Presentation on theme: "CE 510 Hazardous Waste Engineering"— Presentation transcript:
1CE 510 Hazardous Waste Engineering Department of Civil EngineeringSouthern Illinois University CarbondaleInstructors: Jemil YesufDr. L.R. ChevalierLecture Series 7:Biotic and Abiotic Transformations
2Course GoalsReview the history and impact of environmental laws in the United StatesUnderstand the terminology, nomenclature, and significance of properties of hazardous wastes and hazardous materialsDevelop strategies to find information of nomenclature, transport and behavior, and toxicity for hazardous compoundsElucidate procedures for describing, assessing, and sampling hazardous wastes at industrial facilities and contaminated sitesPredict the behavior of hazardous chemicals in surface impoundments, soils, groundwater and treatment systemsAssess the toxicity and risk associated with exposure to hazardous chemicalsApply scientific principles and process designs of hazardous wastes management, remediation and treatment
3Abiotic and Biotic Transformations Chemical and physical transformationsHydrolysis, Redox reactions, Photolysis,…BioticTransformation of contaminants through biological processesResults in mineralization of both natural and engineered organic compounds
4BIOLOGICAL TREATMENT OF HAZARDOUS WASTE DEGRADATION OF ORGANIC WASTE BY THE ACTION OF MICROORGANISMSThis degradation alters the molecular structure of the organic compound
5TWO DEGREES OFDEGRADATIONMINERALIZATIONComplete breakdown of organic compound into cellular mass, carbon dioxide, water and inert inorganic residualsBIOTRANSFORMATIONBreakdown of organic compound to daughter compound
6Schematic diagram of biodegradation process bacterialcellAAAAAAAn organic reactant A is bound to an extracellular enzyme
7Schematic diagram of biodegradation process bacterialcellAAAAAAThe enzyme transports the organic reactant A into the cell.
8Schematic diagram of biodegradation process The organic reactant provides the energy to synthesize new cellular material, repair damage, and transport nutrients across the cell boundaryCO2ABH20CO2
9Schematic diagram of biodegradation process Transport of chemicals across the cell boundaryEnzyme bound chemicalsAAbacterialcellAbacterialcellAAAAAAAAAAACO2ABBreakdown of chemicalsH20CO2
10Definitions Microbes need carbon and energy source (electron donors) Light – phototrophs – carry out photosynthesisChemical sources – chemotrophsInorganic source – lithotrophAmmonia, NH3, Ferrous iron, Fe2+, Sulfide, HS-Manganese, Mn2+NH3 + O2 NO2- + H2O + EnergyOrganic source – organotrophsExamples include the food you eatC8H O2 8CO2 + 5H2O + EnergyAutotrophs – obtain carbon from carbon dioxide6CO2 + Energy + 6H2O C6H12O6 + 6O2Heterotrophs – obtain carbon from organic matterC8H O2 8CO2 + 5H2O + Biomass
11Definitions Microbes also need electron acceptor Source: Newell et al., 1995The 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
12Governing Variables Chemical structure and Oxidation state Persistent hazardous wastes – some halogenated solvents, pesticides, PCBs xenobioticsBranching, hydrophobicity, HC saturation and increased halogenation are reported to decrease rates of biodegradation and reactivityOxidation state of a contaminant is an important predictor of abiotic and biotic transformationThis number changes when an oxidant acts on a substrate.Redox reactions occur when oxidation states of the reactants change
13Class Example What is the average oxidation state of carbon in Methane TCATCEPCE
15Governing Variables Presence of reactive species Availability Abiotic and biotic transformations require the presence ofOxidantHydrolyzing agent (nucleophile)MicroorganismsAppropriate transforming speciesAvailabilitySorptionNAPLs
16Other Variables Dissolved oxygen Temperature pH Aerobic and anerobic biodegradationsTemperatureTwo fold increase in reaction rate for each rise of 10ºCEmpirical equation in biological treatment engineering: k2 = k1 Θ(T2-T1)pHOptimal pH for growth varies
17Oxidation-Reduction (Redox) Reactions Living organisms utilize chemical energy through redox reactionsThis is a coupled reactionTransfer of electrons from one molecule to anotherElectron acceptor - Oxidizing agentsElectron donor - Reducing agents
18Redox Reactionse-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 - acceptorse-
19Redox Reactions e- e- Oxidation Process in which an atom or molecule loses an electronReductionProcess in which an atom or molecule gains an electrone-
20Redox Reactions e- e- Oxidation Process in which an atom or molecule loses an electronNa(s) Na+ + e-ReductionProcess in which an atom or molecule gains an electrone-Cl2(g) + 2e- 2Cl-
21Redox Reactions These “half reactions” occur in pairs. Together they make a complete reaction.2Na(s) 2Na+ + 2e-Cl2(g) + 2e- 2Cl-Na(s) + Cl 2(g) Na+ + 2Cl-
22Tables for Half Reactions ReductionStandardPotentialHalf-ReactionE° (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)Fe3+(aq) + e- -> Fe2+(aq)0.77Ag+(aq) + e- -> Ag(s)0.8Hg2+(aq) + 2e- -> Hg(l)0.852Hg2+(aq) + 2e- -> Hg22+(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)2.87These equations are written as reductions.For oxidation, the equation would be in reverse.Eo would also change signs.
24Redox 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
25Redox EquationsTo determine whether a chemical is oxidized or reduced, consider Eo from the standard reduction table. For the pairs below:CO2/C6H12O6 and O2/H2O6CO2 + 24H+ +24e- = C6H12O6 Eo = VO2(g) + 4H+ + 4e- = 2H2O Eo = 0.82 VThe negative E0 value indicates that this reaction should be written in reverse (oxidation)
26Balancing Redox Equations Consider 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)
27SolutionGlucose 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.Write the two half reactions
28Solution 2. Balance the main elements other than oxygen and hydrogen 3. Balance oxygen by adding H20 and hydrogen by adding H+
29Solution 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.
31ExampleBalance the redox reaction of sodium dicromate (Na2Cr2O7) with ethyl alcohol (C2H5OH) if the products of the reaction are Cr+3 and CO2strategy
32Strategy Balance the principal atoms Balance the non-essential ions Balance oxygen with H2OBalance hydrogen with H+Balance charges with electronsBalance the number of electrons in each half reaction and add togetherSubtract common items from both sides of the equation.
35Free Energy of Formation, Gfo Energy released or energy required to form a molecule from its elementsBy convention, Gf0 of the elements (O2, C, N2) in their standard state is zero.Some representative values Gf0 are given on the next slide
36Free Energy of Formation, Gfo CompoundGfo, kJ/moleC6H12O6CO2-394.4O2H20CH4-50.75N20104.18Using Gf0 you can calculate whether a reaction will occur. For the reactionaA + bB cC + dDDGo = cGfo(C)+dGfo(D) –aGf0(A) – bGfo(B)
37Class 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
38Solution DGo = cGfo(C)+dGfo(D) – aGf0(A) – bGfo(B) CompoundGfo, kJ/moleCO2-394.4O2H20CH4-50.75DGo = cGfo(C)+dGfo(D) –aGf0(A) – bGfo(B)=(-394.4)+2( )-(-50.75)-2(0)= kJ/moleThis is a large negative value, the reaction will proceed as written.CH4 + 2O2 CO2 + 2H20
39Relationship between DGo and DEo The electromotive force, Eo is related to ΔGoWhereΔGo = the Gibbs energy of reaction at 1 atm and 25oCn = number of electrons in the reactionF = caloric equivalent of the faraday = kcal/volt-moleEo is related to the equilibrium constant, K, by:Where:R=universal gas constant= kcal/mol-oKT=temperature(oK)
40Binary Fission 1 2 4 8 16 32 P = Po(2)n P = Po(2)nPo is the initial population at the end of the accelerated growth phaseP is the population after n generations
42Microbial Growth Lag Phase Bacterial numbers(log)LagPhaseAdjustment to new environment, unlimited source of nutrient and substrateTime
43Microbial Growth Accelerated growth phase Bacterial numbers(log)LagPhaseAccelerated growth phasebacteria begin to divide at various ratesTime
44Microbial Growth Exponential growth phase differences in growth rates not as significant because of population increaseBacterial numbers(log)LagPhaseAccelerated growth phaseTime
45Microbial GrowthStationary phase substrate becomes exhausted or toxic by-products build up resulting in a balance between the death and reproduction ratesBacterial numbers(log)Exponentialgrowth phaseLagPhaseAccelerated growth phaseTime
46Microbial Growth Stationary phase Death phase Lag Phase Exponential Bacterial numbers(log)LagPhaseExponentialgrowth phaseAccelerated growth phaseTime
47Rates of Transformation Kinetics of transformations are difficult to quantifyFurthermore, soil, groundwater and hazardous waste treatment systems are so complex that the exact transformation pathway cannot be elucidatedHowever, the prediction of rates is necessary in order toPerform site characterizationPerform facilities assessmentDesign treatment systems
48Rates of Transformation Generalized equationC = Contaminant concentrationk = proportionality constant (units dependent on reaction order)n = reaction order
52Text Problem 7.4 Where, k=3X10-15 L/cell-h The biodegradation rate of benzo[a]pyrene has been described by the expressionDuring 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.Where, k=3X10-15 L/cell-h[C] = conc. of benzo[a]pyrene[X] = biomass conc.
53Solution[X] = 7.1X1011 cell/L t = 240 days Co = 25 ug/L k’ = k[X] = (3x10-15 L/cell-hr)(7.1x1011 cell/L) = hr-1 Therefore, C = Coe-k’t = (25 ug/L) e-( hr-1 x 240 hr) = 15 ug/L…end of solution
54Michaelis-Menton Kinetics 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)
56Class ExampleDescribe how you would get Km and Vmax from the following data.Initial Conc. (mg/L)Initial Rate (mg/(L-min))81.2141.6232.4322.7472.85565
57Summary of Important Points and Concepts Biotransformation refers to the breakdown of a chemical into daughter compounds whereas mineralization is the complete breakdown of a compoundRedox reactions can be used to determine the biological or chemical oxidation/reduction of wasteEstimates of the kinetics of waste reduction are necessary to assess and design treatment of hazardous waste.