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: Constructed wetlands (CWs) have been used as a green technology to treat various wastewaters for several decades. CWs offer a land-intensive, low-energy, and less-operational-requirements alternative to conventional treatment systems, especially for small communities and remote locations. However, the sustainable operation and successful application of these systems remains a challenge. Hence, this paper aims to provide and inspire sustainable solutions for the performance and application of CWs by giving a comprehensive review of CWs' application and the recent development on their sustainable design and operation for wastewater treatment. Firstly, a brief summary on the definition, classification and application of current CWs was presented. The design parameters and operational conditions of CWs including plant species, substrate types, water depth, hydraulic load, hydraulic retention time and feeding mode related to the sustainable operation for wastewater treatments were then discussed. Lastly, future research on improving the stability and sustainability of CWs were highlighted. Copyright © 2014 Elsevier Ltd. All rights reserved.Bioresource Technology 10/2014; 175C:594-601. DOI:10.1016/j.biortech.2014.10.068 · 5.04 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 10/2012; 32(5). DOI:10.1007/s13157-012-0333-5 · 1.44 Impact Factor
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ABSTRACT: In this study, six mesocosms, including three subsurface flow constructed wetlands (SSF CWs) and three sand filters (without plants) were set up at the campus of Nanyang Technological University, Singapore. The objective of this study was to compare the removal efficiencies of chemical oxygen demand (COD), nitrogen (N) and total phosphorus (TP) under batch and continuous operational modes. Three factors, namely, with/without the presence of vegetation, operational modes (batch and continuous) and hydraulic residence time were investigated by two statistical models including factorial design and its rationale analysis and a quadratic polynomial regression model with ANOVA, to find the relationships between the contaminant removal efficiencies and the affecting factors, as well as to determine the dominant variables and how each of them interact for each parameter.Wetlands 04/2013; 33(2). DOI:10.1007/s13157-013-0389-x · 1.44 Impact Factor