Bio Degradation Of Pollutants

Transformation and Degradation of Pollutants Important Variables for Contaminant Transformations 2. Chemical Structure of the Contaminant 3. Presence of Transforming Species 4. Physical Availability of the contaminant. 5. Dissolved Oxygen 6. pH 7. Temperature

Abiotic Transformation of Pollutants 1. 2. 3.

Nucleophilic Substitution Elimination Reaction Oxidation/Reduction

OH = One of the most important oxidants found in air, water and biological systems. Sources of OH Radical: g. Fenton Reaction h. Reaction of Ozone wigth NOx

Biodegradation Reactions and Pathways of Hazardous Contaminants

Microbial Transformation of Pollutants Microorganisms involved in Biotransformations 2. Bacteria 3. Fungi 4. Algae 5. Protozoan

Classification of Bacteria in Microbial Metabolism 1. Based on Energy Sources b. Chemotrophs c. Phototrophs 2. Based on Sources of Carbon e. Autotrophs f. Heterotrophs 3. Based on Sources of Electrons h. Organotrophs i. Lithotrophs

Microbial Population

Microbial Growth Pattern

Stationary Phase

Log Phase Lag Phase

Time

Death Phase

Conceptual Basis for Biodegradation Reaction

Contaminant

+ Xox

Product

+ Xred

Redox Couple Substrate Redox Couple »

Eo’ (V)

•

Succinate + CO2 + 2H + 2e a-ketoglu + H2O

-0.67

•

AcetylcoA + CO2 + 2H + 2e  Pyruvate + COAsH

-0.48

•

A-ketoglu + CO2 + 2H + 2e isocitrate

-0.38

• • • •

Acetaldehyde + 2H + 2e  ethanol Pyruvate + 2H + 2e  Lactate Oxaloacetate + 2H + 2e  Malate Fumarate + 2H + 2e  Succinate

-0.20 -0.19 -0.17 0.03

ETS Couple (Aerobic Respiration 2H + 2e - H2

-0.42

Ferridoxin (Fe3+) + 1e  Ferridoxin (Fe2+) NAD + H+ + 2e --- NADH

-0.32

NADP + H+ + 2e - NADPH

-0.32

FAD + 2H + 2e - FADH2

-0.18

-0.42

ETS Couple (Aerobic Respiration

• • • • • • • • •

2H + 2e - H2 Ferridoxin (Fe3+) + 1e  Ferridoxin (Fe2+) NAD + H+ + 2e --- NADH NADP + H+ + 2e - NADPH FAD + 2H + 2e - FADH2 Cytb(Fe2+) + 1e  Cytb(Fe2+) Cytc (Fe3+) + 1e  Cytc (Fe2+) Cyta3 (Fe3+) + 1e  Cyta3 (Fe2+) 0.55 O2 + 4H +4e - 2H2O

ETS Couple (Anaerobic Respiration SO42- + 3H

+ 2e - HSO3- + H2O

-0.52

NO3-

+2H + 2e  NO2- + H2O

+0.42

NO2-

+ 8H + 6e  NH4+ + 2H2O

+0.44

Fe3+

+ 1e - Fe2+

+0.77

-0.42 -0.42 -0.32 -0.32 -0.18 0.10 0.25 0.82

Dependence of Bacteria on Electron Acceptor • Aerobic Reaction- O2 is the e- acceptor • • • •

Anaerobic Process: 3 Pathways 1. Anaerobic Respiration 2. Fermentation 3. Methanogenesis

Aerobic Metabolism Pathways • • • • • •

Emden-Meyerhof Pathway TCA Electron Transport System Glucose Metabolism: Glucose  Pyruvate 2 ATP and 2 NADH 2 Pyruvate  2 AcetyCoA 2 NADH • 2 AcetylcoA  4 CO2 + 2 H2O 6 NADH, 2 FADH, 2 ATP

• Lactate Fermentation • Glucose + 2 NAD+ + 2 ADP + 2Pi  2 Pyruvate + 2 NADH + 2 H+ + 2 ATP • 2 NADH + 2 H + 2 Pyruvate  2 Lactate • Glucose + 2 ADP + 2Pi  2 Lactate + 2 ATP Ethanol Fermentation Glucose + 2 NAD+ + 2 ADP + 2Pi  2 Pyruvate + 2 NADH + 2 H + 2 ATP 2 Pyruvate - 2 Acetaldehyde + 2 CO2 2 Acetaldehyde + 2 NADH + 2 H - 2 Ethanol + 2 NAD+ Glucose + 2 ADP + 2 Pi - 2 Ethanol + 2 CO2 + 2 ATP

Methanogenesis: CH3COOH -- CH4 + CO2

•

Important Bacteria in Hazardous Waste Systems:

•

White Rot Fungus or Wood Rot Fungus Examples: Phanerochaete Chrysosporum Phanerochaete sordida -These fungi have been shown to degrade PAH, PCB, pentachlorophenol, DDT through the activity of extracellulase peroxidase enzyme Important Bacteria in Hazardous Waste Systems: i. Pseudomonas j. Nocardia k. Mycobacterium l. Arthrobacteria m. Bacillus

Biodegradation Reactions and Pathways of Hazardous Contaminants • 1. Contaminants pass through the cell membrane. • 2. Compounds too large to pass through the cell membrane may be partially degradaded by exoenzymes which are secreted through the cell wall. • 3.The following reactions will occur in the cytoplasm: Hydroxylation, Hydrolysis, Dehalogenation, Dealkylation and Reduction • 4. Dehydrohalogenation

Oxidative Processes for which Oxygen is the Electron Acceptor • Monooxygenases are characterized by their ability to introduce one of the atoms of O2 into an organic substrate, S and the other being incorporated into a molecule of water. • S + O2 + AH + H+ -- SO + A + H2O • • • • • •

Reactions catalyzed by Monooxygenases: 1. Hydroxylation at Saturated and Unsaturated Carbon 2. Epoxidation of Olefin 3. Baeyer-Villiger Oxidation of Ketones 4. Oxidation at S and N 5. Heteroatom Dealkylation

Protoporphyrin Ring

N

N

Fe2+ N

N

CO2-

S(Cys-Protein)

CO2-

S(O)

S, 1e Fe3+

4+

Fe=O

S

Fe2+---S

H2O

3+ H+ S--- Fe

O2, e, H+ OOH

1e Fe3+(O -) -------> H+ Fe3+(OOH) Fe2+P + O2 -----> Fe3+ (O2-) -----> 2 Homolytic Bond Cleavage

Fe3+(OOH)----> Fe4+(O2-) + HO .

Heterolytic Bond Cleavage

Fe3+(OOH)---->Fe4+P(O2-) + HO-

• Cytochrome P450Dependent monooxygenase delivers oxygen to the substrate in the form of a heme-iron oxo complex • Responsible for the majority of biological hydroxylation, epoxidation, and heteroatom dealkylation

Hydroxylation of Alkane Fe3+P(OOH) + CH4  Fe4+P(O2-) + CH3. +H2O Fe4+P(O2-) + CH3. ---> Fe3+P-OCH3 -- [Fe3+P] + HOCH3

Hydroxylation of Benzylic Carbon, Amines and Mercaptans -Hydroxylation of the substrate can occur following the removal of one electron from the aromatic ring.

HO

Epoxidation of Alkene

R Fe3+P(OOH)

R

.

+. R

R

Fe4+P(O-2) + HO.

Fe3+P(OOH) + CH2=CH2  Fe3+P(OH) + epoxide

Fe4+PO. + CH3NH2 ----> Fe4+PO- + CH3NH2+. ----> CH2=NH2+

O

Fe4+P(O2-)

Enzyme Recycling PFe3+ + CH3-N+-OOH

O

Fe4+O. + -S-

Enzyme Recycling

------> Fe4+-O- + -S+-

Fe3+ +

O -S-

Fe3+PO-N(CH3)3+

Initial Degradation of Benzene