Future Plans for Implementation
Bench-Scale Bioreactor
|
|
| Our team has worked hard to realise a real-world solution for our project. The Bangalore BioInnovation Centre were interested to know about our project and is willing to provide support to help us take this opportunity further and develop and test a bench scale model. Taking our bioreactor model from a 3-D/Theoretical model to a working bench-scale model in the future is something we are very enthusiastic about. Although modelling on the computer provides valuable insights, we would like to run several experiments to validate the working principle of our bioreactor and also its efficiency. Building a bench-scale model will also enable us to improve certain aspects of our design even further. |
Prototype Recapture Mechanism
Through a survey conducted by our team targeting AC and refrigerator repair shops, we learned that the leakage through these coolant devices is a larger issue than we had anticipated. The gasses need to be topped off in these appliances regularly, and their leakage causes accumulation in the stratosphere leading to Ozone depletion and Climate change. Hence, it was imperative that we develop solutions for the problem of direct emissions.
Faced with this challenge, the DryLab team brainstormed how to solve the problem of sequestering the halocarbons from their point of release and making them available for degradation in the bioreactor. The team devised using an adsorbent to adsorb the gasses, which could be desorbed by simple physical changes such as temperature or pressure changes. The usage of adsorbent meant that the whole process was reversible, and the adsorbent would be recovered and available for use after a cycle.
A literature survey for materials with cost-effective desorption procedures suggested the use of Activated Charcoal and Activated Carbon Fibres (ACF), which had high adsorption capacity for these refrigerants[2][3]. In addition, they were cheaply and readily available in bulk quantities. Activated Carbon Fibre also offered an extremely advantageous method of desorption: passing an electrical current through it would cause it to heat up, leading to desorption of the gasses.
Activated Carbon based adsorbents, however, have a critical flaw. They are non-specific adsorbents, meaning they are good at adsorbing other gasses besides the ones we are interested in. Given the rate of leakage of the coolants, our team figured out that due to the non-specificity, the recovery rate of gasses from any such filter would be very low. Hence, we tried to find specific adsorbents for halocarbons and stumbled upon a class of porous materials at the cutting edge of modern research.[4]
These mixed-ligand MetalOrganic Frameworks (MOFs), LIFM-66,67-mix, show high uptake (about 1g of gas per g of adsorbent) of commonly used HCFCs and HFCs at room temperature and atmospheric pressure[1]. Further, the uptake can also be regulated by engineering the material. We took inputs from Professor Subinoy Rana, Materials Research Centre, IISc, to know about these classes of materials, the feasibility of synthesis and the cost of synthesis. Since these materials are not available at an industrial scale, they have to be synthesized in the lab. From our discussions, we learnt that synthesizing these molecules will be time-consuming. Hence, we decided to first prototype a potential solution and plan for synthesis after prototyping.
Different cooling systems employ different technologies and in many scenarios finding the exact point of leakage is not easy. Hence, we have taken the case study of mobile air conditioners in cars to build a prototype for future implementation. This is primarily because all emissions are localized to the chamber beneath the hood, which provides a very instructive model for prototyping.
It's been shown that air conditioning units in cars are major emitters of CFC-12, HCFC-22, and HFC-134a, with the emission reaching more than 300 mg per vehicle per hour in hot and humid tropical conditions. Hence, the potential of capturing these gasses from the hood of the vehicle is immense in a tropical city like Bengaluru, which is plagued by bad traffic conditions. The mixing ratio measurements for these mobile refrigeration units place the location of emissions along the tubes that conduct these gases inside the hood. This led us to the proposition of placing the prototype filter with the adsorbent beneath the hood of the car, capturing the gasses as they get leaked and flushed out of the hood. What is further conducive to this system, is the possibility of building an ecosystem around it. Cars require regular maintenance, and during the maintenance, filters and components are usually replaced. This would give rise to a scenario where the filter is replaced during regular maintenance, and the used up filter can be used to desorb the gases and regenerate the filter for repeated application.
This would help us with the double advantage of cutting off the direct halocarbon release from one of the leading causes of direct emissions, and the desorbed gases can be remediated with our proposed bioreactor device, solving a facet of the innumerable ways vehicles contribute to climate change.
In the future, we wish to model the prototype for certain car models and test it. During the testing, we plan to initially use activated carbon-based adsorbents as an alpha model to understand the gas flow and capture. Once we have optimised the alpha model, we plan to move to a beta prototype where we wish to implement a real scale model with the MOF-based adsorbent. With this model, we wish to capture the real-time performance of the prototype.
ZNO Based Gas Sensor
A gas sensor generally has a metal oxide crystal present in it. A property that is held by certain metal oxides is that they have a large number of vacancies present in their lattice as well as on their surface. These vacancies behave as sites for gases to occupy wherein these gas molecules are adsorbed onto the surface or get into the vacancies. This adsorption and insertion of gas molecules leads to a change in the resistance of the crystal.
ZnO is a metal oxide that is used generally for this purpose. However, on going to Microsoft workshop and after a thorough literature survey, we found out that MnO2 is a metal oxide that adsorbs volatile organic compounds and halocarbons well and can be used for this purpose. These gas sensors are cheap in price and easy to acquire as well.
In order to measure the change in resistance, an electronic circuit involving operational amplifiers that act as a differential amplifier must be used wherein the difference between the voltage from the metal oxide and that of a reference a subtracted and amplified.
Two chambers, one with our Halocarbon degrading system and another with our control can be setup. A gas sensor circuit would exist in both these chambers. The concentration of the halocarbons in the Halocarbon degrading chamber with the bacteria would change with time, this would lead to a change in resistance and thereby showcase an amplified voltage signal. This could be used to find concentration of Halocarbons as a function of time.