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
Anaerobic respiration
Anaerobic respiration
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
Biochemical Pathways
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Biochemical Pathways
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
Biochemical Pathways
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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
Biological growth...
= mS
Ks S
Substrate Concentration(S)
Speci
ficgrowthrate()
Max. ratem
m/2
ks
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Haldane kinetics(under toxic conditions)
Biological growth...
= 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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Aerobic Biodegradation Process
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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Aerobic Biodegradation Process
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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Aerobic Biodegradation Process
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 Biodegradation Process
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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Anaerobic Biodegradation Process
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
Anaerobic Biodegradation Process
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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.
Biological Nitrogen Removal
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Biological Nitrogen Removal
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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Biological Nitrogen Removal
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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Biological Nitrogen Removal
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)