Impact of plant density and microbial composition on water quality from a free water surface constructed wetland

AIMS: To correlate microbial community composition and water quality changes within wetland cells containing varying plant densities and composition in a free water surface (FWS) constructed wetland. METHODS AND RESULTS: Water chemistry was monitored weekly for nitrate, orthophosphate, and suspended solids, at various sites throughout the wetland for 6 months. Treatment ponds with 50% plant cover had about a 96.3% nitrate removal. The average change between the influent and effluent was 50-60% nitrate removal and 40-50% orthophosphate removal. Community profile of total DNA, generated by using denaturing gradient gel electrophoresis (DGGE), was used to determine the major microbial composition associated with the wetland sediment, rhizosphere, and surface water. Bacterial cloned libraries were constructed, and 300 clones were analysed by amplified ribosomal DNA restriction analysis (ARDRA) and grouped into operational taxonomic units (OTUs). A total of 35, 31, and 36 different OTU were obtained from sediment, rhizosphere, and surface water, respectively. The bacterial members within the dominant group of our clone library belonged to unclassified taxa, while the second predominant group consisted of members of the phylum Proteobacteria. The dominant organisms within the class were in the gamma, beta, and delta classes. CONCLUSION: Microbial diversity as determined by Shannon-Weaver index (H) was higher in the wetland cells with 50% plant density than the 100%. This was in agreement with the most efficient wetland contaminant removal units. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides evidence that wetlands with 50% plant cover may promote the growth of diverse microbial communities that facilitate decomposition of chemical pollutants in surface water, and improve water quality.     

Nitrogen removal efficiencies in a free water surface constructed wetland in relation to plant coverage

Vegetation coverage is considered to be a key factor controlling nitrogen removal in wetlands. We describe the use of newly designed stainless steel incubation chambers to detect shifts in the in situ nitrate reduction activities associated to areas covered with common reed (Phragmites australis) and cattail (Typha latifolia) in the sediment of a free water surface constructed wetland (FWS-CW). Activities were measured at six different positions and times of the year and were related to physicochemical and hydraulic variables. Mean nitrate + nitrite reduction activities varied from 11.1 to 69.4 mg N/m²/h and showed a high variability within sediment types. Ammonification rates accounted for roughly 10% of the total nitrate reduction and were especially relevant in vegetated areas. Measured activities were highly above total nitrogen removal efficiencies estimated in the three parallel treatment cells of the Empuriabrava FWS-CW, indicating the potentiality of the system. In situ nitrate reduction activities correlated well with physichochemical characteristics such as pH and temperature. Additionally, differences in the total nitrogen removal efficiencies were detected between the three treatment cells and were related to changes in the water retention time. The plant species effect was detected in treatment cells of comparable hydraulic loads in which vegetation belts dominated by Typha latifolia were shown to have greater nitrogen removal efficiencies.     

垂直流人工湿地的设计及净化功能初探

阐述了垂直流人工湿地小试系统的设计,并测试其冬季污水净化效果,垂直流人工湿地由下地流和上行流方式的两池组成,对受污染地面水体中的CODCr,BOD5和TSS的去除率分别为53．6％,78．7％和80．2％,对细菌,总大肠菌,粪大肠菌和藻类的平均去除率分别达99．4％,85．9％,89．7％和97．7％,。对KN,HN4^ -N和TP的平均去除率分别为39．2％,16．5％和25．8％,各系统对污染物的去除作用无明显差异。系统出水NO3^-N浓度高于进水,而有植物系统中又高于无植物的对照,表明湿地植物的存在有利于硝化,表明下行流－上行流人工湿地在冬季仍能较好地改善水质,是一种有效的水处理技术,对水体水质改善和水生态系恢复具有重要意义。     

Side-by-side comparison of horizontal subsurface flow and free water surface flow constructed wetlands and artificial neural network (ANN) modelling approach

A horizontal subsurface flow (HSSF) and a free water surface flow (FWSF) constructed wetlands (4 m² of each) were set up on the campus of Harran University, Sanliurfa, Turkey. The main objective of the research was to compare the performance of two systems to decide the better one for future planning of wastewater treatment system on the campus. Both of the wetland systems were planted with Phragmites australis and Canna indica. During the observation period (10 months), environmental conditions such as pH, temperature and total chemical oxygen demand (COD), soluble COD, total biochemical oxygen demand (BOD), soluble BOD, total suspended solids (TSS), total phosphate (TP), total nitrogen (TN) removal efficiencies of the systems were determined. According to the results, average yearly removal efficiencies for the HSSF and the FWSF, respectively, were as follows: total COD (75.7% and 69.9%), soluble COD (85.4% and 84.3%), total BOD (79.6% and 87.6%), soluble BOD (87.7% and 95.3%), TN (33.2% and 39.4%), and TP (31.5% and 6.5%). Soluble COD and BOD removal efficiencies of both systems increased gradually since the start-up. After nine months of operation, above 90% removal of organic matters were observed. The treatment performances of the HSSF were better than that of the FWSF with regard to the removal of suspended solids and total COD at especially high temperatures. In FWSF systems, COD concentrations extremely exceeded the discharge limit values due to high concentrations of algae in spring months.The performance of the two systems was modelled using an artificial neural network-back-propagation algorithm. The ANN model was competent at providing reasonable match between the measured and the predicted concentrations of total COD (R = 0.90 for HSSF and R = 0.96 for FWSF), soluble COD (R = 0.90 for HSSF and R = 0.74 for FWSF) and total BOD (R = 0.94 for HSSF and R = 0.84 for FWSF) in the effluents of constructed wetlands.     

Nitrous oxide emissions from surface flow and subsurface flow constructed wetland microcosms: Effect of feeding strategies

The effects of continuous and intermittent feeding strategies on nitrogen removal and N₂O emission from surface flow and subsurface flow constructed wetlands were evaluated in this study. Microcosm wetlands planted with Phragmites australis were constructed and operated with different feeding strategies for the 4-month experiment. Results showed the intermittent feeding strategy could enhance the removal of ammonium effectively in the subsurface flow constructed wetlands, although it had no significant effect for the surface flow wetlands. And the intermittent feeding mode could promote the emission of N₂O. The amount of N₂O-N emission from the subsurface flow constructed wetlands with intermittent feeding mode was about 5 times higher than that with continuous feeding strategy and the emission rate ranged from 0.09 ± 0.03 to 7.33 ± 1.49 mg/m²/h. Compared with the surface flow constructed wetlands, the N₂O emission in the subsurface flow constructed wetlands was affected significantly by the intermittent feeding mode.     

Comparison of the performance of horizontal and vertical flow constructed wetland planted with Rhynchospora corymbosa

Treatment performance of horizontal flow (HF) and vertical flow (VF) constructed wetland planted with Rhynchospora corymbosa were compared. The average porosity of the CW beds were 0.55, hydraulic retention time (HRT) of 3?days, hydraulic loading rate (HLR) and Organic Loading rate were 0.058?m/day and 3.96 (g·BOD/m²·day), respectively with a volumetric flow rate of 0.14 m³/day. The pollutant concentration of graywater before and after its introduction to the CWs was measured using standard sampling and analyses methods. The mean removal efficiencies (RE) for HF and VF CWs were BOD, 35% and 35.4%; COD, 61.9% and 56.7%; TN, 87% and 92%; TP, 95% and 65%; TSS, 86% and 59.6%; pH, 8.8% and 12.8%, respectively. The graywater was highly contaminated in terms of nutrient and organic load. The mean values of the parameters tested for different CWs were significantly different (P?≤?0.05). This comparative study favored HF over VF Constructed wetland with HF found to be a viable alternative for graywater treatment for organics, nutrients and suspended solids removal. The result provided insight into the performance of CWs planted with R. corymbosa.     

Design and performance of a pilot-scale constructed wetland treatment system for natural gas storage produced water

To test the hypothesis that water produced from natural gas storage wells could be treated effectively by constructed wetland treatment systems, a modular pilot-scale system was designed, built, and used for treating gas storage produced waters. Four simulated waters representing the range of contaminant concentrations typical of actual produced waters were treated, and the system's performance was monitored. Freshwater wetland cells planted with Schoenoplectus californicus and Typha latifolia were used to treat fresh and brackish waters. Saline and hypersaline waters were treated by saltwater wetland cells planted with Spartina alterniflora and by reverse osmosis. Effective removal of cadmium, copper, lead, and zinc was achieved by the pilot-scale system. Results suggest that use of specifically designed constructed wetland treatment systems provides a flexible and effective approach for treating gas storage produced waters over a wide range of compositions.     

Adaptation of wastewater surface flow wetland formulae for application in constructed stormwater wetlands

Over the past 30 years, the use of constructed wetlands for wastewater treatment has been a topic of significant research culminating in a good data base from which simplistic equations have been derived to aid in the design of these facilities to meet long term water quality treatment performance criteria. Over the past decade, the use of treatment wetlands has extended to stormwater and combined sewer overflow (CSO) management applications. Designing constructed wetlands for stormwater and CSO applications have unique challenges stemming from the highly stochastic nature of the hydraulic and pollutant loading on a stormwater wetland compared with wastewater treatment systems. This paper explores the possibility of adapting the simplistic models for wastewater wetlands for interim use in developing design guidelines for stormwater wetland systems. A procedure that takes into account the unsteady intermittent nature of stormwater inflows to these wetlands has been incorporated into one of these simplistic models and a case study presented to demonstrate the application of the procedure.     

Evaluation of a lab-scale tidal flow constructed wetland performance: Oxygen transfer capacity, organic matter and ammonium removal

Oxygen transfer capacity and removal of ammonium and organic matter were investigated in this study to evaluate the performance of a lab-scale tidal flow constructed wetland. Average oxygen supply under tidal operation (350 g m⁻² d⁻¹) was much higher than in conventional constructed wetlands (<100 g m⁻² d⁻¹), resulting in enhanced removal of BOD₅ and NH₄⁺. Theoretical oxygen demand from BOD₅ removal and nitrification was approximately matched by the measured oxygen supply, which indicated aerobic consumption of BOD₅ and NH₄⁺ under tidal operation. When BOD₅ removal increased from 148 g m⁻² d⁻¹ to 294 g m⁻² d⁻¹, neither exhausted oxygen from the aggregate matrix during feeding period (111 g m⁻² d⁻¹) nor effluent dissolved oxygen (DO) concentration (2.8 mg/L) changed significantly, demonstrating that the oxygen transfer potential of the treatment system had not been exceeded. However, even though DO had not been exhausted, inhibition of nitrification was observed under high BOD loading. The loss of nitrification was attributed to excessive heterotrophic biofilm growth believed to induce oxygen transfer limitations or oxygen competition in thickened biofilms.     

COD,nutrient removal and disinfection efficiency of a combined subsurface and surface flow constructed wetland: A case study

A constructed wetland system composed of a subsurface flow wetland, a surface flow wetland and a facultative pond was studied from July 2008 until May 2012. It was created to treat the domestic sewage produced by a hamlet of 150 inhabitants. Monthly physicochemical and microbiological analyses were carried out in order to evaluate the removal efficiency of each stage of the process and of the total treatment system. Pair-wise Student's t-tests showed that the mean removal of each considered parameter was significantly different (α = 0.05) between the various treatment phases. Two-way ANOVA and Tukey's HSD tests were used to find significant differences between wetland types and seasons in the removal efficiency of the considered water quality parameters. Significant differences in percent removal efficiency between the treatment phases were observed for total phosphorus, total nitrogen, ammonia nitrogen and organic load (expressed as Chemical Oxygen Demand). In general, the wastewater treatment was carried by the sub-superficial flow phase mainly, both in growing season and in quiescence season. Escherichia coli removal ranged from 98% in quiescence season to >99% in growing season (approximately 2–3 orders of magnitude). The inactivation of fecal bacteria was not influenced by the season, but only by the treatment phase.     

Diversity and distribution of bacteria in a multistage surface flow constructed wetland to treat swine wastewater in sediments

Applied Microbiology and Biotechnology - Managing waste produced from swine farming operations is a significant agricultural and environmental challenge. Confined animal feeding operations...     

Characterization of rhizosphere prokaryotic diversity in a horizontal subsurface flow constructed wetland using a PCR cloning-sequencing based approach

Performance of biological wastewater treatment systems may be related to the composition and activity of microbial populations they contain. However, little information is known regarding microbial community inhabiting these ecosystems. The purpose of this study was to investigate archaeal and bacterial diversity, using cultivation-independent molecular techniques, in a constructed wetland receiving domestic wastewater. Two 16S rRNA gene libraries were constructed using total genomic DNA and amplified by PCR using primers specific for archaeal and bacterial domains. A high microbial diversity was detected. The Proteobacteria phylum is the most abundant and diversified phylogenetic group representing 31.3 % of the OTUs, followed by the Bacteroidetes (14.8 %), Planctomycetales (13.8 %), Actinobacteria (12 %), and Chloroflexi (8.2 %). Sequences affiliated with minor phylogenetic divisions such as the TM7, Nitrospira, OP10, and BRC1 are represented by <6 % of total OTUs. The Archaea domain was represented by the Thaumarchaeota phylum dominated by the Candidatus Nitrososphaera genus.     

Characterization of enterococci populations collected from a subsurface flow constructed wetland

Aims: The aim of this study was to identify and characterize the population of Enterococcus sp. in domestic wastewater as it flows through a constructed wetland. Methods and Results: Four hundred and eighty‐four Enterococcus isolates were collected from the inlet, various sites within and from the outlet of a plastic lined constructed wetland in College Station, TX. The wetland treated septic tank effluent that passed sequentially through two 1·89 m³ septic tanks and a 1·89 m³ pump tank allowing 48 l doses at a 24 l min^?1 rate. The Enterococcus isolates were identified to species using the commercial Biolog system. The 484 Enterococcus isolates were comprised of ten different species, including Enterococcus faecalis (30·6%), Enterococcus pseudoavium (24·0%), Enterococcus casseliflavus (12·8%), Enterococcus faecium (11·2%), Enterococcus mundtii (7·9%), Enterococcus gallinarum (6·2%), Enterococcus dispar (3·7%), Enterococcus hirae (2·1%), Enterococcus durans and Enterococcus flavescens both 0·8%. Of the 88 isolates collected from the inlet, only 9·1% of the isolates were identified as Ent. faecalis and Ent. pseudoavium (36·4%) was identified as the predominant species. Whereas of the 74 isolates collected from the outlet, the predominant species were identified as Ent. faecalis (29·7%). Species identification varied among sites within the wetland, but often Ent. faecalis was the predominant species. Conclusions: Our data suggest that while Ent. faecalis is the predominant species of Enterococcus found in domestic wastewater, the populations may shift during treatment as the wastewater flows through the constructed wetland. Significance and Impact of the Study: We found that shifts in Enterococcus species composition occurred during domestic wastewater treatment. This has implications for the identification of faecal pollution based on the presence of specific bacterial types associated with domestic wastewater.     

Design and management of free water surface constructed wetlands to minimize mosquito production

Constructed wetland technology has broad applications for the treatment of many types of wastewaters and provides an ecological approach to mitigate the release of nutrients and toxic materials into the environment. However, design features, maintenance activities and the characteristics of the wastewater undergoing treatment contribute differentially to potential levels of mosquito production and, consequently, to threats to human and animal health from mosquito-borne pathogens. Of the variables typically considered when designing free-water surface constructed wetlands for the improvement of water quality of municipal and agricultural wastewaters, organic loading (i.e., biochemical oxygen demand, total suspended solids), nutrients (nitrogen and phosphorus), and the configuration and maintenance of emergent vegetation can have strong effects on mosquito production. The production of Culex vectors of encephalitides and filarial worms is directly related to loading rates of organic matter and bottom-up enrichment of larval mosquito resources and their interaction with design features and management practices that reduce the physical and biological factors causing mortality of immature mosquitoes. As loading rates of organic matter and nutrients decline, the diversity of mosquitoes produced by treatment wetlands tends to increase and the relative abundance of Anopheles species, which are capable of vectoring the causative agents of malaria, increases in temperate man-made wetlands. Habitat features and management practices that create intermittently inundated substrate can lead to the production of other mosquitoes (i.e., Aedes, Psorophora) with floodwater life histories. Constructed wetland technology is expected to play an increasing role in water treatment and reclamation in tropical and subtropical countries where virulent mosquito-borne pathogens already cause significant levels of morbidity and mortality.     

Bacterial structure and spatiotemporal distribution in a horizontal subsurface flow constructed wetland

In this study, bacterial community structure in a horizontal subsurface flow constructed wetland (HSF-CW) planted with Phragmites australis was investigated using the 16S rRNA cloning–sequencing technique. Two layer depths were considered: the rhizosphere zone (RH) and the deep-layer zone (DL) in different sampling periods. Bacteria-specific primers 008F and 1492R were used to amplify the 16S rRNA genes and construct six clone libraries. A total of 1,284 individual sequences were used to assess the HSF-CW diversity. Phylogenetic analysis of RH and DL clone libraries shows that 41.57 and 42.17 % of the 16S rRNA sequences are affiliated with the Proteobacteria in the RH and the DL, respectively. The remaining major phylogenetic groups are Bacteroidetes, Planctomycetes, and Chloroflexi with 11.78, 9.36, and 7.6 %, respectively, in the RH and 11.38, 6.48, and 7.65 % in the DL, respectively. Minor divisions such as Verrucomicrobia, TM7, Nitrospira, and Gemmatimonadetes represented <6 % of the total sequences, while 14.2 % were unidentified Bacteria. Among the Proteobacteria, the Alphaproteobacteria subclass is represented in both locations, while the Deltaproteobacteria and Gammaproteobacteria subclasses were predominant in the RH and the DL, respectively. Results suggest that Archaea and Bacteria in the HSF-CW are the essential actors in the nitrogen cycle and that the established microbial community is efficient in nitrogen removal from wastewater.     

Long term performance of a constructed wetland for landfill leachate treatment

The constructed wetland (CW) was developed as a pilot integrated system for the capital city's old sanitary landfill site. It consisted of three interconnected beds, two of vertical flow and one of horizontal flow stage. The CW covered 311 m² with an intermittent hydraulic load of 0.5 cm d⁻¹, filled with sand media and planted with reeds and cattails. The performance efficiency of the CW systems was evaluated for 7 years through physical and chemical parameters. Some monitored parameters varied noticeable. The efficiency for COD was 50%, BOD₅ (59%), ammonia nitrogen (51%), nitrate (negative), total phosphorus (P) (53%), sulfates (negative), sulfides (49%), chlorides (35%), and Fe (84%). The average concentrations of suspended solids, COD, BOD₅, nitrate, total P, sulfates, sulfides, and Fe were below limits after treatment. The ratio between N and P showed a limited level of P for biological processes. The performance of the system did not vary significantly with regard to temperature, however, it varied with precipitation. The results showed that the CW system, as a tertiary system or as an independent system, could be a low-cost alternative for the treatment of leachate from old landfill sites.     

Influence of operating conditions on the degradation kinetics of an azo-dye in a vertical flow constructed wetland using a simple mechanistic model

A simple mechanistic model of a pulse-fed vertical flow constructed wetland is presented. In this work, the model is shown to accurately reproduce measurements of outlet flow and outlet concentration obtained while treating a synthetic wastewater containing the azo-dye, Acid Orange 7 (AO7). Application of the model to results obtained in summer and winter gave a unique apparent first-order kinetic constant (4.1 × 10^?7 s^?1), indicating that the activation energy is low. The treatment efficiencies determined while operating in a pseudo-stationary state for a high AO7 inlet concentration of 692 ± 92 mg L^?1 were 68 ± 5 and 70 ± 21% in summer and winter, respectively, for a flooding level of 21% and a pulse feeding of 13 min each 3 h. At the end of these trials (lasting more than 1 year), the system clogged. This occurrence was accurately modelled by including a variation in the free surface area with the liquid height above the bed surface. The model was then applied to design a robust dye wastewater treatment system producing water suitable for discharge to aquatic bodies. Model sensitivity to positive and negative evapotranspiration, that mimic variations in rainfall and temperature, and to variations in the rate constant, accounting for different azo-dyes biodegradability, was analyzed.