Objective: Bioscavenging of heavy metal ions from wastewater by peanut shells

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Objective Bioscavenging of heavy metal ions
from wastewater by peanut shells

• The term heavy metal refers to any metallic
  chemical element that has a relatively high
  density and is toxic and poisonous at low
  concentrations.
• Examples of heavy metals include mercury(Hg),
  Cadmium(Cd), Arsenic(As), Chromium(Cr), Lead(Pb),
  etc.
• Heavy metals are the natural components of the
  earths crust.
• They cannot be degraded or destroyed.
• As trace elements, some heavy metals ex. copper,
  selenium, zinc are essential to maintain the
  metabolism of the human body. However, at higher
  concentration they can lead to poisoning.
• Heavy metal poisoning could result from drinking
  water contamination (ex. lead pipes), high
  ambient air concentrations near emission sources
  or intake via the food chain.

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• Heavy metals are dangerous because they tend to
  bioaccumulate.
• Bioaccumulation means an increase in the
  concentration of a chemical in a biological
  organism overtime, compared to the chemicals
  concentration in the environment. Compounds
  accumulate in living things any time they are
  taken up and stored faster than they are broken
  down (metabolized) or excreted.
• Heavy metals can enter a water supply by
  industrial and consumer waste, or even from
  acidic rain breaking down soils and releasing
  heavy metals into streams, lakes , rivers and
  ground water.

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Environmental and Health RisksEffects of Cadmium
on the environment

• Cadmium is bio-persistent and , once absorbed by
  an organism, remains resident for many years
  (over decades for humans) although it is
  eventually excreted.
• In humans , long term exposure is associated
• Renal dysfunction
• Obstructive lung disease linked to lung cancer.
• Produces bone defects (osteomalacia,
  osteoporosis) in humans and animals
• Increased blood pressure and effects on
  myocardium in animals
• The average daily intake for humans is estimated
  as 0.15 micrograms from air and 1 microgram from
  water.
• Smoking a packet of 20 cigrettes can lead to the
  inhalation of around 2-4 microgram of cadium.

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• Cadmium is produced as an inevitable byproduct of
  zinc or occasionally lead refining, since these
  metals occur naturally within the raw ore.
• The most significant uses of cadmium are
• In nickel/cadmium batteries
• Cadmium coatings provide good corrosion
  resistance , particularly in high stress
  environments such as marine and aerospace
  applications where high safety and reliability is
  required.
• Cadmium is used as pigments , stabilizers for PVC
  , in alloys and electronic compounds.
• Present in several products including phosphate
  fertilizers, detergents and refined petroleum
  products.

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Effects of Chromium on the environment

• Chromium is used in metal alloys and pigments for
  paints, cement, paper, rubber etc.
• Low level exposure can irritate the skin and
  cause ulceration.
• Long term exposure can cause kidney and liver
  damage.
• Damage to circulatory and nerve tissue. Chromium
  accumulates in aquatic life, adding to the danger
  of eating fish that may have been exposed to high
  levels of chromium.

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Effects of Copper on the environment

• Copper is an essential substance to human life,
  however in high doses it can cause anemia, liver
  and kidney damage, stomach and intestinal
  irritation.
• Copper normally occurs in drinking water from
  copper pipes, as well as from additives designed
  to control algal growth.

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Effects of lead in the environment

• In humans exposure to lead can result in a wide
  range of biological effects depending on the
  level and duration of exposure.
• Various effects occur over a broad range of
  doses, with the developing fetus and infant being
  more sensitive than the adult.
• High levels of exposures may result in toxic
  biochemical effects in humans which in turn cause
  problems in the synthesis of hemoglobin, effects
  on the kidneys, gastrointestinal tracts, joints
  and reproductive system, and acute or chronic
  damage to the nervous system.
• At intermediate concentrations, there is a
  persuasive evidence that lead can have small,
  subtle, sub clinical effects, particularly on
  neuro psychological developments in children.
• Some studies suggest that there may be a loss of
  up to 2 IQ points for a rise in blood lead levels
  from 10 to 20 microgram/dl in young children.

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The most important disasters with heavy metals

• 1932 Minamata
• 1952 Minamata Syndrome

• Sewage containing mercury is released by chissos
  chemicals works into Minimata Bay in Japan. The
  mercury accumulation sea creatures, leading
  eventually to mercury poisoning in the
  population.
• The incidents of mercury poisoning appear in the
  population of Minamata Bay in Japan, caused by
  consumption of fish polluted with mercury,
  bringing over 500 fatalities. Since then, Japan
  has had the strictest environmental laws in the
  industrialized world.

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• Water used to extinguish a major fire carried
  fungicide containing mercury into the Upper
  Rhine. Fish are killed over a stretch of 100 km.
• Contaminated after environmental disaster toxic
  chemicals in water from a burst dam belonging to
  a mine contaminated the Coto de Donane nature
  reserve in southern Spain. The mud containing
  sulfur, lead, copper, zinc and cadmium flow down
  the Rio Guadiman. Experts estimate that Emopes
  largest bird sanctuary as well as Spain,
  agriculture and fisheries, will suffer permanent
  damage from the pollution.

• 1986 Sandoz
• 1998 Spanish nature reserve

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The commonly used procedures for removing metal
ions from aqueous streams includeMethod/Descript
ion Disadvantage

• Reverse Osmosis Heavy metals are separated by
  semi-permeable membrane at a pressure greater
  than osmotic pressure caused by the dissolved
  solids in wastewater.
• Electrodialysis The ionic components (heavy
  metal) are separated through the use of semi
  permeable ion selective membranes. Application of
  an electrical potential between the two
  electrodes causes a migration of cations and
  anions towards respective electrodes, because, of
  the alternate spacing of cation and anion
  permeable membranes, cells of concentrated and
  dilute salts are formed.

• It is an expensive method
• Formation of metal hydroxides which clog the
  membrane.

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Method/Description Disadvantages

• Ultrafiltration Pressure driven membrane
  operations that use porons membranes for the
  removal of heavy metals.
• Ion exchange Metal ions from dilute solutions
  are exchanged with ions held by electrostatic
  forces on the exchange resin.
• Chemical Precipitation is achieved by the
  addition of coagulants such as alum, lime, iron
  salts and other organic polymers.

• The generation of sludge.
• High cost and partial removed of certain ions.
• Large amount of sludge containing toxic compounds
  produced during the process.

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Biosorption

• The search for new technologies, involving the
  removal of toxic metals from wastewater has
  directed attention to biosorption, based on metal
  binding capacities of various biological
  materials.
• Biosorption can be defined as the ability of
  biological materials to accumulate heavy metals
  fro wastewater through metabolically mediated or
  physico-chemical pathways of uptake (Fourest and
  Roux, 1992).
• The major advantages of biosorption over
  conventional treatment methods include
  (Kratochvil and Volesky, 1998 a)
• Low cost
• High efficiency
• Minimization of chemical and/or biological sludge
• Regeneration of biosorbent
• Possibility of metal recovery

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• The biosorption process involves a solid phase
  (sorbent or biosorbent, biological material) and
  a liquid phase (solvent, normally water)
  containing a dissolved species to be sorbed
  (sorbate metal ions).
• Due to higher affinity of the sorbent for the
  sorbate species, the latter is attracted and
  bound there by different mechanisms.
• The process continues till equilibrium is
  established between the amount of solid-bound
  sorbate species and its portion remaining in the
  solution. The dgree of sorbent affinity for the
  sorbate determines its distribution between the
  solid and liquid phases.

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Biosorbent Material

• Agricultural products and by-products is an
  abundant waste material, and needs proper
  disposal.
• When disposed by burning in site, it generates
  CO2 and other forms of pollutions. This creates a
  need for conversion of agricultural products and
  by products to useful and value added products.
• One possible avenue could be as inexpensive ion
  exchange or sorbent material which could remove
  toxic metal ions from aqueous solutions.
• This idea has been investigated by a number of
  authors (Table 1).

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Sources Cited

• http//www.lenntech.com/heavy-metals.htm
• Biosorption of heavy metals N. Ahalya, T.V.
  Ramachandra and K.D. kanamadi
• http//www.ces.iisc.ernet.in/energy/water/paper/bi
  osorption/biosorption.htm