CE 510 Hazardous Waste Engineering

1. CE 510Hazardous 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 MINERALIZATION Complete breakdown of organic compound into cellular mass, carbon dioxide, water and inert inorganic residuals BIOTRANSFORMATION Breakdown of organic compound to daughter compound

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

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

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 CO2 A B H20 C O2

9. Schematic diagram of biodegradation process Transport of chemicals across the cell boundary Enzyme bound chemicals A A bacterial cell A bacterial cell A A A A A A A A A A A CO2 A B Breakdown of chemicals H20 C O2

10. 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

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 • Methane • TCA • TCE • PCE

14. Solution • Methane (-IV) • TCA (0) • TCE (I) • 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: k2 = k1Θ(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- The tendency of a substance to donate electrons or accept electrons is expressed as the reduction potential Eo (measured in volts) Negative Eo – donors Positive Eo - acceptors e-

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

20. Redox Reactions e- • Oxidation • Process in which an atom or molecule loses an electron Na(s)Na+ +e- • Reduction • Process in which an atom or molecule gains an electron e- Cl2(g) + 2e- 2Cl-

21. Redox 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-

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

23. Tables for Half Reactions 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. CO2/C6H12O6 and O2/H2O

25. Redox Equations To determine whether a chemical is oxidized or reduced, consider Eo from the standard reduction table. For the pairs below: CO2/C6H12O6 and O2/H2O 6CO2 + 24H+ +24e- = C6H12O6 Eo = -0.43 V O2(g) + 4H+ + 4e- = 2H2O Eo = 0.82 V The negative E0 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 CO2/C6H12O6 and O2/H2O. (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. • Write the two half reactions

28. Solution 2. Balance the main elements other than oxygen and hydrogen 3. Balance oxygen by adding H20 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 (Na2Cr2O7) with ethyl alcohol (C2H5OH) if the products of the reaction are Cr+3 and CO2 strategy

32. 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.

33. Solution

34. Solution

35. Free Energy of Formation, Gfo • 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

36. Free Energy of Formation, Gfo Using Gf0 you can calculate whether a reaction will occur. For the reaction aA + bB  cC + dD DGo = cGfo(C)+dGfo(D) – aGf0(A) – bGfo(B)

37. Class Example One 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

38. Solution DGo = cGfo(C)+dGfo(D) – aGf0(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. CH4 + 2O2 CO2 + 2H20

39. Relationship between DGo and DEo The electromotive force, Eo is related to ΔGo Where ΔGo = the Gibbs energy of reaction at 1 atm and 25oC n = number of electrons in the reaction F = 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-oK T=temperature(oK)

40. 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

41. Microbial Growth Bacterial numbers (log) Time

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

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

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

45. Microbial Growth Stationary phase substrate becomes exhausted or toxic by-products build up resulting in a balance between the death and reproduction rates Bacterial numbers (log) Exponential growth phase Lag Phase Accelerated growth phase Time

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

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