Peculiarities of nitrogen compouds removal from wastewater in constructed wetlands

Abstract

In limited companies (LTD) ‘Pastogė’ and ‘Nikola’ constructed wetlands of vertical flow (VFCW) are arranged, while limited company (LTD) ‘Agaras’ contains two-stage constructed wetlands of horizontal flow (HFCW). In all the objects the supplied wastewater is pre-treated (primary treatment). Having compared the efficiency of ammonium and nitrite nitrogen removal in two types of constructed wetlands (VFCW and HFCW) it was determined that larger amounts of total nitrogen are removed in HFCW (38.1%) rather than in VFCW (24.4%), however in VFCW smaller amounts of ammonium and nitrite nitrogen are discharged with wastewater. No significant effect of the fluctuations of ambient temperature on the removal of ammonium and nitrite nitrogen was observed in HFCW (difference of average values of cold and warm periods was 3-8%). Rather reliable relation (R2 = 0.738) was determined between ammonium nitrogen concentrations in wastewater outflow and HFCW load according to total nitrogen, however ammonium nitrogen amounts in treated wastewater (when filter load according to total nitrogen is 0.3 to 4.6 g m-2 d-1) exceeded the maximum allowable concentration (MAC) and were fluctuating from 6 to 32 mg l-1.