through a porous medium, usually a bed of sand or other medium. Settled water (Sedimentation effluent) turbidity range 1-10 TU – due to residue of flocs particles. So turbidity need to be reduce to less than 0.3 Common materials for granular bed filters: • Sand (slow, rapid or high) • Anthracite coal • Dual media (Coal plus sand) • Mixed media (coal, sand & garnet)

13. Disinfection • Disinfection is used in water treatment to reduce pathogens (diseases-producing microorganisms) to an acceptable level • Treatment of water with chemicals to kill bacteria” • Two objectives: • Primary disinfection : Kill any pathogen in water • Secondary (residual) disinfection : Prevent pathogen re-growth in the water. • Method use : • Should be harmless and unobjectionable to the consumer • Should be able to retain a residual disinfecting effect for a long period

14. Disinfection- properties • Destroy bacteria / pathogens within a practicable period of time, over an expected range of water temperature • Effective at variable compositions, concentration and conditions of water treated. • Neither toxic to humans and domestic animals nor unpalatable • Not change water properties • Have residual in a sufficient concentration to provide protection against recontamination • Can be determined easily, quickly, and preferably automatically. • Dispensable at reasonable cost • Safe and easy to store, transport, handle and supply • Not form toxic by-products due to their reactions with any naturally occurring materials in water.

15. Disinfection- Methods • Chlorination- chlorine • Ultra violet Radiation • Ozonation