ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2009/2010) ‘Biological Treatment’ By; Mrs Hafiza Binti Shukor

ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRYSEM 1 (2009/2010)

‘Biological Treatment’

By; Mrs Hafiza Binti Shukor


OBJECTIVES OF BIOLOGICAL TREATMENT To transform (eg. Oxidize) dissolved

and particulate biodegradable constituents into acceptable end products

Capture and incorporate suspended and nonsettleable colloidal solids into a biological floc or biofilm

Transform or remove nutrients such as nitrogen and phosphorus.

Remove specific trace organic constituents and compounds.


ROLE OF MICROORGANISMS IN WW TREATMENT

To remove dissolved and particulate carbonaceous BOD and the stabilization of organic matter found in ww.

microorganisms are used to;oxidize (convert) the dissolved and

particulate carbonaceous organic matter into simple end products and additional biomass.

Remove N2 and P in ww treatment process Oxidizing NH3 (nitrification) to nitrite and

nitrateReduce the oxidized nitrogen to gaseous

nitrogen. Biomass (S.G > H2O) can be removed from the

treated liquid by gravity settling.

OgHfCOnewcellsedPOcNHbOismmicroorgana 223

432 )()(


TYPES OF BIOLOGICAL PROCESS FOR WW TREATMENT

A)Suspended Growth ProcessB) Attached Growth Process

A) Suspended Growth ProcessBiological treatment processes in which

microorganism responsible for the conversion of the organic matter or other constituent to gases or cell tissue.

The microorganism responsible for treatment are maintained in liquid suspension by appropriate mixing methods.

Operated with a +ve DO conc but applications exist where suspended growth anaerobic reactors are used such as for high organic conc industrial ww and organic sludges.

Most common suspended growth process used is activated sludge process and aerated lagoon


influenteffluent

sludgeReturn activated sludge

air

Plug flow aeration tank clarifier

influenteffluent

sludgeReturn activated sludge

Complete-mixaeration tank

clarifier

Plug Flow Activated Sludge Process

Complete-Mix Activated Sludge Process


activated sludge: microbial aggregates (flocs) in the aeration tank.

Flocs stay in suspension with mixing by aeration.

Recycle of the activated sludge is crucial to maintaining a high concentration of cells.

Activated sludge?


Barrack

Grit Chamb

er

Secondary

clarifier

Disinfection

Aeration

Tanks

Primary Clarifier

screenings grit sludge Waste sludge (optional)

effluent

sludge

Return activated sludgeWaste sludge

(optional)

Activated Sludge Process

influent

Barrack

Settling Pond Disinfectio

n

Aerated

Lagoon

screenings Waste sludge (optional)

effluent

sludge

Aerated Lagoon

influent


B) Attach Growth ProcessThe microorganisms responsible for the conversion of organic material or nutrients are attached to an inert packing material.The organic material and nutrients are removed from the wastewater flowing past the attached growth also known as biofilm.Packing materials used include;

Rock Gravel Sand Wide range of plastic Other synthetic materials.

Can be operated as aerobic as aerobic or anaerobic processes.


Attach Growth Process (continue….)

The packaging can be submerged completely in liquid or not submerged with air or gas space above the biofilm liquid layer.The most common aerobic attach growth process used is trickling filter and rotating biological contactors


Trickling Filter Process

Rotating Biological Contactors

Barrack

Grit Chamb

er

Secondary

clarifier

Disinfection

Trickling

Filters

Primary Clarifier

screenings grit sludgeWaste sludge

(optional)

effluent

sludge

recycle

influent

Barrack

Grit Chamb

er

Secondary

clarifier

Disinfection

RBS units

Primary Clarifier

screenings grit sludge

effluent

sludge

influent


Trickling Filter with Rock Packing

Tower Trickling Filter with Plastic Packing

influenteffluent

sludgeRecycle (optional)

Trickling Filter with Rock Packing

clarifier

influenteffluent

sludgeRecycle (optional)

Trickling Filter with Plastic Packing

clarifier


CLASSIFICATION OF MICROORGANISM

AUTOTROPHIC HETEROTHROPHIC CHEMOHETROTHROPHIC

PhotoautotrophicEnergy source – lightCarbon source – CO2

Photoheterotropic Energy source – onorganic redox reactionCarbon source – CO2

Aerobicoxygen as final electron acceptor

Chemoautotrophic Energy source – inorganic redox reactionCarbon source – CO2

ChemoheterotropicEnergy source – lightCarbon source – organic

AnaerobicNO3

- , SO42-, and CO2 as

electron acceptorNOTE;Autotrophic- organism that derive cell carbon from CO2

Heterothrophic – organism use organic carbon for formation new biomass


MICROORGANISM IN WW

Bacteria: major componentFungi: low pH, toxicity, N

deficient wasteProtozoa: gazing on bacteriaRotifers: multicellular

organism (help to floc formation)

Algae: supply oxygen to ww.Organic/ inorganic particle


Aerobic heterotrophic bacteria are main “activated”organisms.

→Microbial community is highly diverse and competative.

Floc formation is really key –individual bacteria do not settle fast enough to be captured in the settling tank. Cells not in flocs are washed out.

The suspended flocs particles are called “activated”.


-

BACTERIAL GROWTH & BIOMASS YIELD

BIOMASS GROWTHMostly organic materialsAn increase of biomass can be measured by VSS, particulate COD or TSSOther parameter to indicate biomass growth are DNA, protein content and ATP.VSS used as an apparent indicator of biomass production (measure of reactor solid in general)BIOMASS YIELD

)(__

__,_

consumedutilizedsubstrateg

producedbiomassgYYieldBiomass


-

RATE OF UTILIZATION OF SOLUBLE SUBSTRATE

SK

kXSr

s

su Rate of substrate

conc change due to

utilization (g/m3.day)

Max specific substrate utilization rate,

g substrate/g microb .day

Biomass (microorganism) conc, g/m3Growth-limiting substrate conc in solution, g/m3

Half velocity constant (substrate concat one-half the max specific substrate utilization rate, g/m3)

Substrate= the term used to denote the organic matter or nutrients that are converted during biological treatment or that may be limiting in biological treatment. Eg. Carbonaceous organic matter is ww is referred as the substrate that is converted during biological treatment.


-

Sub

stra

te u

tiliz

ati

on r

ate

, -r

suSubstrate concentration, mg bsCOD/L

ks

max

Rate of change of substrate utilization vs biodegradable soluble COD conc based on saturation type model.From figure, max

substrate utilization rate occurs at high substrate conc.

In practice, biological treatment systems are designed to produce an effluent with extremely low substrate value.

When the substrate is being used at its max rate, the bacteria are also growing at their max rate.


-

The max specific growth rate of bacteria is related to the max specific substrate utilization rate as follow;

kYm

max specific bacterial growth

rate, g new cells/g cells.day

max specific substrate

utilization rate, g/g.day

True yield coefficient, g/g

SK

kXSr

s

su SKY

XSr

s

m

su


-

RATE OF BIOMASS GROWTH WITH SOLUBLE SUBSTRATE

Relation between the rate growth & rate of substrate utilization is applicable in both batch and continuous culture systems.

xkYrr

xkxrdt

dxr

dsug

dg

g

Endogenous decay;

Net biomass production rate

Endogenous decay coefficient, gVSS/gVSS.day


-

d

s

su

sug

sug

m

s

g

s

mg

s

mg

g

kSk

ykSx

kdx

x

yr

dt

dx

x

concbiomassxbydevidex

kdx

x

yr

x

r

kdxyrr

ykwherekdx

Sk

kXSyr

kdxSk

XS

y

yr

kdxSk

XSr

kdxxdt

dxr

1

.)..(.......................

,..............

Net Biomass Growth;

System boundry

influenteffluent

sludge

Return activated sludge


clarifierQ, So, Xo (Q-Qw), S, Xe

Qw, S, Xw

Qr, S, XR

S, X,V


In the aeration tank, contact time is provided for mixing and aerating influent ww with the microbial suspension, generally referred to as the mixed liquor suspended solids (MLSS) or mixed liquor volatile suspended solids (MLVSS)

SUSPENDED GROWTH PROCESSSchematic of activated sludge unit


Biomass Mass Balance

-Rate of accumulation of microorganism within the system boundary

Rate of flow microorganism into the system boundary

Rate of flow accumulation of microorganism out of the system boundary

Net growth of microorganism within the system boundary

= +

VrXQXQQQXVdt

dxgRwewo

.


-

VrXQXQQQXVdt

dxgRwewo

.

dt

dx

VQ

oXwQ

eXRX

gr

Where,= rate of change of biomass concentration in reactor measured as gVSS/m3.day= reactor volume (aeration tank)m3= influent flowrate, m3/day

=concentration fo biomass in influent, gVSS/m3= waste sludge flowrate, m3/day= concentration of biomass in effluent, gVSS/m3

= concentration of biomass in return line from clarifier, gVSS/m3= net rate of biomass production, gVSS/m3.day


Assumption;Xo = 0 (neglected) Steady state condition prevail (dx/dt)=0

VrXQXQQQXVdt

dxgRwewo

.

VrXQXQQgRwew

XkYrrdsug

VXkYrXQXQQ

dsuRwew

Where,

d

su

Rwewk

X

YrVXXQXQQ /

÷VX


-

d

su

Rwewk

X

YrVXXQXQQ /

Rwew

XQXQQ

VXSRT

Inverse above equation


- Rwew

XQXQQ

VXSRT

Sludge Retention Time (SRT)

Important designOperating parameter for activated sludge processIs average time the activated sludge solid are in the systemIs determine by dividing the mass of solid in the aeration tank by the solids removed daily via the effluent and by washing for process control


-

Substrate Mass BalanceIs a mass balance for substrate utilization in an AERATION TANK

Accumulation

Inflow Outflow

Generation

= +

VrQSQSVdt

dSsuo

.

Influent soluble substrate concentration, g/m3

Outflow soluble substrate concentration, g/m3

Assumption,At steady state, dS/dt=0

VrQSQSVdt

dSsuo

.


-

d

s

d

s

d

s

s

o

s

o

suo

kSRTYkSK

S

kSRTSK

YkS

kSK

YkS

SRT

Hence

Sk

kXS

Q

VSS

Q

V

Sk

kXSSS

VrSSQ

11

1

1

,

SRTk

SSYSRTx

kSRTYk

kXSS

kSRTYkQ

VkXSS

Sk

S

Q

VkXSS

d

o

do

do

s

o

1

1

11

The reactor biomass conc is a function of SRT


-Rw

XQ

VXSRT

If no return sludge flow where all sludge produce present in the effluent clarifier tank…….the SRT equation become;

System boundry

influenteffluent

sludge


clarifierQ, So, Xo (Q-Qw), S, Xe

Qw, S, Xw

S, X,V


-

Solid Production

Solid production from biological reactor represent the mass of material must be removed each day to maintain the process.Solid production in terms of TS,VSS and biomass.SRT provide expression to calculate total sludge produce daily from activated sludge process.

SRT

VXP T

VSSTX

Total solid waste daily (gVSS/d)

Total MLVSS conc in aeration tank, gVSS/m3

Volume of reactor (m3)


-

SRT

VXP

TX

Biomass waste daily (gVSS/d)

Niomass conc, gVSS/m3

Volume of reactor (m3)

To find amount of biomass wastes perday (Px), the biomass concentration, X can be used in place of XT in equation before;


Mixed Liquor Solid Concentration

Total MLVSS in aeration tank

Biomass conc

nbVSS conc, xi

=+

iTXXX

Comprise of;nbVSS in influentnbVSS in wastenbVSS produce from cell debris duty to decay ratio


Designed based on loading (the amount of organic matter added relative to the microorganisms available)

Commonly called the food-to-microorganisms ratio, F/M

F measured as BOD. M measured as volatile suspended solids concentration (VSS)

F/M is the amount of BOD/day per amount of MLVSS in the aeration tank

Design of Activated Sludge


Food to Microorganism (F/M) Ratio

Defines as BOD @ COD applied perunit volume of mixed liquor

X

S

VX

QS

biomassmicrobialtotal

ratesubstrateappliedtotal

M

F oo

__

___

Where;F/M = food to biomass ratio (g BOD or COD/g VSS.day)Q=influent ww flowrate, m3/daySo=influent BOD @ COD conc, g/m3V=aeration tank volume ,m3.X=mixed liquor biomass conc in the aeration tank , g/m3 =hudraulic retention time of aeration tank, V/Q,day


Sludge Volume Index (SVI)

where V is volume of settled sludge after 30 min

Sludge settleability is determinedby sludge volume index (SVI)

SVI (ml/g) = ___________

MLSS

V x 1000

Final settling tank

sludge 1-L

mL


EXAMPLE ; ACTIVATED SLUDGE PROCESSAn activated sludge plant is set at SRT value of

10day. The reactor volume is 20 000m3 and MLSS conc is 400g/m3. Determine;a)The sludge production rate.b)The sludge washing flowrate when washing from reactor.c)The sludge washing flowrate when washing from recycle line. The concentration of suspended solid in recycle line is 10 000 g/m3. The solid loss in secondry rectifier is neglegible.


THE END

Documents

ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2009/2010) ‘Biological Treatment’ By; Mrs Hafiza Binti Shukor