Philadelphia University
Faculty of Engineering
Department of Civil Engineering
First Semester, 2013/2014
ENVIRONMENTAL
ENGINEERING
441
Lecture 2:
Water Chemistry
PHYSICAL AND CHEMICAL PROPERTIES OF WATER
1 - Organic compounds
2- Inorganic compounds
1.
2.
3.
Nutrients
Metal
Non-Metal
1- ORGANIC SUBSTANCES
The main element of organic compounds is Carbon.
 Organic substances may be

Natural occurring organic substances includes protein,
lipids, carbohydrates and plant pigments
 Synthetic organic chemicals
 Pesticides and agrochemicals
 Surface active agent including emulsifier, wetting agent,
foams, detergents
 Halogenated hydrocarbons ( CHCl3, CHBr3, CHCl2Br, etc


Over 120 toxic organic compounds listed on the
USEPA Priority Pollutant List including pesticides
and solvents
2- INORGANIC CHEMICALS
A -Nutrients: Two nutrients are essential for the
growth of organisms:
Nitrogen
 Phosphorus
 Both are indictors of water pollution

NITROGEN (N)
Source (s)
 Elements for protein, chlorophyll and biological
compounds
 Decomposition of compounds
 animals and human wastes, chemicals (fertilizers)
Effect (s)
 NO3- poisoning to human specially babies below
than 6month old and animals
 NO3-> NO2-(in acidic condition) – will substitute
O2 in blood vessel
PHOSPHORUS (P)
Exist in a form of “inorganic”, and “organic
phosphate”.
Source (s):
readily present in soil
 fertilizers
 human wastes (“organic phosphate”
 domestic wastes (element in detergent)

effects (s)
Cellular activity and aquatic plants
 > 0.2 mg/L – disturb coagulation processes in water
treatment plants

INORGANIC CHEMICALS
B) Ions – anions and cations
 Major Ions (conc. In mg/L) such as Ca, Mg, Na,
K, SO2, Cl, NO3, HCO3
 Minor Ions: Conc in ug/L such as Al, Cu, Fe,
Mn
Source (s):
 Minerals readily available from nature
 Effect (s):
 Colour, odour, taste and turbidity
 Deteriorate health (at high concentration)
METALS – NON TOXIC AND TOXIC
C) Heavy metals: such as As, Ba, Cd, Cr, Pb, Hg, Se,
Ag
Source (s)
 human activities such as mining and industries
Effect (s):
 dangerous disease such as cancer, abortion and
deformation in newborn baby
SOLIDS(IMPURITIES) TYPES OF SOLIDS
1.
2.
3.
Dissolved Solids (in Liquid) cannot be removed from
liquid without accomplishing a phase change such
as distillation, precipitation, adsorption, extraction
or high pressure membrane
Suspended solids (filterable solids) those solids that
can be filtered by a glass fiber filter disc can be
removed from water by physical methods such as
sedimentation, filtration and centrifugation.
Colloidal particles
1.
2.
3.
Size in range between dissolved substances and
suspended particles
Can be removed by high-force centrifugation or
filtration – very small pore size
Measured by turbidity
SOLID
Measured in mg/L
 Sources (s):

Inorganic compounds such as clay, sand
 Organic compounds such plant fibre, human wast


Effects (s):
Aesthetics
 Adsorption point/centre for chemical and microorganism
 Health aspect

PHYSICAL
AND
PROPERTIES OF WATER
CHEMICAL
To illustrate the quality of a tested water qualitatively and quantitatively.
Physical
1.
2.
3.
4.
5.
Suspended Solids
Turbidity
Odor
Taste
Temperature
Chemical






TDS
Alkalinity
Hardness
Fluoride
Metals
Nutrients
Biological

Microorganisms
CHARACTERIZATION OF
WATER
1- TURBIDITY
Turbidity: The presence of suspended material such
as clay, silt, finely divided organic mater, and other
particulate material in water
The unit of measure is a Turbidity Unit (TU) or
Nephlometric Turbidity Unit (NTU)
It’s a measure of the cloudiness
River values range from 2 to 200mg/L of SiO2
The EU drinking water upper limit is 10mg/L with a
guideline value of 1mg/L
2-COLOR

Color in water is caused by dissolved minerals,
dyes or humic acids (decomposition of lignin)
from plants.
Apparent Color: Color that is partly due to
suspended solids (SS)
 True Color (water treatment): Color that is
contributed by dissolved solids (DS) after removal of
SS


Color itself is not usually undesirable from the
stand point of health- it indicates that water
needs appropriate treatment
3- ODOR
Many organic and inorganic chemicals are
odorous including algae and other organisms
 H2S – hydrogen sulfide sometimes present in
ground water and wastewater.
 Threshold odor is determined by diluting a
sample with odor –free water until the last
perceptible odor is detectable (dilution factor)

4-TASTE

Like odor, may be due to decaying microorganisms or algae or due to high conc. of salts
such as Ca & Mg
5- TEMPERATURE


One of the most important parameters in natural
surface waters.
It influences the number and type of microorganism
species present and their rate of activities;
affect most chemical reactions;
 affect solubility of gases e.g oxygen decrease with increase
temp. Conc of O2 around 8mg/L @ 25 degree Celsius



In WWTP, T above 36oC, the aerobic MO population
tends to be less effective as WW purifiers
In rivers, as increased water temp reduces the
amount of oxygen in water, thereby making river less
desirable for fish, particularly salmonoids.
PH
The negative log of the hydrogen ion concentration
 pH of most mineral waters is 6 to 9
 If pH is out side the range 6 – 9, it might kill off the
active microbiological population including the
aquatics organisms
 pH is important in ensuring proper chemical
treatment

ALKALINITY
Alkalinity measures the buffering capacity of the
water against changes in pH; measuring the
amount of acid needed to lower the pH in a water
sample to a specific endpoint (4.5).
 Water that has a high alkalinity can accept large
doses of acids or bases without altering the pH
significantly.
 Waters with low alkalinity, such as rainwater or
distilled water, can experience a drop in the pH
with only a minor addition of an acid or base.
 Alkalinity is expressed as mg (CaCO3)/L

In water the only significant contribution to
alkalinity are carbonate species and free H+ and
OH_
 Acid base reaction
H2CO3
H+ +HCO3

HCO3-
H+ + CO32-
ELECTRICAL CONDUCTIVITY/
CONDUCTIVITY
It is a measure of the ability of an aqueous
solution to carry an electric current by the
movement of ions.
 The higher the numbers of ions, the higher
magnitude of conductivity
 Pure water has 0.05uS/cm (microsiemens/cm)
 Sea water has about 40000 uS/cm
 Groundwater 200-1500

TOTAL HARDNESS



The sum of the divalent metallic cations (Ca & Mg).
These cations reacts with soap to form precipitate and
with other ions present in water to form scale in
boilers.
Measured as mg CaCO3/L
Two kinds of hardness:
carbonate hardness; temporary in characteristics,
precipitated through boiling
 non-carbonate hardness- chloride and sulfate; permanent
in characteristic, eliminated through chemical softness /
ion exchange


WT goal is to provide water with a hardness of less in
the range of 75 to 120mg/L as CaCO3 by using
softener
HARDNESS
Measure of “multivalent” cations in water such as
Ca2+,Mg2+, Fe2+, Mn3+
 Ca2+ and Mn2+are very important


Source (s):


natural mineral on earth
effect (s):
excessive soap usage (a waste !)
 precipitate form on hardware
 precipitate in pipe – temperature and pH increases

DISSOLVED OXYGEN
One of the most important measures of water quality
is dissolved oxygen. Oxygen, although poorly soluble in
water, is fundamental to aquatic life. Without free
dissolved oxygen, streams and lakes become
uninhabitable to aerobic organisms, including fish and
most invertebrates.
It is found that the concentration of DISSOLVED
OXYGEN in water is SMALL
Dissolved oxygen is inversely proportional to
temperature, and
the maximum amount of oxygen that can be dissolved
in water at 0°C is 14.6 mg/L to 7.6 at 30C.
FLUORIDE

Source (s):


Minerals
Effect (s):
not good for health if it is taken in high concentration
 concentration of 1 mg/L is good for the growth of
children teeth
 excessive concentration – color on teeth and problem in
bone growth


Fluoride
ODOUR

Source (s)
inorganic compounds such asminerals, metals, salts
 organic compound from petroleum and/or degradation
of organic matter
 Effect(s)

Aesthetici
 health problems [reaction from sources and other chemicals
such as chlorine (Cl)


Dissolved oxygen in water is consumed by the oxidation
of dissolved ammonia (NH3)and ammonium ion (NH4+)to
form the nitrate ion (NO3⎯).



NH3(aq) + 2O2(aq) + OH-----NO3-(aq) + 2H2O(aq)
The most common substance oxidized by oxygen in water
is ORGANIC MATTER OF BIOLOGICAL ORIGIN
Such organic matter (such as dead plant material
like polymerized carbohydrate below), is oxidised
by dissolved oxygen.

e.g. CH2O+O2(aq) ------ CO2(g) + H2O(aq)

Under oxygen free (anaerobic) conditions
dissolved organic matter will decompose if
appropriate bacteria are present:

2CH2O ----CH4+ CO2
Such anaerobic conditions are common in
SWAMPS and at the bottom of deep lakes
 The Methane (CH4) produced in this process
bubbles up towards the surface of the swamps
and is the reason that methane used to be known
as ‘marsh 'or ‘swamp 'gas

ANALYSIS OF ORGANIC SUBSTANCES
Various parameters are used as a measure of the
organic strength of wastewater:
BOD –Biochemical oxygen demand
 COD –Chemical oxygen demand
 TOC –Total organic carbon
 VSS –Volatile suspended solid

BIOCHEMICAL OXYGEN DEMAND
The quantity of oxygen utilized by a mixed population
of micro organisms to biologically degrade the
organic matter in the wastewater under aerobic
condition.
BOD is the most important parameter in water
pollution control.
it is used a measure of organic pollution as a basis
for estimating the oxygen
Needed for biological processes, as and indicator
of process performance
Expressed in milligrams of oxygen required per liter of
wastewater (mg/L).
BIOCHEMICAL OXYGEN DEMAND
BOD : BOD5: is the amount of dissolved oxygen
used up from the water by microorganisms as they
break down organic material at 20C over a 5-day
periods.
BOD5 for Rivers if > 5 mg/L, they considered polluted
 BOD For MWW range 150-1000mg/L

CHEMICAL OXYGEN DEMAND
COD





Determine the amount of oxygen needed to oxidize
the organics in a water or wastewater using a strong
oxidizing chemical agent- Potassium dichromate
rather than using micro-organisms as in BOD
It measures the total organic carbon with the
exception of some aromatics such as benzene which
are not oxidized in the reaction.
Indirectly measure amount of organic matter in the
water sample
Faster determination of oxygen demand in a water
sample, than BOD
It takes shorter time ( 2hrs) compared to 5 days for
BOD5
The EU upper limit of 125mg/L for treated
wastewaters prior to discharge to rivers
RELATION BETWEEN COD AND BOD
COD > BOD
 COD ~ ultimate BOD
 COD/BOD ~ 2, biodegradable organic
 COD >> BOD, non-biodegradable organic

TOTAL
ORGANIC CARBON- TOC
TOC- : measures all carbon as CO2 in mg/L
 Inorganic carbon ( HCO3, CO2, CO3, etc) must be
removed prior test by acidifying and aerating the
sample.
 Theoretically the COD is 2.66 times greater than
TOC

SOLIDS- Sources of Suspended Solids
Suspended Solids
Inorganic
-Clay
-Silt
Source – Surface
Waters; Domestic
WW; Industrial
WW
Organic
-Plant Fiber
-Biological Solids (Algae
Cells; Bacteria;)
Source – Surface Waters;
Domestic WW; Industrial
WW
Immiscible liquids
-Oils
-Grease
Source- Surface
waters; Domestic WW
and Industrial WW
MICROBIOLOGICAL CHARACTERISTICS



Water must be free from diseases-producing organisms
(pathogen). These organisms include viruses, bacteria,
protozoa, helminthes (worms)
Techniques for comprehensive bacteriological examination
are complex and time consuming
Indicative tests were developed to indicate the relative
degree of Microbial contamination:
Escherichia Coli (E. Coli)- intestinal Tracts
 Aerobactor aerogenes- Urinary tracts
 Total Coliform test


Two protozoa
Giardia cysts
 Cryptosporidium oocycts
 Both pathogens carried by animal and cause gastrointestinal
illness

BIOLOGICAL
Indicator microorganism
Their presence shows that pollution has occurred and
suggests the TYPE and LEVEL of pollution.
Indicator microorganism properties:
 Can be used for all types of water
 Always present when pathogen is present
 Always absent when pathogen is absent
 Easily experimented and give reliable results
 Typical indicators used are coliform group
 Coliform group:
 fecal coliform e.g.E.Coli
 Total coliform e.g.
 fecal coliform,
 Soil coliform
 and others
