Hydraulic reliability of a horizontal wetland for wastewater treatment in Sicily

Knowledge Atlas on the Relationship between Water Management and Constructed Wetlands—A Bibliometric Analysis Based on CiteSpace

Water management is a crucial resource conservation challenge that mankind faces, and encouraging the creation of manmade wetlands with the goal of achieving long-term water management is the key to long-term urban development. To summarise and analyse the status of the research on the relationship between water management and constructed wetlands, this paper makes use of the advantages of the bibliometric visualization of CiteSpace to generate country/region maps and author-collaboration maps, and to analyse research hotspots and research dynamics by using keywords and literature co-citations based on 1248 pieces of related literature in the core collection in the Web of Science (WoS) database. The existing research shows that the research content and methods in the field of constructed-wetland and water-management research are constantly being enriched and deepened, including the research methods frequently used in constructed wetlands in water management and in the research content under concern, the functions and roles of constructed wetlands, the relevant measurement indicators of the purification impact of constructed wetlands on water bodies, and the types of water bodies treated by constructed wetlands in water management. We summarise the impact pathways of constructed wetlands on water management, as well as the impact factors of constructed wetlands under water-management objectives, by analysing the future concerns in the research field to provide references for research.

Evaluation of substrate clogging in a full-scale horizontal subsurface flow treatment wetland using electrical resistivity tomography with an optimized electrode configuration

This study investigated the spatial distribution of clogging matter in a full-scale horizontal subsurface flow treatment wetland (HSSF TW) based on an electrical resistivity tomography (ERT) method, comparing the performance of two different electrode configurations (i.e., Schlumberger and Wenner arrays). The results indicated that during the draining phase, the substrate apparent resistivities of the full-scale HSSF TWs were negatively correlated with the clogging matter fraction (v/v), and a functional relationship between the two parameters was established using a first-order k-C* model. The detected clogging matter fraction (v/v) based on the Schlumberger array showed higher accuracy (linear slope = 0.900, R-squared = 0.902) than the Wenner array (linear slope = 0.685, R-squared = 0.685). Most of the severe substrate clogging in the full-scale HSSF TW occurred within a 10-m flow distance, and the distribution of the clogging matter showed different characteristics at different substrate depths. From a cross section positioned 1 m from the inlet, the average clogging matter fraction (v/v) at a 0-0.30 m depth (23.1 ± 14.9%) was significantly higher than that at a 0.30-0.80 m depth (5.0 ± 2.1%). The clogging matter at a 5-m flow distance was evenly distributed at different substrate depths. Only a few localized clogging zones were observed in the cross section at a 10-m flow distance. This study provided an accurate and feasible method for investigating the volume fraction of clogging matters containing different organic contents and demonstrates the spatial heterogeneity of clogging matter in HSSF TWs.

Metal removal processes in a pilot hybrid constructed wetland for the treatment of semi-synthetic stormwater

This study investigates the reliability of a pilot hybrid constructed wetland (H-CW), located in Eastern Sicily (Italy). To address the uncertainty associated with implementing representative monitoring during highly variable storm events, unique to Mediterranean conditions, a recipe for semi-synthetic stormwater was used to evaluate the removal efficiency of the system. This was characterised by metals (Cd, Cr, Fe, Pb, Cu, Zn) and relative concentrations typically found in urban stormwater runoff (SR). Approximately one month of intensive monitoring activities were carried out and quality analyses were conducted on three matrices comprising the pilot H-CW: water, biomass (Canna indica, Typha latifolia), and volcanic gravel substrate. Metal retention in early clogging matter (SS) was also examined. The results showed a significantly high H-CW efficiency for the removal of all metals (70-98%) already at the horizontal flow unit outflow, confirming its strategic role. A metal mass balance analysis was also conducted to describe the retention capacity and influence of each system component on the overall efficiency (ranging from 87.8% for Cr to 99.2% for Pb). Metal removal was mostly related to sediment and substrate processes, while plants exhibited root bioaccumulation and phytostabilisation capacity even with a limited impact on overall system retention. The pilot H-CW exhibits characteristics suitable for the treatment of metal-enriched stormwater runoff and validates the useful application of decentralised natural systems for water resource management.

Monitoring of horizontal subsurface flow constructed wetlands for tertiary treatment of municipal wastewater

This paper explores the feasibility of the electrical resistivity (ER) method as non-invasive technique to detect dysfunctions of full-scale tertiary wastewater treatment wetlands, such as clogging, that ultimately limit the system lifetime and performance. ER measurements were carried out according to the Werner’s method on two (overloaded) horizontal subsurface wetlands (HSF-CW1 and HSF-CW2) operated in parallel since the end of 2017, while still achieving satisfactory treatment efficiencies. Layered clog-induced preferential flow pathways through the HSF-CW beds and premature deterioration of the wetland’s liner with a possible development of dead zones associated with a low/heterogeneous density of vegetation could be confirmed by analysis of ER profiles. These results suggest that the ER method is a promising and feasible technique, as simplified then adapted/adopted to local context, for better monitoring and assessment of treatment wetlands with early process failure.

Evaluation of Different Methods to Assess the Hydraulic Behavior in Horizontal Treatment Wetlands

While there have been numerous studies on the rate and development of clogging in horizontal subsurface treatment wetlands (HSTWs) and, consequently, the effects on its hydraulic characteristics, research has not shown a clear understanding of the processes. The existing methods for measuring the impact of clogging provide limited information on the extension and degree of the phenomenon. This study aimed to evaluate the capacity of various measurement techniques to assess the degree and variation in space and time of clogging in HSTWs. Hydraulic conductivity at saturation (Ks) measurements were conducted using a newly implemented scheme, the drainage equation method, and traditional tracer tests, which were carried out in a full-scale HSTW system, located in Sicily, Italy, during 2019. After five years of operation, the results highlighted a severe decrease in Ks (<1000 m day−1) in the inlet zone (despite the fact that the filter gravel was replaced in 2017), a very high reduction of Ks along the central path inside the bed, a nonuniform flow through the HSTW, the presence of stagnant zones, and a reduction of the porosity of the bed gravel. Nonetheless, the mean values of the physical–chemical and bacteriological parameters at the hybrid treatment wetland (hybrid TW) outlet indicated that the partial clogging had no significant effect on the quality of the discharged water. Moreover, the results obtained using the different measurement techniques (in terms of both the Ks values and the flow distribution inside the bed) were consistent with each other and with results obtained previously for the same system. Finally, the most efficient combination of methods to assess clogging in HSTWs was identified.

A novel horizontal subsurface flow constructed wetland planted with Typha angustifolia for treatment of polluted water

Rapid population growth and urbanization has put a lot of stress on existing water bodies in most developing countries such as the Marriott Lake of Egypt. Three constructed wetland configurations including Typha angustifolia planted with enhanced atmospheric aeration by using perforated pipes networks (CWA), planted without perforated pipe network (CWR), and a control non-planted and without perforated pipes wetland (Control) were used in the study. Changes in physicochemical properties and microbial community over four seasons and hydraulic loading rate (HLR) (50, 100, 200, 300, and 400 L day^-1 m^-1) were monitored using influent from Marriott Lake in Egypt. Overall, the removal performance followed the sequence CWA>CWR>control. Turbidity removal of 98.4%; biochemical oxygen demand (BOD₅) removal of 83.3%; chemical oxygen demand (COD) removal of 95.8%; NH₃-N removal of 99.9%; total nitrogen (TN) removal of 94.7%; NO₃^--N and NO₂^--N increased; total P (TP) removal of 99.7%, Vibrio sp. of 100%, Escherichia coli 100%; total bacterial count of 92.3%; and anaerobic bacteria reduction of 97.5% were achieved by using CWA. Seasonal variation and variation in HLRs had significant effect on performance. The modified planted CWA system enhances the removal of pollutants and could present a novel route for reducing the cost associated with integrating artificial aeration into wetlands.

Time-domain induced polarization as a tool to image clogging in treatment wetlands

During the last decade, treatment (artificial) wetlands have flourished all over Europe for the treatment of sewages from small communities thanks to their low cost of operation. The clogging of the filter of these wetlands is an issue affecting their efficiency and considered as their main operational problem. The present work shows the results of the application of a geophysical method called time-domain induced polarization. It is used to non-intrusively image, in 3D, the clogging of the gravel filters in a quick and efficient way. Induced polarization characterizes the ability of a porous material to reversibly store electrical charges when submitted to an electrical field. The material property characterizing this ability is called normalized chargeability. A set of laboratory experiments allows to determine an empirical relationship between the normalized chargeability and the weight amount of clogging. Induced polarization measurements have been performed in the field over a treatment wetland to get a 3D reconstructed image (tomography) of the normalized chargeability. From this tomography and the previously defined relationship, we are able to image in 3D the distribution of clogging and where it is concentrated in the filter. We can therefore identify the areas requiring preventive measures to minimize this clogging issue.

The influence mechanism of bioclogging on pollution removal efficiency of vertical flow constructed wetland

The effect of change of hydraulic characteristic and microbial community on pollution removal efficiency of the infiltration systems in the bioclogging development process remain poorly understood. In this study, therefore, the pollutant removal as a response to hydraulic conductivity reduction and the change of diversity and structure of microbial communities in vertical flow constructed wetlands (VFCWs) was investigated. The results indicated that the richness and diversity of the bacterial communities in the columns at different depths were decreased, and the microbial communities of the genus level were changed in the process of bioclogging. However, the variation of microbial communities has a low impact on the purification performance of VFCWs because the abundance of function groups, respiratory activity, and degradation potentiality of microorganisms remain steady or even get improved in the columns after bioclogging. On the contrary, the hydraulic efficiency of VFCWs decreased greatly by 16.9%, 9.9%, and 57.1% for VFCWs filled with zeolite (Column I), gravel (Column II), and ceramsite (Column III), respectively. The existence of short-circuiting and dead zones in the filter media cause the poor pollution removal efficiency of VFCWs due to the short contact time and decrease of oxygenation renewal, as well as low activity in the dead zone.

Treatment of Winery Wastewater with a Multistage Constructed Wetland System for Irrigation Reuse

This paper reports a study on the performance of a multistage constructed wetland (CW) system adopted for winery wastewater and on the analysis of its suitability for irrigation reuse. The CW system treats about 3 m3·day−1 of wastewater produced by a small winery located in Sicily (insular Italy). Wastewater samples were collected at the CW inlet and outlet for physical–chemical and microbiological quality characterization. CW efficiency was evaluated on the basis of water quality improvement and of the achievement of Italian and EU irrigation reuse regulation limits. The CW system showed Chemical Oxygen Demand (COD) and Total Suspended Solids (TSS) mean removal rates of about 81% and 69%, and a maximum removal of about 99% (for both COD and TSS) occurred during grape harvest phase. The CW removal efficiencies for nutrients were 56% for TN and 38% for PO4-P, considering their low average concentrations at CW inlet. The CW system evidenced an effluent average quality compatible with the limits imposed by the Italian regulation and EU proposal regulation on the minimum requirement for water reuse. The CW vegetated area showed regular growth and vegetative development; phytotoxicity phenomena were not detected. The results of the study suggest the important role of CW systems in the treatment of winery wastewater and for their subsequent reuse in agriculture.

Biomonitoring of urban wastewaters treated by an integrated system combining microalgae and constructed wetlands

The objectives of the present study were to apply different, toxicological assays for monitoring the toxicity of treated and untreated urban effluents produced at a university campus. The research was conducted at the wastewater treatment plant of the University of Santa Cruz do Sul, (UNISC), from october 2018 to april 2019. An integrated system with, anaerobic reactor (AR), microalgae (MA) and constructed wetlands (CWs) was, proposed for detoxification of the wastewaters produced at the university campus with a hydraulic detention time of 17 days. Daphnia, magna (ecotoxicity) and Allium cepa (phytotoxicity, cytotoxicity, and, genotoxicity) were used as tools to monitor the efficiency of the integrated system. Obtained results showed that the integrated system (MA, + CWs) presented good COD and BOD5 reductions, besides removal rates of, almost 98% for N-NH3, being much more efficient than the UNISC wastewater, treatment plant (UWTTP). The results of ecotoxicity presented the raw wastewaters (RW) as slightly toxic and an absence of ecotoxicity in all the treatments steps. Regarding phytotoxicity, the results showed no significant differences between the treatments. The cytogenetic assays indicated a significant increase in mitotic index (MI) (p < 0.001) after treatment by CWs compared to the final treatment UWTTP while the results, regarding binucleated cells (BNC) did not present significant differences, among the treatments. Micronucleus (MN) indexes were significantly different between the UWWPT and the integrated system (p < 0.01). In relation to chromosome aberrations (CA) the results indicate a significant difference between the CWs and UWWTP treatments (p < 0.01) and, RW and CWs (p < 0.001), confirming the detoxifying potential of the integrated system when compared to UWWPT. Thus, the results of the present research highlight the relevance in the proposition of the integrated system as an alternative of cleaner technology to the detriment of conventional technologies applied in wastewater treatment.

Hydrological and hydraulic behaviour of a surface flow constructed wetland treating agricultural drainage water in northern Italy

A surface flow constructed wetland (SFCW) treating agricultural drainage water was investigated with the aim to detect modifications in hydrological and hydraulic characteristics after more than a decade of operation. Ponded infiltration tests were conducted to estimate the saturated hydraulic conductivity, K_s, of the surface soil layer at the point scale. At the global scale, infiltration rate, i, was computed from the water balance to detect leakages from the pervious wetland surface. Tracer tests were conducted to analyse the existence of preferential flow inside the system and to estimate its hydraulic retention time (HRT). Clogging phenomena occurred given a mean K_s value of 30 mm h^-1 was measured near the SFCW inlet, that was 9.61 times lower than the value at the outlet zone. The estimated infiltration losses were two orders of magnitude lower than infiltration measured at the point scale. The results also confirmed the existence of a moderate amount of preferential flow paths and dead zones in the SFCW as the actual HRT (6.7 days) was shorter than the nominal one (8.1 days). Despite this, it can be concluded that the system performance is still good after 17 years of operation.

Comparative study about the performance of three types of modified natural treatment systems for rice noodle wastewater

In this study, three semi-pilot scale systems (vertical flow constructed wetland, multi-soil layering, and integrated hybrid systems) for treating real rice noodle wastewater were operated parallelly for the first time in a tropical climate at a loading rate of 50 L/(m²·d) for more than 7 months to determine the optimal conditions and to compare their treatment performance. The results demonstrated that these systems were appropriate for the removal of organics, suspended solids, and total coliform (Tcol). The highest reductions in chemical oxygen demand (COD_Cr, 73.2%), phosphorus (PO₄-P, 54%), and Tcol (4.78 log MPN/100 mL inactivation) were obtained by the integrated hybrid system, while the highest removal efficiencies of ammonium (NH₄-N, 60.64%) and suspended solids (80.49%) were achieved in the vertical-flow-constructed wetland and multi-soil layering systems respectively.

Constructed wetlands combined with disinfection systems for removal of urban wastewater contaminants

The removal efficiency of an urban wastewater treatment plant (WWTP) to obtain an effluent suitable for agriculture reuse was evaluated in a one-year period, taking into account the Italian wastewater limits and the recent European proposal for the minimum requirements water quality for agricultural irrigation. The secondary effluent of WWTP was treated by three full-scale horizontal sub-surface flow (H-SSF) constructed wetlands (CWs), working in parallel, planted with different macrophytes species, and combined with a UV device and a lagooning system running in series. The H-SSF CW system effectively reduced physico-chemical pollutants and its efficiency was steady over the investigation period, while, Escherichia coli densities always exceed the Italian limits required for wastewater reuse in agriculture. The UV system significantly reduced the microbiological indicators, eliminating E. coli, in compliance with the Italian regulation, and somatic coliphages, although a variable efficacy against total coliforms and enterococci, especially in winter season, was achieved. Although the lagooning unit provides a high removal of the main microbial groups, it did not reduce physico-chemical parameters. Even if the overall performance target, for the whole treatment chain, met the recent log₁₀ reduction (≥5.0), required by the European Commission, the persistence of enterococci, especially in winter season, poses a matter of concern for public health, for the potential risk to serve as a genetic reservoir of transferable antibiotic-resistance.

Assessment of clogging in constructed wetlands by saturated hydraulic conductivity measurements

This study aims at defining a methodology to evaluate K_s reductions of gravel material constituting constructed wetland (CW) bed matrices. Several schemes and equations for the Lefranc's test were compared by using different gravel sizes and at multiple spatial scales. The falling-head test method was implemented by using two steel permeameters: one impervious (IMP) and one pervious (P) on one side. At laboratory scale, mean K values for a small size gravel (8-15 × 10^-2 m) measured by the IMP and the P permeameters were equal to 19,466 m/d and 30,662 m/d, respectively. Mean K_s values for a big size gravel (10-25 × 10^-2 m) measured by the IMP and the P permeameters were equal to 12,135 m/d and 20,866 m/d, respectively. Comparison of K_s values obtained by the two permeameters at laboratory scale as well as a sensitivity analysis and a calibration, lead to the modification of the standpipe equation, to evaluate also the temporal variation of the horizontal K_s. In particular, both permeameters allow the evaluation of the K_s decreasing after 4 years-operation and 1-1.5 years' operation of the plants at full scale (filled with the small size gravel) and at pilot scale (filled with the big size gravel), respectively.