Aerobic and Anaerobic Biological Processes Basics

8/11/2019 Aerobic and Anaerobic Biological Processes Basics

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Aerobic and Anaerobic

Biological Processes: BasicsProf. S.N.Upadhyay

Department of Chemical Engineering & Technology

Institute of Technology

Banaras Hindu UniversityVaranasi221 005


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Keywords

Wastewater

Biological Processes

Biological Growth

Applications


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Raw Water

Wastewater


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1.Wastewater:

Domestic Wastewater

Industrial Wastewater


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Industrial Wastewater...

Eg: Starch industry wastewater

Major component-

COD = 10,000-20,000 mg/L Effects of discharging into natural

receiving bodies

- 20 m3/ton of starch

- high COD

- high suspended solids

- cyanide exposure


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2.Biological Processes

Aim: any form of life-

survive & multiply

Need for energy &organic molecules as

building blocks

Made of C, H, O, N, S, P

and trace elements


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Biological Processes...

Cell: derives energy from

oxidation of reduced foodsources

(carbohydrate, protein & fats)


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Micro-organisms

Tiny automatic reactors

Highly efficient

Cheaper to operate than man made reactorsSelf-adjusting and self-maintaining


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Microorganisms

Classification:

Heterotrophic- obtain energy from

oxidation of organic matter

(organic Carbon)

Autotrophic- obtain energy from oxidation of

inorganic matter

(CO2, NH4, H+ )

Phototrophic- obtain energy from sunlight


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Biological Oxidation

Biological oxidation is the conversion of elements fromorganic form to their highly oxidized inorganic forms, aprocess known asmineralization, with the help ofmicroorganisms.

Organic-C + O2CO2Organic-H + O2H20

Organic-N + O2NO-3

Organic-S + O2S02-

4

Organic-P + O2PO3-

4

Oxidation of organic molecules inside the cell can occur inaerobic or anaerobic manner


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Aerobic Biodegradation Process

Waste oxidation is aerobic when terminal oxidizing

agent is oxygen. The general equation is

CXHY OZN+ O2+ (microorganisms, nutrients)H2O +

CO2+ NH3+ new biomass

Only thermodynamically favorable reactions occur

(The domestic wastewater has sufficient nutrients,

but some industrial effluents have less N and Pcontents. The ratio of BOD5: N: P should be about

100:5:1.)


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Anaerobic Biodegradation ProcessWaste oxidation is anaerobic when oxygen is not

the terminal oxidizing agent.Here also only thermodynamically favorable

reactions occur

CXH

YO

ZN + (microorganisms, nutrients) CH

4+

H2O + CO2+ NH3+ new biomass

(4C3H702NS + 8H204CH3COOH + 4CO2+

Cysteine

4NH3+ 4H2S + 8H)

and

(4CH3COOH + 8H 5CH4 + 3CO2 + 2H2O)


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Electron acceptor Type of reaction Metabolic byproduct

Oxygen

Nitrate (NO-3)

Manganese (Mn4+)

Ferric iron (Fe3+)

Sulphate (SO2-

4)

Carbon dioxide

Aerobic

Anaerobic respiration

Anaerobic

Anaerobic



Carbon dioxide, water

Nitrogen gas, carbon dioxide

Manganese (Mn2+)

Ferrous iron (Fe2+)

Hydrogen sulfate

Methane

Electron Acceptors and Byproducts in Aerobic and Anaerobic Processes

Biological Oxidation


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Aerobic Degradation Pathway

Biochemical Pathways


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Anaerobic Degradation Pathway



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Glucose

EPM Pathway

Pyruvic Acid

ADP ATP

Energy

Lactic Acid TCA Cycle H+ Respiration H2O

CO2

O2


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Aerobic pathways contains-EMP pathways, TCA cycle, respiration

Anaerobic pathways contains-

EMP pathways

Released energy stored as ATP molecules

Excess food is stored as glycogen

C6H12O6+ 6O2+38 ADP + 38 Pi 6 CO2+38 ATP + 44 H2O



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3. Biological Growth

- Exponential growth (batch)

- Monod kinetics

- Haldane kinetics

under toxic conditions

- Other Models


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Biological Growth

Growth environment should provide sufficient nutrients,

It should be free from toxic substances, It should have appropriate pH (5-9; for optimal growth- 6-8)

It should have appropriate temperature (psychrophils 45C), and

It should have correct DO (1 -2 mg/l for aerobic)

C HOPKINS

Cafe Mgr


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Kinetic Models

Un-structured Models

Structured Models

Segregated Models Non-segregated Models

Simplicity of un-structured and non-

segregated models make them moreapplicable


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Kinetic Models


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Biological Growth

Nt= Noexp (t)

Or

Xt= Xoexp (t)

= ln 2/Td


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Exponential growth

Biological growth...

dX

dt = X

Log

No.ofCells

Time

L

agphase

Log

growthph

ase

Stationaryphase

Deathphase


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Monod kinetics


= mS

Ks S

Substrate Concentration(S)

Speci

ficgrowthrate()

Max. ratem

m/2

ks


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Haldane kinetics(under toxic conditions)


= m

S

K S S i Ks i . /

Substrate Concentration(S)

Specific

growthrate()

i


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Contois Model

Moser Model

Teisser Model

SxK

S

s max

SKs1

max

)1(/

maxskse


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Apparatus for Treatability Study


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Apparatus for Biological Treatability Study


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4. Applications

1. Carbonaceous removal - aerobic

- anaerobic

2. Nitrogen removal - nitrification

- denitrification

3. Sulfide removal - anaerobic SO4 reduction

- aerobic HS- oxidation


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Micro-organisms oxidize waste to produce energy to enable them to

synthesize new molecules for building new cells. Thus microbial

metabolism has two parts- catabolism (meaning breaking down) for

energy and anabolism (meaning build-up) for synthesis.

Catabolism

CXHY OZN+ O2+ (microorganisms, nutrients) H2O + CO2+ NH3+

Energy + other end-products

Anabolism

CX

HY

OZ

N

+ Energy + (microorganisms, nutrients)C5

H7

NO2

(new

biomass)

Autolysis (Endogenous Respiration)

C5H7 NO2 + O2+ (microorganisms, nutrients) 2H2O + 5CO2+ NH3+

energy


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The catabolic, anabolic and autolytic reactions of aerobicbiological oxidation. In a real (finite time) continuous

biological reactor some of the organic matter in the influent

escapes oxidation; in batch culture at infinite time the

unmetabolized fraction is zero

Aerobic Degradation


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Microorganisms thrive in oxygen rich environment and break

down and digest waste

Organic carbon present in the effluent is used as carbon and

energy source and it serves as electron donor

The enzymes involved in the process are- di- , mono-

oxygenases, and peroxidases. The first enzymes act only on

aromatic compounds whereas the second ones act on both

aliphatic and aromatic compounds. Peroxidases are effective

in degrading lignins


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Final degradation products are- carbon dioxide, water, and

microbial biomass (sludge)

When the food becomes limiting, the microorganisms

consume their own protoplasm to obtain energy (catabolism

or endogenous respiration)

Biomass concentration decreases continuously until the

energy content reaches a minimum so as to be considered

biologically stable for disposal into environment. An organic

mass (e g sludge) with an oxygen uptake rate of less than orequal to 1 mg O2/h/g can be considered to be stabilized.


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Anaerobic Biodegradation Process

Microorganisms thrive in oxygen deficient environment

Organic matter is converted into stable end-products through several

independent, consecutive, and parallel reactions. In general there are six

main steps:

Hydrolysis of complex organic biopolymers (carbohydrates, lipids, and

proteins) into monomers (sugars, short and long chain fatty acids, and

amino acids) by a consortium of hydrolytic and acidogenic bacteria. The

volatile fatty acids (VFAs) thus formed mostly include- acetic, propionic,

and butyric acids

Fermentation of amino acids and sugars by hydrolytic bacteria

Anaerobic oxidation of long chain fatty acids and sugars/alcohols by

hetero-acetogenic bacteria


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Anaerobic oxidation of long chain fatty acids and sugars/alcohols by

hetero-acetogenic bacteria

Anaerobic oxidation of intermediate products such as volatile fatty

acids (other than acetate) by hetero-acitogenic bacteria

Conversion of hydrogen to methane by methanogenic bacteriautilizing hydrogen

Conversion of acetate to methane by methanogenic bacteria utilizing

acetate


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Un-dissolved carbohydrates and proteins are

hydrolyzed through a separate path. The hetero-

acetogenic bacteria grow in close association with

the methanogenic bacteria during final stage of theprocess. Conversion of fermentation products by

hetro-acetogens is thermodynamically possible only

when the hydrogen concentration is sufficiently low,

requiring a close symbiosis amongst the classes ofbacteria.


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Flow of Carbon During Anaerobic Degradation of Organic Material



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Comparison between Aerobic and

Anaerobic Processes


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Comparison between Aerobic and

Anaerobic Processes

Parameter Aerobic Anaerobic

Gaseous product No methane 2.4 kg CO2/kg

COD

CH4, a combustible gas

(24MJ/cu m) 1 kg CO2/kg

COD

Sludge disposal cost Very high, around 50% ofthe total cost

10% of that in the aerobicprocess

Nutrient requirement Substantial 20% lower than aerobic

Gaseous emission Volatile organic

compounds are released

into air

No such problem

Electron acceptor Only oxygen Several electron acceptors

Degradation of aromatic

compounds

Less suitable More suitable


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Comparison of Aerobic and Anaerobic Degradation of Aromatic Components

Anaerobic Aerobic

Channeling +H2O, 2H,-2H,+CO2,+CH4 O2

Central

intermediates

Benzoyl CoA,

resorcinoploroglucinol

Catechol,

protocatechuategentisate

Ring attack 2 or 4H +H2O O2

Central

intermediates

Easy to reduce or hydrate Easy to oxide

Cleavage of

the ring

Hydrolysis of 3-oxo

compound

Oxygenolysis


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Nitrogen Removal

Bi l i l Nit R l


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Nitrification

Urea is the principal form in which human body excretes excess nitrogen;

it is rapidly hydrolyzed to ammonia. Nitrification is bio-oxidation of

ammonia to nitrate with the help of nitrosomonas and nitrobacter, which

obtain their cell carbon from CO2 and energy from the oxidation of

inorganic compounds.

Nitrosomonas(3.33 g O2/1 g NH4-N)

55NH4++ 76O2+ 5CO2--- C5H7O2N + 54NO2

-+ 52H2O + 109H+

Nitrobacter (1.11 g O2/1 g NO2-N)

400NO2-+ 195O2+ 5CO2+ NH3+ 2H2O400NO3

-+ C5H7O2N

Biological Nitrogen Removal

Bi l i l Nit R l


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Nitrification

Nitrifying bacteria have extremely slow doubling time (12 d) compared

to common aerobic sewage bacteria (0.25 1.5 h). They are active in

aerated lagoons, oxidation ditches, and stabilization ponds or when the

concentration of organic compound is low (bottom 0.5 m of a low rate

trickling filter). Nitrification is desirable when the treated wastewater is to

be used for irrigation (nitrate as nutrient) or when it is to be dischargedinto a water body (ammonia- toxic to fish). In stabilization ponds, nitrate

promotes algal-bacterial symbiosis.



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Factors affecting nitrification

* Temperature

* Substrate concentration

* Dissolved oxygen

* pH

* Toxic and inhibitory substances

)2.7(83.01)15(095.04

4 pHeDOK

DO

NNHK

NNH T

ON

m


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Denitrification* Assimilatory denitrification

reduction of nitrate to ammonium by microorganism for protein

synthesis

* Dissimilatory denitrification

reduction of nitrate to gaseous nitrogen by microorganism

nitrate is used instead of oxygen as terminal electron acceptor

considered an anoxic process occurring in the presence of nitrateand the absence of molecular oxygen

the process proceeds through a series of four steps

NO NO NO N O N3-

2

-

2 2


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Factors affecting denitrification

* Temperature

* Dissolved oxygen

* pH


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Biological Sulfate Removal

* Sulfate removal cycle

anaerobic

SO4-- HS - S 0(O2 deficient)

(O2excess)

Aerobic and Anaerobic Biological Processes Basics

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