A critical review of sulfide and methane control in urban sewer systems using nitrogen compounds

Sewer gases, primarily hydrogen sulfide and methane, are detrimental to the wastewater infrastructure and environment by causing odour, corrosion, and greenhouse gas emissions. This article critically reviewed the dosing strategies, working mechanisms and effectiveness of widely used nitrogen compounds including nitrate, nitrite, free nitrous acid (FNA), free ammonia (FA), and organic silicon quaternary ammonium salt (QSA) in mitigating sewer emissions. Nitrate and nitrite play pivotal roles in increasing redox potentials and introducing microbial sulfide and methane oxidation. FNA and FA, known for their potent inhibitory and biocidal properties, effectively reduce sulfate reduction and methane production by disrupting cell membranes, altering intracellular pH, and blocking metabolic pathways. A systematic summary of the control effectiveness and associated change of microbial community were conducted based on different dosing strategies involving continuous or intermittent dosing patterns with constant, diurnal, dynamic and shock concentration profiles. Beyond their effectiveness in controlling emissions, nitrogen compounds like nitrite and FNA are effective in mitigating sewer concrete corrosion but also raise concerns about potential nitrous oxide (N₂O) emissions. The innovative use of urine to produce FNA and FA may lead to a closed-loop strategy to achieve sustainable sewer emission control. This comprehensive review covering the dosing strategies, mechanisms, and effectiveness of nitrogen compounds will support the further development and optimal implementation.