title: Oxygen-induced dynamics of nitrous oxide in water and off-gas during the treatment of digester supernatant.
abstract: Nitrous oxide (N(2)O) is a potent greenhouse gas and of special concern in wastewater treatment. It is formed in biological wastewater treatment under both aerobic and anaerobic conditions. A major reason for high N(2)O emissions is low oxygen concentration during nitrification. In this full-scale study of N(2)O emissions from a sequencing batch reactor for treating digester supernatant, the oxygen concentration was reduced stepwise to investigate how N(2)O emissions were influenced. N(2)O concentrations were measured online in water and off-gas. A distinct relationship was found between low oxygen concentration and high N(2)O emissions. N(2)O was formed in water during both nitrification and denitrification. Decreased oxygen concentration during nitrification led to increased nitrite concentration, which in turn led to increased N(2)O concentration in the subsequent denitrification phase. When the nitrification resumed, accumulated N(2)O was stripped off to the atmosphere. Very high concentrations of N(2)O, over 56,000 ppmv, were measured in the off-gas. Furthermore, the maximum amount of N(2)O emitted during one cycle corresponded to 107.6% of the total nitrogen load (21.9% of total nitrogen present in the bulk liquid at the beginning of the cycle). This is among the highest emission levels ever measured from a full-scale municipal plant for digester supernatant.
authors.affiliation: VA-Ingenjörerna AB, Trädgårdsgatan 12, SE-702 12 Örebro, Sweden E-mail: fredrik.stenstrom@vaing.se; Water and Environmental Engineering, Department of Chemical Engineering, Lund University, SE-221 00 Lund, Sweden.
authors.forename: F
authors.initials: F
authors.lastname: Stenström
authors.affiliation: IVL Swedish Environmental Research Institute, P.O. Box 210 60, SE-100 31 Stockholm, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Tjus
authors.affiliation: Water and Environmental Engineering, Department of Chemical Engineering, Lund University, SE-221 00 Lund, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: la Cour Jansen
mesh_terms: D058465:Nitrification; D009609:Nitrous Oxide / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D009609:Nitrous Oxide; D010100:Oxygen