NITROGEN CONVERSION PROCESSES WHEN TREATING WASTEWATER IN SOIL SYSTEMS - THE IMPORTANCE OF AMMONIUM ADSORPTION / Kväveomvandlingsprocesser vid behandling av avloppsvatten i ett markbehandlingssystem - Ammoniumadsorptionens betydelse
The objective of this study was to determine the importance of ammonium adsorption compared to other nitrogen separation and transformation processes, when infiltrating wastewater into vertical soil treatment systems. Mass balance calculations based on literature values were employed, but also complementary column experiments were performed to quantify the ammonium adsorption capacity of sand with respect to grain size, degree of water saturation, influent concentration, and clay content. The mass balance calculations indicated that even though the ammonium adsorption capacity is low in sand, this capacity is not completely utilised during the warm seasons due to a continuous nitrification when the conditions are favourable. Therefore, an increased adsorption capacity would not automatically have a significant impact on the nitrogen retention. The column experiments showed that about 30-40 mg NH4-N/kg sand was adsorbed at an influent concentration of 25 mg NH4-N /L. Grain size and degree of water saturation did not have a significant impact on the adsorption capacity, but a higher ammonium influent concentration resulted in an increased adsorption of ammonium.