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Presentation on theme: "A PRESENTATION ON ACTIVATED SLUDGE PROCESS AND KINETICS OF ASP."— Presentation transcript:


2 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 O 2 so as to enrich with aerobic micro-organisms. Activated Sludge Process

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 The organisms oxidize a portion of organic Matter present in sewage into CO 2,water and energy. Organic matter + O 2 + Bacteria CO 2 + H 2 O+ NH 3 +Energy + other end products Oxidation

5 In second phase the other microbes get converted into new bacterial cells using a part of energy released in oxidation Organic Matter+O 2 +Bacteria+Energy New microbial cells Synthesis

6 Finally the new microbial cells begin to consume their own cell tissue to obtain energy for cell maintenance. New microbial cell tissue + 5O2 5CO 2 +NH 3 +2H 2 O+Energy Endogenous Respiration

7 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. Description of Activated sludge processes:- 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 Secondaryclarifier Effluent SLUDGE RETURN SLUDGE WASTE Reactor Compressed air air Primaryeffluent 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 Secondaryclarifier Effluent SLUDGE RETURN SLUDGE WASTE Reactor Compressed air air Primaryeffluent STEP FEED AREATION

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

13 Secondaryclarifier Effluent SLUDGE RETURN SLUDGE WASTE Reactor Primaryeffluent Extended Aeration

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

15 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. Growth And Food Utilization

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 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:- 1) Temperature 2) pH 3) Toxicants

19  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. Kinetics of activated Sludge process Assumptions:

20 A,T, V a, X,S e Secondary Clarifier Clarifier Q, S o Q(1+R) X, S e ( Q-Qw), Xe, Se Q w, X r, S e RQ, X r, S e ACTIVATED SLUDGE KINETIC MODEL

21 Microorganism and Substrate Mass Balance Rate of accumulation = Biomass in + Biomass of biomass in system growth - biomass out (dX/dt)V = QX o + V [r g - k d X ] –QX r g = μ m XS /(K s +S) (dX/dt)V = QX o + V[μ m XS/(K s +S) - kdX ] - QX r g = Growth rate of biomass K d = Endogenous decay coefficient.

22 (dX/dt)V = Zero QX = VX [μ m S/(K s +S) - k d ] Q/V = μ m S/(K s +S) - k d =1/θ θ = Hydraulic retention time Hydraulic retention time

23 Mean Cell Retention Time The time for which the cells remain in the system. It is given as- θ c = Mass of solids Mass of solids in system leaving system/day θ c = VX/(Q w X w + Q e X e )

24 Substrate Balance Equation (dS/dt)V = QS o – QS – V[μ m XS/ Y(K s +S)] For Steady State Y=Decimal fraction of Food mass converted to biomass dS/dt = Zero (S o – S) = θ[μ m XS/Y(K s +S)]

25 X = μ m (S o - S)/K(1+k d θ) X = Y(S o - S)/(1+k d θ) Effluent concentration Effluent substrate concentration S = K s (1+θk d )/θ(Yk - k d )-1



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