1. Physical Treatment Processes
of Industrial Waste

2. Introduction of wastewater treatment methods and steps
Bar Rack/
Comminutor
Grit Chamber
Equalization Basin
Primary Settling
Biological Treatment
Secondary Settling
Advance
Wastewater Treatment
Refer Table 5-1: Typical physical unit operations
PRETREATMENT PROCESS
PRIMARY PROCESS
SECONDARY PROCESS
TERTIARY PROCESS
e.g: Depth Filter, Membrane filter, adsorption, Ion exchange, gas stripping etc

3. PRETREATMENT PROCESS -bar screen/ bar rack-
Retain solid found in influent WW to the treatment plant
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Principle role
Coarse screen Remove coarse materials (e.g. sticks, rags, etc) from the flow stream that could :
damage subsequent process equipment
Screening
Reduce overall treatment process reliability & effectiveness
Contaminate waterway
Fine screen (used in place of/following coarse screen) Where greater removals of solids are required to remove coarse materials (e.g. sticks, rags , etc) from the flow stream that could
Protect process equipment
Eliminate materials that may inhibit the beneficial reuse of biosolid

4. PRETREATMENT PROCESS -bar screen/ bar rack-
May consists of parallel bars, rods or wires (coarse screen)
perforated plate (fine screen)
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The flow passes through the screen and the large solids are trapped on the bars for removal.
Bar Screen/ Bar Rack
The bar screen may be coarse (6 – 150 mm/ 0.25 – 6 inch openings) or fine (< 6 mm/0.25 inch openings).
The bar screen may be manually cleaned or mechanically cleaned (performed frequently enough to prevent solids buildup and reduce flow into the plant)

5. PRETREATMENT PROCESS
-bar screen/ bar rack-

6. PRETREATMENT PROCESS
-bar screen/ bar rack-

7. Grit chamber are provided to
PRETREATMENT PROCESS
-GRIT chamber-
Remove grit (sand, egg shells or other heavy solid materials) that tends to settle in corners, bends, reducing flow capacity and ultimately clogging pipes and channels.
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Grit chamber are provided to
Protect moving mechanical equipment from abrasion
Grit Chamber
Reduce formation of heavy deposits in pipelines, channels & conduits
Reduce the frequency of digester cleaning caused by exessive accumulation of grit
Grit removal processes use gravity/velocity, aeration or centrifugal force to separate the solids from the wastewater.
The most common method of grit disposal is transport to a landfill. In some large plants, grit is incinerated with solids

8. PRETREATMENT PROCESS -GRIT chamber-
Once screened, the wastewater passes into two aerated grit chambers. Low-pressure air entering the grit chamber creates a rolling motion that causes grit and dense solids to settle to the tank bottom.

9. -Comminutors & Macerators-
PRETREATMENT PROCESS
-Comminutors & Macerators- -
used to intercept coarse solid & shred them in the screen channel
The solids are cut up into a smaller, more uniform size of for return to the flow stream for subsequent removal.
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The use of comminutor and macerator is adventageous in a pumping station to:
Comminutors & Macerators
Protect pump againts clogging by rags & large objects
Eliminate the need to handle & dispose of screenings
However, shredded solid (plastic bags, rags) tends to form ropelike strands & can clog pump impellers, sludge pipelines & heat exchangers).
Design consideration:
may be preceded by grit chambers to prolong life
Constructed with bypass arrangement

10. -Comminutors & Macerators-
PRETREATMENT PROCESS
-Comminutors & Macerators- -
Macerators

11. Bar Screen / communitor
PRETREATMENT PROCESS
-FLOW EQUALIZATION- -
To minimize fluctuations in WW characteristics in order to provide optimum conditions for subsequence process
To provide adequate dampening of organic fluctuations in order to prevent shock loading to biological system
Provide adequate pH control
Provide cont. feed to biological system
Provide capacity for controlled discharge
To prevent high conc. of toxic materials from entering the biological treatment plants. Q Q t t
Effluent for further treatment
Bar Screen / communitor
Grit Removal
Equalization Basin
Primary Treatment

12. PRETREATMENT PROCESS -FLOW EQUALIZATION- - In-line arrangement:
all of the flow passes through the equalization basin
Can be used to achieve considerable amount of constituent conc. and flowrate damping.
Off-line arrangement:
Only flow above predetermined flow limit is diverted to equalization basin
Used to capture ‘first flush’ from combined collection system

13. Volume requirements for equalization tank
Obtain from ‘Cumulative volume vs Time of day’ graph
(refer textbook page 336)
Volume = vertical distance from point of tangency to the straight line representing the average flowrate

14. PRIMARY PROCESS Objectives:-
( primary & secondary process handle MOST of the NON-TOXIC wastewater)
Objectives:
Prepare WW for biological treatment (stabilize organic)
Remove + 60% SS and 35% BOD5 in sewage
Important because the reduction of the suspended solids and BOD5
1)lowers the O2 demand,
2)decreases the rate of energy consumption and
3)Reduces operational problem with downstream biological treatment
4)remove scum (grease, oil, plastics, and other floatable materials)
and inert particulate matter which are not removed in grit chamber
Principle form of primary treatment: SEDIMENTATION
Note: sedimentation tank = sedimentation basin, clarifier,
settling basin, settling tank

15. secondary PROCESS Objectives: Devices/structures: -
Speed up natural process of breaking down biodegradable organics
Remove up to 85 % SS and BOD5
Devices/structures:
Activated sludge, extended aeration, rotating biological contacting (RBC), trickling filter, aerated lagoons, sequencing batch reactor etc
Biological degradation of soluble organics.
Mostly aerobically in an open aerated lagoon
Speed up natural processes of breaking down biodegradable organics
Cannot remove N, P, heavy metals, pathogens, bacteria and viruses.
After treatment, microorganism and other carried over solids are allowed to settle.
A fraction of sludge is recycle
Excess sludge along with sediment solids has to be disposed off.

16. Tertiary/advanced PROCESS-
Objectives:
Nutrients removal, chlorination and dechlorination
Process added after biological treatment in order to remove specific group/ types of residual
Can remove + 95% BOD5, P, SS, bacteria and N
Devices/structures:
Filtration –removes SS
Granular Activated Carbon – removes organics
Chemical oxidation – removes oxidizable organics
Expensive to process LARGE VOLUME of WW

17. Selection of treatment process
Depends on the degree of treatment required to bring the quality of raw wastewater to a permissible level of treated wastewater
(eg. Effluent from the treatment plant)
of organic matter or by substance added to the WW.
Selection of treatment process
This ensures that the final effluent is either safe for disposal or acceptable for specific reuse or recycling.
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Other significant factor that will influence the selection of a treatment system
Availability of funds and land at the treatment site
The topography of land at the treatment site
Non-availability of suitable mechanical equipment and skilled personnel for running and maintaining the plant.
Ref: (Karia and Christian,2006)

18. Selection of treatment process
The points to keep in mind while selecting the treatment process
of organic matter or by substance added to the WW.
Reduction of inorganic material component of wastewater is much easier and cheaper than removal of organics contents of wastewater
Removal of suspended solids from wastewater requires lesser time and efforts than of colloidal and dissolved solids
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In many countries, the Environmental Protection Act requires at least the secondary treatment system for all publicly owned treatment works such as municipal wastewater treatment plant, so that effluent requirements of 30mg/L for BOD and 100mg/L of SS are achieved.
Ref: (Karia and Christian,2006)

19. Basic design consideration Essential consideration
criteria
Strength & characteristics of WW
Essential consideration
Flow rate and their fluctuations
Mass loading

20. Basic design consideration -strength & characteristics of ww-
The strength of wastewater is normally expressed in terms of pollution load, which is determined from the concentrations of significant physical, chemical and biological content of wastewater.
of organic matter or by substance added to the WW.
Strength & characteristics of WW
Characteristics of WW depend on the quality of water used by the community, culture of population, type of industries present & treatment given by industries to their WW.
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The strength of WW measured as mass per unit volume of WW
(Units: mg/L )
If characteristics of raw WW show the concentration of specific constituents like BOD & SS within the standard permissible limits, there is no need to treat the WW.

21. Basic design consideration -FLOW RATE AND THEIR FLUCTUATIONS-
Is the quantity or volume of wastewater in terms of rates
of organic matter or by substance added to the WW.
FLOW RATE &
THEIR
FLUCTUATIONS
It is the total quantity of wastewater generated daily and to be treated every day.
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The volume of WW depend on the water consumption by the population for its various activities
The flow rate units:m3/day or m3/s or MLD (million Litres per Day)
Normally a treatment plant is designed on the daily average flow basis which is known as plant capacity.
Example: 1 MLD (Million Litres per Day) plant means = the plant designed for 1 – ML daily average flow of WW

22. Basic design consideration
-mass loading- -
The mass pollution load is defined as flow rate & strength of WW & is expressed as load per unit time
of organic matter or by substance added to the WW.
MASS LOADING
Example:
WW having 1000 m3/d flow & 200 mg/L (g/m3) BOD has the mass pollution load of BOD equal to 200 kg/d
(1000 m3/d X 200 g/m3 X 10-3 g/kg)
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In the case of treatment plant that receives flow of combined sewerage system, the seasonal variation in the rainy season will lower down the BOD & SS concentration due to the dilution because of the added amount of storm water. On the other hand, a higher concentration of BOD & SS may be observed during the dry weather period.
Therefore, in almost all cases, a flow-weighted average should be used because it is more accurate method of analysis

23. Basic design consideration Flow-weighted average
-mass loading- -
Flow-weighted average
Where ,
XW = flow –weighted average concentration on the constituent
Xi = average concentration of the constituent during the “i”
time period
Qi = average flow rate during “i” time period

24. Basic design consideration
-design criteria- -
of organic matter or by substance added to the WW.
The data determined through the research and laboratory scale model studies as well as those obtained from the operational experience of field and pilot scale WW treatment facility. The values of such guideline parameters are called design criteria and available in the literature.
The most frequently assumed criteria for designing a conventional WW treatment plant (WWTP):
Detention period or time
Flow through velocity
Settling velocity
Surface loading over flow rate
Weir loading rate
Organic loading VSS loading)
Food to Microorganism ratio, F/M
Mean cell Residence Time
Hydraulic Loading
Volumetric Loading
Basin geometry (L:B:D) length, breadth and depth ratio.

25. Physical treatments

26. Sedimentation process
Process of heavier solid particles in suspension, settle to the body of tank by gravity
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Removal of SS from WW
Depends on
Velocity of flow
Size and shape of particles
Sedimentation
Viscosity of water
Types of particles
Discrete /non-flocculant particles
Size & velocity constant during the settling
Flocculant particles
Size & velocity fluctuates during the settling
Common operation & found almost in WWT plant
LESS COSTLY than many other treatment processes

27. Particles settling theory
The settling of discrete particles can be analysed by means of the classic laws of sedimentation by Newton & Stokes.
Gravitational force,
Frictional drag force,
Refer page 363 in text book

28. Design of sedimentation PROCESS
In the design of sedimentation basin, the settling velocities of the particles MUST be KNOWN.
The knowledge of settling velocity of particle is used to determining the depth of a treatment unit to separate the suspended solids (particulate matter) by gravity settling and for checking the adequacy of length or diameter of a tank to remove particles before the effluent flows out of the basin.
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sedimentation
Where,
vc = particle settling velocity
Q = flowrate of WW
A = surface of sedimentation tank

29. sedimentation PROCESS
Idealized discrete particles settling in 3 different type of basins
Inlet zone
Outlet zone
Sludge zone
RECTANGULAR BASIN
CIRCULAR BASIN
UPFLOW BASIN
Settling
zone

30. Types of basin
Circular Basin
Rectangular Basin

31. Classification of particles settling
Type 1
Discrete
Type 3
Zone
Type 2
Flocculant

32. Type 1 : discrete
Particles DOES NOT change in size, shape & density during the settling process
Particles settle discretely at a constant velocity
Settle as individual particles & do not flocculate
Occurs during:
Presedimentation for sand removal
Grit Chamber

33. Type 2 : flocculant Flocculate during sedimentation
Particles size constantly changing
Settling velocity is changing increase with depth & extent of flocculation
Occurs during:
Alum or iron coagulation
Primary sedimentation basins

34. Type 3: zone
The floc particles adhere together & the mass settle as a blanket (layer)
Distinct clear zone & sludge zone present
Concentration HIGH (greater than 500 mg/L)
Occurs during:
Activated sludge sedimentation
Sludge thickeners
Solid settle
water

35. Type 3: zone High of sludge liq interface B B Transition zone B A A A
Compression
Zone C C
Settling Zone D
Dense solid D D
Settling properties of flocculated sludge
Initially, all the sludge is at uniform concentration A
A settling proceeds, the collapsed solid on the bottom of the settling unit (D) build up at constant rate.
C is zone of transition through which the settling velocity decrease as a result of high conc. of solid.
Through the transition zone C, the settling velocity will decrease due to the increasing density & viscosity of the suspension surrounding the particles.
When the rising layer of settle solid reaches the interface, a compression zone occur.

36. Design criteria
The following design criteria are generally assumed to design a Primary Settling Tank / Sedimentation
A) GENERAL
No. of Tanks
2 or more (usually)
Types of tanks
Circular or rectangular
Removal of Sludge and Scum
Mechanical (usually)
Tank bottom slope
mm/m
Speed of sludge scraper
0.02 – 0.05 rpm
Refer Table in textbook

37. Design criteria B) DIMENSIONS C) TECHNICAL Range Typical
Rectangular Tank
Length (m)
15-100 30
Width (m)
3-30 10
Depth
2.5-5 4
Circular Tank
Diameter (m)
3-60
Depth (m)
3-5
Bottom slope, (mm/mm)
0.02 – 0.05
0.03
C) TECHNICAL
Range
Typical
Detention Time, t (hr)
1.0 – 4.0
2.0
Flow Through velocity (m/min)
0.6 – 3.6
0.9
SLR (m3/m2/hr) at average flow
1.2 – 2.5
1.6
Peak Hourly Flow
2.0 – 5.0
4.2
WLR (m3/m/d)
250

38. SEDIMENTATION /clarification PROCESS
Primarily used in WWT to separate solids from liquids in effluent streams.
Types
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Clarifiers
Criteria for sizing clarifier (settling tank)
Tank depth at the side wall
Overflow rate (surface loading rate)
Detention time
Scour velocity

39. Criteria for sizing clarifier (settling tank)
-overflow rate (surface settling rate)-
Definition: The average daily flow rate divided by the surface area of the tank.
Clarifiers
Average daily flowrate
(m3/day)
overflow
surface settling rate
(m3/m2d)
Total surface area of the tank
(m2)

40. Criteria for sizing clarifier (settling tank) Average daily flowrate
-depth of tank-
The water depth at the side wall measuring from the tank bottom to the top of the overflow weir.
Depth of tank
Effluent weir
Exclude the additional depth resulting from slightly sloping bottom that is provided in both circular and rectangular clarifiers.
Influent
Influent H
Occupied
with sludge
Effluent weir loading (typical= 250 m3/m.d) is equal to quantity of WW flowing divided by the total weir length, Lw
Average daily flowrate
(m3/day)
Total weir length
(m)

41. Criteria for sizing clarifier (settling tank) Average daily flowrate
-detention time-
length of time a particle or a unit volume of WW remains in a reactor
Detention time
Tank volume (m3)
Detention time =
(day)
Average daily flowrate
(m3/day)

42. Criteria for sizing clarifier (settling tank)
-Scour velocity
horizontal velocity through the tank to avoid resuspension of settled particles
Scour Velocity
Where:
VH = horizontal velocity that will just produce scour (m/s)
k = cohesion constant that depends on type of material being scoured (unitless)
s=specific gravity of particles
g=acceleration due to gravity (9.81 m/s2)
d=diameter of particles
f=Darcy-Weisbach friction factor (unitless)

43. of organic matter or by substance added to the WW.
flotation
Used for the removal of lighter SS, oil & grease.
of organic matter or by substance added to the WW.
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Also used to concentrate biological sludge and to separate both the fine solid and a liquid particles from the liquid phase
Flotation
Introducing fine gas (air) bubbles into the liquid phase.
Bubbles will attach to the particulate matter , thus increase the buoyant force, cause the particle to rise to the WW surface .
Floated particles are collected by skimming operation .
Thus, the operation is just the opposite of that of gravity sedimentation where particles get removed at the bottom of the tank.
Degree of particle removal can be enhanced by addition of chemical additives
Advantage: Removal of smaller particles in a shorter time and more complete.

44. Example of Flotation System

45. flotation Frequently used in industrial WW treatment
Flotation system
Systems Based on Formation of Air Bubbles
Dispersed-Air flotation
Vacuum flotation
Dissolved-Air flotation
Systems based on recirculation of effluent
Effluent is recirculation
Effluent is not recycled
Frequently used in industrial WW treatment
Frequently used in Municipal WW treatment

46. flotation
Systems Based on
Formation of Air Bubbles
Dispersed-Air flotation
Vacuum flotation
Dissolved-air flotation
WW is first saturated with air either directly in the aeration tank or by introducing air at the pump side (at Patm)
Then partial vacuum is applied. This results in generation of small air bubbles which attached themselves to the particles and make them rise,
forming a scum blanket.
Typically a cylindrical tank maintain under vacuum is applied and continuously fed with WW
air bubbles are formed by introducing the air in the form of gas phase directly into the liquid phase either by a revolving impeller or through air diffusers at the atm pressure.
Flotation is achieved first by dissolving the air in the WW or in a portion of treated effluent (liquid) under high pressure in the pressurizing or retention tank and then reducing the pressure of the WW through a pressure-reducing valve to atmospheric level during feeding it to the flotation tank to form the rising air bubbles.

47. Systems based on recirculation of effluent
flotation
Systems based on recirculation of effluent
In large treatment plants, normally 15-20% of the effluent is recycled
Small treatment plants operate without recycling the effluent.
Example: Dissolved-air Flotation (DAF)
Effluent is recirculated
Effluent is not recycled
A predetermine fraction of effluent from the flotation unit is taken to the pressurized tank where it is pressurized, and the air is dissolved below the saturation level.
The flow is then mixed with the influent entering the flotation unit through a pressure-reducing valve so that air bubbles come out from the recycled flow and get attached with the particles of incoming raw wastewater that are to be removed by flotation.
Wastewater influent is first retained for some time in the pressure tank where pressure of wastewater is increased to as high as kPa and air is dissolved in it.
Then the flow is fed to the flotation unit through a pipeline having a pressure-reducing valve.
As the pressure is released from wastewater, the dissolved air comes out of the solution as fine bubbles which are used for particle separation by flotation.

48. Dispersed-Air Flotation

49. Dissolved-Air Flotation (no recycle)
Please refer diagram in your textbook

50. Dissolved-Air Flotation (with recycle)
Please refer diagram in your textbook

51. flotation Design consideration
Quantity of air required for formation of air bubbles
Concentration of particles to be removed
Design consideration
Particle rise velocity or buoyant force
Solids loading rate
Air/solid ratio

52. For system with recycle For system without recycle
flotation
Dissolved air flotation units are usually designed on the basis of the air to solid ratio, A/S, using the following equations:
For system with recycle
For system without recycle
Where,
A = volume of air (ml)
S = mass of solids (mg)
1.3 = weight of 1ml of air (mg)
sa = solubility of air in (ml/L)
(temp depended funct)
Refer page
f = fraction of air dissolved at pressure P (atm)
P = operating pressure (atm)
Sa = influent suspended solids or sludge solids
(mg/L)
R = pressurized recycled flow (m3/d)
Q = mixed liquor flow (m3/d)

53. Typical Design Criteria
flotation
Typical Design Criteria
Hydraulic retention time, HRT
20-30min
(for efficient primary clarification)
Rising velocity of air-solid mix
Rising rate or surface loading rate
0.06 – 1.63 m3/min-m2
when no flocculants
are used
2.56 – 12.7 cm/min
when flocculants
20 – 60 cm/min

54. filtration
Employ for the removal of SS, following coagulation in physical-chemical treatment or as tertiary treatment following the biological WW treatment process
SS are removed using granular filter medium (depth filter) principally by straining mechanism, consists of surface removal and depth removal
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Filtration
The efficiency of filtration process is depends on
character of media
character of SS
temperature
flow rate
bed depth
time (throughput volume)
Primary design/operating parameters
Quality (SS conc.) of effluent
Headloss through the filter & accesories
Note: Headloss is the reduction of total head or pressure drop of a liquid as it moves through a system.

55. filtration the total head loss reaches maximum point (high enough)
The filter run terminates when:
the total head loss reaches maximum point (high enough)
excess SS or turbidity appears in the effluent.
Filtration
Filtration rate will effect :
The build up of head loss
the effluent quality attainable
The head loss through the filter can be described by D’Archy’s Law
Where,
V = superficial approach velocity (ft/min).
Kp = coefficient of permeability (ft/min). This will change with time
hf = frictional head loss (ft)
L = depth of filter (ft).

56. filtration Material Shape Relative Density Porosity (%)
Effective Size (mm)
Silica sand
Rounded
2.65 42
Angular 53
Ottawa sand
Spherical 40
Silica gravel
anthracite 55
garnet
angular 46
The selection of medium filters is depends on the type of filter and operation.
See example in Table 11-6, 11-8, 11-9

57. MEMBRANE PROCESS concentration gradient pressure electrical potential
Use to separate dissolved and colloidal constituents from WW
Components in water are driven through a membrane under the driving force of:
concentration gradient
pressure
Membrane Process
electrical potential
The size of the opening in the membrane are a major determinant of species that can pass because the opening present a physical barrier to any substances that are larger than openings.
A semi permeable membrane is SELECTIVE to the species it passes.
Semi permeable membrane
Permeate
Retentate
The liquid passing through the membrane
The fraction not passing through the membrane.

58. MEMBRANE PROCESS size of separation separation mechanism
Membrane process classification
(Refer Table in textbook)
separation mechanism
membrane’s material
Thickness= μm,supported by porous substrate
Flat sheets,fine hollow fiber,or tubular form
For WW treatment,typically organic membrane.
E.g:polypropylene, cellulose acetate, aromatic polyamides and TFC
MF, UF = straining
NF = straining & diffusion
RO= diffusion
size of separation
Macropores= >50 nm
Mesopores=2-50 nm
Micropores= <2 nm
For RO = very fine pores, known as dense
nature of driving force
Hyrostatic pressure difference (MF, UF, NF, RO)
concentration difference (dialysis)

59. Membrane process

60. Membrane process Membrane Operation in MF and UF:
Cross flow
2 types: a) without reservoir
b) with reservoir
Feed water is pumped with cross flow tangential to the membrane.
Water that does not pass through the membrane is recirculated after blending with additional feed water
Cross flow with resorvoir-water that does not pass through membrane is recirculated to storage tank.
Direct feed or dead-end
No cross flow
All water applied to membrane passes through the membrane
Refer page 1112 , Figure

61. Membrane process
OSMOTIC PRESSURE – balancing pressure difference between pressure and chemical potential , occur when two solutions having different solute conc. are separated by semipermeable membrane.
REVERSE OSMOSIS (RO) –if a pressure gradient opposite in direction and greater than osmotic pressure, flow from the more concentrated to the less concentrated region will occur

62. Membrane process The flux of water through the membrane (Eq 11-43);
Where,
Fw = flux of water (mass/area.time)
A= area of the membrane
kw = water mass transfer coefficient
∆Pa = average imposed pressure gradient
∆π=osmotic pressure gradient
Qp = permeate stream flow

63. MEMBRANE PROCESS
The flux of solute depends on the concentration gradient and resistance parameter.
Where,
Fi= flux of solute, kg/m2s
ki = solute mass transfer coefficient, m/s
ΔCi = solute concentration gradient, kg/m3
Cp = conc of solute in the permeate,kg/m3
Qp = permeate stream flow, m3/s
A = membrane area, m2
Membrane Process
Measurement of the ability of membrane to reject the passage of a species i,
Rate of Rejection =
Where,
Ri = rejection rate
Cif = conc of species i in the feed
Cp = conc of species i in permeate

64. MEMBRANE PROCESS
Fouling of a membrane increase resistance to flow and reduces the flux of water through a membrane
Backwashing or chemical treatment may be applied to remove foulants.
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Membrane Process
Irreversible fouling of membranes is the most serious problems.
Oxidizing agents such as chlorine or ozone attack membranes and change their structures.

65. THANK YOU