Pilot-scale Horizontal Subsurface Flow Research Articles

Treatment of Slaughterhouse Wastewater through a Series System: Upflow Anaerobic Reactor and Artificial Wetland

Slaughterhouse wastewater is characterized by high concentrations of organic matter. This creates a need to explore methods for its treatment before discharge. This study evaluated the efficiency of an integrated treatment process consisting of a laboratory-scale upflow anaerobic sludge blanket reactor and a pilot-scale horizontal subsurface flow wetland. This treatment was used for (i) the removal of organic matter through anaerobic–aerobic microbiological processes, (ii) the conversion of organic matter from hydraulic processes, and (iii) for bioremediation and phytoremediation. The treatment system was evaluated at hydraulic retention times (HRTs) of 7.5, 5.0, and 2.5 d; during the investigation, the influence of the HRTs on the removal efficiency of the system was evaluated. High efficiencies of 85% and 75% were obtained for CODT and BOD, respectively, at an HRT of 7.5 d. The highest overall efficiency for the removal of total solids was observed at an HRT of 2.5 d. The results obtained confirm the feasibility of implementing the suggested system as an alternative for the adequate and sustainable treatment of slaughterhouse wastewater, and the system can be applied to slaughterhouses with similar conditions to those in this study.

Environmental performance of constructed wetland planted with monocultures and polycultures for wastewater treatment

The effects of culture systems and seasonality on the environmental impact of constructed wetlands (CWs) remain understudied. This study aims to quantify the environmental impact of common and ornamental plants in a pilot-scale horizontal subsurface flow (HSSF) CW planted with monocultures and a polyculture. Eight scenarios were evaluated, differentiated by plant type, culture system, and season (warm season, cold season). Environmental performance was evaluated using the life cycle assessment (LCA) methodology. The environmental impact index (ƐP), based on eutrophication reduction (kgP removed), and net environmental benefit (NEB) indicators were also calculated. The results showed that a CW planted with polycultures reduced FE by 5–17% compared to those planted in monocultures. However, the polyculture had the highest environmental impact in the GW category, up to 1.5–9 times higher than that of monocultures. Furthermore, there was better performance in the cold season in all scenarios. Specifically, NEB showed an environmental benefit for freshwater eutrophication and a negative benefit for global warming. The ƐP indicator was inversely proportional to the elimination of phosphorus, with the polyculture CW reaching the highest values of 3399 kgCO2eq/kgP removed in the warm season. The assessment of environmental impact patterns could support the development of strategies for better environmental performance of CWs, with polycultures used as an alternative wastewater treatment.

Removal of Two Triazole Fungicides from Agricultural Wastewater in Pilot-Scale Horizontal Subsurface Flow Constructed Wetlands

Myclobutanil is a systemic fungicide belonging to the triazole group, which is frequently detected in environmental samples. Triticonazole, also a triazole fungicide, controls soil and seed-borne diseases and it is mainly used as a seed-coating pesticide. Both myclobutanil and triticonazole are considered as persistent pollutants in the environment, raising concerns about their environmental fate and ecotoxicity potential. The purpose of the present study was to investigate the efficiency of four pilot-scale horizontal subsurface flow (HSF) constructed wetlands (CWs) to remediate myclobutanil and triticonazole from artificially polluted water. Daily loading of the four CWs took place from March 2022 to July 2022 with contaminated water fortified with myclobutanil and triticonazole. Three of the CWs, encoded WMG-R, WMG-C, and WMG-U, with medium gravel (MG) as porous media and the fourth, with code name WFG-R, fine gravel (FG). Common reed (R, Phragmites australis) was planted in the WMG-R and WFG-R units, and cattail (C, Typha latifolia) in the WMG-C unit. The WMG-U unit with no plant was used as a control unit. The results showed that the removal rate follows the pattern: WFG-R (88.4%) > WMG-R > (83.4%) > WMG-C (59.3%) > WMG-U (36.6%) and WFG-R (88.5%) > WMG-C (71.0%) > WMG-R > (70.9%) > WMG-U (49.2%) for myclobutanil and triticonazole, respectively. The most significant factors influencing the fungicides’ dissipation were the porous media content and the plant species.

Phosphorus uptake by macrophyte plants in monocultures and polycultures in constructed wetlands for wastewater treatment

Phosphorus uptake by common and ornamental plants was studied in pilot-scale horizontal subsurface flow (HSSF) constructed wetlands (CWs) with monocultures and polycultures. Three HSSF CWs were planted with monocultures of Phragmites australis (HSSF-Phr), Schoenoplectus californicus (HSSF-Sch) and Cyperus papyrus (HSSF-Cyp), and one polyculture was planted with C. papyrus and Zantedeschia aethiopica (HSSF-Cyp/Zant). During the experimental period, removal efficiency, growth characteristics, biomass production and phosphorus uptake were evaluated in the cold season (fall/winter) and warm season (spring/summer). In general, the cold season showed better performance with an order of HSSF-Cyp/Zant > HSSF-Cyp > HSSF-Sch > HSSF-Phr in the evaluated parameters. The removal efficiencies were 33%, 27%, 23% and 12%, respectively. The biomass production and density of the HSSF treatments ranged from 1.5 to 5.4 kg dry weight (DW)/m2, and 435 to 1298 individuals/m2 with higher values for HSSF-Sch. The tissue phosphorus content was 5 to 20% higher belowground in all plants, including ornamentals. Phosphorus uptake was higher for polyculture (HSSF-Cyp/Zant) and monoculture (HSSF-Cyp) planted with ornamentals, with a mean of 30 g P/m2. Also, the polyculture was not affected by the seasons, reaching up to 27% phosphorus uptake by the plants. According to our results, the ornamental species of the polyculture contribute to the phosphorus uptake.

Pyraclostrobin Removal in Pilot-Scale Horizontal Subsurface Flow Constructed Wetlands and in Porous Media Filters

Pyraclostrobin is a fungicide extensively used for the control of various fungal diseases and is frequently detected in environmental samples. Natural systems, such as constructed wetlands (CWs) and gravity filters, are effective and environmentally friendly treatment systems, which can reduce or eliminate pesticides from the environment. The aim of this study was to investigate the capacity of two pilot-scale CWs (porous media: cobbles and fine gravel, planted with Phragmites australis) and six gravity filters (filling material: bauxite, carbonate gravel and zeolite) to remove pyraclostrobin from polluted water originating from spraying equipment rinsing sites. For this, experiments were conducted to test the performance of the above natural systems in removing this fungicide. The results showed that the mean percent pyraclostrobin removal efficiencies for cobbles and fine gravel CW units were 56.7% and 75.2%, respectively, and the mean percent removals for HRTs of 6 and 8 days were 68.7% and 62.8%, respectively. The mean removal efficiencies for the bauxite, carbonate gravel and zeolite filter units were 32.5%, 36.7% and 61.2%, respectively, and the mean percent removals for HRTs 2, 4 and 8 days were 39.9%, 43.4% and 44.1%, respectively. Regarding the feeding strategy, the mean removal values of pyraclostrobin in gravity filter units were 43.44% and 40.80% for continuous and batch feeding, respectively. Thus, these systems can be used in rural areas for the treatment of spraying equipment rinsing water.

Effect of HRT and seasons on the performance of pilot-scale horizontal subsurface flow constructed wetland to treat rural wastewater

Abstract To find the effect of Hydraulic Retention Time (HRT) and seasons on the performance of horizontal subsurface flow constructed wetland (HSSF CW) in treating rural wastewater, a pilot scale unit 2.5 m × 0.4 m × 0.3 m size bed planted with Typha latifolia and Phragmites australis was operated for a 12-month duration. During the study 2, 4, 6, 8, and 10 days of HRT were maintained in winter, summer, and rainy seasons. The removal efficiency obtained ranged from 62.09 to 87.23% for Chemical Oxygen Demand, 69.58% to 93.32% for Biochemical Oxygen Demand5 (BOD), 31.55% to 59.89% for Ammonia Nitrogen (NH4-N), 15.18% to 52.90% for Total Kjeldahl Nitrogen (TKN), 21.02% to 50.21% for Phosphate Phosphorus (PO43− P), 19.82% to 48.23% for Total phosphorus (TP), 74.93% to 93.10% for Faecal Coliform (FC) and 69.93% to 90.23% Total Coliform (TC). Overall, results showed that the performance of the unit was good. For statistical analysis two way ANOVA test followed by Tukey's test was used with a 95% level of significance. It was observed that the removal efficiency of the pollutants was increased with an increase in HRT. HRT of 6 days was found as adequate for significant removal of organic matter (COD and BOD). Seasonal removal efficiencies followed the order of summer > rainy > winter for all the parameters, but the difference was not statistically significant.

Microbial activity enhancement in constructed wetlands operated as bioelectrochemical systems

Treatment wetlands (TW) operated as bioelectrochemical systems (BES-TW) provide a higher degree of treatment than conventional TW. Yet, the fundamental processes or mechanisms for the envisaged better performance of BES-TW over conventional TW remains poorly understood. This work aimed to determine to which extent microbial activity enhancement could be the reason behind this treatment performance increase. To this purpose, pilot-scale horizontal sub-surface flow BES-TW operated under three different configurations were continuously fed with real urban wastewater. BES-TW were evaluated for COD and ammonia removal efficiency, and two techniques of microbial activity assessment were applied. Configurations, tested in duplicate, were: control TWs without electrodes (C-TW), TWs operated as microbial fuel cells (MFC-TW), and TWs operated as microbial electrolysis cells (MEC-TW). Microbial activity was assessed by measuring the enzymatic activity (EA) (FDA hydrolysis technique) and the aerobic activity (AA) (estimated through respirometry). Results showed that BES-TW outperformed C-TW in terms of both microbial activity enhancement and contaminants removal efficiency, especially in the case of MEC-TW. More precisely, this configuration showed an average improvement of 17%, and 56% in COD removal and EA efficiencies, respectively, compared to C-TW. Regarding AA activity, although MEC-TW seemed to outperform the rest of the configurations, differences were not statistically significant. This work demonstrates that TWs operated as BES increase the overall enzymatic activity of the treatment bed and this, in turn, is the leading cause to a higher degree of treatment performance.

Performance of a Pilot-Scale Constructed Wetland and Medium-Term Effects of Treated Wastewater Irrigation of Arundo donax L. on Soil and Plant Parameters

On marginal lands in the Mediterranean basin, giant reed (Arundo donax L.) represents one of the most interesting perennial crops due to high levels of biomass production. Considering periodic water shortage during the summer months in this area, the reuse of treated wastewater (TWW) would seem to be a good opportunity for the growth of the species. The aim of this study was to assess the medium-term effects of irrigation using freshwater (FW) and TWW on soil characteristics and growth in giant reed plants. TWW was obtained from a pilot-scale horizontal subsurface flow constructed wetland system (HSSF CWs) with a total surface area of 100 m2. A split-plot design for a two-factor experiment was used with three replications. Medium-term TWW irrigation increased organic matter and plant nutrients in the soil; however, pH was not affected. Plants irrigated with TWW showed greater growth (+10.49% in height, +12.75% in stem diameter, +11.51% in above-ground biomass) than those irrigated with FW. The higher heating value of crop residues ranged between 16.83 (FW-irrigated plants) and 17.00 MJ kg−1 (TWW-irrigated plants). Results show that HSSF CWs produces TWW, which can be an alternative source of water for growing giant reed with high biomass performance.

Treatment of Combined Dairy and Domestic Wastewater with Constructed Wetland System in Sicily (Italy). Pollutant Removal Efficiency and Effect of Vegetation

Dairy wastewater (DWW) contains large amounts of mineral and organic compounds, which can accumulate in soil and water causing serious environmental pollution. A constructed wetland (CW) is a sustainable technology for the treatment of DWW in small-medium sized farms. This paper reports a two-year study on the performance of a pilot-scale horizontal subsurface flow system for DWW treatment in Sicily (Italy). The CW system covered a total surface area of 100 m2 and treated approximately 6 m3 per day of wastewater produced by a small dairy farm, subsequent to biological treatment. Removal efficiency (RE) of the system was calculated. The biomass production of two emergent macrophytes was determined and the effect of plant growth on organic pollutant RE was recorded. All DWW parameters showed significant differences between inlet and outlet. For BOD5 and COD, RE values were 76.00% and 62.00%, respectively. RE for total nitrogen (50.70%) was lower than that of organic compounds. RE levels of microbiological parameters were found to be higher than 80.00%. Giant reed produced greater biomass than umbrella sedge. A seasonal variation in RE of organic pollutants was recorded due to plant growth rate Our findings highlight the efficient use of a CW system for DWW treatment in dairy-cattle farms.

Post treatment of anaerobically treated brewery effluent using pilot scale horizontal subsurface flow constructed wetland system

The anaerobic process is considered to be a sustainable technology for the treatment of wastewaters rich in organic matter mainly due to its lower energy consumption and production of value-added products such as biogas and organic fertilizer. However, it cannot be seen as providing ‘complete’ environmental solution as its treated effluents would typically not meet the desired discharge limits in terms of residual carbon, nutrients and other pollutants. This has given impetus to subsequent post treatment in order to meet the environmental standards and protect the receiving water bodies and environment. The aim of this study was to evaluate the post-treatment potential of a pilot scale two-stage horizontal subsurface flow constructed wetland (HSSFCW) system planted with Cyperus alternifolius and Typha latifolia, respectively, for enhanced removal of residual carbon and nutrient from an up-flow anaerobic sludge blanket (UASB) reactor treated brewery effluent. A pilot scale two-stage HSSFCW was integrated with the UASB reactor, and its performance efficiency was assessed for the removal of total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), ammonium–nitrogen (NH4–N), total phosphorous (TP), and orthophosphate (PO43−). Macrophytes aboveground biomass and nutrient accumulation potential were also determined following standard methods. The results from this study showed that Cyperus alternifolius planted CW cell removed 68.5% TSS, 74.2% COD, 55.7% TN, 68.6% NH4–N, 41.1% TP and 48.1% PO43−. Moreover, further polishing with Typha latifolia planted CW cell enhanced the removal efficiencies to 89% TSS, 92% COD, 83.6% TN, 92.9% NH4–N, 74.4% TP, and 79.5% PO43−. Strong linearity and Pearson correlation was found between macrophyte biomass and nutrient accumulation in each CW cell (Cyperus alternifolius: R2 = 0.91, r = 0.97 for TN; R2 = 0.92, r = 0.96 for TP; and Typha latifolia: R2 = 0.96, r = 0.98 for TN and TP), and showed substantial nutrient reduction with cumulative nutrient accumulation of 1290 gTNm−2 and 708.7 gTPm−2 in the complete system. The performance of the pilot CW system as a tertiary treatment for brewery wastewater showed that the effluent meets the permissible discharge standards throughout the year excluding phosphorous.

Advanced Treatment of Tail Water Using Pilot-scale Horizontal and Vertical Subsurface Flow Constructed Wetlands in Low-temperature Seasons

There were significant differences in the working efficiency and mechanism of constructed wetlands between low temperature and suitable temperature conditions. This study designed a horizontal subsurface flow constructed wetland (HFCW) and a vertical subsurface flow constructed wetland (VFCW) to explore their performance differences in advanced treatment of sewage based on contaminant degradation analysis including the removal of organic matters, total nitrogen (TN), and total phosphorus (TP), as well as the analysis of microbial community structure. The results showed that when the COD concentration of influent was between 37.50 to 80.00 mg·L-1, the concentration of total nitrogen and total phosphorus were within the first level A criteria specified in the discharge standard of pollutants for municipal wastewater treatment plant at the continuous flow of 2 m3·d-1:①Both HFCW and VFCW showed stable degradation ability of organic matter in influent and good resistance to high organic load. ②Supplementation of the carbon source significantly improved the nitrogen removal efficiency of two subsurface flow constructed wetlands. HFCW achieved the average removal rate of TN at 76.01%, and the average removal rate of TN by VFCW reached 71.69% after the carbon addition. In contrast, dosage of an external carbon source showed limited effect on phosphorus removal. Furthermore, it worked more effectively for performance improvement of HFCW than that of VFCW. ③The analysis of microbial community structure in wetland substrate and plant rhizosphere samples revealed that Proteobacteria, Firmicutes, and Verrucomicrobia were the dominant phylum in two series of wetland samples. For the dominant microbiota at the genus level, there were more significant differences in microbial community structure in wetland substrate samples than that in plant rhizosphere samples. Hydrogenophaga, Erysipelothrix, and Devosia contributed the most to the differences between the microbial communities of HFCW and VFCW. Overall, the species diversity and abundance of microbial samples from VFCW was higher than those from HFCW.

Effects of Irrigation with Different Sources of Water on Growth, Yield and Essential Oil Compounds in Oregano.

Aromatic plants can benefit from the use of treated wastewater to satisfy their water requirements, but the effects on the essential oil yield and quality need an assessment. The aims of this study were to assess the effects of freshwater and treated wastewater obtained from a Sicilian (Italy) pilot-scale horizontal subsurface flow constructed wetland system on plant growth and yield, essential oil yield and composition of oregano (Origanum vulgare ssp. hirtum (Link) Ietswaart) and soil characteristics. The system had a total surface area of 100 m2 and was planted with giant reed and umbrella sedge. An experimental open field of oregano was set up close to the system. Two years and two different sources of irrigation water were tested in a split-plot design for a two-factor experiment. Treated wastewater was characterized by higher values of mineral and organic constituents than freshwater. The results highlight that short-term irrigation with freshwater and treated wastewater, in both years, led to increased plant growth, dry weight and essential oil yield of oregano plants. However, it did not significantly affect the essential oil content and composition in comparison with the control. Furthermore, the year and source of irrigation water did not significantly vary the chemical composition of the soil. Our results suggest that treated wastewater can be considered an alternative to freshwater for the cultivation of oregano due to the fact that it does not greatly influence the yield quality and quantity of this species in the short-term.

The Nutrient Removal Ability and Microbial Communities in a Pilot-Scale Horizontal Subsurface Flow Constructed Wetland Fed by Slightly Polluted Lake Water

A pilot-scale horizontal subsurface flow constructed wetland (HFCW) was established to investigate the feasibility of removing nutrients from natural water in Lake Xijiu, Jiangsu Province, China. The HFCW, planted with reeds (Phragmites communis) and irises (Iris tectorum Maxim), was operated for 227 days. The mean removal efficiency of NH4+-N was 36.7%, of total nitrogen (TN) 70.2%, of total phosphorus 75.3%, of permanganate index (CODMn) 35.8%, and of Chlorophyll a 70.0%. The effluent concentrations of these pollutants were all within the Grade III threshold of China’s water quality standards for surface water. Correlation analysis showed that TN removal was related to the CODMn concentration in the influent (r2 = 0.65) and was closely related to the temperature (r2 = 0.91). The HFCW had a water production efficiency of 98%–99% over the entire operational period, which suggests that it did not block easily. Results from 16S rDNA high-throughput sequencing showed that Proteobacteria (40.65%) dominated at the phylum level. At the genus level, the relative abundance of Nitrosomonadaceae (3.57%) was highest in autumn and the spatial distribution from the front to the back varied slightly from 2.57% to 2.99%. Our results will help researchers to develop optimal designs for HFCW systems to treat slightly polluted water.

Horizontal subsurface flow constructed wetland for tertiary treatment of dairy wastewater: Removal efficiencies and plant uptake

There are different physicochemical and biological methods to treat effluents. However, their efficiency is not enough to meet the effluents discharge limits. For this reason, it could be possible to employ a polished treatment. A suitable alternative for this goal could be constructed wetlands (CWs). The aim of the present research was to evaluate contaminants removal efficiency of a pilot scale horizontal subsurface flow constructed wetland (HSSFW) for tertiary treatment of dairy wastewater. A vegetation study was also conducted in order to determine the role of plants on nutrient removal. A pilot scale HSSFW planted with Typha domingensis was built in a dairy factory, after the biological treatment. The substrate used was river gravel. During a seven-month research period, thirty-two samples (influent and effluent) were taken and analyzed to determine physicochemical and microbiological parameters as well as removal efficiencies. Biomass, TP, TKN and organic matter content in plants was determined at the beginning and end of the monitoring period. Suspended solids showed significant differences between inlet and outlet, with a mean removal efficiency of 78.4%. For BOD and COD, mean removal efficiencies were respectively 57.9 and 68.7%. Removal percentages for TKN, Nitrates and TP were lower than other parameters (25.7%, 47.8% and 29.9%, respectively). Fecal Coliform bacteria decreased one order of magnitude in final effluent. In the case of Escherichia coli and Pseudomona aeruginosa results were variable. Total biomass increased 4.6 times at the end of the monitoring period. The study of plants indicated its important contribution in terms of contaminant uptake and retention. HSSFW would be an advisable alternative as a tertiary treatment of dairy wastewater.

Effects of treated greywater irrigation regimes and mulches on yield of Capsicum chinense under surface drip irrigation system

A field study was conducted to determine the effects of combine treatment of greywater application rates and mulches types on growth and yield of Capsicum chinense in Omu-Aran, Nigeria. Greywater (GW) was treated using a pilot-scale horizontal sub-surface flow constructed wetlands (HSSF CW) vegetated with Canna indica plants. Four irrigation levels (60, 80, 100 and 120% of ETc) and four mulches types (Black plastic film BM, Silver plastic film SM, Rice straw RS and un-mulched Control) were applied to the potted plants. The experiment was laid out in a split-plot design, with main plots as irrigation levels and mulches types as sub-plots. C. indica plants were found to be effective in GW Phytoremediation treatment in CW. The maximum fruit yield was observed for T10 (I100SM) 4666.70 kg/ha due to reflective mulch ability to increase light and heat to plant resulting to a higher yield. Significant difference was observed between the mean yield of I60 and other irrigation regimes, whereas between I80 to I120 there was no significant difference in mean yield recorded. Silver mulch combined with full irrigation with treated greywater effluent was found to be the best of all treatments in the study.

Performance of pilot-scale horizontal subsurface flow constructed wetland coupled with a microbial fuel cell for treating wastewater

This work presents a new hybrid technology for treating wastewater along with electricity generation. The main objective of this work was to integrate a microbial fuel cell (MFC) into a horizontal subsurface constructed wetland (HSSF-CW-MFC) at a pilot scale for improving the wastewater treatment performance of HSSF-CW. The HSSF-CW-MFC was tested on three different organic loading rates: 0.15, 0.30, and 0.52 kg COD/m3/d at a set hydraulic retention time. The HSSF-CW-MFC was further studied for establishing the influence of electron transfer using conductive material (artificial electron acceptor) on wastewater treatment performance. During the efficient electron transfer (system run in closed-circuit operation), 33.7% higher chemical oxygen demand (COD) removal was achieved in comparison to the hindered electron transfer (system run in open circuit) condition. The results illustrate that efficient electron transfer from bottom anaerobic zones to the aerobic zone of the HSSF-CW helps in enhancing the treatment performance. The maximum power and current densities achieved were 11.67 mW/m3and 17.15 mA/m3, respectively.

Performance of horizontal sub-surface flow constructed wetlands with different flow patterns using dual media for low-strength municipal wastewater: a case of pilot scale experiment in a tropical climate region

The work presented in this paper is based on the pilot study that was performed to investigate the role of flow pattern in the constructed wetlands (CWs) on the treatment performance of real low-strength municipal wastewater. Four identical pilot-scale horizontal sub-surface flow constructed wetlands (HSSF-CWs) were installed, out of which three beds were planted with a common macrophyte, whereas one was kept as a control. The distinction in the hydraulic design was baffles, vertical up-down (CW2) and side slits (CW3), and the third bed (CW1) was kept horizontal plain type (without baffles). The filter media used in all the beds was dual type, coarse and fine gravel. Monitoring was carried out to determine BOD5, COD, TSS, NH4+-N, TN, and TP concentrations at different sampling points. Results show that the baffled beds performed better compared to the non-baffled in the order of CW2 > CW3 > CW1 > Control. The highest removal efficiency was measured in the CW2 with a reduction in BOD5 (86%), COD (77%), TSS (80%), NH4+-N (59%), TN (66%), and TP (64%). The statistical method used also showed that the flow pattern has an impact on the treatment performances of the CWs.

Investigation of pilot-scale constructed wetlands treating simulated pre-treated tannery wastewater under tropical climate

Tannery wastewater is characterized by high and variable concentrations of diverse pollutants, which makes it difficult and costly to treat. In the search for sustainable treatment options for tannery effluents, two pilot-scale horizontal subsurface flow (HSF) constructed wetlands (CW) were built and operated for the treatment of synthetic water of quality similar to that of pre-treated tannery effluents. Five different loading phases were examined with gradual increase of inflow COD, NH4+-N and Cr loads until reaching and exceeding the typical composition of a tannery effluent. High COD and NH4+-N removals were observed (82 and 96%, respectively), and almost complete Cr removal in the outflow, which met the Venezuela national standards for environmental discharge. Plant uptake was measured, but microbial processes appear to be the main ammonium transformation/removal mechanism. Nitrogen, chlorophyll and Cr in the plant aerial parts and roots indicated the capacity of Phragmites sp. to grow and survive even under high loads. The measured heterotrophic bacteria in the substrate and rhizomes indicated the biofilm development and the oxidation of organic matter and nitrogen. Water losses via evapotraspiration were also measured and reached 14%. Overall, the tested CW design proved to be a sustainable and feasible alternative for the treatment of tannery wastewater in tropical climates.

Purification of water contaminated with Hg using horizontal subsurface constructed wetlands.

As a global pollutant, Hg (Hg) since the turn of the last century has received increased attention. Decreasing the emission of Hg into the food chain and the atmosphere is an effective way to reduce the Hg damage. The current study provided information about pilot-scale horizontal subsurface flow (HSSF) constructed wetlands (CWs) to remove different Hg species in polluted water. Synthetic wastewater was fed to two HSSF CWs, one was planted with Acorus calamus L and the other was unplanted as a control. The total Hg (THg), dissolved Hg (DHg), and particulate Hg (PHg) from five sites along the HSSF CWs were analyzed to describe the process of Hg removal. Results show that the CWs have high removal efficiency of Hg which is more than 90%. The removal efficiencies of THg and DHg from the unplanted CW were 92.1 ± 3.6% and 72.4 ± 13.1%, respectively. While, the removal efficiencies of THg and DHg in planted CW were 95.9 ± 7.5% and 94.9 ± 4.9%, which were higher than that in blank CW. The PHg was mainly removed in the first quarter of the CWs, which was also revealed by the partition coefficient Kd. To a certain extent, the effect of plants depends on the hydraulic retention time (HRT). The results in the current study show the potential of the HSSF-CWs for restoration from Hg-contaminated water.

Efficiency of pilot-scale horizontal subsurface flow constructed wetlands and microbial community composition operating under tropical conditions

This study assesses the microbial diversity of Thalia geniculate (L.) and Cyperus articulates (L.) in the rhizosphere in planted and unplanted systems with respect to removal efficiency in an experimental horizontal sub-surface constructed wetland pilot plant. The pilot-scale units consisted of six (6) cells of concrete of 0.94 × 0.6 × 0.4 m arranged in a parallel configuration. 29 L d−1 were distributed to the cells by gravity. The hydraulic retention time was 3 days and influent and effluent measurements of COD and nutrients were monitored with standard methodology. Bacteria samples were isolated from the roots of plants and gravel in selective media and incubated at 37 °C. Isolates were biochemically characterized and genotyped with group-specific primers. Results showed that systems planted with T. geniculata removed greater proportions of COD (82%), NH4+–N (83%) and PO42–P (83%) than C. articulatus (85, 74 and 72%, respectively) and unplanted wetland systems (80, 72 and 66%, respectively). Bacterial typing revealed several phyla were most abundant, α-Proteobacteria followed by β-Proteobacteria and there was a significant difference (p < 0.05) in CFU between planted and unplanted treatments. The bacterial community varied with respect to plant species or unplanted and demonstrated significant effects to contaminants removal efficiency.