Dynamics of Wastewater Treatment Systems

Transcription

1 Dynamics of Wastewater Treatment Systems Gustaf Olsson Lund University, Sweden

2 Models Models for understanding mechanisms design control

3 Mass Balances Conservation of mass: (rate of change of vessel contents) = (rate of inflows) (rate of outflows) + (rate generated) (rate consumed)

4 Simple respirometer The DO (S O ) concentration: ds o = dt Respiration rate r : r = rmax K r o S o + S o

5 Dissolved Oxygen Dynamics

6 DO responses Air flow rate Oxygen concentration

7 Dissolved oxygen dynamics Oxygen transfer rate: rate = K a S S ) L ( O, sat O V DO mass balance: d( VS dt O ) = q S q S + K a ( S S ) V in O, in out O L O, sat O + r V

8 Controlled DO response Air flow rate Change in inlet DO (disturbance) DO conc InletDO conc Change in DO setpoint

9 Controlling the DO response Influencing the K l a K a const u L air u air = u airo + K ( S S O, ref O )

10 Organic carbon removal

11 Carbon removal activated sludge Influent Bio reactor Effluent Aeration Sludge recirculation Sludge outtake

12 Simple nutrient control

13 Simple biological kinetics Process Components Nutrient N Biomass B Kinetics Aerobic heterotrophic growth 1 YB 1 µˆ K N sn + s N X B

14 Simple bioreactor response Biomass Influent substrate decrease Substrate

15 Soluble carbon removal

16 Carbon removal kinetics Process Components Nutrient Oxygen Biomass Kinetics Aerobic heterotrophic growth 1 Y H YH 1 Y H 1 µˆ H K S ss + s S K O so + s O X H Heterotrophic decay 1 f P -1 b H X H

17 Carbon removal response Biomass Decrease in influent substrate Increase in air flow

18 Carbon removal

19 Nitrogen removal

20 Pre-denitrification plant Influent Anoxic reactor Aerobic reactor Effluent Internal recirculation Sludge recirculation Sludge outtake

21 Nitrogen Removal Process Ammonium Dissolved oxygen Nitrification Nitrate Easily degradable organic matter Denitrification Free gaseous nitrogen

22 N removal basic mechanisms

23 Nitrogen removal kinetics Processes Aerobic heterotrophic growth Anoxic heterotrophic growtn Aerobic autotrophic growth Heterotrophic decay Autotrophic Carbon Components Oxygen NH 4 NO 3 Biomass Biomass heterotrophic autotrophic Kinetics decay

24 Nitrification (batch)

25 Denitrification (batch)

26 Phosphorous removal

27 Plant design for bio-p removal Influent Bio-P reactor Anoxic reactor Aerobic reactor Effluent Internal recirculation Sludge recirculation Sludge outtake

28 P removal Processes Fermentation P release P uptake PAO growth PHA breakdown PP breakdown PAO breakdown Components S F fermentable COD S A volatile fatty acids Dissolved oxygen Phosphate PHA polyhydroxylalkanoates PP polyphosphate PAO

29 P removal basic mechanisms

30 P release basic mechanisms Fermentation of fermentable COD to VFA. VFA used by the organisms to store carbon as poly-hydroxylalkanoates (PHA) P release from poly-phosphate into solution while VFA is converted to PHA

31 P uptake basic mechanisms P uptake from solution to PP using the PHA and DO Growth of PAO biomass, utilizing PHA and DO

32 P removal mechanisms Anaerobic condition: no dissolved oxygen nor nitrate present Aerobic or anoxic conditions: Concnetration nitrate in reactor and/or dissolved oxygen presentcondition PO4-P, ppm Net P uptake Phosphate Accumulating Organism (PAO) PHA storage Accumulated poly phosphate storage PHA storage Accumulated poly phosphate storage Easy degradable organic matter, VFA Phosphate Carbon dioxide Phosphate

33 20 Typical nutrient variations NO3 NH4 PO4 15 NH 4 PO 4 ppm 10 5 NO sep 28-sep 29-sep 30-sep 01-okt 02-okt 03-okt 04-okt 05-okt 06-okt

34 P release

35 P uptake

36 Hydraulic models

37 Simple tank hydraulics q out = const N b α h q in qout Volume V Area A dv dt = A dh dt = q in q out

38 Settling

39 Multilayer model Overflow Layer 1... Feed Layer m-1 Layer m Layer m Layer n Underflow

40 Multilayer model Underflow Solids flux dxi hi Ai qu dt i = m + 1,..., n ( x x ) + A ( f f ) = i 1 i i i 1 C2x f = x v = x C e i i i i i 1 i

41 Settler Feed Flowrate Increase

42 Settler Underflow Decrease

43 Settler Profile 5 layers

44 Settler Profile 10 layers

45 Settler Profile 20 layers

46 General dynamic models

47 State model dx = f ( x( t), u( t), d( t), p) dt y( t) = g ( x( t), u( t), d( t), p) x(t) = state variables u(t) = manipulated input variables d(t) = disturbances input variables y(t) = output variables

48 Input-output models ( ) p t d t u t y h dt dy ), ( ), ( ), ( = ) ( ) (... ) 2 ( ) ( ) (... ) 2 ( ) ( ) ( t v t n t u b t t u b t t b u t n t y a t t y a t t y a t y n n = Time discrete form:

49 Summary Mass balances of substrates, organisms and dissolved oxygen Processes for C, N and P removal Settler dynamics is crucial Many different time scales