Stakeholders' Influence on the Filter's Design
Engaging with various stakeholders has been largely infuencial in the future implementation of our
research. This is a filtration system that is comprised three parts: a hydrocyclone, media binding
reactor and biosecurity mechanism. The function of each of these parts is explained in greater detail
on our Applied Design
This page documents how each aspect of the filtration system, and the modelling associated with this, has been shaped by knowledge gained from both internal and external stakeholders. It also includes how they have helped us consider the potential implication of the waste associated with the filtration system.
The idea for using a hydrocyclone came about from Plymouth Marine Laboratory who currently utilise them in their
research. Additionally, we found out after speaking to a representative at South West Water that they use hydrocyclones
at some of their sites depending on their requirements as hydrocyclones need to be designed specific to their purpose.
Initially, we wanted to model the effectiveness of different hydrocyclone designs in the aim of optimising their separation efficiency using Computational Fluid Dynamics, this uses information about the hydrocyclone to create a 3D mathematical model on a grid that can be rotated and viewed from different angles. However, after a meeting with a PhD student at the University of Exeter, who has specialised knowledge in this area, we realised that this would not be feasible in the timeframe of our project.
Acting upon this, we changed plan and decided to use experiments to find the most effective hydrocyclone for our purpose. Since we had found out previously that the flowrates of the filtration system could highly effect shape of the hydrocyclone required, we made sure to coordinate these experiments with the flowrates required for the metal binding reactor. We designed the hydrocyclones using a software called Autodesk Fusion 360, then 3D printed them so that we could perform the experiments and alter the design accordingly to improve its efficiency. We have now designed a fully functioning hydrocyclone that separates sediment efficiently at the flowrates of our system.
Metal Binding Reactor
We wanted guidance on was the most suitable media to use inside the metal binding reactor to grow the E. coli on, therefore went to speak with a representative from Taunton Aquarium who
suggested using silica sand as it would be able to withstand the high acidity of the contaminated water. After
experimentation with this idea, we concluded this was not particularly effective as the media was so fine it escaped
through the outflow pipes. On finding this out we went to Plymouth Marine Laboratory, they suggested a low cost option
using polypropylene scaffold torus structures as the media and a surfactant to encourage the E. coli to adhere to the
surface of the tori. We are implemented this method in our experiments in the lab.
Click here to find out more about these experiments.
Additionally, we designed a model to inform the future implementation of the metal binding reactor as it is unique to our project. The model can guide future-users on the most efficient flowrate and volume of the metal binding reactor to use for their purpose. It was suggested to us by the Centre for Biomedical Modelling and Analysis at the University of Exeter to create a user-interface for the model to make it easily accessible to the potential users, therefore, as you can see by following the "Modelling Page" link below, we have implemented this within our wiki.
Additionally, it can be used to resolve the issue, highlighted by the representatives at South West Water, of knowing when the metal binding reactor is saturated as it informs when the E. coli in the metal binding reactor are too saturated to still be efficient, therefore, the filter needs changing. This can be used in conjunction with the 'backwash' method suggested by these representatives, in which we would require two or more filters in series such that one can be turned offline without leading to a complete shutdown. Then we would pass water through the offline filter to be tested. The model can then help inform how often the water should be tested and can be rescaled for more accuracy based on these results.
We are very aware that biosecurity is an important aspect to consider as part of the future implementation of a system
that involves genetically modified organisms. Additionally, we were informed by stakeholders at Greenpeace
that their policy on the use of GM organisms is to ensure that they are used within a closed environment. This lead us to design a closed filtration system in which our genetically modified E. coli are contained within. We considered the biosecurity aspect by looking into ways of killing
the organisms after they pass our of the metal binding reactor. Our initial ideas were to use ozone or UV. Speaking to a
number of stakeholders highlighted concerns with both of these methods. Ozone could contaminate the water
if used in the high quantities we would require to kill all of the bacteria and UV may not be effective
enough for our purpose. We acted upon this information and performed experiments to test the effectiveness of UV.
The conclusion was that it would not be suitable for our requirements, since there were around 10 million times
too many bacteria left after irradiating for 10 minutes. Following finding this out we spoke to PML who
suggested the use of copper alginate beads.
After one of our presentations on Responsible Research and Innovation, in which we detailed how stakeholder engagement has been integral in the development of our filtration system, a member of staff at the University of Exeter approached us with concerns about this method of biosecurity. His concerns were that the bacteria may be intrinsically resistant to the copper in the copper alginate beads due to being exposed to them in the water. Whilst the effectiveness of this method has been looked into, it has only been considered a laboratory condition and is yet to have any industrial testing. Therefore, another consideration that needs to be taken into account is the life span of the beads, how long they would last before breaking down and potentially releasing copper into the water, as this risk would then counteract the issue being tackled.
On a visit to a South West Water site concern was expressed over the waste associated with our filtration system. Considering this, we looked into ways of obtaining the metals extracted so that they can be sold on and therefore less waste would be produced. More detail into how this could be achieved is on our Future Page.