Chapter 15
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Presentation Transcript- Chapter 15 Negative Impacts of Biogeochemical Cycling
- Conflicts between natural cycles and human activities • The ever-growing need for more food has impacted microbial cycling of nutrients • replacement of forests and grasslands with agricultural crop land has altered rates of above-ground photosynthesis as well as below ground soil properties • Disturbance to steps in nutrient cycling has had a global impact • acid rain • “greenhouse” effect
- Acid Rain Prevailing winds Precipitation 2H2O + SO2H2SO4 + 2H+ H2O + NO2 HNO3 + H+ CO2, NO2, SO2 Unbuffered lakes & streams become acidic Fish kills, inhibition of photosynthesis Coal, oil Has occurred in eastern Canada & Skandanavia
- Microbial Influenced Corrosion “Classic” generalized steel corrosion • Ship hull corrosion • Buried pipelines • Bridges
- H2O H+ + OH- Corrosion Reactions O2 + 2H2O 4OH- and/or MeOH (rust) H+ H H2 Fe3+ Me+1, +2, +3 e- Feo Metal Meo CATHODE ANODE
- SRB-influenced corrosion of carbon steel Fig 15.2
- Concrete sewer pipe corrosion Softens concrete Fig 15.3 H2S + O2→ H2SO4 H2SO4 + Ca(OH)2→ CaSO4 + 2H2O
- Pitting corrosion of stainless steel at weldmentcourtesy of Greg Kobrin, E.I. du Pont de Nemoirs Co., Inc.
- Pit in carbon steel coupon in presence of sulfate-reducing bacterial biofilm
- Blue water corrosion products
- Cut-away view of inside of copper tubing showing nature of corrosion products
- pitting
- Mechanisms Proposed • Production of acidic by-products of metabolism • Binding of Cu ions by EPS • Alteration of integrity and porosity of normally protective Cu oxide film due to presence of bacterial cells and EPS
- ACIDS PRODUCED BY MICROBES • INORGANIC ACIDS • Sulfuric acid • Nitric acid • Carbonic acid • ORGANIC ACIDS • Low molecular weight • Acetic acid • Lactic acid • Butyric acid • High molecular weight • Acidic polysaccharides
- Color of “first-draw” water
- Sphingomonas capsulata Staphylococcus warneri Erythrobacter longus Methylobacterium sp. These bacteria could promote release of Cu when growing as a biofilm on Cu surfaces in contact with simulated potable water. Bacteria Isolated from Sites Experiencing Cu Release in Auckland, NZ
- Stainless steel coupon in simulated wet storage environment for spent nuclear fuel rods
- Acid Mine Drainage • Results in yellow precipitate (“yellow-boy”) formation in streams (adducts) draining out of abandoned mines. • Precipitate is KFe3(SO4)2(OH)6
- Acid Mine Drainage Abiotic reaction • Sulfuric acid formed from oxidation of pyrite (Fe2S) • Forms solutions with pH of less than 2 • Low pH causes many metals that are insoluble at neutral pH to dissolve • Hence, acid mine drainage contains high dissolved metal concentrations • Copper • Arsenic • Aluminum 4FeS2 (pyrite) + 14O2 + 4H2O 4Fe2+ (OH)3- + 8SO42- + 8H+
- Ferric iron as major oxidant of pyrite • Consensus reaction: 2+ FeS2 + 6Fe(H2O)6 + 3H2O → Fe2+ +S2O3 + 6Fe(H2O)6 + 6H+ • As pH drops, a sulfur- and iron-oxidizing bacteriumAcidithiobacillus ferrooxidans begins to participate in the reaction • This bacterium usesFeS2 as an energy source • This bacterium has a pH optimum for growth around 2.0
- Other microbes involved in acid mine drainage • Archaea (thermophiles) • Sulfolobus spp. • Acidianus • Bacteria • Thiomicrospira spp. • Pyrite oxidation is an exothermic reaction and gives off heat • Tailings impounds can reach temperatures of 60oC Pink biofilm
- Procaryotes in the aqueous phase of AMD • Chemolithoautotrophs (dominant populations) • Acidithiobacillus ferrooxidans • Leptospirillum spp. • Acidiphilium spp. • Minor populations • Ferroplasma acidophilum • Thermoplasma acidophilum
- Reactions involved in AMD • Fe2+ + 1/2O2 + 2H+→ 2Fe3+ + H2O • Rate limiting step in acid leaching reaction • Acidithiobacillus ferrooxidans can accelerate rate of this step • Fate of Fe3+ • Fe3+ + 3H2O → Fe(OH)3↓ + 3H+ or • FeS2 + 14Fe3+ + 8H2O → 15Fe2+ + 2SO42- + 16 H+ • This reaction produces acid and regenerates Fe2+ which can be reoxidized by Acidithiobacillus ferrooxidans • This combination of reactions creates a loop that speeds the oxidation of pyrite
- Metal recovery-bioleaching • Direct bioleaching • MS + 2O2→ MSO4 where MS is • CuFeS2 - chalcopyrite • CuS2 - chalcocite • CuS – covellite • Microbe gains energy when the Cu1+ is oxidized to Cu2+
- Metal recovery-bioleaching • Indirect metal leaching • CuS + 2Fe2(SO4)3→ 2CuSO4 + 4FeSO4 + So • 2FeSO4 + 1/2O2 + H2SO4 → Fe2(SO4)3 + H2O • Copper is spontaneously oxidized by the presence of Fe3+ and acid, and then the Fe2+ that is produced from this reaction is reoxidized biologically by A. ferrooxidans • The Cu2+ can be recovered from solution by spontaneous precipitation by scrap iron • Cu2+ + Feo → Fe2+ + Cuo
- Metal recovery-bioleaching
- Ozone Formation Major component of photochemical smog O2 + hv→ O + O 2O2 + 2O + Metal → 2O3 + Metal 3O2 + hv → O3 O3 + hv →O + O2 O3 + O → 2O2 2O3 + hv →3O2
- Photodissociation of N2O N2O derived from denitrification NO is another component of photochemical smog. N2O + hv N2 + O* N2O + O* 2NO
- Role of Denitrification and CO2 Production on Greenhouse Effect • Greenhouse gases absorb long-wave radiation originating from the Sun that is reflected off the Earth’s surface. • CO2, chlorofluorocarbons (CFCs), CH4, N2O N2O is very efficient in absorbing long-wave radiation (200x better than CO2). CO2, CFC N2O In upper atmosphere, solar radiation can photolytically convert N2O to NO, which reacts with and destroys ozone Earth surface
- Destruction of ozone layer in stratosphere-ozone hole • N2O + hv N2 + O* • N2O + O* 2NO • NO + Ozone (O3) N2O + O2 • O3 + hv O + O2 • 2O3+ hv 3O2 What has led to the increase in N2O? More land under agricultural use More use of N fertilizers Only 50% of N fertilizer is used by crops More opportunity for denitrification
- Inhibition of Denitrification • Addition of more chemicals to crop land • 2-ethynylpyridine • 2-chloro-6-(trichloromethyl)pyridine • thiourea • Will these chemicals introduce new problems by their introduction to the environment?
- Nitrate accumulation and contamination of surface water and groundwater • If you inhibit denitrification, there is the possibility that more nitrate will accumulate • Nitrate does not bind to soil particles • can migrate as a dissolved ion in water and move rapidly to groundwater • Most states have nitrate levels in aquifers that exceed EPA drinking water standards (>10 mg/L)
- NO3 levels in groundwater across the U.S
- Public Health Concern • blue baby syndrome (methemoglobinemia) • infants less than 6 months of age have not developed the acidic conditions that prevent the growth of denitrifying bacteria that convert nitrate to nitrite • nitrite accumulates, competes with oxygen at binding site on hemoglobin, and causes cyanosis • Solution: feed babies bottled water
- In adults, formation of nitrites in adult stomach can lead to formation of nitrosamines, which are known to be carcinogenic in test animals • Prevention • do not over-fertilize agricultural soils • Best Management Practices • controlled release of ammonia fertilizer • avoid use of nitrate fertilizer
- Halomethanes and other haloorganics Halomethanes are an important source of chlorine and bromine radicals in the atmosphere React with and deplete ozone Synthetic chemicals previously used as refrigerants Halomethanes are synthesized by marine algae, kelp and seaweeds chloromethane (CH3Cl) chloroform (CHCl3) bromoform (CHB3) formed by haloperoxidase enzymes formed to protect alga from grazers
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