Growth and biodegradation

Phases of growth

Lag phase, exponential phase, stationary phase, death phase

Stationary Phase

Equal rate of growth and death

Exponential Phase

High growth rate

Oligotrophic

low nutrient

Copiotrophic

High nutrient

Dormant cells

Viable but low growth rate

VBNC

sub-lethally injured but still viable, cannot be cultured.

Anaerobic metabolism

synthesis of cell constituents and metabolites

Catabolic metabolism

Breakdown of cell constituents and metabolites

Biodegradation

Breakdown of organic pollutants by microbes.

Mineralisation

Oxidation of contaminants into co2 and water.

5 Factors of microbial degradation

Enzyme, bioavailability, toxicity of pollutant, env. conditions, contaminant structure.

Xenobiotic

Foreign chemical substance in the bilogical system, includes pollutants, pharmaceuticals etc.

Momooxygenase

Catalyst for oxidation of methane and trichloroethane

Co-metabolism

Partial oxidation due to the action of non-specific enzyme.

Bioavailability

Portion of pollutant that a microbe can utilise.

Controlling factors of bioavailability

Sorption and solubility

Bioavailability

Can be enhanced by bio-surfactants.

Toxicity

Leads to disruption in membrane integrity.

QSAR Model

quantitative-structure activity relationship

C:N ratio of xenobiotic

20:1 or lower

C:N ratio for microbes

5:1 or 10:1

degree of branching

Less bioavailability

Vadose zone

Initial low population

High electronegativity

Difficult of biodegrade

Aliphatic

Industrial solvent waste and petroleum industry, less branching

Toxic for microbes

<C8

Waxy substances, low solubility, low bioavailability

>C16

Saturated aliphatics

Oil reserves underground do not degrade.

C10 to C18

Readily degraded in aerobic conditions.

Addition of fumarate

Degradation in molecules of high mol. weight (metabolic intermediate)

Mono and distributed aliphatics.

Degrade more easily under aerobic condition

Highly halogenated aliphatics

Degrade more easily under anaerobic condition.

Treatment of halogenated aliphatic hydrocarbon

Anaerobic to remove Cl, aerobic to degrade the HC.

Co-oxidation

oxidation of two compounds where degradation of one compound depends on the first.

Metals in the environment

Cannot be degraded easily, persistent, valance state and bioavailibility can be altered microbially, serious threat.

Three classes of metals

Metals, Metalloids, Heavy Metals

Toxicity of metals

depends on speciation

Metals in environment

Mining, nuclear processing, landfills, electronics etc.

4 was by with meals enter the environment

precipitation, sorption, bioavailability, volatility.

Total metal concentration

bioavailable + non-bioavailable fraction

Speciation of metals

Soil conditions and microbes

hH-Eh diagram

Shows the range in which chemical species are stable, whether mineral is at equilibrium with its surroundings or subject to chemical transformation.

Factors of speciation and bioavailability

Metal chemistry, CEC, redox potential, pH

High CEC

large no. of particles to bind to the particles’ surface, low toxicity.

Low CEC

Less no. of particles to bind to the particles’ surface, high toxicity.

Oxidising environment (800-0mV)

Soluble cations

Reducing environment (0- -400mV)

Metals will precipitate

High pH

Low bioavailability

low pH

Free ions, increase solubility, increase bioavailability.

Soil washing

Addition of acids and chelates like EDTA, moves metal contaminants into water

Excavation

Problem- this metal removal leads to exposure to oxygen.

Soil incineration

Problem- this metal removal destroys the soil.

Metal immobilisation

Increase pH and add organics

Organics in metal immobilisation

increase electrostatic attraction and sorption.