Safe surface concept in vertical flow constructed wetland design to mitigate infection hazard (original) (raw)
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Environmental Management, 2002
Constructed wetlands are widely used all over the world for the treatment of municipal wastewaters, which are characterized by high concentrations of pathogens. The objectives of this study were (1) to study the effect of solar radiation and temperature on the ability of a constructed wetland to reduce the concentration of total coliforms (TC), and (2) to evaluate the relationship between the presence of Salmonella spp. in the outflow and the concentration of TC. The results of this study showed that under Mediterranean environmental conditions, the percentage reduction in coliforms was lower during winter compared to all other seasons. Maximum removal of coliforms was achieved under conditions of high solar radiation and temperature. In addition, solar radiation was found to play a greater role in coliform die-off at low temperatures than at high temperatures. Finally, it was found that the probability of Salmonella spp. appearance in the outflow of the wetland was related to the concentration of TC. The increase in coliform bacteria in the effluents also increased the chances of Salmonella appearance. The risk of Salmonella spp. appearance in the outflow is minimized when the concentration of TC is below 10 2 /100 mL.
The removal of sanitary indicator bacteria (total coliforms, faecal coliforms, and faecal streptococci) was studied in an experimental constructed wetland system consisting of (1) a 2-m 3 threechamber sedimentation tank, (2) a 5 m 2 vertical flow constructed wetland, (3) a filter-unit with calcite aimed at removing phosphorus, and (4) a 10 m 2 vertical flow constructed wetland. The indicator bacteria were enumerated before and after each unit of the wetland system during four monitoring episodes with different loading conditions. At a hydraulic loading rate of 520-1,370 mm/d, the first-stage vertical flow beds removed about 1.5 log-units of total coliforms, 1.7 log-units of faecal coliforms and 0.8 log-units of faecal streptococci. In the second stage bed receiving lower loadings both in term of concentration and quantity (260-690 mm/day), the eliminations were lower. It was not possible in the present study to identify any seasonal effects, but no measurements were done during summer. Recycling of treated effluent back to the sedimentation tank did not affect elimination. Area-based rate constants for the vertical flow wetland receiving effluent from the sedimentation tank averaged 3.2 m/d for total coliforms, 3.3 m/d for faecal coliforms and 2.1 m/d for faecal streptococci. The rate constants depended on loading rates. It is suggested that filtration is a major removal mechanism for bacterial indicator organisms in vertical flow constructed wetland systems.
Pan Africa science journal, 2022
Constructed wetlands (CWs) polish wastewater prior to discharge into aquatic receptacles. Size variabilities of substrates used in CWS may have effects on the treatment efficiencies though there is scanty information regarding this aspect in VSSF CWs. To address this knowledge gap, a laboratory scale mesocosm experiment was set up to investigate the potential of a VSSF CW to reduce organic matter and FIB using various gravel substrate aggregate sizes. This consisted of three gravel size treatment units; <12.5, 12.5-18 and 18-24 mm in triplicates. 70 liters of pre-treated wastewater from the final wastewater stabilization pond (WSP) of Egerton University's WSPs system was added to the units, allowed to settle for 6 weeks for development of biofilms, followed by periodic feeding of equal wastewater quantity on weekly basis and influent and effluent samples collected for 8 weeks for analysis. Results disclosed reduction efficiency of 95.2, 94.3 and 88.4 % for E coli in the fine, medium and coarse gravel aggregates respectively. Less than 20 % reduction efficiency was recorded for BOD5 in all gravel aggregate sizes. There was no significant variation on performance of the three gravel aggregate sizes in reduction of both FIB and BOD5 (p˃0.05). Poor performance in BOD5 reduction was related to absence of wetland macrophytes in the study. The relatively high reduction efficiency for FIB was attributed to other factors and processes such as predation, mechanical interactions, starvation, microbial interactions and natural die-offs. The study recommends assessing the combined effect of increasing the retention time, use of wetland macrophytes and incorporating various gravel aggregate sizes in order to increase the efficiency of VSSF CW in reduction of FIB and organic matter.
Removal of Pathogenic Bacteria in a Horizontally Fed Subsurface Constructed Wetland Hybrid System
J
The management of effluents and their treatment is a fundamental issue in water management, the removal of different types of contaminants is another relevant issue for public health and the environment. Bacteria are one of the main types of contaminants in untreated water discharged to receiving bodies. The objective of this research was to evaluate the removal efficiency of pathogenic bacteria in a horizontal feeding subsurface artificial wetland that treats wastewater originated from the Boca de Río Technological Institute, Veracruz, Mexico. A hybrid system composed of seven cells with three types of substrates and ornamental type vegetation was designed; the indicators evaluated were the concentration of total and fecal coliforms and the efficiency of bacterial removal in the stages of the system. The artificial wetland system demonstrated a significant reduction (p < 0.05) between the different cells of the system. The values of pathogenic bacteria removal obtained in the we...
Studies on the processes of bacteria elimination in constructed wetlands
2006
that simulates natural wetlands for human use and benefits" (Hammer, 1989). Constructed wetland systems are designed to maximize the physical, chemical and biological abilities of natural wetlands to reduce the pollutants and microbial pathogens in wastewater. There are basically two types of constructed wetland design: the free water phase and the subsurface flow constructed wetlands. The free water surface wetland typically consists of a basin or channels with a barrier to prevent leakage, soil to support the roots of the emergent vegetation, and water at a relatively shallow depth flowing through the systems. The water surface is exposed to the atmosphere, and the intended flow path through the system is horizontal. Subsurface flow wetlands are comprised of beds filled with porous media and planted with emergent vegetation such as cattails (Typha spp.), bulrush (Scirpus Cryptosporidium spp. (Thurston et al. 2001) and Campylobacter (Hagendorf et al., 2000) were also investigated. However, traditional indicators (E. coli, coliforms and fecal enterococci) may sometimes have shorter life times than pathogens: Stenström & Carlander (2001) reported a survival time of 252-396 days for Clostridum perfringens in the sediment of a free water surface constructed wetland, whereas E. coli and fecal enterococci only survived 27-53 days under the same conditions; Karapinar and Gönül (1991) reported that, when incubated in sterile spring water, Y. enterocolitica grew in the first three weeks and survived 64 weeks, whereas after 1 week of incubation the number of E. coli in water started to decrease and after 13 weeks no E. coli was detected. enteropathogenic E. coli (Pommepuy et al., 1996), Helicobacter pylori (Adams et al., 2003), and E. faecalis (Signoretto et al., 2000). Pathogenic bacteria that converted to VBNC forms may still be virulent. This phenomenon has been observed for
Water Research, 2001
}The aims of this project were to assess bacterial populations (abundance, biomass and viability) in the influents and effluents of four constructed wetlands, and to analyse the effect of such biological treatment on these bacterial characteristics. Using the BacLight probe it was possible to determine the total abundance, the proportion of intact vs. damaged cells, and the lengths, widths and biovolumes, of bacteria in each of the samples. The reduction in bacterial concentration was higher (67%) in the wetland used for secondary treatment than in those used for tertiary treatment (15-39%). The proportion of damaged cells was higher in the influent (i.e. settled sewage) of the wetland used for secondary treatment (78%) than in the influents of those wetlands used for tertiary treatment (45-70%). This suggested that the majority of bacteria in the settled sewage were dead or damaged, and that these were removed from the wastewaters more effectively than were undamaged cells during conventional secondary treatment (in this case, using rotating biological contactors or RBCs). In each wetland, the proportion of damaged cells was higher in the influent than in the effluent, suggesting that, as with RBCs, damaged bacteria were removed more effectively within the wetland than undamaged bacteria. The majority of bacteria leaving the constructed wetlands used for tertiary treatment, and 50% of those leaving the secondary treatment wetland, were physically intact and therefore probably viable. Although there was a decrease in the abundance of total bacteria with treatment, bacterial biomass did not necessarily decrease with the treatment.
Journal of Water and Health
The objective of this study was to evaluate the removal of fecal indicator bacteria and select bacterial pathogens (total coliforms, Escherichia coli, Shigella spp., Salmonella spp. and Pseudomonas aeruginosa) in vertical flow constructed wetlands (VF-CWs) with earthworms and solar disinfection (SODIS) as post-treatment of effluent from a septic tank. There was no significant difference between them in removing bacteria using a VF-CW with earthworms (VF-CW W/E) and without earthworms (VF-CW N/E). Both VF-CWs did not completely remove pathogens; however, with the SODIS technology receiving the effluent from VF-CW W/E, for E. coli, Shigella spp., Salmonella spp. and P. aeruginosa, the values were reduced below the limit of detection and 4.3 log unit average reduction for total coliforms, with 6 h in SODIS.
Effect of entrance shape on the performance of constructed wetland
Journal of American Science, 2010
In order to investigate the effect of entrance shape on the performance of free water surface (FWS) and subsurface flow (SSF) constructed wetlands treating wastewater, four pilot-scale units were constructed and operated continuously in parallel experiments. For this study the treatment scheme consisting of filtration unit followed by constructed wetland unit (FWS or SSF). Two different shapes of entrance were examined (rectangle and triangle). The results indicated that the triangle shape entrance enhances the performance of constructed wetland in the term of COD, BOD, TSS, bacteriological indicators such as fecal coliform (FC), fecal streptococci (FS), Pseudomonas aeruginosa (PS) and Salmonellae (Sal.). The performance of FWS with triangle entrance for removal of COD, BOD and TSS was more than 73, 83 and 81%, respectively. FC, FS and PS were removed by 10 4 , 10 3 and 10 2 MPN/100 ml, respectively. While Salmonellae was removed completely. [Journal of American Science 2010; 6(9):787-795]. (ISSN: 1545-1003).
2021
Bacteria are frequently studied in constructed wetlands (CWs) due to their effective involvement in pollutants purification processes. In this study, aerobic, anaerobic and total bacteria densities and their vertical distribution profile within pilot-scale vertical flow CWs planted with different plant species were investigated. Five beds were planted in monoculture with Andropogon gayanus, Chrysopogon zizanioides, Echinochloa pyramidalis, Pennisetum purpureum and Tripsacum laxum, and one unplanted bed was used as control. At the end of the treatment trial, bacteria were collected by taking cores of sediment samples at the corners and the center of each bed following six layers in the vertical profile. In fact, the presence of plants on CWs improved the bacterial density and removal efficiencies in the system, with yields from 5.9 to 24.1% regardless the pollutant. However, few anaerobic bacteria were obtained in the different wetlands, and unable to reduce NO3−, excluding for beds ...
Desalination, 2009
The removal of faecal coliforms (FC), Escherichia coli, somatic coliphages and F-specific bacteriophages was monitored over a period of 2 years in two vertical flow constructed wetlands (VFCWs) and four intermittent sand filters (ISFs) that treat pond effluent. Tracer tests (NaCl) were performed to estimate the hydraulic retention time (HRT) of the filters. The contribution of Phragmites australis to the removal of the faecal indicators was examined. The effect of media characteristics (depth, type of sand), hydraulic load and water application schedule on disinfection was also addressed. Planted and non-planted vertical sand filters were equally effective in removing microorganisms. The disinfection capacity was very sensitive to the depth and operation of the filters. HRT was the key parameter regarding filter disinfection capacity. Bacterial indicators were removed at a higher rate than viral ones. Somatic coliphages were removed at higher rates than F-specific bacteriophages.