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• Iron and Manganese are frequently found in groundwater and insome surface waters.
• They do not cause health problems, but
• They cause aesthetic problems:-Discoloration of water (iron = reddish water, manganese = brown or black water)-Staining of plumbing fixtures-Impartation of a bitter taste of the water-Stimulation of the growth of microorganisms
• Economic problems include damage to textiles and food. Iron residue in pipesincreases pumping head and decreases carrying capacity. It may also clog pipesand corrode through them.
• Hardness is the presence of positively charged metallic ions in thewater. Calcium, magnesium, iron, strontium, barium, etc…
• It is of concern in domestic water consumption because hard waterincreases soap consumption, leaves a soapy scum in the sink, cancause water heater electrodes to burn out quickly. In industrial uses,it can damage equipment.
• It is expressed in mg/l as CACO3.
• Hardness (mg/l) = Metal ion concentration * 50/ Eq. Wt. of M
• The ion exchange is the most frequently used process for softeningwater.
• Raw water contains suspended particles of color, turbidity, andbacteria that are too small to settle in a reasonable time period andcannot be removed by simple filtration.
• The object of coagulation is to alter these particles in such a way asto allow them to adhere to each other. Thus they can grow to a sizethat will allow removal by sedimentation and filtration.
• Coagulation is considered to be a chemical treatment process asopposed to the physical treatment operations of flocculation,sedimentation, and filtration that follow.
• Coagulation is the reaction between one of these salts and water. Thesimplest coagulation process occurs between alum and water. Whenalum is added to water, a chemical reaction occurs that producespositively charged aluminum ions. The overall result is the reductionof electrical charges and formation of sticky substance called “Floc”.
• Liquid alum is preferred in water treatment because:o Ease of handlingo Lower costso Less labor requiredo Less storage spaceo Greater accuracy in measuremento Elimination of nuisanceo Easier maintenance
• Detention Time : 20 to 60 seconds• The tanks are usually, baffled horizontally into two or three compartments in-
order to provide sufficient residence time.• Tanks should also be vertically baffled to minimize vortexing.• Chemicals should be added below the impeller, point of most mixing.
• Flocculation is the physical process of slowly mixing the coagulated water.
• It’s a gentle mixing process
• The primary objective of flocculation is to bring particles in contact with oneanother so they will collide, stick together, and grow to a size that will easilysettle.