Testing in Finland
Our oceanographic pH sensor was tested with the Finnish Environmental Institute (SYKE) from January to May.
Initially we spent time in the SYKE MRC laboratories testing the sensor and training the guys in Finland who would be looking after the sensor for us. During these three weeks, and after initial debugging, we obtained a baseline set of results using a commercially available Palmer Potentiostat in brackish Baltic sea water. By utilizing the varying stations from the Finmaid voyages, we were able to see the effects of a large gradient of salinity (from 5ppt to 17.3ppt). Our initial concern was that the lower end salinity may affect the conductivity of the system creating problems for the measurement, however the results showed our system was easily able to handle the lower salinity waters – good news!
Following these open water tests we integrated our sensor into a flow loop system. Overnight testing demonstrated the systems ability to handle the relevant pressure (1 bar) and flow rate (5 liters per minute). Once we confirmed the sensor was performing well in the flow loop we introduced an AFT Sunburst pH sensor and a Contros pCO2 into the flow line. However, on doing this we discovered a repeating noise within our data which, on further investigation, was caused by the Contros system. We believe that the Contros membrane may be the culprit and we are looking into this, but for the remaining tests the Contros pCO2 was removed from the flow loop and the results were looking good.
With the flow loop up and running, the next step was to simulate the acidification of the ocean waters in the lab. To this end, two processes were trialed; the first was the addition of CO2 gas to the water samples collected. However, this route posed difficulty in achieving constant and appropriate steps in pH for a calibration to be achieved. Considering this, we then tried with the addition of carbonated water. This technique was much more controlled and gave the potential/current plots shown below for different pH waters, validated by the AFT-pH system.
During these trials both the pH and reference signals began to drift over time, and since the drift was consistent for both electrodes, we suspected that the Ag reference electrode had been damaged or worn away. After analyzing the photos sent by the Syke team, it was apparent that the coating had been worn away and a leak path had been found on the original design. A quick redesign was imagined, produced and shipped to the lab where it was exchanged for the old design – problem solved!
For the remainder of the project, the systems were loaded on to a fixed platform at FMI Uto station and on the Silja Serenade ferry which travels daily between Helsinki and Stockholm, both for around 40 days.
Through the information gathered within this project, a new revision of the ANB Sensors pH sensor has been developed. The feedback on the ease of use, deployment, and ease of data retrieval has all been positive. All debugging issues have been resolved. With the deployment of the sensor in the Uto station and Silja Serenade we have been able to collect real-world data that has allowed for the next revision to increase the TRL and allow for commercialization in late 2019.
We would like to thank the team at Syke for their hard work and commitment.