Practical-Characteristics of Waste Water

Waste Water Parameters
BS 8th Semester CEES

Characteristics
• The characteristics of wastewater can be classified
under following three heads:
• Physical Characteristics
• Chemical Characteristics
• Biological Characteristics
Physical Characteristics
 Color
 Odor
 Temperature
 Turbidity
Color
The color of the sewage indicates the freshness of sewage. If it’s color is greyish brown or
yellowish, it indicates fresh sewage. With passage of time, as putrefaction starts it begins to get
black. The color of stale and septic sewage is black ( When all the oxygen has disappeared from
sewage, it becomes septic). Other colors may also be formed due to presence of some specific
industrial waste. The color of the sewage can normally be detected by the naked eye.
Odor
The odor of a fresh sewage is not offensive or practically it can be considered odorless, but as it
starts to get stale, it begins to give offensive odor. Within 3 to 4 hours, all oxygen present in the
sewage gets exhausted and it starts emitting offensive odor (particularly, by hydrogen sulphide
gas which is formed due to anaerobic decomposition of sewage).
Temperature
• The temperature has an effect on the biological activity of bacteria present in the
sewage and it also affects the solubility of gases in sewage. It affects the viscosity of
sewage as well (more is the temperature, lesser is the viscosity of sewage).
• The normal temperature of sewage is slightly higher than the temperature of the water
supply because of the additional heat due to exothermal utilization of water. Also
when the wastewater flows in a closed pipes, its temperature further increases.
• The average temperature of sewage is about 20 0 C which is near about ideal

temperature of sewage for biological activities. At higher temperature coupled with
the lower dissolved oxygen activities can cause serious problems in disposal of waste
water.
Turbidity
• Sewage is normally turbid, representing dirty dish water or wastewater from baths
having other floating matter like fecal matter, pieces of paper, cigarette ends,
match sticks, greases, vegitable débris, fruit skins, soaps, etc..
• The turbidity depends on the quantity of solid matter present in suspension state.
• The turbidity can be determined by the turbidity rod or by turbidimeter.
Chemical characteristics of Waste Water
The Chemical Characteristics of sewage helps in indicating the stage of sewage decomposition, its
strength, and extent and type of treatment required for making it safe the chemical characteristics
of sewage includes.
 pH
 Alkalinity
 Dissolved Oxygen
 BOD
 Chemical oxygen demand (COD)
 Nitrogen compounds,
 Phosphorus,
 Solids
pH
• The pH value of sewage is the logarithm of reciprocal of hydrogen ion concentration

(pH= -log[H+]) present in the sewage. It is thus an indicator of the acidity or the
alkalinity of sewage. If the pH value is less than 7, the sewage is acidic and if the pH
vale is more than 7, the sewage is alkaline.
• The fresh sewage is alkaline, with passage of time pH tends to fall due to production of
acid by bacterial action in anaerobic or nitrification processes. However with treatment
of sewage the pH tends to rise.
• Determination of pH is important because efficiency of certain treatment methods

depends on it. Especially the biological treatment, for better result the pH of sewage
should be around 7.0 in biological treatment as microorganisms can flourish in that
pH range.
• pH can be determined using pH meter.

Dissolved oxygen
Dissolved oxygen refers to the level of free, non-compound oxygen present

in water or other liquids. It is an important parameter in assessing water
quality because of its influence on the organisms living within a body of
water.
• Its presence in untreated wastewater indicates that the waste water is
fresh.
• Similarly, its presence in treated wastewater effluent indicates that
the considerable oxidation has been accomplished during the
treatment stages.
• While discharging the treated wastewater into receiving waters, it
is essential to ensure that at least 4 mg/l of DO is present in it. If
DO is less, the aquatic animals like fish etc. are likely to be killed
near the vicinity of disposal. The presence of DO in wastewater is
also desirable because it prevents the formation of obnoxious
odour.
• DO determination also helps to find the efficiency of biological
treatment. DO content of sewage is determined by winklers method.
The actual quantity of DO is governed by following factors
• Solubility of Oxygen
• Temperature (DO decreases as temperature increases)
• Purity ( Salinity, suspended solids etc.) of water. DO
decreases as salinity increases.
Organic Matter
There are two types of organic matter

(i) Biodegradable or biologically active
(ii) Non biodegradable or biologically inactive
Organic matter is often assessed in terms of oxygen required to

complete oxidize the organic matter to CO2, H2O, and other
end products of Oxidation.
Biochemical Oxygen Demand
 BOD is defined as the amount of oxygen required by the
microorganisms (mostly bacteria) to carry out decomposition of
biodegradable organic matter under aerobic conditions.
 The greater the BOD in a particular water body, the lesser oxygen is available for
the aquatic life forms in that particular water body. Aquatic life forms would be
stressed, suffocate and ultimately die due to high BOD.
 Normally measured by a 5-d test conducted at 20oC.
 The BOD5 domestic waste is normally in the range of 100 to 300 mg/L.
 The sources of BOD are leaves, woody debris, topsoil, animal manure,
food-processing plants, wastewater treatment plants, feedlots, failing
septic systems, urban stormwater runoff, and effluents from pulp and
paper mills.
BOD5
• The polluted water will continue to absorb oxygen for many months, and it is not
practically feasible to determine the ultimate oxygen demand.
• Hence the 5 days period is generally chosen for the standard BOD test, during
which oxidation is about 60 to 70 % complete, while within 20 days period
oxidation is about 95 % to 99 % complete. A constant temperature of 20o C is
maintained during incubation.
• The BOD value of 5 Day incubation period is commonly written as BOD5 or simply
as BOD.
• Another reason for selecting 5 days as standard duration is to avoid interference of

nitrification bacteria. Nitrification starts after 6th or 7th day. Sanitary engineers
are generally interested in carbonaceous BOD only, so by selecting 5 days we
generally get only the carbonaceous BOD.
BOD5 Test
The sample is first diluted with a known volume of specially prepared dilution
water. Dilution water contains salts and nutrients necessary for biological
activity and phosphate as buffer to maintain pH around 7 to 7.5. The diluted
water is fully aerated. The initial D.O of the diluted sample is measured. The
diluted sample is then incubated for 5 days at 20o C. The D.O. of the diluted
sample after the incubation period is found out. The difference between the
initial D.O. of the diluted sample after the incubation period is found out. The
difference between the initial D.O value and the final D.O. value will indicate
the oxygen consumed by the sewage sample in aerobic decomposition in 5
days. The BOD in mg/lit or ppm is then calculated by using the equation:
Limitation of BOD Test
Following are the imitation of BOD Test:

• It measures only the biodegradable organic matter.
• Time duration of the test is very long i.e. 5 days, so if quick results are
needed it is not useful.
• Pretreatment is needed if the sample contains toxic waste.
• Nitrifying bacteria can cause interferences and could give higher results.
• It is essential, to have high concentration of active bacteria present in the
sample.
Chemical Oxygen Demand
 It is a measure of the capacity of water to consume oxygen during
the decomposition of organic matter and the oxidation of
inorganic chemicals such as Ammonia and nitrite.
 Measuring Principle: Chemical oxygen demand is measured by
incubating a water sample with a strong chemical oxidant under
specific conditions of temperature and for a particular period of
time. A commonly used oxidant is potassium dichromate
(K2Cr2O7) which is used in combination with boiling sulfuric
acid (H2SO4). This procedure gives combined oxygen demand of
organic as well as inorganic chemicals
Alkalinity
 This is a measure of the wastewater’s capability to neutralize acids

 It is measured in terms of bicarbonate, carbonate, and hydroxide alkalinity
 Alkalinity is essential to buffer (hold the neutral pH) of the wastewater
during the biological treatment processes
Dissolved Gases
 These are gases that are dissolved in wastewater.

 The specific gases and normal concentrations are based upon the
composition of the wastewater.
 Typically industrial wastewater contains oxygen in relatively low
concentration, and usually carbon dioxide, methane and hydrogen
sulfide are also present (if septic conditions exist)
Biological Characteristics
The sewage contains many microorganisms like bacteria, algae,

fungi, protozoa, etc. bacteria being the most predominant.
Most of the bacteria found in the sewage are harmless non

pathogenic bacteria. They are helpful in oxidation and
decomposition of sewage.
A little no. of bacteria, however, are disease producing pathogens,

which are the real danger to the health of the public.

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Waste Water Parameters

BS 8th Semester CEES

• The average temperature of sewage is about 20 0 C which is near about ideal

• The pH value of sewage is the logarithm of reciprocal of hydrogen ion concentration

• Determination of pH is important because efficiency of certain treatment methods

• pH can be determined using pH meter.

Dissolved oxygen refers to the level of free, non-compound oxygen present

There are two types of organic matter

Organic matter is often assessed in terms of oxygen required to

• Another reason for selecting 5 days as standard duration is to avoid interference of

Following are the imitation of BOD Test:

 This is a measure of the wastewater’s capability to neutralize acids

 These are gases that are dissolved in wastewater.

The sewage contains many microorganisms like bacteria, algae,

Most of the bacteria found in the sewage are harmless non

A little no. of bacteria, however, are disease producing pathogens,

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