Effects of Plant Material as Carbon Sources on TN Removal Efficiency and N2O Flux in Vertical-Flow-Constructed Wetlands

Abstract

A nitrate-dominant synthetic wastewater simulating slightly polluted water with low C/N and poor biochemical availability was treated in lab-scale vertical-flow (VF)-constructed wetlands, which had Phragmites australis planted with different types of external carbon sources: Platanus acerifolia leaf litters, P. australis litters, glucose and a blank test with no external carbon sources. A comparison of the TN removal and N 2 O flux performances among the four wetland reactors indicated higher TN removal efficiencies and N 2 O release fluxes in the VF wetland columns with external carbon sources, as measured by the percentage removal of TN (P. acerifolia leaf litters 82.49 %, P. australis litters 70.55 %, glucose 62.50 % and blank 46.45 %) and N 2 O flux (P. acerifolia leaf litters 2275.22 μg·m −2 ·h −1 , P. australis litters 1920.53 μg·m −2 ·h −1 , glucose 1598.57 μg·m −2 ·h −1 and blank 1192.08 μg·m −2 ·h −1 ). This was primarily because of an improved supply of organic carbon from the external carbon sources for heterotrophic denitrification. And, the nitrogen released from the decomposition of plant materials resulted in the N 2 O release fluxes to some extent. However, employing P. acerifolia leaf litters and P. australis litters as external carbon sources caused net increases in organics of the final effluent water. Overall, the results not only demonstrated the potential of using external plant carbon sources in VF wetlands to enhance the TN removal efficiency but also showed a risk of excessive organic release and greater N 2 O flux feedback to global warming. Hence, future studies are needed to optimise the quantity and method for adding external carbon sources to VF-constructed wetlands so that sufficient nitrate removal efficiency is achieved and the N 2 O flux and organic pollution are minimised.

Type of constructed wetlands influence nutrient removal and nitrous oxide emissions from greenhouse wastewater

“…Although the O 2 concentration and COD:N ratio influence N 2 O emissions, the high concentration of NO 2 is the most important operational parameter leading to N 2 O emissions in wastewater treatment (Kampschreur et al, 2009;Kelso et al, 1997Kelso et al, , 1999Saeed and Sun, 2012;Zhang et al, 2014). Indeed, we observed a positive correlation (r 2 = 0.870; P < 0.001) between cumulative N 2 O flux and NO 2 exposure in our CWs (Figure 3).…”

“…Indeed, we observed a positive correlation (r 2 = 0.870; P < 0.001) between cumulative N 2 O flux and NO 2 exposure in our CWs (Figure 3). Similarly, a strong positive relationship between N 2 O flux and NO 2 exposure (r 2 = 0.945) was observed for VSS treating synthetic wastewater with different types of external C sources (Zhang et al, 2014). Under limited O 2 concentration, it was also reported that a NO 2 concentration higher than 50 mg N L -1 results in increased N 2 O production (Castro- Barros et al, 2016), which is in line with our FWS results where the outlet concentration of NO 2 was ~57 mg N L -1 .…”

“…Nitrite can also accumulate under conditions that prevent complete NO 3 reduction, as observed in Table 1. Such situations were reported in wastewater with high availability of organic C or incomplete anaerobic conditions where NO 3 is preferred to NO 2 as the electron acceptor (Alleman, 1985;Kelso et al, 1999;Zhang et al, 2014). Although denitrification is a dominant process in NO 3 -rich environments with low C supplies, dissimilatory nitrate reduction to ammonium (DNRA) is a dominant process under high-C and NO 3 -rich conditions (Reddy and DeLaune, 2008).…”

Colmatação e desempenho de sistemas alagados construídos de escoamento horizontal subsuperficial ao longo de oito anos de operação

“…Diante dessas condições, o tempo de detenção hidráulica (TDH) é reduzido, podendo levar ao decréscimo na eficiência dos sistemas (ROUSSEAU; VANROLLEGHEM. ; DE PAUW, 2004;ZHANG et al, 2014).…”

Macrofauna in a Full-scale Vertical Flow Constructed Wetland during Vegetative Growth Stage

“…The efficiency of N removal in constructed wetlands was improved via stimulated nitrification potentials by introduced earthworms 5) . Zhang et al (2014) 6) demonstrated that litter from Phragmites australis that served as an external carbon sources enhanced the total N removal efficiency, by improving the supply of organic carbon for heterotrophic denitrification. Decomposition of P. australis litter depends on faunal involvement 7) .…”