Water Pollution and Control
Sources and Characteristics of Chemical Industrial wastewater:
Sources
of Waste Water:
Wastewater from the chemical industry can come from many sources,
including:
Manufacturing: The production of organic chemicals,
plastics, synthetic materials, and other chemicals
Petrochemicals: The production of petrochemicals,
such as polymers for plastics and synthetic fibers
Inorganic chemicals: The production
of inorganic chemicals, such as acids and alkalis
Agricultural chemicals: The
production of agricultural chemicals, such as fertilizers, pesticides, and
herbicides
Industrial wastewater can contain a variety of contaminants, including:
·
Organic and inorganic matter: Toxic and
hazardous substances, dyes, and metal ions
·
Impurities: Dissolved contaminants such as
salts and light liquids like oils
·
Interfering substances: Grease,
clay, or sand
·
Pollutants: Microplastics, residues of
pharmaceuticals and detergents, viruses, bacteria, fungi, poisons, and heavy
metals.
Wastewater in the
chemical industry has many characteristics, including physical, chemical, and
biological characteristics:
·
Physical characteristics
Include
temperature, solids, color, odor, and turbidity:
Temperature: Higher
temperatures speed up reaction rates, which can improve the removal of
contaminants.
Solids: Total
suspended solids (TSS) and total dissolved solids (TDS) affect turbidity.
Color: Fresh
sewage is usually brown or yellowish, but over time it can turn black.
Odor: Wastewater
with sewage usually has a strong odor.
Turbidity: Wastewater
has higher turbidity due to suspended solids.
·
Chemical characteristics
Include pH, alkalinity, nitrogen, phosphorus, and
other chemical impurities:
Chemical oxygen demand (COD): A
common method to measure organic content
Total organic carbon (TOC): A
common method to measure organic content
Chlorides, sulfates, and heavy metals: Chemical
impurities in wastewater
·
Biological characteristics
Include organisms
like bacteria, algae, protozoa, and viruses:
Biochemical
oxygen demand (BOD): A common method to measure organic
content
Microbial
population: A biological characteristic of
wastewater
·
Turbidity
Turbidity is a measure of how clear water is, or how many particles
are suspended in it. Turbidity is a
measurement of how much light is scattered or blocked by particles in
water. When water has high turbidity, it appears cloudy or muddy because
the particles absorb and scatter light rays.
Turbidity can be
caused by many things, including:
Natural events: Heavy
rains, snowmelt, windstorms, and erosion can wash soil, fertilizers, and other
materials into waterways.
Human activities: Logging,
mining, agriculture, dredging, and untreated wastewater can all increase
turbidity levels.
Turbidity is
measured using turbidity sensors attached to current meters, or by satellite
imagery.
Standards
The World Health
Organization recommends that drinking water have a turbidity of no more than 5 NTU
·
pH
The pH of water measures how acidic or basic it is, and is an important
indicator of water quality:
The pH scale ranges from 0 to 14, with 7 being
neutral. A pH less than 7 indicates acidity, while a pH greater than 7
indicates a base.
Pure water: Pure water has a pH of 7, which is neutral.
Tap water: Tap water typically has a pH between 6.5 and 8.5.
Other common liquids: The pH of some common liquids includes:
Wine: 2.3–3.8
Beer: 4.0–5.0
Milk: 6.3–6.6
Seawater: 8.3
You can measure pH with a strip of litmus paper,
which changes color depending on whether the substance is acidic or
basic: Red: Acidic Blue: Basic
The Environmental Protection Agency (EPA) says that the safe pH
range for drinking water is 6.5–8.5. Water with a pH outside of this
range is not recommended for drinking.
·
Total Suspended solids
Total suspended solids (TSS) are solid particles in water that are
too large to settle and are suspended in the water. TSS can be organic or
inorganic in origin and can range in size from a few microns to being visible
to the naked eye.
TSS is a key parameter in water quality assessment and environmental
monitoring. It can impact water quality in the following ways:
·
Turbidity: TSS can make water cloudy,
which reduces the amount of sunlight that reaches plants and algae. This
can reduce the amount of oxygen produced and photosynthesis activity, which can
lead to low-oxygen conditions and dead zones.
·
Aquatic life: TSS can harm aquatic life in
several ways:
o
Toxic compounds: Solid particles can contain
toxic compounds.
o
Clogged gills: Soil and silt in the water can
clog fish gills.
o Bury fish eggs: When TSS
settles at the bottom of a body of water, it can bury fish eggs and nursery
areas.
·
Wastewater pollution: TSS is a
major cause of wastewater pollution.
TSS is measured in milligrams per
liter (mg/l). The amount of TSS can vary depending on the source of the
water and any treatments it has undergone.
TSS can be calculated using the
equation:
TSS (mg/L) = (A – B)/C,
Where, A is the final dried weight of
the filter in mg
B is the initial dried weight of
the filter in mg
C is the volume of water filtered
in L.
·
Total solids:
Total solids (TS)
in water is the sum of the total suspended solids (TSS) and total
dissolved solids (TDS).
Total solids are
the amount of foreign matter in water that remains after evaporation and drying
at a specific temperature. The solids in water can be volatile (organic)
or non-volatile (inorganic or fixed).
Suspended solids
These are
particles that are not chemically bonded to water molecules and do not pass
through a 2-micron filter. Examples include silt, clay, plankton, algae,
and fine organic debris.
Dissolved solids
These are
particles that are chemically bonded to water molecules and pass through a
2-micron filter. Examples include calcium, chlorides, nitrate, phosphorus,
iron, and sulfur.
Water clarity
High levels of total
solids can make water less clear, which reduces the amount of sunlight that can
penetrate the water.
Aquatic organisms
The balance of
dissolved solids in water is important for the health of aquatic
organisms. Too many dissolved salts can dehydrate organisms, while too few
can limit their growth.
Drinking water
Drinking water
typically has a TDS below 500 parts per
million (ppm).
·
Biological Oxygen Demand (BOD)
Biochemical oxygen
demand (BOD) is a measure of how much oxygen is needed to break down organic
matter in water. It's an important indicator of water quality and is used
to assess the degree of organic pollution in water.
BOD
is measured by incubating a water sample in the dark at 20°C for five
days. The difference in dissolved oxygen between the beginning and end of
the incubation period is used to calculate the BOD.
A
higher BOD means that oxygen is depleted more quickly in the water, which can
stress, suffocate, and kill aquatic organisms.
BOD is used in
wastewater treatment plants to measure waste loads, the effectiveness of BOD
removal, and the concentration of effluent discharged into water bodies.
Unpolluted natural waters should have a BOD of
5 mg/L or less. Raw sewage may have BOD levels ranging from
150–300 mg/L.
Calculation of BOD:
The formula to calculate
biochemical oxygen demand (BOD) is:
BOD= (DO1−DO2) * Dilution Factor / Volume of Sample
Where, DO1
is the dissolved oxygen (DO) measurement at the beginning of the test
DO2 is
the DO measurement after a 5 day period at 68°F (20°C).
The BOD value is reported in
milligrams per liter (mg/L).
BOD is a measure of how much oxygen
microorganisms consume in water bodies. It's an important parameter for assessing
water quality and is used in wastewater treatment plants to measure waste loads
and treatment efficiency
Example
A
15 ml water sample is diluted to 300 ml with nutrient solution and incubated in
the dark for five days at 20 OC. The initial dissolved oxygen
concentration is 9.05 mg/l and the final concentration is 4.25 mg/l. The blank
for the dilution water decreased in dissolved oxygen
concentration from 9.05 mg/l to 8.80 mg/l. Estiamte BOD 5
The formula to calculate biochemical oxygen demand (BOD) is:
BOD= (DO1−DO2) * Dilution Factor / Volume of Sample
DO1
is oxygen dissolved in sample = (9.05-4.25) mg/l
= 4.80 mg/l
DO2
is oxygen dissolved in Blank= (9.05 -8.80) mg/l
= 0.25 mg/l
Dilution
factor= 300
Volume
of sample= 15
BOD
= (4.80-0.25) * 300/15
= 91 mg/l
·
Chemical Oxygen Demand (COD):
Chemical Oxygen Demand (COD)
is a measure of the amount of oxygen required to oxidize organic and
inorganic compounds in water. It's used to assess water quality and the
amount of organic pollutants in a water body.
A water sample is
oxidized with a strong oxidizing agent, like potassium dichromate (K2Cr2O7), in
the presence of a strong acid. The amount of oxidizing agent consumed is
then measured, which reflects the COD of the water sample.
COD can indicate
the presence of all forms of organic matter, both biodegradable and
nonbiodegradable. High COD levels can be caused by things like solid
waste, soluble organic compounds, and emulsified oils.
COD is used to
monitor water treatment plant efficiency, identify pollution sources, and
more. It's also used in wastewater management to reduce COD levels.
The
USPH recommends a maximum COD content of 4.0 mg/L for drinkable water, while
the World Health Organization recommends a COD content of 10 mg/L.
Chemical oxygen demand (COD) is calculated using a laboratory assay that
measures the amount of organic matter in a water sample. The COD can be
calculated using the following formulas:
COD = (C/FW)·(RMO)·32
This formula estimates the COD from the
concentration of oxidizable compounds in the sample.
COD (mg/l) = (a-b)(N) x 8,000 /
sample size (ml)
This formula uses the amount of Fe(NH4)2(SO4)2 used
for the blank and sample, the normality of the titrant, and the sample
size.
COD, mg/L = (B-A)N x 8000/
sample volume, mL
This formula uses
the volumes of FAS used in titrating the blank and sample, and the normality of
FAS.
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