1.1Water Treatment Plants:-
Natural water is rarely of satisfactory quality for human consumption or industrial use and always need to be treated .The objectives of water treatment are to produce water that is safe for human consumption; water is appealing aesthetically to the consumer, and water at a reasonable cost.
When the water is destines for human consumption, its clarity is very important. When the turbidity was used as a control parameter, it provides these key benefits to a municipal drinking water treatment plant operator (Internet 1):
• Improves plant efficiency by optimizing proper chemical dosage.
• Insures the production of high quality, safe water for public distribution.
• Indicates incoming water quality.
• Ensures compliance with regulatory standards.
There are three treatment configurations of raw water depending on its quality (Wiesner & Mazounie, 1989) which include:(1)the conventional treatment which is used to describe a process train that includes coagulant feed, rapid mixing, flocculation, sedimentation, and filtration. (1)Direct filtration includes coagulant feed, rapid mixing, flocculation, and filtration where McCormick and King (1982) noted that direct filtration can be used for turbidity (0–10) NTU, color range of (0–15) color units, (0–1000) units/ml of algae, but Henery and Heinke (1996) state that it's effective for waters with low to moderate turbidity (5–20) NTU. (1)In- line filtration includes coagulant feed, rapid mixing, and filtration.

A typical conventional plant conation's a "train " of unit processes which are physically and chemically removes undesirable matter in order to produce potable water as shown in Figure (1.1)

Figure (1.1), Schematic of Surface Water Treatment Plant

The first step in treatment is coagulation which is a chemical treatment process that destabilizes colloidal particles to form of gelatinous precipitates (the floc), which settle more easily. The coagulant used is always alum AL2(SO4)3.18H2O, FeCl3, FeSO4, and polyelectrolyte also may be used . The coagulant aid may be added to produce heavier strength floc to prevent floc from breaking up before settling, and to use smaller doses of main coagulant. When alum is added to the water and mix rapidly at least 30 second, alum reacts with alkalinity in water. If insufficient alkalinity is available for this reaction, the pH must be raised by adding lime, Ca(OH)2, or sodium carbonate, Na2CO3.

After period of rapid mixing, flocculation process will begin, it refers to the gentle stirring or agitation of the destabilized particles to promote particle collision and formation of floc. Sedimentation allows the floc leaving flocculation tanks to separate from the liquid through gravitational forces. If the plant is operated properly, the effluent of settling tank is of high quality. Most turbidity and microorganisms should be removed, leaving only a few particles suspended in the liquid. When settled water passes through the filter, the remaining suspended particles are removed and accumulated in interstices between the sand grains until they have been largely filled then the filter must be cleaned to renew its capacity for removing floc particles.
Chlorine is added as needed for distribution, to ensure residual chlorine in the final water within desirable limits. The final step is the storage tank from which pumps can withdraw finished water for delivery into the distribution system.

1.2 Water Treatment Plant Evaluation for Particulate Contaminant Removal:-
The purpose of water treatment is producing water with lower turbidity may be treatment goal for a number of reasons. Compliance with water quality regulations is one. Another would be removal of particulate contaminants, such as Giardia cysts or asbestos fibers. Logsdon,(1987) mentions that ineffective removal of turbidity may be related to several factors that include the physical condition of the facilities, the hydraulics of treatment processes, the quality of water, and the competence of the operating staff. He stated that evaluation of water treatment may be done from the following:
1. Evaluation of the plant through the valuable information of the water utility's offices and laboratory.
2. Blueprint and diagrams of the facility can be used for making preliminary hydraulic evaluation and also evaluation of flow patterns, short circuiting and detention times by performing a tracer study.
3. A schematic diagram of the plant can be used to show the treatment processes used, the points of chemical addition, and the types of chemicals used.
4. evaluation of unit by comparison the chemical, microbiological, and physical quality of raw water and treated water to know how much improvement in water quality is attained by treatment?, How often does raw water vary, and what are the influences of raw water quality changes on treated water quality?

1.3 Objectives of the Study:-
The water treatment plant should be capable of yielding safe water with the actual capacity; therefore, the main objectives of this study are the following:
1. Studying the characteristics of the raw water of river Euphrates and it's suitability to be treated by the plant facilities.
2. Studying and comparing the characteristics of the treated water with the national and international drinking standards.
3. Evaluating and comparing the performance of the treatment plant facilities within each streamline with ideal plant operation.

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