Bioremediation

Bioremediation is the cleaning up of toxic contaminants in the environment using the activity of microbes. It removes the contaminants from the soil and water.

It is a waste management technique.

It is mainly concerned with the treatment of hazardous substances such as oil sludge in the soil and radioactive wastes in efflents.

Microbes act as catalysts to reduce the level of hazardness of toxic chemicals. The reduced level of toxic chemicals in the soil and water does not affect the living beings.

     Bioremediation is done in the following ways-     

1.      In situ bioremediation
2.      Composting
3.      Landfarming
4.      Digestion in above groung reactors
5.      Phytoremediation        

1. In situ Bioremediation

     The removal of oil contaminants naturally from the soil by adding enough nutrients to the soil is called in situ bioremediation.

There is no need to add microbial inoculants to the contaminated soils.

Addition of inorganic fertilizers to soils, speeds up the rate of soil degradation by the naturally existing microbes.

In situ bioremediation is very cheap to workout.

It is suitable for treating large areas contaminated with low level of oil spills.

2. Composting

     The process of degrading explosive wastes by adding them to a  pile of decaying organic matter is known as composting.

Compost is a maximum of decayed organic matter,and rich in microorganisms.

These microorganisms can degrade explosive wastes that cannot be treated easily.

Explosives such as trinitrotoluene(TNT), hexahydro-trinitro-triazine(RDX), octahydro-tetranitro-tetrazocine(HMX) and tetryl in liquids are treated by composting.

      The liquid, containg explosive wastes, is added to a decaying pile of organic matter in a large compost pit.

       Microbes in the decaying organic matter degrade the explosive chemicals and reduce their concentration in the compost

       About 90% of explosive wastes are degraded within 80 days in compost piles at 55*C.

       It is further lowered to less than 1% within 150 days. At that time composting is also over.

       The compost pile is excavated from the pit and used to fertilize the soil as usual.

       The method is cheaper than incineration of explosive wastes.

3. Landfarming

     The piling of oil sludge on a flat land to degrade oil wastes by microbes existing in the sludge, is know as landfarming.

     It is done on a stretch of flat land with clay soil in order to prevent the seepage of contaminated water.

     Light loamy soil is spread uniformly to a height of half a foot. Oil sludge is pilled over the loamy soil to a height of one foot. It is graded to have a gentle slope to prevent waterlogging and a ridge along the periphery of the sludge pile to prevent surface run - off.

    Nitrates, phosphates and powdered limestones are uniformly spread over the sludge.

    The sludge is watered to have 20% water saturation in the pile.

    The microbial growth is maximum when the PH is between 7 and 8 and temperature is between 20*C and 30*C.

    The microbes degrade 50-70% of oil wastes in the sludge within 4 months.

     Again another layer of sludge may be paid over the first pile for degradation. After full degradation of oil wastes, the sludge material is excavated and put onto its original place from which it was excavated.

     Landfarming has the following drawbacks:

        1. Microbial degradation of oil sludge is very slow and incomplete.

        2. Concentration of heavy metals increases simultaneously in landfarming soils.

        3. After landfarming, the lands are useless for cultivation.