Vertical Subsurface Flow Research Articles

Evaluation of attenuation of pharmaceuticals, toxic potency, and antibiotic resistance genes in constructed wetlands treating wastewater effluents

The performance of constructed wetlands (CWs) in the removal of pharmaceutically active compounds (PhACs) is generally evaluated on the basis of chemical analysis. In this work, we used a combination of chemical, toxicological, and molecular analyses to assess the attenuation of PhACs, toxic potency and antibiotic resistance genes (ARGs) in a field study of three CWs serving as tertiary treatment of wastewater treatment plants. First, 17 PhACs were analysed chemically, of which 14 were detected and seven at concentrations >0.1μg/l. Even though some of the individual PhACs were moderately or highly removed in the CWs investigated, median removal of overall PhACs was approximately 50% in the vertical subsurface flow CW (VSF-CW) with a lower hydraulic loading rate while the removal in the other two free water surface flow CWs (SF-CWs) was negligible. Second, toxic potency of wastewater extracts was assessed in a range of bioassays. Estrogenicity was overall attenuated in CWs, while the neurotoxic potency of wastewater extracts did not decrease after passage through the two CWs investigated. Third, the VSF-CW and one of the SF-CW showed a positive removal of an integrase gene and three ARGs tested. The increased concentrations of ARGs in the other SF-CW, as well as the increase of total bacteria in all CWs, may relate to regrowth of resistance-carrying bacteria. Finally, multivariate analysis shows that most PhACs are positively correlated to the observed toxic potency. Additionally, low removal of organics and nutrients seems to parallel with low removal of PhACs. ARGs positively correlated with organics, nutrients and some PhACs, and the integrase gene but not to the respective antibiotics. The insufficient removal of PhACs, toxic potency, and ARGs indicates the need of an optimal design of CWs as tertiary treatment facilities.

CONSTRUCTED WETLANDS AS BIOFILTERS IN CLOSED RECIRCULATING TANK CULTURE SYSTEMS OF ASIAN TIGER SHRIMP (PENAEUS MONODON)

The study was conducted to monitor the real-time status of toxic compounds to P. monodon in intensive recirculating aquaculture system integrated constructed wetlands (CWs) designed with surface flow (SF), vertical subsurface flow (VF) and horizontal subsurface flow (HF), and to examine removal efficiency of contaminants in different CWs. Plants used in the system were cattail (Typha sp.), elephant grass (Pennisetum purpureum) and unplanted systems used as referenced samples. Recirculating rate per day was 50 % of total water volume in tanks. Water from culture tanks was purified by passing through SF, VF and HF then return to original tanks without water exchange in entire study period. After 72 days, concentration of NO2-N, NH4-N and NO3-N was building up over study period and was not significantly different among treatment systems (except the concentration of NO3-N). At the end of study period, NH3 concentration was below the toxic threshold for P. monodon in according to Circular No. 45/2010/TT-BNNPTNT. P. monodon grew slowly and the survival rate was as low at 30 %, 43 % and 60,5 % in the HF, SF and VF systems, respectively. The average water volume added in each tank in entire study period was 393 ± 1,7 L. Despite of low survival and growth rates, the integration of CWs in intensively recirculating shrimp systems helps to improve water quality in accordance to Circular No. 45/2010, to diminish pollutant discharging and to maximize efficiency of water use which minimizes environmental pollution.

Applicability of Constructed Wetlands for Water Quality Improvement in a Tea Estate Catchment: The Pussellawa Case Study

Water in agricultural catchments is prone to pollution from agricultural runoff containing nutrients and pesticides, and contamination from the human population working and residing therein. This study examined the quality of water in a drainage stream which runs through a congested network of ‘line houses’ (low-income housing, typically found arranged in straight ‘lines’ on estates) in the tea estate catchment area of Pussellawa in central Sri Lanka. The study evaluated the applicability of vertical subsurface flow (VSSF) and horizontal subsurface flow (HSSF) constructed wetlands for water polishing, as the residents use the stream water for various domestic purposes with no treatment other than possibly boiling. Water flow in the stream can vary significantly over time, and so investigations were conducted at various flow conditions to identify the hydraulic loading rate (HLR) bandwidth for wetland polishing applications. Two wetland models of 8 m × 1 m × 0.6 m (length × width × depth) were constructed and arranged as VSSF and HSSF units. Stream water was diverted to these units at HLRs of 3.3, 4, 5, 10, 20, and 40 cm/day. Results showed that both VSSF and HSSF wetland units were capable of substantially reducing five-day biochemical oxygen demand (BOD5), total suspended solids (TSS), fecal coliform (FC), total coliform (TC), ammonia nitrogen (NH4+-N), and nitrate nitrogen (NO3−-N) up to 20 cm/day HLR, with removal efficiencies of more than 64%, 60%, 90%, 93%, 70%, and 59% for BOD5, TSS, FC, TC, NH4+-N, and NO3−-N, respectively, in the VSSF wetland unit; and more than 66%, 62%, 91%, 90%, 53%, and 77% for BOD5, TSS, FC, TC, NH4+-N, and NO3−-N, respectively, in the HSSF wetland unit.

Numerical Simulation of Contaminant Removal in a Vertical Subsurface-Flow Constructed Wetland

Numerical Simulation of Contaminant Removal in a Vertical Subsurface-Flow Constructed Wetland

Fate of heavy metals in vertical subsurface flow constructed wetlands treating secondary treated petroleum refinery wastewater in Kaduna, Nigeria

ABSTRACTThis study examined the performance of pilot-scale vertical subsurface flow constructed wetlands (VSF–CWs) planted with three indigenous plants, i.e. Typha latifolia, Cyperus alternifolius, and Cynodon dactylon, in removing heavy metals from secondary treated refinery wastewater under tropical conditions. The T. latifolia-planted VSF–CW had the best heavy metal removal performance, followed by the Cyperus alternifolius-planted VSF–CW and then the Cynodon dactylon-planted VSF–CW. The data indicated that Cu, Cr, Zn, Pb, Cd, and Fe were accumulated in the plants at all the three VSF–CWs. However, the accumulation of the heavy metals in the plants accounted for only a rather small fraction (0.09–16%) of the overall heavy metal removal by the wetlands. The plant roots accumulated the highest amount of heavy metals, followed by the leaves, and then the stem. Cr and Fe were mainly retained in the roots of T. latifolia, Cyperus alternifolius, and Cynodon dactylon (TF < 1), meaning that Cr and Fe were only partially transported to the leaves of these plants. This study showed that VSF–CWs planted with T. latifolia, Cyperus Alternifolius, and Cynodon dactylon can be used for the large-scale removal of heavy metals from secondary refinery wastewater.

Effect of plant harvesting on greenhouse gas emission from vertical subsurface flow constructed wetlands treating low-strength sewage

Effect of plant harvesting on greenhouse gas emission from vertical subsurface flow constructed wetlands treating low-strength sewage

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

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

Removal of organic carbon, nitrogen, emerging contaminants and fluorescing organic matter in different constructed wetland configurations

The elimination of organic carbon, nitrogen, five emerging organic contaminants (EOCs) and fluorescence signature was evaluated in two treatment lines comprising different constructed wetland (CW) configurations: (i) partially saturated vertical subsurface flow (SVF) wetland (treatment line 1) and (ii) unsaturated vertical subsurface flow (UVF), horizontal subsurface flow (HF) and free water surface (FWS) wetlands in series (treatment line 2). Results showed important differences between the different CW configurations. The highest removal of BOD5 (81%), COD (67%), TOC (72%) and fluorescing organic matter were observed in the UVF wetland, whereas the HF and FWS wetlands were the most efficient units for total nitrogen removal (60 and 69%, respectively). The SVF wetland showed a greater performance in the reduction of total nitrogen than the UVF bed (52 vs. 35%). In addition, the SVF wetland exhibited a higher removal of the EOCs caffeine (95 vs. 90%), trimethoprim (99 vs. 87%) and sulfamethoxazole (64 vs. 4%), as opposed to DEET (34 vs. 63%), whose removal was superior in the UVF unit. Sucralose was negligibly removed in all the CWs. PARAFAC analysis of fluorescence measurements revealed that the proteinaceous tryptophan-like fluorescent component was the most highly removed one in all the investigated CWs (>28%) and, particularly, in the UVF wetland (66%), whereas humic and fulvic-like components resulted recalcitrant to decomposition. Increases of fluorescence intensities were often observed for fulvic-like substances in CWs operating with saturation of the bed, and these were particularly relevant in the SVF unit. Finally, important correlations (r>0.7) between the tryptophan-like fluorescent component and the wastewater quality parameters COD and BOD5 suggest fluorescence spectroscopy asan useful monitoring tool for water treatment efficiency in CW systems.

Removal of cadmium in subsurface vertical flow constructed wetlands planted with Iris sibirica in the low-temperature season

In this study, the evergreen Iris sibirica plant was planted in a constructed wetland during the low-temperature season. Microcosmic subsurface vertical flow constructed wetlands (MVFCWs) were fed with simulated Cd polluted river water for three months under different Cd supply and the seasonal growth changes and Cd uptake ability of Iris sibirica were investigated. The treatment performance of MVFCWs and removal mechanisms and distribution of Cd were evaluated. The amount of rhizospheric microorganisms (bacteria, fungi, and actinomyces) and the enzyme activities (urease, sucrase, alkaline phosphatase and catalase) were also monitored. Iris sibirica proves to be a good accumulator of Cd with the highest accumulation of Cd in below-ground parts of 443.3mg/kg when exposed to 8mg/L Cd for three months. Under 1, 2, 4 and 8mg/L Cd supply in low-temperature seasons, the MVFCWs exhibit average Cd removals of 94.9%, 97.4%, 95.6% and 96.2%, respectively. The predominant removal process of Cd in MVFCWs is substrate adsorption, which accounts for about 50% of Cd removal. Under the same Cd supply, the removal rates of Cd, amount of rhizospheric microbes and activities of enzymes in planted wetland are higher than those in unplanted wetland.

High-frequency measurement of N2O emissions from a full-scale vertical subsurface flow constructed wetland

In the last few years, the emission of nitrous oxide (N2O) from constructed wetlands has become a topic of increased interest. Most N2O emission measurements made so far are based on limited grab-samples, leading to sparse temporal resolution in the data. Using a high sampling frequency strategy, gaseous and dissolved N2O emissions from a two-stage vertical subsurface flow constructed wetland, treating domestic raw wastewater, were investigated. The monitoring period that lasted 3 weeks corresponded to an entire operation cycle of the filters including the feeding and rest periods.Gaseous N2O fluxes exhibited remarkable temporal fluctuations with contrasted emission rates between the feeding and rest periods, as well as high variability within a given period. Total potential emission rates (gaseous+dissolvedN2O fluxes) were found to be similar in both stages, with a mean value over the entire operation cycle of 1.50 and 1.78mgN/m2/h in Stage 1 and Stage 2, respectively. The dynamic behavior of the emissions was found to be correlated to the changes in the biogeochemical conditions within the filters. A positive relationship between gaseous N2O emissions and oxygen concentrations in filter media was observed during conditions favoring nitrification and denitrification, suggesting that N2O can be emitted from both processes.

Impacts of silver nanoparticles on the nutrient removal and functional bacterial community in vertical subsurface flow constructed wetlands

The widespread utilization of silver nanoparticles (AgNPs) in industrial and commercial products inevitably raises the release into wastewater. In this study, the influences of AgNPs (0, 50 and 200μg/L) on the performance and microbial community of CWs were evaluated. Compared with the control system (without AgNPs), the COD removal was not affected, whereas the TN, NH4+-N, and TP removals were evidently affected in presence of AgNPs, and the effects had a positive relation with AgNPs concentration. In addition, AgNPs were effectively removed from wastewater and mainly accumulated in the soil layer and plant tissues. The illumina high-throughput sequencing results indicated that there were obvious variations in the microbial community at different AgNPs concentrations, associated with the variations of CW performance. Sequencing analyses also showed that Proteobacteria, Acidobacteria, Bacteroidetes were the dominant phyla. These results may provide valuable information and reference for evaluating the effect of AgNPs on constructed wetlands.

Modelling approaches for simulating wetland pollutant dynamics

ABSTRACTA number of black box and process-based modelling approaches, their strengths/limitations, and future applications for simulating contaminant dynamics in constructed wetlands (CWs) have been reviewed. Scanning of literature reveals that most of the CW modelling approaches are limited to the simulation of only nutrient and organic pollutant load dynamics. Performance analysis of the various process/black box-based models for simulating pollutant dynamics in vertical subsurface flow, horizontal subsurface flow, and hybrid CW systems further reveals that most of the existing modelling approaches have not not so far been able to account for the changing climatic conditions and the heavy metal dynamics. The paper thus highlights the gaps in the knowledge in the current state of the art for simulating wetland pollutant dynamics and suggests mechanisms for increasing the scope of such modelling approaches in the proper design and operation of the CW systems.

Effectiveness of the Horizontal, Vertical and Hybrid Subsurface Flow Constructed Wetland Systems in Polishing Municipal Wastewater

This study aimed at comparing the performance of horizontal, vertical and hybrid subsurface flow system in polishing wastewater effluent from the maturation pond at Gusii wastewater treatment plant, Kenya. The treatments were monitored for six weeks duration for chemical oxygen demand, total suspended solids, total nitrogen and total phosphorous against Kenya’s National Environmental Management Authority standards for effluent discharge. Among the systems planted with Vetiver grass, the hybrid subsurface flow system significantly removed the pollutants more efficiently than the single operated systems. The Vetiver planted hybrid subsurface flow wetland systems achieved the highest removal of COD, TN, TP and TSS at 82.4, 87.9, 65 and 94.6%, respectively as compared to other wetland systems. The planted vertical subsurface flow removed COD, TN and TP at 72.9, 75.7, and 50.7%, respectively more efficiently than the horizontal subsurface flow system that achieved removal of COD, TN and TP at 65.3, 70.0 and 43.8%, respectively. The planted horizontal subsurface flow wetland however showed better TSS removal at 89.9% compared to 83.2% achieved by vertical subsurface flow system. The unplanted systems exhibited a similar trend whereby the hybrid subsurface flow systems achieved better performance than the single systems though with significantly (P≤0.05) lower organics and nutrients removal efficiencies compared to the planted systems.

Influence of Different Porous Media and Ornamental Vegetation on Wastewater Pollutant Removal in Vertical Subsurface Flow Wetland Microcosms

Abstract To investigate the effects of porous media and ornamental plants on pollutant removal in vertical subsurface flow constructed wetlands (CWs), 24 microcosm systems were tested from March to...

Mineral Processing Residue Use as Substrate in a Modular Engineered Wetland for Wastewater Treatment

Safeguarding the water quality of Poyang Lake, China’s largest freshwater lake, is essential for long-term regional water resource sustainability. The use of locally-available mineral processing residues as reactive substrate in engineered wetlands may provide a cost-effective treatment alternative for mixed agricultural and domestic wastewaters entering Poyang Lake. In this study, Chinese iron- and steel-making slags and a titanium mineral processing residue with high nutrient removal capacity were identified in laboratory experiments. A pilot-scale modular wetland system consisting of free water surface, and vertical and horizontal subsurface flow units, all planted with locally-available vegetation, was constructed at the Poyang Lake Modelling Experiment and Research Base in Jiangxi Province. Assessment of nutrient removal efficiency and effluent water quality was undertaken to inform upscaling and optimization of the modular unit process wetland design. The pilot-scale wetland system removed 55% of inorganic N in influent wastewater and was particularly effective in P attenuation, removing 81% of total P. The environmentally-acceptable pH of wetland system effluents, along with low concentrations of dissolved metals and the absence of potential for either N- or Si-limitation, indicated that the modular wetland system examined was potentially suitable for treatment of mixed wastewater entering Poyang Lake. The use of the selected mineral processing residues as reactive substrate in engineered wetland systems enhanced pollutant removal processes in the modular engineered wetland system, effectively attenuating pollutants in mixed wastewater.

Effects of physical clogging on the performance of a lab-scale vertical subsurface flow constructed wetland system and simulation research

The accumulation of inorganic solids and the corresponding change in performance indicators over time in the top layer of vertical subsurface constructed wetlands (SSF CWs) with a constant contaminant loading rate were studied in laboratory. Concentration of total suspended solids (TSS) in outflow had a significant correlation with that of the inflow at the 0.01 level. Total suspended solids (TSS) reduction rate remained steady during the experimental period (46.4%±8%), resulting in a linear relationship between both accumulated solids and effective porosity, and continued operation time (R2 was 0.871 and 0.797, respectively). The infiltration rate declined rapidly during the first 60days of operation, followed by a fluctuation period of about 80 days, with a descending tendency slowing down in infiltration rate after this point. A significant correlation was observed between accumulated solids and porosity (P<0.01; Pearson correlation coefficient: −0.776). Porosity also correlated with infiltration rate (P<0.05), but no direct correlations were observed between the level of accumulated solids and infiltration rate (P=0.109). Formulas were effectively employed to quantify the relationship among these indicators, with a good fit established between the simulated and the measured values.

Constructed wetlands and solar-driven disinfection technologies for sustainable wastewater treatment and reclamation in rural India: SWINGS project.

SWINGS was a cooperation project between the European Union and India, aiming at implementing state of the art low-cost technologies for the treatment and reuse of domestic wastewater in rural areas of India. The largest wastewater treatment plant consists of a high-rate anaerobic system, followed by vertical and horizontal subsurface flow constructed wetlands with a treatment area of around 1,900 m2 and a final step consisting of solar-driven anodic oxidation (AO) and ultraviolet (UV) disinfection units allowing direct reuse of the treated water. The implementation and operation of two pilot plants in north (Aligarh Muslim University, AMU) and central India (Indira Gandhi National Tribal University, IGNTU) are shown in this study. The overall performance of AMU pilot plant during the first 7 months of operation showed organic matter removal efficiencies of 87% total suspended solids, 95% 5-day biological oxygen demand (BOD5) and 90% chemical oxygen demand, while Kjeldahl nitrogen removal reached 89%. The UV disinfection unit produces water for irrigation and toilet flushing with pathogenic indicator bacteria well below WHO guidelines. On the other hand, the AO disinfection unit implemented at IGNTU and operated for almost a year has been shown to produce an effluent of sufficient quality to be reused by the local population for agriculture and irrigation.

Study on treatment of aquaculture wastewater using a hybrid constructed wetland

This paper reported the pollutant removal performances of a hybrid wetland system for the treatment of aquaculture wastewater. The system consisted of two treatment stages: a subsurface vertical flow (VF) wetland, followed by a horizontal flow (HF). The aquaculture wastewater with the different concentrations such as eutrophy and mesotrophy was treated using hybrid constructed wetland. The experimental results showed that the removal efficiencies of eutrophy aquaculture wastewater achieved 56%, 71%, 73% for nitrite, phosphate and nitrate, respectively. At the same conditions, it can be found that the removal efficiencies of mesotrophy aquaculture wastewater achieved 39%, 74%, 73% for nitrite, phosphate and nitrate, respectively.

Enhancement of the complete autotrophic nitrogen removal over nitrite process in a modified single-stage subsurface vertical flow constructed wetland: Effect of saturated zone depth

This study was conducted to explore enhancement of the complete autotrophic nitrogen removal over nitrite (CANON) process in a modified single-stage subsurface vertical flow constructed wetland (VSSF) with saturated zone, and nitrogen transformation pathways in the VSSF treating digested swine wastewater were investigated at four different saturated zone depths (SZDs). SZD significantly affected nitrogen transformation pathways in the VSSF throughout the experiment. As the SZD was 45cm, the CANON process was enhanced most effectively in the system owing to the notable enhancement of anammox. Correspondingly, the VSSF had the best TN removal performance [(76.74±7.30)%] and lower N2O emission flux [(3.50±0.22)mg·(m2·h)−1]. It could be concluded that autotrophic nitrogen removal via CANON process could become a primary route for nitrogen removal in the VSSF with optimized microenvironment that developed as a result of the appropriate SZD.

Unraveling the active microbial populations involved in nitrogen utilization in a vertical subsurface flow constructed wetland treating urban wastewater.

The dynamics of the active microbial populations involved in nitrogen transformation in a vertical subsurface flow constructed wetland (VF) treating urban wastewater was assessed. The wetland (1.5m2) operated under average loads of 130gCODm-2d-1 and 17gTNm-2d-1 in Period I, and 80gCODm-2d-1 and 19gTNm-2d-1 in Period II. The hydraulic loading rate (HLR) was 375mmd-1 and C/N ratio was 2 in both periods. Samples for microbial characterization were collected from the filter medium (top and bottom layers) of the wetland, water influent and effluent at the end of Periods I (Jun-Oct) and II (Nov-Jan). The combination of qPCR and high-throughput sequencing (NGS, MiSeq) assessment at DNA and RNA level of 16S rRNA genes and nitrogen-based functional genes (amoA and nosZ-clade I) revealed that nitrification was associated both with ammonia-oxidizing bacteria (AOB) (Nitrosospira) and ammonia-oxidizing archaea (AOA) (Nitrososphaeraceae), and nitrite-oxidizing bacteria (NOB) such as Nitrobacter. Considering the active abundance (based in amoA transcripts), the AOA population revealed to be more stable than AOB in both periods and depths of the wetland, being less affected by the organic loading rate (OLR). Although denitrifying bacteria (nosZ copies and transcripts) were actively detected in all depths, the denitrification process was low (removal of 2gTNm-2d-1 for both periods) concomitant with NOx-N accumulation in the effluent. Overall, AOA, AOB and denitrifying bacteria (nosZ) were observed to be more active in bottom than in top layer at lower OLR (Period II). A proper design of OLR and HLR seems to be crucial to control the activity of microbial biofilms in VF wetlands on the basis of oxygen, organic-carbon and NOx-N forms, to improve their capacity for total nitrogen removal.