Unit - 3

Water quality

3.1 Water quality: Physical, Chemical and bacteriological characteristics of water, Health effects of various water characteristics, Standards of drinking water. (WHO 2011, CPHEOO, IS 10500). Water borne diseases

• Water fine refers back to the chemical, physical, and organic traits of water primarily based totally at the requirements of its usage. It is maximum often utilized by connection with a hard and fast of requirements towards which compliance, usually performed through remedy of the water, may be assessed.
• The maximum not unusual place requirements used to display and investigate water fine carry the fitness of ecosystems, protection of human contact, increase of water pollutants and situation of consuming water. Water fine has a great effect on water deliver and commonly determines deliver options.
• Contaminants that can be in untreated water encompass microorganisms which include viruses, protozoa and bacteria; inorganic contaminants which include salts and metals; natural chemical contaminants from business tactics and petroleum use; insecticides and herbicides; and radioactive contaminants. Water nice relies upon at the neighborhood geology and ecosystem, in addition to human makes use of which include sewage dispersion, business pollution, use of water our bodies as a warmth sink, and overuse (which can also additionally decrease the extent of the water).
• The United States Environmental Protection Agency (EPA) limits the quantities of sure contaminants in faucet water furnished through US public water structures. The Safe Drinking Water Act authorizes EPA to difficulty varieties of requirements: number one requirements adjust materials that probably have an effect on human fitness; secondary requirements prescribe aesthetic qualities, people who have an effect on taste, odor, or appearance.
• The U.S. Food and Drug Administration (FDA) policies set up limits for contaminants in bottled water. Drinking water, which include bottled water, can also additionally moderately be anticipated to comprise at the least small quantities of a few contaminants.
• The presence of those contaminants does now no longer always suggest that the water poses a fitness risk. In urbanized regions across the world, water purification era is utilized in municipal water structures to take away contaminants from the supply water (floor water or groundwater) earlier than it's miles allotted to homes, businesses, colleges and different recipients. Water drawn immediately from a stream, lake, or aquifer and that has no remedy might be of unsure nice in phrases of potability.

3.1.1 Physical, chemical and bacteriological characteristics of water

Physical Characteristics:

Following physical parameters are used to calculate the physical quality of water.

1. The Colour
2. Taste and Odour
3. Temperature
4. Turbidity

1. Colour:

• The pure natural water does not have any colour. The presence of any organic and in-organic matter in the water gives the colour like green, blue, black, red etc.
• When the industrial waste gets mixed up with the surface water the colour is added to the natural water.
• It is necessary to investigate the source of this chemical contamination must be indentified to reduce the danger of water pollution.
• The changes in the colour of water can be qualified by making use of the space photometer.
• The unit of measurement of intensity of colour in the water is cobalt-platinum (copt) unit.

2. Taste and Odour:

• In fact the pure water is tasteless and odourless. The organic matter, industrial wastes, gives a different odour and the taste also changes.
• In case of stored water, the odour and tastes are developed. The underground water, mainly.
• The well water gets a typical taste and odour also because it gets some dissolved chemicals when it percolates through the rocks. Such water is also called as hard water.

3. Temperature:

• We generally prefer to consume cool water but if the water is warm the growth of micro-organisms is promoted and the taste, odour and colour also get changed.

4.Turbidity:

• It is the suspended matter like mud, clay, algae and micro-organism that make the water turbid.
• This turbidity can be measured by using turbidity meter and the unit of measurement is Nephelometric Turbidity unit (NTU).
• The unit of measurement is PPM or mg/per litre on silica scale e.g. Are mg of colloidal silica suspended in one litre of distilled water, produces one unit of turbidity.

Chemical Characteristics:

Following Chemical parameters are used to calculate the chemical quality of water.

1. Total Dissolved Solids (TDS)
2. PH
3. Hardness

1. Temporary hardness
2. Permanent hardness

1.Total Dissolved Solids (TDS)

• They are composed of inorganic salts, mainly the chlorides, sulphates and bi-carbonates of calcium, magnesium, potassium and sodium.
• The industrial waste makes the addition of these TDS. It also is added in case of underground water which collects those inorganic components in the process of percolation.
• The TDS in the water can be measured by simple evaporation method or by using TDS meter. The unit of measurement of T.D.S. Is mg/l (mg/per litre).

2. PH

• It is the value of hydrogen ion concentration in the water on the base of the pH value, it is called as acidic or alkaline.
• The normal pH value of water is seven, if it is less than seven, the water is called acidic water, if it is more than seven it is called as Alkaline water.
• The pH value is measured by pH meter or by using pH paper, which changes its colour when dipped in the water.
• By using the colour code, the pH value can be measured.

3.Hardness

• The hardness to the water is of two types:

a. Temporary hardness:

• It is caused by soluble bicarbonates which can be removed by boiling the water.

b. Permanent hardness:

• It is caused by sulphate and chlorides of calcium and magnesium. It can be removed by using iron exchange methods.

The following components make the water hard:

• Sodium, Iron and manganese, chlorides, sulphate, Nitrates. The Fluorides in the water is an important parameter of good quality of water.
• If the concentration is less than 1.0 mg/l, it gives rise to dental caries among the children and if it is more than 1.5 mg/1, it may cause dental and skeletal flurosis.
• The fluoride content in the water is measured by spectrophotometer.
• The toxic materials like heavy metals, pesticides, industrial chemicals, can have acute effects as the human being if consumed in large quality or for a long period.

Biological Characteristics:

The presence of micro-organism like bacteria and Virus make the water contaminated. All the micro organism are not harmful to human beings but the micro organism which are pathogenic cause water bome diseases.

Biological Tests:

For the Biological or Bacteriological following tests are observed.

1. Total count of Bacteria
2. Bactria coli (B-coli) Test or E Coli Test

1.Total count of Bacteria:

• In this, the total number of bacteria present in one millilitre of sample water are counted. The sample water is diluted one millilitre water is diluted in 99 ml of sterilized water.
• Then 1 ml diluted water is mixed with 10 ml of agar of gelatine i.e. culture medium. This mixture is then kept in the Incubator at 37°C temperature for 24 hours or may be at 20°C temperature for 48 hours.
• After this required period the sample is taken out from the incubator and then the colonies of bacteria are counted under microscope.
• This product of the number of colonies and the dilution factor will give the total number bacteria/per ml of the undiluted water sample.

2. Bactria coli (B-coli) Test OR E Coli Test

• Two tests are designed for B-coli. The 1st test is known as presumptive test and the 2nd test is known as the confirmative test.
• In case of 1st i.e. the presumptive test, a definite amount of diluted water sample water, is kept, in standard fermentation tubes, which contain, lactose broth, as a culture medium.
• These tubes are kept in the incubator at 37°C temperature for 24 hrs to 48 hrs.
• If, after this period, a gas is produced in these fermentation tubes, it is an indication of presence of B coli and if these is no gas formation it is an indication of no-presence if B-coli in the sample. In the 2nd i.e. the confirmation test some sample from presumptive tube is taken and is placed in another fermentation tube which contains Brilliant green lactose bile, as a culture medium.
• It is also kept in the incubator at 37°C temperature for 48 hrs. If it again produces gas that confirms the presence of B-coli and water is unsafe for consumption purpose.
• Now a days, an another method has been introduced to find out the B-coli. In is known as "Membrane Filter Technique." It is a very simple technique. The sample water is filtered through a sterilized membrane of special design to collect all the bacteria, present in the sample water. The membrane is then put contact of culture medium i.e. M-Endo's medium, in the incubator at 37°C temperature for 24 hrs.
• After the incubation period the membrane is kept under the Microscope to count the colonies of Bacteria. Previously the standard statistical tables were referred to determine the Most Probable Number (MPN) of B coli per 1000 ml, MPN indicates the density of bacteria in the water sample.
• As the new technique 'Membrane filter' has been. Introduced the MPN methods are not used.
• In drinking water at least 5 samples of 100 ml, each should be collected and tested. The number of C-coli colonies per std sample should not be more than 4 per 100 ml of sample water.

Key takeaways:

• The U.S. Food and Drug Administration (FDA) policies set up limits for contaminants in bottled water. Drinking water, which include bottled water, can also additionally moderately be anticipated to comprise at the least small quantities of a few contaminants.

3.1.2 Health effects of various water characteristics

• Contaminants that can be in untreated water consist of microorganisms together with viruses, protozoa and bacteria; inorganic contaminants together with salts and metals; natural chemical contaminants from business procedures and petroleum use; insecticides and herbicides; and radioactive contaminants.
• Water excellent relies upon at the nearby geology and ecosystem, in addition to human makes use of together with sewage dispersion, business pollution, use of water our bodies as a warmth sink, and overuse (which may also decrease the extent of the water).
• The United States Environmental Protection Agency (EPA) limits the quantities of positive contaminants in faucet water supplied through US public water structures. The Safe Drinking Water Act authorizes EPA to problem varieties of requirements: number one requirements modify materials that doubtlessly have an effect on human fitness; secondary requirements prescribe aesthetic qualities, people who have an effect on taste, odor, or appearance.
• The U.S. Food and Drug Administration (FDA) rules set up limits for contaminants in bottled water.  Drinking water, which includes bottled water, may also moderately be predicted to comprise at the least small quantities of a few contaminants.
• The presence of those contaminants does now no longer always imply that the water poses a fitness risk. In urbanized regions across the world, water purification generation is utilized in municipal water structures to do away with contaminants from the supply water (floor water or groundwater) earlier than it's far dispensed to homes, businesses, colleges and different recipients. Water drawn without delay from a stream, lake, or aquifer and that has no remedy might be of unsure excellent in phrases of potability.
• The burden of polluted ingesting water disproportionally consequences under-represented and prone populations. Communities that lack those smooth ingesting-water offerings are liable to contracting water-borne and pollution-associated ailments like Cholera, diarrhoea, dysentery, hepatitis A, typhoid, and polio.
• These groups are frequently in low-profits regions, wherein human wastewater is discharged into a close-by drainage channel or floor water drain without enough remedy, or is utilized in agricultural irrigation.

3.1.3 Standards of drinking water(WHO 2011,CPHEOO, IS10500)

• Drinking water, that is, the water whose organoleptic, physicochemical, and organic houses meet human organic desires and has neither shadeation nor smell, ought to have a flavor decided through the presence of physiologically important salts of calcium, magnesium, sodium, and potassium in corresponding concentrations without which metabolism withinside the human organism is not possible.
• What greatest parameters ought to the water own to be absolutely secure from the organic and physiological factors of view? For the primary time withinside the global in 1853, in Brussels, on the International Congress of Hygienists, an try turned into made to set a general for ingesting water, which might consist of best 9 controllable additives.
• Among them there have been vitally vital materials along with magnesium, calcium, overall mineralization (decided especially through the presence of salts of sodium and potassium), and the content material of oxygen withinside the water, sulfates, chlorides, nitrates, and ammonium.
• However, the age of industrialization, a quick improvement of the agroindustrial complicated and the emergence of megapolises with compact agreement of humans, whose wide variety dramatically increased, commenced at the planet.
• A in addition improvement of civilization have become not possible with out the advent of civilized structures of water deliver and a complicated of water disposal facilities. In reference to the worsening of the ecological nation of floor and underground reassets the difficulty of water pleasant control, utilized by humans for ingesting purposes, have become greater acute. As a end result of a low pleasant of ingesting water actual threats to the sanitary-epidemiological scenario in diverse areas of the planet cropped out. And best early withinside the twentieth century the primary general for ingesting water seem withinside the USA.
• After nearly a century after adoption in Brussels of the primary advice for ingesting water pleasant a file of the World Health Organization (WHO) turned into published, which today, at the start of the twenty first century, proposes to convey beneathneath law ninety five indices of which 26 are poisonous materials, whose presence in ingesting water is undesirable. The US general regulates 102 indexes in ingesting water, in which entire absence is needed for as many as 35 poisonous indexes.
• A excessive degree of technogenic load on water bodies, using imperfect technology of water conditioning, and secondary infection of the water in distribution networks bring about the ingress to the ingesting water of a widespread quantity of inorganic and natural pollution whose joint impact at the human organism reasons the impact of synergism acknowledged in chemistry and biology, posing actual danger to human fitness. In the scenario that has taken form there may be in precept no opportunity to offer the populace of any u . s . Or continent with pleasant and secure for human fitness ingesting water [1–4].
• A boom of the pleasant of the water being managed through a countrywide general in diverse international locations of the arena does now no longer resolve the difficulty of acquiring secure ingesting water on the centralized water conditioning stations either. All this requires the ever greater costly system and difficulty of technological processes. Against the historical past of such catastrophic adjustments withinside the pleasant of the surroundings the tracking of numerous tens of materials in ingesting water reasons, to mention the least, a marvel. A marvel is likewise because of a lack of knowledge of the truth that during pursuit of “technical progress,” even growing the quantity of controllable additives in ingesting water numerous instances as much, one can't supply any ensures that it's far in truth ingesting water and secure for human fitness.
• Even using underground water at gift does now no longer continually assure the pleasant of the ingesting water obtained, specially if one takes under consideration the truth that an absolute majority of natural be counted withinside the surroundings beneathneath the impact of diverse physicochemical and ecological elements undergoes biotransformation into unknown and, maximum often, into unpredictable compounds.
• According to the aforementioned synergism the outcomes of or greater compounds of poisonous nature of every in my view taken substance boom if so if this substance first of all isn't poisonous.
• Hence the senselessness of the use of conventional procedures to the evaluation of ingesting waters follows. The belief itself of “normalizing most allowable concentrations in ingesting water of various toxicants” purportedly secure for human fitness is, as a be counted of truth, immoral.

Key takeaways:

• Water excellent relies upon at the nearby geology and ecosystem, in addition to human makes use of together with sewage dispersion, business pollution, use of water our bodies as a warmth sink, and overuse (which may also decrease the extent of the water).

Indian and WHO drinking standard:

• The quality of drinking water depends upon various parameters such Physical, Chemical, and as Microbiological.
• The quality of water used for drinking must be followed to achieve good health and to control various water borne or water induced diseases.
• In the third world countries like the Asian and African countries about 90% of the total morbidity cases, in a year, are related to the consumption of water which does not maintain the given standards of drinking water.
• There are various agencies who play an important role in specifying the norms to fix the water quality standards such as-

1. Indian Standards Institution (I.S.I)
2. World Health Organisation (W.H.O)
3. United States Public Health Service (U.S.P.H.S)
4. Indian Council of Medicine Research (I.C.M.R)

• Let us study the norms put forth by I.S.I. (IS.10500) in 2010 for drinking water specifications:

Quality of water as per IS 10500 (2012):

Table: Physical parameters 

3.1.4 Water born diseases

Human health gets affected by the consumption of contaminated water, either directly or through food. The water related diseases may be grouped as:

1. Water borne diseases
2. Water based or water induced diseases
3. Water related vector diseases
4. Water diseases

1.Water Borne Diseases:

• These diseases are caused by the consumption of contaminated water having virus or bacteria. The viral diseases are viral hepatitis A, hepatitis E, Poliomyelitis and rotavirus diarrhoea.
• The Bacterial diseases are, Typhoid, and Paratyphoid fever, Bacillary dysentery, E Coli diarrhoea and Cholera etc.
• Excess levels of nitrates cause blood disorders, the pesticides in the drinking water may cause cancer and neurological disorders. It may cause infertility.

2.Water Based or Water Induced Diseases:

• Aquatic organism that live a part of their life cycle in water and the rest as a parasite in human body lead to several diseases e.g. Guinea worm disease is spread through Cyclops.
• The round worm, thread worm, live in the small intestine mainly of children.

3.Water Related Vector Diseases:

• The insects such as mosquitoes that breed in stagnant water, causes Malaria, Filasia, Dengue fever.
• Among these Dengue fever causes very high mortality.

4.Water Scarcity Diseases:

• In the areas having, scarcity of water and lack of sanitation, there is a high incidence of diseases, such as Tuberculosis (T.B.), Leprosy, Tetanus etc.
• They are the results of poor personal and social hygiene, mainly in the rural areas of India. It may cause the diseases like Trachoma, Conjunctivitis and scabies.
• All the above diseases can be put under control if the safe drinking is made available and the level of personal and social hygiene is improved by the government and non-government organizations.

Key takeaways:

• In the third world countries like the Asian and African countries about 90% of the total morbidity cases, in a year, are related to the consumption of water which does not maintain the given standards of drinking water.

3.2 Water treatment: Objective of treatment, unit operations and processes, house hold & community based rural water treatment, decentralized water treatment, flow sheet of conventional water treatment plant

Screening

It is the first operation in wastewater treatment to remove most of the bigger and longer visible objects such as trees, branches, sticks, rags, boards, animals etc present in raw water of surface water sources as the screens protect pumps and other mechanical equipments and to prevent clogging of valves and other appurtenances.

Types of Screens

Screens are of three types depending upon the size of opening-

a)     Coarse screens

b)    Medium screens

c)     Fine screens

a) Coarse Screens –

• They are also known as racks. Spacing between bars is 50 mm or more than this. These screens help in removing large floating objects from sewage. The material separated by coarse screens consists of rags, woods, sticks and paper etc. which will putrefy and must therefore be disposed of by incineration, burial or dumping.
• Coarse screens consist of parallel iron rods placed vertically or at a slight slope of about 2 to 10 cm centre to centre.
• The coarse screens are also now normally kept inclined at about 45-60° so as to increase the opening area to reduce the flow velocity and thus making the screening more effective. Velocity of wastewater through screen should not be more than 0.8 to 1 m/sec. The material which is collected on the upstream side of screens is removed either manually or mechanically. In mechanically cleaned screens, a rack traverses the front of the screen either continuously or intermittently. Mechanical cleaning is done at large plants with mechanically operated rakes while manual cleaning is done at small plants with hand operated rakes.

b) Medium Screens –

• In this type of screen, spacing between the bars is 6-40 mm. These screens will ordinarily collect 30-90 litres of material per million litre of Sewage. Screenings (material removed by screens) usually contain some quantity of organic material which may putrefy and become offensive, therefore, be disposed of by incineration or burial (not by dumping).
• Rectangular shaped coarse and medium screens, made up of steel are now-a-days widely used at sewage treatment plants. These are fixed parallel to one another at desired space on a rectangular steel frame and are called bar screens which are set in screen chamber.
• Now-a-days, these screens are generally kept at about 30-60° to the direction of flow so as to increase the opening area and to reduce the flow velocity and thus making the screen more effective. Screens can be either fixed or movable depending upon whether the screens are stationary or capable of motion. Fixed screens are permanently set in position while movable can be moved bodily for the purpose of cleaning.

c)    Fine Screens –

• In this type of screen, spacing between bars is 1.5 mm to 3 mm size. It removes about 20% of suspending solids from sewage. These screens are made up of fine wire, brass or bronze plates with openings less than 1 cm. Metal used should be resistant to rust and corrosion.
• They may be disc or drum type and operated continuously by electric motors. These screens often get clogged and are to be cleaned frequently. They are, therefore, used for treating industrial wastewater or for municipal waste containing industrial wastewater. Cleaning frequency is governed by head loss through the screen. More the screen openings clogged more will be the head loss.

Key takeaways:

• Coarse screens consist of parallel iron rods placed vertically or at a slight slope of about 2 to 10 cm centre to centre.

3.2.1 Objective of treatment

Some of the primary targets of the water remedy method are:

1. To lessen the impurities to a sure degree that doesn't purpose damage to human health.

2. To lessen the objectionable colour, odour, turbidity and hardness.

3. To make water secure for drinking.

4. To get rid of the corrosive nature of water affecting the pipe.

5. To make it appropriate for a extensive kind of commercial functions consisting of steam generation, drying, etc.

3.2.2 Unit operation and process

• The direction covers the principle unit tactics of traditional floor water treatment. The following unit technique might be explored in element through lectures, laboratory classes and workshops:
• Coagulation: Theory of coagulation and flocculation tactics: colloidal balance and mechanisms of destabilization, speedy and sluggish mixing, coagulation in practice, herbal coagulants, coagulation kinetics, outcomes of coagulation.
• Sedimentation: Hydrodynamic ideas of sedimentation and flotation, Stokes law, ideas of discrete settling, flocculent settling and hindered settling. Horizontal and vertical non-stop go with the drift basins, settling tanks, form of inlets and outlets. Design of a square horizontal sedimentation tank. Dissolved air flotation: Key layout parameters, Henry's law, nucleus theory, Stokes law, charge of upward thrust theory, hydraulic loading charge, solids loading
• Filtration: General advent to diverse styles of filtration systems, mechanical filtration, sluggish sand filtration, speedy sand filtration (pilot experiments, elimination mechanisms, hydraulics, clear out elements, charge control, backwashing, multi-layer filtration, applications, layout considerations, clear out arrangements, modelling, optimisation).
• Design components of the distinctive filtration types.

3.2.3 House hold and community based rural water treatment

• Over a thousand million human beings nonetheless lack get entry to to secure ingesting water today. Waterborne illnesses as a result of intake of dangerous ingesting water are a chief fitness burden in maximum of the growing nations withinside the world.
• Lack of secure water perpetuates poverty. Safe ingesting water and sanitation are the situation for bodily fitness and intellectual, social and affordable interest and improvement.
• The high-satisfactory of ingesting water being provided is regularly overlooked even though the get entry to to water deliver has been extended substantially.
• However, ingesting water provided via way of means of centralised remedy structures is probably to get infected because of bad distribution networks, control and unhygienic coping with previous to intake.
• To deal with the water at family degree with the intention to guarantee the microbial (and chemical) high-satisfactory collectively with secure water garage and right hygiene practices ought to appreciably make contributions to attain the millennium improvement goals.
• Household-degree Water Treatment and Safe Storage (HWTS) can lessen episodes of diarrhoeal illnesses via way of means of 39% (WHO 2007a). According to the WHO (WHO 2007b) HWTS dramatically improves microbial water high-satisfactory; substantially reduces diarrhoea; is a few of the handiest of water, sanitation and fitness interventions; is particularly cost-effective; and may be unexpectedly deployed and brought up via way of means of inclined populations.

3.2.4 Decentralized water treatment

• Decentralized wastewater structures (additionally called decentralized wastewater remedy structures) convey, deal with and dispose or reuse wastewater from small and low-density communities, homes and dwellings in far flung areas, man or woman public or non-public properties.
• Wastewater float is generated whilst suitable water deliver is to be had in the homes or near them.
• Decentralized wastewater structures deal with, reuse or dispose the effluent in fairly near place to its supply of generation. They have the reason to shield public fitness and the herbal surroundings with the aid of using decreasing extensively fitness and environmental hazards.
• They also are referred as "decentralized wastewater remedy structures" due to the fact the primary technical project is the good enough preference of a remedy and/or disposal facility. A normally used acronym for decentralized wastewater remedy system, is DEWATS.

Key takeaways:

• Filtration: General advent to diverse styles of filtration systems, mechanical filtration, sluggish sand filtration, speedy sand filtration (pilot experiments, elimination mechanisms, hydraulics, clear out elements, charge control, backwashing, multi-layer filtration, applications, layout considerations, clear out out arrangements, modelling, optimisation).

3.2.5 Flow sheet of conventional water treatment plant

3.3 Aeration: Purpose, types of aerators, design of cascade aerator

• Aeration of liquids (normally water) is executed with the aid of using: passing air via the liquid by way of the Venturi tube, aeration generators or compressed air which may be blended with diffuser(s) air stone(s), in addition to great bubble diffusers, coarse bubble diffusers or linear aeration tubing.
• Ceramics are appropriate for this purpose, regularly concerning dispersion of great air or fueloline bubbles via the porous ceramic right into a liquid. The smaller the bubbles, the extra fueloline is uncovered to the liquid growing the fueloline switch efficiency.
• Diffusers or spargers also can be designed into the device to motive turbulence or blending if desired. Porous ceramic diffusers are made with the aid of using fusing aluminum oxide grains the use of porcelain bonds to shape a strong, uniformly porous and homogeneous structure.
• The clearly hydrophilic cloth is effortlessly wetted ensuing withinside the manufacturing of great, uniform bubbles.
• On a given extent of air or liquid, the floor place modifications proportionally with drop or bubble size, the very floor place wherein trade can occur. Utilizing extraordinarily small bubbles or drops will increase the price of fueloline switch (aeration) because of the better touch floor place. The pores which those bubbles byskip via are normally micrometre-size.

3.3.1 Purpose

• To smooth (laminate) the glide of faucet water on the faucet.
• Production of aerated water or cola for ingesting purposes. Secondary remedy of sewage or business wastewater through use of aerating mixers/diffusers.
• To boom the oxygen content material of water used to residence animals, consisting of aquarium fish or fish farm
• To boom oxygen content material of wort (unfermented beer) or must (unfermented wine) to permit yeast to propagate and start fermentation.
• To dispel different dissolved gases consisting of carbon dioxide or chlorine. In chemistry, to oxidise a compound dissolved or suspended in water.
• To result in blending of a frame of in any other case nonetheless water.

3.3.2 Type of aerators

1. Diffused Air Aeration

• In subtle air aeration approach compressed air is blown via the sewage and air is subtle in sewage via way of means of diffuser. Diffusers are of types: Plate diffuser and Tube diffuser
• Plate Diffuser: They are rectangular/rectangular plates made from crystalline alumina or excessive silica sand. In this approach the compressed air is blown via a perforated plate diffuser. The air comes out via the holes of the diffuser plate and rises upward withinside the shape of bubbles. Thus the sewage absorbs oxygen from the air.
• Tube Diffuser: It includes a perforated tube suspended withinside the waste water close to the lowest and may be taken out at the same time as cleaning. The compressed air is dent via the tube. The air comes out via the holes with wonderful pressure and agitates the sewage.

2. Mechanical Aeration

• In this technique the floor of sewage is agitated violently with the assist of a few mechanical device to inspire absorption of oxygen from atmosphere. There are widely recognized sorts of mechanical aerator.
• Vertical floor aerator and Horizontal floor aerator: They include electrically pushed propellers (vanes) set up in both a floating or constant supports. They throw the majority liquid (sewage) via air and oxygen switch takes place each on the floor of the droplets and on the floor of the majority liquid and is then combined through the currents produced through agitation. In this technique the overall performance is severely tormented by ice formation in winter.

3. Combine Aerator

• In this system, subtle air aeration and mechanical aeration are integrate in a unmarried unit. The widely recognized form of such mixture is Dorroco aerator.
• The aeration of sewage is executed through air diffusers in addition to mechanical aerators. Air diffuser plates are placed at the lowest of tank and the submerged paddles rotate withinside the course contrary to that during which the compressed air rises up from the air diffusers. Paddles are circled through a motor on a horizontal shaft with a velocity of 10-12 rpm.

3.3.3 Design of cascade aerator

How it Works

• With Cascade Aerators, aeration is achieved through herbal draft devices that blend cascading water with air this is obviously inducted into the water glide. Cascade water is pumped to the pinnacle of the aerator, and cascades over a sequence of trays.
• Air is obviously inducted into the water glide to perform iron oxidation and a few discount in dissolved gasses. WesTech’s Cascade Aerators are of non-corroding, all aluminum or stainless creation and haven't any transferring parts, making them protection loose and cheaper to shop for and operate.

CALCULATE LAKE SURFACE AREA 

• Multiply the length of the lake (in feet) by the width of the lake (in feet) to get the square feet of the surface.   Area = L x W

• Divide the surface area (in square feet) by 43,560 to get the number of surface acres.  SURFACE AREA =  NUMBER OF ACRES       43,560

CALCULATE NUMBER OF AERATORS 

Number of aerators = Number of acres (rounded upward) Example:  The lake is 220ft. Wide x 370 ft. Long (220' x 370' = 81,400 sq. Ft   =  1.87 acres (rounded up to 2 acres). 43,560 Lake requires either: (1) 1 - 1/2 hp aerators for normal conditions or (2) 2 hp aerators for warm climates or lakes with a history of high algae problems.

Key takeaways:

• Aeration of liquids (normally water) is executed with the aid of using: passing air via the liquid by way of the Venturi tube, aeration generators or compressed air which may be blended with diffuser(s) air stone(s), in addition to great bubble diffusers, coarse bubble diffusers or linear aeration tubing.

3.4 Coagulation and Flocculation: Definition, Principles, types of coagulants and reactions, coagulant doses, types of mixing and flocculation devices

Coagulation

• Coagulation is the chemical water remedy method used to dispose of solids from water, via way of means of manipulating electrostatic costs of debris suspended in water.
• This method introduces small, relatively charged molecules into water to destabilize the costs on debris, colloids, or oily substances in suspension. Selecting the proper coagulant for a device will decorate usual device performance, and specifically enhance solids elimination performance via way of means of improving clear out out and clarifier performance.
• There are many wastewater remedy packages that require coagulation reactions, along with getting rid of colloidal solids from water, demulsifying oil emulsions (“emulsion breaking”), and in paint detackification. There also are many sorts of coagulants to be had to satisfy unique desires of a remedy method. In general, coagulation precedes flocculation in a chemical water remedy method.

Fig: Coagulation

• Particles in water convey an electrostatic price on their surface. Common examples consist of clay, silica, iron, paints, or even oil. These small, suspended debris are stabilized in suspension & hard to dispose of through mechanical methods.
• A suspension of solids in water normally includes numerous debris sizes. A lab evaluation of “particle length distribution” will assist outline the dimensions of debris in addition to the relative quantity of every length particle withinside the suspension.
• Particles over 100μm are usually considered “settleable solids” and without problems settle out of suspension. Particles sized 10-100μm are usually considered “turbidity” and are regularly addressed in a wastewater remedy machine with coagulation. Particles smaller than 10μm are “colloidal debris”, which might be nearly continually dealt with with coagulation due to the fact it's far pretty luxurious to dispose of small debris the usage of simplest mechanical water remedy like filtration.

Flocculation

• Smaller suspended debris and chemical complexes too small to settle with the aid of using gravity are known as colloids. Most of those may be eliminated with the aid of using chemical precipitation, called coagulation-flocculation (C-F), a way that has been used to take away ugly color, smell, and flavor in water in view that 2000bc.
• This approach is used mechanically in big municipal disinfection plants, however is straightforward sufficient for use on the family degree and outdoors82,259,294 (Box 88-8). Coagulation is finished with addition of the ideal chemical that alters the bodily kingdom of dissolved and suspended solids, inflicting debris to paste collectively on touch due to electrostatic and ionic forces.71,322 Aluminum salts (alum), iron, and lime (alkaline chemical compounds basically containing calcium or magnesium and oxygen) are regularly used, without problems to be had coagulants. Rapid blending is essential to acquire dispersion of the coagulant.
• The 2d stage, flocculation, is a in basic terms bodily system received with the aid of using extended mild blending to growth interparticle collisions and sell formation of large debris. The flocculate debris are big sufficient that they may be eliminated with the aid of using sedimentation or with the aid of using filtration with enormously big pore size, which include a tightly woven cloth.180 To make clear water with the aid of using C-F withinside the field, upload 10 to 30 mg of alum consistent with liter of water.
• The genuine quantity isn't always essential, so it could be accomplished with a pinch of alum, lime (calcium oxide), or each for every gallon of water, the usage of extra if the water may be very cloudy. Next, stir or shake rapidly for 1 minute to combine the coagulant, then agitate lightly and regularly for at the least five mins to help flocculation. Settling calls for at the least 30 mins, and then the water is cautiously decanted or poured via a fabric or paper filter. The system may be repeated, if necessary.

3.4.1 Definition

• Coagulation is the chemical water remedy procedure used to take away solids from water, via way of means of manipulating electrostatic prices of debris suspended in water. This procedure introduces small, exceptionally charged molecules into water to destabilize the prices on debris, colloids, or oily substances in suspension.

3.4.2 Principles

• Coagulation – flocculation is physico-chemical technique that helps the agglomeration of pleasant particles (colloids) contained in water to shape a floc that may be effortlessly filtered from water.
• Effluent (waste water) ought to be dealt with earlier than it's far discharged or earlier than the water is re-used.
• Coagulation – flocculation facilitates get rid of compounds from effluent and thereby makes it viable to split water and particles.

3.4.3 Type of coagulants and reactions

• The typically used metallic coagulants fall into trendy categories: the ones primarily based totally on aluminum and people primarily based totally on iron. The aluminum coagulants encompass aluminum sulfate, aluminum chloride and sodium aluminate.
• The iron coagulants encompass ferric sulfate, ferrous sulfate, ferric chloride and ferric chloride sulfate. Other chemical substances used as coagulants encompass hydrated lime and magnesium carbonate.
• The effectiveness of aluminum and iron coagulants arises basically from their capacity to shape multi-charged polynuclear complexes with more suitable adsorption characteristics.
• The nature of the complexes fashioned can be managed via way of means of the pH of the system. When metallic coagulants are introduced to water the metallic ions (Al and Fe) hydrolyze unexpectedly however in a incredibly out of control manner, forming a sequence of metallic hydrolysis species. The performance of speedy mixing, the pH, and the coagulant dosage decide which hydrolysis species is powerful for remedy.
• There has been sizeable improvement of pre-hydrolyzed inorganic coagulants, primarily based totally on each aluminum and iron to provide the perfect hydrolysis species irrespective of the method situations at some point of remedy. These encompass aluminum chlorohydrate, polyaluminum chloride, polyaluminum sulfate chloride, polyaluminum silicate chloride and varieties of polyaluminum chloride with natural polymers.
• Iron bureaucracy encompass polyferric sulfate and ferric salts with polymers. There also are polymerized aluminum-iron blends. The important benefits of pre-polymerized inorganic coagulants are that they may be capable of feature successfully over extensive tiers of pH and uncooked water temperatures. They are much less touchy to low water temperatures; decrease dosages are required to acquire water remedy goals; much less chemical residuals are produced; and decrease chloride or sulfate residuals are produced, ensuing in decrease very last water TDS.  
• They additionally produce decrease metallic residuals. Pre-polymerized inorganic coagulants are organized with various basicity ratios, base concentrations, base addition rates, preliminary metallic concentrations, growing older time, and growing older temperature. Because of the extraordinarily unique nature of those merchandise, the exceptional method for a selected water is case unique, and desires to be decided via way of means of jar testing. For example, in a few programs alum can also additionally outperform a number of the polyaluminum chloride formulations1.
• PoIymers are a big variety of herbal or artificial, water soluble, macromolecular compounds which have the capacity to destabilize or decorate flocculation of the components of a frame of water. Natural polymers have lengthy been used as flocculants. For example, Sanskrit literature from round 2000 BC mentions the usage of beaten nuts from the Nirmali tree (Strychnos potatorum) for clarifying water – a exercise nonetheless alive these days in components of Tamil Nadu, wherein the plant is called Therran and cultivated additionally for its medicinal properties.
• In trendy, the benefits of herbal polymers are that they may be simply freed from toxins, biodegradable withinside the surroundings and the uncooked merchandise are regularly regionally to be had. However, the usage of artificial polymers is greater widespread.
• They are, in trendy, greater powerful as flocculants due to the extent of manipulate made viable at some point of manufacture. Important mechanisms regarding polymers at some point of remedy encompass electrostatic and bridging effects. Figure 1 suggests schematic levels withinside the bridging mechanism. Polymers are to be had in numerous bureaucracy along with solutions, powders or beads, oil or water-primarily based totally emulsions, and the Mannich types.
• The polymer rate density affects the configuration in solution: for a given molecular weight, growing rate density stretches the polymer chains via growing electrostatic repulsion among charged units, thereby growing the viscosity of the polymer solution.

3.4.4 Coagulant doses

• Typical coagulant dosage ranges from 0.5 to 20 ppm. Inorganic coagulants generally require a higher dose than polymeric coagulants.
• The best technique for determining the proper dosage of coagulant is to feed the product in-line and measure the SDI in the filter effluent as a function of coagulation feed rate.

3.4.5 Type of mixing

1. Rapid or Flash mixing 

It is the process by which a coagulant is rapidly and uniformly dispersed through the mass of water. This process usually occurs in a small basin immediately preceding or at the head of the coagulation basin. Generally, the detention period is 30 to 60 seconds and the head loss is 20 to 60 cms of water. Here colloids are destabilised and the nucleus for the floc is formed.

2.Slow mixing

Slow mixing brings the contacts between the finely divided destabilised matter formed during rapid mixing.

3.4.6 Flocculation devices

Perikinetic and Orthokinetic Flocculation

• The flocculation process can be broadly classified into two types, perikinetic and orthokinetic.
• Perikinetic flocculation refers to flocculation (contact or collisions of colloidal particles) due to Brownian motion of colloidal particles. The random motion of colloidal particles results from their rapid and random bombardment by the molecules of the fluid.
• Orthokinetic flocculation refers to contacts or collisions of colloidal particles resulting from bulk fluid motion, such as stirring. In systems of stirring, the velocity of the fluid varies both spatially (from point to point) and temporally (from time to time). The spatial changes in velocity are identified by a velocity gradient, G. G is estimated as G=(P/aV)1/2, where P=Power, V=channel volume, and v= Absolute viscosity.

Mechanism of Flocculation

• Gravitational flocculation: Baffle type mixing basins are examples of gravitational flocculation. Water flows by gravity and baffles are provided in the basins which induce the required velocity gradients for achieving floc formation.
• Mechanical flocculation: Mechanical flocculators consists of revolving paddles with horizontal or vertical shafts or paddles suspended from horizontal oscillating beams, moving up and down.

Key takeaways:

• A suspension of solids in water normally includes numerous debris sizes. A lab evaluation of “particle length distribution” will assist outline the dimensions of debris in addition to the relative quantity of every length particle withinside the suspension.

References:

1. CPHEOO manual, New Delhi, Ministry of Urban Development G.O.I.

2. Water supply and sewage by M.J.Mcghee Mc. Graw Hill

3. Environmental Pollution Control Engg. By C.S.Rao Mc. Graw Hill