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env. chemistry, baird cann

Env. Chemistry, Baird

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env. chemistry, baird cann

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    1. Env. Chemistry, Baird & Cann

    2. Env. Chemistry, Baird & Cann

    3. Env. Chemistry, Baird & Cann

    4. Env. Chemistry, Baird & Cann Burying Garbage in Landfills Main method of deposal of municipal solid waste; GB & N. Am. 85-90% of municipal & commercial solid waste landfilled (lowest cost), 6% incinerated (Japan & Denmark >50% of domestic waste), 6% recycled or reused

    5. Env. Chemistry, Baird & Cann

    6. Env. Chemistry, Baird & Cann

    7. Env. Chemistry, Baird & Cann Stages in Decomposition of Garbage in a Landfill Three stages In the first, short, aerobic stage, oxygen is available to the waste and it oxidizes organic materials to CO2 and water with the release of heat. In the second, anaerobic acid phase, the process of acidic fermentation occurs, generating ammonia, hydrogen, and carbon dioxide gases and large quantities of partially degraded organic compounds, especially organic acids. pH 5.5-6.5; high BOD

    8. Env. Chemistry, Baird & Cann Stages in Decomposition of Garbage in a Landfill Three stages Third -anaerobic—or methanogenic—stage starts about six months to a year after coverage and can continue for very long periods of time. Anaerobic bacteria work slowly to decompose the organic acids and hydrogen that were produced in the second stage. pH rises to 7-8. Methane generation usually continues for a decade or two and then drops off relatively quickly. Lower BOD

    9. Env. Chemistry, Baird & Cann Leachate from a Landfill Leachate control leachate collection and removal system, followed by treatment liner placed around the walls and bottom of the landfill. 2-mm-thick high-density polyethylene or natural clay Treatment is analogous to sewage treatment (chapter 10)

    10. Env. Chemistry, Baird & Cann Incineration of Garbage Controlled combustion –reduces volume Most common MSW incinerator are one stage mass burn units; two stage modular are more modern (1st stage 760oC; then gases & airborne particles are burned more completely >870oC in the second stage Bottom ash –noncombustible material Fly ash –finely divided solid mater in stack, usually trapped; high in inorganics, 10-25% of ash mass, contains heavy metals, dioxins & furans –most toxic of ashes. Low density & small particle size can lead to inadvertent disposal. Diposed of in hazardous waste landfills, vitrified or made into asphalt

    11. Env. Chemistry, Baird & Cann Incineration of Garbage Main env. concern air pollution Baghouse filter –woven fabric filter, effective for particles over 0.5 ľm Gas scrubbers –liquid stream that passes through gas removing some gases & particles; e.g. if lime in stream removes acids like HCl, heavy metal are ppt. by alkaline liquids Overall incinerators in the US are believed to be a major source of mercury, dioxins & furans, & a moderate source of Cd & Pb

    12. Env. Chemistry, Baird & Cann Green Chemistry: Polyasparate- A Biodegradable Antiscalant & Dispersing Agent Chemical are used to prevent the buildup of scale (calcium carbonate & sulfate) in water handling systems & furnaces Polyacrylate (PAC) is typically used (several hundred million pounds)–nontoxic but not biodegradable; removed at the sewer treatment & landfilled

    13. Env. Chemistry, Baird & Cann Green Chemistry: Polyasparate- A Biodegradable Antiscalant & Dispersing Agent Polyaspartate –effective antiscalant/dispersing agent, biodegradable Thermal polyasparate (TPA) produced from aspartic acid (naturally occurring amino acid) through heating, only by-product is water

    14. Env. Chemistry, Baird & Cann Recycling of Household & Commercial Waste The four Rs to reduce the amount of materials used (sometimes called source reduction); to reuse materials once they are formulated; to recycle materials to recover components that can be refabricated; and to recover the energy content of the materials if they cannot be used in any other way.

    15. Env. Chemistry, Baird & Cann Recycling of Household & Commercial Waste Preconsumer recycling -the use of waste generated during a manufacturing process Postconsumer recycling -the reuse of materials that have been recovered from domestic and commercial consumers paper (especially newspapers and cardboard), aluminum (especially beverage cans), steel (especially food cans), and plastic and glass containers.

    16. Env. Chemistry, Baird & Cann Recycling of Household & Commercial Waste Recycling –labor, energy & pollution, unstable prices –sometimes hard to justify on economic grounds alone (landfill space) The best cases for recycling require minimum of reprocessing are closer to reuse -such as newspaper to make paperboard or insulation, reusing glass or plastic containers

    17. Env. Chemistry, Baird & Cann Recycling of Metals Metal recycling makes sense from economics & energy conservation e.g. Recycling Al saves 95% energy costs to produce from bauxite ore; energy accounts for about 25% of cost to make an Al can –economic savings; recycling steel cans saves about 2/3 the energy

    18. Env. Chemistry, Baird & Cann Recycling of Glass Production of paper, glass & plastics does not require any significant change in oxidation state thus no great energy savings from recycling Modern low-polluting high efficiency furnaces to produce glass cannot handle a high proportion of used glass, thus too much used glass may in more pollution and energy use

    19. Env. Chemistry, Baird & Cann Recycling of Paper In developed countries largest fraction of solid waste; production of virgin paper requires only 25% more energy (transportation & deinking requires significant amounts of energy) Chemicals (bleaching agents, bases, detergents etc.) are required to reprocess paper but significantly less than to produce virgin paper Limit to recycling paper (fibers become shorter) –newsprint can be recycled 6-8 times 1990s about 40% of paper in the US is recycled, Europe >50%

    20. Env. Chemistry, Baird & Cann Recycling of Tires N. America about 330 million tires are discarded each year (about 3 billion already stored in waste piles) –tire fires are not uncommon producing tremendous amounts of smoke, CO, & toxins such as PAHs and dioxins About 10% of tires are used as a filler for asphalt Pyrolysis –shredded tires, thermal degradation produces low grade gaseous & liquid fuels (high in aromatics –not a good fuel) and char (carbon black)

    21. Env. Chemistry, Baird & Cann Recycling of Plastics Polymeric organic compounds (Table 12-1) e.g. polyethylene (HDPE cloudy white, #2; LDPE #4) Polyvinyl chloride PVC (#3) Polypropylene (#5) Polystyrene (#6) Polyethylene terephthalate (PET #1)

    22. Env. Chemistry, Baird & Cann

    23. Env. Chemistry, Baird & Cann Recycling of Plastics Per capita annual use in N. Am. 30 kg; second most common constituent of garbage Opposition to incineration & capacity of landfills are two reasons why plastics are recycled US 80% of recycled plastics are PET & HDPE (about 50% each). Sweden & Germany manufacturers are responsible for collecting & recycling packaging used in their products. US recycling rate of PET bottles dropped from 45% 1994, to 34% 1996. Curbside recycling in about ˝ of urban communities in the US (late 1990s)

    24. Env. Chemistry, Baird & Cann Recycling of Plastics Resistance –virgin plastic low cost raw material & energy input Some suggest that capturing the energy from incineration of plastics is the best route. Aids in the incineration of domestic garbage –although plastics constitute only 10% of the mass of garbage it represents more than 33% of the energy content. Others counter the environmental impact costs need to be added in and the formation of dioxins, furans & HCl

    25. Env. Chemistry, Baird & Cann Ways of Recycling Plastics 1. Reprocess the plastic (a physical process) by remelting or reshaping. Usually the plastics are washed, shredded, and ground up, so that clean, new products can then be made. 2. Depolymerize the plastic to its component monomers by a chemical or thermal process so that it can be polymerized again. 3. Transform the plastic chemically into a low-quality substance from which other materials can be made. 4. Burn the plastic to obtain energy (energy recycling).

    26. Env. Chemistry, Baird & Cann Green Chemistry: Development of Recyclable Carpeting US 4.5 billion pounds (800 million square yards) of carpet are landfilled annually, only 4% recycled Not biodegradable, made from petroleum, takes up valuable landfill space Traditionally backing is PVC, interferes with the processing for recycling Backing can be made with polyolefins which allows for closed-loop recycling (EcoWorx) Carpet is ground and the heavier backing is separated from the light fiber (nylon-6) by elutriation. Backing can be extruded as new backing & the nylon 6 depolymerized and repolymerized to virgin polymer The manufacturer provides a system for returning the used carpeting

    27. Env. Chemistry, Baird & Cann Green Chemistry: Development of Recyclable Carpeting Advantages Recycling requires no additional petroleum feedstocks; this benefits not only the environment, but also the economic bottom line. Recycling reduces the amount of landfill space needed. The polyolefin-backed carpeting is 40% lighter –lowering shipping fuel consumption, cost, and pollution. The use of polyolefins eliminates the energy-intensive heating process required for PVC In carpet backing (including PVC backing), significant amounts of inorganic fillers are used to provide loft and bulk. Traditionally, virgin calcium carbonate was employed for this purpose. EcoWorx contains 60% class C fly ash (a waste by-product from the burning of lignite or sub-bituminous coal) as a filler

    28. Env. Chemistry, Baird & Cann Life Cycle Assessments life cycle assessment (or analysis), LCA—an accounting of all the inputs and outputs in a product’s life, from raw material extraction to final disposal The results of a life cycle assessment can be used in two ways: to identify opportunities within the life cycle to minimize the overall environmental burden of a product and to compare two or more alternative products to determine which is the more environment-friendly.

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    30. Env. Chemistry, Baird & Cann Soils & SedimentsBasic Soil Chemistry Soils are composed of weathered rock that are silicate minerals –polymeric structures of Si & O Many variations in structure & additional elements such as Al, Na, H, K, Mg, Ca & Fe are often present

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    32. Env. Chemistry, Baird & Cann Basic Soil Chemistry Over time soil particles react with water to form clay minerals (<2ľm) –colloids –dense packing poor drainage; outer layer of cations

    33. Env. Chemistry, Baird & Cann

    34. Env. Chemistry, Baird & Cann Basic Soil Chemistry In addition to minerals soil is composed of organic matter, water & air Organic matter derived from plant material (partially decomposed cellulose, proteins and lignin), called humus, gives soil its dark color, many colloidal particles

    35. Env. Chemistry, Baird & Cann Acidity & Ion Exchange Capacity of Soil Oxidation of minerals at the soil surface can produce acids e.g. pyrite Cation-exchange capacity (CEC) –quantity of cations that are reversibly absorbed per mass of material, for clays typically 1-150 centimoles/kg Acid rain releases bases cations from soil by exchange with H+, neutralization, once these cations are depleted Al is released

    36. Env. Chemistry, Baird & Cann Acidity & Ion Exchange Capacity of Soil Soils where there is low rainfall -high pH if soil contains Na2CO3 Soils which are too high in pH can be lowered by addition of S –releases H+ as it is oxidized (by bacteria, Fe3+ or Al3+) to SO42- and reacts with water

    37. Env. Chemistry, Baird & Cann Acidity & Ion Exchange Capacity of Soil Acidity is primarily determined by H+ & OH- and reserve acidity from COOH & OH groups in organic materials (help to buffer the soil against large changes in pH Liming soil involves addition of CaCO3

    38. Env. Chemistry, Baird & Cann Acidity & Ion Exchange Capacity of Soil Arid climates salts move upward, salts also accumulate at the surface in semiarid climates where poor quality irrigation water is used & salts remain after evaporation Liberation of ions on the surface

    39. Env. Chemistry, Baird & Cann Acidity & Ion Exchange Capacity of Soil Hydrolysis of silicates produces cations & OH-, in arid climates reaction with CO2 occurs producing bicarbonate & carbonate ions which accumulate in the soils resulting in a high pH

    40. Env. Chemistry, Baird & Cann Sediments Layers of mineral & organic deposits found at the bottom of bodies of water Sediments are important sinks for heavy metals, pesticides, PAHs, PCBs and other organics 7% of all US watersheds pose a risk to people who eat fish from them. Prominent pollutants are PCBs & mercury, also PAHs & DDT and its metabolites

    41. Env. Chemistry, Baird & Cann

    42. Env. Chemistry, Baird & Cann Binding of Heavy Metals to Soils & Sediments Ultimate sink for heavy metals & many toxic organics is deposition & burial in soils & sediments Heavy metals may accumulate in upper layers of soil making them available to agricultural plants

    43. Env. Chemistry, Baird & Cann Binding of Heavy Metals to Soils & Sediments Humic substances have a strong affinity to heavy metals. The COOH & OH groups in humic & fulvic acids bind to the metals Heavy metals are retained by soil in three ways: by adsorption onto the surfaces of mineral particles, by complexation by humic substances in organic particles, and by precipitation reactions (HgS, CdS).

    44. Env. Chemistry, Baird & Cann Sediments Provide an Historical Record

    45. Env. Chemistry, Baird & Cann Mine Tailings Mine tailings –left over material from mining processing, generally fine grained slurries that are mineral rich & often contain toxic materials such as CN used to extract the ore; generally kept in a holding pond on site, the water is left to evaporate & the tailings may be treated to remove heavy metals, nitrates & excess acidity Largest environmental threat is failure of the dam (due to flooding) for the holding pond One controversial alternative to storage is to pump the tailings 100m or more into the ocean

    46. Env. Chemistry, Baird & Cann Remediation of Contaminated Soil Three main types of remediation: containment (capping of the contaminated site with impermeable material) or immobilization (solidification and stabilization –portland cement, vitrification) Mobilization -soil washing (injecting fluids -water, EDTA, oxidizing agents, surfactants), soil vapor vacuum extraction, thermal desorption Destruction –incineration, bioremediation

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    48. Env. Chemistry, Baird & Cann

    49. Env. Chemistry, Baird & Cann Remediation of Contaminated Soil Electrochemical

    50. Env. Chemistry, Baird & Cann Remediation of Contaminated Soil In situ chemical oxidation can oftenbe used to remediate soils (and groundwater) contaminated with chlorinated solvents and/or with BTEX Permanganate ion, MnO4, is used for TCE, PCE, and MTBE deposits, whereas ozone or hydrogen peroxide is used for BTEX and PAHs or,in some cases, for the C2 chlorinated solvents as well

    51. Env. Chemistry, Baird & Cann Analysis & Remediation of Contaminated Sediments Can contaminated sediments recontaminate water body? Technique for extracting only materials that are soluble in water or weak acids (not total amounts of toxics) Remediation Cover with clean soil Dredging Treatment with chemicals –CaCO3 immobilizes heavy metals

    52. Env. Chemistry, Baird & Cann Bioremediation of Wastes & Soils Recalcitrant or biorefractory -substances that resist bioremediation If a bioremediation technique is to operate effectively, several conditions must be fulfilled: waste must be susceptible to biological degradation and in a physical form that is susceptible to microbes appropriate microbes must be available environmental conditions, such as pH, temperature, and oxygen level, must be appropriate

    53. Env. Chemistry, Baird & Cann Bioremediation of Wastes & Soils 1989 Exxon Valdez oil spill one of the largest bioremediation projects May take place under aerobic or anaerobic conditions Fungi are useful in remediation of DDT, 2,4,5-T and PAHs

    54. Env. Chemistry, Baird & Cann Bioremediation of Organochlorine Contamination PCBs –two adjacent Hs (one ortho to attachment of the rings) must be present for the aerobic process to begin –process begin with hydroxylation followed by C-C cleavage

    55. Env. Chemistry, Baird & Cann Bioremediation of Organochlorine Contamination Anaerobic degradation of PCBs (even perchlorinated compounds react) proceeds via Cl H subtitution

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    57. Env. Chemistry, Baird & Cann Phytoremediation of Soils & Sediments Plants can remediate pollutants by three mechanisms: the direct uptake of contaminants and their accumulation in the plant tissue (phytoextraction, hyperaccumulators) the release into the soil of oxygen and biochemical substances such as enzymes that stimulate the biodegradation of pollutants the enhancement of biodegradation by fungi and microbes located at the root–soil interface.

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    59. Env. Chemistry, Baird & Cann Nature of Hazardous Wastes US 500,000 hazardous waste sites, 300,000 leaking underground storage tanks, Superfund estimated $31 billion Types ignitable and burn readily and easily corrosive because their acid or base character allows them to easily corrode other materials reactive in senses not covered by ignition or corrosion, i.e., by explosion radioactive

    60. Env. Chemistry, Baird & Cann Management of Hazardous Wastes Source reduction: The deliberate minimization, through process planning, of hazardous waste generation in the first place –green chemistry Recycling and reuse Treatment: The use of any physical, chemical, biological, or thermal process—including incineration—that reduces or eliminates the hazard from the waste. Disposal –solids in proper landfills, liquids in deep underground wells

    61. Env. Chemistry, Baird & Cann Incineration of Toxic Wastes Special incinerators –destruction & removal efficiency (DRE) >99.9999% (“six nines”) Rotary kiln incinerators

    62. Env. Chemistry, Baird & Cann Supercritical Fluids

    63. Env. Chemistry, Baird & Cann Supercritical Fluids Destruction of organic wastes using supercritical water oxidation –wastes are added to water & the mixture is subjected to high pressure & temperature (400-600oC) –organics & oxygen solubility increase –hydrogen peroxide may be added to produce radicals

    64. Env. Chemistry, Baird & Cann Nonoxidative Processes Closed loop chemical reduction process (no chance for formation of dioxins & furans) –achieved using hydrogen gas at 850oC, produces methane and hydrides of oxygen, nitrogen, sulfur & chlorine Chemical dechlorination

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