Scale Subsurface Flow Research Articles

Development and Design of Laboratory Scale Subsurface Flow Constructed Wetland System

Wetlands have traditionally functioned as a natural filtration system. Constructed wetlands (CWs) are a cost-effective and efficient green technology for treating many different types of wastewaters. The efficiency of constructed wetland depends upon the type of media, vegetation, effluent concentration, and applied hydraulic load. The objective of the present paper is to Development and Design a laboratory scale constructed wetland system. The important considerations in the design are the size of the wetland, aspect ratio, depth of each layer, and slope. The length, width, and height of the CWs are 1.2 m; 0.3 m; and 0.65 m; respectively. The total volume of CWs is 0.234 m3 and the treatment section in the system consists volume of 0.135 m3. Twelve sampling points are provided to collect the water from the different layers (media) of the wetland. An aeration pipe is provided at the bottom of CWs. With the laboratory scale constructed wetland system, we can analyze the different types of wastewater.

Full scale subsurface flow constructed wetlands for domestic wastewater treatment: 3 years' experience

In the present study, a horizontal subsurface flow constructed wetlands divided three equal parts was designed and constructed at a full scale to treat wastewater of Yörükçal village located in Black Sea region. Three macrophytes namely Juncus acutus, Cortaderia selloana, and Phragmites australis were used in each wetland system. The total surface area of all wetlands is 520 m2. The average removal efficiencies of J. acutus, C. selloana, and P. australis were obtained as 57, 56, and 54% for BOD; 51, 33, and 27% for TN; 55, 58, and 46% for OM; 45, 39, and 32% for orthophosphate; 22, 38, and 24% for ‐N; 13, 20, and 24% for TSS; 33, 44 and 39% for , respectively. One‐way analysis of variance (ANOVA) between groups was applied to determine any difference in the removal of all parameters between the plant types and months depending on the mean values of pollutant removal. Due to the problems such as costs of construction, maintenance and repair, and reduced flow rate encountered especially during the collection of wastewater in rural regions and transport to wastewater treatment plants in the city, the in‐situ treatment applications may be unavoidable. According to the results, Constructed Wetlands (CW) designed correctly are economically and environmentally to treat wastewater of rural settlements. © 2018 American Institute of Chemical Engineers Environ Prog, 37: 1348–1360, 2018

Greywater Treatment Using Horizontal, Vertical and Hybrid Flow Constructed Wetlands

The performance evaluation of three pilot scale subsurface flow constructed wetlands (CW), i.e. horizontal flow (HFCW), vertical flow (VFCW) and a baffle type-hybrid (HYCW) was studied. The units were continuously fed with greywater and were planted with Phragmites australis . The inflow concentrations of BOD, COD, TSS, NO 3 , TP and FC were in the range of 72–120 mg/l, 216–320 mg/l, 224–320 mg/l 10.3–14.6 mg/l, 2.9–3.8 mg/l and 50–120 CFU/100 ml respectively. The average removal efficiencies of BOD, COD, TSS, TP, TN and FC in HYCW were 95 ± 2%, 96 ± 3%, 98 ± 2%, 92 ± 2%, 98 ± 2% and 98 ± 2% respectively and comparatively more than the other two constructed wetlands.

Performance of tropical vertical subsurface flow constructed wetlands for leachate treatment at different hydraulic loading rates

This study is focused on the investigation of three different types of plant species namely; Narrow leaf Cattail (Typha angustifolia), Green Bulrush (Scirpus atrovirens) and Umbrella Palm (Cyperus alternifolius) for treatment of leachate. Twelve laboratory scale subsurface flow constructed wetland models were operated in batch mode. Four models, each containing similar plant species were fed with synthetic leachate having four different concentrations (25%, 50%, 75% and 100%) and 7 days HRT was given. The duration of a batch run was 12 weeks. Removal efficiencies of BOD5, COD, PO43-, TC, and TN were measured. Evapotranspiration (ET) loss of each test run was also assessed. According to the results, the constructed wetland planted with Umbrella palm and fed with 25% leachate showed the best pollutant removal efficiencies of 99.26% for BOD5, 99.61% for COD, 98.78% for TN and 97.34%for TC. Highest ET potential of 93.57% was also observed from the constructed wetland with umbrella palm fed with 25% leachate. Two way ANOVA analysis was carried out for each plant species and leachate concentration and the Umbrella Palm species was identified as the best for leachate treatment. Key words: Constructed wetlands, landfill leachate, plant species and pollutant removal

Factors affecting the performance of horizontal flow constructed treatment wetland vegetated with Cyperus papyrus for municipal wastewater treatment

ABSTRACTThe effect of hydraulic loading rate (HLR) and hydraulic retention time (HRT) on the bioremediation of municipal wastewater using a pilot scale subsurface horizontal flow constructed treatment wetland (HFCTW) vegetated with Cyprus papyrus was investigated. Different HLRs were applied to the treatment system namely 0.18, 0.10, and 0.07 m3/m2. d with corresponding HRTs of 1.8, 3.2, and 4.7 days, respectively. The flow rate was 8 m3/d, and the average organic loading rate (OLR) was 0.037 kg BOD/m3/d. Results showed that the performance of the HFCTW was linearly affected by decreasing the HLR and increasing the HRT. The highest treatment efficiency was achieved at HRT (4.7 days) and HLR (0.07 m3/m2. d). The percentage reductions of chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS) were 86%, 87%, and 80%, respectively. Satisfactory nutrient removal was obtained. Also, removal of 2–3 logs of bacterial indicators of pollution was achieved. The dry biomass of Cyperus was 7.7 kg/m2 and proved to be very efficient in nitrification processes due to high diversity of the roots that increase the treatment surface area.

Evaluation of Ageratum conyzoides in field scale constructed wetlands (CWs) for domestic wastewater treatment.

Ageratum conyzoides were evaluated in field scale subsurface flow constructed wetlands (CWs) to quantify its nitrogen (N) and phosphorus (P) uptake and compare with wetland plants (Pistia stratiotes, Typha latifolia and Canna indica). The two-field scale subsurface flow CWs, located in the International Crops Research Institute for Semi-Arid Tropics, received wastewater from an urban colony. The CW1 and CW2 had the same dimensions (length:10 m, width:3 m, total depth:1.5 m and sand and gravel:1 m), similar flow rates (3 m3/d), hydraulic loading rates (HLRs-10 cm/d) and hydraulic retention time (HRT-5 days) from July 2014-August 2015. The vegetation in both CWs consisted of Pistia stratiotes, Typha latifolia, Canna indica, and Ageratum conyzoides, respectively. The CW1 (% reduction with respect to concentrations) reduced total suspended solids (TSS) (68%), NH4-N (26%), NO3-N (30%), soluble reactive P (SRP) (20%), chemical oxygen demand (COD) (45%) and fecal coliforms (71%), while the CW2 (%-reduction with respect to concentrations) reduced TSS (63%), NH4-N (32%), NO3-N (26%), SRP (35%), COD (39%) and fecal coliforms (70%). Ageratum conyzoides can be used in combination with Pistia stratiotes, Typha latifolia and Canna indica to enhance removal of excessive N, P and fecal coliforms from domestic wastewater.

Estimation of chromium reduction potential of two wetland plants using pilot scale constructed wetlands

Two parallel pilot scale sub-surface flow constructed wetlands (SSFCW) are designed and fabricated. The two natural wetland plants selected for the present study are Cyperus alopecuroides and Canna indica. These plant species are grown in constructed wetland tanks A (with Canna indica) and B (with Cyperus alopecuroides) for two months by supplying fresh tap water. After the plants are grown healthy, potassium dicromate solution of different concentrations is introduced into both the tanks in a constant rate flow of 25 ml/min in plug flow manner from inlet tanks. The hydraulic retention time (HRT) is maintained as five days. After 5 days the effluent is collected at the outlet and tested for chromium (VI). The experiment is continued for four months and chromium VI in the outlet waters is analysed. At the end of the experiment, plants are harvested and seperated into leaves, rhizomes and roots. They are seperately analysed for total chromium concentration. Bio-concentration Factor (BCF) and Translocation Factor (TF) are also estimated.

Evaluating Wastewater Treatment Efficiency of Two Field Scale Subsurface Flow Constructed Wetlands

Constructed wetlands (CWs) are human-made systems designed to treat a variety of industrial, domestic and agricultural wastewaters. We study here the efficiency of domestic wastewater treatment by two field scale subsurface flow CWs under different hydraulic loading rates (HLRs). Each CW had inlet and outlet chamber for wastewater collection with Pistia stratiotes (water lettuce), two treatment sections consisting of sand and gravel media and four plant species Typha latifolia (Broadleaf cattail) and Cymbopogon citratus (lemon grass - first CW) and ( Pennisetum purpureum schum and Pennisetum americanum L (Hybrid napier) and Urochloa mutica (Paragrass - second CW). The wastewater source was from a residential urban colony. The HLRs for the first and second CW for a three-month period averaged 4.45 cm/day and 5.77 cm/day respectively. The CW was monitored for quality of wastewater inflows and outflows and nutrient accumulation in plants and sand media. Results showed that the chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen and total phosphate removals in the first and second CW over a three-month period averaged 42%, 74%, 39% and 41% and 34%, 82%, 14% and 35% respectively. Both the CWs showed similar rates of TSS removal irrespective of the type of wetland plant species. Over the three-month period, average COD, total nitrogen and the phosphate removals were greater in the first CW compared to the second CW. These results confirm the efficacy of field scale subsurface flow CWs to improve the quality of domestic wastewater in rural communities of developing countries like India.

Assembly of a Wetland on a Laboratory Scale for Post-Treatment of Domestic Wastewater

Water is present in many routine activities performed by man. However, these activities have been generating wastewater who require treatment before being cast into water bodies. The constructed wetlands are alternative wastewater treatment low cost of construction and maintenance, therefore do not require electricity and chemical application. Perform well in the removal of polluting effluent load and have advantages of being aesthetically pleasing due to the presence of aquatic plants. This work presents a proposal to mount a wetland constructed for the post-treatment of domestic wastewater in laboratory scale subsurface flow and intermittent, macrophyte was used mini papyrus (Cyperus isocladus) and substate fragments ceramic tiles.

Interactions and connectivity between runoff generation processes of different spatial scales

AbstractMonitoring runoff generation processes in the field is a prerequisite for developing conceptual hydrological models and theories. At the same time, our perception of hydrological processes strongly depends on the spatial and temporal scale of observation. Therefore, the aim of this study is to investigate interactions between runoff generation processes of different spatial scales (plot scale, hillslope scale, and headwater scale). Different runoff generation processes of three hillslopes with similar topography, geology and soil properties, but differences in vegetation cover (grassland, coniferous forest, and mixed forest) within a small v‐shaped headwater were measured: water table dynamics in wells with high spatial and temporal resolution, subsurface flow (SSF) of three 10 m wide trenches at the bottom of the hillslopes subdivided into two trench sections each, overland flow at the plot scale, and catchment runoff. Bachmair et al. () found a high spatial variability of water table dynamics at the plot scale. In this study, we investigate the representativity of SSF observations at the plot scale versus the hillslope scale and vice versa, and the linkage between hillslope dynamics (SSF and overland flow) and streamflow. Distinct differences in total SSF within each 10 m wide trench confirm the high spatial variability of the water table dynamics. The representativity of plot scale observations for hillslope scale SSF strongly depends on whether or not wells capture spatially variable flowpaths. At the grassland hillslope, subsurface flowpaths are not captured by our relatively densely spaced wells (3 m), despite a similar trench flow response to the coniferous forest hillslope. Regarding the linkage between hillslope dynamics and catchment runoff, we found an intermediate to high correlation between streamflow and hillslope hydrological dynamics (trench flow and overland flow), which highlights the importance of hillslope processes in this small watershed. Although the total contribution of SSF to total event catchment runoff is rather small, the contribution during peak flow is moderate to substantial. Additionally, there is process synchronicity between spatially discontiguous measurement points across scales, potentially indicating subsurface flowpath connectivity. Our findings stress the need for (i) a combination of observations at different spatial scales, and (ii) a consideration of the high spatial variability of SSF at the plot and hillslope scale when designing monitoring networks and assessing hydrological connectivity. Copyright © 2013 John Wiley & Sons, Ltd.

Effectiveness of vegetation on phosphorus removal from reclaimed water by a subsurface flow wetland in a coastal area

This work was conducted to evaluate the effectiveness and influence factors of vegetation on phosphorus (P) removal from reclaimed water in constructed wetlands. Comparisons were conducted between one pilot scale subsurface flow wetland (P-SSFW) and two demonstration subsurface flow wetlands, which were series-wound and named as first subsurface flow wetland (F-SSFW), and second subsurface flow wetland (S-SSFW), respectively. The three wetlands had the same vegetation and substrate, but different pH values, total dissolved solids (TDS) and P loads. Results showed that the P content in the vegetation shoots of the F-SSFW was 2.16 mg/g, while 2.31 mg/g in the S-SSFW and 2.69 mg/g in the P-SSFW. These differences were likely caused by the higher pH and TDS in the reclaimed water. The P content also differed among the tissues of the plant, which were 5.94-6.44 mg/g, 2.20-2.77 mg/g, 1.31-1.46 mg/g and 1.53-1.88 mg/g in the flowers, leaves, stems, and roots, respectively. The greatest discrepancy was observed in the leaves, indicating that the environment of the wetlands had the greatest influence on the leaves. When the total phosphorus (TP) load was lower, the proportion of P removed by vegetation assimilation was 16.17% in the P-SSFW, 12.90% in the F-SSFW and 13.29% in the S-SSFW. However, the relative removal efficiency by vegetation among the three wetlands did not vary greatly from that observed in other studies. Moreover, the influence of pH, TDS and TP load was not as great as the influence of the vegetation species, type of substrate, influent style or climate.

Variations in Phosphorus Speciation in Pilot Scale Subsurface Flow Wetlands Constructed with Blast Furnace Slag and Gravel

AbstractVariations in phosphorus (P) speciation were compared for two types of pilot scale wetlands: a blast furnace slag‐based constructed wetland (SCW), and a gravel‐based constructed wetland (GCW). Synthetic secondary effluent was used as the influent of the wetlands, which contained 1.1 mg/L P with more than 95% present as soluble reactive P (SRP). However, dissolved organic phosphorus (DOP) and particulate phosphorus (PP) emerged in the water along both wetlands. The levels of these three P species varied between the two wetlands. The GCW was more efficient than SCW at removing SRP, but showed a different trend. SRP decreased continually in the SCW, while it increased at the end of the GCW due to biological release. DOP was constant in SCW and GCW, and the mean value was 0.023 and 0.020 mg/L, respectively. The mean values of PP in the GCW ranged between 0.093 and 0.216 mg/L; much higher than the 0.05 ± 0.01 mg/L measured in the SCW. Sequential extractions showed that iron bound PP (Fe‐PP), aluminum bound PP (Al‐PP), organic PP (Org‐PP) and occluded PP (Oc‐PP) were the major components of PP at most locations of the GCW. Fe‐PP decreased from 0.53 to 0.14 mg/L in the upper layer, with DO steady at about 0.15 mg/L at the bottom. Oc‐PP increased at each layer. Al‐PP and Org‐PP were steady in the first 140 cm of the GCW, but decreased sharply at the end. Considering the variation of SRP, DOP and PP fractionations, it can be seen that PP exchanged intensively with SRP in the GCW, and might act as an intermediate in the P removal process. Part of the SRP was first transformed into PP, and then absorbed by substrates or deposited in the wetlands. P removal was mainly via Ca precipitation in the SCW, but involved multiple mechanisms in the GCW, such as precipitation, adsorption and biological interactions. The multiple P removal mechanisms might be the reason for the low proportion of SRP, and the better P removal efficiency observed in the GCW.

Comparison of microfauna communities in full scale subsurface flow constructed wetlands used as secondary and tertiary treatment

In order to evaluate the microfauna composition and distribution in two horizontal subsurface flow constructed wetlands used as secondary and tertiary treatment a full-scale wastewater treatment plant was monitored during five months. Results indicate that total microfauna abundance in the wetland treating primary influents is around five times higher than that found in the wetland treating secondary influents. Ciliated protozoa and microflagellates are the most important microfauna groups in both wetlands; microflagellates in terms of abundance and ciliates in terms of biomass. The most abundant ciliate species in the wetland treating primary influents are polysaprobic organisms as Dexiostoma campylum, Trimyema compressum, and to a lesser extend Metopus spp. On the other hand, the most important ciliate species found in the wetland treating secondary influents are mainly aerobic ciliates as Vorticella comvallaria-complex, Aspidisca cicada, Litonotus lamella and some ciliates belonging to the group of the scuticociliates and Hypotrichidae. The sort of the organic matter treated (particulated or dissolved) is at least as important as the amount of it in order to explain microfauna dynamics in constructed wetlands.

Upscaling Schemes and Relationships for the Gardner and van Genuchten Hydraulic Functions for Heterogeneous Soils

Upscaled soil hydraulic properties are needed for many large‐scale hydrologic applications such as regional and global climate studies and investigations of land–atmosphere interactions. Many larger scale subsurface flow and contaminant transport studies also require upscaled hydraulic property estimates. The objectives of this study were to develop a methodology for upscaling hydraulic property functions using a p‐norm approach, to examine how p‐norm values differ for two commonly used soil hydraulic property models (the Gardner and van Genuchten functions), and to investigate the relative sensitivities of p‐norms and the effective hydraulic parameters to the degree of soil heterogeneity (expressed in terms of variances and auto‐correlation lengths of the hydraulic parameters) and other environmental conditions. The p‐norm approach expresses upscaling schemes such that it reduces their sensitivity to uncertainties (heterogeneities) in site conditions. The upscaling schemes are obtained as the result of two new criteria proposed to upscale soil hydraulic properties in this study—one preserving the ensemble vertical moisture flux across the land–atmosphere boundary, and a second preserving the ensemble soil surface moisture content. The effective soil hydraulic parameters of a heterogeneous soil formation are then derived by conceptualizing the formation as an equivalent homogeneous medium that satisfies the upscaling criteria. Upscaling relationships between the Gardner and van Genuchten models can then also be established for steady‐state vertical flow using the statistical structures of the hydraulic parameters of these two models as estimated from field measurements. The upscaling scheme is demonstrated using hydraulic property data collected at 84 locations across a site in the Mojave Desert. Our results show that the p‐norms generally vary less in magnitude than the effective parameters when the variances of the hydraulic parameters increase. We also show that, in general, p‐norm values are better defined for the van Genuchten model than the Gardner model. Hydraulic parameter auto correlations, as defined by correlation lengths, were found to have little impact in relating the upscaling schemes (p‐norm values) for the two hydraulic property models, but correlation between the hydraulic parameters within the hydraulic property models can significantly affect p‐norm relationships.

Towards an integrated performance model for subsurface flow constructed wetlands

Detailed investigations have been conducted on a set of four pilot scale subsurface flow (SSF) constructed wetlands in order to characterise heat transfer, mass dispersion and biological performance mechanisms. These studies have followed the beds from post construction through unplanted hydraulic base line studies to the current status of mature stands of Phragmites australis. Experimental observations indicate that in unplanted beds, daily thermal fluctuations are depth dependent and range from 1 to 9 degrees Celsius. These fluctuations result in daily thermal inversions, and enhanced mixing and oxygen transport. For planted beds, thermal fluctuations are depth independent, and have a constant amplitude of 2 degrees Celsius. Planted beds may be thermally stratified. Lithium tracer studies corroborate these results for the planted bed. In addition, performance studies indicate that organic pollutant removal is probably limited to organic suspended solids removal, with subsequent biological breakdown. Current first‐order plug flow models can not account for these operational issues. A combined model is necessary to account for lateral dispersion, temperature gradients and settling of suspended solids to accurately reflect real biological removal mechanisms.

Hydraulic tracer studies in a pilot scale subsurface flow constructed wetland

Current design procedures for Subsurface Flow (SSF) Wetlands are based on the simplifying assumptions of plug flow and first order decay of pollutants. These design procedures do yield functional wetlands but result in over-design and inadequate descriptions of the pollutant removal mechanisms which occur within them. Even though these deficiencies are often noted, few authors have attempted to improve modelling of either flow or pollutant removal in such systems. Consequently the Oxley Creek Wetland, a pilot scale SSF wetland designed to enable rigorous monitoring, has recently been constructed in Brisbane, Australia. Tracer studies have been carried out in order to determine the hydraulics of this wetland prior to commissioning it with settled sewage. The tracer studies will continue during the wetland's commissioning and operational phases. These studies will improve our understanding of the hydraulics of newly built SSF wetlands and the changes brought on by operational factors such as biological films and wetland plant root structures. Results to date indicate that the flow through the gravel beds is not uniform and cannot be adequately modelled by a single parameter, plug flow with dispersion, model. We have developed a multiparameter model, incorporating four plug flow reactors, which provides a better approximation of our experimental data. With further development this model will allow improvements to current SSF wetland design procedures and operational strategies, and will underpin investigations into the pollutant removal mechanisms at the Oxley Creek Wetland.

A critical evaluation of a pilot scale subsurface flow wetland: 10 years after commissioning

A pilot scale subsurface flow wetland, commissioned in 1986, has been continuously operated since 1990 at a hydraulic load of 330 mm/day and a corresponding organic load of 1200 kg/ha·day. At these loading rates preliminary evidence suggests that the microbial biomass in the wetland was dominated by anaerobes. Attempts to increase the hydraulic load resulted in surface flooding which was attributed to suspended solids clogging the surface. Despite short circuiting, revealed by tracer studies, COD removal exceeded 70%. The hydraulic flow through the wetland was modelled and was described as modified plug flow with a degree of back mixing. A comparative costing exercise revealed that the unit treatment cost of a combination of a subsurface flow wetland/nitrification column, surface flow wetland was lower than that of an activated sludge system treating the same volume of effluent.

A critical evaluation of a pilot scale subsurface flow wetland: 10 years after commissioning

A pilot scale subsurface flow wetland, commissioned in 1986, has been continuously operated since 1990 at a hydraulic load of 330 mm/day and a corresponding organic load of 1200 kg/ha day. At these loading rates preliminary evidence suggests that the microbial biomass in the wetland was dominated by anaerobes Attempts to increase the hydraulic load resulted in surface flooding which was attributed to suspended solids clogging the surface. Despite short circuiting, revealed by tracer studies, COD removal exceeded 70%. The hydraulic flow through the wetland was modelled and was described as modified plug flow with a degree of back mixing. A comparative costing exercise revealed that the unit treatment cost of a combination of a subsurface flow wetland/nitrification column, surface flow wetland was lower than that of an activated sludge system treating the same volume of effluent.

Hydraulic tracer studies in a pilot scale subsurface flow constructed wetland

Current design procedures for Subsurface Flow (SSF) Wetlands arc based on the simplifying assumptions of plug flow and first order decay of pollutants. These design procedures do yield functional wetlands but result in over-design and inadequate descriptions of the pollutant removal mechanisms which occur within them. Even though these deficiencies are often noted, few authors have attempted to improve modelling of either flow or pollutant removal in such systems.Consequently the Oxley Creek Wetland, a pilot scale SSF wetland designed to enable rigorous monitoring. has recently been constructed in Brisbane, Australia. Tracer studies have been carried out in order to determine the hydraulics of this wetland prior to commissioning it with settled sewage. The tracer studies will continue during the wetland's commissioning and operational phases. These studies will improve our understanding of the hydraulics of newly built SSF wetlands and the changes brought on by operational factors such as biological films and wetland plant root structures.Results to date indicate that the flow through the gravel beds is not uniform and cannot be adequately modelled by a single parameter, plug flow with dispersion, model. We have developed a multiparameter model, incorporating four plug flow reactors, which provides a better approximation of our experimental data. With further development this model will allow improvements to current SSF wetland design procedures and operational strategies, and will underpin investigations into the pollutant removal mechanisms at the Oxley Creek Wetland.

Rootzone dynamics in constructed wetlands receiving wastewater: a comparison of vertical and horizontal flow systems

Profile conditions were examined in both small experimental and pilot scale sub-surface flow wetlands. The study systems differed in their hydraulic design. The experimental systems had a vertical up-flow design whereas the pilot system was a horizontal flow trench design. Both systems were found to have significant physical, chemical and biological gradients within the sub-surface profile. System age and plant root density appear to be important factors in determining profile differentiation within the experimental systems. Root densities were found to be partitioned between the upper and lower layers on a 70%/30% split, respectively. However, in the experimental systems as the systems aged and root densities increased beyond 112-251 g.m−2 chemical water quality differentiation in the profile disappeared. Pilot scale systems were found to have physical gradients within the profile as evidenced by hydraulic short-circuiting. Vertical root density distribution is proposed as a major cause of this condition in horizontal flow systems.