1. Give brief introduction about coagulation.
A large portion of the suspended particles in water and wastewater is sufficient small so that their removal is sedimentation tank with responsible detention and time and settling velocity is impossible.
Such a particle are know as colloids.
In water and wastewater treatment the removal of collage is through to be a two step process in which coagulation is the first step where the reaction of the chemical cognite with alkalinity and colloids forms the micro flocks and the flocculation is the second step which involves gentle and prolonged mixing of the disable is collides to promote their agglomeration i.e, to form the readily Settable flocs.
Coagulation means edition of one and more chemicals to condition the small particles for subsequent processing by flocculation.
2. Make a table of 8th class of dispersion.
3. Enlist and explain the properties of colloidal solution.
- Genral Property :
In case of general property of colloidal solution the terms stability play an important role to understand the fundamental of colloidal particles.
In this context stability can be through of resistance of colloidal particles to remove by physical means.
The stability of colloids is due to their size and electric property which affected by nature of colloid and Chemistry of colloid dispersion.
The polite particles are very small in size but their surface area in relation to mass is very high.
In order to remove polite particles they must somehow be disabilized.
- Mechanical properties
There are three types of mechanical properties:
- Brownian Motion
- Diffusion
- Sedimentation
1. Brownian Motion :
When colidal particles are view under the Ultra microscope, the colloidal particles appeared to be moving continuously in zig-zag motion.
The continuous zig-zag motion or moment of colladel particles in colloidal solution flow as Brownian moment.
The moment is due to the high velocity or energy of molecule aur dispersion medium bombarding against the colloidal particles from all direction with varying force creating zig-zag random motion.
Colloidal particles being heavier have slower speed.
Brownian moment is responsible for stability of colloidals as it opposes gravitational force and prevents the colloidal particles from settling.
2. Diffusion :
Diffusion is the result of Brown and moment.
The colladel particles diffuse from higher concentration.
However due to bigger size they diffuse lasser speed.
The rate of diffusion is expressed by fick's law :
dm/dt = - DA * DC/DX
Where,
- DM = mass of substance.
- dt = time
- A = Area
- D = diffusion coefficient
- - dc / DX = concentration gradient Concentration gradient.
3. Sedimentation :
The colladel particle settle down under the influence of gravity at a various low rate the phenomena is called sedimentation.
It is used to determine the molecular mass of molecules.
- Optical properties:
When light passes through solution its parts become visible due to the scattering of light by colloidal particles.
The phenomena is called tyndal effect.
If a strong conveying beam of light is passed through a solution placed in a dark medium/room , the path of light become visible.
Ine case off true solution no scattering of light occurs.
The Tyndall effect help to confirm the heterogeneous nature of colloidal solution.
- Electrical Properties :
when a potential difference in carrot across two Platinum electrodes immersed in colloidal solution.
The particles of disperse move downwards either positive or negative electrode.
The moment of colladal particles under the action of electric field is known as electrophoresis.
Demonstration Of Electrophoresis :
Take a colloidal solution in u-tube.
Place to platinum electrode into arms of u-tube such as they deep in the colloidal solution.
When high potential difference is applied across the electrode it is observed that the y level of colloidal solution on the negative electrode side and rise up on the positive electro side.
On reaching to positive electrode, the colladel particles get discharge, as result of neutralization of charge the colloidal particles aggregate and settle down at the bottom.
If the colloidal particles move townwards depositive day carry negative charge on the other hand if the solution particles migrates town were negative day are positive charge.
From the direction of colloidal particles it is possible to find out the charge of colloids.
- Electro-osmosis.
A colloidal solution is electrically charged solution.
When moment of disperse of poladal solution is prevented by suitable means the dispersion medium can be made to move under effluence of applied electric potential.
The electro osmosis may be defined as movement of dispersion medium under specific potential when particles of disperse phase are prevented from moving.
Demonstration of electro-osmosis.
This process carried out in a special design appears which consists bigger tube having two side denoted by T &T'.
The apparatus divided into 3 components : A,B and C by means of semipermeable membrane.
Two platinum electrode are inserted in outer compartment B and C.
A colladal dispersion is placed in Central compartment a and outer compartment are filled with water.
The water in compartment B and C extend to side tube T and t'.
The function of membrane is used to prevent movement of colloidal particles.
Therefore when a potential difference is applied across the electrode the dispersion medium being to move.
If the particle carry positive charge the dispersion medium States moving downward positive electrode anode and the level of water in decide to T will rise indicating the present of negative charge on dispersion medium.
If the particle carry negative charge the dispersion medium state moving downward negative electrode cathode and the level of water in the side tube T' will rise indicates the presence of positive charge on dispersion medium.
- Physical properties :
(A) heterogeneous character :
Colladel particles from heterogeneous mixture of disperse phase and dispersion medium because they have large size than that of molecules.
(B) Flirtability :
As we have discussed that particles of the Coral can be filter by using membrane or Filter paper.
(C) Stability :
Colladal solution are quite stable as very few large sizeed particles are able to settle at very slow settling rate.
(D) Visibility :
Particles cannot be seen easily even under ordinary microscope as their size as less than that of wavelength of visible light.
4. Describe the characteristic of colloids.
A colloids is a very small particle causing colour and turbidity.
Collides may be defined as particles ( ~0.2 micrometre ) and is suspension by its extremely small (1 to 20 Mili microns) it state of hydration and its surface electrical charge.
Some importance characteristic of colloids are :
- Extremely small size particles passing surface electric charge.
- Most colloidal particles in water and wastewater carry the sum electric charge e.g. they are negatively charged.
- Size of particles is the most significant property responsible for the stability of the solution.
- Exhibit brownian moment in quition liquid.
- Collidals are essentially nonsentalible because of small size small surface electrical charge and low particle height.
- Colloidals have very large ratio of surface area to mass/volume enhance the surface phenomena for instant electrostatic repulsion, also become important in stability of colloids.
5. Enlist and explain the example of types of colloids.
Collapse are commonly classify as the affinity the disperse phase for the dispersing liquid.
System are referred as,
- Hydrophilic ( Water loving )
Hydrophilic colloids are relatively dispersed in water and their stability depends on mark affinity for water rather than upon the negative charge that the process.
Example : soaps, soluble starch and protein, synthetic detergent.
2. Hydrophilic :
This colloids have a no affinity for water and remain 'stable' due to the 'electric charge' they process.
Example : Metal oxides colloids, clay and sulphides.
Electrostatic replusion between the charged collides particles produce a stable solution i.e. colloidal dispersion.
6. Draw a chart of major classification of properties of colloidal dispersion.
7. Write a short note on electric double layer along with figure.
An electric double layer is phenomenal that play a fundamental role in the mechanism of electrostatic stabilization of colloidal particles.
Particles gain negative electric charge where negatively charged ions on the dispersion medium are absorb on the surface of the colloidal particles.
A negatively charged particle attracts the positive counter ions surrounding the particles.
As so in figure electric double layer is the layer surrounding a particles of disperse phase including the ions types of on the particle surface.
The electric double layer is electrically neutral.
An electrically double layer consist 3 parts :
- Surface charge
- Stern layer
- Diffuse layer
Surface charge :
Charge iron absorb on the particle surface.
Stern layer :
Counter ions Attracted to the particle surface and closely attached to it by electrostatic force.
Diffuse layer :
Diffuse contain free ions with higher concentration of the counters ions.
The ions of the diffuse layer are affected by electrostatic force of the charge particle.
The electrical potential within the electro double layer has a maximum value on the particle surface.
The potential drop with increase of distance from surface and reaches 0 at the boundary of the electric double layer.
When colladal particles move in dispersion medium a liar of surrounding liquid remain attached the particle.
The boundary of the electric double layer is called shear plane (slipping Plane)
The value of electric potential at the stripping plane is called zeta potential which is very important parameter in theory of introduction of poladal particles.
Zeta Potential is calculate as,
mv, Z= V°Kzu/EEo
Where
- V° = Electrophoretic mobility
- VE = Electrophoretic velocity of migrating particles. ( Micrometer per second)
- E = electric field at particle , V/cm
- e= permitivity relative to vaccum = 78.54 for water.
- E0 = permitivity in vaccum = 8.854188 * 10^-12 N/V^2
- Kz = shape constant of 4Ï€ or 6Ï€.
8. Discuss the particle stability and DLVO theory with neat sketch.
PARTICLE STABILITY :
Particles in natural water remains table when there is balance between the electrostatic force of the charged particle and attractive force no as wanderwaals force.
Because of the particles have net negative charge the principal mechanism controlling stability is electrostatic repulsion.
Wonderwal sports arise from magnetic and Electronic resonance went to particles approach one other.
Because of double layer extends further into solution than the wanderwaals force and energy barrier is from that prevents particles from aggregating.
The DLVO Theory:
The theory is known as DLVO Theory after the individual who developed it ( Derjaguin & Landau, verwey & Overbeek ).
It is the explanation of stability of colloidal suspension.
It described the balance between two forces electrostatic replusion force and wanderwaals attraction force.
Replusion force becomes significant when two coloured approach each other and there electric double layer being to interfere.
Some energy is required to overcome the replusion force.
So that the reviews and cow is Di figure indicates the energy that much overcome in particles are force together.
It has Max value which is related to surface potential when they almost touch and decrease to zero outside the double layer.
Van der Waals attraction is result of forces between molecules and each colloidal particle.
One molecule of the colloidal has a Van der Waals attraction to each molecule in other collage which means attraction force.
The cow which represented and attractive energy indicates variation in vendor valves force between colloidal particles.
The DLVO theory explain the tendency of colloidals to agglomerate to separate by combining two curves of repulsion and attraction.
The point of maximum replus energy is called Energy barrier in the colloidal system.
Population are addicted in control means to aggregate the particles at secondary minimum point.
The primary minimum indicates the corals are in the particle at secondary minimum point.
9. Briefly explain the jar test in detail with diagram.
The jar test is common laboratory procedure used to determine optimum operating condition for water and wastewater treatment.
This method allow existing in pH variation coagulation or polymer dose, alternating mixing speed, testing of different covalent or types on a small scale in order to predict functioning of a large scale treatment operation.
Jar test Apparatus :
The jar testing Apparatus consists of 6 pendle which mix the content of 6 1 l container.
One container act as a control while the operating condition can be varied among ki remaining 5 container.
RPM gauge at the top centre of device allow for the uniform control of the mixing speed in all the containers.
Jar test procedure :
Filled the jar testing Apparatus containers with sample water one container will be used as control and other containers can be adjust depending on what condition are being tested.
At cogulant to each container and stir approximately 100 RPM for 1 minute. The rabbit mixing helps to disperse the cogulant throughout each container.
Reduce string speed to 25 to 35 RPM and continue mixing for 52 20 minutes the slower mixing speed helps promote flogs for motion by enhancing particles collision which lead to large flocs.
Residual turbidity vs cogulant dose is done is then plotted and optimal condition can be determined.
The values that are obtained through experiment are correlated and adjust in order to account for the actual treatment system.
10. Enlist and explain mechanism of coagulation along with diagram.
Coagulation Theory :
- Adsorption & charge neutralization.
- Sweep coagulation
- Inter particle bridging
- Ionic layer compression
1. Adsorption and charge neutralization
The nature rather than the quantity of the ions are of prime importance in the theory of adsorption and charge neutralization.
The Aluminium sulphate alum is used as in cogulant.
The ionization of alum in water produced the sulphate ions and Aluminium cations the sulphate and may remind in the form or combine with other cations.
However the Al3+ react immediately with water to form a variety of Aqua Metallic ions and hydrogen.
The Aqua Metallic and does form become part of iron cloud surrounding the colloids and because they have a greater affinity for surface are absorb on to the surface of the colloid where they neutralize the surface charge.
Once the surface charge has been neutralized the ionic cloud disappear and also Electro potential disappear so that contact occurs freely.
Overdozing with covalents can be result in resta stabilizing the suspension.
This phenomena is known as adsorption and charge neutralization of colloidal Suspension and colloidal particles.
2. Sweep coagulation :
Certain metal solids are added to water wastewater in sufficient or higher amount Rapid formation of flocs will occur.
Colloidals mein as a tiny particles for this flocks or may become enmeshed it's sticky surface and form large particle.
Remove of colloids in this manner is a frequently refer to as swift floc cogulation mechanism.
At low colloidals particles excess amount of coagulant is required to produce a large amount of logs that will enmeshed the relatively few colladal particles as it settle.
3. Inter Particle bridging :
Large molecules maybe from when aluminium ferric salt dissociates in water.
Synthetic polymer also may be used instant of or to metallic salt.
This polymer maybe linear or branch and are high surface reactive.
Several collars may become attached to one polymer and several of the polymer colloidal groups may become enmeshed, resulting in stable mass.
Metallic polymer form by addition of aluminium ferric salt are positively charged while synthetic polymer carry the positive or negative or maybe neutral charge.
4. Ionic layer compression :
The quantity of ions in the water surrounding a colloid has an effect on the function of electrostatic potential.
So in figure a hi ionic concentration comparison the diffuse layer and predominantly compost counter ions turnover the surface of colloid.
If this layer is sufficient compress than Van der Waals force will be predominantly across the College particles and that attraction particle across and no Energy barrier will exist.
Coagulant such as Al and ferric salt used in water treatment plant to compress the diffuse layer.
11. Enlist the different types of coagulants used in coagulation process with formula.
There are two types of coagulants:
- Primary coagulants
- Coagulant aids.
The primary coagulants neutralize the electric charge of the particle in the water which cause the particle clump together.
Coagulants aids at density to slow settling flogs and add toughness to the flocked so that they will not break the mixing and settling process.
Coagulants chemicals are either metallic salts or polymer.
Polymer are man made organic compounds made up long Chain of smaller particles.
Polymer can be positively charged negatively charge or neutrally charged.
Coagulants :
- Hydrated copperas
- Chlorinated copperas
- Sodium aluminate
- Lime
- Alum
Hydrated copperas :
- Can't remove colour
- pH > 8.5 work's in
- Dosage: 14 mg/l
- Cheap as compare to alum
- Lime added for efficiency
Chlorinated copperas :
- Can remove colour
- pH range is large ( work in large range )
Sodium aluminate : (Na2Al2O4)
- Remove temporary and permanent hardness.
- No need of alkalineity.
- Works pH 6.6 to 8.5 drinking water.
- Used in boiler.
Lime :
Used in amount of phosphate and ammonia is high in water.
Alum :
Chemical formula [ Al2(so4 )3 • 18 H2O ]
- Alarm required alkalinity.
- Does not work in acidic pH.
- Addition of lime for providing alkalinity.
12. Give the difference between coagulation and Flocculation
| Coagulation | Flocculation |
| Coagulation is the chemical process unit Process. | Flocculation is a physical process unit operation. |
| Coagulation does not involved physical mixing process. | Flocculation involves physical mixing process. |
| Coagulation such as inorganic salts of Al and Fe that neutralize the suspended particles are added during coagulation. | Flocculants such as an organic polymer that involves in bridging and straightening the floats is added and it also increase the rate of settling. |
| It is an important step in water treatment. | Flocculation is also an important process in wastewater treatment. |
| It involve in the addition of the coagulation to enhance the clothing of suspended particles in water. | It involves in formation of visible flocks by mechanical or physical mixing. |
| Incogulation colloidal form the micro flocs. | Inflocution gentle mixing of colladell switch are this stabilized and promote to agglomerate. |
| Coagulation is used in water treatment plant and industrial scale and laboratory scale applications. Coagulation is the addition and Rapid mixing of coagulant. |
Flocculation is used in water treatment plant if necessary. Flocculation is consist of gentle mixing and form Rapid settling flocs. |
14. Define Flocculation with Description.
Floccasion can be define as the slow mixing operation of disabilize collides to establish the intimate contact between the disabilized colloids so as the promote their agglomeration.
The purpose of of wastewater flocculation is form of aggregate or flocs from finely divided particles and from chemical distabized particles.
Flocculation is the transport step that being about the collisions between the stabilized particles needed to form larger particle that can be remove readily by settling or filtration.
Although not Used routinely, location of wastewater by mechanical or air aggregation maybe consider for,
- Increasing removal of suspended solids and BOD primary setting facilites
- Conditioning waste water containing certain industries waste.
- Improving performance of secondary settling Tank flowing in activated sludge process.
- As a pre treatment step for the filtration of secondary effluent.
Flocculation is the transport step that being about the collisions between the stabilized particles needed to form larger particle that can be remove readily by settling or filtration.
Flocculation, generally increase the overall total solids removal.
Flocculation increase the settling rate as indicate by the increasing value.
0 is the angle with horizontal of flow average particle settling velocity.
Since Cello tanks appear to include more floquation they are preferred to Deep tanks to prevent scouring of the settle particles.
15. Enlist and explain the types of flocculation along with the figure.
Types of flocculation :
- Micro Flocculation ( Peri kinetic Flocculation )
- Macro flocculation ( Ortho kinetic Flocculation)
Micro Flocculation :
Micro Flocculation also known as Peri Kinetic Flocculation.
Microsofacation is the term used for the agglomeration of the particles brought about by the random thermal motion of fluid molecules.
The random thermal motion of fluid molecules is also known as Brown and motion.
Micro flocculation is significant for particles that are in the size range of 0.0001 to about 1 micrometer.
Macro Flocculation :
Micro flocculation is the also know as Ortho Kinetic flocculation.
Macro Flocculation is the term used to refer to the aggregation of particles greater than 1 or 2 micrometer.
Macro flocculation can be brought by ,
Particles can be brought together by inducing velocity gradient in fluid containing the particles be flocculated.
In above figure faster moving particles will be overtake slower moving particles in a velocity field.
If the particles that colloidals sink together a large particle will be form that will be easier to remove by gravity separation.
In micro flocculation by different settling large particles overtake smaller particles during gravity settling.
When the two particles collars are sink together large particle is form that settle at the rate is greater than that of the large particle before the two particles collided.
16. Enlist different types of floc calculator with description.
1. Paddle flocculator :
(A) Horizontal sharp pendal flocculator :
Horizontal flocculator are generally rectangular in shape.
(B) verticals are flocculator :
Vertical circulator are generally square in shape
The types of flocculator usually required less maintenance since the eliminate submerged bearing and packaging.
2. HYDRAULIC FLOCCULATOR:
In hydraulic circulator the flow of water is so excellence by small hydraulic structure that a straight action result.
(A) Baffled Channel Flocculator :
The types of flocculator is Well suited for very small treatment plant.
The efficiency however is highly depend on the depth of water in the baffled channel.
Flocculator with vertical flow through chamber are mostly used for medium and large size water treatment plant.
(B) Alabama Type Flocculator :
Alabama Type Flocculator hydraulic flocculators separate chamber placed in series through which the water in in two direction.
The water flows from one chember to the next entering is through outlets turn upward.
For effective flocculation in each chamber the outlet should be placed at the depth of about 2.5 0 m below the water level.
(C) Peddle Bed Flocculators :
Hindi steps of flocculators flow is direct it through gravel media in a vertical time provide a large number of words opening in which flocculation will occur.
Large gravel media are used to provide large word openings for mixing and prevent clogging.
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