Contaminant Hydrogeology VI

1. Contaminant Hydrogeology VI Гидрогеология Загрязнений и их Транспорт в Окружающей Среде Yoram Eckstein, Ph.D. Fulbright Professor 2013/2014 Tomsk Polytechnic University Tomsk, Russian Federation Fall Semester 2013

2. Selected Topics in Environmental Chemistry

3. Acid Base Properties • Water autodissociates (self dissociation) – 2H2O ↔ H3O+(aq) + OH–(aq) Kw= 1.01 x10‐14@ 25 °C • Neutral water has a pH = 7.0

4. Acid Base Properties • Amphiprotic (Brǿnsted acid or base ) - pH < 7 can be due to organic acids from  decaying  organic matter – (COOH)2 + H2O ↔ H3O+(aq) + COOHCOO–(aq) Ka= 5.6 ×10‐2 - pH>7 can be due to soluble carbonates from rocks and/or other sources

5. Redox Chemistry in Natural Waters Oxidation and reduction (Redox) reactions play an important role in the geochemical processes that occur in surface- and ground-water. Redox reactions are defined as reactions in which electrons are transferred. The species receiving electrons is reduced, that donating electrons is oxidized. Redox reactions determine the mobility of many inorganic compounds as well as biologically important materials such as nitrogen and sulfur. In addition, redox conditions govern the particulars for the biological degradation of complex hydrocarbon contaminants

6. Redox Chemistry in Natural Waters • Most important oxidizing agent in  natural waters is dissolved molecular  oxygen • Half‐reaction in Acidic Solutions • O2+4H++4e- 2H2O Half‐reaction in Basic Solutions • O2+2H2O+4e- 4OH-

7. Redox Chemistry in Natural Waters • [O2] in water is small • Henry’s law ~ “The concentration of a  gas in a liquid at a specific temperature  is proportional to the partial pressure of  the gas above the liquid”. • The equilibrium constant for the gas/ liquid system is given by Henry’s  Law Constant KH • O2(g) O2(aq) KH= 1.3 x10‐3 mol L‐1atm‐1 • =

8. REDOX Reactions in Aquatic Environments Many elements can exist in a number of oxidation states in near-surface geologic environments, including the macroelements C, N, O, S, Mn and Fe, and important contaminants including As, Se, Cr, Hg, U, Mo, V, Sb, W, Cu, Ag, and Pb. The oxidation state of these elements, in large part, determines the speciation and biogeochemical fate of these elements. Generally, pH and Eh (pE) are considered the master geochemical variables controlling the geochemical reactions of elements in geologic and aquatic environments.

9. REDOX Reactions in Aquatic Environments Redox potential is a an intensity parameter of overall redox reaction potential in the system (similar in concept to pH), not the capacity of the system for specific oxidation or reduction reactions. The redox value of standard half reactions (Eo) and details of how to calculate redox capacity can be found in any elementary chemistry text. The following inorganic oxidation reactions consumedissolved oxygen in surface- or ground-water: Sulfide Oxidation 2O2 + HS- = SO42- + H+ Iron Oxidation O2 + 4Fe+2 + 4H+ = 4Fe3+ + 2H2O Nitrification 2O2 + NH4+ = NO3- + 2H+ + H2O Manganese (II) Oxidation O2 + 2Mn2+ + 2H2O = 2MnO2 + 4H+ Iron Sulfide Oxidation 15O2 + 4FeS2 + 14H2O = 4Fe(OH)3 + 8SO42- + 16H+

10. REDOX Reactions in Aquatic Environments The following redox reactions consume organic matter in surface- or ground-water: (1) Aerobic Degradation CH2O + O2 = CO2 + H2O (2) Denitrification 5CH2O + 4NO3- = 2N2 + 5HCO3- + H+ + 2H2O (3) Manganese (IV) Reduction CH2O + 2MnO2 + 3H+ = 2Mn2+ + HCO3-+ 2H2O (4) Ferric Iron Reduction CH2O + 4Fe(OH)3 + 7H+ = 4Fe2+ + HCO3- + 10H2O (5) Sulfate Reduction 2CH2O + SO42- = HS- + 2HCO3- + H+ (6) Methane Fermentation 2CH2O + H2O = CH4 + HCO3- + H+

11. Redox Classification of Natural Waters • Oxic waters - waters that contain measurable dissolved oxygen. • Suboxic waters - waters that lack measurable oxygen or sulfide, but do contain significant dissolved iron (> ~0.1 mg L-1). • Reducing waters (anoxic) - waters that contain both dissolved iron and sulfide.

12. O2 Aerobes Oxic H2O Dinitrofiers NO3- N2 Maganese reducers Post - oxic MnO2 Mn2+ Iron reducers Fe(OH)3 Fe2+ SO42- Sulfate reducers Sulfidic H2S CO2 Methanogens CH4 Methanic H2O H2 The Redox ladder The redox-couples are shown on each stair-step, where the most energy is gained at the top step and the least at the bottom step. (Gibb’s free energy becomes more positive going down the steps)

13. BOD and CODBOD and Aquatic Ecosystems

14. Biochemical Oxygen Demand (BOD) • The capacity ofthe organic and biological matter in a  sample of  natural water to consume oxygen  via catalytic processing of microorganisms present or • The amount of oxygen required by  aerobic micro-organisms to  decompose the organic matter in a sample of water • Easily determined by measuring O2before and after sealing a water  sample seeded  with bacteria

15. Chemical Oxygen Demand (COD) • Indirectly measures amount of  oxygen needed to  decompose all  organic substances (artificial  and  natural) by using dichromate ion to oxidize biological and organic matter in a natural water sample • Since stable organics, & anything that  can be  oxidized are targeted too – so it has always larger  values than BOD

16. BOD and Aquatic Ecosystems

17. BOD and Aquatic Ecosystems Rate of the BOD decay in a stream (typically 0.2/day)

18. Anaerobic Decomposition of Organic Matter Anaerobic (O2 free) decomposition of organic matter by microorganisms (fermentation) can produce CH4 and CO2 2CH2 O Bacteria CH4 + CO2 organic matter – In swamps the methane bubbles up to the surface and may ignite – In some rural communities (India, China), ‘digestor units’ convert bio‐organic waste to methane – Process can also occur in landfills

19. Anaerobic Decomposition of Organic Matter In lakes the lack of oxygen creates a reducing environment at the bottom • Insoluble Fe3+ (+e‐) Soluble Fe2+ • Mixing does occur with seasons

20. Sulfur in Natural Waters Hydrogen sulfide: Sources include, volcanoes, hot springs, swamps (anaerobic bacteria), 10 – 15% from anthropogenic sources (oil refinery, natural gas wells, paper mills, ore smelting, etc)

21. Sulfur in Natural Waters H2S Solubility 4370 ml/L at 0 °C; 1860 ml/L at 40 °C H2S + 2O2 H2SO4 Some anaerobic bacteria can decompose various sulfur containing organic matter (amino acids, etc) and produce, amongst other things, hydrogen sulfide, CH3SH, CH3SSCH3, etc. 2SO42-+3CH2O+4H+ 2S+3CO2+5H2O Overall reaction showing how some anaerobic bacteria can use sulfate ion as the oxidizing agent to decompose organic matter (important in seawater , where sulfate concentration is much higher than fresh water

22. Acid Mine Drainage (AMD) FeS2Pyrite FeS2Marcasite FexSxPyrrhotite Cu2S Chalcocite CuSCovellite CuFeS2 Chalcopyrite MoS2Molybdenite NiSMillerite PbS Galena ZnSSphalerite FeAsSArsenopyrite “Outflow of acidic water (pH<3.0) from abandoned coal or metal/ore mines” – Typically occurs when certain geology is exposed (mining, construction etc) to water or air resulting in the oxidation of these minerals

23. Acid Mine Drainage (AMD) 2FeS2 + 7O2 + 2H2O2Fe2+ + 3SO42- + 4H+ (I) 4Fe2++ O2+ 4H+ 2H2O + 4Fe3+ (II) 4Fe3+ + 12H2O 4Fe(OH)3 + 12H+ (III) First step produces acidity Second step is usually slow, but can be catalyzed by acidic bacteria, & consumes some of the H produced in (I) 3rd step the Fe3+ is soluble in high pH water initially produced; however as AMD becomes more diluted the hydroxide precipitates, giving the yellowish brown color (kills!!)

24. Acid Mine Drainage (AMD) 4FeS2 + 14Fe3+ + 8H2O 15Fe2+ + 2SO42- + 16H+ Fe3+ then catalyses further production of acidity, without the need for O2

25. Consequences and Some Solution to AMD Consequences • High acidity leads to leaching of various metals – Heavy metals (Fe, Cu, Pb, Zn, Cd, Co, Cr, Ni, and Hg) – Metalloids (As Sb) – Other metals & elements Al, Mn, Si, Ca, Na, K, Mg and Ba – Whatever maybe present • Can get pH < 0! • Discoloration of waterways, choking & killing of aquatic organisms (fish, plant, microorganisms, etc)

26. Consequences and Some Solution to AMD Solutions • Some mines near natural limestone deposits which can neutralize the AMD • Limestone chips can be added • Addition of calcium oxide or hydroxide • Anaerobic bacteria • Sealing the mines

27. The pEScale Used to characterize the reducing nature of natural water • Low pE ~ lots of electrons available thus water is very reducing • High pE ~ few electrons available so dominant species are oxidizing in nature • It is defined as – log10 of the effective concentration (or activity of) electrons in water – Analogous to pH scale, recall you really don’t have bare protons, so don’t really have bare electrons’, – Dimensionless numbers (i.e. no units) • Along with pH it can be used to determine the dominant species in a body of water

28. Example Using pE Scenario: Traditional leather tanning industries soak the hides in an aqueous solution of chromium (III). Suppose the waste water from the tannery contains 26 mg/L chromium (III). As it enters a river, the dissolved oxygen can oxidize the chromium (III) to dichromate. If the water in the river is well aerated and has a pH of 7.0, what’s the dominant species? Step I O2 + 4H+ + 4e- 2H2O Large amounts of dissolved O2 in H2O; dominant process is reduction of O2 pE = pEo – (1/n) logQ

29. Example Using pE • O2 + 4H+ + 4e- 2H2O • Step I • pE = pEo – (1/n) logQ • pEo = Eo/(0.0591) = 1.229/0.0591 = = 20.795 • pE= 20.795 – (1/4)log{1/(PO2 [H+]4)} = • = 14.63 • • Can use this step for any well aerated water system, as long as you know the pH • • Assumption O2 in equilibrium with the water • • Assumption is no dissolved CO2

30. Example Using pE • Cr2O72-(aq) + 14H+(aq) + 6e- 2Cr3+(aq) + 7H2O • Step 2: Calculate pEo • pEo = Eo/0.0591 = 1.33/0.0591 = 22.504 • Step 3: set up the correct expression for Q, & substitute in your known values • 14.63 = 22.504 – • - (1/6)log{[Cr3+]/([Cr2O72-][10-7]14)} • The chromium and oxygen are in the same water system, so they are at equilibrium i.e. same pE!!!

31. Example Using pE • Step 4: Simple rule of logs re‐arrange the • expression • 14.63 = 22.504 – (1/6)log(1/[10-7]14) – • - (1/6)log([Cr3+]/([Cr2O72-][10-7]14) • Step 5: Simplify the expression • 14.63 = 8.504 - (1/6)log([Cr3+]/[Cr2O72-]) • -36.756 = log([Cr3+]/[Cr2O72-]) • and finally: 1.75 × 10-37= [Cr3+]/[Cr2O72-] • This small number means the dichromate dominates! Which is very toxic, and carcinogenic

32. Acid Base Chemistry in Natural Waters Natural waters contain lots of CO2 – Source mostly from air, but can be from decomposition of organics – Easily forms carbonic acid – Acid easily dissociates – Reason rain water slightly acidic – the pH of CO2 saturated water is 5.6 @ 25 °C, given that the [CO2] is 365 ppm

33. Carbon Cycling in Ecosystems

34. Carbon Dioxide and Water CO2 + H2O ↔ H2CO3 (KH= 10-1.5mol/atm·L) H2CO3 ↔ HCO3- + H+ (H1a≈ 10-6.3mol/L) HCO3- ↔ CO32- + H+ (H2a≈ 10-10.3mol/L)

35. Acid Base Chemistry in Natural Waters Oceans are a large sink for atmospheric CO2 – Sequestration of CO2 in the ocean would increase the acidity of surrounding waters – Increased acidity could be detrimental to some ocean life – Increase in atmospheric CO2 has decreased ocean pH ~ 0.1

36. Biotransformation andBiodegradation Aerobic Anaerobic

37. Biotransformation • Biotransformation is the chemical modification (or modifications) made by an organism on chemical compounds such as (but not limited to) nutrients, amino acids, toxins, etc. • If this modification ends in mineral compounds like CO2, NH4+, or H2O, the biotransformation is called mineralisation.

38. Biotransformation • Biotransformation of various pollutants is a sustainable way to clean up contaminated environments. These bioremediation and biotransformation methods harness the naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a huge range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radionuclides and metals.

39. Biotransformation • Biological processes play a major role in the removal of contaminants and pollutants from the environment. Some microorganisms possess an astonishing catabolic versatility to degrade or transform such compounds. New methodological breakthroughs in sequencing, genomics, proteomics, bioinformatics and imaging are producing vast amounts of information.

40. Biotransformation • As we learn more through functional genomic analysis of various bacterial species, biological processes are gradually replacing some older physico-chemical methods; • Some technologies that have been used are: • high-temperature incineration • various types of chemical decomposition (e.g., base-catalyzed dechlorination) • UV oxidation.

41. Biotransformation

42. Biotransformation • Microbes will adapt and grow at subzero temperatures, as well as extreme heat, desert conditions, in water, with an excess of oxygen, and in anaerobic conditions, with the presence of hazardous compounds or on any waste stream. • The main requirements are an energy source and a carbon source. • Because of the adaptability of microbes and other biological systems, these can be used to degrade or remediate environmental hazards.

43. Biotransformation We can subdivide these microorganisms into the following four groups: • Aerobic • Anaerobic • Ligninolytic fungi • Methylotrophs

44. Biotransformation • Aerobic bacteria • In the presence of oxygen. • Examples of aerobic bacteria recognized for their degradative abilities are Pseudomonas, Alcaligenes, Sphingomonas, Rhodococcus, and Mycobacterium. These microbes have often been reported to degrade pesticides and hydrocarbons, both alkanes and polyaromatic compounds. • Many of these bacteria use the contaminant as the sole source of carbon and energy.

45. Biotransformation • Anaerobic bacteria • In the absence of oxygen. • Anaerobic bacteria are not as frequently used as aerobic bacteria. • There is an increasing interest in anaerobic bacteria used for bioremediation of polychlorinated biphenyls (PCBs) in river sediments, dechlorination of the solvent trichloroethylene (TCE), and chloroform.

46. Biotransformation • Ligninolytic fungi • Fungi such as the white rot fungus Phanaerochaetechrysosporium have the ability to degrade an extremely diverse range of persistent or toxic environmental pollutants. • Common substrates used include straw, saw dust, or corn cobs.

47. Biotransformation • Methylotrophs • Aerobic bacteria that grow utilizing methane for carbon and energy. • The initial enzyme in the pathway for aerobic degradation, methane monooxygenase, has a broad substrate range and • is active against a wide range of compounds, including the chlorinated aliphaticstrichloroethylene and 1,2-dichloroethane.

48. Environmental Factors in Biotransformation • Nutrients • Although the microorganisms are present in contaminated soil, they cannot necessarily be there in the numbers required for ioremediationof the site. Their growth and activity must be stimulated. • Biostimulation usually involves the addition of nutrients and oxygen to help indigenous microorganisms.

49. Environmental Factors in Biotransformation • These nutrients are the basic building blocks of life and allow microbes to create the necessary enzymes to break down the contaminants. • All of them will need nitrogen, phosphorous, and carbon • Carbon is the most basic element of living forms and is needed in greater quantities than other • elements. In addition to hydrogen, oxygen, and nitrogen it constitutes about 95% of the weight of cells.

50. Composition of a microbial cell