An Innovative in Situ Monitoring of Sulfate Reduction within a Wastewater Biofilm by H2S and SO42- Microsensors.

Microelectrodes can be used to obtain chemical profiles within biofilm microenvironments. For example, sulfate (SO42-) and hydrogen sulfide (H2S) microelectrodes can be used to study sulfate reduction activity in this context. However, there is no SO42- microelectrode available for studying sulfate reduction in biofilms. In this study, SO42- and H2S microelectrodes were fabricated and applied in the measurement of a wastewater membrane-aerated biofilm (MAB) to investigate the in situ sulfate reduction activity. Both the SO42- and H2S microelectrodes with a tip diameter of around 20 micrometers were successfully developed and displayed satisfying selectivity to SO42- and H2S, respectively. The Nernstian slopes of calibration curves of the fabricated SO42- electrodes were close to -28.1 mV/decade, and the R2 values were greater than 98%. Within the selected concentration range from 10-5 M (0.96 mg/L) to 10-2 M (960 mg/L), the response of the SO42- microelectrode was log-linearly related to its concentration. The successfully fabricated SO42- microelectrode was combined with the existing H2S microelectrode and applied on an environmental wastewater biofilm sample to investigate the sulfate reduction activity within it. The H2S and SO42- microelectrodes showed stable responses and good performance, and the decrease of SO42- with an accompanying increased of H2S within the biofilm indicated the in situ sulfate reduction activity. The application of combined SO42- and H2S microelectrodes in wastewater biofilms could amend the current understanding of sulfate reduction and sulfur oxidation within environmental biofilms based on only H2S microelectrodes.