Experimental investigation on hydrogen sulfide production, wastewater characteristics and microbial ecology profiles in anaerobic sewer lines using a sewer physical twin

Over the past decade, considerable emphasis has been placed on the development of digital twins for water and wastewater applications. However, physical twins - if properly designed - offer a higher quality comparison with the real system that cannot be achieved by a digital twin. This paper focuses on experimental investigations of hydrogen sulfide formation in anaerobic sewer lines through biochemical pathways using a sewer physical twin (SPT). The SPT was conceived to independently control sewage residence time, horizontal pipe velocity, and other important sewer parameters (scouring velocity, well shear, etc.) able to affect hydrogen sulfide production, wastewater characteristics and microbial ecology distribution both in the bulk flow and in the biofilm. The SPT, constructed with three identical parallel lines to allow robust data collection and benchmarking of in-sewer treatment strategies for odor control, was operated for over 200 days using real sewage. Longitudinal wastewater fractionation studies and microbial ecology profiles confirmed the presence of active hydrolysis and fermentation processes, with a mature biofilm. The activity of sulfate-reducing bacteria (SRB) decreased as the biofilm thickness decreased, while the concentration of hydrogen sulfide followed the opposite trend. The addition of ferrous ions effectively controlled the concentration of dissolved sulfide, resulting in the formation of ferrous sulfide. Distinct bacterial populations were identified for the bulk wastewater and the biofilm, with SRB and methanogens being predominant in the biofilm and sulfur-oxidizing and facultative bacteria more abundant in the bulk wastewater. In conclusion, this study successfully demonstrated that the SPT accurately mimics the observed trends in full scale associated with sulfide emissions thus providing data with high reproducibility, satisfactory accuracy, and novel insights into system performance. It is anticipated that the SPT will play a crucial role also in laboratory and pilot studies associated in adjacent areas including sewer epidemiology and GHG emissions to allow high quality data collection under a variety of operating conditions and sewer process dynamics.