Controlling Nitrogen Removal Processes in Improved Vertical Flow Constructed Wetland with Hydroponic Materials: Effect of Influent COD/N Ratios

Abstract

Discharge of nitrogen (N) with wastewater causes eutrophication in surface water. On the other hand, nutrient-rich wastewater can be valuable for agriculture. Tailoring N removal or conservation is important to meet the requirements of different water end uses. Improved vertical flow constructed wetlands with hydroponic materials (CWH) as substrata were developed at lab scale in a greenhouse and studied to optimize N removal in CWH. This study investigated the effect of influent COD/N ratios of 5/1 and 15/1 on the removal or conservation of N in CWHs with Syngonium as vegetation and three substrata, pumice, cocopeat, and mineral wool. CWH with pumice showed the highest TN removal at both COD/N ratios. The Syngonium plant significantly contributed to the additional 50% TN removal in CWH. Nitrification of above 90% was observed at both studied COD/N ratios, indicating sufficient oxygenation due to the vertical pulse flow operated CWH. The denitrification process was enhanced at a higher COD/N ratio of 15/1 compared to 5/1 by around 10–40%. The occurring nitrification and denitrification indicate the coexistence of aerobic and anaerobic conditions in CWH, and balancing these conditions is necessary for future applications to remove N for its specific end use, i.e., irrigation water (high standards) or discharge to surface water (low standards).

Sediment Fungal Communities of Constructed Wetlands Dominated by Zizania latifolia and Phragmites communis and Their Effect on Organic Pollutant Removal

“…The removal rates (R%) of all examined pollutants presented in percentage are calculated by R% = 100(C in − C out )/C in (1) where C in denotes the pollutant content at the inlet and C out stands for that at the outlet.…”

“…As an economical and ecological water treatment technology, constructed wetland (CW) has been widely used in organic pollutant removal [1,2]. Effective removal of organic pollutants can be achieved by a number of biotic and abiotic processes in CW including plant uptake [3][4][5], microbial degradation [6][7][8], substrate adsorption, filtration and precipitation [9][10][11].…”

“…The global surface areas of wetlands and wetland plant species are in steep decline. The establishment of constructed wetlands aimed at removing organic pollution can greatly contribute to the enhancement of threatened wetland ecosystems and the associated biodiversity [1,2]. The perennial plants, Zizania latifolia and Phragmites communis, are the species commonly used in CW because of their high growth and reproduction rates and, thus, relatively high water purification abilities [29,30].…”