Vertical Subsurface Flow Constructed Wetlands Research Articles

The critical role of microplastics in the fate and transformation of sulfamethoxazole and antibiotic resistance genes within vertical subsurface-flow constructed wetlands

Constructed wetlands (CWs) are reservoirs of microplastics (MPs) in the environment. However, knowledge about the impact of MPs on antibiotic removal and the fate of antibiotic resistance genes (ARGs) is limited. We focused on sulfamethoxazole (SMX) as a representative compound to examine the effects of MPs on SMX removal and the proliferation and dissemination of two SMX-related ARGs (sul1 and sul2) in vertical subsurface-flow CW (VFCW) microcosm. The presence of MPs in the substrate was found to enhance the proliferation of microorganisms owing to the large specific surface area of the MPs and the release of dissolved organic carbon (DOC) on MP surfaces, which resulted in a high SMX removal ranging from 97.80 % to 99.80 %. However, the presence of MPs promoted microbial interactions and the horizontal gene transfer (HGT) of ARGs, which led to a significant increase in the abundances of sul1 and sul2 of 68.47 % and 17.20 %, respectively. It is thus imperative to implement rigorous monitoring strategies for MPs to mitigate their potential ecological hazards.

Effect of varying retention times and feeding schemes on the performance of vertical constructed wetlands planted with vetiver grass in treating dairy wastewater in the Philippines

AbstractAdequate wastewater treatment from the dairy industry before disposal is still lacking in the Philippines, particularly in small‐scale sectors. This limitation is due to the high cost and expertise required from conventional wastewater treatment systems. One option is using constructed wetlands, a nature‐based solution with low cost, less specialized expertise and maintenance requirements and high wastewater treatment efficiency. To further evaluate the application of constructed wetlands in the Philippines, this paper studied the wastewater from the manufacturing processes of the Dairy Training Research Institute, University of the Philippines Los Baños (DTRI‐UPLB). It is a small dairy farm inside the University with economic constraints in using a conventional wastewater treatment system. The main aim of this study is to determine the effect of using vertical subsurface flow constructed wetlands (VSSFCW) planted with Vetiver grass (Chrysopogon zizanioides) in sand and gravel media to treat the DTRI‐UPLB effluent, using very low retention times (4 and 8 h), with daily and alternate days of wastewater feeding into the VSSFCW. The average removal efficiencies for total suspended solids (TSS), biological oxygen demand for (BOD5), total phosphorus (TP), and Total Kjeldahl Nitrogen (TKN) are 88.34%, 93.56%, 78.42%, and 94.63%, respectively. Moreover, alternate wastewater feeding provided a statistically significant increase in the performance of VSSFCW, while there is no statistical difference between the two retention times evaluated. Finally, it was observed that plant age significantly affects the performance of VSSFCW setup but should be explored further with longer operation times and additional nutrient uptake analysis.

The Vertical Subsurface Flow Constructed Wetland (VSSFCW) Performance Using Typha angustifolia and Ipomoea aquatica for Tofu Wastewater BOD and COD Removal

Tofu is one of the most popular foods in Indonesia. in the production process, it produces quite a high BOD and COD which are around 5.000-10.000 mg/L and 7.000-14.000 mg/L in liquid waste effluent. Tofu wastewater effluent that exceeds the quality standard of soybean processing industry wastewater into river waters without prior treatment and reduction can certainly cause environmental damage. On the other hand, tofu wastewater made from soybeans with high nutritional content has the potential for sustainable use. Therefore, an effective, and sustainable wastewater treatment process to minimize environmental damage and increase the circular economy is needed. In situ wastewater treatment utilizing an equalization tank and a wetland with a Vertical Subsurface Flow Constructed Wetland (VSSFCW) type connected by a distribution tank using Typha angustifolia and Ipomoea aquatic plants were employed to treat tofu wastewater in order to reduce the organic matter inside wastewater measured by BOD and COD levels. The treatment plants were able to reduce approximately 68,53% of BOD levels and 70,29% of COD levels with Typha angustifolia as a phytoremediator and about 56,96% of BOD levels and 59,04% of COD levels with Ipomoea aquatica as a phytoremediator. Typha angustifolia has better resistance and adaptability than Ipomoea aquatica to tofu wastewater. A wetland-based system can potentially be developed considering the sustainability opportunities of using phytoremediator plants.

Constructed Wetlands as Nature-Based Solutions for Wastewater Treatment in the Hospitality Industry: A Review

The hospitality industry is increasing its awareness of how the integration of nature-based solutions can decrease its environmental impact while maintaining or increasing the service level of the sector. Constructed wetlands (CWs) constitute a promising sustainable solution for proper in situ domestic wastewater treatment. This literature review elucidates the status of CWs implementation in the hospitality industry to help foster the exchange of experiences in the field and deliver examples of approaches in different contexts to support future applications of this technology. Most of the studies reported in the literature were conducted in Europe, but studies emanating from Asia and South America are also available. The design of CWs, the horizontal and vertical subsurface flow CWs (HSFCW, VSFCW), and hybrid systems have been reported. The average removal efficiencies of the systems ranged from 83 to 95% for biochemical oxygen demand, 74 to 94% for chemical oxygen demand, 78 to 96% for total suspended solids, 75 to 85% for ammonium, 44 to 85% for ammonia, 50 to 73% for nitrate, 57 to 88% for total Kjeldahl nitrogen, 51 to 58% total nitrogen, and 66 to 99% for total phosphorus. The majority of the systems were implemented as decentralized treatment solutions using HSFCWs, with the second most common design being the hybrid CW systems in order to reduce area requirements, increase treatment efficiency, and prevent clogging. Overall, CWs are a promising sustainable solution which may support access to adequate sanitation worldwide as well as safe wastewater recycling and reuse, leading to more sustainable tourist destinations.

Enhanced nitrogen removal from rural domestic sewage via partial nitrification-anammox in integrated vertical subsurface flow constructed wetland

This study aimed to improve the removal of nitrogen treating rural domestic sewage by developing a novel strategy for achieving partial nitrification-anammox (PNA) in an integrated vertical subsurface flow constructed wetland (VSFCW). The influent ammonia was oxidized to nitrite in the partial nitrification VSFCW (VSFCWPN), and 5 mg/L of hydroxylamine was added under the appropriate dissolved oxygen concentration level (1.2 ± 0.2 mg/L) to stabilize the average nitrite accumulation rate at 88.24% and maintain the effluent NO2--N/NH4+-N ratio at 1.26 ± 0.15. The effluent from VSFCWPN was introduced to the following chamber (VSFCWAN), where ammonia and nitrite were removed by the autotrophic anammox process. This implementation achieved high removal efficiencies for chemical oxygen demand, total nitrogen, and PO43--P, reaching 86.26%, 90.22%, and 78.94%, respectively, with influent concentrations of 120.75 mg/L, 60.02 mg/L, and 5.05 mg/L. Substrate samples were collected from 10 cm height (PN1, AN1) and 25 cm height (PN2, AN2). Microbial community analysis showed that Nitrosomonas dominated the community composition in VSFCWPN, with an increase from 1.61% in the inoculated sludgePN to 16.31% (PN1) and 12.09% (PN2). Meanwhile, Ca. Brocadia accounted for 44.81% (AN1) and 36.50% (AN2) in VSFCWAN. These results confirm the feasibility of the proposed strategy for establishing PNA and efficiently treating rural domestic sewage in an integrated VSFCW.

Proposing a Wetland-Based Economic Approach for Wastewater Treatment in Arid Regions as an Alternative Irrigation Water Source

Point and nonpoint wastewater sources have a detrimental, negative effect on agriculture, soil, surface, and groundwater supplies. In this research, a wastewater treatment system made up of a sedimentation tank, a horizontal subsurface flow constructed wetland (HSSF-CW), a vertical subsurface flow constructed wetland (VF-CW), and a storage tank was proposed, designed, and cost estimated. Small populations in underdeveloped nations with dry and semi-arid climates can use the treatment system as an affordable construction, maintenance, and operational solution for wastewater treatment. The system will protect agricultural lands and groundwater from pollution. The system can service 6000 capita and has a wastewater discharge of 780 m3/d in the developing arid region in El-Moghra Oasis western desert of Egypt, where the 1.5 million acres used for the land reclamation project based on groundwater irrigation. The relaxed tanks in a series model based on the areal loading rates and background pollutants concentrations (P-K-C*) was utilized to size the HSSF and VF-CWs. The results indicated that the HSSF-CW design treatment surface area was 2375 m2, and the hydraulic surface loading (q) and hydraulic retention time (RT) were 0.33 m/d and 0.55 d, respectively, and utilizing Phragmites australis and Papyrus for the biological treatment. The expected overall cumulative removal efficiencies were 96.7, 70, and 100% for the biological oxygen demand (BOD), total phosphors (TP), and fecal coliforms (FC), respectively. The VF-CW indicates that there was a 2193 m2 design treatment surface area, q = 0.36 m/d, and RT of 0.63 d. The expected BOD, TP, and FC removal efficiencies were 75, 33.3, and 92.7%, respectively. In order to simplify the design stages and the cost estimation, design and investment cost curves were established for a population range from 500 to 9000. The total monthly water loss due to evapotranspiration for the HSSF and VF-CWs indicates a range from 3.7 to 8.5%, respectively. The total investment cost analysis for the proposed system corresponding to 780 m3/d wastewater discharge of indicates a total investment cost of EUR 146,804 and EUR 24.46/per-capita equivalent (P.E). This approach can be used by decision makers in the Mediterranean region and Middle Eastern countries to improve the water quality using social and economic criteria, leading to the effective implementation of ecological restoration projects as a low-cost treatment system and adding a nonconventional water source that can be used in irrigation.

Phytoremediation potential of Schumannianthus dichotomus in vertical subsurface flow constructed wetland

Schumannianthus dichotomus (Murta) is a naturally abundant wetland plant species in Bangladesh that has significant economic and aesthetic values. This species is perennial, and fast-growing in the nutrient-abundant swamp and marshes, moreover, it can thrive in a shaded and semi-shaded environment. Although it has all the potential to be a prominent Constructed Wetlands (CW) plant, no considerable study has yet been reported on the phytoremediation potential of the plant. The study was conducted to scrutinize the contaminants removal efficiency of the Murta plant in a lab-scale vertical subsurface flow constructed wetland (VSSFCW). Two CW columns were installed for the experiment: one kept planted (experimental) with the Murta plants and the another remained unplanted (control). Afterward a two months stabilization period, water samples were analyzed from the influent storage tank and both the experimental and control systems effluent at 24 h hydraulic retention time (HRT) for one month study period. The CWs were operated in the batch mode, for completing one cycle it run for one day, in keeping the flow 0.012m3/d and the hydraulic loading rate (HLR) 0.13 m3/d/m2. The results indicated higher reduction capability in the planted CW: 61.60 ± 2.85% Biochemical oxygen demand (BOD5), 53.98 ± 11.84% Chemical oxygen demand (COD), 70.25 ± 15.33% Nitrate (NO3-N), and 39.36 ± 30.85% Nitrite (NO2-N) reduction occurred in the column. Conversely, the unplanted CW reduced 43.31 ± 9.37% BOD5, 45.34 ± 8.88% COD, 9.92 ± 5.32 % NO3-N, and 15.87 ± 25.07% NO2-N. The study reports the reduction efficacy of the biochemical pollutants enhanced with the increase of the influent concentration. The average concentration of physical parameters of the influent, planted and unplanted CW was, respectively: 7.62±0.28, 6.8±0.16, 6.94±0.14 pH; 1107±140.50, 1199.03±57.48, 1050.75±96.18 μS/cm electrical conductivity (EC); 545.67±72.26, 533.51±84.12, 596.34±33.13 mg/L total dissolved solids (TDS); 0.55±0.07, 0.59±0.03, 0.52±0.02% salinity; 919.06±111.64, 835.27±39.53, 952.20±66.01 Ώ-cm resistivity; and 3.20±1.77, 5.15±1.00, 5.03±0.96 mg/L dissolved oxygen (DO). Therefore, 62% dissolved oxygen (DO) increased in the planted CW column than the influent sample water, whereas 59% DO enhance in the control. After all, the study suggests that S. dichotomus has significant organic reduction efficacy in the VSSFCW system, and could be regarded as an efficient CW plant.

Wetland plant-derived biochar enhances the diclofenac treatment performance in vertical subsurface flow constructed wetlands

Diclofenac (DFC) is a pharmacologically active compound frequently detected in various receiving waters. To improve the efficiency of constructed wetlands in removing DFC, biochar (BC) is added as a substrate. The study mainly involved the effect of adding wetland plant-derived BC to vertical subsurface flow constructed wetlands (VSF-CWs) on the DFC removal process. In addition, the study discussed the effects of the initial DFC concentration (0.05–1.00 mg L−1), pH (5.5–8.5), and hydraulic retention times (HRTs, 1–7 d) on the removal process and fluctuations in the microbial community. Preliminary results of the study showed optimal removal (>90%) achieved at an initial DFC concentration of 0.75–1 mg L−1, a pH of 6.5–7.5, and an HRT of 7 d. Moreover, no significant effects on the removal efficiency of conventional water quality parameters were observed. Non-metric multidimensional scaling results revealed a reshaped community structure, which was altered by the initial DFC concentration. DFC concentration is a key factor in the variation of microbial communities and controls the quantitative evolution of the species in experimental units. Therefore, the addition of BC to CWs effectively enhanced the removal efficiency of DFC and provided a viable and effective improvement of the CWs.

Purification of Micro-Polluted Lake Water by Biofortification of Vertical Subsurface Flow Constructed Wetlands in Low-Temperature Season

In this study, a novel lab-scale biofortification-combination system (BCS) of Oenanthe javanica and Bacillus series was developed to improve the treatment ability of vertical subsurface flow constructed wetlands (VSFCW) at low temperatures (0–10 °C). The results showed that BCS-VSFCW overcame the adverse effects of low temperature and achieved the deep removal of nutrients. In addition, the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) by BCS-VSFCW were 38.65%, 28.20%, 18.82%, and 14.57% higher than those of blank control, respectively. During the experiment, Oenanthe javanica and low temperature tolerant Bacillus complemented each other in terms of microbial activity and plant uptake. Therefore, VSFCW combined with Oenanthe javanica and low temperature tolerant Bacillus has a promising future in low temperature (<10 °C) areas of northern China.

Biochar composite with microbes enhanced arsenic biosorption and phytoextraction by Typha latifolia in hybrid vertical subsurface flow constructed wetland

Arsenic contamination of ground water is a worldwide issue, causing a number of ailments in humans. As an engineered and integrated solution, a hybrid vertical subsurface flow constructed wetland (VSSF-CW) amended with BCXZM composite (Bacillus XZM immobilized on rice husk biochar), was found effective for the bioremediation of arsenic contaminated water. Biological filter was prepared by amending top 3 cm of VSSF-CW bed with BCXZM. This filter scavenged ∼64% of total arsenic and removal efficiency of ∼95% was achieved by amended and planted (As + P + B) VSSF-CW, while non-amended (As + P) VSSF-CW showed a removal efficiency of ∼55%. The unplanted and amended (As + B) VSSF-CW showed a removal efficiency of ∼70%. The symbiotic association of Bacillus XZM, confirmed by SEM micrographs, significantly (p ≤ 0.05) reduced reactive oxygen species (ROS) and malondialdehyde (MDA) accumulation in Typha latifolia, hence, increasing the plant growth (2 folds). An increase in the indole acetic acid (IAA) and arsenic accumulation in plant was also observed in As + P + B system. The removal efficiency of the system was compromised after 4th consecutive cycle and 48 h was observed as optimum retention time. The FTIR-spectra showed the involvement of -N-H bond, carboxylic acids, –CH2 stretching of –CH2 and –CH3, carbonyl groups, -C-H, C–O–P and C–O–C, sulphur/thiol and phosphate functional groups in the bio-sorption of arsenic by BCXZM filter. Our study is a first reported on the simultaneous phytoextraction and biosorption of arsenic in a hybrid VSSF-CW. It is proposed that BCXZM can be applied effectively in CWs for the bioremediation of arsenic contaminated water on large scale.

Simultaneous removal of ibuprofen, organic material, and nutrients from domestic wastewater through a pilot-scale vertical sub-surface flow constructed wetland with aeration system

Pharmaceutical compounds in wastewater are currently becoming emerging concern as the utilization of drugs in anthropogenic activities. This research analyzed the effectiveness of pilot-scale vertical subsurface flow constructed wetland (VSSFCW) planted with Scirpus grossus using an aeration system for simultaneous removal of ibuprofen, chemical oxygen demand (COD) and nutrients (NH3-N, NO3-N, and PO4-P) from domestic wastewater. The constructed wetland (CW) platforms (500 L capacity) filled with gravel and sand and planted with native species of S. grossus were used to treat pharmaceutical content in domestic wastewater continuously for 21 days. Three experiments were performed with hydraulic retention time (HRT) of 3, 4 and 5 days. Aeration rates of 0, 1, and 2 L/min were employed for each HRT. The combined effect of HRT, exposure period, and aeration to simultaneously remove ibuprofen, organic materials, and nutrients were examined statistically using Two-way ANOVA and Tukey HSD test. Filtration and adsorption mechanisms of ibuprofen compound by sand medium matrix were proven to occur using solid phase extraction method. The removal efficiency of ibuprofen and COD were dependent on the applied aeration and HRT (p < 0.05). A longer HRT increased the removal efficiency of ibuprofen, while it did not significantly affect the nutrient removal (p ≥ 0.05). The VSSFCW under 2 L/min aeration and HRT of 5 days has removed 99.3% of ibuprofen, 88.2% of COD, 99.1% of ammonia, 72.9% of nitrate-nitrogen, and 83.2% of orthophosphate with effluent successfully met the effluent Standard B set by Malaysian Government. Therefore, the VSSFCW planted with S. grossus becomes a technically feasible method for treating sewage containing pharmaceutical compounds.

Mechanistic understanding of the pollutant removal and transformation processes in the constructed wetland system.

Constructed wetland systems (CWs) are biologically and physically engineered systems to mimic the natural wetlands which can potentially treat the wastewater from the various point and nonpoint sources of pollution. The present study aims to review the various mechanisms involved in the different types of CWs for wastewater treatment and to elucidate their role in the effective functioning of the CWs. Several physical, chemical, and biological processes substantially influence the pollutant removal efficiency of CWs. Plants species Phragmites australis, Typha latifolia, and Typha angustifolia are most widely used in CWs. The rate of nitrogen (N) removal is significantly affected by emergent vegetation cover and type of CWs. Hybrid CWs (HCWS) removal efficiency for nutrients, metals, pesticides, and other pollutants is higher than a single constructed wetland. The contaminant removal efficiency of the vertical subsurface flow constructed wetlands (VSSFCW) commonly used for the treatment of domestic and municipal wastewater ranges between 31% and 99%. Biochar/zeolite addition as substrate material further enhances the wastewater treatment of CWs. Innovative components (substrate materials, plant species) and factors (design parameters, climatic conditions) sustaining the long-term sink of the pollutants, such as nutrients and heavy metals in the CWs should be further investigated in the future. PRACTITIONER POINTS: Constructed wetland systems (CWs) are efficient natural treatment system for on-site contaminants removal from wastewater. Denitrification, nitrification, microbial and plant uptake, sedimentation and adsorption are crucial pollutant removal mechanisms. Phragmites australis, Typha latifolia, and Typha angustifolia are widely used emergent plants in constructed wetlands. Hydraulic retention time (HRT), water flow regimes, substrate, plant, and microbial biomass substantially affect CWs treatment performance.

Hybrid constructed wetlands system for domestic wastewater treatment under tropical climate: Effect of recirculation strategies on nitrogen removal

The objective of the present study was to evaluate the performance of a domestic wastewater treatment system based on hybrid constructed wetlands (CWs) under tropical climate. Moreover, the effect of different recirculation strategies particularly on nitrogen removal was also evaluated, including an analysis of nitrogen balance. The system was composed of a septic tank (pre-treatment), a horizontal subsurface flow and a vertical subsurface flow CWs. Three systems were analyzed: with the ornamental species Sagittaria lancifolia, the cattail Typha dominguensis and without vegetation as control. Evapotranspiration in the CWs was monitored during the warmest period of the year. First, the three systems were operated in serial mode evaluating two contact times of 2 d and 4 d. The three hybrid CWs were able to remove more than 92% of organic matter (COD, BOD5 and TOC), 88% of TSS and 99% (equivalent to 4.5 log10 units) of pathogens (Total Coliforms and Escherichia coli), regardless of plant selection and contact time. However, applying a contact time of 4 d resulted in higher removal of pathogens. Concerning nutrients removal, the combination of a contact time of 4 d and vegetation was required to achieve removal efficiencies over 66% for nitrogen and 90% for phosphorus. Finally, two recirculation strategies (RS) using a contact time of 4 d were evaluated in order to enhance nitrogen removal: RS1 (to the horizontal units) and RS2 (to the septic tank). The results yielded removal efficiencies similar to those obtained during serial operation in the case of organic matter (COD and BOD5) and phosphorus regardless of the RS applied. However, the removal of TSS decreased with RS2 as expected, due to the new load of solids coming from the septic tank. Nevertheless, nitrogen removal was increased over 85% in the hybrid CWs with vegetation, satisfactorily achieving system optimization. The highest nitrogen removal efficiency (≈ 97%) was obtained with the combination of RS2 and the plant species T. dominguensis. However, the use of the ornamental species S. lancifolia was not discarded since it provides an additional aesthetic benefit.

Enhanced removal of nutrients and coliforms from domestic wastewater in cattle dung biochar-packed Colocasia esculenta-based vertical subsurface flow constructed wetland

The efficiency of Colocasia as well as cattle dung biochar addition in a constructed wetland, is not well documented in published literature. In this study, Colocasia esculenta-based vertical subsurface flow constructed wetland (VSSFCW) packed with heterogonous gravels and cattle dung biochar was established to examine the removal of nitrate (NO3-N), ammonium N (NH4+-N), sulfate (SO4−2), phosphate (PO4-3), chemical oxygen demand (COD), total N (TN), and total coliforms from domestic wastewater. To achieve the goal, three setups of VSSFCWs; SB (medium + biochar (10 % v/v)); SBP (medium + biochar + Colocasia); SP (medium + Colocasia) were established and wastewater characteristics (pH, DO, NO3-N, NH4+-N, TN, SO4−2, PO4-3, COD, and total coliforms) were monitored after each 24 h interval for 40 d after 70 d of initial acclimatization of the setups. SBP showed the highest average removal efficiency for COD (92.6 %), NO3-N (81.7 %), NH4+-N (81.2 %), SO4−2 (85.4 %), PO4-3 (69.5 %), total coliforms (97 %) than SB and SP during of the 40 d treatment period. Plant uptake rate was also measured and biochar amended VSSFCW showed the highest values of leaf area, biomass growth (2.58–3.44-folds). N-uptake (36.81 g N m−2), and P-uptake rate (12.3 g P m−2) than SP setup. The treated domestic wastewater by biochar amended VSSFCWs compliance with the limit set by the national pollution monitoring agency of India. Role of aeration and varying wastewater strength (especially COD load) in the performance of Colocasia-based CWs’ could be undertaken as a research problem for future studies to develop an efficient engineered wetland system for on-site wastewater treatment.

The feasibility of combined coagulation flocculation and constructed wetland as green technology for sustainable leachate treatment

This study aims to determine the feasibility of coagulation flocculation processing using Moringa oleífera seed powder (MOSP) and vertical sub surface flow constructed wetlands (VSSFCW) to process leachate landfill (LL). The method used is to do a jar test to determine the optimum conditions and then proceed with VSSFCW processing. In the coagulation flocculation process, the optimum conditions were obtained with a dose of 175 mg/L, pH 6.5 and a speed of rapid mixing of 100 rpm for 10 minutes. This optimum condition is able to reach the percentage of COD, turbidity and Mn removal of 35.27%, 69.48%, and 94.83%, respectively. However, the effluent value is still above the Minister of Environment regulation standard No. 5/2014 regarding the standard quality of wastewater for the parameters of COD and Mn that is equal to 584.19 mg/L for COD and 6.98 mg/L for Mn, while for turbidity meets the standard of 69.83 mg/L. Further processing with VSSFCWs can improve the quality of LL effluent resulting from coagulation flocculation 66.36 mg/L; 4.97 mg/L for turbidity and 0.12 mg/L for Mn or with efficiencies of 88.64%, 92.88% and 98.22%. These results were obtained at the optimum HRT conditions for 10 days.

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.

VERTICAL SUBSURFACE FLOW AND FREE SURFACE FLOW CONSTRUCTED WETLANDS FOR SUSTAINABLE POWER GENERATION AND REAL WASTEWATER SELECTIVE POLLUTANTS REMOVAL

A vertical subsurface flow constructed wetland (VSSFCW) and a free surface flow constructed wetland (FSFCW) were set for the objective of comparison the performance of two systems in order to make a decision of the better one for future installation of wastewater treatment system and power generation. Both of the constructed wetlands were planted with Cyperus Alternifolius. During the observation period (19 days or 456 hours), environmental conditions such as pH, temperature, total chemical oxygen demand (COD), phosphate (PO4), nitrate (NO3), total suspended solids (TSS), total dissolved solids (TDS), Pb, Cu, and Cd removal efficiencies of the systems were determined. According to the results, final removal efficiencies for the VSSF and FWSF, respectively, were: COD (94.3% and 94.3%), PO4 (84.3% and 75.3%), NO3 (100% and 100%), TSS (96.8% and 85.6%), Pb (65.8% and 81.4%), Cu (more than 94.7% and 89.4%), Cd (85.7% and 88%). The treatment performances of the VSSF were better than that of the FWSF with regard to the removal of suspended solids and nutrients. In FWSF systems, electricity generation performed better than VSSF of 31.4 mV especially with batch system during one wastewater feed is loaded among all of the nineteen days with maximum voltage of 33.7 mV and decreased gradually as oxygen depletion in cathode chamber and less metabolism processes have occurred.

Removal of Pb and Zn in municipal wastewater by a consortium of four aquatic plants in vertical subsurface flow constructed wetland (VSF-CW)

ABSTRACT The ability of a consortium of three emergent aquatic plants; Veronica anagallis-aquatica, Mentha longifolia, and Cyperus iria and one free-floating Nasturtium officinale was evaluated in outdoor vertical subsurface flow-constructed wetland (VSF-CW) experiments to remove lead and zinc elements in municipal wastewater. All species were able to withstand unsuitable conditions, as shown by the 100% survival rate. The percentage Pb and Zn removal rate under the synergetic condition of the consortium attained 92% and 97%, respectively. This was consistent with the highest removal capacity (14.3 and 17.1 mg/d/g) and highest metal uptake values (12.4 and 170.2 mg/plant) calculated for Pb and Zn, respectively. Free-floating N. officinale was considered suitable candidate for Zn phytoextraction (BAFs and TF >1). Emergent species have taken up high Zn in their roots, and are, therefore considered strong excluders of Zn, via phytostabilization (BAFs > 1 and TF <1). All species eliminated Pb from wastewater by rhizofiltration (BAFs and TF <1).

Purifying effect of biochar-zeolite constructed wetlands on arsenic-containing biogas slurry in large-scale pig farms

To explore the purifying effect of vertical subsurface flow constructed wetlands (CWs) on arsenic-containing biogas slurry in pig farms under natural conditions in the field, vertical subsurface flow CWs with water spinach-Pennisetum sinese as the core was constructed in this study. Under the condition of biogas slurry with different dilution ratios (2, 4, 6; v/v) was fed to the wetlands and different substrates (biochar and zeolite) were added to the wetlands, respectively, the removal efficiency of the pollutants in biogas slurry by CWs were investigated. The enrichment of arsenic (As) in wetland substrates and three wetland plants (water spinach, green Pennisetum sinese and purple Pennisetum sinese) was analyzed. The results showed that, the removal rate of ammonia nitrogen (NH4+-N) in biogas slurry at low dilution ratio was always higher in the CWs, while that of total phosphorus (TP), chemical oxygen demand (COD) and As was higher in biogas slurry at high dilution ratio at first and then was just the opposite. The addition of zeolite and biochar could enhance the decontamination effect of CWs. Zeolite had better removal effect on NH4+-N, TP and COD, while biochar showed better removal effect on As. At low dilution ratio, the enrichment of As was high in the wetland sediments and three wetland plants. Adding biochar and zeolite increased the enrichment and absorption of As by sediments, water spinach and purple Pennisetum sinese, which was more significant by adding zeolite than biochar. However, they slightly reduced the absorption of As by green Pennisetum sinese. The detailed effluent quality assessment showed TP and NH4+-N to be significant pollution factors. The CWs treated with zeolite showed a higher purifying effect, while the CWs added without the two substrates had a lower purifying effect. This study provides a theoretical basis for the practical application of CWs in livestock and poultry wastewater treatment.

Kinetic modelling and performance evaluation of vertical subsurface flow constructed wetlands in tropics

The design of vertical subsurface flow (VSSF) constructed wetlands (CWs) uses kinetic models to calculate the area based on the kinetic reaction rate constant (k) specific to local environmental conditions and target pollutants. Currently, kinetic modelling does not fully account for the impact of the hydraulic loading rate (HLR), which influences the wetland performance. This study used four experimental VSSF CWs operated at HLRs of 5, 10, 20 and 40 cm/day to investigate the applicability of three first order kinetic models combining plug-flow and continuous stirred tank reactor (CSTR) flow patterns. The target pollutants were BOD5, NH4+ and NO3-. For each pollutant, estimated k values varied between different HLRs and between plug flow and CSTR models. Assessment of uncertainty in kinetic modelling showed that all three models exhibit a similar trend in predicting the concentrations of BOD5 and NH4+ at 5–20 cm/day HLRs. A substantial removal of BOD5 (>88 %) and NH4+ (>70 %) were found for the investigated HLRs, although NO3- removal was not satisfactory. The HLR had a positive impact on mass removal rates (MRRs) for BOD5 and NH4+. Accordingly, 20 cm/day was deemed as the highest viable HLR for designing effective VSSF wetlands for the removal of BOD5 and NH4+. All three models can be employed to design VSSF wetlands at 20 cm/day HLR to treat BOD5 using k values of 0.352 (k-C), 0.380 (k-C*) and 0.996 (CSTR) m/day and to treat NH4+ using k values of 0.170 (k-C), 0.173 (k-C*) and 0.273 (CSTR) m/day.