Nutrient removal in tropical subsurface flow constructed wetlands under batch and continuous flow conditions.
ABSTRACT The aim of this investigation was to evaluate the influence of batch versus continuous flow on the removal efficiencies of chemical oxygen demand (COD), nitrogen (N) and total phosphorus (TP) in tropical subsurface flow constructed wetlands (SSF CW). The quantitative role of the higher aquatic plants in nutrient removal in these two operational modes was also investigated. Results indicated no significant difference (p > 0.05) in COD removal between batch and continuous flow modes for either the planted or unplanted treatments. Furthermore, the batch-loaded planted wetlands showed significantly (p < 0.05) higher ammonium removal efficiencies (95.2%) compared with the continuously fed systems (80.4%), most probably because the drain and fill batch mode presented systematically more oxidized environmental conditions. With respect to TP removal, for both planted and unplanted beds, there was significant enhancement (p < 0.05) in batch flow operation (69.6% for planted beds; 39.1% for unplanted beds) as compared to continuous flow operation (46.8% for planted beds; 25.5% for unplanted beds). In addition, at a 4-day hydraulic retention time (HRT), the presence of plants significantly enhanced both ammonia oxidation and TP removal in both batch and continuous modes of operation as compared to that for unplanted beds. An estimation of the quantitative role of aeration from drain and fill operation at a 4-day HRT, as compared to rhizosphere aeration by the higher aquatic plant, indicated that drain and fill operation might account for only less than half of the higher aquatic plant's quantitative contribution of oxygen (1.55 g O2 per m2 per day for batch flow versus 1.13 g O2 per m2 per day for continuous flow).
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ABSTRACT: In this study, an intermittent-aerated subsurface flow constructed wetland (SFCW) A was set up to assess its performance in decentralized rural sewage treatment. A conventional SFCW B and a subsurface wastewater infiltration system (SWIS C) were also constructed for comparison. Alternate anaerobic and aerobic conditions were well developed by intermittent aeration. High removal of organic pollutants (29.3gm(-2)d(-1)), ammonium nitrogen (3.5gm(-2)d(-1)) and total nitrogen (3.3gm(-2)d(-1)) were obtained simultaneously in SFCW A compared with SFCW B and SWIS C. Fluorescence in situ hybridization analysis proved that the intermittent aeration obviously enhanced the growth of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in SFCW A. These results suggest that intermittent aeration strategy is reliable to enhance the performance of SFCWs in decentralized rural sewage treatment.Bioresource Technology 03/2013; · 5.04 Impact Factor
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ABSTRACT: Constructed wetlands are engineered systems relying on natural microbial, biological, physical and chemical processes to treat wastewater. Treatment performance tends to decrease in colder temperatures, so that ways to enhance the performance in northern climates has been sought. In China, the first constructed wetland was built in China in 1987 and since then, about 450 systems have been constructed throughout the country. At least 67 constructed wetlands are located in northern China and have reported significant seasonal changes of treatment efficiencies. This paper reviews current engineering practices including case studies showing ways to increase winter treatment effectiveness in cold climates. These measures include: (1) internal improvement of system design and setup of the system, (2) optimization of winter operation, and (3) external incorporation of pre- and post-treatment technologies. Various measures to raise the temperatures of these systems in the winter were compared in several constructed wetlands (40 and 50°N). For example, plastic film mulch can be used with thermal insulation; however, the operators of constructed wetlands often use ice to cover the system due to lower cost and maintenance. This review demonstrates that the effectiveness of constructed wetlands in cold climates can be improved through better operation strategies.Wetlands 04/2014; · 1.28 Impact Factor
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ABSTRACT: The treatment efficiencies of floating treatment wetlands (FTWs) containing two types of macrophytes, Typha angustifolia and Canna iridiflora, were investigated in a pilot scale study in the tropical climate of Sri Lanka. In batch experiments, over 80 % of biological oxygen demand (BOD5) and ammonium (NH 4+-N) removal was observed, while nitrate (NO 3−-N) removal was over 40 %. Typha angustifolia showed slightly higher BOD5, NH 4+-N and NO 3−-N removal than Canna iridiflora. Because of higher and steady root growth, Typha angustifolia resulted in a better performance and has a greater potential to extract nutrients from wastewater and allow water-plant interactions than Canna iridiflora whose root mat is thick and compact. Similar to the batch system, the continuous flow systems performed better at most times with Typha angustifolia. FTWs with Typha angustifolia may be considered a possible solution for lake restoration where there are space and cost constraints.Wetlands 01/2012; 32(5). · 1.28 Impact Factor