Nitrogen balance estimation in a subsurface flow constructed wetland planted with Heliconia psittacorum for domestic wastewater treatment

Abstract

The influence of vegetation (Heliconia psittacorum) and the main nitrogen elimination mechanism were studied via the mass balance method in a subsurface flow constructed wetland (HFSS). Six HFSS lab-scale units (microcosms) were built and filled out vertically with gravel and coarse sand. Three of the lab-scale units were planted with Heliconia sp., and the remaining three were left unplanted and run as control units. All of the experimental units were operated with an organic surface load of 5.68 g N m-2 d-1, and a theoretical hydraulic retention time (HRT) of 1.0 day. Results showed a higher N load removal efficiency in the planted units (29.6%) compared to the unplanted ones (24.3%). The nitrogen balance showed that coupled nitrification/denitrification was the main N removal mechanism, since its contribution to the overall removal was 66.7 and 69.7% in planted and unplanted units, respectively. Meanwhile, N accumulation in the support media removed 21.4 and 22.0 % in planted and unplanted units, respectively. N assimilation via physiological activity of Heliconia sp. was responsible for only 0.6 % of the total removal. Despite this low removal rate, it was evident that plants contributed indirectly to N removal in the planted units via atmospheric oxygen translocation and the assemblage of a more diverse microbial community in the rizospheric habitat.

Keywords

• denitrification
• Heliconia psittacorum
• nitrogen balance
• nitrogen removal
• plant uptak
• constructed wetland