Pilot-scale Constructed Wetland System Research Articles

The efficacy of Vetiveria zizanioides in horizontal subsurface flow constructed wetland for treating textile wastewater

Textile wastewater discharged into rivers often triggers a decrease in water quality and causes harm to its aquatic ecosystem. Textile wastewater, which may contain nutrients, organic compounds, and heavy metals, can be managed using a constructed wetland system. Vetiver grass is known for its ability in treating polluted waters, though the information related to its potential in controlling textile wastewater pollution in riparian areas is still limited. This study aimed to determine the efficacy of a pilot scale constructed wetland system using vetiver grass (Vetiveria zizanioides) for the removal of several pollutants in a riparian area polluted by textile wastewater. The wastewater flowed horizontally through the sub-surface layer of the system with a hydraulic retention time of two days. The wastewater was diluted to 20%. Three systems were made by varying the porous size of planting media using coarse gravel, fine gravel, and sand. The systems were then run for three months. Of the three constructed wetland systems, the highest removal efficiency (RE) was achieved for the NH4 + parameter with an average removal efficiency higher than 60%. The highest nutrient RE was achieved by the system with sand in the growing media, with NH4 + RE of more than 80%. RE values were fluctuating until the end of the experiment, which might occur because the system was not yet stable. It may take longer operation time to get a better system performance in removing the pollutants contained in the textile industry waste.

The use of biochar and crushed mortar in treatment wetlands to enhance the removal of nutrients from sewage.

An experimental study was carried out using in pilot-scale constructed wetland systems, operated in parallel to treat raw sewage. Each system consisted of a vertical flow (VF) unit that was filled with biochar as the main media, followed by a horizontal flow (HF) unit filled with crushed cement mortar. Hydraulic loading (HL) ranged 340-680mm/day was applied on the VF wetland units, where high total nitrogen (TN) mass removal rate (20-23g N/m2d) was obtained, demonstrating that biochar media had a beneficial effect on the degradation of nitrogenous pollutants. Total phosphorus (TP) removal percentage (concentration based) was ≥ 86% in HF wetlands packed with mortar materials. In one system, the flow direction of the sewage was directed by the deployment of downflow pipes and vertical baffles, aiming to facilitate the formation of aerobic and anaerobic zones in the wetland matrices. The effects of such arrangement were analyzed by comparing pollutant removal efficiencies in the two systems. On average, 99, 96, 93, and 86 percentage removals were obtained for ammonia (NH4-N), TN, biochemical oxygen demand (BOD), and TP, respectively, during the experiments. Biochar and crushed mortar proved to be a highly effective combination as media in subsurface flow constructed wetlands for wastewater treatment.

Performance of a hybrid pilot-scale constructed wetland system for treating oil sands process-affected water from the Athabasca oil sands

Mining leases in the Athabasca oil sands (AOS; near Ft. McMurray, Canada) produce large volumes of oil sands process-affected water (OSPW) that contain potentially problematic constituents requiring treatment prior to surface water discharge into receiving aquatic systems. The aim of this research was to identify constituents of concern (COCs) in OSPW sourced from an AOS external tailings facility and design a hybrid pilot-scale constructed wetland treatment systems (CWTS) to decrease concentrations of COCs and subsequently mitigate risks. COCs were identified based on comparisons to ambient water quality thresholds for the protection of aquatic life (i.e. Canadian Environmental Quality Guidelines [CEQGs], Alberta Environment Water Quality Guidelines [Alberta WQGs], and United States Environmental Protection Agency Water Quality Criteria [USEPA WQC]) and toxicity endpoints. Performance of the hybrid pilot-scale CWTS was evaluated by rate and extent of COC removal and change in toxicity as measured by an aquatic invertebrate Ceriodaphnia dubia. Following characterization of OSPW, specific COCs were identified as: naphthenic acids (NAs), oil and grease (O/G), metals/metalloids (Al, B, Cu, Ni, Se, and Zn), chloride, and total suspended solids (TSS). A hybrid pilot-scale CWTS was designed to promote treatment processes to alter (transfer and transform) COCs using sequential reducing and oxidizing wetland reactors and a solar photocatalytic treatment reactor using fixed film titanium dioxide (TiO2). Performance criteria were achieved as the CWTS decreased concentrations of NAs, O/G, and metals below protective thresholds and decreased toxicity to C. dubia. Results from this study provide proof-of-concept data to inform hybrid passive or semi-passive treatment approaches (i.e. constructed wetlands) that could be used to mitigate COCs contained in OSPWs.

Assessment of Secondary Treatment Efficiency of Dairy Wastewater using Pilot Constructed Wetland with Hair Waste Modified Substrate

Background/Objectives: This work is conducted to study the secondary treatment efficiency of dairy wastewater using Constructed Wetland (CW) with keratin (hair) waste modified substrate. Methods/Statistical Analysis: A pilot Horizontal Sub-Surface Flow (HSSF) constructed wetland was built using HDPE plastic crates. Lemongrass ( Cymbsopoganflexuosus ) was planted in the constructed wetland system as the primary vegetation. Modification of substrate was done using keratin (hair) waste. Two dairy industries were considered based on the products manufactured. Batch feeding process with Hydraulic Retention Times of 24 h, 48 h and 72 h was adopted. Findings: The following parameters were analysed and studied; Bio-chemical Oxygen Demand, Chemical Oxygen Demand, Total Kjeldahl Nitrogen, Total Phosphorus and pH. The effect of varying Hydraulic Retention Times and modification of substrate by keratin waste were also studied. Results showed good removal efficiency of the pollutants by the pilot-scale constructed wetland system. Based on the analysis of the experimental trials, it was observe that the growth of Cymbopoganflexuosus had a positive impact on the removal efficiency of the pollutants considered. The modification of substrate by keratin waste also increased the removal efficiency of the pollutants. Proper stabilization of the CW system will have positive impact on the removal of TP by keratin waste modified substrate layer as the major removal of phosphorus is done by uptake from plant roots and even though if soil acts as an adsorbent and phosphorus having the tendency to be trapped on adsorbents, as hair is a good adsorbent. High BOD/COD ratio was also observed for the treated effluent. Application/Improvements: Modification of substrate by hair is not recommended for short hydraulic retention times as the compaction of modified substrate layer tends to restrict the movement of water resulting in lower flow rate.

Performance comparison of plant root biofilm, gravel attached biofilm and planktonic microbial populations, in phenol removal within a constructed wetland wastewater treatment system

This study was performed in order to understand the relative contribution of a constructed wetland (CW) system's various components to phenol degradation (100 mg∙L-1) under controlled plant biomass/gravel/ water experimental ratios. This was done by division of a pilot-scale CW system into its components, with or without their associated bacteria: (i) gravel, plant and water; (ii) gravel and water; (iii) water; (iv) gravel; (v) plant; (vi) control (sterile water). The highest phenol biodegradation rate occurred for the gravel-attached biofilm followed by root-attached biofilm and planktonic population, which recorded a similar rate to each other and a much lower rate than the gravel-attached biofilm. A control containing CW planktonic inactivated bacteria (autoclaved water) did not impact phenol removal, revealing that microbial populations are the major factor in phenol removal. The differences in the phenol removal achieved could be attributed to higher numbers of specific phenol degraders on the gravel surface, compared to lower numbers of root-attached and planktonic bacterial fractions, as isolated using phenol-agar plates which contained phenol as the sole carbon source. The main contributor to our findings appears to be the larger surface area provided by the gravel bed compared to plant roots.

Microbial population dynamics in response to bioaugmentation in a constructed wetland system under 10 °C

Compound microbial inocula were enriched and applied to a pilot-scale constructed wetland system to investigate their bioaugmentation effect on nitrogen removal under cold temperature (10°C). The results showed a 10% higher removal efficiency of ammonia and total nitrogen compared to a control (unbioaugmented) group. The microbial community structures before and after the bioaugmentation were analyzed through high throughput sequencing using Miseq Illumina platform. A variation of species richness and community equitability was observed in both systems. It is demonstrated that, based on the response of both the performance and microbial community, bioaugmentation using compound microbial inocula can fine tune the bacterial population and enhance the nitrogen removal efficiency of a constructed wetland system.

Municipal Wastewater Treatment with Phragmites australis L. and Typha latifolia L. for Irrigation Reuse. Boron and Heavy Metals

In this work, we compared the performance of Phragmites australis and Typha latifolia for depurating primary-treated urban wastewater and evaluated their suitability for irrigation reuse. Macrophytes were planted in two pilot-scale constructed wetland systems (CWs) and monitored during a 2-year experiment (2002–2003). CW efficiency was evaluated in terms of both mass removal and water quality considering boron (B) and the following heavy metals: aluminium (Al), arsenic (As), beryllium (Be) manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), selenium (Se) and vanadium (V). The accumulation of the elements, both in plant tissues and sandy substrate layer, and their offtake with the macrophyte harvest were also measured. In quantitative terms, the established CW systems showed high removal efficiency for Al (96 %), Cu (91 %), Pb (88 %) and Zn (85 %), while lower efficiencies were observed for Fe (44 %), Co (31 %) and B (40 %). The sediment played a strategic role in the adsorption and accumulation of wastewater pollutants, while plants acted as phytostabilizers since element root concentrations were generally from one to two orders of magnitude higher than those observed in the other parts. The results were less favourable in terms of water quality because the high evapotranspiration counteracted the depuration process by concentrating the elements in the outflow water. Outflow water contained more B (68 %), Mn (196 %) and, in the case of CW managed with Phragmites, also Fe (73 %) than inflow water, breaking the Italian guidelines for irrigation reuse. Integrating solutions to reduce the high evapotranspiration of CWs with more efficient pre-cleaning systems are necessary to obtain better removal efficiencies that reduce the effect of ET on water quality.

Effects of Simulated Oilfield Produced Water on Early Seedling Growth After Treatment in a Pilot-Scale Constructed Wetland System

Seed germination and early seedling growth bioassays were used to evaluate phytotoxicity of simulated oilfield produced water (OPW) before and after treatment in a subsurface-flow, pilot-scale constructed wetland treatment system (CWTS). Responses to untreated and treated OPW were compared among seven plant species, including three monocotyledons: corn (Zea mays), millet (Panicum miliaceum), and sorghum (Sorghum bicolor); and four dicotyledons: lettuce (Lactuca sativa), okra (Abelmoschus esculents), watermelon (Citrullus lanatus), and soybean (Glycine max). Phytotoxicity was greater in untreated OPW than in treated OPW. Exposures to untreated and treated OPW enhanced growth in some plant species (sorghum, millet, okra, and corn) relative to a negative control and reduced growth in other plant species (lettuce, soybean, and watermelon). Early seedling growth parameters indicated that dicotyledons were more sensitive to test waters compared to monocotyledons, suggesting that morphological differences between plant species affected phytotoxicity. Results indicated the following sensitivity scale for plant species: lettuce > soybean > watermelon > corn> okra≈millet >sorghum. Phytotoxicity of the treated OPW to lettuce and soybean, although concentrations of COCs were less than irrigation guideline concentrations, suggests that chemical characterization and comparison to guideline concentrations alone may not be sufficient to evaluate water for use in growing crops.

Treatment of oil and grease in produced water by a pilot-scale constructed wetland system using biogeochemical processes

Constructed wetland treatment systems (CWTSs) can effectively remove many constituents that limit beneficial use of oilfield produced water. The objectives of this investigation were: (1) to assess the effect of mass loadings of oil and grease (O & G) on treatment performance in pilot-scale subsurface flow and free water surface CWTS series having sequential reducing and oxidizing cells, and (2) to evaluate effects on treatment performance of adding a pilot-scale oil–water separator. Increase in O & G mass loading from 5 to 20mgmin−1 caused decreases in both dissolved oxygen concentration and sediment redox potential, which affected treatment performance. Biogeochemical pathways for removal of O & G, iron, and manganese operate under oxidizing conditions, and removal rate coefficients for these constituents decreased (0.905–0.514d−1 for O & G, 0.773–0.452d−1 for iron, and 0.970–0.518d−1 for manganese) because greater mass loading of O & G promoted reducing conditions. With increased mass loading, removal rate coefficients for nickel and zinc increased from 0.074 to 0.565d−1 and from 0.196 to 1.08d−1, respectively. Although the sequential reducing and oxidizing cells in the CWTS were very effective in treating the targeted constituents, an oil–water separator was added prior to wetland cells to enhance O & G removal at high inflow concentration (100mgL−1). The oil–water separator removed approximately 50% of the O & G, and removal extents and efficiencies approximated those observed at 50mgL−1 inflow concentration during treatment without an oil–water separator.

Treatment of ammonia in pilot-scale constructed wetland systems with clinoptilolite

Clinoptilolite was investigated as a sorptive medium for use in constructed wetland treatment systems (CWTSs) based on its affinity for ammonia and high surface area for attachment of periphytic biofilms. Results from a batch sorption experiment indicate that the clinoptilolite studied has an affinity for ammonia described by the Freundlich equation q=0.72Ce0.57 for equilibrium ammonia-N concentrations from 0.07 to 30.1mg/L. During a 10-day sampling period, a pilot-scale CWTS planted with Schoenoplectus californicus and containing 1000g clinoptilolite removed significantly more (p-value=8.8×10−3) ammonia-N (mean outflow 4.5mg/L, standard deviation=4.1) than a control system containing no clinoptilolite (mean outflow 8.6mg/L, standard deviation=2.7). Nitrification was detected in samples of clinoptilolite from the treated CWTS using nitrifying bacteria activity reaction tests (n-BARTs). Ammonia removal was not affected by addition of clinoptilolite to a pilot-scale CWTS planted with Typha latifolia, and nitrification activity was not detected in samples of clinoptilolite. These data illustrate that clinoptilolite can increase ammonia removal and nitrifying activity in CWTSs receiving ammonia concentrations equal to or greater than ∼6–10mg/L when conditions required to support nitrification including hydrosoil redox are provided.

Seasonal Performance of an Outdoor Constructed Wetland for Graywater Treatment in a Temperate Climate

The seasonal treatment efficiency of a pilot-scale constructed wetland system located outdoors in a semi-arid, temperate climate was evaluated for graywater in a comprehensive, 1-year study. The system consisted of two wetland beds in series--a free water surface bed followed by a subsurface flow bed. Water quality monitoring evaluated organics, solids, nutrients, microbials, and surfactants. The results showed that the wetland substantially reduced graywater constituents during fall, spring, and summer, including biochemical oxygen demand (BOD) (92%), total nitrogen (85%), total phosphorus (78%), total suspended solids (TSS) (73%), linear alkylbenzene sulfonate (LAS) surfactants (94%), and E. coli (1.7 orders of magnitude). Except for TSS, lower removals of graywater constituents were noted in winter--BOD (78%), total nitrogen (64%), total phosphorus (65%), LAS (87%), and E. coli (1.0 order), indicating that, although wetland treatment slowed during the winter, the system remained active, even when the average water temperature was 5.2 +/- 4.5 degrees C.

Biogeochemical process approach to the design and construction of a pilot-scale wetland treatment system for an oil field-produced water

Using a process-based approach, a pilot-scale constructed wetland system was designed and built for treating water produced from an oil field in sub-Saharan Africa. The characteristics of the oil field-produced water were compared with water quality guidelines for irrigating crops and watering livestock to identify constituents of concern (COC) requiring treatment. The COC identified in the produced water include oil, grease, and metals (Zn, Ni, Fe, Mn). A pilot-scale constructed wetland treatment system was then designed and built based on biogeochemical pathways (i.e., sorption, oxidation, and reduction) for transferring and transforming the identified COC to achieve target concentrations meeting water quality guidelines. The pilot-scale treatment system consisted of three series of wetland cells, with four cells in each series. Two series of subsurface flow wetland cells were constructed with each cell having a two-layer hydrosoil of pea gravel and medium-size gravel planted with Phragmites australis. In addition, a series of free water surface wetland cells was constructed, with each cell containing sandy hydrosoil and planted with Typha latifolia. The design allows adjustment of parameters (i.e., hydraulic retention time and organic content of the hydrosoil) to promote the conditions needed to achieve treatment of COC through the identified biogeochemical pathways. This study provides an example of the design and construction of a pilot-scale wetland treatment system using a process-based approach.

Performance of a pilot-scale constructed wetland system for treating simulated ash basin water

A pilot-scale constructed wetland treatment system (CWTS) was designed and built to decrease the concentration and toxicity of constituents of concern in ash basin water from coal-burning power plants. The CWTS was designed to promote the following treatment processes for metals and metalloids: precipitation as non-bioavailable sulfides, co-precipitation with iron oxyhydroxides, and adsorption onto iron oxides. Concentrations of Zn, Cr, Hg, As, and Se in simulated ash basin water were reduced by the CWTS to less than USEPA-recommended water quality criteria. The removal efficiency (defined as the percent concentration decrease from influent to effluent) was dependent on the influent concentration of the constituent, while the extent of removal (defined as the concentration of a constituent of concern in the CWTS effluent) was independent of the influent concentration. Results from toxicity experiments illustrated that the CWTS eliminated influent toxicity with regard to survival and reduced influent toxicity with regard to reproduction. Reduction in potential for scale formation and biofouling was achieved through treatment of the simulated ash basin water by the pilot-scale CWTS.

Characterization of microbial communities in a pilot-scale constructed wetland using PLFA and PCR-DGGE analyses

Phospholipid fatty acid (PLFA) analysis and 16S ribosomal DNA polymerase chain reaction amplification-denaturing gradient gel electrophoresis (PCR-DGGE) were used to determine microbial communities and predominant microbial populations in water samples collected from a pilot-scale constructed wetland system. This pilot-scale constructed wetland system consists of three types: subsurface-flow (SSF), surface-flow (SF) and a floating aquatic plant (FAP) system. Analysis of PLFA profiles indicated primarily eukaryotic organisms, including fungi, protozoa, and diatoms were observed in all three wetland systems. Biomarkers for Gram-negative bacteria were also detected in all samples analyzed while low proportions of biomarkers for Gram-positive bacteria were observed. Biomass content (total PFLA/sample) was highest in water samples collected from both SF and FAP system while highest metabolic activity was observed in FAP system. This is consistent with the observed highest metal removal rate in FAP system. Sequence analysis of the predominant PCR-DGGE DNA fragments showed 0.92 to 0.99 similarity indices to Beta-proteobacteria, Flavobacterium sp. GOBB3-206, Flexibacter-Cytophaga-Bacteroides group, and Gram-positive bacteria. Results suggest diverse microbial communities including microorganisms that may significantly contribute to biogeochemical elemental cycles.

Effect of plants and filter materials on bacteria removal in pilot-scale constructed wetlands

Due to the lack of testing units or appropriate experimental approaches, only little is known about the removal of bacteria in constructed wetlands. However, improved performance in terms of water sanitation requires a detailed understanding of the ongoing processes. Therefore, we analyzed the microbial diversity and the survival of Enterobacteriaceae in six pilot-scale constructed wetland systems treating domestic wastewater: two vertical sand filters, two vertical expanded clay filters and two horizontal sand filters (each planted and unplanted). Samples were taken from the in- and outflow, from the rhizosphere, and from the bulk soil at various depths. Colony-forming units of heterotrophic bacteria and coliforms were analyzed and the removal of bacteria between the in- and outflow was determined to within 1.5–2.5 orders of magnitude. To access the taxon-specific biodiversity of potential pathogens in the filters and to reduce the complexity of the analysis, specific primers for Enterobacteriaceae were developed. While performing PCR–SSCP analyses, a pronounced decrease in diversity from the inflow to the outflow of treated wastewater was observed. No differences were observed between the bulk soil of planted and unplanted vertical filters. Some bands appeared in the rhizosphere that were not present in the bulk soil, indicating the development of specific communities stimulated by the plants. The fingerprinting of the rhizosphere of plants grown on sand or expanded clay exhibited many differences, which show that different microbial communities exist depending on the soil type of the filters. The use of the taxon-specific primers enabled us to evaluate the fate of the Enterobacteriaceae entering the wetlands and to localize harboring in the rhizosphere. The most abundant bands of the profiles were sequenced: Pantoea agglomerans was found in nearly all samples from the soil but not in the effluent, whereas Citrobacter sp. could not be removed by the horizontal unplanted sand and vertical planted expanded clay filters. These results show that the community in wetland system is strongly influenced by the filtration process, the filter material and the plants.

Removal of N, P, BOD5, and Coliform in Pilot-Scale Constructed Wetland Systems

ABSTRACT Pilot-scale surface-flow (SF), subsurface-flow (SSF), and floating aquatic plant (FAP) constructed wetland system designs were installed and evaluated to determine the effectiveness of constructed wetlands to treat tertiary effluent wastewater in a Midwestern U.S. climate (central Illinois). Average ammonia-nitrogen (N) concentrations decreased approximately 50% in the SSF system design, suggesting that this design had the highest nitrification rate. Nitrate-N concentrations decreased by over 60% in the FAP system design, possibly due to dissimilatory reduction or plant uptake. Total phosphorus (P) concentration reductions of 25 to 40% were observed in all three system designs. Five-day biochemical oxygen demand (BOD5) and dissolved oxygen (DO) results suggested that biodegradation was highest in the SSF system design and lowest in the FAP system design. Greater than 90% concentration reductions of total coliform and E. coli recovered were also observed following treatment in all three system designs. The FAP system design appeared to yield the highest concentration reduction efficiency for E. coli, possibly due to increased sunlight and related bacteriocidal ultraviolet light exposure. Ongoing experiments will test regularly for a variety of vegetative, water quality, and biological conditions for longer time periods in order to gain a better understanding of the pilot constructed wetland system design kinetics.

Phosphate and ammonium distribution in a pilot-scale constructed wetland with horizontal subsurface flow using shale as a substrate

Phosphate (P) and ammonium (N) distributions were investigated in a pilot-scale constructed wetland system (CWS) with horizontal flow. Shale was selected as a substrate, on the basis of its P adsorption capacity as well as its suitability for plant growth, investigated in an earlier study. The system was set up in a greenhouse, and comprised of four tanks with and four tanks without Phragmites australis (common reed). Sampling ports were installed along the length of each tank, and at three different depths, in order to facilitate three-dimensional monitoring of nutrient distribution over the period of study (11 months). In the planted systems, H 2PO − 4-P (ortho-P) and NH + 4-N concentrations were low (0.5–1.0 g m −3) at all depths throughout their length. Generally, ortho-P and NH + 4-N concentrations decreased exponentially along the transect from the tank inlet to the outlet. In the unplanted systems, higher values (0.5–16.5 g m −3) of ortho-P were observed. NH + 4-N in the unplanted systems was relatively high (10–30 g m −3) throughout the period of investigation. In both planted and unplanted tanks, NO − 3-N concentrations were very low at the inlets (0.02–0.05 g m −3), and increased only slightly towards the outlets. Although the presence of P. australis had a significant effect ( p<0.05) on P and N concentrations at all depths and along the length of the tanks, the nutrient distribution followed the same trend as in unplanted tanks. The results were consistent with the theoretical removal model which predicts an exponential decrease in pollutant concentrations to a background value approaching zero along the transect from wetland inlet to the outlet. A modification of the model was suggested where a first order area-based reduction rate constant k (m d −1) would be replaced with ( k p+ k s), k p representing the rate constant for the removal by the plants, and k s the rate constant for the removal by the substrate, and associated microbial populations they support. Approximate values for k p+ k s of 0.084 m d −1 (P) and 0.065 m d −1 (N) and for k ṡ of 0.069 m d −1 (P) and 0.034 m d −1 (N) were obtained. The hydraulic residence time, flow characteristics and permeability of the shale was investigated by a bromide (Br −) tracer. The tracer breakthrough curves showed a similar pattern in all tanks, with about 66% of the flow occurring through the bottom zone (0.35 m). The actual hydraulic residence time (6 days) was slightly higher than the nominal one. The tracer study also enabled the calculation of the volumetric rate constants, k ν and approximate values of 0.075 d −1(P) and 0.060 d −1(N) were obtained for planted and 0.061 d −1(P) and 0.020 d −1(N) for unplanted tanks. The results obtained from this pilot scale study, provide a better understanding of nutrient distribution and flow patterns that take place within CWS, and should enable more rational design parameters to be developed that help to optimise future large-scale systems.