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Revision as of 18:22, 17 September 2015

Research

Since our target was to reduce air pollution, we targeted genes that act on NOx and SOx gases. Research was done extensively and the following genes were found to be best fitting for our project-

NrfA (Nitrite reductase)-

Since Nitric oxide NO is a major greenhouse gas, the reduction of NO from the air is an important task to address global warming concerns. NO is found primarily in motor exhausts, and Oxides of nitrogen (NOX) are key oxidants that have a role in the photochemical production of ozone, whilst also being linked with an increase in the oxidising capacity of the atmosphere.
The nitrite reductase NrfA is encoded within the nrfA operon that is found in enteric bacteria such as E. coli. The primary function of NrfA is to enable the use of nitrite as a respiratory electron acceptor, forming ammonia as a final product. Nitric oxide (NO) is a proposed intermediate in the six-electron reduction of nitrite and NrfA can use exogenous NO as a substrate[1]. This enzyme is a periplasmic protein and therefore contains a signal sequence to redirect it to the periplasmic space after the protein is formed. While no intermediates of the reaction are released, NrfA is also able to reduce various oxides other than NO such as, hydroxylamine (H(2)NOH), and nitrous oxide (N(2)O), but notably also sulfite(SO3(2-)), providing the only known direct link between the nitrogen and sulfur cycles.


NosZ (Nitrous Oxide Reductase)-

Nitrous oxide is a potent greenhouse gas, whose atmospheric concentration has been increasing since the introduction of the Haber Bosch process led to the widespread use of nitrogenous fertilizers. One of the pathways to its destruction is reduction to molecular nitrogen by the enzyme nitrous oxide reductase found in denitrifying bacteria.
NosZ, a gene coding for nitrous oxide reductase, extracted from Pseudomonas aeruginosa PAO1, is known to convert N2O to harmless Nitrogen gas (N2). It has two copper centers, a binuclear CuA center, similar to the one found in cytochrome c oxidase, and the CuZ center, a unique tetranuclear copper center now known to possess either one or two sulfide bridges.

References :

  • Clarke, TA., Mills, PC. et al (2008). Escherichia coli cytochrome c nitrite reductase NItalic textrfA.. Methods in Enzymology. 437: 63-77.
  • Structure and function of formate-dependent cytochrome c nitrite reductase, NrfA, Einsle O, Methoda in Enzymology
  • Review, Nitrous oxide reductase Sofia R. Pauleta, Simone Dell’Acqua, Isabel Moura

    • Prototype

    Why the "Pollution Crusader Device"?

    The alarming levels of pollution in Delhi are not hidden from any of us. Delhi has been ranked the first most polluted metropolis in the world, and is one of the most heavily polluted cities in India. In the period between 2000-2011, PM10 levels in Delhi's air jumped by as much as 47 per cent.
    Hence we came up with idea of using biology to cater to this problem. To come with a solution that is both sustainable and effective. We started with making Eco.coli that could reduce (NO)x emissions.
    We further instigated the problem and found that one of the largest contributions to rising pollution in Delhi is the exhaust from automobiles and other devices using petrol and diesel as fuel. The main components of Diesel engine exhaust are: Respirable Suspended Particulate Matter:
  • NOx
  • SOx
  • CO2
  • CO
    • All these emissions are responsible for causing harmful health impacts on living beings, and deteriorate the environmental conditions of planet earth.
    RSPM and NOx when combined, form a deadly combination which drastically affects human health.
    RSPM when inhaled acts like an abrasive and wears the lining of respiratory tract exposing soft spots where NOx reacts and causes severe issues. So we decided to eliminate soot and NOx as the primary objective.
    Analysis of soot:
    Soot is of two types: hydrophilic as well as hydrophobic. Hydrophilic soot dissolves in water, whereas hydrophobic soot dissolves in organic solvents like alcohol. To get rid of both the hydrophilic and hydrophobic components, we decided to use a solution of acetic acid in water as the solvent. Acetic acid, being an organic solvent, dissolves the hydrophobic part, and water, dissolves the hydrophobic soot. Using acetic acid, however, offers an added advantage as well. Being an acid, it reduces the PH of the medium and hence decreases the solubility of acidic NOx and SOx, from the exhaust into this solvent. Thus, the tank containing this solvent dissolves soot and NOx, Sox gases move out with the exhaust. The exhaust out of this tank is now passed into the desooter tank. The desooter tank has the following main design components:
  • Water tank
  • Fresh water inlet
  • Exit of tar
  • Level meter
  • Sparger
    • The exhaust gases enter the desooter tank at high temperature(200-250 C), and hence they cause the water in the tank to evaporate when they pass through it. Hence, a level meter is required to keep a check on the water level left in the tank, and hence supply fresh water accordingly through the fresh water inlet.
    A provision of tar exit is needed to remove this tar slurry continuously out of the tank. Spargers are needed to form bubbles of exhaust gas in the mixture. Blowers are also attached to the system to compensate for the back pressure generated in the system at each step.
    Now, we needed to condense the water vapor which flow along with exhaust gases out of this tank. This was required so that these excess water vapor do not clog the silica gel at the outlet of the tank. For this, we attach a heat exchanger at the outlet of the tank. It’s a cross flow type heat exchanger, with which we did some slight innovations to increase the efficiency of the condensation process. Cold water flows through the exchanger pipes and steam flows on the outside. We here filled the outside of the pipe portion of the exchanger with metal ball bearings. These ball bearings, through conduction, cool down to acquire the temperature(similar to) of the flow pipes and hence increase the surface area available to the vapor for condensation, speeding up the condensation process. The remaining exhaust, congaing NOx, Sox and some amount of water vapor now passes over the silica gel tank at the outlet of this desooter tank.
    Studies showed that NOx and SOx, in the presence of water vapor, react over Alumina-silica gel(SiO2.Al203) to lead to an oxidation reduction reaction forming NO and H2SO4. This was a remarkable discovery as the NRFA bacteria we are working with, effectively reduce NO into harmless forms, and hence we needed NO as the output from this tank. Thus, the NO rich gas from this tank is passed into the next tank containing NRFA bacteria for further action. H2SO4 produced is extracted and used for industrial purposes.


    FUTURE SCOPE OF THE PROJECT AND TARGETS TO BE ACHIEVED:

    To optimize the design of the desooter tank and the entire contraption, to increase efficiency and reduce the cost of the process. To ultimately make the process so cheap and efficient that it can replace SCR in big engines, industries and power plants. Use the soot (obtained as dissolved in water) to make ink to ultimately make the process self-sustainable and bring down the processing cost to negligible amounts by accounting for commercial selling of this ink obtained. This will also further reduce environmental repercussions as soot now is converted into a useful product, rather than being dumped into the environment To work on developing and optimizing the desooter tank design to reduce power consumption in the blower, as well as the heat exchanger.
    Hence, through optimization, we aim to finally reach a design which gets the engine to work efficiently at even higher trade-off points. Conventionally, diesel engines are operated at temperature ranges which are not very high, as operation at high temperature leads to higher amount of NOx in the exhaust. Thus, they are always operated at a trade-off temperature lower than these high temperature values, to reduce NOx emission, however, also leading to a decrease in the engine’s efficiency, and increased amounts of CO and soot emission (due to more unburnt C content in the exhaust now). SC-R’s are not efficient enough, and thus, do not lead to a significant increase in the trade-off temperature. Thus, if an efficient and cost effective design of this NRFA driven pollution crusader device is realized, it would bring about a remarkable change in the automobile and diesel engine industry, and increase the efficiency of these devices, while reducing both the cost, and carbon footprints on the environment.