Product Design Report – Premium

This Report has been introduced to outline the ways in which current design could be improved by increasing the complexity and cost of the unit, but ultimately to operate more effectively and efficiently. It should be noted that this will be purely conceptual and may neglect some sections of the unit. Please refer back to the full design report for the budget unit wherever possible.

The best way to come up with a solution to a problem is to clearly define the problem or in this case sections of the unit that may have been somewhat compromised to achieve a more affordable overall cost.

Bioreactor walls

It was noted that the best performing material would be #4 grade electro polished 316L SS, due to its superior tensile and torsional strength, corrosion resistance and very well defined properties and responses in Bioprocessing.

To overcome the issue of removing the ability to carry out visual inspections a viewing glass can be fitted. This should if styled correctly provide a more premium feel to unit.

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O2 diffusion into fermentation broth

To improve the levels of diffused oxygen in the unit would aid more efficient respiration of the bacteria and provided an effective control system was arranged to ensure these levels were maintained the effective yields of lipase production should be increased more easily maintained. The obvious choice would be to go for a conventional ring sparger arrangement providing somewhere near 0.5 vvm of air into the unit. However, considering the ever-present constraint of space, and the pursuit of finding creative solutions, something else may be considered.

Take the original magnetic stirrer with its impeller style blades providing vertical mixing. Mould the metal with channels running through it that pass to the trailing edge of the blades. The air can be forced out at a defined pressure dependant on outlet nozzle size, to achieve enough effective trust to power the impeller. This design would only benefit such a small unit and would likely only work on such a small impeller, however mixing and air supply could be combined into a single rotating blade. Again it should be noted that a control system would be required to ensure both effective O2 diffusion and mixing, if it is at all possible.

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0.22 µm filter material

The first point to note would be that, based on the superior corrosion and abrasion resistance of ceramic membranes, it would be advisable that these be selected based on the predicted, more extensive lifetime the premium product should have. These filter membranes would also be able to withstand more aggressive cleaning procedures and hence should need to be cleaned on a less regular basis as a greater level of flux should be recovered each time.

Pall Corporation suggests the following cleaning arrangement for the removal of fats, oils and proteins form their ceramic membranes;
● Solution- 0.5M NaOH with 200ppm Cl2
● Time - 30 - 60 mins
● Temperature - 50oC
● Mode of action is hydrolysis and oxidation
(From table 6.4 page 284 Cheyran 1998 source: Pall Filtron 1995):

The above cleaning operation will be used in conjunction with fluid velocities of 2 m/s of the aforementioned NaOH solution through the membranes channels.

A cleaning cycle of 45 minutes has been selected; a 30 minute cycle time for a chlorine containing solution is optimum (Cheyran 1998 pp. 279), however the mean time suggested by Pall Corporation has been selected.

Reduced filter cleaning time

One limitation of the 0.22 µm filter is that it is, by nature, perpendicular to the flow, which means it is very difficult to clean without completely stopping the flow an hence operation, which would not be ideal. However, since the filter area required is significantly less than the area of the splitter wall between the tanks there should be the possibility of housing more than one filter within the wall that can quickly replace the filter that is currently in operation without human intervention.

The simplest way of doing this would be to have a number of filters housed in a carriage, much like bullets in a revolver. After a set period of time, or once the flow rate through the membrane drops below a set value (flow meter required) then the carriage would rotate to quickly replace the existing filter with the next ‘clean’ filter. Once the unit is stopped for cleaning, the carriage with filters can be removed, cleaned and returned.

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Introduce an enzyme filter

As the unit stands there is total loss of the unused nutrients that pass through the 0.22 µm filter. To improve the efficiency of the unit, by recycling the nutrients and water currently in the system, hence concentrating the enzyme product stream, a cartridge filter operating in tangential flow can used. The filter will work by allowing water and nutrient s to pass through (permeate), however the larger enzyme molecules will not be allowed to pass through (retentate). The concentrated enzyme solution will remain in the filter cartridge and will be drawn out at a specified rate using a peristaltic pump. Again a control system would be beneficial. The permeate will pass into what is the current holding tank and will be fed back round to the fermentation tank via another peristaltic pump.

Based on the lipases molecular weight of approx. 50 kDa (http://www.uniprot.org/uniprot/Q9ZG91) a molecular pore size of 10 kDa would be ideal for use in the secondary filter to achieve a sufficient degree of separation without overly affecting the flux across the membrane.

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Enzyme filter operation

Back-flushing

Permeate back pressure

Turbulence

Introduction of a pre-filter

Introduce a chlorine filter

Exponential feed flow rate

One way flow valves

Intelligent enzyme release mechanism