Bioremediation

Bioremediation, a term which we commonly use basically means; detoxification of waste using biological systems So, it could be plants... it could be microbes Now to tell a little more about the process of purification that is taking place in the Bheri: The raw sewage has to pass through a sieving procedure where the core suspended material is released The water moves into a flat basin which is there - which in created in such a way that the water depth should be between 50-150 cm A flat bottom which has been treated with alkali – lime ensures that there is an alkaline pH which is a must for decreasing the coliform count Now the water which is rich in organic content, is released there There is a manual aeration which takes place and because of that the dissolved oxygen concentration is kept pretty high Now with sunlight penetrating till the bottom- as it's a flat surface - through and through aeration and sunlight ensures that plankton grows there Well, if plankton is allowed to grow for indefinite time, it results in plankton bloom and that's a problem - nutrification. But that doesn't happen So before it reaches a plankton bloom, fishlets are released there and they consume or feed upon the plankton So it's the initial planktons - the phytoplanktons and the zooplanktons which consume them Again the phytoplankton is growing and now the fishlets are released, which feed on the phytoplankton as well as the zooplankton Thus, the entire organic matter in the raw sewage which came here is consumed by these planktons and that in turn becomes fish feed So you do not need to actually add additional feed Whereas the water which is there is purified When you check the quality in terms of coliform count -when you compare the raw sewage water to the water in the Bheri post growth (of fish) there is a 96-99% decrease in the coliform count There is immense decrease in the metal content. Now the water which is left after the fish growth, is good enough to be used for irrigation in the surrounding fields Each Bheri has surrounding fields Not only that- it's not just the water which is being used After every round of cultivation each year there is a period when the Bheri is dried The silt which deposits at the bottom-which is absolutely fertile is picked up and spread on these surrounding farms As a result it's a fertile soil which is there and the depth of the Bheri is maintained at 50-150cm So that's the kind of purification which takes place As a result, the wastewater is purified Fish is produced Environmental damage is prevented And there is water, as well as fertile soil for irrigation In addition, it also generates a lot of human resource that is, in terms of employment So this leads to production of one third of the fish that is required And also a major portion of the vegetables that is required for the entire city So, it is one of the best examples of integrated resource recovery in the world. And what I have been or my entire group has been able to do till now we can say for sure that this is a boon to the city of Calcutta and it absolutely needs to be preserved without which the detoxification or bioremediation activity will be severely hampered Since we do not have formal wastewater treatment plants This is the natural system which purifies the entire waste