Heavy metals in drinking water

1. Heavy Metals In Drinking Water
 Introduction
 The term heavy metal refers to any metallic
chemical element that has a relatively high
density and is toxic or poisonous at low
concentrations. Examples of heavy metals
include mercury (Hg), cadmium (Cd), arsenic
(As), chromium (Cr), thallium (Tl), and lead (Pb).

2. Mercury
Mercury is a toxic substance
which has no known function in
human biochemistry or physiology
and does not occur naturally in
living organisms. Inorganic
mercury poisoning is associated
with tremors, gingivitis and/or
minor psychological changes,
together with spontaneous
abortion and congenital
malformation.

3. Mercury Emitting from
The major natural source of
mercury is the degassing of
the Earth’s crust, emissions
from volcanoes and
evaporation from natural
bodies of water World-wide
mining of the metal leads to
indirect discharges into the
atmosphere

4. Mercury in Water and Drinking Water
Elemental mercury is typically released from industrial
processes, agricultural processes, household,
commercial and medical products containing mercury,
sewage discharge and sediment.
Inorganic mercury is found in batteries and is used in
the chemical industry and it is produced from elemental
mercury through the process of oxidation. Inorganic
mercury is the most common form that is present in
drinking water .

5. Organic mercury
(primarily methyl mercury) is
produced by specific bacterial
organisms in surface waters that
convert inorganic mercury into
organic mercury, which is the form
of mercury that poses a significant
threat to human health. Methyl
mercury is ingested typically by fish
and bio accumulates both in the
tissues of fish and the humans that
eat these fish. Large predatory fish
can contain as much as 100,000 times
more methyl mercury than the
surrounding water medium.

6. How To Remove mercury from the water
Removing mercury from the water can be
achieved using four processes:
1) Coagulation/Filtration
4) Lime Softening
3) Reverse Osmosis
2) Granular Activated Carbon

7. Coagulation/filtration
is a common treatment which uses AlSO4 that
reacts with the mercury to form a solid which
can precipitate out of the water. The sludge
then must be disposed of in a hazardous waste
landfill. This process is beneficial because it
costs very little and is reliable.

8. Granular activated carbon
uses porous carbon media. This media is a very
heavy charcoal material. As the water passes
through, the dissolved contaminants are
absorbed and held on the solid surface. This
process has its limitations because the
effectiveness depends on the concentration of
mercury in the water.

9. Lime Softening
uses excess Ca(OH) to raise the pH level and
then the heavy metal precipitates out as Hg(OH).
A benefit of this method is lower costs and
proven reliability.

10. Reverse osmosis
water is pushed through a semi permeable
membrane. A Common membrane material is a
polyamide film. This produces high quality
water, but is fairly expensive.