Unit - 2

Principles of Water Treatment

Q1) Explain Water Treatment and principles of water treatment.

A1)

Water treatment:

• Water remedy is any technique that improves the best of water to make it suitable for a particular cease-use. The cease use can be consuming, business water supply, irrigation, river go with the drift maintenance, water endeavor or many different uses, which include being adequately again to the environment.
• Water remedy gets rid of contaminants and unwanted components, or reduces their attention in order that the water turns into suit for its preferred cease-use.
• This remedy is essential to human fitness and lets in human beings to gain from each consuming and irrigation use.

Water treatment: principles of unit operations and processes

• Water and waste water vary simplest with inside the manner that solids attention may be extra in waste water and in order to be there in water too if the equal is taken from the river water which makes the remedy method to each the equal besides that filtration is on straining the finer debris in water remedy and is toward organic motion of microorganism at the trickling clear out to put off natural solids.
• Unit operations are the bodily operations to put off the impurities gift with inside the water and waste water wherein because the unit tactics are the chemical and organic conversion at the repute of the impurities that they'll be without difficulty eliminated via way of means of chemical or organic tactics, each are carried out mainly to make the nice colloidal debris to coalesce
• Develop in length to be eliminated from the water or waste Screens are in use from the consumption shape wherein they save you the floating count number to go into the pumping gadgets, and nice and coarse monitors are in use to deal with waste water to save you the access of floating wastes and coarse solids into the remedy.
• Sedimentation is definitely detaining water for an enough time on the whole in stagnant or enormously stagnant function to make the float speed of water much less than the settling speed of the stable debris that they without being pushed via way of means of horizontal pressure settles down via way of means of gravity.

Q2) Explain operations included in water treatment.

A2)

The following are the processes of water treatment:

1. Coagulation/Flocculation:

• During coagulation, liquid aluminum sulfate (alum) and/or polymer is brought to untreated water (uncooked water).
• When blended with the water, this reasons the tiny debris of dust gift to paste collectively or coagulate.
• These companies of dust debris then be part of to shape larger, heavier debris known as flocs, which might be simpler to do away with via way of means of settling or filtration.

2.     Sedimentation:

• As the water and the floc debris development through the remedy process, they circulate into sedimentation tanks. Here, the water movements slowly, inflicting the heavy floc debris to settle to the lowest.
• The floc that collects at the lowest of the tank is referred to as sludge, and is piped to drying lagoons. In direct filtration, the sedimentation step isn't always included, and the flock is eliminated via way of means of filtration only.

3.     Filtration:

• Water flows via a clear out designed to take away debris from inside it. The filters are fabricated from layers of sand and gravel, and in a few cases, beaten anthracite.
• Filtration collects the suspended impurities in water, improving the effectiveness of disinfection. These filters are robotically wiped clean with the aid of using backwashing.

4.     Disinfection:

• Water is disinfected earlier than it enters the distribution device to make certain that any disease-inflicting microorganisms are destroyed. Chlorine is used due to the fact it's miles a completely powerful disinfectant, and residual concentrations may be maintained to defend towards viable microbial infection with inside the water distribution device.

5.     Sludge Drying:

• Solids that are collected and settled out of the water by sedimentation and filtration are removed to drying lagoons.

6.     Fluoridation:

• Water fluoridation is in which network water elements are handled with awareness of the loose fluoride ion. This is adjusted to a surest stage to lessen dental decay. We're required to fluoridate according with the NSW Fluoridation of Public Water Supplies Act 1957.

7.     PH Correction:

• Lime is delivered to filtered water to alter the pH and stabilize the obviously tender water. This minimizes corrosion with inside the distribution system, and inside customers’ plumbing.

Q3) Draw water treatment flow chart and explain.

A3)

Fig: Water treatment flow chart

1. Source: This is the factor from we have to take water to treat.
2. Intake Well: this is the first unit of water treatment process which supplies water to other units.
3. Screen: this unit performs the operation of screening, i.e., the large debris and other materials will be removed from this unit.
4. Aerators: using this unit we able to remove harmful gases from water by throwing water in open air. There are various types of aerator that are used to perform this operation.
5. Coagulant Tank: This unit is used to remove the organic and inorganic waste from the water.
6. Flash Mixer: Flash or speedy blending level is composed in including chemical compounds to uncooked water to foster coagulation, attracting debris which do now no longer settle or aren't filtered
7. Clarifloccation: In the Clariflocculator, the water enters the flocculator, wherein the flocculating paddles beautify flocculation of the feed solids. As heavy debris settle to the bottom, the liquid flows radially upward withinside the clarifier zone.
8. Filter Bed: The main function of filter bed is to collect filtered media.
9. Disinfection: This is the unit used for application of chemical agent to destroy the growth of microorganisms.
10. Distribution System: This is the system that will be used to distribute the purified or treated water for the use of commercial, industrial, institutional, etc. purposes.

Q4) What is the criteria for site selection for WTP?

A4)

The following factors are to be taken into consideration at the same time as choosing a website for water remedy plant:

General Considerations:

• The making plans layout engineer, whilst choosing web sites for leisure remedy centers, ought to make certain that the deliberate facility will now no longer reason interference or detractions from the natural, scenic, aesthetic, scientific, or ancient cost of the vicinity.
• In addition, topographic, geological, hydrogeological, and atmospheric elements and situations ought to be taken into consideration whilst designing the remedy facility for a leisure vicinity. For particular issues concerning web website online choice, space, and get right of entry to requirements.

Aesthetics

• The clothier ought to make certain that distinguishing capabilities that make the vicinity of leisure cost aren't degraded. Vertical constructing production need to supplement or decorate adjoining architectural and environmental capabilities.
• Aesthetic elements are critical sufficient to the cost of any leisure vicinity that extra production, operation, and renovation expenses to maintain the splendor of the web website online can be justified.

Topography

• Topography ought to be taken into consideration if most usage of gravity go with the drift thru the whole device is to be achieved. Many leisure regions are nicely tired and lightly sloping. Flat terrain commonly calls for a choice regarding pumping of wastewater to a few factors in the plant earlier than good enough gravity go with the drift may be obtained. Additional pumping expenses can be essential for a remedy facility on a website far flung from tourist concentrations.

Geology and Hydrology

• The ability or disability of geological formations underlying the leisure centers to help hundreds ought to be taken into consideration whilst choosing a website.
• Rock formations at once have an effect on the excavation expenses. The absorptive ability of underlying soils is a critical web website online choice parameter for diverse remedy structures.
• For example, land disposal structures require soils with excessive permeability for powerful remedy.
• To keep away from groundwater contamination, seepage charge needs to normally now no longer exceed 0.three mm/d (/in/d). Adequate soil exploration is crucial in web website online choice to protect towards immoderate seepage and towards structural failure. Selected references are to be had to decide soil traits and anticipated properties

Atmospheric situations

• The atmospheric situations of a candidate web website online ought to be evaluated all through the making plans phase; those consist of temperature, pressure, air movements, humidity, cloudiness, and precipitation.
• Generally, it's far pleasant to find leisure remedy centers downwind from visitation facilities to decrease scent and aerosol problems.
• If the development of a leisure remedy facility at a far-flung web website online isn't feasible, the layout engineer ought to do not forget different alternatives, which includes putting in a panorama and/or ornamental display screen across the remedy plant and restricting the scent from the plant beneath neath ordinary running situations.

Q5) Define Aeration and principle of aeration.

A5)

Aeration:

The process of exposing the large content or surface of water to the atmospheric air is called as aeration.

The following are the objectives of aeration:

• To increase percentage of oxygen
• To reduced dissolve gases
• To destroy bacteria of some extent

Principle of aeration:

• Aeration brings water and air in near touch on the way to get rid of dissolved gases and to oxidize dissolved metals, along with iron, hydrogen sulfide, and risky natural chemicals (VOCs).
• This manner is normally the primary predominant manner at ingesting water remedy plant, and happens with inside the secondary remedy tactics of activated sludge remedy in wastewater remedy plants.
• A lightly allotted oxygen deliver in an aeration device is critical to powerful wastewater remedy for fostering microbial growth.
• According to the Missouri Rural Water Association, the performance of aeration relies upon on the quantity of floor touch among air and water.
• This is normally managed with the aid of using the dimensions of the water drop or air bubble.
• Aeration brings water and air in near touch with the aid of using exposing drops or skinny sheets of water to the air or with the aid of using introducing small bubbles of air and permitting them to upward thrust thru the water.

Q6) Describe types of aeration.

A6)

1. Using fountain spray/nozzles:

• By the usage of Fountains, Spray Nozzles Water is discharged below the impact of fountain action, with inside the shape of first-class spray. Spraying consequences with inside the formation of extraordinarily minute droplets of water.
• This will increase its floor place of touch with air. Spray nozzles are positioned in a pool of water. As shown in figure.

2.     Cascade Aerator:

• With Cascade Aerators, aeration is performed via way of means of herbal draft devices that blend cascading water with air this is clearly inducted into the water go with the drift. Cascade water is pumped to the pinnacle of the aerator, and cascades over a sequence of trays.
• Air is clearly inducted into the water go with the drift to perform iron oxidation and a few discounts in dissolved gasses. WesTech’s Cascade Aerators are of non-corroding, all aluminum or stainless production and don't have any transferring parts, making them renovation unfastened and less expensive to shop for and operate.

Fig: Cascade Aerator

• A simplest cascade consists of 3 to 4 steps either circular or straight type as shown in figure.
• Water is allowed to fall through height of 1 to 3 m. This may be in open in air.

3.     Trickling Bed or Multiple Trays:

• In this method water is pumped into a feeding tank placed at a height and allowed to trickle down through a perforated pipe on the beds filled with sand, broken coke, slag of size 5 to 7.5 cm.

Fig: Trickling bed

• A trickling clear out is a kind of wastewater remedy device. It includes a hard and fast mattress of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or different wastewater flows downward and reasons a layer of microbial slime (biofilm) to grow, overlaying the mattress of media.

Q7) What is the necessity of aeration?

A7)

• Oxygen is critical for lifestyles to exist, above and beneath the water.
• To maintain a pond and its population healthy, it's far crucial to have the proper quantity circulating with inside the water.
• Nature normally components sufficient quantities of aeration thru wind, rain, and different means. However, in lawn ponds extra vitamins which include runoff, grass clippings, and leaves from neighboring timber can depart a pond desiring greater oxygen.
• The loss of oxygen can bring forth adverse consequences so it’s crucial to live vigilant, in particular in hotter temperatures.
• Here are a number of the maximum not unusual place caution symptoms and symptoms for inadequate oxygen: Fish gasping on the surface, normally with inside the early morning Foul odors emitting from the pond Excessive quantities of string algae
• If you do now no longer see any of those symptoms, you will be in luck. However, it’s nonetheless crucial to ensure your pond is well oxygenated to keep away from destiny problems.
• Aeration brings water and air in near touch that allows you to cast off dissolved gases (including carbon dioxide) and oxidizes dissolved metals including iron, hydrogen sulfide, and unstable natural chemical substances (VOCs).
• Aeration is frequently the primary important procedure on the remedy plant. During aeration, parts are eliminated or changed earlier than they are able to intrude with the remedy processes. Aeration brings water and air in near touch through exposing drops or skinny sheets of water to the air or through introducing small bubbles of air (the smaller the bubble, the better) and allowing them to upward thrust thru the water.
• The scrubbing procedure as a result of the turbulence of aeration bodily gets rid of dissolved gases from answer and lets in them to break out into the encircling air.
• Aeration additionally enables cast off dissolved metals thru oxidation, the chemical mixture of oxygen from the air with positive unwanted metals withinside the water.
• Once oxidized, those chemical substances fall out of answer and turn out to be debris withinside the water and may be eliminated through filtration or flotation.

Q8) What are the reasons for water get polluted and give pleasant taste and odor?

A8)

• Taste and smell can input water in lots of manners.
• Surface water reassets can emerge as infected via algal blooms or via commercial wastes or home sewage introducing flavor- and smell-inflicting chemical compounds into the water.
• Groundwater resources may be stricken with dissolved minerals, consisting of iron and manganese, which input the water while it passes via rocks underground.
• Tastes and odors also can input both kind of water with inside the uncooked water transmission device and with inside the remedy plant because of algal growths, accrued particles and sludge, or disinfection byproducts.
• The distribution device will have some of the equal reasons of flavor and smell referred to above, with the addition of troubles because of cross-connections and occasional go with the drift zones.
• Experience has proven that a substance that produces a smell in water nearly always imparts a notion of flavor as well; however, flavor is normally attributed to mineral materials gift with inside the water, however maximum of those minerals do now no longer reason odors.
• When water has an awesome flavor however no smell, the flavor is probably the end result of inorganic materials. Anyone who has tasted alkaline water has skilled its biting bitterness. Salts now no longer simplest provide water a salty flavor however additionally make a contribution to a sour flavor.
• In addition to herbal reasserts, water can tackle a one-of-a-kind satiation or flavor, or each, from human infection of the water.
• Organic substances can produce each flavor and smell in water. Petroleum-primarily based totally merchandise are in all likelihood the high members to each of those troubles in water.

Q9) Explain Oxidation.

A9)

• In maximum cases, oxidation is the exceptional approach for controlling flavor and smell troubles. Oxidation may be accomplished with the subsequent chemicals: Potassium permanganate, most customarily used and is a completely robust oxidant.
• According to the California Department of Health Services Water Treatment Plant Operation, a dosage variety of 0.1 to 0.five mg/l can manage flavor and smell troubles. Ozone is likewise powerful oxidizing of flavor and smell compounds.
• Ozone adjustments the traits of the flavor and smell further to decreasing the extent of the smell-generating compound.
• Ozone dosages of two mg/l to five mg/1 were used. Several pilot research have proven that the mixture of ozone and hydrogen peroxide can be advanced to the usage of ozone alone.
• Chlorine dioxide or chorine also are powerful techniques of flavor and smell manage, however use as a manage chemical should be evaluated cautiously because of the formation of THMs and chlorophenol whilst organics are present.

Q10) What are the methods of removal of taste and odour?

A10)

1. Taste and odors taking place within side the distribution gadget is in most cases the end result of corrosion of pipe cloth and/or boom of iron microorganism, which includes crenothrix and leptorix, the water main.
2. If the water has excessive sulfates and is permitted to face in useless ends, flavor and smell issues can be compounded with the aid of using sulfate-decreasing microorganism.
3. These issues may be rectified best with the aid of using right layout of the gadget, which includes getting rid of useless ends and supplying good enough manner of flushing the gadget.
4. Maintenance crews have to maintain the water traces smooth with the aid of using frequently flushing out deposits and the microorganisms that gather inside those deposits.
5. Water remedy flowers also can reduce flavor and smell issues with the aid of using preserving a good enough residual of chlorine to fight the boom of microorganism with inside the gadget and with the aid of using the usage of anti-corrosion measures, both with the aid of using adjusting the pH of the water or with the aid of using including corrosion inhibitors to the completed water.

Q11) What is sedimentation, Explain plain and chemically assisted sedimentation?

A11)

1. Sedimentation:

• Sedimentation is a bodily water remedy manner the usage of gravity to do away with suspended solids from water.
• Solid debris entrained with the aid of using the turbulence of transferring water can be eliminated evidently with the aid of using sedimentation with inside the nonetheless water of lakes and oceans.
• Settling basins are ponds built for the motive of doing away with entrained solids with the aid of using sedimentation.

2. Plain Sedimentation:

• Plain sedimentation is the manner of doing away with suspended topics from the water with the aid of using retaining it quiescent in tanks, in order that suspended be counted can also additionally calm down within side the backside because of pressure of gravity.
• Chemical-aided sedimentation of sewage is similar to chemical coagulation, flocculation and sedimentation in water remedy.
• The colloidal and finely dispersed solids which cannot be eliminated with the aid of using undeniable number one sedimentation alone, as they own extraordinarily low settling velocities, are aggregated into settle able debris with the aid of using addition of chemical substances called coagulants in chemical-aided sedimentation.

3. Chemically Assisted Sedimentation:

• Chemical-aided sedimentation includes the unit procedures and operations of chemical coagulation, flocculation and sedimentation.
• The colloidal and finely dispersed solids found in sewage are typically negatively charged and consequently do now no longer agglomerate evidently into settle able mass.

• Addition of chemical coagulants outcomes in destabilization, aggregation and binding collectively of colloidal and finely dispersed solids with the aid of using any individual or a couple of mechanisms of-

(i)                            Ionic Layer compression;

(ii)                          Adsorption and rate Neutralization;

(iii)                        Enmeshment in Precipitate; and

(iv)                        Antiparticle Bridging. When chemical coagulant is introduced to sewage and carefully blended with it an insoluble, gelatinous, flocculent precipitate referred to as floe is formed.

• The floes are the polymers of hydroxometal complexes that are heavy and settle able. The floes are adsorbed on colloidal and finely dispersed solids and neutralize their rate or shape bridging among colloidal and finely dispersed solids if the polymers are of the identical rate as that on colloidal and finely dispersed solids.

Q12) What are the types of sedimentation?

A12)

Types of sedimentation:

• Settling basins and clarifiers are designed to preserve water in order that suspended solids can settle. By sedimentation principles, the correct remedy technology needs to be selected relying at the unique gravity, length and shear resistance of debris.
• Depending on the scale and density of debris, and bodily houses of the solids, there are 4 kinds of sedimentation processes:

Type 1 – Dilutes, non-flocculent, free-settling (each particle settles independently.)

Type 2 – Dilute, flocculent (debris can flocculate as they settle).

Type 3 – Concentrated suspensions, quarter settling, hindered settling (sludge thickening).

Q13) Describe types of sedimentation tanks.

A13)

The following are the types of sedimentation tanks:

1. Horizontal float tanks

• The quality form of sedimentation is to fill a jar or tank with water, leave by myself for a prolonged enough time for particles to settle and then decant off the following water without the sediment.
• In workout that isn't frequently viable in treating water for townships, and therefore sedimentation tanks are operated continuously.
• The quality method of sedimentation is to use rectangular tanks with horizontal float thru them. The water with the particles in suspension is brought at one prevent of the tank, then due to the fact the water flows to the opportunity prevent of the tank settlement of particles within sid the water occurs.

Fig: Horizontal flat tank

• The cause is that a huge percentage of the settling particles control to achieve the tank floor in advance than the water is drawn out of the tank on the hollow prevent. The tank is ready with a mechanism to scrape the sediment from the hollow prevent decrease again to the inlet prevent and into the hopper from in which it can be discharged hydraulically.
• In the format of such tanks special hobby has to get hold of to the inlet and outlet ends simply so the water flows from one prevent to the prevent as uniformly as possible.
• Partly because of the truth rectangular tanks have a huge footprint, multi-layer tanks (i.e., or three decks) have been built.

2.     Radial float tanks

• Radial float tanks are spherical with the inlet for the water at the center and a peripheral outlet.
• Attention desires to be paid to the format of inlet to resource uniform distribution of float to the whole of the tank.
• The sediment is scraped to an applicable hopper for its discharge. Some spherical tanks encompass greater capabilities within side the center for flocculation (i.e., premix designs) or maybe recirculation of settled particles (i.e., premix-recirculation designs).

Fig: Radial float tank

• The clean precept shows that overall performance of removal of particles is dominated thru manner of the vicinity available for settlement.
• A technique to offering a huge are with a small footprint is to use inclined plates or tubes. These are generally constructed with lightweight fabric in modular form which can be without issue placed in a concrete or steel tank
• In the co-present-day affiliation, the water flows downward many of the plate’s n the path of particle settlement. In the counter-present day affiliation, the water flows upward many of the plates toward the path of particle settlement.
• In cross-float the water flows all through the plates, i.e., horizontal, at right angles to the path of particle settlement.
• Inclined tubes can be applied in each co-present day or counter-present day modes, but in most instances within side the latter.

3.     Ballasted sedimentation

• The density difference amongst water and the particles produced in water treatment thru manner of coagulation, flocs, in present day is small. Therefore, they settle slowly. Methods of easy sedimentation (i.e., horizontal, radial and inclined sedimentation) are preceded thru manner of a sluggish mixing technique called flocculation.

Fig: Ballasted sedimentation

• The purpose of flocculation is to assist coagulated particles to collide and adhere as a way to become big particles that might settle faster, and for the particle duration distribution to be as small as possible.
• The density of floc particles can be prolonged thru manner of software program of a ballasting agent which consist of Mennonite or quality sand.
• The settling rate of floc ballasted with quality sand can be three or greater times faster than floc that is not ballasted, and is generally settled in a tank with counter-present day inclined plate gadget placed over a hopper in which the settled sludge is accrued.

4.     Floc blanket sedimentation

• The first floc blanket tanks had an inverted pyramidal shape topped thru manner of a quick vertical section. (‘Floc blanket’ is applied in desire to ‘sludge blanket’.
• This is because of the truth the view is taken that floc within side the suspension remains functioning as floc want to, supporting to remove the particles within side the incoming water.

Q14) Explain Tube Settlers.

A14)

• Tube settlers make use of a couple of adjoining tubular channels which are sloped at a nominal 60° attitude and integrate to shape an expanded powerful settling region.
• The length and form of the tubular channels range with the aid of using manufacturer. Brentwood's tube settler layout functions a trapezoidal form created with the aid of using thermoforming PVC sheets.
• Except with flocculation the sedimentation pace Vs of debris and Flow Q cannot be changed. By growing the most effective variable - tank region – we lower the floor loading qa and consequently boom the settling performance. To boom tank region, extra horizontal surfaces should be installed.
• Obviously, this isn't always realistic in order that horizontal plates are changed with the aid of using willing plates. The extra floor region of the willing plates is created with the aid of using their projection in horizontal direction.
• Nowadays settling plates are changed with the aid of using plastic modules due to the fact they've a decrease cost, are less difficult to hold and to install.
• Lamella clarifiers boom the settling region with the aid of using five to ten times! Also fantastic is that incoming water could be bogged down and redirected to waft among lamella plates which improves the waft pattern. Another gain is that willing plates bring about a countercurrent waft – one upward waft of water and one downward circulation of sludge.
• As in a water pipe frictional forces get better as nearer water receives to the pipe floor.

Q15) Give design criteria for plain sedimentation tank.

A15)

Design of plain sedimentation tank:

1. In this type of sedimentation tank its capacity depends upon volume of water to be treated. The length depends on velocity of flow and the detention period.
2. The detention period may vary from 4 to 6 hrs.
3. The width of tank varies from 10 to 12m. The depth of tank varies from 2 to 4m.

Due to low velocity of flow the heavier particles are settle down to bottom of the tank and at some interval the sludge is removed from sludge removal pipes.

Design steps:

Fig: Rectangular sedimentation tank

1. Using daily demand of water find out Capacity

Capacity of sedimentation tank = Water to be treated(lit/hr) * detention time

2.     Length of tank = Flow velocity * Detention Time

3.     Depth of tank = Capacity of tank / (Length*width) (Add free board into result)

4.     Dimension of tank: L*B*D

5.     Overflow Rate = Discharge/Surface area