Difference between revisions of "Team:Brasil-USP/Project/Reactor"
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<p><center>Figure 2- Figure 2. In the first flask <i>Acidithiobacillus ferrooxidans</i> is incubated in the medium to activate sulfur metabolism, while in the last two flasks the bacteria is in the media for devulcanization with tire powder.</center></p> | <p><center>Figure 2- Figure 2. In the first flask <i>Acidithiobacillus ferrooxidans</i> is incubated in the medium to activate sulfur metabolism, while in the last two flasks the bacteria is in the media for devulcanization with tire powder.</center></p> | ||
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+ | As it is possible to see, the tire powder floats, suggesting that an intense stirring will be needed in the bioreactor. Feng <i>et al.</i> described a 7 L batch using <i>Acidithiobacillus ferrooxidans</i>, they used a 3 step batch with different pHs, 400 rpm and 30°C in a 40-day process [5]. <br> | ||
+ | We would also pretend to make the devulcanization in a fed-batch process in a stirred tank, for initial parameters we could start with a two pH step batch, starting with 4, which is the one that there are more bacterial growth and after achieving a high cell concentration we could decrease the pH to get the best TetH active. <br> | ||
+ | After the devulcanization is ready, as soon as the particulate floats, we think it will be possible to separate it from the media as in a clarification process, wash it and introduce it into the second bioreactor. <br> | ||
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Revision as of 04:13, 18 September 2015
Project
Bioreactors and Reactor
Table of contents
texto
As said previously, we intend to implement our process in scaled up bioreactors. The whole process would be divided in 3 stages, as proposed in figure 1.Bioreactor 1 - Devulcanization
The process that takes place in this first bioreactor is the devulcanization of tire particulates. Tires are vulcanized, a process required to confer hardness and resistance to natural rubber forming sulfur bonds, that cross-link the polyisoprene chains of the natural rubber. This process allows tires to be used in the tire manufacturing procedure but, at the same time, makes it more difficult for the tire to be reused/recycled, turning the devulcanization into a very important step in our project, even if at this moment we are not genetically engineering it but only optimizing its cultivation in rubber presence.
This bioreactor will contain a special strain of Acidithiobacillus ferrooxidans, which were kindly provided by Professor Denise Bevilaqua, from UNESP (Estadual University of São Paulo). This microorganism is a wild bacteria that has the gene for tetrathionate hydrolase (TetH), which is able to reduce inorganic sulfur compounds [1]. TetH has its maximal activity in a pH range from 3 to 4, adding to that, the bacterial ideal growth is in pH 4, what let us think that the ideal bioreactor pH would be 4 [1]. Though Professor Denise Bevilaqua, who provided us the Acidithiobacillus ferrooxidans strain, recommends that this bacteria should be cultivated at 30°C, while TetH has its best activity at 25°C [2]. To achieve the best relation between bacterial growth and tire devulcanization some tests with different temperatures and pHs should be performed. The ideal stirring in cultivation is 150 rpm, to scale up maybe the rotation will also change.
Acidithiobacillus ferrooxidans is being maintained in a simple culture medium that Professor Denise Bevilaqua provided us; its composition is as follows (g/L): (NH4)2SO4 0,5; MgSO4.7H2O 0,5; K2HPO4 0,5 and FeSO4 33,3. To activate the microorganism sulfur metabolism, it is necessary to use a different culture medium with sulfur instead of iron (g/L): (NH4)2SO4 0,5; MgSO4.7H2O 0,5; K2HPO4 0,5 and S 10. This medium composition were also informed by Professor Denise Bevilaqua. Once the sulfur metabolism is activated, the bacteria can be incubated with the tire scrapes or powder, in order to initiate the devulcanization process as shown in Figure 2. The medium required for this process is very similar (g/L): (NH4)2SO4 1,5; MgSO4.7H2O 0,5; K2HPO4 0,05; Ca(NO3)2 0,01; KCl 0,05 and FeSO4.7H2O 4,43.
As it is possible to see, the tire powder floats, suggesting that an intense stirring will be needed in the bioreactor. Feng et al. described a 7 L batch using Acidithiobacillus ferrooxidans, they used a 3 step batch with different pHs, 400 rpm and 30°C in a 40-day process [5].
We would also pretend to make the devulcanization in a fed-batch process in a stirred tank, for initial parameters we could start with a two pH step batch, starting with 4, which is the one that there are more bacterial growth and after achieving a high cell concentration we could decrease the pH to get the best TetH active.
After the devulcanization is ready, as soon as the particulate floats, we think it will be possible to separate it from the media as in a clarification process, wash it and introduce it into the second bioreactor.
Bioreactor 2 - Degradation
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Chemical Reactor
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References
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