Presentation on theme: "Chapter 21 - Microorganisms and Metals"— Presentation transcript:
1Chapter 21 - Microorganisms and Metals ObjectivesKnow the common toxic metals and the main sources that they come fromKnow factors affecting metal bioavailability in the environmentKnow why are metals are toxic to microorganism and their mechanisms for resistanceBe able to discuss some general approaches for metal remediation
2Top 20 Hazardous Substances List ATSDR/EPA 2003ArsenicLeadMercuryVinyl ChloridePolychlorinated Biphenyls (PCBs)BenzeneCadmiumPolycyclic Aromatic HydrocarbonsBenzo(a)pyreneBenzo(b)fluoranthene11. Chloroform12. DDT13. Arochlor 125414. Arochlor 126015. Dibenz[a,h]anthracene16. Trichloroethylene17. Chromium (+6)18. Dieldrin19. Phosphorus, white20. ChlordaneFive of the top 20 EPA hazardous substances are metals.
3Metals in the Environment Range for Soils (mg/Kg)Ave. for Soils(mg/Kg)AluminumArsenicCadmiumCalciumChromiumCopperIronMercuryMagnesiumLead10,000 – 30,0001 – 500.01 – 0.77,000 – 500,0001 – 1,0002 – 1007,000 – 550,0000.01 – 0.3600 – 6,00071,00050.0613,7001003038,0000.035,00010* Required metals
4Common metal contaminants found in Superfund sites Metal Occurrence (%)Lead (Pb)Arsenic (As)Zinc (Zn)Nickel (Ni)Mercury (Hg)Barium (Ba)Cadmium (Cd)
5Metals and Metalloids of Concern Quantities Produced and Uses Arsenic- As 43,000 tons/yr (1995)used in: insecticides, herbicides, seed additives, woodpreservatives, desiccants, ceramics, glass (0.2-1%) additivesCadmium- Cd 14,500 tons/yr (1995)used in: battery-powered cellular telephones, camcorders,personal computers, pigments, stabilizers, coatings and alloysCobalt- Co 18,500 tons/yr (1994)used in: alloys, nuclear industry, pigment in glazes, UVprotectant in eye protective equipment, paint additive, catalystin the petroleum industry.Lead- Pb 1,510,000 metric tons/yr in the US (2002)(a large portion is recycled) over half of lead is used by theauto industry in batteries. Other uses include manufacture ofcable sheathings, sheet, pipe foil and tubes, solders,alloys,ammunition, and paints.
6Mercury- Hg 10,000 tons/yr (1980)major uses include electrical apparatus, the electrolyticpreparation of chlorine and caustic soda, the manufacture ofmildew-proof paint and in industrial and control instruments.Nickel- Ni 875,00 tons/yr (1995)used in alloys, plating, batteries, magnets, electricalcontacts,electrodes, spark plugs, machinery parts, and as a\catalyst.
7Metals in the Environment Total metal vs. bioavailable metalFactors that affect metal bioavailability1. metal sorption by soil (organic matter, clay minerals, metal oxides)2. pHhigh pH bioavailabilitymetal phosphates/carbonateslow pH bioavailabilityfree ionic species3. redox potentialhigh Eh bioavailabilityfree ionic specieslow Eh bioavailabilitymetal phosphates/carbonates/sulfides
8Bioavailable vs. total cadmium in soil – example Total Cd addedmg/KgBioavailable Cdmg/LBrazitoGila3944836468661,7771,059351020100Note that a very small fraction of the total metal is actually bioavailable (defined here as soluble in water). The majority of the metal is sorbed or precipitated.
9Despite the fact that low amounts of metals in the environment are bioavailable, as the graphs below demonstrate, it does not take much metal to induce toxicity.
14General remediation approaches for metals These are based on mechanisms of metal resistance and include:Removal of metals from wastestreams using biomass as asorbentIn situ precipitation of metals by creating anaerobic conditionsRemoval of metals from soil using metal-complexing agents,e.g. biosurfactantsVolatilization of metals, e.g. SeleniumPhytostabilization of metals, e.g. mine tailings
15Example of a successful bioremediation Zinc smelter (100 yrs old) with 135 mg/L zinc and 1300 mg/L sulfate in groundwater.(Budelco in the Netherlands)Cleanup was mandated, choices included:Ion exchange – good Zn removal, no sulfate removal, costlyLiquid membrane extraction – good Zn removal, no sulfate removal, costlyBioremediation using SRBsThe SolutionAfter pilot-scale testing, a commercial plant with an 1800 m3 bioreactor was constructed to treat 6000 m3 of groundwater per day ( 55-gallon drum every 3 seconds).
16Three effluents are generated: Solid sludges that are returned to the smelter to recover the precipitated Zn.Liquid containing 80% sulfur mostly as H2S or S0. This is passed into an aerobic fixed film bioreactor. Here sulfate oxidizers convert H2S to S0.Gas that contains 40% H2S, 60% CH4, and a small amount of CO2. The H2S is removed by passing through a zinc sulfate solution, and the CH4 is burned.Aqueous effluent design criteriaZinc < 0.3 mg/L Original 135 mg/LCadmium < mg/LSulfate < 200 mg/L Original 1300 mg/L
17What would you add as an electron donor in the UASB?? ZnSO4 solutiondischargeCH4flareBiofilterscrubberH2S + CH4vaporvaporTiltedplatesettlerH2SliquidSFFGroundwaterSO42-, Zn2+UASBS0liquidO2dischargesandfilterZnS solidsZnS +biomasssludgeS0 + biomassSolids tozinc smelterWhat would you add as an electron donor in the UASB??