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Three new baffle flow constructed wetlands (CWs), namely the baffle horizontal flow CW (Z1), baffle vertical flow CW (Z2) and baffle hybrid flow CW (Z3), along with one traditional horizontal subsurface flow CW (Z4) were designed to test the removal efficiency of nitrogen (N) and phosphorus (P) from the septic tank effluent under varying hydraulic retention times (HRTs). Results showed that the optimal HRT was two days for maximal removal of N and P from the septic tank effluent among the four CWs. At this HRT, the Z1, Z2, Z3 and Z4 CWs removed, respectively, 49.93, 58.50, 46.01 and 44.44% of TN as well as 87.82, 93.23, 95.97 and 91.30% of TP. Our study further revealed that the Z3 CW was the best design for overall removal of N and P from the septic tank effluent due to its hybrid flow directions with better oxygen supply inside the CW system. [ABSTRACT FROM AUTHOR]

Vertical flow constructed wetland (VFCW) is a promising technique for removal of excess nutrients and certain pollutants from wastewaters. The aim of this study was to develop a STELLA (structural thinking, experiential learning laboratory with animation) model for estimating phosphorus (P) removal in an artificial VFCW (i.e., a substrate column with six zones) grown with umbrella papyrus ( Cyperus alternifolius ) species under a wetting-to-drying cycle. Simulations showed that rate of soluble P (SP) leaching was highest at the top zone (i.e., Zone 1) and decreased gradually with increasing zone number due to the adsorption, clogging, and plant uptake when the SP flowed through the zones. Our simulations further revealed that the best time for an optimal removal of SP from the wastewater was within the first week because the adsorption capacity of the substrate in the VFCW was highest at this time period. In general, the cumulative amounts of total P (TP) were in the following order: adsorption (53.3%) > leaching (13.5%) > uptake (0.49%). Adsorption of P was a major mechanism for P removal from the VFCW system. This study suggested that the STELLA model developed is a useful tool for estimating P removal from wastewater in VFCWs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Baffled subsurface-flow constructed wetland (CW) is a new type CW. [•] Very significant correlation exists between the activity of urease and the rate of N removal in this CW. [•] Activity of urease in the CW is an important indicator for N removal from wastewaters. [Copyright &y& Elsevier]

Mangroves play an important role for removing nutrients, heavy metals, and other pollutants in wetland ecosystems. This study investigated the physiological responses of a mangrove plant (i.e., Sonneratia apetala Buch-Ham) to different wastewater pollution levels. Four different treatments, namely three concentration levels (i.e., normal, five-time-greater than normal, and ten-time-greater than normal) of wastewaters and one control (i.e., salted water), were used to grow the mangrove plants. Results showed that the height and biomass of the plant increased with wastewater pollution levels. No significant differences in root and catalase activities were observed among different treatments, whereas the increases in peroxidase and superoxide dismutase activities were attributed to the need for detoxification. In general, leaf chlorophyll content increased with wastewater pollution levels due to the increase in nutrient contents. [ABSTRACT FROM AUTHOR]

Abstract: Constructed wetlands are becoming increasingly popular worldwide for removing contaminants from domestic wastewater. This study investigated the removal efficiency of nitrogen (N) and phosphorus (P) from wastewater with the simulated vertical-flow constructed wetlands (VFCWs) under three different substrates (i.e., BFAS or blast furnace artificial slag, CBAS or coal burn artificial slag, and MSAS or midsized sand artificial slag), hydraulic loading rates (i.e., 7, 14, and 21cmd−1), and wetland operational periods (0.5, 1, and 2 years) as well as with and without planting Canna indica L. The wastewater was collected from the campus of South China Agricultural University, Guangzhou, China. Results show that the percent removal of total P (TP) and ammonium N (NH4 +-N) by the substrates was BFAS>CBAS>MSAS due to the high contents of Ca and Al in substrate BFAS. In contrast, the percent removal of total N (TN) by the substrates was CBAS>MSAS>BFAS due to the complicated nitrification/denitrification processes. The percent removal of nutrients by all of the substrates was TP>NH4 +-N>TN. About 10% more TN was removed from the wastewater after planting Canna indica L. A lower hydraulic loading rate or longer hydraulic retention time (HRT) resulted in a higher removal of TP, NH4 +-N, and TN because of more contacts and interactions among nutrients, substrates, and roots under the longer HRT. Removal of NO3 −N from the simulated VFCWs is a complex process. A high concentration of NO3 −N in the effluent was observed under the high hydraulic loading rate because more NH4 +-N and oxygen were available for nitrification and a shorter HRT was unfavorable for denitrification. In general, a longer operational period had a highest removal rate for nutrients in the VFCWs. [Copyright &y& Elsevier]

Abstract: The vertical-flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewaters. This study investigated the uptake and removal of total nitrogen (TN) by Cyperus alternifolius from domestic wastewaters in simulated VFCWs. A total of eight simulated VFCW treatments, including two different substrates, two different wet-to-dry ratios, and with and without C. alternifolius species (2×2×2=8), were employed for an operation period of 2 years in this study. Results show that more TN was removed from the influent with the presence of C. alternifolius compared to without this plant species. A linear correlation existed between the aboveground biomass and its TN content. An increase in total biomass by 100g resulted in an increase in TN accumulation in the aboveground biomass by 2.4g. Large amounts of TN were removed by the aboveground biomass compared to those by substrate adsorption. Results suggest that C. alternifolius played a discernable role in removal of TN from wastewaters in the simulated VFCWs. [Copyright &y& Elsevier]