Water and waste water engineering

2. Biological Unit Process
It makes use of microbes for removal of mainly dissolved
matter from waste water.
Aerobic biological unit process: The treatment which is carried
out by microorganism in the presence of oxygen.
Anaerobic biological unit process: The treatment which is carried
out by aerobes in the absence of oxygen
Biological Unit Process
Aerobic Biological Unit process Anaerobic Biological Unit process

3. Aerobic Biological Unit process
Trickling Filtration Activated Sludge Process Aerobic Stabilization
Pond
Lagoons
Anaerobic Biological Unit process
Suspended Growth Process Attached Growth Process
Trickling FilterSludge Digestion Plant

4. Trickling Filter in Waste Water Treatment
Plant
GC PST TF SST DU
SDT
S
SDB
From outfall sewer
Sludge flow
Digested sludge
Disposal
Supernatant Recycled

5. S = Screen Chamber
GC = Grit Chamber
PST = Primary Sedimentation Tank
TF = Trickling Filter
DU = Disinfection Unit
SST = Secondary Sedimentation Tank
SDB = Sludge Drying Beds
SDT = Sludge Digestion tank

6. Trickling Filter
It consists of a fixed bed of rocks, stone or gravel over which waste
water flows downward and causes a layer of microbial slime to grow,
covering the bed of media.

7. Activated Sludge Plant

8. Activated Sludge Process
• Process for treating sewage using aeration and a
biological floc composed of bacteria and protozoa.
• An aeration tank where air (oxygen) is injected in the
mixed liquor. This is followed by a settling tank
(usually referred to as "final clarifier" or "secondary
settling tank") to allow the biological flocs (the sludge
blanket) to settle, thus separating the biological sludge
from the clear treated water.

9. Difference between Trickling filter &
Activated Sludge Plant
No Trickling filter Activated Sludge Plant
1. Bacteria grow on surface of
stone medium
Bacteria grow on surface of
suspension condition
2. It may remove BOD5 of 70 to
80%
It may remove BOD5 of 90%
3. Initial Cost is Higher Initial Cost is Less
4. No Skill supervision required Skill supervision required
5. It is attached growth system It is suspended growth system
6. Discharge is very large Discharge is very small
7. No sludge Bulking Problem Sludge Bulking Problem Arise

10. Aerobic Stabilization Pond
Designed and built for waste water treatment to reduce the organic content and
remove pathogens from water. They are man-made depressions confined by earthen
structures.

11. Design criteria of oxidation ponds
1. Dimensions Length of Tank = 2 times width
Depth of Tank = 1 to 1.5 m
2. Detention Period = 20 to 30days
3. Area of each unit = 0.5 to 10hectare
4. Free Board = 1m

12. Aerobic Stabilization Lagoons
• Similar to Oxidation pond
• Lagoon is a water body that is
formed near coastal areas.
• It is shallow and has a small link with
sea or the ocean though it is also
separated from the ocean water with
reefs or a low sandbank.

13. Sludge Digestion Plant

14. Sludge Digestion Bed

15. Thank You
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