Amid the challenges of climate change, aging infrastructure, and urbanization, environmental engineers must develop resources efficient wastewater treatment. This dissertation presents advancements in our understanding of how sulfur can reduce the resource intensity of nitrogen removal from wastewater. This research evaluates how hydrogen sulfide affects nitrogen cycling in three wastewater treatment systems: two full-scale treatment processes that employ different redox environments, thereby supporting distinct microbial communities, and one lab-scale bioreactor. Studies using microbial communities from full-scale treatment processes showed sulfide can be used to reduce the aeration demands of treatment by inhibiting nitrite oxidizing bacteria. Results show that not all nitrifying communities are created equal with respect to sulfide inhibition; the effect of sulfide on nitrification is community specific. In a lab-scale membrane aerated biofilm reactor, consistent with the full-scale systems, nitrite oxidizing bacteria were more inhibited by sulfide than ammonia oxidizing bacteria. But nitrite sinks masked the inhibition of nitrite oxidizing bacteria. For example, nitrite was rapidly reduced to ammonia and during reactor monitoring this process appeared to be inhibition of ammonia oxidizing bacteria. Finally, biofilm modeling was used to evaluate the conditions under which sulfide-based denitrification can be employed in a membrane aerated biofilm. Overall the results show that hydrogen sulfide could have beneficial impacts on nitrogen removal in engineered system. The effect of hydrogen sulfide is complex because microbial communities are adaptable, and microbial community response depends on reactor configuration. Ultimately this knowledge can spur the development of technologies that use hydrogen sulfide to remove nitrogen from wastewater.
