Nitrate removal from tail water by integrated vertical-flow constructed wetlands at a high hydraulic loading rate

Abstract

A B S T R A C TNitrate removal rates of two pilot-scale integrated vertical-flow constructed wetlands (IVCWs) treating tail water, under a hydraulic loading rate (HLR) of 250 mm/d with a mean influent NO À 3 -N concentration of 24.4 mg·L À1 , were evaluated. Mean NO À 3 -N removal efficiencies of 15.5 and 18.5% with mass removal rates of 1.01 g·m À2 ·d À1 and 1.16 g·m À2 ·d À1 for IVCW 1 (planted with Canna indica and Pontederia cordata) and 2 (planted with Typha orientalis and Arundo donax var. versicolor), respectively, were achieved. The removal rate constants as fitted by the first-order area-based model averaged 0.046 and 0.055 m·d À1 , respectively. Since NO À 3 -N was the dominant nitrogen form in the effluent, denitrification was the limiting step in nitrogen removal despite of favorable pH and anaerobic conditions in the wetland beds. Low availability of carbon source, high HLR, and low temperature could be the probable influencing factors for the observed low NO À 3 -N removal efficiencies. However, IVCW could be used to treat tail water for nitrate removal at a comparable high loading rate.

Comparative evaluation of total phosphorus removal performances for treatment of domestic and secondary wastewater using integrated vertical-flow constructed wetlands: two years’ experience

“…The pilot-scale IVCWs employed in this study have been depicted elsewhere [22,23]. Briefly, four parallel IVCWs, each composed of a sequence of a down-flow cell and another identical up-flow one, were constructed with bricks and concrete in a garden near the Donghu Lake, Wuhan, China (coordinates: 30˚33Ń , 114˚23´E; elevation: 27 m).…”

A review on effective design processes of constructed wetlands

“…It was reported that NO 3 -N removal was only 7% in HFCW without carbon addition, but it increased to 70% when the COD/NO 3 -N ratio was maintained at 3.5:1 by the addition of sucrose. Similarly, in FSF CW complete NO 3 -N removal was observed when the COD/NO 3 -N ratio was between 3.5:1and 5:1, but further increase in C/N ratio did not increase the NO 3 -N removal (Chang et al 2013;Fang et al 2018). COD/NO 3 -N ratio below 2 limited the NO 3 -N removal because maximum organic matter removal took place in top layers of CW which reduced the carbon source for de-nitrification in bottom layers (Fang et al 2018) Another important parameter in CW is temperature since it affects the microbial community.…”

“…Low C/N ratio wastewater is generally treated using anaerobic ammonium oxidation and simultaneous nitrification and de-nitrification but involves a huge amount of energy consumption (Li et al 2018). According to Chang et al (2013), carbon is an important parameter in NO 3 -N removal since it acts as an electron donor for the denitrification process. It was reported that NO 3 -N removal was only 7% in HFCW without carbon addition, but it increased to 70% when the COD/NO 3 -N ratio was maintained at 3.5:1 by the addition of sucrose.…”