ENVIRONMENTAL SCIENCE
AND ENGINEERING
CE102
Water Quality Characteristics
Physical Characteristics
 Colour, Turbidity, Taste, Odour, Temperature
Chemical Characteristics
 pH, TDS, Total (Alkalinity, Hardness),
Calcium,
Magnesium, Fluoride, Chlorides, Sulphates, Nitrates, Total
Nitrogen, Chloramines, Residual Chlorine, Iron, Ag, Cu, Zn
Biological Characteristics
Pathogens
Color
Color in drinking-water may be due to the presence of organic matter such as
Humic Substances, metals such as Iron and Manganese, or highly colored
industrial wastes
Term ‘color’ is used to mean True Color – Due to Dissolved Solids
Term ‘Apparent Color’ includes not only the color due to substances in
solution but also that due to Suspended Matter or Colloid Solids
Measured by comparing the color of water sample with other standard glass tubes
containing solutions of different standard Platinum Cobalt (Pt-Co) color intensities
Normally expressed as Hazen Units (Dissolve 1.246 g potassium chloroplatinate
(equivalent to 500 mg metallic platinum ) and 1.00 g crystalline cobaltous chloride
(equivalent to 250 mg metallic cobalt) in distilled water containing 100 ml of
concentrated hydrochloric acid. Dilute to 1000 ml with distilled water. This standard
solution is equivalent to 500 Hazen Units(HU) or True Color Unit (TCU)
Humic Substances can be defined as “a general category of naturally
occurring, biogenic, heterogeneous organic substances that can
generally be characterized as being yellow to black in color, of high
molecular weight (MW) and refractory” (Aiken et al., 1985b)
Indian
Standards
IS 10500:1983
IS 10500:1991
IS 10500:2012
IS 14543:2004
Desirable Limit
(HU/TCU)
-5
5
2
Permissible Limit in
Absence of Alternate
Sources (HU/TCU)
-25
15
--
Taste & Odour
 The Dissolved Organic materials or the inorganic Salts or dissolved gases may impart taste
and odor
 Gasses: H2S,CH4, CO2, O2 + Organic Matter
 Minerals: NaCl, Iron Compounds, Carbonates & Sulphates
 Taste expressed by Flavor Threshold Number (TKN)
 Odour expressed by Threshold Odour Number (TON)
 The character and intensity of taste and odour discloses the nature of pollution or the
presence of microorganisms
 TON =
𝐴+𝐵
𝐴
=
𝑽𝒐𝒍.𝒐𝒇 𝑹𝒂𝒘 𝑾𝒂𝒕𝒆𝒓 𝑺𝒂𝒎𝒑𝒍𝒆 + 𝑽𝒐𝒍.𝒐𝒇 𝑫𝒊𝒔𝒕𝒊𝒍𝒍𝒆𝒅 𝒘𝒂𝒕𝒆𝒓 𝒖𝒔𝒆𝒅 𝒇𝒐𝒓 𝑫𝒊𝒍𝒖𝒕𝒊𝒐𝒏
𝑽𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝑹𝒂𝒘 𝑾𝒂𝒕𝒆𝒓 𝑺𝒂𝒎𝒑𝒍𝒆
 Permissible Limit is 1:3
Nephelometric Turbidity unit
Indian
Standards
Desirable Limit
(NTU)
Permissible Limit in Absence
of Alternate Sources (NTU)
IS 10500:1983
Agreeable
Agreeable
IS 10500:1991
Agreeable
Agreeable
IS 10500:2012
Agreeable
Agreeable
IS 14543:2004
Agreeable
Agreeable
Turbidity
Reduction of transparency due to the presence of particulate matter such as clay or silt,
finely divided organic matter, plankton or other microscopic organisms - First Attempt
was made in the year 1900 to determine turbidity
Originally turbidity was measured by Jackson candle turbidity meter
 A water sample is poured into the tube until the visual image of the candle flame,
as viewed from the top of the tube
 When the intensity of the scattered light equals that of the transmitted light, the
image disappears; the depth of the sample in the tube is read against the ppmsilica scale, and turbidity was measured in Jackson Turbidity Units (JTU)
 The calibration was done based on suspensions of silica - consistency in
standard formulation was difficult to achieve
Nowadays turbidity is measured by applying Nephelometry - technique
to measure level of light scattered by the particles at right angles to
the incident light beam
Scattered light level is proportional to the particle concentration in
the sample
Higher the intensity of scattered light, higher the turbidity
 Formazin polymer is generally used as turbidity standard because it is
more reproducible than other types of standards used previously
Unit of expression is Nephelometric Turbidity Unit (NTU)
Typical series of Formazin
turbidity standards shown in
NTU/FTU
Turbidity - Measurements
Turbidity – Limits & its Importance
 Turbidity < 40 Units - No Issues
 Turbidity > 40 Units - Dilute the Sample and calculate
using the following equation:
𝐴 ∗ (𝐵 + 𝐶)
𝐶
A : Turbidity units found in diluted sample,
B : Volume in ml of dilution water used, and
C : Volume of sample in ml taken for dilution
𝑇𝑢𝑟𝑏𝑖𝑑𝑖𝑡𝑦 𝑈𝑛𝑖𝑡𝑠 =
Indian
Standards
Desirable Limit
(NTU)
Permissible Limit in
Absence of Alternate
Sources (NTU)
IS 10500:1983
10
25
IS 10500:1991
5
10
IS 10500:2012
1
5
IS 14543:2004
2
--
Why it is Important ?
Turbidity is important because it
affects both the acceptability of
water to consumers, and the
selection and efficiency of treatment
processes, particularly the efficiency
of disinfection with chlorine since it
exerts a chlorine demand and
protects microorganisms and may also
stimulate the growth of bacteria
Solids (Dissolved, Suspended)
Total Dissolved Solids: A well-mixed water sample (100 mL) is filtered through a
standard glass fiber filter (2.0 µm pore size), and the filtrate is evaporated to dryness in a
weighed dish and dried to constant weight at 180°C for 1 hour
TDS↑ Hardness ↑
3
𝑚𝑔 𝑜𝑓 𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑠𝑜𝑙𝑣𝑒𝑑 𝑆𝑜𝑙𝑖𝑑𝑠/𝐿 =
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓𝑑𝑟𝑖𝑒𝑑 𝑟𝑒𝑑𝑖𝑠𝑢𝑒 + 𝑑𝑖𝑠ℎ − 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑖𝑠ℎ
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒
∗ 10
Total Suspended Solids: A well-mixed water sample (100 mL) is filtered through a
weighed standard glass-fiber filter (2.0 µm pore size) and the residue retained on
the filter is dried to a constant weight at 103 - 105°C for 1 hour
If the suspended material clogs the filter and prolongs filtration, it may be
necessary to increase the diameter of the filter or decrease the sample volume
𝑚𝑔 𝑇𝑜𝑡𝑎𝑙 𝑆𝑢𝑠𝑝𝑒𝑛𝑑𝑒𝑑 𝑆𝑜𝑙𝑖𝑑𝑠/𝐿 =
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓𝑓𝑖𝑙𝑡𝑒𝑟 + 𝑑𝑟𝑖𝑒𝑑 𝑟𝑒𝑑𝑖𝑠𝑢𝑒 − 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑓𝑖𝑙𝑡𝑒𝑟
{𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒}
∗ 103
Solids – Temperature
Drying at 103°C ensures the removal of all free water, provided that the drying
period is long enough, and minimizes the loss of water of crystallization
Water of Crystallization - Water that occurs inside crystals, this water is not
bonded to the crystal but embedded during the crystallization of the mineral
Ex - CaSO4·2H2O Gypsum contains two water molecules in their crystals
Residues dried at 103 - 105°C may retain not only water of crystallization but also
some mechanically blocked water
 Residues dried at 180 ± 2°C will lose almost all
mechanically occluded water (water molecules
trapped in mineral matrix). Some water of
crystallization may remain, especially if sulfates
are present
 550°C is about the lowest temperature at
which organic matter, particularly carbon residues
resulting from pyrolysis of carbohydrates and
other organic matter, can be oxidized at
reasonable speed, while Inorganic salts are stable
Solids (Fixed, Volatile)
“Fixed Solids” is the term applied to the residue of Total, Suspended, or Dissolved
Solids after heating to dryness for a specified time at a specified temperature
(550°C for 1 hour). The weight loss on ignition is called “Volatile Solids”
Total Fixed Solids - approximation of the Mineral Matter Present (Inorganic)
Total Volatile Solids - approximation of the Organic Material Present
This test is accomplished by a combustion procedure in which organic matter is
converted to gaseous CO2 and H2O, and thus volatilized, while the temperature is
controlled to prevent decomposition and volatilization of inorganic substances as much
as is consistent with complete oxidation of the organic matter
• 𝑚𝑔 𝑉𝑜𝑙𝑎𝑡𝑖𝑙𝑒 𝑆𝑜𝑙𝑖𝑑𝑠/𝐿 =
• 𝑚𝑔 𝐹𝑖𝑥𝑒𝑑 𝑆𝑜𝑙𝑖𝑑𝑠/𝐿 =
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑟𝑒𝑑𝑖𝑠𝑢𝑒+𝑑𝑖𝑠ℎ 𝑏𝑒𝑓𝑜𝑟𝑒 𝑖𝑔𝑛𝑖𝑡𝑖𝑜𝑛 − 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓𝑟𝑒𝑑𝑖𝑠𝑢𝑒+𝑑𝑖𝑠ℎ/𝑓𝑖𝑙𝑡𝑒𝑟 𝑎𝑓𝑡𝑒𝑟 𝑖𝑔𝑛𝑖𝑡𝑖𝑜𝑛 ∗103
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓𝑟𝑒𝑑𝑖𝑠𝑢𝑒+𝑑𝑖𝑠ℎ/𝑓𝑖𝑙𝑡𝑒𝑟 𝑎𝑓𝑡𝑒𝑟 𝑖𝑔𝑛𝑖𝑡𝑖𝑜𝑛 − 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑖𝑠ℎ/𝑓𝑖𝑙𝑡𝑒𝑟 ∗103
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒
Solids Standards
Indian
Standards
IS 10500:1983
Desirable Limit
(mg/L)
1000
Permissible Limit in Absence
of Alternate Sources
--
IS 10500:1991
IS 10500:2012
IS 14543:2004
500
500
500
2000
2000
--
Environmental Significance
 Laxative or reverse effects on people whose bodies are not used to the higher
levels
 Imparts taste to water
 Water stain glassware
Experiment - Solids
Experiment - Solids
Dissolved Solids
Suspended Solids
Settleable Solids
Settleable Solids is applied to solids in
suspension that will settle, under gentle
(period of inactivity or dormancy)
conditions, because of the influence of
gravity
Fill an Imhoff cone to the 1-L mark with a well-mixed sample. Settle for 45
min, gently agitate sample near the sides of the cone with a rod or by spinning,
settle 15 min longer, and record volume of settleable solids in the cone as
milliliters per liter (mL/L)
Reported as volume (mL/L) basis
Solids Analysis Application in Env. Engg.
Application
TS
VS
TDS
Drinking Water
x
Natural Waters
x
Municipal Wastewater
Industrial Wastewater
x
x
Sludge
x
x
x
TSS
VSS
x
x
x
x
x
Example Problem
Given the following data:
• Weight of a dish = 48.6212 g
• 100 mL of sample is placed in a dish and
evaporated
• Weight of the dish and dry solids = 48.6432 g
• The dish is then placed in a 550°C furnace, then
cooled. Weight = 48.6300 g
• Find the total, fixed, and volatile solids
(expressed as mg/L)
pH -
Universally to express the intensity of the acid or
alkaline condition of a solution
 Expressed on a scale ranging from 0 to 14
 Logrithm of Reciprocal of Hydrogen ion activity (moles/L)
 Recommended pH range for treated drinking waters is 6.5 to 8.5
 It is a factor that must be considered in chemical coagulation,
disinfection, water softening, and corrosion control
 In wastewater treatment employing biological processes, pH must
be controlled within a range favorable to the particular organisms
involved
Indian
Standards
Desirable Limit
Permissible Limit in Absence of
Alternate Sources
IS 10500:1983
6.5 to 8.5
--
IS 10500:1991
6.5 to 8.5
--
IS 10500:2012
6.5 to 8.5
--
IS 14543:2004
6.5 to 8.5
--
pH should preferably be determined at the time of sample collection
pH value obtained in the lab may not be the same as that of water at the time of
collection of samples due to loss-or absorption of gases, reactions with sediments,
hydrolysis and oxidation or reduction taking place within the sample bottle
 Pure water dissociates to yield a concentration of Hydrogen Ions equal to about
10-7mol/L
+
−
𝑯𝟐𝑶 ↔ 𝑯 + 𝑶𝑯
−
H2O dissociates to− produce one 𝑶𝑯 ion for each H+ ion, it is obvious that about
10-7mol/L of 𝑶𝑯 ion is produced simultaneously
By substitution into the equilibrium equation, we obtain,
+
−
𝑯 {𝑶𝑯 }
=𝑲
{𝑯𝟐𝑶}
+
−
𝑲𝑾 = 𝑯 𝑶𝑯 = {10-7}{10-7} = {10-14}
Kw = is known as Ionization Constant for water and changes with change in
Temperature
The pH of water is a measure of the acid–base equilibrium and, in most
natural waters, is controlled by the carbon dioxide–bicarbonate–carbonate
equilibrium system
An increased carbon dioxide concentration will therefore lower pH, whereas a
decrease will cause it to rise
The pH of the water entering the distribution system must be controlled to
minimize the corrosion of water mains and pipes in household water systems
Failure to do so can result in the contamination of drinking-water and in
adverse effects on its taste, odour, and appearance
For effective disinfection with chlorine, the pH should preferably be less than 8
The pH of water determines the solubility (amount that can be dissolved in the
water) and biological availability (amount that can be utilized by aquatic life) of
chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) and
heavy metals (lead, copper, cadmium, etc.)
+
𝑝𝐻 = −𝑙𝑜𝑔 𝐻 𝑜𝑟
1
𝑝𝐻 = log{ +}
𝐻
pH is usually represented from 0 to 14, with pH 7 at 25ᵒC
representing absolute neutrality
Example: In a water treatment plant, the pH values of upcoming and outgoing
water are 7.2 and 8.4 respectively. Assuming a linear variation of pH with time,
determine the average pH value of water
Iron & Manganese
These are present in insoluble forms in significant amounts in nearly all soils
Fe exists in soils and minerals mainly as insoluble Ferric Oxides (Fe2O3) and Iron
Sulfide (FeS) (pyrite)
It occurs in some areas also as Ferrous Carbonate (siderite), which is very slightly soluble
Further, groundwaters usually contain significant amounts of CO2, appreciable amounts
of Ferrous Carbonate may dissolved by the reaction shown in the equation,
FeCO3(s) + CO2 + H2O → Fe2++ 2HCO3Under reducing (anaerobic) conditions, however, the ferric iron (Fe3+) is reduced to
ferrous iron (Fe2+)
Fe imparts a taste to water which is detectable at very low concentrations
Mn exists in the soil principally as Manganese Dioxide (MnO2), which is very
insoluble in water containing CO2
Under reducing (anaerobic) conditions, Manganese in the dioxide form is reduced from an
oxidation state of III to II
Humans suffer no harmful effects from drinking waters containing Fe & Mn
Iron & Manganese
 Groundwaters that contain appreciable amounts of Fe or Mn or both are always empty of
dissolved oxygen and are high in CO2 content. The Fe and Mn are present as Fe (II) and Mn
(II). The high CO2 content indicates that bacterial oxidation of organic matter has been extensive,
and the absence of dissolved oxygen shows that anaerobic conditions were developed
 It has been shown, on the basis of thermodynamic considerations, that Mn(IV) and Fe(III) are
the only stable oxidation states for Fe & Mn in oxygen-containing waters. Thus, these forms can
be reduced to the soluble Mn (II) and Fe (II) only under highly anaerobic reducing conditions.
 Both Fe & Mn interfere with laundering operations, impart objectionable stains to plumbing
fixtures, and cause difficulties in distribution systems by supporting growths of iron bacteria
 Iron bacteria are small living organisms which
naturally occur in soil, shallow groundwater, and surface
waters. These nuisance bacteria combine Fe (or Mn)
and oxygen to form deposits of "rust," bacterial cells,
and a slimy material that sticks the bacteria to well
pipes, pumps, and plumbing fixtures. The bacteria are
not known to cause disease, but can cause
undesirable stains, tastes and odors
Iron & Manganese
Indian
Standards
IS 10500:1983
IS 10500:1991
IS 10500:2012
IS 14543:2004
Desirable Limit (Fe)
(mg/L)
0.3
0.3
0.3
0.1
Permissible Limit in
Absence of Alternate
Sources
1
No relaxation
No relaxation
--
Indian Standards Desirable Limit (Mn)
(mg/L)
Permissible Limit in
Absence of Alternate
Sources
IS 10500:1983
IS 10500:1991
IS 10500:2012
0.1
0.1
0.1
0.5
0.3
0.3
IS 14543:2004
0.1
--
Source of Fluoride: Occurs in Igneous and Sedimentary Rocks
Fluoride occurs as
 Sellaite [MgF2],
 Fluorite Or Fluorspar [CaF2],
 Cryolite [Na3AlF6],
 Fluorapatite [3Ca3(PO4)2 Ca(F,Cl2)],
 Apatite [CaF2.3Ca3(PO4)],
 Topaz [Al2SiO4(F,OH)2],
 Fluormica (phlogopite) [KMg3(Si3Al)O10(F,OH)2],
 Biotite [K(Mg,Fe)3AlSi3O10(F,OH)2],
 Epidote [Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH)],
 Amphibole such as tremolite [Ca2Mg5Si8O22(OH)2],
 Hornblende [Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)2],
 Mica, Clays, Villuanite and Phosphorite
 Fluoride minerals such as Fluorite and Cryolite are not readily soluble in water under
normal pressure and temperature
 Under alkaline conditions and range of specific conductivity between 750 and
1750 µS/cm, dissolution rate of fluorite minerals increase (Saxena and Ahmed, 2001)
 The weathering of Granitic rocks results in increased fluoride content in
groundwater
 Longer residence time in aquifers with fractured fluoride rich rocks enhance
fluoride levels in the groundwater
 Nalgonda, India contain fluoride rich minerals such as Fluorite (0 to 3.3%),
Biotite (0.1 to 1.7%) and Hornblende (0.1 to 1.1%) (Ramamohana Rao et al., 1993)
Fluoride
 The discovery of high consumption of Fluoride (two-edge sword) being harmful for
humans and animals was made in India in 1937 (Nalgonda-Telangana)
 When present in concentration of < (0.8-1.0 mg/L) – Cause Dental Caries (Tooth Decay)
due to formation of excessive cavities in the teeth of young children during calcination of their
permanent teeth
 Fluoride makes the tooth more resistant to acid attack from bacteria
 When fluoride compounds are in your mouth, they can actually make teeth stronger and
prevent cavities
• Higher Fluoride Concentration of (1.5-2.0 mg/L) – Discoloration of teeth (Dental Fluorosis)
• Dental Fluorosis: Tooth Enamel (which is stronger than bone) is the outer covering of teeth
which is principally made up of Hydroxyapatite (96%) (Ca10(PO4)6(OH)2) and is made from
calcium and phosphate
• Fluoride displaces the hydroxide ions from hydroxyapatite to form Fluorapatite (Ca10(PO4)6F2)
• On prolonged continuation of this process the teeth become hard and brittle
• Dental fluorosis : Tooth becoming colored from yellow to brown to black
• At still higher concentration, (> 3.0 mg/L) Skeletal Fluorosis which affects the bone and
ligaments
• Fluorosis is a crippling disease resulted from deposition of fluorides in the hard and soft
tissues of body
Dental Fluorosis
Fluoride - Limits
Indian Standards
IS 10500:1983
IS 10500:1991
IS 10500:2012
IS 14543:2004
Desirable Limit (F)
(mg/L)
0.6 – 1.2
1.0
1.0
1.0
Permissible Limit in
Absence of Alternate
Sources
Desirable
1.5
1.5
1.5
Alkalinity
Alkalinity of a water is a measure of its capacity to Neutralize Acids or its ability to
maintain a relatively constant pH
Alkalinity in natural water is due to:
1. Salts of Weak Acids
 Carbonate, bicarbonate
 Borate, Silicate, Phosphate
 A few organic acids resistant to
biological oxidation (humic subs)
 In polluted or anaerobic waters
(Acetic, Propionic acid, H2S)
2. Weak or Strong Bases
 Ammonia
 Hydroxides
Alkalinity
The major portion of the alkalinity in natural waters is caused by three major classes
of materials which may be ranked in order of their association with high pH values
as follows
1. Hydroxide
2. Carbonate
3. Bicarbonate
Alkalinity is an important parameter in
evaluating the Optimum Coagulant Dosage
Carbon dioxide (CO2) dissolves in water to
form carbonic acid (H2CO3), which
dissociates and is in equilibrium with
bicarbonate (HCO3-) and carbonate (CO3-)
ions
CO2 (Gas) ↔ CO2 (Dissolved)
CO2 (Dissolved)+ H2O ↔ H2CO3 ↔ H+ + HCO3- ↔ 2H+ + CO32-
Alkalinity
Measured volumetrically by titration with N/50 H2SO4 (N/EW = N/50), and is
reported in terms of equivalent CaCO3
It is most convenient to have the standard titrating agent of such strength that 1
mL is equivalent to 1 mg of the material being measured
Samples whose initial pH is > 8.3, the titration is made in two steps:
In the first step the titration is conducted until the pH is lowered to 8.3, the point
at which phenolphthalein indicator turns from pink to colorless (Phenolphthalein
Alkalinity)
OH- + H+ → H2O
CO32- + H+ → HCO3The second phase of the titration is conducted until the pH is lowered to about 4.5,
corresponding to the methyl orange end point (Orange to Pink) (Total Alkalinity)
HCO3- + H+ → H2CO3
When the pH of a sample is < 8.3, a single titration is made to a pH of 4.5
Alkalinity
 @ pH 10 - All OH- are neutralized
 @ pH 8.3 – All CO32- converted to HCO3 Titration till pH 8.3- Phenolphthalein Alkalinity
 Titration till pH 4.5- Total Alkalinity (till H2CO3)
 Total Alkalinity is the amount of acid required
to lower the pH of the solution to 4.5
Alkalinity - Calculations
There are three methods commonly used to make calculations:
1. From Alkalinity Measurements Alone
 Based on empirical relationships for the calculation of the various forms of alkalinity
from Phenolphthalein and Total Alkalinities
 This is used by technicians and others who do not have a knowledge of the
fundamental chemistry involved
 This method are only approximate for samples with pH > 9
2. From Alkalinity + pH Measurements
 This procedure gives sufficiently accurate estimates for most practical purposes, and
also makes use of Phenolphthalein & Total Alkalinity Measurements
 In addition, an accurate initial pH measurement is required for the direct calculation
of OH- alkalinity
3. From Equilibrium Equations
 Various equilibrium equations for H2CO3 are used to compute the concentrations of
the various alkalinity forms
 This method gives reasonably accurate results for constituents, even when present in the
fractional mg/L range, provided that an accurate pH measurement is made
1. From Alkalinity Measurements Alone
From the Measurements of Phenolphthalein and Total Alkalinities - calculation of
other three types of alkalinity, Hydroxide, Carbonate, and Bicarbonate, are made
Assumption: That both hydroxide and bicarbonate alkalinity cannot exist
together in the same sample
This permits only five possible situations to be present, which are as follows:
1. Hydroxide Only
2. Carbonate Only
3. Hydroxide + Carbonate
4. Carbonate + Bicarbonate
5. Bicarbonate Only
1. From Alkalinity Measurements Alone
When…
OH-
CO32-
HCO3-
T=P
P
0
0
T= 2P
2P
0
2(T-P)
0
T>2P
0
T-2(T-P) =
(2P-T)
0
2P
T-2P
P=0
0
0
T
T<2P
2. From Alkalinity + pH Measurements
 Measurements are made for pH, Phenolphthalein, and Total Alkalinity
 This will allow calculation of Hydroxide, Carbonate, and Bicarbonate Alkalinity
𝑲𝒘
1. Hydroxide Alkalinity (from pH Measurement)
−
𝑶𝑯 =
+
[𝑯 ]
Since a hydroxide concentration of 1 mol/L is equivalent to 50,000 mg/L of alkalinity as CaCO3
𝑯𝒚𝒅𝒓𝒐𝒙𝒊𝒅𝒆 𝑨𝒍𝒌𝒂𝒍𝒊𝒏𝒊𝒕𝒚 = 𝟓𝟎, 𝟎𝟎𝟎 ∗ 𝟏𝟎(𝒑𝑯 −𝒑𝑲𝒘)
At 25ᵒC, pKw = 14.00. However, it varies from 14.94 at 0ᵒC to 13.53 40ᵒC
2. Carbonate Alkalinity
Carbonate Alkalinity = 2 (Phenolphthalein Alkalinity – Hydroxide Alkalinity)
3. Bicarbonate Alkalinity
Bicarbonate Alkalinity = Total Alkalinity - (Carbonate Alkalinity + Hydroxide Alkalinity)
3. From Equilibrium Equations
Total Alkalinity is a measure of the equivalent concentration of all cations
associated with the Alkalinity-Producing Anions, Except Hydrogen Ion
[H+] +
𝑨𝒍𝒌𝒂𝒍𝒊𝒏𝒊𝒕𝒚
𝟓𝟎,𝟎𝟎𝟎
= [HCO3- ]+ 2[CO32-] + [OH-]
The equilibrium equations that must be considered are those for water 𝑶𝑯
+
and for the second ionization of carbonic acid is 𝑲𝑨𝟐 =
𝑯 [𝑪𝑶𝟑𝟐
−
[𝑯𝑪𝑶𝟑 ]
−]
−
=
𝑲𝒘
+
[𝑯 ]
Alkalinity – CO2 – pH
pH Changes due to Aeration of water
 Aeration: To remove CO2, NH3, and VOCs
 CO2 removal from water, tends to decrease [H+] and pH
increases
Alkalinity of Boiler Waters
 CO2 is insoluble in boiling water and so is removed with the steam
 This causes an increase in pH and a shift in alkalinity forms from
HCO3- to CO32- and from CO32- to OH-, as indicated below
HCO3- ↔ CO32- + H2O+ CO2
CO32- + H2O ↔ 2OH-+ CO2
 If Ca2+ levels are high, precipitation of CaCO3(s) may occur.
pH – CO2 - Alkalinity
 Respiration & Photosynthesis affect addition or removal of CO2
 Addition of CO2 reduces the pH of a system
 Removal of CO2 increases the pH of a system
Alkalinity – CO2 – pH
pH Changes in the presence of Algal Bloom
 Algae use CO2 for their photosynthetic activity
 Diurnal variations in pH due to algal photosynthesis and respiration
are common in surface waters
 Many shallow surface waters support extensive algal blooms and
they found to grow rapidly when the pH values are as high as 10
 Algae can continue to extract CO2 from water until an inhibitory
pH is reached, which is usually in the range of pH 10 to 11
 As pH increases, alkalinity forms change
 Total Alkalinity remains constant unless CaCO3 precipitation
occurs
HCO3- ↔ CO32- + H2O+ CO2
Ca 2+ + CO32- ↔ CaCO3 (s)
This precipitation usually happens before pH levels have exceeded 10
The CaCO3 precipitated as a result of removal of CO2 through algal action produces the Marl Deposits
in lakes
Marl Deposits are the Precursors of Limestone
Alkalinity Data - Application
Chemical Coagulation
– Chemicals used for coagulation of water and wastewater react with water to form insoluble
Hydroxide precipitates. The H+ ions released react with the alkalinity of the water. Thus,
the alkalinity acts to buffer the water in a pH range where the coagulant can be effective
Water Softening
– Alkalinity - major point to be considered in calculating lime and soda ash
requirements in softening of water
Corrosion Control
– Used to calculate the Langelier saturation index (degree of saturation of Calcium Carbonate
in water)
Indian
Desirable Limit Permissible Limit in
Buffer Capacity
Standards
(mg/L)
Absence of Alternate
 Used for evaluating the buffering
capacity of wastewaters and sludges
IS 10500:1983
 Also used to assess natural waters
IS 10500:1991
ability to resist the effects of acid rain
IS 10500:2012
IS 14543:2004
Sources
--
--
200
600
200
600
200
--
Hardness
Soft Water - Forms lather easily with soap
Hard water - Needs more soap to form lather
 Because of dissolved chemicals in the hard water react with soap to form a scum
Types of Hardness
1. Temporary Hardness (Easily removed by boiling)
Due to the presence of HCO3- of Ca2+ & Mg2+
2. Permanent Hardness (Cannot be removed by boiling)
Due to the presence of Cl- & SO42- of Ca2+ & Mg2+
Hardness - Causes
 Hardness is caused by Multivalent Metallic Cations
 In general, hard waters originate in areas where the
topsoil is thick and limestone formations are
present
 Soft waters originate in areas where the topsoil is thin and
Limestone formations are sparse or absent
Health Significance
 Calcium needed for healthy bones and teeth
 Magnesium needed for effective metabolism
Hardness – Determination
Complete Cation Analysis – Accurate
 Atomic Absorption Spectroscopy (AAS)
 Inductively Coupled Plasma (ICP)
 Ion Chromatography (IC)
𝑚𝑔
50
2+ (mg/L) *
+
𝐻𝑎𝑟𝑑𝑛𝑒𝑠𝑠
(
𝑜𝑓
𝐶𝑎𝐶𝑂
)
=
MC
 Ion Specific Electrodes (ISE)
3
𝐿
𝐸𝑊 𝑜𝑓 𝑀𝐶2
Cation Conc. (mg/L) Anion
20
ClNa+
15
SO42Ca2+
10
NO3Mg2+
2
Alkalinity
Sr2+
Conc. (mg/L)
40
16
1
50
Cation
Ca2+
Mg2+
Sr2+
Conc. (mg/L)
15
10
2
EW
20
12.2
43.8
Hardness (mg/L as CaCO3)
=(15*50) /(20) = 37.5
?
?
Hardness – Determination
EDTA – Titrimetric Method
 Initially, water sample is buffered to pH 10.1 using
ammonia buffer solution
 Erichrome Black T (EBT) (indicator dye - Blue
Color), is then added to the solution containing Ca2+
& Mg2+ ions. Color of solution turns to wine red
MC2+ + EBT → [M.EBT]Complex
 Ethylenediaminetetraacetic Acid (EDTA), the titrant
(0.02 N), complexes with Ca2+ & Mg2+ ions, and the
indicator will turn blue which is the end point of
the titration
MC2+ + EDTA → [M.EDTA]Complex
𝐻𝑎𝑟𝑑𝑛𝑒𝑠𝑠 (
𝑚𝑔
𝑜𝑓
𝐿
𝐶𝑎𝐶𝑂3) =
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐸𝐷𝑇𝐴 ∗𝑁∗ 50∗1000
𝑉𝑜𝑙𝑢𝑒𝑚 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒 𝑇𝑎𝑘𝑒𝑛 (𝑚𝐿)
Hardness – Types
w.r.t the metallic ion
(1) Calcium Hardness
(2) Magnesium Hardness
w.r.t the anions associated with the metallic ions
(1) Carbonate Hardness (2) Noncarbonate Hardness
Calcium Hardness
 Calcium usually found in highest conc. in natural water
 Calcium in water results from deposits of lime stone, gypsum
 Calcium is one of the principal cations in water hardness
 These cations form insoluble salts with soap and decrease
the cleaning effectiveness of soap
 They also form hard water deposits in hot water heaters
𝐶𝑎𝑙𝑐𝑖𝑢𝑚 𝐻𝑎𝑟𝑑𝑛𝑒𝑠𝑠 (
𝑚𝑔
𝑜𝑓
𝐿
𝐶𝑎𝑙𝑐𝑖𝑢𝑚 𝑖𝑜𝑛 𝐶𝑜𝑛𝑐. =
𝐶𝑎𝐶𝑂3) =
𝐶𝑎 𝐻𝑎𝑟𝑑𝑛𝑒𝑠𝑠
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐸𝐷𝑇𝐴 ∗𝑁∗ 50∗1000
𝑉𝑜𝑙𝑢𝑒𝑚 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒 𝑇𝑎𝑘𝑒𝑛 (𝑚𝐿)
𝑚𝑔
𝐶𝑎𝐶𝑂3
𝐿
∗𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡.𝑜𝑓 𝐶𝑎𝑙𝑐𝑖𝑢𝑚
𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝐶𝑎𝑙𝑐𝑖𝑢𝑚 𝐶𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒
Total Hardness – Calcium Hardness = Magnesium Hardness
Temporary or Carbonate Hardness: Metallic Cations is associated with Bicarbonate
and Carbonate ions which tend to precipitate at elevated temperatures such as occur in boilers or
during the softening process with lime
Ca(HCO3)2 → CaCO3 ↓ + CO2 ↑+ H2O
Mg(HCO3)2 → Mg (OH) 2 ↓ + 2CO2 ↑
Permanent or Non-Carbonate Hardness: Contains
Chlorides or Sulphates of
calcium or magnesium or of both and can’t be removed by boiling
CaCl2 → Ca2+ + 2ClMgSO4 → Mg2++ SO42When Alkalinity < Total Hardness:
Carbonate Hardness = Alkalinity
When Alkalinity ≥ Total Hardness:
Carbonate Hardness = Total Hardness
Non-Carbonate Hardness = Total Hardness - Carbonate Hardness
Pseudo-Hardness: Sea, brackish, and other waters that contain appreciable amounts
of Na+. Sodium is not a hardness-causing cation, and so this action which it exhibits
when present in high concentration is termed Pseudo-hardness
Hardness
Reactions for the Precipitation of CaCO3
Reactions for the Dissolution of CaCO3
Hardness - Limits
Indian
Standards
Desirable Limit
(mg/L)
Permissible Limit in
Absence of Alternate
Sources
IS 10500:1983
300
--
IS 10500:1991
300
600
IS 10500:2012
200
600
IS 14543:2004
Not Available
Not Available
Hardness – Problem
A Sample of Water having pH 7.2, has the following Conc. of ions
Ions
Ca2+
Mg2+
Na+
K+
HCO3SO42-
Conc. (mg/L)
40
10
11.8
7
110
67.2
Cl-
11
Calculate TH, CH, NCH, Alkalinity
Hardness – Solution
Ions
Ca2+
Mg2+
Na+
K+
HCO3SO42Cl-
Molecular
Conc. (mg/L)
Weight
(mg/mmol)
40
40.1
10
24.3
11.8
23.0
7
39.1
110
61.0
67.2
96.1
11
35.5
Sum of Cations
175.6
Z
2
2
1
1
1
2
1
Equivalent
Conc. (mg/L
Conc. (eq/L)
Weight
as CaCO3)
(Col.2/Col.5)
(mg/meq.)
(Col.6*50)
20.05
1.998
99.8
12.15
0.823
41.2
23.0
0.51
25.7
39.1
0.179
8.95
61.0
1.8
90.2
48.05
1.4
69.9
35.5
0.031
15.5
=
Sum of Anions
=
175.6 mg/L as CaCO3
99.8
141
166.7
175.65
90.2
160.1
175.6
Hardness – Solution
Total Hardness
Total Hardness
=
Sum of (Ca2+ & Mg2+)
=
99.8 + 41.2
=
141 mg/L as CaCO3
Carbonate Hardness : Portion of Hardness associated with CO32- or HCO3Total Hardness
=
141 mg/L as CaCO3
Carbonate Hardness
=
90.2 mg/L as CaCO3
Non-Carbonate Hardness
=
141 - 90.2 mg/L as CaCO3
=
50.9 mg/L as CaCO3
•
•
•
•
•
•
•
•
Chlorides
Chloride one of the major inorganic anions in saltwater and freshwater
It originates from the dissociation of salts, such as NaCl or CaCl2 in water (taste producing salts)
Chloride occurs in all natural waters in varying concentration
Low [Cl-]
Upland & Mountain Supplies
High [Cl-]
River & Groundwaters
Very High [Cl-]
Sea & Ocean Waters
As mineral content ↑ chloride content ↑
Human urine, contain Cl- - consumed with food and water - averages about 6 g of Cl- per person per
day
Indian Standards Desirable Limit Permissible Limit in Absence
(mg/L)
of Alternate Sources
IS 10500:1983
250
--
IS 10500:1991
250
1000
IS 10500:2012
250
1000
IS 14543:2004
200
--
Chlorides - Determination
• (1) Argentometric Method (Mohr Method)
(2) Potentiometric Method
• (3)Mercuric Nitrate Method
(4) Ferricyanide Method
(5) Ion Chromatography
Argentometric Method (Mohr Method)
• AgNO3 (0.0141 N) as titrant (1 ml of AgNO3 = 0.5
mg Cl- ion)
• Cl- precipitated as white AgCl (Ag+ + Cl- ↔ AgCl(s))
• Indicator: Potassium Chromate
• As conc. of Cl- ions approaches extinction, Ag+ ion
conc. increases to a level at which the solubility
product of Silver Chromate is exceeded and it begins
to form a Reddish Brown precipitate (2Ag+ + CrO42↔ Ag2CrO4(s))
• Endpoint: Color change to Reddish-Brown
• An excess of Ag+ is needed to produce a visible
amount of Ag2CrO4(s), - Blank must be determined
& subtracted from all titration
Chlorides – Analysis - Precautions
1.
2.
3.
A uniform sample size must be used, preferably 100 mL, so that ionic concentrations needed to
indicate the end point will he constant.
The pH must he in the range of 7 to 8 because Ag+ is precipitated as AgOH(s) at high pH levels and
the CrO42- is converted to Cr2O72- at low pH levels
A definite amount of indicator must be used to provide a certain concentration of CrO42-;
otherwise Ag2CrO4 may form too soon or not soon enough
𝐶𝑙
−
(
𝑚𝑔
)
𝐿
=
𝑚𝐿 𝑜𝑓 𝐴𝑔𝑁𝑂3 −𝐵𝑙𝑎𝑛𝑘 ∗ 0.0141 𝑁 ∗35.45 ∗1000
𝑉𝑜𝑙𝑢𝑒𝑚 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒 𝑇𝑎𝑘𝑒𝑛 (𝑚𝐿)
Chlorides - Significance
• Too much of Cl- in soil, can accumulate in leaf
tissue, resulting in leaves with a scorched or
burned appearance.
• Trees with scorched leaves have brown or dead
tissue on the tips, margins, or between the veins
of the leaf.
• Evapotranspiration tends to increase Cl- and
salinity at the root zone of irrigated plants,
making it difficult for crops to take up water due
to osmotic pressure differences between the water
outside the plants and within the plant cell
• Interferes in COD Analysis
Water Treatment
Treatment – Surface Water
Treatment – Surface Water
Treatment – Ground Water
Aeration
Air in Water
Water in Air
Aerator
 Aeration brings water and air in close contact in order to remove dissolved gases
(such as carbon dioxide) and oxidizes dissolved metals such as iron, hydrogen
sulfide, and volatile organic chemicals (VOCs)
 Aeration is often the first major process at the treatment plant
Size Range of Particles of Concern in Water Treatment
Sedimentation
Separation of Unstable & Destabilized SS by force of gravity
Applications in Water Treatment:
1) Settling of coagulated and flocculated waters prior to filtration
2) Settling of coagulated and flocculated water in a softening plant
3) Settling of treated waters in Fe and Mn removal plant
Applications in Wastewater Treatment:
1) Grit removal
2) Suspended solids removal in primary clarifier
3) Biological floc removal in activated sludge
Settling or Sedimentation
 Settling - A unit operation in which solids are drawn toward a source of
attraction. The particular type of settling that will be discussed in this section
is gravitational settling. It should be noted that settling is different from
sedimentation
 Sedimentation - The condition whereby the solids are already at the bottom
and in the process of sedimenting. Settling is not yet sedimenting, but the
particles are falling down the water column in response to gravity. Of course,
as soon as the solids reach the bottom, they begin sedimenting. In the
physical treatment of water and wastewater, settling is normally carried out in
settling or sedimentation basins
Settling Depends on..
1. Characteristics of the Particles
I.
Discrete particles : Particles whose size, shape and specific gravity do not
change with time (Ex: Inert particles such as Sand Grains)
II. Flocculating particles : Particles whose size, shape and specific gravity change
with time. (Example – Clay)
2. Concentration of Particles in Suspension
I.
Dilute Suspensions : Suspensions in which the conc. of particles is not
sufficient to cause significant displacement of water as they settle or in which the
particles will not be close enough for velocity field interference to occur
II. Concentrated Suspensions : Suspensions in which the conc. of particles is too
great to meet the conditions mentioned for dilute suspensions
Sedimentation Tank Basins
Rectangular
Circular
Hopper - Bottom
SedimentationTank Design - Circular Basins
Settling Basins
Advantages
1.
2.
3.
4.
5.
Simplest technology
Energy input - Less
Relatively inexpensive to install and operate
No specialized operational skills
Easily incorporated into new or existing facilities
Disadvantages
1.
2.
3.
4.
Low hydraulic loading rates
Poor removal of small suspended solids
Large floor space requirements
Re-suspension of solids and leeching
Coagulation Overview
Colloidal Particles
• Difficult to settle
• Pass through small pores of conventional filters
How to remove colloidal particles?
• By Aggregation (making them bigger sizes)
Why aggregation is difficult?
• Small size of particles
• Physical and Electrical forces
How to Aggregate?
• Use of Chemical Agents
Coagulation & Flocculation
 Colloidal particles size ranging 10-6 mm (1 nm) - 10-3mm (1 µm)
 Colloidal impurities in surface water cause water to appear turbid or may impart color
 It is difficult to separate colloids from water because
– Colloids do not settle by gravity
– They are so small particles that pass through the pores of most common filtration
media
Measurement of Colloid Concentration
 Surface area might be an excellent measure of colloid concentration but it’s a
difficult measurement and standard suspended solids measurement won’t work
because the colloids will pass through most filters
 The best method of quantifying colloid concentration is Nephelometry or the
measurement of light scattered by the colloids
 Since colloid size is on the order of the wavelength of visible light they will
scatter incident visible light
 Intensity of incident light is measured at right angles to the light source
 The percent of “deflected” light is proportional to the colloid concentration
 A standard colloid concentration is used to calibrate the system
 The colloid concentration is often expressed as TU (turbidity units)
Coagulation & Flocculation
 Coagulation involves the addition of a chemical coagulants for the purpose of conditioning the
suspended, colloidal, and dissolved matter for subsequent processing by flocculation or to
create conditions that will allow for the subsequent removal of particulate and dissolved matter.
 Flocculation is the aggregation of destabilized particles (particles from which the
electrical surface charge has been reduced) and precipitation products formed by the addition of
coagulants into larger particles known as flocculant particles or, more commonly, ‘‘floc.’
Coagulation
 The chemistry is extremely complex.
 Because metal coagulants Hydrolyze
to form Acid Products that affect
pH that in turn affects the solubility
of the coagulant
Selection of the type and dose of
coagulant depends on,
 The characteristics of the coagulant
 Concentration and type of
particulates,
 Concentration and characteristics of
Natural Organic Matter (NOM),
 Water temperature, and water quality
Coagulation-Stoichiometry
 Each mole of trivalent ion will produce 1 mole of the metal hydroxide and 3
moles of hydrogen ions
Al3+ + 3H2O ↔ Al (OH)3, am↓ + 3H+
Fe3+ + 3H2O ↔ Fe (OH)3,am↓ + 3H+
 The ‘‘am’’ subscript refers to amorphous solids (hours old), which have a much
higher solubility product than crystalline precipitates
 Chlorinated Copperas: Ferric Chloride + Ferric Sulfate
Alum Eff. pH : 6.5-8.5
Ferric Chloride Eff. pH :
3.5 - 6.5 & > 8.5
Ferric Sulfate Eff. pH :
4.0 -7.0 & > 9.0
Coagulation-Stoichiometry
 When alum is added to water and aluminum hydroxide precipitates, the
overall reaction is,
Al2(SO4)3·14H2O → 2Al(OH)3↓ + 6H+ + 3SO42- + 8H2O
 Ferric chloride:
FeCl3 + 3H2O → Fe(OH)3↓ + 3H+ + 3Cl Ferric sulfate:
Fe2(SO4)3 · 9H2O → 2Fe(OH)3↓ + 6H+ + 3SO42- + 3H2O
 After Al(OH)3 or Fe(OH)3 precipitates, the species remaining in water are the same
as if H2SO4 or HCl had been added to the water
 Thus, adding alum or ferric is like adding a strong acid
 When alum reacts with bicarbonate alkalinity,
Al2(SO4)3·14H2O + 3Ca(HCO3)2 → 2Al(OH)3↓ + 3CaSO4 +14 H2O+ 6CO2 ↑
Alkalinity-Coagulation Relationships
Addition of Metallic salts release Hydrogen ions:
Al2(SO4)3·14H2O → 2Al(OH)3↓ + 6H+ + 3SO42- + 8H2O
 Hydrogen ions neutralize alkalinity
 1 mg/L alum neutralize 0.5 mg/L alkalinity
Low alkalinity must be buffered to maintain coagulation
 Lime Ca(OH)2 or soda ash (Na2CO3)
Coagulation-Stoichiometry
Ferrous Sulfate (Copperas):
Fe2(SO4)3·7H2O + 3Ca(OH)2 → Fe(OH)2 {Ferrous Hydroxide}+ CaSO4 + 7H2O
Fe2(SO4)3·7H2O + 3Ca(HCO3)2 → Fe(HCO3)2 + CaCO4 + H2O
Fe(HCO3)2 + 2Ca(OH)2 → Fe(OH)2 + 2CaCO3 + 2H2O
4Fe(OH)2 + O2 + 2 H2O → 4Fe(OH)3↓
Chlroniated Copperas:
6 (Fe2(SO4)3·7H2O) + 3Cl2 → 2Fe2(SO4)3 + 2FeCl3 + 42H2O
2Fe2(SO4)3 + 3Ca(OH)2 → 2 Fe(OH)3 ↓ + 3CaSO4
2FeCl3 + 3Ca(OH)2 → 2 Fe(OH)3 ↓ + 3CaCl2
Alum vs Iron Salts
 Iron Salts produce heavy floc & remove more suspended matter than Alum
 Iron Salts being good oxidising agents, can remove H2S and its corresponding
taste and odour from water
 Iron Salts can be used over a wider range of pH
 Iron Salts cause staining and promote growth of iron and bacteria in
distribution system
 Iron salts imparts corrosiveness to water than Alum
 Handling of Iron Salts needs more skill and control as they are corrosive and
deliquescent
 No skilled labour for Alum
Softening
 Softening Process of removing hardness from water
 Carbonate Hardness is defined as the concentration of Ca2+ and Mg2+
and other polyvalent cations in water that are associated with the anions
that comprise alkalinity (e.g., HCO3−, CO32−)
 Noncarbonate Hardness is defined as the concentration of Ca2+ and
Mg2+ and other polyvalent cations in water that are associated with no
alkalinity anions (e.g., SO42−, Cl−)
 The presence of hardness causes scale in pipes and hot-water heaters, high
soap consumption, and the deterioration of fabrics
 Removing hardness, termed Softening, may be accomplished either by
chemical precipitation as insoluble compounds, ion exchange, or
membrane processes
Softening by Chemical Precipitation
 Precipitation softening relies on the relative insolubilities of CaCO3 and
MgOH
 The choice of precipitating chemicals (lime and caustic soda) depends
upon the raw-water quality and economics
 Lime–soda ash softening has been a traditional process for the removal
of hardness, consisting of both carbonate and noncarbonate hardness,
from water supplies
 Lime is used to remove chemicals that cause CH
 Soda ash is used to remove chemicals that cause NCH
Softening by Chemical Precipitation
 Commercial Lime is in the forms of
quicklime (CaO) and hydrated lime
(Ca(OH)2 )
 Quicklime is granular and usually greater
than 90 percent CaO with magnesium
oxide (MgO) the primary impurity
 Quicklime is less expensive than
hydrated lime, it must be hydrated or
slaked to Ca(OH)2 before it is used for
 Lime Softening can effectively remove
softening
heavy metals (e.g., Pb, Cr, Hg, As), Fe
 Powdered, hydrated lime contains about
and Mn, turbidity, and some organic
70 percent Ca(OH)2
compounds including a substantial
 Soda ash is a grayish-white powder and
amount of NOM and kill algae, bacteria,
is nearly 98 % Na2CO3
and viruses
Lime Soda Softening
Lime :
Soda :
Ca(OH)2 or CaO → Ca2+ + OH-
Reactions:
Na2CO3 → Na+ + CO3=
Ca2+ + CO3= ↔ CaCO3 (s)
Mg2+ + 2OH- ↔ Mg(OH)2 (s)
Lime Softening: Carbonate Hardness
CO2 + Ca(OH)2 → CaCO3(s) + H2O
Ca2+ + 2HCO3− + Ca(OH)2 → 2CaCO3(s) + 2H2O
Detailed Equations:
H2CO3 + Ca(OH)2 ↔ CaCO3(s) + 2 H2O
Ca(OH)2 ↔ Ca2+ + 2OHH2CO3 + OH- ↔ HCO3- + H2O
HCO3- + OH-↔CO3= + H2O
Ca2+ + CO3= ↔ CaCO3(s)
Lime Softening: Carbonate Hardness
Mg2++ 2HCO 3−+ 2Ca(OH)2→ 2CaCO3(s) + Mg(OH)2(s) + 2H2O
Detailed Equations:
Ca(OH)2 ↔ Ca2+ + 2OH2HCO3- + 2OH- ↔ 2CO3= + 2H2O
Mg2+ + 2OH- ↔ Mg (OH)2(s)
2Ca2+ + 2CO3= ↔ 2CaCO3(s)
Filtration
Filtration
 Removing particles from water
 Removal of particles (solids) from a suspension (two-phase system
containing particles and liquid) by passage of the suspension
through a porous medium
 The most common granular filtration technology in water treatment is
Rapid Filtration
 The term is used to distinguish it from Slow Sand Filtration, an older
filtration technology with a filtration rate 50 to 100 times lower than
rapid filtration
Principal Features of Rapid Filtration
The most important features are
1. A filter bed of granular material that has been processed to a more
uniform size than typically found in nature
2. The use of a coagulant to precondition the water
3. Mechanical and hydraulic systems to efficiently remove collected
solids from the bed
Mechanism
Mechanism
Mechanical straining
Biological Action
Electrolytic action
Uniformity of Filter Media
 Media uniformity allows the filters to operate at a higher hydraulic
loading rate with lower head loss but results in a filter bed with void
spaces significantly larger than the particles being filtered
 As a result, straining is not the dominant removal mechanism
 Instead, particles are removed when they adhere to the filter
grains or previously deposited particles
 Particles are removed throughout the entire depth of the filter bed by a
process called depth filtration, which gives the filter a high capacity for
solids retention without clogging rapidly
Coagulation Pre-treatment
 If particles are not properly destabilized, the natural negative surface
charge on the particles and filter media grains cause repulsive
electrostatic forces that prevent contact between particles and media
 Properly designed and operated rapid filters can fail quickly if the
coagulant feed breaks down or the raw water quality changes and the
coagulant dose is not adjusted accordingly
Dual Media Filter
Stages in Rapid Filtration
 Filtration stage, during which particles accumulate,
 During the filtration stage, water flows downward through the filter
bed and particles collect within the bed
 Backwash stage, during which the accumulated material is
flushed from the system
 During the backwash stage, water flows in the direction opposite to
remove the particles that have collected in the filter bed
Conventional Filtration
Classification of Filters
According to type of Granular Medium used
1. Single Media (Sand or Anthracite)
2. Dual Media (Anthracite and Sand)
3. Multi Media (Anthracite, Sand, Garnet)
According to Flow
1. Gravity Filter - Open to Atmosphere
2. Pressure Filter - Closed
According to Rate of Filtration
1. Rapid Sand
2. Slow Sand
Materials Used in Filter Media
 The common materials are sand, anthracite coal, garnet, and ilmenite
 Anthracite is harder and contains less volatile material than other types of coal
 Garnet (group of minerals containing a variety of elements, often
appearing reddish or pinkish) and ilmenite (is an oxide of Fe and Ti) are
heavier than sand and are used as the bottom layer in tri media filters
 In addition to these four minerals, Granular Activated Carbon is sometimes
used as a filter material when adsorption and filtration are combined in a
single unit process
Filter- Examples
Backwash
Water Quality Management
 Water quality is affected by natural factors:
– Historical uses in the watershed
– Geometry of the watershed area
– Climate of the region
 Good water quality protects drinking water as well as wildlife
Point Sources of Pollutants
 Point sources include domestic sewage and industrial wastes
 Point sources - collected by a network of pipes or channels and
conveyed to a single point of discharge in receiving water
 Municipal sewage - domestic sewage and industrial wastes that are
discharged into sanitary sewers - hopefully treated
 Point source pollution can be controlled by waste minimization and
proper wastewater treatment
Nonpoint Sources
 Urban and agricultural runoff
that
are
characterized
by
overland discharge
 This type of pollution occurs
during rainstorms and spring
snowmelt
 Pollution can be reduced by
changing land use practices
Combined Sewer Flow
 Nonpoint pollution from urban storm water collects in combined
sewers
 Combined sewers- carry both storm water and municipal sewage - older
cities
Combined Sewer Overflow
 Eliminating this involves:
– Construction of separate storm and sanitary sewers
– Creation of storm water retention basins (Rainwater Harvesting)
– Expanded treatment facilities to treat the storm water
 Combined sewers are not prohibited by the U.S. because removal would
disrupt streets, utilities, and commercial activities
Oxygen- Demanding MATERIAL
 Dissolved Oxygen (DO) - fish and other higher forms of aquatic life
that must have oxygen to live
 Oxygen - Demanding Material - anything that can be oxidized in the
receiving water resulting in the consumption of dissolved molecular
oxygen - BOD, COD
 Almost all naturally occurring organic matter contributes to the
depletion of DO
Nutrients
 Nitrogen and phosphorus are considered pollutants when too much
present in high conc.
 High levels of nutrients cause disturbances in the food web
 Organisms grow rapidly at the expense of others
 Major sources of nutrients (N, P):
–
–
–
–
Phosphorus-based detergent
Fertilizer and agricultural runoff
Food-processing wastes
Animal and human waste
Pathogenic Organisms
 Include bacteria, viruses, and protozoa from diseased persons or
animals
 Water is made unsafe for drinking, swimming, and fishing
 Antibiotic-resistant bacteria are the most dangerous
 Bacteria are found in both urban and rural environments with no
observable pattern
Pathogenic Organisms
 Serious Outbreaks of these cause great suffering
 Escherichia(E.) Coli - indicator of fecal coliform bacteria
 Salmonella (typhoid fever)
 Shigella (dysentery)
 Cryptosporidium - protozoa
 Giardia- protozoa
Suspended Solids
 Suspended solids - organic and inorganic particles that are carried by
wastewater into a receiving water
 A slower flow causes particles to settle and form sediment
 Colloidal particles - do not settle, cause an increase in the turbidity of
surface water
 Organic suspended solids - exert oxygen demand
 Inorganic suspended solids - result from soil erosion
Suspended Solids
 Suspended solids - organic and inorganic particles that are carried by
wastewater into a receiving water
 A slower flow causes particles to settle and form sediment
 Colloidal particles - do not settle, cause an increase in the turbidity of
surface water
 Organic suspended solids - exert oxygen demand
 Inorganic suspended solids - result from soil erosion
Suspended Solids
With an increase in the amount of sediment comes
– Increase of turbidity
– Decrease of light penetration
– Increase in amount of bacteria
– Increase in solids settled on the bottom which causes animal habitats
to be destroyed
Salts
 Total dissolved solids - TDS
 Water collects salt as it passes over soil during irrigation practice
 Too much salt can cause crop damage and soil poisoning
Heat Impacts
An increase in the Temp of water
can cause:
– Increase in DO which leads to
a deterioration in water quality
– Large fish kills
– Blocked migration of fish
– Altered genetic makeup in fish
Water Pollution Problems in Streams - Self purification
Dilution and decay of degradable, oxygen-demanding wastes and
heat in a stream
Dissolved Oxygen Depletion
(From: Environmental Science: A Global Concern, 3rd ed. By W.P Cunningham and B.W. Saigo, WC Brown Publishers, 1995
Transport characteristics that affect concentration
 Velocity
 Dilution (mixing)
 Dispersion
 Degradation (mass loss)
 Adsorption (to soils)
 Sedimentation (to bottom)
 Aquatic Life (attached)
v
Effect of Oxygen-demanding wastes on rivers
 Depletes the dissolved oxygen in water
 Threatens aquatic life that require DO
 Concentration of DO in a river is determined by the rates of
photosynthesis of aquatic plants and the rate of oxygen consumed by
organisms
Biochemical oxygen demand
 Biochemical oxygen demand (BOD) - oxidation of an organic
compound is carried out by microorganisms using the organic matter as
a food source
 Bioassay - to measure by biological means
 BOD is measured by finding the change in dissolved oxygen
concentration before and after bacteria is added to consume organic
matter
BOD
 Ultimate BOD - maximum
amount of oxygen consumption
possible when waste has been
completely degraded
 Numerical value of the rate
constant k of BOD depends on:
– Nature of waste and T
– Ability of organisms in the
system to use the waste
Temperature
 Oxygen consumption speeds up as the
temperature increases and slows down
as the temperature decreases
 Oxygen consumption is caused by the
metabolism of microorganisms
 BOD rate constants depend on:
– Temperature of receiving water
throughout the year
– Comparing data from various
locations at different T values
Dissolved Oxygen DO
 If the discharge of oxygendemanding wastes is within the
self-purification capacity, the DO
is high
 If the amount of waste increases,
it can result in detrimental changes
in plant and animal life
 Aquatic life cannot survive
without DO
 Objective of
water quality
management is to assess the
capability of a stream to absorb
waste
Oxygen-Sag Curves
Do Sag Curve
 DO concentration dips as oxygen-demanding materials are oxidized and
then rises as oxygen is replenished from atmosphere and photosynthesis
 Major sources of oxygen:
– Reaeration from the atmosphere
– Photosynthesis of aquatic plants
 Factors of oxygen depletion:
–
–
–
–
BOD of waste discharge
DO in waste discharge is less than that in the river
Nonpoint source pollution
Respiration of organisms and aquatic plants
Oxygen-Sag Curves
What is an oxygen sag curve?
– Is the dip in dissolved oxygen observed when BOD waste water is
discharged continuously into a river
– The extent of the sag is determined by BOD level in the
wastewater stream, by the rate of discharge, and by other factors
such as temperature and river characteristics (flow rate, turbulence,
etc)
– An oxygen sag curve is also observed due to a one-time discharge of
BOD waste into a lake
– In that case, the DO drop is with time instead of distance downriver
– Continuous discharge of BOD waste into a lake results in a decrease
in steady-state DO level (not a “sag” followed by a recovery)
Dynamics of Oxygen Depletion & Dissolution
Figure on left shows a model framework to
calculate:
DO as a function of distance downstream from
a point source discharge; or
DO as a function of time after a single “spike”
discharge of BOD wastewater
DO falls when decomposition rate > dissolution
rate and DO rises when decomposition rate <
dissolution rate
Rate of decomposition (deoxygenation)
 Linearly proportional to BOD level
 BOD falls exponentially with time
 Rate of oxygen dissolution (reaeration)
 Linearly proportional to the oxygen deficit:
DOsat - DOactual
Wastewater Treatment
RWE
Raw water
Community
WWE
Wastewater engineering
 Quickly drain off the wastewater away from the community
 To make wastewater fit for dispose or environmental friendly
RWE
Raw water
Community
Disposal
Treatment of
Wastewater
Conveyance
Collection
 Wastewater is a term that is used to describe waste material that includes
industrial liquid waste and sewage waste that is collected in towns and
urban areas and treated at urban wastewater treatment plants
 Wastewater treatment: A process to convert wastewater - which is water no
longer needed or suitable for its most recent use - into an effluent that can be
either returned to the water cycle with minimal environmental issues or
reused
Wastewater
Contaminants
Suspended solids
Biodegradable
organics (e.g., BOD,
COD)
Pathogenic bacteria
(e.g., E-coli)
Nutrients (N & P)
Wastewater Sources
Residences
human and animal excreta and
waters used for washing, bathing, and
cooking
―
Commercial institution
Dairy and industrial establishment
― slaughterhouse waste, dairy waste,
tannery wastewater, etc.
Where does the
water from the
washer go?
When you flush the
toilet where does
the contents go?
By gravity flow, the waste is on its way to your local
wastewater treatment plant!
Why to treat wastewater?
 Causes a demand for dissolved oxygen (lower DO levels of streams)
 Adds nutrients (nitrate and phosphate) to cause excessive growth
 Increases suspended solids or sediments in streams (turbidity increase)
Objectives of WWT

Reduce organic content i.e., BOD

Removal/reduction of nutrients i.e., N,P

Removal/inactivation of
pathogenic microbes
Levels of Treatment
Primary
 removal by physical separation of grit and
large objects (material to landfill for
disposal)
 Sedimentation and screening of large
debris
Secondary
 Biological and chemical treatment
 aerobic microbiological process (sludge)
organic matter + O2
CO2 + NH3 + H2O
Primary treatment
Typical materials that are removed during primary treatment
include
 fats, oils, and greases
 sand, gravels and rocks
 larger settle-able solids including human waste
 floating materials
Methods used in primary treatment
 Bar screens
 Grinding
 Grit Chamber
 Sedimentation Tank - primary Settling tank
 Chlorination of effluent
Biological treatment
 activated sludge
 trickling filter
 oxidation ponds
Secondary treatment
Activated sludge process
 Primary wastewater mixed with bacteria-rich (activated) sludge and air or
oxygen is pumped into the mixture
 Both aerobic and anaerobic bacteria may exist
 Promotes bacterial growth and
decomposition of organic matter
 BOD removal is approximately
85%
 Microbial removal by activated
sludge
 80-99% removal of bacteria
 90-99% removal of viruses
Trickling filters
 Trickling filters are beds made of coke
(carbonized coal),
limestone chips or
specially fabricated plastic media
 Optimize their thickness by insect or worm
grazing
 The primary wastewater is sprayed over
the filter and microbes decompose
organic material aerobically
 Low pathogen removal
 Bacteria, 20-90%
 Viruses, 50-90%
 Giardia cysts, 70-90%
Stabilization or oxidation ponds
 Oxidation ponds are a few meters deep, and up to a hectare in size
 They are low cost with retention times of 1 to 4 weeks. Odor and mosquitoes can be a problem
 Pathogen removal:
Stabilization ponds are the preferred wastewater treatment
 Bacteria, 90-99%
process in developing countries due to low cost, low
maintenance
 - Virus, 90-99%
This is balanced by larger land requirement
 Protozoa, 67-99%
 Mechanisms include the long detention time, high pH (10- 10.5) generated by photosynthesis,
predation, sunlight, temperature
Sludge Treatment Processes
Thickening (water removal)
Digestion (pathogen inactivation and odor control)
Conditioning (improved dewatering with
alum and high temp, 175-230° C)
Dewatering (pathogen inactivation and odor control)
Incineration (volume and weight reduction)
Final disposal
Wastewater Treatment
Alternatives
 Septic Tanks
 Constructed Wetlands
 Composting
Wastewater treatment
5R Concept
Introduction
 At the center of social and economic development, WATER is vital for energy
generation, agriculture, industry, environmental management and cultural development
 World Bank points out that
 ~4.5billion people lack sanitation services and
 ~2.1 billion people lack clean drinking water
 World Economic Forum’s Global Risks Report, 2017 states that water scarcity is
becoming the largest global risk, due in part to climate change, which will lead to more
intense droughts, floods, glacial melting, and unpredictable precipitation
 Other Driving Factors for water scarcity:
 Improving living standards
 changing consumption patterns
 Irrigated agriculture expansion
Uneven Water Distribution
 Uneven distribution of water resources
highlights the problems of worldwide
water scarcity
 Worldwide predictions indicated severe
water scarcity prevails
 in locations with either high population
density (e.g., in North Africa, Australia,
Arabian peninsula, London, San Francisco
Bay, and Hainan island)
 in
areas of
intensely irrigated
agriculture (Great Plains in the United
States)
 or both (India, eastern China, and the
Nile delta)
Distribution of water availability
(bottle size representing annual water
stock m3/person).
Managing urban water
 Used
water from household
activities is called gray water, and
it is not heavily polluted
 Contrasting is black water, which
comes from toilet flushing
 Black water is a relatively small
fraction of the flow (parts of toilet
flushing, only 30% of total
household utilization) but contains
most of the BOD, nitrogen,
phosphorus, and bacteria of health
concern
 Blue line indicates that storm water can be collected to be part of the supply, and
gray water and black water also can be treated and returned as a supply - thus,
“wasted waters” become new source
“wasted waters” become new sources
 Projects of “wasted waters” reuse have been applied and were not
successful, such as one initiated in Hamburg (German)
 Public Utilities Board in Singapore processed water reclamation and
reuse in1966 but, failed because of costly and unreliable technology
 Public acceptance of recycled
water also withdrawn “wasted
waters”
reuse
project
promotion, such as failure cases
of Toilet to Tap campaign in
California (USA) and Drinking
Sewage
campaign
in
Toowoomba (Australia)
5R Generation
 It approaches to manage urban water
 It harvests storm water, gray water and black water in
several forms
 It offers promise for moving solutions for
urban water scarcity in practice
 Recover (storm water)
 Reduce (toilet flushing water)
 Recycle (gray water)
 Resource (black water) and
 Reuse (advanced-treated wastewater)
 5R generation integrates newer technologies,
available for practice only in recent years, to
gradually replace traditional wastewater treatment
systems to enhance water utilization
Recover
Reduce
Resource
Recycle
Reuse
Framework of 5R generation
Recycle
B
 Applicable
in common-use
settings, such as community
and shopping centers, hotels,
and office buildings
Recover (storm water)
 It focuses on urban storm water and includes
technologies for collection, treatment, and storage
 Storm water often requires less treatment than
municipal waste-waters, and its collection offers an
added benefit of reducing pollution and erosion
issues in receiving water bodies
 After storm water is collected from a drain, creek,
roof, or pond, it can be treated to achieve quality
requirements for different purposes
 Storage is a major challenge for Recover, due to
space constraints
 Traditionally, storm water is temporarily held
behind dams or in tanks to balance supply and
Mobile treatment and storage
demand, but alternatives are being sought
for storm water
 Wetlands are also being applied for storm water storage
 Recover in 5R generation was built to collect storm water from roofs, and mobile treatment
and storage of the storm water can be used when rainfall is heavy
Reduce (toilet flushing water)
 Reduce in 5R generation mainly uses high
efficiency, water-saving toilets to minimize
the flushing volume, which contributes for
approximate 30%of the black water flow
 Reducing the water for flushing is a direct
method to address scarcity in urban areas
 A vacuum toilet uses only 0.5–2 L water
(adjustable) per flush, compared to ~10
L/flush for a typical conventional toilet
 Vacuum flushing already is widely applied
for toilets in airplanes and high-speed
trains, and it is beginning to be used in homes
and hotels
Vacuum Toilet
Recycle (gray water)
 Recycle in 5R generation mainly involves processing and recycling gray water in a
household or community system
 Gray water is generated from kitchen and bathroom sinks, showers and bathtubs, and
laundry discharges, and it excludes toilet discharge which could be applied for toilet
flushing and irrigation after reuse
 According to lifestyle, living standard, population structure (age, gender), customs,
water infrastructure, and the degree of water scarcity, gray water varies typically from
90 to 120 L/person/day, indicating a huge volume recyclable gray water as potential
water source
 Based on civil wastewater calculation, 50%–70% of total domestic wastewater, which
could be classified into gray water, only contains 30% of the organic matter and 9%–
20% of the nutrients
Resource (black water)
 Resource in 5R generation mainly involves capturing resources from black water in a
household or community water system.
 Household wastewater normally consists around 30% black water, making black water
a non-trivial water source if it is not discharged immediately to the sewer
 Black water was ignored in the water-recycle system, as it typically was discharged
directly into a sewer for transport to a municipal wastewater treatment plant
 Biochemical oxygen demand (BOD) and nutrients(phosphorus and nitrogen) usually
are the most valuable resources in black water
 Recently, recovery of black water has become a hot topic, and anaerobic digestion is
the most effective method for treatment and recovery of black water
Reuse (advanced-treated wastewater)
 Even when Recover, Reduce, Recycle, and Resource are well implemented in a
community, some wastewater is going to a conventional wastewater-treatment plant
 That water also can be reused for a range of purposes, if the effluent quality is
sufficient for the purpose
 Thus, 5R generation includes Reuse to overcome water-quality deficiencies
 At municipal wastewater treatment plants, advanced treatment, which aims to remove
suspended, colloidal, and dissolved constituents remaining after biological treatment,
is applied to improve effluent quality
 Bed filtration, surface filtration, micro- and ultra-filtration, reverse osmosis, electro
dialysis, adsorption, air stripping, ion exchange, advanced oxidation, distillation,
chemical precipitation, chemical oxidation, and disinfection are the typically advanced
technologies used to improve effluent quality