Use of the natural microbial populations in cleaning the toxic and hazardous contaminants in the environment is Bioremediation. Microbes act as catalysts to reduce the level of hazardness of toxic chemicals. It mainly covers the treatment of hazardous substances such as oil sludges in the soil and radioactive wastes in effluents.
It can be done -
Composting - it is decayed organic matter having a rich amount of micro organisms. These microorganism can degrade the wastes efficiently that can not be easily possible otherwise.
The process of degradation of explosive wastes by introduce it to a mixture of decaying organic matter is known as composting. For ex: TNT (Trinitrotoluene), Octahydro-tetra-nitro-tetrazocine (HMX) in liquids are treated by composting.
The polluted liquid is added to a mass decaying organic matter in a large compost pit. Microbes presents in the mixture degrade the chemicals and reduce their concentration. About 90% of wastes are degraded in 80 days at 550C. It is further lowered to less than 1% in 150 days. Here the mass excavated from the pit is used to fertilized the soil. This method proved to be very cheap.
Land farming - The oil sludge contains oil wastes that can be degraded by the microbes is land farming which includes piling and maintenance of oil sludge. It is done on a stretch of land with clay soil in order to prevent seepage of contaminated water.
Light loamy soil is spread uniformly. Oil sludge is piled over the soil. A slope is maintained to extract water logging and off course a ridge along the periphery of the sludge pile to prevent surface run off.
Nitrates, Phosphates and powered limestones are sprinkled over the sludge. The sludge watered to have 20% water saturation in the pile. Microorganisms growth is max at 7 - 8 pH and 200C - 300C temp. 50 - 70% oil wastes are degraded within 4 months. Again a next layer of sludge can be piled over the first degraded pile.
This process have some limitations like it is very slow and incomplete, in land farming soil heavy metal concentration increases and after land farming land become useless in terms of cultivation.
In situ Bioremediation
In situ bioremediation is the addition of enough nutrients to the soil having oil contaminants in order to remove them. Naturally existing microbes present in the soil speeds up the oil degradation after the addition of inorganic fertilizer to the soil. This process is very effective for low level oil contaminants.
Digestion in Fermenters -
Fermenters are above ground reactors (large concentrate tanks) maintained to treat oil sludges and sewage.
1) Contaminated soil is introduced in the reactor. It is watered and stirred well to form slurry.
2) Plastic spheres, granulated charcoal, diatomocoeus earth etc. are mixed with the slurry to increase the area for microbial growth.
3) Anaerobic bacteria grow well in the anaerobic conditions and degrade the waste. So the conditions are maintained.
4) After Anaerobic degradation sludge is transferred to another reactor having maintained Aerobic conditions. The freshly introduce microbes, mineralizes the waste.
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