Volatile gases- Hydrogen sulphideGravity Aerators (Cascades): In gravity aerators, water is allowed to fall by gravity such that a large area of water is exposed to atmosphere, sometimes aided by turbulence.Fountain Aerators : These are also known as spray aerators with special nozzles to produce a fine spray. Each nozzle is 2.5 to 4 cm diameter discharging about 18 to 36 l/h. Nozzle spacing should be such that each m3 of water has aerator area of 0.03 to 0.09 m2 for one hour.Injection or Diffused Aerators : It consists of a tank with perforated pipes, tubes or diffuser plates, fixed at the bottom to release fine air bubbles from compressor unit. The tank depth is kept as 3 to 4 m and tank width is within 1.5 times its depth. If depth is more, the diffusers must be placed at 3 to 4 m depth below water surface. Time of aeration is 10 to 30 min and 0.2 to 0.4 litres of air is required for 1 litre of water.
TREATMENT OF WATERGUIDED BY:- SHUBHAM BAPHANAEr. Ravi Parmar sir CE (3RD YEAR)Er. Sugandh singh sir 0862CE101115
The available raw water must betreated and purified before they canbe supplied to the public for domesticuse or any industrial use. The extent oftreatment of water depends uponfollowing two-1.Characteristics and quality of available water.2.Quality requirements for the intended use.
Parameters Desirable-Undesirable If no alternative source available, limit extended uptoPHYSICAL Turbidity (NTU unit) < 10 25Colour (Hazen scale) < 10 50 Taste and Odour Un-objectionable Un-objectionableCHEMICAL pH 7.0-8.5 6.5-9.2 Total Dissolved Solids 500-1500 3000 mg/l Total Hardness mg/l 200-300 600 (as CaCO3)Chlorides mg/l (as Cl) 200-250 1000 Sulphates mg/l (as 150-200 400 SO4) Fluorides mg/l (as F ) 0.6-1.2 1.5Nitrates mg/l (as NO3) 45 45
Unit treatment Function (removal)Aeration, chemicals use Colour, Odour, TasteScreening Floating matterChemical methods Iron, Manganese, etc.Softening HardnessSedimentation Suspended matter Suspended matter, a part ofCoagulation colloidal matter and bacteria Remaining colloidal dissolvedFiltration matter, bacteria Pathogenic bacteria, OrganicDisinfection matter and Reducing substances
Source Treatment required1. Ground water and spring water No treatment or Chlorinationfairly free from contamination2. Ground water with chemicals, Aeration, coagulation (ifminerals and gases necessary), filtration and disinfection3. Lakes, surface water reservoirs Disinfectionwith less amount of pollution4. Other surface waters such as Complete treatmentrivers, canals and impoundedreservoirs with a considerableamount of pollution
AERATION:-•Aeration removes odor due to volatile gases and dueto algae and related organisms.•Removes CO2 and reduce corrosion and removemethane and other inflammable gases.•Increases dissolved oxygen content in water. Aeration Gravity aerators Fountain aerators Diffused aerators Mechanical aerators
Settling:-In this Solid particle are separated out from the water.• Clarified floating particle at the top of the sedimentation tank.• Concentrated sludge leaving the bottom of the sedimentationtank.Purpose of settling:-• To remove Coarse dispersed phase.• To remove coagulated and flocculated impurities.• To settle the Sludge.Principle of settling:-• Suspended solid present in water having specific gravity greaterthan that of water tend to settle down by gravity.• Basing in which the flow is retarded is called settling tank.• Theoretical average time for which the water is detained in thesettling tank is called Detention Time.
Types of settling:-1. Type 1 Discrete particle settling:-• In discrete settling individual particles settle independently.• It occurs when there is a relatively low solids concentration.2. Type 2 Flocculent particle settling:-• In flocculant settling, individual particles stick together into clumpscalled flocs.• This occurs when there is a greater solids concentration andchemical or biological reactions alter particle surfaces to enhanceattachment.3. Type 3 Compression:-Compression settling occurs when particles settle by compressingthe mass below4. Type 4 Zone settling:-
Type of settling tank:-1. Intermittent or Quiescent Type tank:- Those which store water for a certain period and keep it in complete rest.2. Continuous Flow type tank:- The flow velocity is reduced and the water is not bought to complete rest as is done in above one.Long Rectangular Settling basin:-• They are hydraulically more stable and flow control for large volume iseasier with this configuration.• Length is 2 to 4 times of widht with bottom to be made slope.
This long rectangular settling basin is divided in four zones:-Inlet zone: Region in which the flow is uniformly distributed over the crosssection.Settling zone: Settling occurs.Outlet zone: Clarified effluent is collected and discharge through outletweir.Sludge zone: For collection of sludge below settling zone.
Circular Basin:-• Circular settling basins have the same functional zones as the longrectangular basin, but the flow regime is different. When the flow enters atthe centre and is baffled to flow radially towards the perimeter, thehorizontal velocity of the water is continuously decreasing as the distancefrom the center increases.• Sludge removal mechanisms in circular tanks are simpler and requireless maintenance.
Design Details:-1. Detention period: for plain sedimentation: 3 to 4 h, and for coagulated sedimentation: 2 to 2.5 h.2. Velocity of flow: Not greater than 30 cm/min (horizontal flow).3. Tank dimensions: L:B = 3 to 5:1. Generally L= 30 m (common) maximum 100 m. Breadth= 6 m to 10 m. Circular: Diameter not greater than 60 m. generally 20 to 40 m.4. Depth 2.5 to 5.0 m (3 m).5. Surface Overflow Rate: For plain sedimentation 12000 to 18000 L/d/m2 tank area; for thoroughly flocculated water 24000 to 30000 L/d/m2 tank area.6. Slopes: Rectangular 1% towards inlet and circular 8%.
Coagulation and flocculation:-• Colloidal particles are difficult to separate from water because they donot settle by gravity and are so small that they pass through the pores offiltration media.• To be removed, the individual colloids must aggregate and grow in size.•The aggregation of colloidal particles can be considered as involving twoseparate and distinct steps: a. Particle transport to effect interparticle collision. b. Particle destabilization to permit attachment when contact occurs.Flocculation:-It is a common practice to provide an initial rapid (or) flash mix for thedispersal of the coagulant or other chemicals into the water. Slow mixing isthen done, during which the growth of the floc takes place.Rapid or Flash mixing is the process by which a coagulant is rapidly anduniformly dispersed through the mass of water. Generally, the detentionperiod is 30 to 60 seconds and the head loss is 20 to 60 cms of water. Herecolloids are destabilised and the nucleus for the floc is formed.Slow mixing brings the contacts between the finely divided destabilisedmatter formed during rapid mixing.
-:Filltration:-To remove or to reduce the remaining impurities still further, the wateris filtered through the beds of fine granular material, such assand, etc. The process of passing the water through the beds of suchgranular materials is known as Filtration. -:Filter material:-1. Sand:-Sand, either fine or coarse, is generally used as filter media The size of sand is measured and expressed by the term called effective size.2. Gravel:- The layer of sand may be supported on gravel, which permits the filtered water to move freely to the under drains.3. Other materials:- Instead of using sand, sometimes anthrafilt is used as filter media. Anthrafilt is made from anthracite. It is cheaper and has been able to give high rate of filtration.
TYPES OF FILTERS1. Slow Sand filter:- They consist of fine sand, supported by gravel. They capture particles near the surface of the bed and are usually cleaned by scraping away the top layer of sand that contains the particles.2. Rapid sand Filter:- They consist of larger sand grains supported by gravel and capture particles throughout the bed. They are cleaned by backwashing water through the bed to lift out the particles.3. Multemedia Filter:- They consist of two or more layers of different granular materials, with different densities. Usually, anthracite coal, sand, and gravel are used. Because of the differences in densities, the layers stay neatly separated, even after backwashing.
Difference Between SSF and RSF:- Slow sand filter Rapid sand filter Base Material varies from 3 to 65 mm varies from 3 to 40 mm in size and 30 to 75 cm in size and its depth is in depth slightly more, i.e. about 60 to 90 cm. Filter sand the effective size In RSF the effective size ranges between 0.2 to ranges between 0.35 to 0.4 mm and uniformity 0.55 and uniformity coefficient between coefficient between 1.8 to 2.5 or 3.0. 1.2 to 1.8. Rate of filtration it is small, such as 100 to it is large, such as 3000 200 L/h/sq.m. of filter to 6000 L/h/sq.m. of area filter area. Post treatment Almost pure water is water may be obtained disinfected slightly to make it completely safe. Disinfection is a must after RSF.
Slow sand filter Rapid sand filterMethod of Cleaning Scrapping and To clean RSF, sand is removing of the top 1.5 agitated and to 3 cm thick layer is backwashed with or done to clean SSF. without compressed air.
DisinfectionThe filtered water may normally contain some harmful disease producingbacteria in int. These bacteria must be killed in order to move the water safefor drinking, and this process of killing bacteria is known as Disinfection orsterilization Menthod of disinfection1. Boiling :- The bacteria present in water can be destroyed by boiling it for a long time.2. Treatment with excess of lime:-Lime is used in water treatment plant for softening. But if excess lime is added to the water, it can in addition, kill the bacteria also.3. Treatment with ozone:-Ozone readily breaks down into normal oxygen, and releases nascent oxygen. The nascent oxygen is a powerful oxidising agent and removes the organic matter as well as the bacteria from the water.4. Chlorination:- The chlorine enters the cell walls of bacteria and kill the enzymes which are essential for the metabolic processes of living organisms.
Chlorine ChemistryChlorine is added to the water supply in two ways. It is most often added asa gas, Cl2(g). However, it also can be added as a salt, such as sodiumhypochlorite (NaOCl) or bleach. Chlorine gas dissolves in water followingHenrys Law. Cl2(g) Cl2(aq) KH =6.2 x 10-2Once dissolved, the following reaction occurs forming hypochlorous acid(HOCl): Cl2(aq)+H2O HOCl + H+ + Cl-Hypochlorous acid is a weak acid that dissociates to form hypochlorite ion(OCl-). HOCl OCl- + H+ Ka = 3.2 x 10-8All forms of chlorine are measured as mg/L of Cl2 (MW = 2 x 35.45 = 70.9g/mol)