This document discusses primary and secondary wastewater treatment processes. It begins by explaining that wastewater treatment involves applying technology to improve water quality by removing solids and contaminants. The primary goals of treatment are to protect public health, improve the environment, and allow for water reuse. The document then describes the steps of primary treatment, which uses physical processes like screening, comminution, grit removal, and sedimentation to remove 40-60% of suspended solids over 2-3 hours. Secondary treatment uses biological processes to further break down remaining organic matter.

1. Presentation
on
Wastewater Treatment
(Primary Treatment & Secondary Treatment)

2. Overview
Wastewater Treatment
Why Wastewater Treatment?
Treatment process
Primary Treatment
Secondary Treatment

3. Wastewater Treatment
 Wastewater treatment consists of applying known technology to
improve or upgrade the quality of a wastewater.
 A process to remove dissolved suspended solid and various
contaminants from water.
 A process that produce an environmentally safe fluid waste stream and
solid waste suitable for disposal or reuse.

4. Why Wastewater treatment?
 To protect the public health, because harmful bacteria are exists in
wastewater that are the causes various diseases.
 To improve environmental quality by removing toxic chemicals
including all solids, plant nutrients, pathogenic microorganisms, odor
and odorous compounds and so on.
 To remove pollutants from wastewater for its recycling.
 To promote recreation and quality of life.
 To preserve aquatic life and wildlife habitat

5. Wastewater Treatment Methods
 Physical process
 No gross chemical or biological changes are carried out and strictly
physical phenomena are used to improve or treat the wastewater.
 Physical wastewater treatment method includes Sedimentation,
Screening, Aeration, Filtration, Floating and Skimming, Degasification,
Equalization etc.
 Chemical process
 Chemical treatment consists of using some chemical reaction or
reactions to improve the water quality.
 Utilizes the chemical properties of the impurities or reagents.

6. Wastewater Treatment Methods (cont’d)
 Chemical wastewater includes Chlorination, Ozonation, Neutralization,
Coagulation, Adsorption, Ion Exchange etc.
Biological process
 Biological treatment methods use microorganisms, mostly bacteria, in the
biochemical decomposition of wastewaters to stable end products.
 Aerobic biological treatment includes Activated sludge treatment
method, Trickling Filtration, Oxidation ponds, Lagoons, Aerobic digestion
etc.
 Anaerobic biological treatment includes Anaerobic Digestion, Septic
tanks, Lagoons etc.

7. Wastewater Treatment Process
According to the water quality to produced, treatment process are
classified into four groups
 Preliminary treatment
 Primary treatment
 Secondary treatment
 Tertiary or advanced treatment

8. Wastewater Treatment Process (cont’d)

9. Primary Treatment
 Primary treatment is designed to remove organic and inorganic solids by the
physical processes of sedimentation and flotation.
 Primary treatment devices reduce the velocity and disperse the flow of
wastewater.
 In primary treatment basically removes identifiable suspended solid and
floating matter and about 40-60% suspended solid are removed from the waste
water stream.
 The solids that remain in suspension as well as dissolved solids will usually be
biochemically treated in subsequent processes for physical separation and
removal in the final (secondary) settling tanks.

10. Primary Treatment (cont’d)
 The detention time for most particles to settle out in primary treatment is
about 2-3 hours.
 Steps involved in primary wastewater treatment
 Removal of larger objects through bar screens
 Comminuting by grinders, cutters, shredders
 Removal of grit
 Sedimentation of rest of the objects

11. Screenings
 To remove large floating materials such as rags, plastic bottles etc. by bar screens or
racks which are made of long, narrow metal bars spaced about 25mm apart.
 There are three different types of screens that may be used, trash racks, manually
cleaned racks, and mechanically cleaned racks.
 Trash racks have the largest openings, 40 to 150 mm, and are used to remove the
largest objects from entering the plant.
 Manually cleaned racks have smaller openings, 25 to 50 mm, and are not often
used, except infrequently used bypass channels.
 Mechanically cleaned racks are have the smallest openings, 1 to 40 mm, so are
obviously used to collect smaller material.
 Two channels of bar screens are always available, allowing for one to undergo
maintenance while the plant is still in operation.

12. Screenings (cont’d)

13. Comminuting
 Removes gritty materials such as sand, gravels, coffee grounds, eggshells,
cinders, pebbles etc. to protect pumps from abrasion and to reduce the
formation of heavy deposits in pipes and channels.
 In the sewer the velocity in not less than 2 ft per second.
 Gritty materials can be settled out of the flow due to gravity if the velocity is
reduced to 1 ft/s, however more lighter suspended solid can not be removed
by this process

14. Grit Removal
 Removes gritty materials such as sand, gravels, coffee grounds, eggshells,
cinders, pebbles etc. to protect pumps from abrasion and to reduce the
formation of heavy deposits in pipes and channels.
 In the sewer the velocity in not less than 2 ft per second.
 Gritty materials can be settled out of the flow due to gravity if the velocity is
reduced to 1 ft/s, however more lighter suspended solid can not be removed
by this process

15. Sedimentation
 Last step of the primary treatment.
 Objective is to produce a liquid effluent of suitably improved quality for the
next stage.
 Rest of the suspended materials are removed using gravity in
large sedimentation tanks (also called clarifying tanks).
 Reduction in BOD and in the amount of waste activated sledges in the activated
sludge plant.
 Wastewater is allowed to settle for about 2 hours in the settling tank and the
settle able solids are removed by gravitation settling under quiescent.

16. Sedimentation (cont’d)
After screening
and gilt removal
the effluent goes to
the sedimentation
tank.
The sludge formed at
the bottom of the tank
is removed either by
vacuum suction or by
racking it to discharge
point at the bottom of
the tank for withdrawn
The clear liquid
produced is called
overflow which
should not contain
any readily settle
able matter.