Effect of photosynthetically elevated pH on performance of surface flow-constructed wetland planted with Phragmites australis

Abstract

Combination of emergent and submerged plants has been proved to be able to enhance pollutant removal efficiency of surface flow-constructed wetland (SFCW) during winter. However, intensive photosynthesis of submerged plants during summer would cause pH increase, which may have adverse effects on emergent plants. In this study, nitrogen transformation of lab-scale SFCW under pH gradient of 7.5, 8.5, 9.5 and 10.5 was systematically investigated. The results showed that total nitrogen (TN) removal efficiency decreased from 76.3 ± 0.04 to 51.8 ± 0.04 % when pH increased from 7.5 to 10.5, which was mainly attributed to plant assimilation decay and inhibition of microbe activities (i.e., nitrite-oxidizing bacteria and denitrifiers). Besides, the highest sediment adsorption in SFCW was observed at pH of 8.5. In general, the combination of submerged and emergent plants is feasible for most of the year, but precaution should be taken to mitigate the negative effect of high alkaline conditions when pH rises to above 8.5 in midsummer.

Integrated Methods for Household Greywater Treatment: Modified Biofiltration and Phytoremediation

“…As a result, it can be concluded that the main removal mechanism of organic nitrogen under anaerobic conditions (denitrification) in the treatment system was the reduction of NO 3 -N to molecular nitrogen (N 2 ) [ 102 ]. On the other hand, Yin et al [ 100 ] stated that, at pH < 8.5, denitrification of gaseous products was the main route of gas loss which was similar to the present study. The reason could also be attributed to the process of converting NH 4 -N to NO 2 -N, followed by the conversion of NO 2 -N to N 2 gas via the denitrification process [ 31 ].…”

“…During the monitoring period, NO 3 -N was found to increase from 4.5 ± 3.3 mg/L in raw GW to 5.3 ± 2.5 mg/L in the efuent of biofltration, but it was found to decrease signifcantly in the efuent of HSSFCW (0.84 ± 0.5) (Figure 9). Tis pattern could be found in many studies on nitrogen transformation [100]. Te increasing trend of NO 3 -N at the biofltration flter outlet indicates that the nitrifying bacteria oxidized NH 4 -N to NO 3 -N [30].…”

Integrated constructed wetlands treating industrial wastewater from seed production

“…Denitrification (in the HSSFCW) also increases the pH (Xiong et al 2011). In both HSSFCW and FCW, intensive photosynthesis by submerged, emerged and floating plants also increases the pH (Yin et al 2016). However, the pH in each treatment system was within the optimum range (6.5-8.5) for biological wastewater treatment processes (Metcalf & Eddy 2004), and the pH of the FCW's final effluent was in the range of 7.2-8, within the TBS pH limit (6.5-8.5) for industrial effluent.…”

Diffuse Water Pollution from Agriculture: A Review of Nature-Based Solutions for Nitrogen Removal and Recovery

“…Comparing different types of CWs, the total activity of microbial communities is largely in the same range, but the growth of heterotrophic bacteria, commonly responsible for denitrification, has usually been higher in VF-SSF CWs than in SF CWs [90]. pH is an influencing factor that can be modulated in order to favor microbial growth [91]. Furthermore, temperature can play a regulatory role in the activation/deactivation of various microbially-mediated processes in CWs.…”