CE 510Hazardous Waste EngineeringDepartment of Civil EngineeringSouthern Illinois University Carbondale

Instructors: Jemil Yesuf Dr. L.R. Chevalier

Lecture Series 7:Biotic and Abiotic Transformations

Course Goals Review the history and impact of environmental laws

in the United States Understand the terminology, nomenclature, and

significance of properties of hazardous wastes and hazardous materials

Develop strategies to find information of nomenclature, transport and behavior, and toxicity for hazardous compounds

Elucidate procedures for describing, assessing, and sampling hazardous wastes at industrial facilities and contaminated sites

Predict the behavior of hazardous chemicals in surface impoundments, soils, groundwater and treatment systems

Assess the toxicity and risk associated with exposure to hazardous chemicals

Apply scientific principles and process designs of hazardous wastes management, remediation and treatment

Abiotic and Biotic Transformations

Abiotic Chemical and physical

transformations Hydrolysis, Redox reactions,

Photolysis,…Biotic

Transformation of contaminants through biological processes

Results in mineralization of both natural and engineered organic compounds

BIOLOGICAL TREATMENT OF

HAZARDOUS WASTE

DEGRADATION OF ORGANIC WASTE BY THE ACTION OF MICROORGANISMS

This degradation alters the molecular structure of the organic compound

TWO DEGREES OF DEGRADATION

BIOTRANSFORMATIONBreakdown of organic compound to daughter compound

MINERALIZATIONComplete breakdown of organic compound into

cellular mass, carbon dioxide, water and inert

inorganic residuals

Schematic diagram of biodegradation process

bacterialcell

A A AA

A

A AA

An organic reactant A is bound to an extracellular enzyme

Schematic diagram of biodegradation process

A

The enzyme transports the organic reactant A into the cell.

bacterialcell

AAA A

A

Schematic diagram of biodegradation process

The organic reactant provides the energy to synthesize new cellular material, repair damage, and transport nutrients across the cell boundary

AB

C O2

CO2

H20

Schematic diagram of biodegradation process

bacterialcell

A A AA

A

A AA

Abacterial

cell

AAA A

A

AB

C O2

CO2

H20

Enzyme bound chemicals Transport of chemicals across the cell boundary

Breakdown of chemicals

Definitions Microbes need carbon and energy source

(electron donors) Light – phototrophs – carry out photosynthesis Chemical sources – chemotrophs

Inorganic source – lithotroph Ammonia, NH3, Ferrous iron, Fe2+, Sulfide, HS-Manganese, Mn2+

NH3 + O2 NO2- + H2O + Energy Organic source – organotrophs

Examples include the food you eat C8H10 + 10.5O2 8CO2 + 5H2O + Energy

Autotrophs – obtain carbon from carbon dioxide 6CO2 + Energy + 6H2O C6H12O6 + 6O2

Heterotrophs – obtain carbon from organic matter C8H10 + 10.5O2 8CO2 + 5H2O + Biomass

Definitions Microbes also need electron acceptor

Source: Newell et al., 1995

The biochemical energy associated with alternative degradation pathways can be represented by the redox potential of the alternative electron acceptorsThe more positive the redox potential, the more energetically favorable is the reaction utilizing that electron acceptor.

See Textbook example 7.7

Governing Variables Chemical structure and Oxidation state

Persistent hazardous wastes – some halogenated solvents, pesticides, PCBs xenobiotics

Branching, hydrophobicity, HC saturation and increased halogenation are reported to decrease rates of biodegradation and reactivity

Oxidation state of a contaminant is an important predictor of abiotic and biotic transformation

This number changes when an oxidant acts on a substrate.

Redox reactions occur when oxidation states of the reactants change

Class ExampleWhat is the average oxidation state of carbon in a) Methaneb) TCAc) TCEd) PCE

Solutiona) Methane (-IV)b) TCA (0)c) TCE (I)d) PCE (+II)

Governing VariablesPresence of reactive species

Abiotic and biotic transformations require the presence of Oxidant Hydrolyzing agent (nucleophile) Microorganisms Appropriate transforming species

Availability Sorption NAPLs

Other Variables Dissolved oxygen

Aerobic and anerobic biodegradations Temperature

Two fold increase in reaction rate for each rise of 10ºC

Empirical equation in biological treatment engineering: k2 = k1 Θ(T2-T1)

pH Optimal pH for growth varies

Oxidation-Reduction (Redox) Reactions

Living organisms utilize chemical energy through redox reactions

This is a coupled reaction Transfer of electrons from one molecule to

another Electron acceptor - Oxidizing agents Electron donor - Reducing agents

Redox Reactionse-

e-

The tendency of a substance to donate electrons or accept electrons is expressed as the reduction potential Eo (measured in volts)

Negative Eo – donorsPositive Eo - acceptors

OxidationProcess in which an atom or molecule loses an electron

ReductionProcess in which an atom or molecule gains an electron

Redox Reactionse-

e-

OxidationProcess in which an atom or molecule loses an electron

ReductionProcess in which an atom or molecule gains an electron

Redox Reactionse-

e-

Na(s) Na+ + e-

Cl2(g) + 2e- 2Cl-

2Na(s) 2Na+ + 2e-

Cl2(g) + 2e- 2Cl-

Redox ReactionsThese “half reactions” occur in pairs.Together they make a complete reaction.

Na(s) + Cl 2(g) Na+ + 2Cl-

Tables for Half ReactionsReduction

StandardPotential

Half-Reaction E° (volts)Li+(aq) + e- -> Li(s) -3.04Ca2+(aq) + 2e- -> Ca(s) -2.76Na+(aq) + e- -> Na(s) -2.71Mg2+(aq) + 2e- -> Mg(s) -2.382H+(aq) + 2e- -> H2(g) 0Fe3+(aq) + e- -> Fe2+(aq) 0.77Ag+(aq) + e- -> Ag(s) 0.8Hg2+(aq) + 2e- -> Hg(l) 0.852Hg2+(aq) + 2e- -> Hg2

2+(aq) 0.9NO3

-(aq) + 4H+(aq) + 3e- -> NO(g) + 2H2O(l) 0.96

O2(g) + 4H+(aq) + 4e- -> 2H2O(l) 1.23O3(g) + 2H+(aq) + 2e- -> O2(g) + H2O(l) 2.07F2(g) + 2e- -> 2F-(aq) 2.87

These equations are written as reductions.For oxidation, the equation would be in reverse.Eo would also change signs.

Tables for Half ReactionsReduction

StandardPotential

Half-Reaction E° (volts)Li+(aq) + e- -> Li(s) -3.04Ca2+(aq) + 2e- -> Ca(s) -2.76Na+(aq) + e- -> Na(s) -2.71Mg2+(aq) + 2e- -> Mg(s) -2.382H+(aq) + 2e- -> H2(g) 0Fe3+(aq) + e- -> Fe2+(aq) 0.77Ag+(aq) + e- -> Ag(s) 0.8Hg2+(aq) + 2e- -> Hg(l) 0.852Hg2+(aq) + 2e- -> Hg2

2+(aq) 0.9NO3

-(aq) + 4H+(aq) + 3e- -> NO(g) + 2H2O(l) 0.96O2(g) + 4H+(aq) + 4e- -> 2H2O(l) 1.23O3(g) + 2H+(aq) + 2e- -> O2(g) + H2O(l) 2.07F2(g) + 2e- -> 2F-(aq) 2.87

A full redox reaction is a combination of a reduction equation and an oxidation equation

Redox EquationsRedox pairs (O/R) are expressed such that the oxidizing agent (electron acceptor) is written on the left, while the reducing agent (electron donor) is written on the right.

To pair two reactions as redox, one of the pairs are written as a reduction, the other as oxidation.CO2/C6H12O6 and O2/H2O

Redox Equations

CO2/C6H12O6 and O2/H2O

To determine whether a chemical is oxidized or reduced, consider Eo from the standard reduction table. For the pairs below:

6CO2 + 24H+ +24e- = C6H12O6 Eo = -0.43 VO2(g) + 4H+ + 4e- = 2H2O Eo = 0.82 V

The negative E0 value indicates that this reaction should be written in reverse (oxidation)

Balancing Redox EquationsConsider the metabolism of glucose by aerobic microorganisms. Write the balanced reaction that combines the redox pairs CO2/C6H12O6 and O2/H2O.

(work as class example)

SolutionGlucose is the energy source, and the electron

donor. It will be oxidized. Oxygen, on the other hand, is the electron acceptor, it will be reduced.

1. Write the two half reactions

)()(

22

26126

reductionOHOoxidationCOOHC

Solution

changenoOHOCOOHC

22

26126 6

2. Balance the main elements other than oxygen and hydrogen

3. Balance oxygen by adding H20 and hydrogen by adding H+

OHHO

HCOOHOHC

22

226126

24

2466

Solution

OHeHO

eHCOOHOHC

22

226126

244

242466

4. Balance the charge by adding electrons

5. Multiply each half reaction by the appropriate integer that will result in the same number of electrons in each. Then add the two half reactions to come up with the balanced reaction.

OHCOOOHC

OHeHO

eHCOOHOHC

OHeHO

eHCOOHOHC

2226126

22

226126

22

226126

666

1224246

242466

244

242466

Solution

ExampleBalance the redox reaction of sodium dicromate (Na2Cr2O7) with ethyl alcohol (C2H5OH) if the products of the reaction are Cr+3 and CO2

strategy

Strategy Balance the principal atoms Balance the non-essential ions Balance oxygen with H2O Balance hydrogen with H+

Balance charges with electrons Balance the number of electrons in each

half reaction and add together Subtract common items from both sides

of the equation.

Solution

Solution

Free Energy of Formation, Gf

o

Energy released or energy required to form a molecule from its elements

By convention, Gf0 of the elements

(O2, C, N2) in their standard state is zero.

Some representative values Gf0 are

given on the next slide

Free Energy of Formation, Gf

o

Compound Gfo, kJ/mole

C6H12O6 -917.22

CO2 -394.4

O2 0

H20 -237.17

CH4 -50.75

N20 104.18

Using Gf0 you can

calculate whether a reaction will occur. For the reactionaA + bB cC + dD

DGo = cGfo(C)+dGf

o(D) – aGf

0(A) – bGfo(B)

Class ExampleOne mole of methane (CH4) and two moles of oxgyen are in a closed container. Determine if the reaction below will proceed as written based on DGo.

CH4 + 2O2 CO2 + 2H20

SolutionCompound Gf

o, kJ/mole

CO2 -394.4

O2 0

H20 -237.17

CH4 -50.75

CH4 + 2O2 CO2 + 2H20

DGo = cGfo(C)+dGf

o(D) – aGf

0(A) – bGfo(B)

=(-394.4)+2(-237.17) -(-50.75)-2(0) = -817.99 kJ/mole

This is a large negative value, the reaction will proceed as written.

Relationship between DGo and DEo

WhereΔGo = the Gibbs energy of reaction at 1 atm and 25oCn = number of electrons in the reactionF = caloric equivalent of the faraday = 23.06 kcal/volt-mole

Eo is related to the equilibrium constant, K, by:

Where:R=universal gas constant=0.00199 kcal/mol-oKT=temperature(oK)

)ln(KnFRTE o

The electromotive force, Eo is related to ΔGo 0nFEGo D

Binary Fission

1 2 4 8 16 32

P = Po(2)n

Po is the initial population at the end of the accelerated growth phase

P is the population after n generations

Microbial Growth Ba

cter

ial n

umbe

rs

(lo

g)

Time

Bact

eria

l num

bers

(log)

Time

LagPhase

Adjustment to new environment, unlimited source of nutrient and substrate

Microbial Growth

Bact

eria

l num

bers

(log)

Time

LagPhase Accelerated growth phase

bacteria begin to divide at various rates

Microbial Growth

Bact

eria

l num

bers

(log)

Time

LagPhase

Accelerated growth phase

Exponential growth phasedifferences in growth rates not as significant because of population increase

Microbial Growth

Bact

eria

l num

bers

(log)

Time

LagPhase

Accelerated growth phase

Exponential growth phase

Microbial Growth Stationary phase substrate becomes exhausted or toxic by-products build up resulting in a balance between the death and reproduction rates

Bact

eria

l num

bers

(log)

Time

LagPhase

Accelerated growth phase

Exponential growth phase

Stationary phase

Death phase

Microbial Growth

Rates of Transformation Kinetics of transformations are difficult

to quantify Furthermore, soil, groundwater and

hazardous waste treatment systems are so complex that the exact transformation pathway cannot be elucidated

However, the prediction of rates is necessary in order to Perform site characterization Perform facilities assessment Design treatment systems

Rates of Transformation

nCkdtCd

Generalized equation

C = Contaminant concentrationk = proportionality constant (units dependent on reaction order)n = reaction order

Zero Order Kinetics

ktCC

CkdtCd

CkdtCd

ot

n

0

First Order Kinetics

ktot

n

eCC

CkdtCd

CkdtCd

1

Second Order Kinetics

.]/['

,

)(0.

.

' OHenzymekkwhereCkdtCd

Therefore

statesteadydtOHd

dtenzymedbut

OHCkdtCd

orenzymeCkdtCd

Text Problem 7.4The biodegradation rate of benzo[a]pyrene has been described by the expression

During a bioremediation project of a contaminated groundwater, the biomass concentration reached a steady state at 7.1X1011 cell/L during treatment and remained at approximately that concentration through out the project. If Co is 25 ug/L and the hydraulic detention time of the groundwater as it passes through the control volume is 10 days, determine the effluent concentration of benzo[a]pyrene as the water exits the system.

XCkdtCd

Where, k=3X10-15 L/cell-h[C] = conc. of benzo[a]pyrene[X] = biomass conc.

Solution[X] = 7.1X1011 cell/Lt = 240 daysCo = 25 ug/L

k’ = k[X] = (3x10-15 L/cell-hr)(7.1x1011 cell/L) = 0.00213 hr-1

Therefore,C = Coe-k’t

= (25 ug/L) e-(0.00213 hr-1 x 240 hr)

= 15 ug/L

XCkdtCd

…end of solution

Michaelis-Menton Kinetics

mKCCVV

max

It is a saturation phenomena described by:

whereV = rate of transformation (mg/Lh)Vmax = maximum rate of transformation (mg/Lh)C = contaminant concentration (mg/L)Km = half-saturation constant (mg/L)

Contaminant Concentration (mg/L)

Rat

e (m

g/L-

min

)

..

Vmax

0.5 Vmax

Km

Michaelis-Menton Kinetics

Class ExampleDescribe how you would get Km and Vmax from the following data.

Initial Conc. (mg/L)Initial Rate

(mg/(L-min))

8 1.2

14 1.6

23 2.4

32 2.7

47 2.8

55 2.8

65 2.8

Summary of Important Points and Concepts Biotransformation refers to the

breakdown of a chemical into daughter compounds whereas mineralization is the complete breakdown of a compound

Redox reactions can be used to determine the biological or chemical oxidation/reduction of waste

Estimates of the kinetics of waste reduction are necessary to assess and design treatment of hazardous waste.