Team:Edinburgh/Implementation

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Implementation

Inspiration for the Super Grinder design was first taken from current commercial communition equipment used in the milling of many different materials, from corn to mineral ore. The general nature of this equipment would mean that it could be easily used to break down many different waste materials on a large scale. However, it is unclear how much modification would be required to make these machines suitable for our requirements, with the amount dependent on the machine chosen and technique of communition decided upon. Some of these modifications to consider may include:

• coating of grinding/shredding surfaces with enzymes immobilised on silica.
• the addition of enzymes immobilised on silica beads to the solution within the machine.

Further research into already existing industrial equipment also indicated that, for our purposes, wet milling would be a more appropriate approach than dry milling. This is due to wet milling requiring a liquid solution, meaning the inclusion of a buffer throughout the process would be simple, essential to the proper working of the immobilised enzymes. Additionally, wet milling is more able to comminute particles to below cell wall size [1], again a necessary requirement for the extraction of valuable molecular products from the waste materials we will be using.

Figure 1 Milling machine design, adapted from Shikinaka et al, 2019 [2]

Perhaps most significantly in this initial research it was found that the repurposing and use of industrial communition equipment for simultaneous mechanical and enzymatic degradation had already been demonstrated by Shikinaka et al. 2019 [2]. In their paper they demonstrated that the inclusion of enzymes in solution within a milling machine, along with adjustments in temperature above the enzyme optimum, increased the saccharification of cedar wood cellulose to 80%. The design of their machine utilised a rotating blade leading to a rotating bead mill, they also recycled the substrate and solution so that it passed through the machine multiple times (Figure 1). Although this paper utilised a slightly different waste material and had the enzymes in solution as opposed to immobilised, it still demonstrated that the addition of enzymes within the mechanical comminution process can result in more efficient degradation.

Other potential design elements were investigated for incorporation into our final design. These included shredding and grinding gears (Figure 2), similar to those used in wastewater treatment [3], with their ability to grind up many different kinds of materials they seem suitable for inclusion as perhaps the first step in the Super Grinder, able to effectively disrupt hard and perhaps difficult to degrade materials such as feathers and crustacean shells. The possibility of including a belt or disk sander design was also mooted as a potential way to break down the initial waste put into the machine. However, this is not a usual element included in commercial milling machines, potentially indicating that it may be impractical due to the generation of high amounts of dust and heat. Despite this, it would still warrant further investigation as to its implementation.

Figure 2 Shredding and grinding gears from wastewater treatment facilities. Adapted from Franklin Miller Incorporated [3]

Bead/ball mills (Figure 3) also seemed an excellent way in which to incorporate immobilised enzymes into the machine, as they are easily scalable, relatively easy to operate and already incorporate beads onto which enzymes could be immobilised. However, in order to be effective the beads used need to have a greater density and size than the substrate they are degrading [5]. Hence, as the beads that were shown to be most effective at immobilising the enzyme tested are all under 100µm, the bead mill may have to be a later or even final step in the machine; when the waste material has already been physically broken down to a powder form.

Figure 3 Bead/ball mill as inspiration for our design.

At the end of this initial research it was concluded that the combination of shredding gears followed by a bead mill would be the best starting point for an effective Super Grinder design (Figure 4). This would allow degradation of raw waste materials to valuable products in one contained machine. In the first step, the shredding gears will grind the waste into a powder form. The number, size and arrangement of the gears would have to be decided through further experimentation to see what most efficiently converts the raw waste to the desired size and density to be further degraded in the bead mill. The bead mill itself would ideally degrade the powder waste to the valuable molecular products, with these then being filtered off, either by centrifugation or via a membrane. The exact details of the mechanism would have to be confirmed and examined in further experimentation, however this initial design seems feasible and a good starting point from which further experiments can be carried out.

Figure 4 Our design for implementation of the SuperGrinder.

References

1. 1. Hockmeyer Equipment Corporation (2021) Wet Milling vs Dry Milling: The Differences, Advantages and Challenges. https://hockmeyer.com/blog/articles/wet-milling-vs-dry-milling-the-differences-advantages-and-challenges/ [Accessed on 27th September 2021]
2. 2. Shikinaka K, Nakamura M, Navarro R, Otsuka Y (2019) Functional Materials from Plant Biomass Obtained by Simultaneous Enzymatic Saccharification and Communition. Trends in Glycoscience and Glycotechnology 32(186): E63-E76. doi: 10.4052/tigg.1967.7E
3. 3. Franklin Miller Incorporated (n.d.) Grinders, Shredders and Comminutors – An Evolving Technology. https://franklinmiller.com/white-papers/grinders-shredders-comminutors-evolving-technology/ [Accessed on 27th September 2021]
4. 4. Rusch H (2007) 21. Marcy Ball Mill - Shenandoah-Dives Mill, 135 County Road 2, Silverton, San Juan County, CO. Library of Congress Prints and Photographs Division Washington, D.C. 20540 USA http://hdl.loc.gov/loc.pnp/pp.print
5. 5. Neikov OD (2009) Chapter 2 - Mechanical Crushing and Grinding, Handbook of Non-Ferrous Metal Powders. Elsevier. ISBN 9781856174220. https://doi.org/10.1016/B978-1-85617-422-0.00002-1

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