v-4-SST-sludge digestion, drying beds- disposal.ppt

waste water

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Micro Planning of Class hours
Alpha Breathing
Recap
Evocation
General Objectives
Specific Objective (1, 2 & 3)
Formative Evaluation I
Specific Objective (4 & 5)
Formative Evaluation II
Discussion
Mind Map
Summary
Stimulating Questions
Attendance

2. Alpha Breathing : (2 Minutes)
The three steps for alpha breathing are
•Breathe in
•Breathe out
•Hold
(Repeat the three steps for 8 times)

3. RECAP

4. Evocation (2 Minutes)

5. Sludge digester

6. Pre requisite Knowledge
•Secondary treatment

7. General Objective: (2 Mins)
Students will able to understand the definition of sludge
digester, construction, operation details of sludge
digester.

8. Specific Objectives:  
Students will able to
1.Define secondary clarifiers (T)
2.Define disinfection of wastewater (E)
3.List the two types of digestion process (E)
4.Explain construction and operation details of anaerobic
sludge digester (T)
5. List the factors affecting sludge digestion process

9. SO1: Define secondary clarifiers or SST
Sedimentation tanks called "secondary clarifiers"
remove flocs of biological growth created in some
methods of secondary treatment
 including 
activated
sludge,
 trickling filters and rotating biological
contactors.
Separates MLSS from aeration tank.
To obtain a very clear and stable effluent having low
concentration of BOD and SS.
Rectangular or circular in shape

10. SO2 : Define disinfection of wastewater
Disinfection normally involves the injection of a chlorine solution
at the head end of a chlorine contact basin.
The chlorine dosage depends upon the strength of the wastewater
and other factors, but dosages of 5 to 15 mg/l are common.
Ozone and ultra violet (uv) radiation can also be used for
disinfection but these methods of disinfection are not in common
use.

11. Chlorine contact basins - rectangular channels, with
baffles to prevent short-circuiting,
 Contact time - 30 minutes.
To meet advanced wastewater treatment requirements,
a chlorine contact time of as long as 120 minutes is
sometimes required for specific irrigation uses of
reclaimed wastewater.
The bactericidal effects of chlorine and other
disinfectants are dependent upon pH, contact time,
organic content and effluent temperature.

12. SO 3: List the two types of digestion
Types
•Anaerobic digestion
•Aerobic digestion (for small treatment plants)

13. SO 4: Explain construction and operation details of anaerobic sludge digester
•Circular RCC tank with hopper bottom and having fixed
or floating type of roof over its top
•Raw sl., is pumped into the tank & when the tank is first
put into operation, it is seeded with the digested sl., from
another tanks.
•Screw pump or power driven mechanical device used to
circulating the sl., from bottom to top.
•In cold countries, the tank may be provided with heating
coils thr., which hot water is circulated in order that the
temp., inside the tank is maintained at optimum digestion
temp., level

14. •Gas (CH
4, CO
2) are collected in gas holders
•DS is settled in the hoppered bottom of the tank is
removed under hydrostatic pressure, periodically once in
week.
•Supernatant liquor lying between the sl., and scum is
removed by suitable pipe provided in the middle part of the
tank.
•Supernatant liquor have higher BOD & suspended solids is
sent back for treatment along with raw sewage in the
treatment plant

16. Sl., from sedimentation tank contains a lot of putrescible org., matter
and if disposed of without t/m, the org., matter may decompose,
producing foul gases & lot of nuisance, pollution & health
hazards.
The process of stabilization of sl., is called SD, and tank where the
process is carried out is called SDT
Sludge digestion process
Sludge gets broken into
• Digested sludge
• Supernatant liquor
• Gases of decomposition

17. Digested sludge
Stable humus like solid matter
Tary black in colour
Reduce moisture content, volume (0.33 times UDS)
FF pathogen, still it have cysts, eggs of bact., protozoa, worms
Supernatant liquor
Liquified & finely divide solid matter, High BOD (3000ppm)
Gases of decomposition
CH
4
- 65-70%, CO
2
- 30% (fuel) other gases Nitrogen, H
2
S

18. Three stages of anaerobic sludge digestion process.
Step 1: Hydrolysis
Step 2: Acidogenesis
Step 3: Methanogenesis

19. Step 1: Hydrolysis or acid fermentation
•I
st
Stage
•Fresh sewage sl., begins to be acted upon by anaerobic and facultative bact.,
called acid formers.
•These organism solubilize the or., solids thr., hydrolysis.
•Soluble products are then fermented to volatile acids & or., alcohols
of lower molecular compounds like propionic acid, acetic acid
•Gases CH
4, CO
2 H
2S are also evolved
•Sl highly acidic, lower pH valve <6
•15 days 21
0
C

20. Step 2: Acidogenesis or acid regression
Intermediate stage
Volatile acids & nitrogenous compounds are attacked by
the bact., form acid carbonates & ammonia compounds
Small amount of H
2S, CO
2
Decomposed sl., give offensive odour, pH 6.8
3 months 21
0
C

21. Step 3: Methanogenesis or Alkaline fermentation
Final stage
More resistant materials like proteins & org., acids are attacked
and broken up by anaerobic bact., called methane formers into
simple substance like ammonia, Org., acids & gases
During this stage liquid separate from solids & DS formed
Stage is granular & stable and does not give offensive odour
DS collected at the bottom called ripened sl.,
DS is alkaline, pH >7
1 month 21
0
C

22. Overall time 4.5 month, 21
0
C
Most widely used method.
Decomposition and stabilization of organic and
inorganic content of the sludge.
Carried out in the absence of oxygen.
Organic matter in the PS and SS is biologically
converted to stable end products like methane and
carbon di oxide.

23. Step 1: Hydrolysis
Higher molecular compounds to lower molecular
compounds – achieved thro’ enzyme moderate
transformations.
Step 2: Acidogenesis
–Lower molecular compounds are converted into
intermediate acidic compounds - acetic acid and fatty
acid – by facultative and anaerobic bacteria. (acid
formers).
Step 3: Methanogenesis:
Cpds formed in step 2 – converted into simple end
products - CO
2 and CH
4. ( by methane formers – strictly
anaerobic bacteria.)

24. »Temperature
»pH
»Seeding with digested sludge
»Mixing and stirring of the raw sludge with digested sludge
SO 5 : Factors affecting sludge digestion process

27. •Sludge digestors
The sludge settled in the sedimentation basin -pumped to
the sludge digestors - temperature of 30° C – 35 ° C is
maintained.
This is the optimum temperature for the anaerobic
bacteria (bacteria that live in an environment that does
not contain oxygen).
The usual length of digestion is 20–30 days but can be
much longer during winter months.
Continual adding of raw sludge is necessary.
 Well-digested sludge should be withdrawn, leaving some
ripe sludge in the digestor to acclimatise the incoming
raw sludge.

29. Drying beds
Digested sludge is disposed on a well –drained sand
and gravel bed .
Tk. of sludge layer : 15 to 20 cm
Water content of sludge can be reduced upto 70%
Sludge volume can be reduced by 60%
The dried sludge is a porous humus-like cake which
can be used as a fertilizer base.

30. Sludge drying beds

32. Sludge drying beds

33. Sludge drying beds

36. Sludge Volume index – Imhoff cone

37. SVI
•The sludge volume index (SVI) is the volume in
milliliters occupied by 1 g of a suspension
after 30 min settling.
•SVI typically is used to monitor settling
characteristics of activated sludge and other
biological suspensions

38. Reading

40. Summary
•SD
•Methods
•SVI