PURIFICATION OF WATER- RAM NAIK.M

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WATER PURIFICATION:

WATER PURIFICATION RAM NAIK. M 4 th Semester

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Purification of water is of great importance.. It can be considered under two categories: Purification of water on Large scale. Purification of water on Small scale.

PURIFICATION OF WATER ON A LARGE SCALE:

PURIFICATION OF WATER ON A LARGE SCALE

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The method of treatment depends upon the Nature of raw water. Desired standards of water quality. The components of typical water purification consists of:

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STORAGE In Natural / Artificial Reservoirs Effects of storage: Physical: Gravity – 90%suspended impurities settle down in one day Oxidizing action Chemical: Organic matter Nitrates, Free Ammonia Aerobic bacteria, dissolved O2 Biological: Only 10% bacteria remains at the end of 1 week Optimum period= 2 weeks. Disadvantages : Prolonged storage may lead to vegetative growths.

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FILTRATION It is the second stage in the water purification. Important as 98-99% bacteria are filtered. There are two types of filters in use: Rapid sand filters Slow sand filters/ biological filters.

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SLOW SAND / BIOLOGICAL FILTERS Used first in 19 th century in Scotland. Elements of slow sand filter: Filter Box: Supernatant water Bed of graded sand Under drainage system Filter-control valves

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Supernatant water : Depth= 1-1.5m Uses: Provides a constant head of water Provides a waiting period (3-12hrs) Sand bed : Thickness= 1m. Effective diameter of sand particles= 0.2-0.3mm Must be clean and free of clay, organic impurities. Uses: Provides a vast surface area(1 cu.m-15,000 sq.) Water percolates slowly and is subjected to many purification processes.

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Rate Of Filtration = 0.1- 0.4 cu.m/hr/sq.m VITAL LAYER : - ripening of the filter. HEART Of Slow Sand Filter. Vital/Biological/Zoogleal layer/Schumtzdecke Slimy, gelatinous layer. Consists of thread like algae, diatoms, plankton… Extends 2-3cm into top layers of sand bed. Uses: Removes oragnic matter Holds back the bacteria Oxidation of ammonia to nitrates Yields bacteria-free water.

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C. UNDER DRAINAGE SYSTEM Porous/ perforated pipes at the bottom. Uses: Outlet for the filtered water Supports the filter medium above. D. FILTER CONTROL VALVES : To regulate the flow of water in and out. Venturi meter: measures bed resistance or loss of head. FILTER CLEANING: Increased bed resistance Necessary to open the regulating valves fully Scrapping top portion of sand bed up to 2 cm depth Time for cleaning the filter After 3-4 years new filter bed is constructed.

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Slow Sand Filtration

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Removal Of The Vital Layer

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Clean Slow Sad Filter Without Water

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Mechanism of action of Slow Sand Filter: 1 .Sedimentation : The supernatant water acts as a settling reservoir. Settleable particles sink to the sand surface. 2. Mechanical straining : Particles too big to pass through the interstices between the sand grains are retained. 3 . Adhesion: The suspended particles that come in contact with the surface of the sand grains are retained by adhesion to the biological layer (Schmutzdecke) 4. Biochemical processes in the biological layer: Removes organic matter, holds back bacteria and oxidizes ammoniacal nitrogen in to nitrates Conversion of soluble iron and manganese compounds into insoluble hydroxides which attach themselves to the sand surfaces

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Advantages of slow sand filter Simple to construct and operate Cost of construction is less Physical, chemical, bacterial quality of water is high. Reduces the bacterial count from 99.9% to 99.99%

RAPID/ MECHANICAL SAND FILTERS:

RAPID/ MECHANICAL SAND FILTERS These are used primarily to remove turbidity after coagulation and flocculation. These could be of Open tanks- Gravity type Paterson’s filters Closed tanks- Pressure type Candy’s filters

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RIVER In Mixing Chamber: Coagulation by Alum (5-40 mg/litre) Violent mixing of alum (minutes) In Flocculation Chamber: Slow stirring of water by paddles(30 minutes) at 2-4 rpm. Flocculent ppt. of Aluminium Hydroxide entangles all particulate, suspended matter along with bacteria In Sedimentation Chamber: Flocculent ppt. settle down (removal is done time to time) Clear water above goes for filtration Rapid Sand Filter: Remaining alum floc layer over sand bed. it holds back bacteria, oxidize organic matter Back washing-by air bubbles or water when floc layer becomes very thick

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MIXING CHAMBER FLOCCULATION CHAMBER SEDIMENTATION TANK FILTERS CLEAR WATER STORAGE CONSUMPTION +ALUM COAGULATION PADDLES 30MIN 2-6hrs CHLORINATION

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Paddles in a flocculation chamber

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Properties Rapid sand filter Slow sand filter Area Small area Large area Rate of filtration(L/m2/hr) 4000-7500 100-400 Sand size (diameter) 0.4-0.7 mm 0.2-0.3 mm Pretreatment Coagulation and sedimentation Sedimentation Filter cleaning Backwashing Scraping Operation More skilled Less skilled Removal of colour Good Better Removal of bacteria 98-99% 99.9%-99.99% Prior water storage Storage needed No need

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DISINFECTION Criteria for satisfactory disinfectant: Destroy the pathogenic organism without being influenced from properties of water (pH, temp. etc.) within a time period Should not be toxic and colour imparting or leave the water impotable Available, cheap, easy to use Leave the residual concentration to deal with recontamination Detectable by rapid, simple techniques in small concentration ranges to permit the control of disinfection process

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Chlorination METHOD OF CHLORINATION Chlorinating equipment (Paterson’s chloronome) for adding gaseous chlorine Action: Kills pathogenic bacteria (no effect on spores and viruses) Oxidize iron, manganese and hydrogen sulphide Reduces taste and odours Controls algae Maintains residual disinfection Mechanism of action: 1. H 2 O+Cl 2 (at pH 7) ------- HCl + HOCl (main disinfectant) HOCl (at pH > 8.5) -------- H + + OCl - (minor action) 2. NH 3 + Cl 2 -------- NH 2 Cl/NHCl 2 /NCl 3 + H 2 O (Mono, Di ,Tri Chloramines)

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PRINCIPLES OF CHLORINATION 1. Water should be clear, free from turbidity 2. Chlorine demand : Chlorine needed to destroy bacteria, to oxidize organic matter and to neutralize the ammonia in water 3.Free residual chlorine for a contact period of 1 hour is essential 4. Breakpoint : P oint when chlorine demand of water is met and free residual chlorine appears 5 . Breakpoint chlorination: Chlorination beyond the breakpoint . The principle of break point chlorination is to add sufficient chlorine so that 0.5 mg/L free residual chlorine is present in the water after one hour of contact time 4. Dose of Chlorine = Chlorine demand + Free residual chlorine

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Tests to measure Residual Chlorine OT Test- Yellow colour ( In 10 seconds-free chlorine, In 15 min-both free and combined chlorine) Ortho Tolidine Arsenite (OTA) Test- Yellow colour Tests both free and combined chlorine separately (Yellow colour due to nitrites, iron, manganese are overcome by OTA test)

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Super chlorination Method of choice for highly polluted waters High dose of chlorine is added after 20 minutes of contact Dechlorination is done with sodium sulphate / sodium thiosulphate to reduce the taste of excess chlorine

Other disinfectants:

Other disinfectants The other methods of disinfections includes: Ozonation UV Radiation Chloramine

Ozonation:

Ozonation Advantages: Shorter contact period Less dosage than chlorine required Strong virucidal Strong oxidizing agent Limitations: Unstable Must be generated onsite Chloramine Advantages : Effective bactericide Fewer byproducts Limitations: Less effective against virus and protozoa Weak disinfectant 0.2-1.5mg/litre 120mm thick film to Quartz-mercury arc lamps Emitting 200-295nm radiation

UV Radiation:

UV Radiation Advantages: Effectively reduces bacteria and viruses Readily available No known toxic byproducts Equipment is easy to operate Short contact time Limitations: Cannot inactivate cysts of Giardia, Cryptosporidium. Not suitable to water with high levels of suspended soils, turbidity.

PURIFICATION OF WATER ON A SMALL SCALE:

PURIFICATION OF WATER ON A SMALL SCALE

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House-hold purification. Boiling Chemical disinfection Bleaching powder Chlorine derivatives Iodine Potassium permanganate Filtration Disinfection of wells. Double pot method.

Boiling:

Boiling Rolling boil- 10-20min Advantages: Simple and effective Kills many waterborne bacteria through the intense heat Uses local available materials Disadvantages: Alters taste of the water, yet harmless. Preferably to be boiled in the same container in which it has to stored. Will not remove mud from ‘murky’ water Time consuming

Chemical disinfection:

Chemical disinfection Bleaching powder : Chlorinated lime. Physical properties: White amorphous powder Pungent smell Unstable Available chlorine- 33% Stabilized bleach Principle: To ensure a free residual chlorine of 0.5mg/lit at the end of 1hr contact period. Disadvantages: Smell Cannot be used for highly polluted and turbid water.

Chlorine derivatives:

Chlorine derivatives Chlorine solution: 200 gm. bleaching powder (25% available chlorine) + 1 liter water = 5% solution 1 drop of this solution---For disinfection of 1 L water High test hypochlorite: Perchloran 60-70% available chlorine More stable Deteriorates lesson storage 3 drops/ liter water , Use water after 30 minutes Chlorine tablets: 1 tab(0.5g) for 20 L water NEERI developed cheaper tablets

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Iodine: Emergency disinfection method. 2drops of 2%ethanol soln. of iodine for 1 liter. Contact period= 20-30min. Disadvantages: High cost Physiologically active. Potassium permanganate : Not recommended Disadvantages: Alters the colour and smell of water. Less effective against disease organisms.

FILTRATION :

FILTRATION Four ghara method: Top: Muddy water II: Sand III: Charcoal IV: Empty glare to collect filtered water Ceramic filters: Water pass through micro-pores of candle placed inside the water container. Bacteria: Unable to pass through the pores, Virus: Can pass through the pores Pasteur-Chamberland filter - porcelain candles, used in labs & dispensaries. Berkefeld filter - industrial earth (keiselgurh) candles, less reliable

Katadyn filter:

Katadyn filter Inner surface is covered by silver catalyst/ katadyn. Principle: Oligodynamic action: certain metals in very small doses act as powerful germicide Cleaning of the filters : Scrubbing with a hard brush under running water candles must be boiled at least once a week.

DISINFECTION OF WELLS:

DISINFECTION OF WELLS

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Find volume of water in well (V in Liters) = 3.14 x h x d 2 x 1000 4 Find the amount of bleaching powder needed by Horrock’s apparatus Bleaching powder (max.100 g) mixed with water in a bucket Allow 10 minutes sedimentation Transfer supernatant chlorine solution to another bucket Deliver chlorine solution in to the well Allow 1 hour contact Do OTA test to measure free residual chlorine If free residual chlorine < 0.5 mg/L Add more bleaching powder

DOUBLE POT METHOD:

Inner pot (28 cm ht) Hole (1 cm dia) Polyethylene foil Hole of 1cm dia Bleaching powder 1kg + 2 kg coarse sand Moist mixture Outer pot (30X25 cm) Rope DOUBLE POT METHOD

DOUBLE POT METHOD/ DOUBLE JAR DIFFUSER:

DOUBLE POT METHOD/ DOUBLE JAR DIFFUSER By NEERI, Nagpur, India. Placed 1 meter below the water level. Effective for chlorination of well (4500 L water) with a daily withdrawal of 450 L water ---2-3 weeks

THANK YOU:

THANK YOU