Our project started in 2020, but as the pandemic progressed we were unable to do the essential lab work and therefore postponed our participation to 2021. Because of this we have had lots of time to think about how we could contribute to solving the H2S issue within land based aquaculture. When landing on this problem, we troubleshooted to search for the most efficient solution that would not be invasive towards the fish in the RAS environment. After careful consideration we landed on making a biosensor that could detect ug/L concentration of H2S, specifically in the range 0-25 ug/L.
The envisioned future of SulFind is that the aquaculture sector uses the biosensor as a preventative method to further enhance fish welfare, and make land based fish farming more beneficial by increased predictability for the farmers. By doing this we could contribute to a sustainable aquaculture sector, and hopefully somewhat reduce overfishing in our already strained oceans.
After consulting researchers, farming facilities, and RAS suppliers, we have reached an implementation of our biosensor that we think is the most ideal. The potential production of H2S happens in and nearby the water treatment section of RAS facilities. Our idea is to lead a portion of the water flowing from these areas to a non-return valve, where the biosensor is placed right after the valve. Considering the sensor being a microfluidic chip, this system requires a minimal amount of water to be led away from the recirculating water. Thus the principle of minimal water waste in RAS facilities is maintained. From our business survey in April it became apparent that any genetically modified biomatter in the tanks was not an option, and that is one of the reasons why we think a non-return valve is a clear solution to gain access to the facility’s water without the biosensor being in contact with the main flow itself. Another advantage to this solution is the amount of control it provides to the farmers. By leading water samples from specific regions of the facility to this pipe, it is possible to anticipate which area creates favourable conditions for H2S production and implement countermeasures before the H2S production occurs. After the biosensor has registered the H2S concentration in the water, the valve will open up on the other side and the water will be guided towards a secure waste station for GMO waste.
Figure 1: Schematic setup for sensor implementation in a RAS facility.
Although our biosensor provides a much higher sensitivity than the more physics-based sensors, it comes with a cost. It is paramount that the correct measures are implemented to ensure the safety of personnel, fish, and consumers. Since we have two different approaches within this project, they require different safety measures. The genetically modified E. Coli biosensor requires far more consideration before being put inside a RAS facility. As this bacteria is an environmental contaminant if certain nourishment and environmental requirements are met, it is crucial to make sure that the E. Coli remains within the biosensor and out of contact with the water circulating the facility. The non-return valve could contribute to this aspect by forcing the water in one direction. Another precaution is to filter the water before entering the non-return valve. This improves our implementation in two ways. First of all, if we use a microfilter with a pore size of about 0.2 microns, this will be an extra protective barrier in a hypothetical situation where the water flow is reversed or the non-return valve is malfunctioning. This is because the bacteria will be unable to pass through the filter. That way, the bacteria are kept away from the rest of the facility. The second way this improves our implementation is through the removal of any potential growth of biofilm on the biosensor. The downside to this measure is frequent replacement of these filters. However, we consider the pros of containing E. Coli and removing the biofouling risk more rewarding than the cons. Another safety aspect to consider is the handling of our device by personnel. If the GMOs are released by either poor handling or malicious intent, it could pose a risk towards the environment, the fish, and the personnel themselves. In addition, such a scenario could worsen the public’s opinion of GMOs. Therefore it is paramount to design the device in such a way that this is not possible. Our other approach with heme proteins requires far less safety measures, since they are not GMOs or GMO products, and cannot replicate. Therefore this approach poses much less of a risk to fish, humans, and the environment. However, we would still like to implement the biosensor in RAS facilities much the same way as for the E. Coli approach. The accumulation of biomass on the biosensor would still be a problem, and the control a non-return valve provides is valuable no matter the approach.
Some other challenges when implementing our biosensor into a RAS facility are different environmental preferences among different fish species, degradation of heme proteins or proliferation of E. Coli in the sensor over time, false positives, and the perception of GMO in the aquaculture sector as we discovered in our business survey. Since not all fish species thrive in the same environment, our sensor might have to be tweaked to fit these parameters. This is something we have not looked into, and needs further research before we can come to any conclusion. The degradation of heme proteins could reduce sensor performance, since the number of fluorescent emittable proteins decreases over time. The same goes for any proliferation of E. Coli, except that there would then be more cells to emit bioluminescence than expected. An effect of this challenge is that it will cause a displacement in the calculated concentration that will be difficult to detect. Since our output values are based on a set number of proteins or bacteria, the scaling would essentially be useless. This suggests that our users, the RAS facilities, would have to regularly swap out the current solution of proteins with a new one in the sensor to ensure steady and predictable output values for the concentration.