Adaptation of an anti-fouling strainer on our plastic OPTOD sensor dedicated to fish farming

By: Aqualabo*

We have decided to test several solutions to limit the clogging of the sensors and facilitate their cleaning following our discussions with users to better assist you in the maintenance constraints related to the field of aquaculture.

In order to study the performance of this new sensor, we compared the performance of a Titanium OPTOD and a plastic OPTOD on which an anti-fouling adaptation was installed. The two sensors were then installed in a port in Lorient (France-Morbihan 56), in the heart of the ocean racing center, in seawater immersion for two measurement campaigns lasting about 40 days (Figure 1).

First measurement campaign from August 28 to October 10, 2022.

The first measurement campaign took place from August 28 to October 10 without any maintenance during the 43 days. The sensors were associated with an ODEON (portable multi-parameter) and the temperature and dissolved oxygen data were recorded continuously with an acquisition time of 2 minutes. After 43 days of immersion, the bodies of both sensors are colonized by algae and the head of the OPTOD Titanium sensor is covered with biofilm and algae.

Although the body of the plastic OPTOD sensor is also covered with algae, the anti-fouling strainer, and in particular the active pellet, are in very satisfactory condition. There is no biofilm present, which has allowed the sensor to continue to measure reliable oxygen levels.

Aqualabo has been a major player in the field of aquaculture for many years, in particular by proposing, for more than 20 years, portable oximeters for the control of dissolved oxygen levels in fish farms. Based on our experience and our proximity to our customers, we have been offering a plastic version of the oxygen sensor (OPTOD plastic) for almost a year now, at a more suitable cost.

However, for more than half of the test period, temperatures were above 20°C, which created favorable conditions for biofilm and algae growth.

Although the body of the plastic OPTOD sensor is also covered with algae, the anti-biofouling strainer and especially the active pellet are in a very satisfactory state, free of biofilm allowing the sensor to continue to measure reliable oxygen levels.

At the end of this first test period, the OPTOD Titanium sensor (blue curve) started to show shifts in measurement while the OPTOD plastic sensor, with the anti-fouling strainer (yellow curve), continued to deliver consistent measurements. After this period of immersion, the dissolved oxygen measurement delivered by the Titanium sensor, without anti-fouling protection, deviates significantly from the measurements delivered by the plastic OPTOD sensor making the operation much less reliable.

The day/night cycles corresponding to the photosynthesis/respiration processes are still remarkable for both sensors; however, the data measured by the plastic OPTOD sensor with anti-fouling protection reflect the dynamics of the environment more accurately.

Second measurement campaign from October 10 to November 29, 2022.

After cleaning, the two sensors are reintroduced into the sea water for a 49-day test campaign under the same conditions as the first test period.

At the end of this second test period, the OPTOD Titanium sensor’s strainer and DOdisk are completely covered with biofilm and the measurements delivered by the sensor cannot be meaningful. The anti-fouling strainer, which is fitted to the OPTOD Plastic sensor, is very satisfactory condition after almost 50 days of maintenance-free immersion. Cleaning the anti-fouling strainer is very easy to perform, whereas cleaning the OPTOD Titanium strainer is more difficult, more invasive and could damage the DOdisk.

In addition, the %Sat dissolved oxygen measurement delivered by the Titanium sensor (blue curve) drops out completely and is no longer reliable. The plastic OPTOD sensor equipped with the anti-fouling strainer continues to function correctly.

Conclusion

The anti-fouling strainer is very effective in limiting the formation of biofouling on the plastic OPTOD sensor. Indeed, it protects the membrane and ensures the continuity of dissolved oxygen measurements after almost 50 days of maintenance-free immersion. The anti-fouling strainer thus allows optimize the manual cleaning frequencies of the DOdisk while preserving it from aggressive maintenance that could deteriorate it.