An Innovative in Situ Monitoring of Sulfate Reduction within a Wastewater Biofilm by HS and SO Microsensors.

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