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Water Quality Diseases caused by water-borne bacteria and other microorganisms Diseases in man can be caused by Pathogenic bacteria Other organisms, such as viruses, protozoa, and worms Bacterial diseases Virus diseases Cholera Infectious hepatitis Typhoid fever Worm diseases Bacillary dysentery Swimmers’ itch Water Quality Parameters Physical WQP Chemical WQP Biological WQP Suspended solids Dissolved oxygen Pathogens Turbidity Alkalinity bacteria Color Hardness viruses Taste and odor Chlorides protozoa Temperature Fluorides parasitic worms Metals Organics (BOD) (pathogen indicators, Nutrients ex: Escherichia coli / pH E-coli) Water Quality Standards – TS266 Physico-chemical characteristics TS266 Undesirable chemicals TS266 Toxic chemicals TS266 Microbioligical characteristics Water Purification Processes in Natural Systems Impurities may be washed from the air eroded from the land surface, or leached from the soil and ultimately found their way into surface waters. The self-purification mechanisms of natural water systems include physical, chemical, and biological processes. Physical Processes Dilution Sedimantation and resuspension Filtration Gas transfer O2 Heat transfer F Chemical Processes Chemical conversions that take place in stream and lakes helps to stabilize the pH that take place in water can change these materials into soluble form so that they will be usable by various aquatic organisms For ex. in the pipes Fe+2 Fe2O3 +2 - Fe(s) + 1/2O2(g) + H2O(l) Fe (aq) + 2OH (aq) +2 + 4Fe (aq) + O2(g) + 4H2O(l) 2Fe2O3(s, red color) + 8H (aq) Corrosion (Fe rusting) Biochemical Processes The sum of the processes by which living organisms assimilate and use food for subsistence, growth, and reproduction is called metabolism. The metabolic processes and the organisms involved are a vital part of the self-purification process of natural water systems. Microorganisms + organics new cells + energy Bacteria Protozoa Other microor.s Water Treatment Storage, coagulation, flocculation, sedimentation, filtration, chlorination and water softening Water Treatment Plant - Flowchart Storage Good number of bacteria of intestinal origin ↓ water-borne diseases may disappear Due to sedimentation bactericidal action of ultraviolet radiation or visible light Bad growth of various forms of algae Due to increase the difficulties of treatment Aeration Goals: Oxygen transfer into the water cascade and step aerators Removal of gaseous and volatile compounds which may be responsible for taste and odor air stripping (for example removal of hydrogen sulfide or chlorine) Cascade aerators used at İvedik Treatment Plant Cascade aeration Spray aeration Screening To remove large floating and suspended debris Various types and sizes: bar screens, band and drum screens, microstrainers All intakes are screened. At river intakes plastic bottles, paper bags, branches of foliage, etc. may collect Coagulation Colloidal particles (1-1000 nm) have insufficient mass to settle down. large repulsive Most naturally occurring particles forces are negatively charged. Addition of coagulants ↓ surface charge and agglomerates form. Al+3 Al+3 Al+3 Al+3 Al+3 Al+3 reduced Larges agglomerates settle down. Al+3 repulsive Al+3 forces Al+3 Coagulants: ferric chloride Al+3 Al+3 Al+3 [FeCl3], aluminum sulfate or alum Al+3 Al+3 [Al2(SO4)3], or lime [Ca(OH)2] Rapid mixing Flocculation Gentle mixing to speed agglomeration of colloidal material. Slow mixing causes small particles to collide and stick together. Particulate diameters ↑ Doubling the particle diameter increases the settling velocity by a factor of 4. slow mixing chemical addition coagulation flocculation sedimentation Sedimentation and settling tanks Designed to ↓ velocity of flow of water to permit suspended solids (SS) and precipitates formed in coagulation and flocculation to settle out by gravity Different type of tanks work good with different types of water no hard and fast rules! Performance of a tank = f (amt. of SS, nature of SS, their shape, relative density, extent of clarification req’d., temp. of water, rate of flow, etc.) Circular radial flow tank Sedimentation tank Rectangular basins Sedimentation and settling tanks DESIGN Lab settling tests Investigate what type of tank has been successful before under similar conditions PLAIN SETTLING No chemicals used By gravity FALLING VELOCITY = f (horizontal flow velocity of water, the size of the particle, the relative density of the particle, the shape of the particle, and the temp. of water) Sedimentation and settling tanks Theoretical velocity of falling spherical particle in slowly moving water, V (Camp, 1946): 2 g d V (cm / s ) r 1 18 g = 981 cm/s2 r = the relative density of the particles = particle/fluid d = the diameter of the particle (mm) = the kinematic viscosity of water (centistokes) = f (T) 1 centistoke = 1 mm2/s Design of settling tanks Flow, Q b Particle X L d Q/bd Time taken = d/V V Time taken = Lbd/Q d Lbd Q FOR COMPLETE REMOVAL: or V V Q A A = plan area of the basin Design of settling tanks This is the limiting speed of fall to Q enable the particle to reach the bottom V of the tank. A All particles with V>Q/A will be removed. Example: Suppose we have a tank of 300 m2 surface area and the rate of inflow is 1.2 m3/s. (a) What is the falling speed of the particles that will be completely removed? (b) What % of the particles with a falling speed of 0.2 cm/s will be removed? (Answers: 0.4 cm/s; 50%) Water Softening Water hardness is caused by multivalent cations, usually calcium and magnesium. The term hard or hardness originated because waters containing such multivalent cations were “hard” to use for laundry. BAD Divalent cations in water react with soaps, reducing effectiveness Precipitates of calcium carbonate onto the walls of water heaters Water Softening Hardness is not a health concern no absolute std.s Concentrations above 150 to 200 mg/L CaCO3 are usually detectable by taste. If hardness is below 50 mg/L CaCO3 it is difficult to remove the soap after the bath or shower. Hardness can be removed by Chemical treatment to ppt divalent cations (addition of lime [Ca(OH)2] or soda ash [Na2CO3]) Ion exchange Filtration Many particles in water are too small to be removed by sedimentation! Particles removed only when they make physical contact with filter medium. Removal occurs due to several mechanisms Straining when particle is larger than the pore they are trapped Sedimentation particles settle down on medium material Interception particles are intercepted by or adhere to the surface of the medium due to inertia Slow sand filtration Filtration Unit at İvedik Treatment Plant Disinfection Disinfection is the destruction or killing of pathogenic microorganisms. Objective of potable water disinfection Kill or inactivate the harmful organisms To leave a residual of disinfectant that will kill or inactivate organisms in the distribution system. Disinfectants gaseous chloride, chloride dioxide, calcium hypochlorite, sodium hypochlorite, etc. Ozone UV Disinfection An ideal disinfectant Chlorine Ozone UV Must kill microorganisms √ √ √X Should leave a residual for the distribution √ X X system Should be inexpensive √ X √ Should not be harmful to humans or create X X √ harmful byproducts Should be safe to handle and use X √X √ Should not harm the environment or create X √X √ an undesirable taste or odor Chick’s Law Harriet Chick in 1900s a method of estimating the destruction of microorganisms by disinfectants as a function of time. dN N0 = initial concentration of microorganisms (no./mL) kN dt N = concentration of microorganisms at time t (no./mL) N t = time of disinfection (hr) ln kt k = an empirical constant descriptive of the particular N0 microorganisms and disinfectant in use (hr-1) İvedik Treatment Plant 13 km north of Ankara 4 units each having a capacity of 564,000 m3/day water quality at the exit of the treatment plant are in accordance with WHO and TS266 standards combined treatment for water from Çamlıdere and Kurtboğazı Dams İvedik Treatment Plant Example – İvedik Treatment Plant Polyelectrolyte Aluminum sulfate Chlorine Slow mixing Kurtboğazı dam Aeration Blending Prechlorination Flocculation Çamlıdere dam chamber and and Coagulation Sedimentation Rapid mixing Sludge Chlorine Filtration Chlorination Equalization tank ANKARA In plant utilization Water quality criteria of clean water exiting İvedik Treatment Plant Quality Parameters Clean Water World Health Spring water From Ivedik Organization Std.s (memba suyu) T.P. Color (Pt-Co) 5 5 3 Taste Tasteless Tasteless Tasteless Odor Odorless Odorless Odorless pH 6.3-7.6 7-8.5 7.5 Turbidity (NTU) 0.3-1.0 5.0 0.5 Iron, Fe (mg/L) 0.1 0.1 None Manganese, Mn 0.05 0.05 None (mg/L) Hardness (FSº) 8.3-12.5 10.0 2.5 Coliform None None None Questions?
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