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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.