This document describes various categories and characteristics used to assess water quality. It discusses 4 categories of water quality: physical, chemical, biological, and radiological. It then provides more details on specific chemical characteristics (pH, chlorides, nitrogen, toxic inorganic/organic substances), biological characteristics (disease-producing organisms), and radiological characteristics. The key water quality parameters described include pH, BOD, COD, TOC, and the presence of pathogens. The document emphasizes the importance of various characteristics for determining water quality and its suitability for uses like drinking water.

1. 4 categories to describe water
qualityPhysical
 Related to the quality of water for domestic use.
 Associated with the appearance of water
 Eg. Color, turbidity, temperature and odour.
Chemical
 Sometimes evidenced by their observed reactions (comparative
performance of hard & soft
waters in laundering)
Biological
 Very important in their relation to public health
 Significant in modifying the physical and chemical characteristic of water
Radiological
 Considered in areas where there is a possibility that the water may have
come in
contact with radioactive substances

2. Chemical Characteristics
• Wastewater contains chemicals such as nitrogen,
phosphorus and levels of dissolved oxygen as well as others
that may affect its composition and pH rating. Highly acidic
or alkaline wastewater is probably trade waste and will
require pre-treatment before discharge to the sewer.

3. Continue….
The hydrogen-ion concentration is an
important quality parameter of wastewater.
The concentration range suitable for the
existence of most biological life is quite narrow
and critical.
Wastewater with an adverse concentration of
hydrogen ion is difficult to treat by biological
means, and if the concentration is not altered
before discharge, the wastewater effluent
may alter the concentration in the
natural waters.
pH

4. Chlorides found in domestic sewage is derived
from kitchen waste, human excreta and urinary
discharges etc.
Water softeners also add large quantities of
chlorides.
Chloride conc. > 250 mg/L – noticeable taste
Domestic water should contain < 100 mg/L
chloride.
CHLORID
E
NITROGE
N
Indicates the presence of organic matter in it.
Appears in the following five forms:
1. Ammonia Nitrogen 2. Organic Nitrogen 3.
Albuminoid Nitrogen 4. Nitrites Nitrogen 5.
Nitrates Nitrogen

5. Major clases ;
a) Nitrates (NO3) -
b)Cyanides (CN)
c)Heavy metals constituents;
– arsenics (As), barium (Ba), cadmium (Cd),
chromium (Cr), lead (Pb), mercury (Hg), selenium (Se),
and silver (Ag)
- effects – cause poisons ( As and Cr 6+)
- chronic disease (Pb, Cd, and Hg)
There are over 120 toxic organic compounds listed
on U.S. Environmental Protection Agency’s Priority
Pollutant List.
Eg; pesticide, insecticides and solvents.
Effects may be acute @chronic.
TOXIC
INORGANIC
SUBSTANCE
S
(Davis and Cornwell, 2008)
Continue….
TOXIC
ORGANIC
SUBSTANCE
S

6. The most widely used parameter of organic pollution
5-day BOD – involved the measurement of the dissolved oxygen used by
microorganisms in the biochemical oxidation of organic
matter.
BOD test results are used to;
Determine the appropriate quantity of oxygen that will be required to
biologically stabilize the organic matter present.
Measure the efficiency of some treatment process
Determine the size of waste treatment facilities.
Determine compliance with wastewater discharge permits.
BOD at 20o
C for 5 days is used as standard test (measure after 5 days in
incubation at 20o
C).
Use bacteria to oxidize biodegradable organic in wastewater sample after
incubation.
BOD can be calculates by measuring DO before & after incubation.
Continue….
Biochemical Oxygen
Demand(BOD)

7. The limitations of the BOD5 test are as
follows:
 A high concentration of active, acclimated seed bacteria
is required.
 Pretreatment is needed when dealing with toxic wastes, and
the effects of nitrifying organisms must be reduced.
 Only the biodegradable organics are measured.
 The test does not have stoichiometric validity after the
soluble organic matter present in solution has been used.
 An arbitrary, long period of time is required to obtain
results.

8. To measure degree of oxidation/ degradation of organics using strong
chemical agent (dichromate in an acid solution).
measure the organic matter in industrial wastewater that contains compounds that
are toxic to biological life.
It oxidizes the reduced compounds in wastewater through a reaction with a mixture
of chromic and sulfuric acid at high temperatures.
Measure difference of amount of K2Cr2O7 before and after heating using ferrous
ammonium sulfate (FAS) as a reducing agent.
Higher than BOD (because more compounds can be chemically oxidized than
can be biologically oxidized)
Ratio BOD/COD varies (usually 1.5: 2 for industrial wastewater containing
biodegradable material (e.g. Food Industry).
For wastewaters with ratios higher than 3, it is assumed that some oxidizable
material in the sample is not biodegradable.
Nonbiodegradable material sometimes is called refractory and found mainly
in wastewater from chemical and pulp & paper industries.
Chemical Oxygen
Demand(COD)
OHCOCrHCrOHC cba 22
32
72 0)( ++⇒++ ++−
(+6) (+3)

9. Differences Between
Biochemical Oxygen Demand
and Chemical Oxygen
Demand(COD)BOD COD
Measures biodegradable
organics
Measures biodegradable
and non biodegradable
organics
Uses oxidizing
microorganism
Uses a strong chemical
agent
Affected by toxic substance Not affected
Affected by temperature Not affected
5 days incubation 3 hrs

10. To determine total organic carbon in an aqueous sample.
The test methods for TOC utilize heat & oxygen, ultraviolet radiation, chemical
oxidants, or some combination of these methods to convert organic carbon to
carbon dioxide which is measured with an infrared analyzer or by other means.
TOC can be used as a measure of its pollution characteristics and in some cases, it
has been possible to relate TOC to BOD and COD values.
Total Organic Carbon(TOC)
Determined based on ‘chemical formula’ of specific organic substances.
Consider ‘biochemical & nitrogenous oxygen’ demand
Theoretical Oxygen Demand
(ThOD)

11. ICROBIOLOGICAL CHARACTERISTICS
Water for drinking & cooking purposes must be made
FREE from disease-producing organisms
(pathogens)
DISEASE
-PRODUCING
ORGANISMS
(pathogens)
Disease-producing organisms (pathogens) – viruses,
bacteria, protozoa and helminths (worms).
Specific disease-producing organism presence in water
are not easily identify.
The techniques for comprehensive bacteriological
examination are COMPLEX and TIME
CONSUMING.
Eg ; Total Coliform Test
Some organism can cause disease in people
oroginate with the fecal discharge of infected individuals
@ animals.

12. RADIOLOGICAL CHARACTERISTICS
Cause by;
The development and use of atomic energy as a power source
The mining of radioactive materials
Naturally occur
It is necessary to establish limiting concentrations for the
intake into the body.
The effect of human exposure to radiation @ radioactive
materials are HARMFUL and any unnecessary exposure
should be avoided.
The amount of radiation to which the individual is normally
exposed varies with the amount of background radioactivity.
Water with high radioactivity is not normal