PROPOSED IMPLEMENTATION
Our team proposed this implementation with the aim of industrial scale production of palladium reducing peptides and the palladium reduction process.
End User
The proposed end-users of the project are the metal recycling industry, the electronics industry and the automobile industry. When palladium is leached chemically, they often exist as a compound, usually at a state of palladium(II). Our proposed end users cannot directly use that palladium. Our project allows a biological method of the further processing of palladium by reduction, using PdRp that is ready for use at a relatively lower price compared to current methods1, which often use expensive chemicals. This can reduce the market price of palladium as more palladium is supplied through recycling, extending the time until it is depleted. As palladium is often used in both the automobile and electronics industries2, our project can also support the recycling of palladium in factories as it has been observed that some products are recycled by the company5. We believe that our project can allow them to reduce palladium from an unrecyclable form.
Implementation
Our proposed implementation consists of 4 parts; they are explained below:
Bioreactor
To achieve large-scale production of peptides, a large amount of E.coli, our chassis for this project, will be needed. To accomplish this, our team will implement a pilot-scale fermenter. Our modified bacteria will replicate and synthesize our PdRp-CBD in the fermenter. Homogenization with large scale homogenizer will be used to lyse the cells. The cell cultures will be forced into a narrow space, which will shear the cell membrane. Here, the PdRp-CBD will be released.
Fig 1, Proposed design of fermenter
Regenerated Amorphous Cellulose Column
As our peptide is fused with a cellulose-binding domain (CBD), the CBD can provide an easy and inexpensive method of purification of the peptide. When the supernatant retrieved from the previous step is poured into the regenerated amorphous cellulose column, the CBD will adhere to the cellulose in the column. After being washed with deionized water, only the PdRp-CBD will remain in the column. The PdRp-CBD can then be eluded using ethylene glycol3.
Fig 2, Schematic representation of Pd-Rp purification using a large CBD column.
Reduction
The purified PdRp-CBD will then be moved to a glossy glass fused steel tank which is resistant in environmets with pH values up to pH 14. The palladium(II) ions will be reduced in a pH 11 environment as pH 11 is the optimal pH for tryptophan to reduce palladium(II) ions. There, the peptides will bind to palladium ions and reduce them to elemental state.
Fig 3, Schematic representation of PdRp reducing palladium(II) ions in a glossy glass gused steel tank.
Centrifugation
Finally, the entire solution will be transferred to a decanting centrifuge or a continuous solids discharge disc stack centrifuge4. The elemental palladium in solid form will be ejected out of the centrifuge. After washing the solid ejections and retransferring them to the centrifuge, pure elemental palladium can be extracted.
Fig 4, Representation of a decanting centrifuge to extract palladium metal.
Safety
This proposed method is relatively safe, as there are no apparent downsides to the approach. Our main concerns are the leakages of palladium and the engineered bacteria into the environment. Both of these situations can cause great harm. However, we believe that these kinds of tragedies can be prevented as long as factories observe sufficient safety precautions.
Obstacles
We believe that there are some obstacles to overcome to improve our system further. Firstly, not all palladium used in the beforementioned industries are palladium (II) compounds; they may also exist as a metal alloy. That way, we would require some other ways to separate the palladium with other metals. Secondly, as we could not have access to a laboratory this year, we are unable to know the yield of our peptides. Thus, we are unable to evaluate whether the system can produce enough peptides to be more efficient than other methods.
References
[1] Akcil, A., et al. Precious metal recovery from waste printed circuit boards using cyanide and non-cyanide lixiviants – A review. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.01.017
[2] Platinum Group Metals (PGM) JM Market Report: Feb 2020. (2020). Focus on Catalysts, 2020(4), 4. doi:10.1016/j.focat.2020.03.018
[3] J;, W. (2014). Purification of a recombinant protein with cellulose-binding module 3 as the affinity tag. Retrieved from https://pubmed.ncbi.nlm.nih.gov/24943312/
[4] Tarleton, E., & Wakeman, R. (2007, October 12). Solid/liquid separation equipment. Retrieved from https://www.sciencedirect.com/science/article/pii/B9781856174213500018?via=ihub
[5] “Business Areas.” Precious Metal Recycling Gold, Silver, Palladium, Platinum, www.silverteam-recycling.com/en/Business-areas/Precious-metals/Precious-metal-recycling.