ACTIVATED SLUDGE MODELS

Hydromantis, Inc.

Objective● A model to predict performance of the

activated sludge process:biomass growthuptake/conversion of key components (carbon, nitrogen, phosphorus, oxygen)hydraulics

Key Model Features

● Mass Balance● Variables● Reactor Hydraulics● Biological Model

Mass Balance

Inputs OutputsReaction

Change = Inputs - Outputs ± Reactions

Mass Balance

Inputs OutputsReaction

Change = Inputs - Outputs ± Reactions

Inert: dSidt

V = Q (Siin - Si)

Mass Balance

Inputs OutputsReaction

Change = Inputs - Outputs ± Reactions

dSodt

V = Q (Soin - So) + KLa (Sost - So)V-our VOxygen:

Variables● State Variables

fundamental variablesimportant for modelling (mass balance)

● Composite Variables (HI term)measurableknowable

IWA Nomenclature● S - Soluble Components● X - Particulate Components

● SubscriptsB - biomassS - substrateO - oxygenN, BH, BA, NO, ND, etc

ASM1 State VariablesSi Soluble inert organics g COD/m3Ss Readily biodegradable (soluble) substrate g COD/m3Xi Particulate inert organics g COD/m3Xs Slowly biodegradable (particulate) substrate g COD/m3Xbh Active heterotrophic biomass g COD/m3Xba Active autotrophic biomass g COD/m3Xu Unbiodegrad. particulates from cell decay g COD/m3So Dissolved oxygen g O2/m3Sno Nitrate and nitrite g N/m3Snh Free and ionized ammonia g N/m3Snd Soluble biodegradable organic nitrogen (in ss) g N/m3Xnd Particulate biodegradable organic N (in xs) gN/m3

CNP State Variables12 CN State Variables +

Slf Readily biodegradable VFA substrate g COD/m3Xbt Stored poly-beta-hydroxy-alkanoates g COD/m3Xbp Active polyP heterotrophic biomass g COD/m3Xpp Stored poly phosphate g P/m3Sp Soluble phosphorus g P/m3

Composite VariablesSi

Ss

Xs

Xbh

Xba

Xu

Xi

SBODu

XBODuBODu

fbod

BOD5

TSS

SCOD

XCOD

COD

VSS

icvivt

Typical Influent COD

non-denit. het.

inertReality ASM1

soluble

particulate

COD

readily biodeg.

rapidhydrolysis

slow hydrolysis

denit. het.

autotrophsinert

1060

100

110

20

591

40

400 total

inert

inert

readily biodeg.

slowly biodeg.

Si

Ss

Xs

Xi

Measurement Fractions

soluble inert

readily biodegradable

rapid hydrolysis

slow hydrolysis

biomass

particulate inert organic

TSS VSS BOD5 BODu COD OUR

particulate inert inorganic

Nitrogen Composite Variables

sTKN

Sno

SnhSnd or N in soluble organic matter

Xnd or N in particulate organic matter

TKN

Total N

Typical Influent NTypical Influent N

Sni

nitrateReality ASM1 Model

solubleinorg.

ammonia

inert

Snh

urea or ammonia

ammonia

Soluble Org.

Suspended

Inert Sol.

readilybiodeg. Rapid hydrolysis

Slow hydrolysisBiomassinert

suspended

Sndslowly biodeg.

inert

readily biodeg.

Xnd

Xni

Petersen Matrix

Kinetic Parameters

Continuity

Component ij Process

1Xb

2Ss

3So

process rate, ρ[ML-3T-1]

1 Growth

2 DecayObserved Rates r = ∑νρ

Biom

ass

[M(C

OD

)L-3

]

Subs

trate

[M(C

OD

)L-3

]

Oxy

gen

[M(-C

OD

)L-3

]

1 -1/Y -(1-Y)

-1 -1Y

µSsk+Ss Xb

b Xb

µ = maximumspecific growth

K = half saturationconstant

b = decay rate

StoichiometricParameters:

Y = true growthyield

mas

s ba

lanc

e

Equation System

µ Ss

K+SsXb

rSs =

Biomass

Substrate

rXb = - b Xb

-1

Y

µ Ss

K+SsXb

Oxygen

rSo = -(1-Y)

Y

µ Ss

K+SsXb - bXb

ASM1 Processes1. Aerobic growth of heterotrophs2. Anoxic growth of heterotrophs3. Aerobic growth of autotrophs4. Decay of heterotrophs5. Decay of autotrophs6. Ammonification of soluble organic N7. Hydrolysis of entrapped organics8. Hydrolysis of entrapped organic N

ASM1 Processes1. Aerobic growth of heterotrophs

conversion of soluble substrate (carbonaceous) to biomassprocess rate - needs substrate and oxygen

– saturation function = Sx/(Ksx + Sx)uses some ammonia uses alkalinity

ASM1 Processes2. Anoxic growth of heterotrophs

similar to aerobic growth of heterotrophs except nitrate nitrogen is used as an electron acceptor (versus oxygen for aerobic growth)switching function = Koh/(Koh + So)adds alkalinity

ASM1 Processes3. Aerobic growth of autotrophs

nitrification (growth of nitrifiers)growth of biomass using soluble ammonia as an energy sourcerequires oxygen and ammonia-nitrogenalso produces nitrate-nitrogenlargest impact on alkalinity

ASM1 Processes4. Decay of heterotrophs

“death” of biomass (predation, lysis)converts heterotrophic biomass to slowly biodegradable substrate and inert particulate materialalso adds particulate organic nitrogen

ASM1 Processes5. Decay of autotrophs

similar to modelling of decay of heterotrophs

ASM1 Processes6. Ammonification of sol. organic N

conversion of soluble organic nitrogen to ammonia

IWA ASM1 Processes7. Hydrolysis of entrapped organics

conversion of slowly biodegradable substrate to readily biodegradable substatefirst order with respect to heterotrophsrequires electron donor (oxygen and/or nitrate)

IWA ASM1 Processes8. Hydrolysis of entrapped organic N

conversion of particulate organic nitrogen to soluble organic nitrogen (which is then converted to ammonia - process 6)similar to hydrolysis of entrapped organics

Death-Regeneration (ASM1) – COD Flow Diagram

SSS S readily biodegrreadily biodegr..

substratesubstrate

XXS S slowly biodegrslowly biodegr..

substratesubstrate

XXS S entrapped slowly entrapped slowly biodegrbiodegr. . substratesubstrate

XXP P (X(XUU))Inerts from Inerts from

decaydecay

XXB,H B,H heterotrophic heterotrophic

biomassbiomass

floc phasefloc phasefluidfluid phasephase

entrapmententrapment((instantaneousinstantaneous))

hydrolysishydrolysis((regenerationregeneration))

decaydecay((deathdeath))

synthesissynthesis

OO22

SSII & X& XI I inertsinerts of of inflinfl..(not (not biologically biologically

transformedtransformed))

Death-Regeneration (ASM1) – Organic Nitrogen Flow Diagram

SSNH NH ammoniaammonia

floc phasefloc phasefluidfluid phasephase

ammonificationammonification

ffnn(X(XB,HB,H) = ) = iiXBXBheterotrophic heterotrophic

biomassbiomassdecaydecay((deathdeath))

XXND ND part. part. biodegrbiodegr..

nitrogennitrogen

hydrolysishydrolysis((regenerationregeneration))

SSNDNDsol. sol. biodegrbiodegr. .

nitrogennitrogen

XXND ND part. part. biodegrbiodegr..

nitrogennitrogen

SSNDNDsol. sol. biodegrbiodegr. .

nitrogennitrogen

ASM1 Modifications● Mantis Model

NO3 - Uptake for N requirementSimultaneous nitrification/denitrification

● TwoStepMantis (CN2lib)Two Step Nitrification

● ASM2d , New Generalbio-P modelling, Chemical P precipitation

● ASM3Storage compounds

● See comparative table on p.129 of the Tech.Ref.

Ammonia tracking

Alkalinity tracking

NO3 as N source for growthAmmonia limiting growth

2 step Nitrification

Substrate Storage

Aerobic Denitrification

Nitrification/Denitrification

2stepMantis

ASM3MantisASM1

BPRFermentation

Precipitation of P with MeOH

Alkalinity as factor limiting growthAlkalinity trackingNO3 as N source for growth

Ammonia limiting growth

Ammonia trackingCOD “Loss”

Nitrification / Denitrification

New GeneralASM2d

Temperature Dependency

µ

T10 30

µT= µ20 • K (T-20)

K = 1.072

Arrhenius Equation

(20oC=68oF)