Removal of colour and turbidity (coagulation, flocculation filtration)

1. REMOVAL OF COLOUR AND TURBIDITY
(COAGULATION, FLOCCULATION FILTRATION)
Granch Berhe
CHAPTER TWOCHAPTER TWO

2. INTRODUCTION

5. Health
Taste and odour
Aesthetics (color and turbidity)
The need to clarify water

6. Turbidity
• Turbidity – negative charged particles (sand, silt, clay,
bacteria, viruses) in the initial source water that need to be
removed to improve treatment.
1. Suspended Solids
2. Colloidal Solids (~0.1 to 1 µm)
3. Dissolved Solids (<0.02 µm)
312

7. Colloid Stability
------ ------
Repulsion
Colloid - A Colloid - B
 Colloids have a net negative surface charge
 Electrostatic force prevents them from agglomeration
 Brownian motion keeps the colloids in suspension
H2O
Colloid
 Colloids – so small: gravity settling not possible

8. REMOVAL OF COLOUR AND TURBIDITY
(COAGULATION/FLOCCULATION PROCESS)

9. •Common treatment steps used to remove turbidity from the initial source
water.
1. Coagulation
2. Flocculation
3. Sedimentation
4. Filtration
Rapid Mixing
Slow Mixing
Settling
Cleaning
The primary purpose of the coagulation/flocculation process is the
removal of turbidity from the water.
The process removes many bacteria which are suspended in the
water and can be used to remove color from the water.

10. What is Coagulation?
 Coagulation is the destabilization of colloids by addition of
chemicals that neutralize the negative charges at rapid mixing
 The chemicals are known as coagulants, usually higher valence
cationic salts (Al3+
, Fe3+
, Na+, Mg2+, etc.)
. 1. Alum- aluminum sulfate
2. Ferric chloride or ferrous sulfate
3. Polymers
 With destabilization, colloids aggregate in size and start to settle

11. Mixing Levels:
Mixing intensity and residence time determine
whether the stated goals will be met.
To determine mixing intensity define as the
average shear intensity (mean velocity gradient) in
the rapid-mix tank.
The Camp-Stein equation is often used to compute
this , however it is an equation which is based on
laminar flow -- a case seldom found in rapid-mix
or flocculation basins so it’s an “average”
approximation.
G
G

12. The Camp-Stein equation is :
0.5
P
G
V
 
= 
×µ 
P = power dissipation (mixer power
transferred to bulk fluid)
V = volume of reactor
u = dynamic viscosity
Large G and small T gives small but dense floc
Small G and large T gives big but light flocs
We need big as well as dense flocs which can be
obtained by designing flocculator with different G
values
Classwork:
What horsepower level do we need to supply to a flocculation basin to
provide a t value 1000 seconds and a Gt of 100,000 for 438 m3
Reactor?
(Given: µ = 0.89 x 10-3
Pa.s; 1 hp = 745.7 watts)
Classwork:
What horsepower level do we need to supply to a flocculation basin to
provide a t value 1000 seconds and a Gt of 100,000 for 438 m3
Reactor?
(Given: µ = 0.89 x 10-3
Pa.s; 1 hp = 745.7 watts)
Retention time, t = Gt/G
Gt = Camp No.

13. What is Flocculation?
Flocculation is the agglomeration of destabilized particles into a
large size particles known as flocs which can be effectively
removed by sedimentation or flotation.

14. Typical layout of a water treatment plant

15. REMOVAL OF IRON AND MANGANESE

21. • Pre-aeration, Post-aeration, and Post-filtration
Table 5.2 Initial Iron and Manganese Test Results
Woodmen Water Treatment Facility Evaluation
Colorado Springs Utilities
Sample
Description Water Quality Parameter (µ g/L)1
Fetot Fedis Mntot Mndis Turbidity
Plant #1 (2/13/01)
Pre-aeration 2600 250 130 130 6.34
Post-aeration 2000 <10 81 <10 7.90
Finished 39 <10 11 <10 0.29
Plant #2 (1/23/01)

22. Treatment Alternatives
• Pre-Cl2
– Addition at the wellhead
– Immediately prior to filters
• Aerated intermediate tank
• Backwash System Enhancement
• Filter Media Replacement
• Filter Media “Cleaning”
– Extended backwashing
– Elevated levels of Cl2
• Ion Exchange
• Sequestration

23. WATER SOFTENING AND ANALYSIS

24. WATER SOFTENING

25. Water with high concentration of calcium and magnesium ions.
Measured in terms of the calcium carbonate equivalent
Hard if it has 100 mg/L or more as calcium carbonate.
Hard water
Removal of hardness from water.
Not a required part of the water treatment process, hard water does not have health consequences.
Is problematic for a variety of reasons
Makes soap precipitate out of water and form a scum, causes bathtub rings
Scale formation in boilers, pipes and cooking utensils, if >300 mg/L
Encrustation in water supply structure
Reaction with soap results in excessive use of soaps and detergents.
Cause taste problems in drinking water
Cathartic and diuretic effect
Shorten the life of fabrics washed in hard water.
Harms many industrial processes,
Softening

26. Enters groundwateras the waterpercolates through minerals
containing calcium ormagnesium.
The most common sources of hardness are
Limestone (which introduces calcium into the water) and
Dolomite (which introduces magnesium.)
Groundwatergenerally has a greaterhardness than surface
water.
Sources of Hardness
Most widespread and troublesome ions, Ca2+
and
Mg2+
Otherdissolved metal like Sr2+
, Fe2+
, and Mn2+
Hardness-causing ions are divalent cations,
Na+
and K+
do not cause hardness.

27. Caused by a variety of divalent cations, primarily calcium and
magnesium.
Cations have a tendency to combine with anions in the water to form
stable compounds
Type of anion found in these salts
Carbonate and
Non-carbonate hardness.
Types of Hardness
Carbonate hardness compounds Noncarbonate hardness
compounds
Calcium carbonate (CaCO3) Calcium sulfate (CaSO4)
Magnesium carbonate (MgCO3) Magnesium sulfate (MgSO4)
Calcium bicarbonate (Ca(HCO3)2) Calcium chloride (CaCl2)
Magnesium bicarbonate
(Mg(HCO3)2)
Magnesium chloride (MgCl2
Calcium hydroxide (Ca(OH)2)
Magnesium hydroxide (Mg(OH)2)Carbonate hardness is caused by metals combined with a form of alkalinity.
Alkalinity is the capacity of water to neutralize acids and is caused by
compounds such as carbonate, bicarbonate, hydroxide, and sometimes
borate, silicate, and phosphate.

28. Carbonate hardness - temporary hardness - can be removed by boiling water
Noncarbonate hardness - cannot be broken down by boiling - permanent
When measuring hardness, we typically consider total hardness
Calcium bicarbonate → Calcium carbonate + Water + Carbon dioxide
Ca(HCO3
)2
→ CaCO3
+ H2
O + CO2
Deposition of calcium carbonate scale in pipes and equipment
CO2
can combine with water to give carbonic acid - corrosion of iron or steel equipment
Calcium sulfate + Sodium carbonate → Calcium carbonate + Sodium sulfate
CaSO4
+ NaCO3
→ CaCO3
+ Na2
SO4
Noncarbonate hardness is the culprit in forming soap scum

29. Types of Treatment
Softened water - a hardness of about 80 to 90 mg/L as calcium carbonate.
Excessively soft water can be problematic - causes corrosion of pipes.
Chemical Precipitation
Similar to removal of turbidity by coagulation/flocculation
Adding lime to raise the pH of water until it is high enough for reactions to
occur which prompt hardness compounds to settle out of the water.
Chemical precipitation using lime will remove carbonate hardness.
Soda ash and lime, both carbonate and noncarbonate hardness may be removed.
In either case, chemical precipitation does not remove all hardness from water.
Reduced as low as 30 to 40 mg/L, although the typical goal is 80 to 90 mg/L.
Chemical precipitation is an effective softening process,
Disadvantages
Requires a lot of operator control
High pH used in lime softening can set colors in water and make them difficult to remove
Produces large quantities of sludge which can create disposal problems.

30. Ion Exchange
Ion exchange softening, also known as zeolite softening,
Passes water through a filter containing resin granules.
Calcium and magnesium are exchanged for sodium from the resin granules.
The resulting water has a hardness of 0 mg/L
 Must be mixed with hard water to prevent softness problems
Does not require flash mixer
Does not require as much operator time
Effective at removing both carbonate and noncarbonate
Often used for waters high in noncarbonate hardness
With a total hardness less than 350 mg/L.
Disadvantages
Sodium ions, health problems for those not supposed to
eat any salt.
Softeners have to be backwashed similar to a filter, and
the recharge water, brine, can cause disposal problems.

31. Other Softening Processes
Other processes can be used to soften water, but they are
generally expensive and only used in rare circumstances
RO water is forced through a
semi-permeable membrane.
Calcium, magnesium, and
dissolved solids are captured
Electrodialysis - passing water between two
plates with opposite electrical charges.
The metals attracted to negative charge
Non-metals are attracted to positive charge.
Both types of ions can be removed
Electrodialysis is used on very hard water,
more than 500 mg/L as calcium carbonate.
Distillation involves the evaporation of water.
The evaporated water leaves behind all hardness compounds,

32. Advantages of
Softening
Softening will deal with the problems caused by hard water - excessive soap use and scaling
being the most troublesome.
Softening often removes iron and manganese, reduces tastes and odors, reduces total
solids content, and removes radioactivity.
The high pH associated with lime softening can aid in disinfection.
When water is stabilized using recarbonation at the end of the lime softening process,
corrosion in the distribution system is avoided.
Disadvantages of Softening
Carry a certain monetary expense.
High pH associated with lime softening favor the formation of hypochlorite as the
dominant free chlorine residual, and hypochlorite is a less powerful disinfectant
than other free chlorine residuals.
The high pH may also increase trihalomethane levels in the water.
If the water is not properly stabilized after treatment, then corrosive water may be
produced which will corrode the distribution system.
Ion exchange softening, as noted above, can also cause problems due to the high levels of
sodium in the treated water.
Both lime softening and ion exchange softening create waste disposal problems.

33. WATER ANALYSIS

36. DETERMINATION OF BOD, COD, TDS AND TOXICITY

37. Parameters that determine water quality
Dissolved oxygen
Biochemical Oxygen Demand
Chemical Oxygen Demand
Dissolved Solids
Nitrogen – ammonia
Bacteriological quality
Parameters that determine water quality
Dissolved oxygen
Biochemical Oxygen Demand
Chemical Oxygen Demand
Dissolved Solids
Nitrogen – ammonia
Bacteriological quality
Dissolved oxygen – amount of actual oxygen dissolved in a
water sample. Higher number = purer water
BOD5 – Actual amount of dissolved oxygen metabolised over 5
days. Higher number = dirtier
BOD – Extrapolated amount of theoretical oxygen that would
be needed to completely metabolise organic waste. Higher
number = dirtier
COD – Actual amount of oxygen required to completely oxidize
organic waste CHEMICALLY. Higher number = dirtier.
TDS – Concentration of dissolved chemicals in water

38. BOD (Biochemical Oxygen Demand) is a measure of the polluting
efficiency of water.
Oxygen is demanded in effluent for the oxidation of inorganic and
organic matter.
 BOD is defined as the amount of oxygen required to carry out the
biological decomposition of dissolved solids under aerobic conditions
at standard temperature.
Where Si = Sample initial in mg/l, Sf = Sample final in mg/l,
Bi= Blank initial in mg/l and Bf = Blank final in mg/l, f =
Dilution factor
Where
BODt = biochemical oxygen demand at t days, [mg/L]
DOi = initial dissolved oxygen in the sample bottle,
[mg/L]
DOf = final dissolved oxygen in the sample bottle, [mg/L]
Vb = sample bottle volume, usually 300 or 250 mL,
Biochemical Oxygen Demand

39. BOD - loss of biodegradable organic
matter (oxygen demand)
Lo
Lt
LorBODremaining
Time
Lo-Lt = BODt
BOD
Bottle
BOD
Bottle
BOD
Bottle
BOD
Bottle
BOD
Bottle

40. COD (Chemical Oxygen Demand) is measure of oxygen required to
oxidize unstable materials in a sample by means of dichromate in acid
solution.
Where B = Blank value, N= Normality, V = Volume of Sample, f = Dilution factor
Where N1 = Normality of FAS,V1 = Volume of FAS, N2 = Normality ofKCr2O7 andV2=Volume of KCr2O7
• COD test is faster than BOD analysis: used for quick assessment of wastewater strength and
treatment performance
• Like the BOD, it does not measure oxidant demand due to nitrogeneous species
• It does not distinguish between biodegradable and non-biodegradable organic matter. As a
result COD's are always higher than BOD's.
Chemical Oxygen Demand
to calculate the normality (N) of FAS

41. The chemical oxygen demand (COD) of a waste
is measured in terms of the amount of
potassium dichromate (K2Cr2O7) reduced by
the sample during 2 hr of reflux in a medium of
boiling, 50% H2SO4 and in the presence of a
Ag2SO4 catalyst.

42. Total Dissolved Solids
Where W1 = weight of dish in gram, W2 = Weight of dish plus sample after treatment in
gram and V = volume of effluent in ml.
Total Dissolved Solids (TDS)" is the concentration of the dissolved chemicals in a sample of
water. Before dissolving, these chemicals could have been a solid or a liquid.

43. An initial DO (dissolving oxygen) of 6.39 mg/l for Blank, 6.45 mg/l for
conventional, 6.45 mg/l for cationized; a final DO of 5.85 mg/l for
blank, 4.47 mg/l for conventional and 4.91 mg/l for cationized were
used to calculate the BOD.
To calculate the COD, use 5 ml of 0.25N KCr2
07
. Quantity of sample
was 1ml each for conventional and cationized; quantity of titrant
(FAS) was 11 ml for blank, 3.7 ml for conventional and 4.6 ml for
cationized.
For TDS; use 50 ml effluent sample each for conventional and
cationized. Weight of dish was 41.9294g for conventional and
42.9124g for cationized. Weight of sample was 43.9275g for dish plus
conventional and 43.4103g for dish plus cationized.
Homework:
Determine the % improvement in BOD, COD and
TDS after cationization

44. Alkalinity

46. Acute ToxicityAcute Toxicity
Single or multiple exposures in a short space of time
(usually less than 24 hours).
Skin Irritation
Vomit
Diarrhea
Single or multiple exposures in a short space of time
(usually less than 24 hours).
Skin Irritation
Vomit
Diarrhea
46
Toxicity
Chronic Toxicity
Non Genotoxicity
1.Water solubility
Water-soluble molecules are generally excreted rapidly by a living organism
2.Water Insolubility
Due to the insolubility, toxicants gets large size particles [0.1 to 3 mm] in the
body which are not transported across cell membranes

47. Genotoxicity
 Mutagens
 Carcinogens
 Teratogens
 Toxicants reach and interact with the DNA.
 Carcinogens attack a nucleophilic site in DNA, which may be a
carbon, nitrogen or oxygen atom, to form a covalent chemical
bond E + [DNA] or E–[DNA]
 The high alkalinity and traces of heavy metals (chromium)
adversely affect the aquatic life and human health.
Genotoxicity
 Mutagens
 Carcinogens
 Teratogens
 Toxicants reach and interact with the DNA.
 Carcinogens attack a nucleophilic site in DNA, which may be a
carbon, nitrogen or oxygen atom, to form a covalent chemical
bond E + [DNA] or E–[DNA]
 The high alkalinity and traces of heavy metals (chromium)
adversely affect the aquatic life and human health.
47
Other worse Effects
Brain function, decreased attention, retardation
Reproduction including miscarriage, untill births
Most sensitive are children <7; immature blood-brain barrier;
effects mental development etc……
Other worse Effects
Brain function, decreased attention, retardation
Reproduction including miscarriage, untill births
Most sensitive are children <7; immature blood-brain barrier;
effects mental development etc……