title: Analysis of nitrogen removal processes in a subsurface flow carbonate sand filter treating municipal wastewater.
abstract: Controlled experiments were carried out in a mesoscale subsurface flow sand filter treating municipal wastewater from a single household. The system consisted of a 50 cm high vertical flow column (pre-filter) with unsaturated flow and a 3 m long horizontal subsurface flow unit (main filter) with saturated flow. Fluxes of nitrogen and carbon were analyzed in 4 different operating conditions (low and high loading, with and without the prefilter unit). Water samples were taken from the inlet, the outlet and within the sand filter at different depths and locations and analysed for water quality (Tot N, NO3-N, NH4-N, TOC, DOC, CODcr, BOD5, SS, pH, and EC) and dissolved gas content (N2O, CH4, and CO2). Emissions of N2O, CH4, and CO2 were measured with the closed-chamber technique adjacent to water quality sampling points. The results show that prefiltering in a vertical, unsaturated flow column changed the incoming ammonium to nitrate during low loading. During high loading part of the ammonium nitrified in the pre-filter was lost by denitrification. Within the horizontal main filter there were two pathways for the incoming nitrate: denitrification and dissimilatory nitrate reduction to ammonium (DNRA).
authors.affiliation: Jordforsk-Norwegian Centre for Soil and Environmental Research, As, Norway. bjorn.klove@oulu.fi
authors.forename: Bjørn
authors.initials: B
authors.lastname: Kløve
authors.forename: Anne-Kristine
authors.initials: AK
authors.lastname: Søvik
authors.forename: Liv
authors.initials: L
authors.lastname: Holtan-Hartwig
mesh_terms: D002244:Carbon / Q000737:chemistry; D005374:Filtration; D006798:Housing; D009584:Nitrogen / Q000302:isolation & purification*; D012822:Silicon Dioxide; D014865:Waste Disposal, Fluid / Q000379:methods*; D014872:Water Movements
chemical_list: D002244:Carbon; D012822:Silicon Dioxide; D009584:Nitrogen