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CE 510 Hazardous Waste Engineering Department of Civil Engineering Southern Illinois University Carbondale Instructors: Jemil Yesuf Dr. L.R. Chevalier.

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Presentation on theme: "CE 510 Hazardous Waste Engineering Department of Civil Engineering Southern Illinois University Carbondale Instructors: Jemil Yesuf Dr. L.R. Chevalier."— Presentation transcript:

1 CE 510 Hazardous Waste Engineering Department of Civil Engineering Southern Illinois University Carbondale Instructors: Jemil Yesuf Dr. L.R. Chevalier Lecture Series 7: Biotic and Abiotic Transformations

2 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

3 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

4 BIOLOGICAL TREATMENT OF HAZARDOUS WASTE DEGRADATION OF ORGANIC WASTE BY THE ACTION OF MICROORGANISMS This degradation alters the molecular structure of the organic compound

5 TWO DEGREES OF DEGRADATION BIOTRANSFORMATION Breakdown of organic compound to daughter compound MINERALIZATION Complete breakdown of organic compound into cellular mass, carbon dioxide, water and inert inorganic residuals

6 Schematic diagram of biodegradation process bacterial cell A A A A A A A A An organic reactant A is bound to an extracellular enzyme

7 Schematic diagram of biodegradation process A The enzyme transports the organic reactant A into the cell. bacterial cell A A A A A

8 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 A B C O2O2 CO 2 H20H20

9 Schematic diagram of biodegradation process bacterial cell A A A A A A A A A bacterial cell A A A A A A B C O2O2 CO 2 H20H20 Enzyme bound chemicals Transport of chemicals across the cell boundary Breakdown of chemicals

10 Definitions  Microbes need carbon and energy source (electron donors) Light – phototrophs – carry out photosynthesis Chemical sources – chemotrophs  Inorganic source – lithotroph Ammonia, NH 3, Ferrous iron, Fe 2+, Sulfide, HS - Manganese, Mn 2+ NH 3 + O 2  NO H 2 O + Energy  Organic source – organotrophs Examples include the food you eat C 8 H O 2  8CO 2 + 5H 2 O + Energy Autotrophs – obtain carbon from carbon dioxide  6CO 2 + Energy + 6H 2 O  C 6 H 12 O 6 + 6O 2 Heterotrophs – obtain carbon from organic matter  C 8 H O 2  8CO 2 + 5H 2 O + Biomass

11 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 acceptors The more positive the redox potential, the more energetically favorable is the reaction utilizing that electron acceptor. See Textbook example 7.7

12 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

13 Class Example What is the average oxidation state of carbon in a) Methane b) TCA c) TCE d) PCE

14 Solution a) Methane (-IV) b) TCA (0) c) TCE(I) d) PCE (+II)

15 Governing Variables  Presence of reactive species Abiotic and biotic transformations require the presence of  Oxidant  Hydrolyzing agent (nucleophile)  Microorganisms  Appropriate transforming species  Availability Sorption NAPLs

16 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: k 2 = k 1 Θ (T2-T1)  pH Optimal pH for growth varies

17 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

18 Redox Reactions e-e- e-e- The tendency of a substance to donate electrons or accept electrons is expressed as the reduction potential E o (measured in volts) Negative E o – donors Positive E o - acceptors

19 Oxidation Process in which an atom or molecule loses an electron Reduction Process in which an atom or molecule gains an electron Redox Reactions e-e- e-e-

20 Oxidation Process in which an atom or molecule loses an electron Reduction Process in which an atom or molecule gains an electron Redox Reactions e-e- e-e- Na (s)  Na + + e - Cl 2(g) + 2e -  2Cl -

21 2Na (s)  2Na + + 2e - Cl 2(g) + 2e -  2Cl - Redox Reactions These “half reactions” occur in pairs. Together they make a complete reaction. Na (s) + Cl 2(g)   Na + + 2Cl -

22 Tables for Half Reactions Reduction Standard Potential Half-ReactionE ° (volts) Li + (aq) + e - -> Li(s)-3.04 Ca 2+ (aq) + 2e - -> Ca(s)-2.76 Na + (aq) + e - -> Na(s)-2.71 Mg 2+ (aq) + 2e - -> Mg(s) H + (aq) + 2e - -> H 2 (g)0 Fe 3+ (aq) + e - -> Fe 2+ (aq)0.77 Ag + (aq) + e - -> Ag(s)0.8 Hg 2+ (aq) + 2e - -> Hg(l)0.85 2Hg 2+ (aq) + 2e - -> Hg 2 2+ (aq)0.9 NO 3 - (aq) + 4H + (aq) + 3e - -> NO(g) + 2H 2 O(l)0.96 O 2 (g) + 4H + (aq) + 4e - -> 2H 2 O(l)1.23 O 3 (g) + 2H + (aq) + 2e - -> O 2 (g) + H 2 O(l)2.07 F 2 (g) + 2e - -> 2F - (aq)2.87 These equations are written as reductions. For oxidation, the equation would be in reverse. E o would also change signs.

23 Tables for Half Reactions Reduction Standard Potential Half-ReactionE ° (volts) Li + (aq) + e - -> Li(s)-3.04 Ca 2+ (aq) + 2e - -> Ca(s)-2.76 Na + (aq) + e - -> Na(s)-2.71 Mg 2+ (aq) + 2e - -> Mg(s) H + (aq) + 2e - -> H 2 (g)0 Fe 3+ (aq) + e - -> Fe 2+ (aq)0.77 Ag + (aq) + e - -> Ag(s)0.8 Hg 2+ (aq) + 2e - -> Hg(l)0.85 2Hg 2+ (aq) + 2e - -> Hg 2 2+ (aq)0.9 NO 3 - (aq) + 4H + (aq) + 3e - -> NO(g) + 2H 2 O(l)0.96 O 2 (g) + 4H + (aq) + 4e - -> 2H 2 O(l)1.23 O 3 (g) + 2H + (aq) + 2e - -> O 2 (g) + H 2 O(l)2.07 F 2 (g) + 2e - -> 2F - (aq)2.87 A full redox reaction is a combination of a reduction equation and an oxidation equation

24 Redox Equations Redox 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. CO 2 /C 6 H 12 O 6 and O 2 /H 2 O

25 Redox Equations CO 2 /C 6 H 12 O 6 and O 2 /H 2 O To determine whether a chemical is oxidized or reduced, consider E o from the standard reduction table. For the pairs below: 6CO H + +24e - = C 6 H 12 O 6 E o = V O 2 (g) + 4H + + 4e - = 2H 2 O E o = 0.82 V The negative E 0 value indicates that this reaction should be written in reverse (oxidation)

26 Balancing Redox Equations Consider the metabolism of glucose by aerobic microorganisms. Write the balanced reaction that combines the redox pairs CO 2 /C 6 H 12 O 6 and O 2 /H 2 O. (work as class example)

27 Solution Glucose 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

28 Solution 2. Balance the main elements other than oxygen and hydrogen 3. Balance oxygen by adding H 2 0 and hydrogen by adding H+

29 Solution 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.

30 Solution

31 Example Balance the redox reaction of sodium dicromate (Na 2 Cr 2 O 7 ) with ethyl alcohol (C 2 H 5 OH) if the products of the reaction are Cr +3 and CO 2 strategy

32 Strategy  Balance the principal atoms  Balance the non-essential ions  Balance oxygen with H 2 O  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.

33 Solution

34

35 Free Energy of Formation, G f o  Energy released or energy required to form a molecule from its elements  By convention, G f 0 of the elements (O 2, C, N 2 ) in their standard state is zero.  Some representative values G f 0 are given on the next slide

36 Free Energy of Formation, G f o CompoundG f o, kJ/mole C 6 H 12 O CO O2O2 0 H20H CH N20N Using G f 0 you can calculate whether a reaction will occur. For the reaction aA + bB  cC + dD  G o = cG f o (C)+dG f o (D) – aG f 0 (A) – bG f o (B)

37 Class Example One mole of methane (CH 4 ) and two moles of oxgyen are in a closed container. Determine if the reaction below will proceed as written based on  G o. CH 4 + 2O 2  CO 2 + 2H 2 0

38 Solution CompoundG f o, kJ/mole CO O2O2 0 H20H CH CH 4 + 2O 2  CO 2 + 2H 2 0  G o = cG f o (C)+dG f o (D) – aG f 0 (A) – bG f o (B) =(-394.4)+2( ) -(-50.75)-2(0) = kJ/mole This is a large negative value, the reaction will proceed as written.

39 Relationship between  G o and  E o Where ΔG o = the Gibbs energy of reaction at 1 atm and 25 o C n = number of electrons in the reaction F = caloric equivalent of the faraday = kcal/volt-mole E o is related to the equilibrium constant, K, by: Where: R=universal gas constant= kcal/mol- o K T=temperature( o K) The electromotive force, E o is related to ΔG o

40 Binary Fission   P = P o (2) n  P o is the initial population at the end of the accelerated growth phase  P is the population after n generations

41 Microbial Growth Bacterial numbers (log) Time

42 Bacterial numbers (log) Time Lag Phase Adjustment to new environment, unlimited source of nutrient and substrate Microbial Growth

43 Bacterial numbers (log) Time Lag Phase Accelerated growth phase bacteria begin to divide at various rates Microbial Growth

44 Bacterial numbers (log) Time Lag Phase Accelerated growth phase Exponential growth phase differences in growth rates not as significant because of population increase Microbial Growth

45 Bacterial numbers (log) Time Lag Phase 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

46 Bacterial numbers (log) Time Lag Phase Accelerated growth phase Exponential growth phase Stationary phase Death phase Microbial Growth

47 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

48 Rates of Transformation Generalized equation C = Contaminant concentration k = proportionality constant (units dependent on reaction order) n = reaction order

49 Zero Order Kinetics

50 First Order Kinetics

51 Second Order Kinetics

52 Text Problem 7.4 The 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 7.1X10 11 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=3X L/cell-h [C] = conc. of benzo[a]pyrene [X] = biomass conc.

53 Solution [X] = 7.1X10 11 cell/L t = 240 days C o = 25 ug/L k’ = k[X] = (3x L/cell-hr)(7.1x10 11 cell/L) = hr -1 Therefore, C = C o e -k’t = (25 ug/L) e -( hr-1 x 240 hr) = 15 ug/L …end of solution

54 Michaelis-Menton Kinetics It is a saturation phenomena described by: where V = rate of transformation (mg/L  h) V max = maximum rate of transformation (mg/L  h) C = contaminant concentration (mg/L) K m = half-saturation constant (mg/L)

55 Michaelis-Menton Kinetics

56 Class Example Describe how you would get Km and Vmax from the following data. Initial Conc. (mg/L) Initial Rate (mg/(L-min))

57 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.


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