BIOREMEDIATION OF SOIL CONTAMINATED WITH

POLYCYCLIC AROMATIC HYDROCARBON

BY RIZWANULLAH

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• volcanoes• chlorophyllous plants, fungi, and bacteria

• Anthropogenic sources of PAHs include:• petroleum• 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• 2)Bioreactor• 3)phytoremediation• 4)Rhizoremediation

• 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 furtherresearch is required to optimise their efficiency and economyfor routine use.

Bioreactors

• The contaminated soil is excavated and removed to aspecific reactor for treatment. • Usually, the soil is slurried with waterand then treated in the reactor, where conditions forbioremediation 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 degradation rate.• After treatment, the material is passed through a water-separation

system and the water recycled.

bioreactor

LAND FARMING TECHNIQUE• Land farming of contaminated material was one of the first forms of

on-site treatment• 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

movement off-site. • 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• 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.