Team:IISER-Pune-India/Applied Design

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Applied Design

We have tried to come up with a device to sequester Lead from the water efflux of industries. Cleaning up a river is not possible, even though required for our local river. Our talk with an engineer from a sewage treatment plant, he gave us some insight into tackling this problem. Since the water body we are concerned with is a river, if we cut off Lead from the source, eventually, the Lead concentration in the river will fall. This meant we had to come up with a device that industries could use to clean their water discharge.

Device

The device shown is how the Lead sequestration device would look. It is a plastic cylinder of volume 1.8L. It has a shaft running along its axis to which three biofilm discs will be attached. There is a water inlet and an outlet to allow the flow of water. The device will be filled to half its volume, i.e., up to the shaft (0.9L). The biofilms are placed at equal distances from each other and the walls of the container.
We want to maximize the area of contact of the biofilm with the water so as to maximize sequestration. Circular biofilms provide the maximum surface area in a cylindrical tank compared to any other shape. A cylindrical tank was chosen because we wanted to rotate the biofilm. Rotation of biofilms is necessary if we want them to survive. This can be seen from the OD graphs of the biosensor experiments.We see that OD drops drastically when cells were exposed to 40μM of Lead for 3hrs. We need to reduce the amount of Lead the cells take in but maximize sequestration. This can be achieved by removing bacteria from Lead at regular time intervals. The design allows half the bacteria to be submerged in Lead at any given moment ensuring that Lead is removed from water without any breaks. Each bacteria stays in a Lead-free environment for half the revolution time, during which it can sequester the free Lead inside it and multiply.
We assume that there is a high Lead concentration in the water discharge from industries, say 30μM. From the bioremediation system graphs, we see that it takes 1000min for 1 cell to sequester 30μM. Assuming there are 10⁸ bacteria on each biofilm. At any given time 1.5*10⁸ bacteria are submerged in Lead. Each bacteria would have to sequester 2*10^-7μM. From the model, we see that this would take less than one minute. This would be true if the bacteria were dispersed uniformly in water. Since they are on biofilms the system will take more time to sequester Lead.
While dividing, each daughter cell can get either half of the parent cell's Lead, or one daughter has most of the Lead. In both cases, not all daughter cells will die. See illustration: