Development and Application of a 3D-Printed Microfluidic Sulfide-Selective Sensor for Online Monitoring of a Hydrogenotrophic Sulfidogenic Bioreactor

A sulfide online-monitoring system (S-OMS) was developed using a 3D-printed microfluidic platform to monitor sulfide in bioreactors. The S-OMS consisted of an electrochemical cell in which a microdevice was 3D-printed with co-polyester filaments and used an internal silver/silver sulfide (Ag/Ag₂S) working electrode and a commercial, external silver/silver chloride (Ag/AgCl) reference electrode. The analytical evaluation showed a wide linear range (1.5-30,400 mg L^-1) with repeatability and reproducibility presenting relative standard deviations of less than 5%. The S-OMS remained stable during working periods ranging from 16 h to 8 days, depending on the operation mode. Real samples from a sulfate-reducing bioreactor were used to validate the S-OMS, and the results were compared with those of a commercial sulfide ion-selective electrode (S^2--ISE), yielding a good linear correlation (<i>R</i>² = 0.92). Moreover, a <i>t</i>-test revealed no significant statistical difference between the two analytical methods. The bioreactor operation resulted in a high sulfate reduction rate and in the accumulation of total sulfide, as measured with the S-OMS, in the bioreactor. However, the H₂S inhibition was offset by an increase in pH and volatile suspended solids (VSS) throughout the operation. Overall, the S-OMS demonstrated robust analytical performance and operational suitability for online monitoring of sulfide in sulfide-producing bioreactors.