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- 1. Lecture No 3 Industrial waste water
- 2. Wastewater is water whose physical, chemical or biological
properties have been changed as a result of the introduction of
certain substances which render it unsafe for some purposes such as
drinking. Wastewater treatment is the process and technology that
is used to remove most of the contaminants that are found in
wastewater to ensure a sound environment and good public
health.
- 3. Objectives of wastewater treatment Reduction of
biodegradable organic substances in the environment: organic
substances such as carbon, nitrogen, phosphorus, sulphur in organic
matter needs to be broken down by oxidation into gases which is
either released or remains in solution. Reduction of nutrient
concentration in the environment: Elimination of pathogens
Recycling and Reuse of water
- 4. Definition of concepts and terminology Stormwater Runoff is
water from streets, open yard etc after a rainfall event which run
through drains or sewers. Industrial wastewater is liquid waste
from industrial establishments such as factories, production units
etc. Domestic wastewater also known as municipal wastewater is
basically wastewater from residences (homes), business buildings
(e.g. hotels) and institutions (e.g. university). It can be
categorized into grey water and black water. Grey water also known
as sullage is liquid waste from washrooms, laundries, kitchens
which does not contain human or animal excreta. Black water is
wastewater generated in toilets. Black water may also contain some
flush water besides urine and faeces (excreta). Urine and faeces
together is sometimes referred to as night soil.
- 5. Sewage is the term used for black water if it ends up in a
sewerage system. Septage is the term used for black water if it
ends up in a septic tank. Sewerage system is the arrangement of
pipes laid for conveying sewage. Influent is wastewater which is
yet to enter in a wastewater treatment plant or liquid waste that
is yet to undergo a unit process or operation. Effluent is the
liquid stream which is discharged from a wastewater treatment plant
or discharge from a unit process or operation. Sludge is the
semi-solid slurry from a wastewater treatment plant.
- 6. On-Site System: this is wastewater disposal method which
takes place at the point of waste production like within individual
houses without transportation. On- site methods include dry methods
(pit latrines, composting toilets), water saving methods (pourflush
latrine and aqua privy with soakage pits and methods with high
water rise (flush toilet with septic tanks and soakage pit, which
are not emptied). Off-Site System:, wastewater is transported to a
place either than the point ofproduction. Off- site methods are
bucket latrines, pour-flush toilets with vault and tanker removal
and conventional sewerage system. Conventional sewerage systems can
be combined sewers (where wastewater is carried with storm
- 7. Septic Tank is an on-site system designed to hold black
water for sufficiently long period to allow sedimentation. It is
usually a water tight single storey tank. Faecal sludge refers to
all sludge collected and transported from on-site sanitation
systems by vacuum trucks for disposal or treatment. Unit Operation:
this involves removal of contaminants by physical forces. Unit
Process: this involves biological and/or chemical removal of
contaminants. Wastewater Treatment Plant is a plant with a series
of designed unit operations and processes that aims at reducing
certain constituents of wastewater to
- 8. Characteristics of wastewater Physical Electrical
Conductivity (EC) indicates the salt content Total Dissolved Solids
(TDS) comprise inorganic salts and small amounts of organic matter
dissolved in water Suspended solids (SS) comprises solid particles
suspended (but not dissolved)in water
- 9. Chemical Dissolved Oxygen (DO) indicates the amount of
oxygen in water Biochemical oxygen demand (BOD) indicates the
amount of oxygen required by aerobic microorganisms to decompose
the organic matter in a sample of water in a defined time period.
Chemical oxygen demand (COD) indicates the oxygen equivalent of the
organic matter content of a sample that is susceptible to oxidation
by a strong chemical oxidant Total Organic Compound (TOC) NH4-N and
NO3-N show dissolved nitrogen (Ammonium and Nitrate, respectively).
Total Kjeldhal Nitrogen is a measurement of organically-bound
ammonia nitrogen. Total-P reflects the amount of all forms of
- 10. Biological Total coliforms (TC) is encompassing faecal
coliforms as well as common soil microorganisms, and is a broad
indicator of possible water contamination. Faecal coliforms (FC) is
an indicator of water contamination with faecal matter. The common
lead indicator is the bacteria Escherichia coli or E. coli.
Helminth analysis looks for worm eggs in the water
- 11. Process of wastewater treatment Physical unit operations
Screening Comminution Flow equalization Sedimentation Flotation
Granular-medium filtration Chemical unit operations Chemical
precipitation Adsorption Disinfection Dechlorination
- 12. Biological unit operations Activated sludge process Aerated
lagoon Trickling filters Rotating biological contactors Pond
stabilization Anaerobic digestion
- 13. Levels of wastewater treatment Pre-treatment Preliminary
treatment Primary treatment Secondary treatment Sludge (biosolids)
disposal
- 14. Pre-treatment Occurs in business or industry prior to
discharge Prevention of toxic chemicals or excess nutrients being
discharged in wastewater Pretreatment removes the large solids
(such as rags and sticks) that are carried in with the wastewater.
These are removed by screens consisting of metal bars spaced at 19
mm intervals which are placed across the influent channels. Tines
(metal combs) rake the collected matter off these, and heavy
objects such as rocks (which would otherwise damage the
equipment)
- 15. Physical Screening is removal of coarse solids by use of a
straining device. Sedimentation is gravity settling of pollutants
out of the wastewater. Flotation is the use of small gas bubbles
injected into the wastewater which causes pollutant particles in
the wastewater to rise to the surface for subsequent removal. Air
stripping is removal of volatile and semi- volatile organic
compounds from wastewater by use of air flow.
- 16. Preliminary treatment
- 17. Bar Screen - catches large objects that have gotten into
sewer system such as bricks, bottles, pieces of wood, etc
- 18. Bar racks, often the first treatment devices to be
encountered by wastewaters en route to renovation, protect pumps
and other equipment from damage. These devices remove objects such
as pieces of product or raw material, broken or dropped items of
maintenance equipment, gloves, plastic wrapper material, or other
foreign objects that inadvertently gain access to the industrys
system of drains and sewers
- 19. Grit Chamber - removes rocks, gravel, broken glass, etc.
Mesh Screen - removes diapers, combs, towels, plastic bags,
syringes, etc.
- 20. Chemical Neutralization is adjustment of alkalinity and
acidity to the same concentration (pH 7). Precipitation (ppt) is
addition of chemicals to wastewater to change the chemical
composition of pollutants so that the newly formed compounds settle
out during sedimentation. Coagulation is use of chemicals to cause
pollutants to agglomerate and subsequently settle out during
sedimentation. Adsorption is use of a chemical which causes certain
pollutants to adhere to the surface of that chemical. Disinfection
is use of a chemical (or other method such as ultraviolet
radiation) to selectively destroy disease-causing organisms.
(Sterilization is the destruction of all organisms.) Breakpoint
chlorination is the addition of chlorine to the level that
chloramines will be oxidized to nitrous oxide and nitrogen, and
chlorine will be reduced to chloride ions.
- 21. Wastewater treatmens
- 22. Primary Treatment a physical process Wastewater flow is
slowed down. The water is left to stand so that solids can sink to
the bottom and oil and grease can rise to the surface. The solids
are scraped off the bottom and the scum is washed off with water
jets. and the suspended solids settle to the bottom by gravity and
is called sludge or biosolids.
- 23. Firstly the wastewater is aerated by air pumped through
perforated pipes near the floor of the tanks. This aeration makes
the water less dense, causing the grit to settle out. As the air
jets are positioned such that the water is swirling as it moves
down the tanks the suspended solids are prevented from settling
out. The air also provides dissolved oxygen for the bacteria to use
later in the process, but the wastewater is not in these tanks long
enough for bacterial action to occur here. The grit is collected in
hoppers and washed, after which it is used for on site land
reclamation and landscaping.
- 24. Sedimentation The water then flows slowly and smoothly
through the sedimentation tanks, where the suspended solids fall to
the bottom and scum rises to the surface, while clarified effluent
passes on. The solids are removed from the bottom of the tanks by
scrapers, and scum is washed off with water jets. The scum and
solids are brought to a common collection point where they are
combined to form 'sludge' and sent off for secondary
treatment.
- 25. Sludge from the primary sedimentation tanks is pumped to
the sludge thickener. - more settling occurs to concentrate the
sludge prior to disposal Primary treatment reduces the suspended
solids and the B.O.D. of the wastewater. From the primary treatment
tanks water is pumped to the trickling filter for secondary
treatment. Secondary treatment will further reduce the suspended
solids and B.O.D. of the wastewater
- 26. Primary treatment
- 27. Secondary Treatment After secondary treatment all effluent,
both solid and liquid, is sufficiently safe to be released into the
environment.
- 28. Secondary treatment Secondary treatment is a biological
process Biological Methods of Wastewater Treatment Biological
treatment of industrial wastewater is a process whereby organic
substances are used as food by bacteria and other microorganisms.
Almost any organic substance can be used as food by one or more
species of bacteria, fungi, cilliates, rotifers, or other
microorganism.
- 29. It requires control of: Temperature moisture pH level of
aeration inhibitors such as metals nutrients Biological treatment
processes must be conducted within the correct temperature range,
with an appropriate moisture level and acidity or alkalinity, and
with the right level of aeration. Temperature limits for the
appropriate bacteria to live, the temperature must be within the
appropriate range. These are usually referred to as mesophilic
(30-40oC) and thermophilic (45-55oC) ranges. Minimum moisture is
always necessary, but other influences, such as aeration, influence
the level of moisture needed. For wastewater treatment, which is
the most common application for biological treatment, minimum
moisture levels are not a concern.
- 30. The capability of the different microbial species to break
down organic wastes depends to a large extent on the pH of the
medium. Methanogens operate between pH 6 and pH 8. When there is a
risk of changes to the acidity, it is advisable to regularly
measure and control the pH. Aerobic processes can only take place
in presence of free oxygen, generally oxygen from the air. For
anaerobic breakdown, oxygen is an inhibitor. The most well-known
bacteria inhibited by oxygen is the pathogenic agent of tetanus,
hence the reason why wounds must always be aerated. Biological
processes can be adversely affected by the presence of inhibitors
such as metals (copper, silver) or chemicals such as pesticides
which may be
- 31. Solids Sludge Solids Sludge from the sedimentation tanks is
digested anaerobically in large tanks, and then further digested in
lagoons before being dried in dewatering beds. In the sludge
digesters the sludge is kept at 37oC and mechanically mixed to
ensure optimum operation. During this time the organic compounds
within the sludge are converted to carboxylic acids and then
finally to methane and carbon dioxide. This gaseous mix is known as
"biogas", and is a valuable source of fuel.
- 32. From secondary treatment on the trickling filter water
flows to the final clarifiers for further removal of sludge. The
final clarifiers are another set of primary sedimentation tanks.
From the final clarifiers the water is discharged back to the
River.