title: Effect of variations in the nitrogen loading rate and seasonality on the operation of a free water surface constructed wetland for treatment of swine wastewater.
abstract: The aim of this study was to evaluate the effects of variations in the nitrogen loading rate (NLR) and seasonality on the operational efficiency of a free-water surface constructed wetland (FWS) and on the processes involved in total nitrogen (TN) removal in treating swine wastewater. The system, which operated for 550 days, consisted of a FWS mesocosm inoculated with Typha angustifolia L., using swine wastewater from a storage lagoon as an influent. After operating with nitrogen loading rates (NLRs) of 2.0 to 30.2 kg TN ha(-1)·d(-1), the FWS reduced total nitrogen (TN) concentration by between 21.6 and 51.0%, achieving maximum removal (48.2 ± 3.0%) when the system operated at a NLR below 15.0 kg TN ha(-1)·d(-1). Moreover, operations over 25.0 kg TN ha(-1)·d(-1) resulted in a 50.6% decrease in the maximum FWS efficiency, which may have been related to increased anoxic conditions (< 0.5 mg O2 L(-1); -169.8 ± 70.3 mV) resulting from the high concentration of organic matter in the system (12.3 ± 10.5 g TCOD L(-1)), which hindered nitrification. Ammonia volatilization is considered the main method to remove TN, with an average value of 14.4 ± 6.5% (3.1-26.2%). Maximum volatilization occurred during the summer (21.5 ± 2.4°C) at an NLR higher than 25 kg TN ha(-1)·d(-1) (26.6%), favored by higher temperatures (17.3-19.7°C), and high NH4(+)-N (>600.0 9 mg NH4(+)-N L(-1)) and pH levels (7.1-7.9). Uptake by plants accounted for 14.9% of the TN removed, with the vegetative peak in summer (height: 105.3 cm; diameter: 2.1 cm) at an NLR of 25.3 ± 0.3 kg TN ha(-1)·d(-1). However, growth decreased to 94.4% at an NLR of over 25.3 ± 0.3 kg TN ha(-1)·d(-1) (>379.9 mg NH4(+)-N L(-1)) in autumn (17.4 ± 2.4°C). This was associated with the period of plant senescence and the effects of ammonium phytotoxicity (379.9-624.2 mg NH4(+)-N L(-1)) and continued to the end of the study with the complete loss of macrophyte species. Finally, 1.5% of the TN removed was incorporated into the sediments where NH4(+)-N is the main form of nitrogen, with an accumulative value of 2.6 g m(-2).
authors.affiliation: a Engineering and Environmental Biotechnology Group , Faculty of Environmental Science & EULA - Chile Center , University of Concepción , Concepción , Chile.
authors.forename: Catalina
authors.initials: C
authors.lastname: Plaza de Los Reyes
authors.affiliation: a Engineering and Environmental Biotechnology Group , Faculty of Environmental Science & EULA - Chile Center , University of Concepción , Concepción , Chile.
authors.forename: Gladys
authors.initials: G
authors.lastname: Vidal
mesh_terms: D000641:Ammonia / Q000737:chemistry; D000818:Animals; D019015:Geologic Sediments / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D012621:Seasons; D013552:Swine; D032401:Typhaceae / Q000378:metabolism; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification; D053833:Wetlands
chemical_list: D000641:Ammonia; D009584:Nitrogen; D062065:Wastewater; D014867:Water; D014874:Water Pollutants, Chemical
keywords: Free water surface constructed wetlands; Typha angustifolia L; nitrogen removal; swine wastewater