POLY AROMATIC HYDROCARBON
• Polycyclic aromatic hydrocarbons (PAHs, also polyaromatic
hydrocarbons) are hydrocarbon compounds containing only carbon
and hydrogen—that are composed of multiple aromatic rings
• PAHs are neutral, nonpolar molecules found in coal and
in tar deposits. They are produced as well by incomplete combustion
of organic matter
Sources of PAHs
• Natural sources include:
• forest and grass fires
• oil seeps
• chlorophyllous plants, fungi, and bacteria
• Anthropogenic sources of PAHs include:
• electric power generation
• refuse incineration
• home heating
• production of coke, carbon black, coal tar, and asphalt
• internal combustion engines
TECHNIQUES FOR BIOREMEDIATION OF PAH
• Mostly used techniques for bioremediation of pah are
• 1)Land farming method
• Current in-situ remediation techniques are considered ineffective for
the removal of most PAHs from contaminated soil.
• On-site 'landfarming' methods have been used successfully (and
within a reasonable period of time) to degrade only those PAHs with
three or fewer aromatic rings.
• Bioreactors have proved most effective for soil remediation, since
conditions for enhanced degradation can be achieved most readily.
• However, bioreactors are still at the development stage, and further
research is required to optimise their efficiency and economy
for routine use.
• The contaminated soil is excavated and removed to a
specific reactor for treatment.
• Usually, the soil is slurried with water
and then treated in the reactor, where conditions for
bioremediation are enhanced.
• The bioreactors are usually of the horizontal-drum and airlift type and
may be batch or continuous, but are usually batch-mode.
• An acclimatised microbial population from a previously treated soil
batch is usually introduced to each new batch to enhance the
• After treatment, the material is passed through a water-separation
system and the water recycled.
LAND FARMING TECHNIQUE
• Land farming of contaminated material was one of the first forms of
• The waste material is applied to the soil as a slurry and the area
managed by fertilization, irrigation, and lime addition to maintain
. optimum conditions of nutrient content, moisture content, and pH
• The area is also tilled to improve aeration and to ensure that
degradation and immobilization of contaminants within the upper
and underlying soil layers occur.
• Micro-organisms used in the degradation process are most often the
indigenous soil population.
• However, specifically adapted microorganisms may be added to the
soil to enhance the process.
• The major disadvantage with land farming is
the possibility of contaminant movement from the treatment area.
• The contaminated soil is removed to a specifically prepared area, which is
usually lined with low, permeability material, such as high-density
polyethylene or clay.
• The bed is managed to optimize degradation with fertilization, irrigation,
pH control, and sometimes microbial and surfactant additions.
• The beds are designed to enhance treatment and minimize contaminant
• They often encompass leachate-collection and sometimes emission-control
systems and are usually situated elsewhere on-site or on the area from
which the contaminated material is removed.
• Composting is another form of prepared-bed type of treatment that
has been used to treat highly contaminated material.
• This is a specific process involving a succession of mesophilic and
thermophilic microorganisms and consists in piling the soil and mixing
with an organic bulking agent, such as straw or wood chips.
• The pile is aerated by either forced aeration or pile turning, and the
moisture content, pH, and nutrient content, etc., are controlled.