1. ACTIVATED SLUDGE PROCESS AND KINETICS OF ASP
PRESENTATION ON
ACTIVATED SLUDGE PROCESS
AND
KINETICS OF ASP

2. Activated Sludge Process
Activated Sludge Process is the
suspended-growth biological treatment
process, based on providing intimate contact
between the sewage and activated sludge.
The Activated Sludge is the sludge
obtained by settling sewage in presence of
abundant O2 so as to enrich with aerobic
micro-organisms.

3. Activated sludge in sewage in presence
of oxygen results into:
Oxidation of organic matter present.
Coagulation and flocculation of
suspended and colloidal matter
Under the activated sludge Process
basically three processes occurs:-

4. Oxidation
The organisms oxidize a portion of organic
Matter present in sewage into CO2,water
and energy.
Organic matter + O2+ Bacteria
CO2+ H2O+ NH3
+Energy + other end products

5. Synthesis
In second phase the other microbes get
converted into new bacterial cells using
a part of energy released in oxidation
Organic Matter+O2+Bacteria+Energy
New microbial cells

6. Endogenous Respiration
Finally the new microbial cells begin to
consume their own cell tissue to obtain
energy for cell maintenance.
New microbial cell tissue + 5O2
5CO2+NH3+2H2O+Energy

7. Description of Activated sludge processes:-
Conventional plug flow:- Settled water and
recycled activated sludge enter the head
end of the aeration tank and are mixed by
diffused air or mechanical aeration. During
the aeration period adsorption, flocculation
and oxidation of organic matter occurs.
Modified aeration:- It is similar to conven-
-tional plug flow except that shorter aeration time and higher F/M ratio are used.

8. Tapered aeration:- Varying aeration rates
are applied over the tank length depending
on the oxygen demand. Greater amounts of
air are supplied to the head end of the
aeration tank, and the amount diminish as
the mixed liquor approaches the effluent
end.

9. Tapered aeration Effluent Reactor Primary effluent SLUDGE WASTE
Compressed
air
Secondary
clarifier
Effluent
Reactor
Primary
effluent
SLUDGE WASTE
SLUDGE RETURN
Tapered aeration

10. Step feed aeration
Generally three or more parallel channels
are used. The settled waste water is introduced at several point in the aeration tank to equalize the F/M ratio, thus lowering peak oxygen demand.

11. STEP FEED AREATION Effluent Reactor SLUDGE WASTE SLUDGE RETURN Primary
Compressed
air
Secondary
clarifier
Effluent
Reactor
SLUDGE WASTE
SLUDGE RETURN
Primary
effluent
STEP FEED AREATION

12. Extended aeration :-
It operate in the endogenous respiration
phase of the growth curve, which requires
a low organic loading and long aeration
time.

13. Extended Aeration Primary effluent Effluent Reactor SLUDGE WASTE
Secondary
clarifier
Effluent
SLUDGE WASTE
SLUDGE RETURN
Extended Aeration

14. Flow Diagram of ASP Raw water Primary Settling tank Secondary Settling
screens
Grit
chamber
aeration
chlorination
Reareation
Activated
Sludge return
Activated Sludge
Pump
Effluent
to disposal
Sludge
Thickener
Sludge
Digestion
To Sludge Drying
Flow Diagram of ASP

15. Growth And Food Utilization
1)Assimilation:-
The microorganisms must first become
assimilated to their surroundings and food
provided also called Lag Phase.
2)Log Growth Phase:-
In this phase the growth is rapid. Here
bacterial cells reproduce binary fission.

16. 3)Stationary Phase:-
In this phase the production of new
cells is roughly offset by death and
endogenous respiration.
4)Endogenous Phase:-
In final phase, the cells are unable
to obtain food from external sources and
result into decrease in biomass
concentrations.

17. The new cell produced undergoes an auto
Cell Growth
The new cell produced undergoes an auto
oxidation which involves the breakdown of
organics in cell itself to produce energy for
the maintenance of remaining cell mass.
Thus, there is continuously a fractional
decrease in cell mass with time.
dX/dt = μ X
dX/dt = the growth rate of biomass, mg/L t
X = the concentration of biomass, mg/L
μ = the growth rate constant,1/t

18. Factors affecting the rate of biomass
production and food utilization:-
Temperature pH
Toxicants

19. Kinetics of activated Sludge process
Assumptions:
Complete mixing in aeration tank.
Influent substrate concentration is constant.
No microbial solids in raw water.
All reactions occur in reactor.
No microbial activity in clarifier.
No Sludge accumulation.
Steady state conditions prevails.

20. ACTIVATED SLUDGE KINETIC MODEL
Q(1+R)
A,T,
Va, X,Se
(Q-Qw),
Xe, Se
X, Se
Q, So
Secondary
Clarifier
Qw, Xr, Se
RQ, Xr, Se

21. Microorganism and Substrate Mass Balance
Rate of accumulation = Biomass in + Biomass
of biomass in system growth - biomass out
(dX/dt)V = QXo + V [rg- kdX ] –QX
rg = μ mXS /(Ks+S)
(dX/dt)V = QXo + V[μ mXS/(Ks+S) - kdX ] - QX
rg = Growth rate of biomass
Kd= Endogenous decay coefficient.

22. Hydraulic retention time
(dX/dt)V = Zero
QX = VX [μmS/(Ks+S) - kd ]
Q/V = μ mS/(Ks+S) - kd =1/θ
θ = Hydraulic retention time

23. Mean Cell Retention Time
The time for which the cells remain in
the system. It is given as-
θc = Mass of solids Mass of solids
in system leaving system/day
θc = VX/(QwXw+ QeXe)

24. Substrate Balance Equation
(dS/dt)V = QSo – QS – V[μ mXS/ Y(Ks+S)]
Y=Decimal fraction of Food mass
converted to biomass
For Steady State
dS/dt = Zero
(So – S) = θ[μ mXS/Y(Ks+S)]

25. Effluent concentration
X = μm(So - S)/K(1+kdθ)
X = Y(So - S)/(1+kdθ)
Effluent substrate concentration
S = Ks(1+θkd)/θ(Yk - kd)-1

26. Thank You