An Innovative in Situ Monitoring of Sulfate Reduction within a Wastewater Biofilm by H(2)S and SO(4)(2−) Microsensors

Microelectrodes can be used to obtain chemical profiles within biofilm microenvironments. For example, sulfate (SO(4)(2−)) and hydrogen sulfide (H(2)S) microelectrodes can be used to study sulfate reduction activity in this context. However, there is no SO(4)(2−) microelectrode available for studying sulfate reduction in biofilms. In this study, SO(4)(2−) and H(2)S 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(4)(2−) and H(2)S microelectrodes with a tip diameter of around 20 micrometers were successfully developed and displayed satisfying selectivity to SO(4)(2)(−) and H(2)S, respectively. The Nernstian slopes of calibration curves of the fabricated SO(4)(2−) electrodes were close to −28.1 mV/decade, and the R(2) 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 SO(4)(2−) microelectrode was log-linearly related to its concentration. The successfully fabricated SO(4)(2−) microelectrode was combined with the existing H(2)S microelectrode and applied on an environmental wastewater biofilm sample to investigate the sulfate reduction activity within it. The H(2)S and SO(4)(2−) microelectrodes showed stable responses and good performance, and the decrease of SO(4)(2−) with an accompanying increased of H(2)S within the biofilm indicated the in situ sulfate reduction activity. The application of combined SO(4)(2−) and H(2)S microelectrodes in wastewater biofilms could amend the current understanding of sulfate reduction and sulfur oxidation within environmental biofilms based on only H(2)S microelectrodes.