Effects of plants and temperature on nitrogen removal and microbiology in a pilot-scale integrated vertical-flow wetland treating primary domestic wastewater

Abstract

Constructed wetlands are continuously being developed due to their cost effectiveness and ecological characteristics. A pilot-scale integrated vertical constructed wetlands (IVCWs) system was implemented for the treatment of primary domestic wastewater from student dorms in a university to investigate the nitrogen transformation properties. The removal efficiency of the total nitrogen of the pilot system ranged from 22.9% to 35.8%, i.e., there was insufficient denitrification in the wetland system. The maximum nitrification intensities of the media in the down-flow wetland and the up-flow wetland of the IVCW were 0.065mg/(kgh) and 0.06mg/(kgh), respectively. The nitrification intensity of the media in the rhizosphere of plants was significantly higher than that in the non-rhizosphere (P<0.01). Larger numbers of the ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were observed in the rhizosphere than in the non-rhizosphere in all the wetland cells, while the numbers of denitrifying bacteria exhibited the profiles contrary to those of the ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. The nitrogen bacteria exhibited temperature-related patterns. The maximum oxygen concentrations at the surface of the roots of Juncus effusus could reach 106μmol/l. The differences between the nitrification intensity, the numbers of bacteria in the rhizosphere and the numbers in the non-rhizosphere were attributed to the oxygen-secretion capacity of the plant roots.