/
Water Treatment Processes
Save to my account
Sign up
Water Treatment Processes
Water Treatment Processes
Study
1
Question
What are the internal treatments for the prevention of scale formation in water?
Answer
1. Colloidal conditioning 2. Phosphate conditioning 3. Carbonate conditioning 4. Calgon conditioning 5. Treatment with sodium aluminate.
2
Question
What are the types of external treatments for scale formation prevention?
Answer
1. Zeolite process 2. Ion-exchange process.
3
Question
What is the lime-soda process and its reaction to hardness-causing salts?
Answer
The lime-soda process is a method for softening water that involves the addition of lime (calcium hydroxide) and soda (sodium carbonate) to remove hardness-causing salts, primarily calcium and magnesium ions. The process can be conducted in both cold and hot conditions, depending on the water chemistry and the desired outcomes.
4
Question
How do you derive the formula for calculating the amount of lime and soda required for softening water?
Answer
The formula derivation involves knowing the concentration of hardness-causing ions (Ca²⁺ and Mg²⁺) in equivalents, using stoichiometry. Typically, the equation considers the mole ratio of lime and soda to the hardness salts. The relationship is as follows: Amount of lime (g) = (Hardness (mg/l) x Volume (liters) x 0.074) Amount of soda (g) = (Hardness (mg/l) x Volume (liters) x 0.065) The constants are derived from the molar mass of the components.
5
Question
How do you calculate hardness in terms of equivalents of calcium carbonate?
Answer
Hardness in water is typically expressed in terms of equivalent calcium carbonate (CaCO3) concentration. To calculate, one must: 1. Determine the concentration of Ca²⁺ and Mg²⁺ ions in mg/l. 2. Convert the concentration to equivalents using the formula: - For Ca²⁺, divide by 20 (molar mass of CaCO3 / charge of Ca) - For Mg²⁺, divide by 12.15 (molar mass of CaCO3 / charge of Mg) 3. Sum the equivalents and convert back to CaCO3 by multiplying by 100.
6
Question
What are the sources of water?
Answer
1. Surface Water: Includes rivers, lakes, and rainwater. 2. Underground Water: Includes spring water and well water.
7
Question
What are the characteristics of rainwater as source water?
Answer
Rainwater is considered the purest form of surface water; however, it can contain dissolved industrial effluents, such as oxides of carbon (C), sulfur (S), nitrogen (N), and suspended solid particles.
8
Question
What are the characteristics of river water?
Answer
River water is fed by rain and springs, has a varied composition due to interactions with the atmosphere, geology, and human activities. It contains minerals (like chlorides, sulfates, bicarbonates of sodium, calcium, magnesium, and iron), organic matter from decomposing plants, and suspended impurities like sand and rock particles.
9
Question
What are the characteristics of lake water?
Answer
Lake water comes from multiple sources including rain, snow, melting ice, streams, and groundwater. It provides a more consistent chemical composition but has higher organic matter due to decomposition of plant material, bacteria, and algae. It typically contains fewer minerals than river or well water.
10
Question
What is the composition of seawater?
Answer
Seawater is the most impure form of water and contains dissolved salts, primarily sodium chloride (3.5% salinity). It receives impurities from rivers and has suspended matter, including disease-causing bacteria, making it unsafe for consumption.
11
Question
What is the significance of municipal water specifications?
Answer
Municipal water should be sparkling clear, odourless, pleasant in taste, perfectly cool, and have turbidity less than 1-5 NTU. It should also be free from objectionable gases and minerals (like lead, arsenic, chromium), have low alkalinity with a pH around 8.0, be reasonably soft, and contain total dissolved solids (TDS) less than 500 ppm.
12
Question
What are the steps involved in the purification of water for municipal purposes?
Answer
1. Screening – removal of large objects (rags, plastics) 2. Sedimentation – gravity separation of suspended solids 3. Sedimentation with coagulation 4. Filtration – further removal of finer particles 5. Disinfection – to eliminate disease-causing organisms.
13
Question
What is the role of the screening process in water purification?
Answer
The screening process is the first operation used at treatment plants to remove large objects such as rags, paper, plastics, and metals that could damage or clog downstream equipment and pipes.
14
Question
What is sedimentation in water purification?
Answer
Sedimentation is a process that uses gravity to remove suspended solids from water, particularly coarse particles like sand and gravel. It involves keeping the water undisturbed to allow heavy particles to settle to the bottom.
15
Question
What is sedimentation with coagulation?
Answer
Sedimentation with coagulation is a process where fine soil particles undergo Brownian motion, resulting in a colloidal suspension in the water that cannot be removed through sedimentation. Coagulation, which neutralizes charges and creates a gelatinous mass, is performed first to aggregate fine sand particles into a bulk mass that can settle under gravity, followed by the sedimentation process.
16
Question
What is coagulation in water treatment?
Answer
Coagulation is a process used in water treatment to neutralize charged particles, forming a gelatinous mass that traps particles, resulting in larger aggregates that can either settle out or be filtered out. It is typically applied prior to sedimentation and filtration to enhance removal of particles.
17
Question
What reagents are commonly used in the coagulation process?
Answer
Common reagents used in the coagulation process include Potash alum (KAlSO4·12H2O), Ferrous sulfate (FeSO4), and Sodium aluminate (NaAlO2).
18
Question
What is Potash alum and its chemical formula?
Answer
Potash alum is one of the most widely used water treatment chemicals globally, with the chemical formula K2SO4·Al2(SO4)3·24H2O.
19
Question
What is the optimal pH range for coagulation using alum?
Answer
The optimal pH range for coagulation using alum is between 6 and 8, where negatively charged forms of alum predominate.
20
Question
What are the advantages of using alum as a coagulant?
Answer
Advantages of using alum include its low cost, wide availability, and ease of use.
21
Question
What are some disadvantages of using alum in water treatment?
Answer
Disadvantages of using alum include the requirement for hydroxide alkalinity, its pH range restrictions, the large quantities needed for dirty water, its limited effectiveness after a specific dosage, and the production of gelatinous sludge that is difficult to de-water.
22
Question
What is ferric chloride and its chemical formula?
Answer
Ferric chloride is a cost-effective inorganic coagulant in the form FeCl3 and is a waste product from steel production.
23
Question
What are the advantages of using ferric chloride as a coagulant?
Answer
Advantages of ferric chloride include its low cost, ability to work over a broad pH range, and ease of use.
24
Question
What are some disadvantages of ferric chloride?
Answer
Disadvantages of ferric chloride include its extreme corrosiveness, which necessitates special piping and storage equipment, along with variable pricing.
25
Question
What is sodium aluminate and its role in water treatment?
Answer
Sodium aluminate (NaAlO2) is obtained from bauxite refineries and is used for treating water with no alkalinity, typically within a pH range of 5.5 to 8.0. It aids in sedimentation by forming aluminum hydroxide floc and precipitating magnesium salts.
26
Question
What is the cost of sodium aluminate for water treatment?
Answer
The cost of sodium aluminate is approximately Rs 50 per kg.
27
Question
How does sodium aluminate affect magnesium hardness in water?
Answer
Sodium aluminate decreases magnesium hardness by precipitating magnesium salts as magnesium hydroxide (MgOH2) while also removing fine suspended and colloidal impurities from the water.
28
Question
What is the overall importance of coagulation and sedimentation in water treatment?
Answer
Coagulation and sedimentation are critical for removing suspended solids and impurities from water, enhancing the quality of treated water and ensuring it is safe for consumption.
29
Question
What is the chemical formula for ferrous sulfate heptahydrate?
Answer
The chemical formula for ferrous sulfate heptahydrate is FeSO4·7H2O.
30
Question
What are the applications of ferrous sulfate (FeSO4)?
Answer
Ferrous sulfate is typically used in applications where a reducing agent or excess soluble iron ions are required.