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).
"The increased removal in control units may also be facilitated due to sequential presence of anaerobic and aerobic conditions in Up-flow constructed wetlands where both mechanisms were in contribution for removal of organic matter as denitrifiction and aerobic biodegradation were played major role for excellent COD removal in control unit  . Also an author  gives apparent reason for COD removal due to combine effect of aerobic and anaerobic organic carbon degradation. As it is known that the uptake of organic matter by plants is of less significant  the organic matter removal is not dependent on the presence/ absence of plant species in constructed wetlands. "
[Show abstract][Hide abstract] ABSTRACT: The use of constructed wetlands for wastewater treatment has been exercised since 1950's and still are being in use. The vertical flow constructed wetlands provide more oxygenated environment and significantly reduce the organic matter as well as microbial species from wastewater. In the present study vertical up-flow constructed wetlands were constructed and used as bio-filter to improve the water quality of secondary treated effluent. The reduction pattern is studied in this research and correlated with plant species and presence of plant. The plant species used in the constructed wetlands were canna and phragmitis. The fibrous rooting system of canna species causes the high aerobic conditions throughout the treatment bed which in turn facilitates higher removal in comparison to phragmitis planted wetland. Removal of nitrogenous compounds like ammonia-nitrogen, TKN and nitrate were observed better in canna planted wetlands than others.
"In general, batch feeding mode can obtain the better performance than continuous operation by promoting more oxidized conditions. Zhang et al. (2012) investigated the influence of batch versus continuous flow on the removal efficiencies in tropical SSF CWs. They indicated that the wetlands with batch flow mode showed significantly higher ammonium removal efficiencies (95.2%) compared with the continuously fed systems (80.4%). "
"Wetlands in the tropics, which are exposed to higher temperatures and direct sunlight throughout the year, have higher year-round plant productivity and a concomitant decrease in the time necessary for microbial biodegradation. This in turn results in more efficient treatment of pollutants (Zhang et al., 2012). "
[Show abstract][Hide abstract] ABSTRACT: Inadequate access to clean water and sanitation has become one of the most pervasive problems afflicting people throughout the developing world. Replication of centralized water-, energy- and cost-intensive technologies has proved ineffective in resolving the complex water-related problems resulting from rapid urbanization in the developing countries. Instead constructed wetlands (CWs) have emerged and become a viable option for wastewater treatment, and are currently being recognized as attractive alternatives to conventional wastewater treatment methods. The primary objective of this review is to present a comprehensive overview of the diverse range of practice, applications and researches of CW systems for removing various contaminants from wastewater in developing countries, placing them in the overall context of the need for low-cost and sustainable wastewater treatment systems. Emphasis of this review is placed on the treatment performance of various types of CWs including: (i) free water surface flow CW; (ii) subsurface flow CW; (iii) hybrid systems; and, (iv) floating treatment wetland. The impacts of different wetland design and pertinent operational variables (e.g., hydraulic loading rate, vegetation species, physical configurations, and seasonal variation) on contaminant removal in CW systems are also summarized and highlighted. Finally, the cost and land requirements for CW systems are critically evaluated.
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