Integrated Constructed Wetland Research Articles

Sewage Derived Microplastic and Anthropogenic Fibre Retention by Integrated Constructed Wetlands

High loads of microplastics and anthropogenic fibres can be discharged from wastewater treatment plants (WWTPs) into surface water bodies. Integrated Constructed Wetlands (ICWs) are potentially well suited to provide a cost-effective mitigation solution at small WWTPs where conventional treatment is prohibitively expensive. This study aimed to assess the microplastic and anthropogenic fibre retention efficiency of two ICWs (Northrepps and Ingoldisthorpe) in Norfolk (UK) over a 12-month period (2022–2023). Analysing a total of 54 water and 23 sediment samples, the findings revealed that Northrepps ICW received on average 349,920 (± 763,776) anthropogenic fibres day−1, with a retention rate of 99.3%. No seasonal variation was observed in retention efficiency. Ingoldisthorpe ICW intermittently received anthropogenic fibres in low concentrations, with an average of 9504 (± 19,872) day−1 and a retention rate of 100%. Microplastics and anthropogenic fibres were prevalent in sediment samples of the first cell of Northrepps ICW, averaging 10,090 items kg−1 dry sediment, while none were found at concentrations above the limit of detection in the second or third cell. Of the 369 fibres analysed by ATR-FTIR, 55% were plastic (dominated by polyester). Of the 140 suspected microplastic fragments analysed by ATR-FTIR, 73% were confidently identified as plastic (mostly polystyrene, polyethylene, or polypropylene). This study demonstrates how ICWs can effectively retain sewage effluent derived microplastics and anthropogenic fibres. However, the accumulation of plastic waste in ICWs may complicate long term management and their cost-effectiveness.

Monitoring of university wastewater within the sewage system and its performance evaluation through integrated constructed wetlands.

Rapid increase in population and industrialization has not only improved the lifestyle but adversely affected the quality and availability of water leading to ample amount of wastewater generation. The major contribution towards wastewater production is from sewage. Regular monitoring and treatment of sewage water is necessary to conserve and enhance the quality of water. The present study focuses on monitoring of sewage water within the sewage system of a residential university. A total of 16 samples from different manholes were collected for physicochemical and heavy metals analysis and compared with final effluent collected from integrated constructed wetlands (ICWs) to assess its removal efficiency. The mean concentrations of influent and effluent were compared with national environmental quality standards (NEQS) for municipal discharge (pH6-9, COD 150mg/L, TSS 200mg/L and TDS 3500mg/L) and international agricultural reuse standards (IARS) (pH6-8, COD <150mg/L, TSS < 100mg/L) respectively. Among all physicochemical parameters, influent values for chemical oxygen demand (COD) (169.56-258.36) mg/L exceeded the limit of NEQS for discharge into inland waters, whereas for total suspended solids (TSS) the concentration exceeded for discharge into STP (406mg/L) and inland waters (202.33mg/L). However, effluent concentrations for all the parameters were found within the permissible limit set by IARS. The removal efficiency for different parameters such as phosphate- phosphorus (PO43-P), COD, TSS, total dissolved solids (TDS) and total kjeldahl nitrogen (TKN) were 52, 53, 54, 35, and 36%, respectively. Heavy metal concentrations were compared with WHO guidelines among which lead (Pb) in effluent and chromium (Cr) in influent exceeded the limit (Pb 0.01 and Cr 0.05mg/L). Interpolation results showed that zone 2 was highly contaminated in comparison to zone 1 & 3. Statistical analysis showed that correlation of physicochemical parameters and heavy metals was found significant (p < 0.05).

Characterization of cephalosporin and fluoroquinolone resistant Enterobacterales from Irish farm waste by whole genome sequencing.

The Enterobacterales are a group of Gram-negative bacteria frequently exhibiting extended antimicrobial resistance (AMR) and involved in the transmission of resistance genes to other bacterial species present in the same environment. Due to their impact on human health and the paucity of new antibiotics, the World Health Organization (WHO) categorized carbapenem resistant and ESBL-producing as critical. Enterobacterales are ubiquitous and the role of the environment in the transmission of AMR organisms or antimicrobial resistance genes (ARGs) must be examined in tackling AMR in both humans and animals under the one health approach. Animal manure is recognized as an important source of AMR bacteria entering the environment, in which resistant genes can accumulate. To gain a better understanding of the dissemination of third generation cephalosporin and fluoroquinolone resistance genes between isolates in the environment, we applied whole genome sequencing (WGS) to Enterobacterales (79 E. coli, 1 Enterobacter cloacae, 1 Klebsiella pneumoniae, and 1 Citrobacter gillenii) isolated from farm effluents in Ireland before (n = 72) and after (n = 10) treatment by integrated constructed wetlands (ICWs). DNA was extracted using the MagNA Pure 96 system (Roche Diagnostics, Rotkreuz, Switzerland) followed by WGS on a MiSeq platform (Illumina, Eindhoven, Netherlands) using v3 chemistry as 300-cycle paired-end runs. AMR genes and point mutations were identified and compared to the phenotypic results for better understanding of the mechanisms of resistance and resistance transmission. A wide variety of cephalosporin and fluoroquinolone resistance genes (mobile genetic elements (MGEs) and chromosomal mutations) were identified among isolates that mostly explained the phenotypic AMR patterns. A total of 31 plasmid replicon types were identified among the 82 isolates, with a subset of them (n = 24), identified in E. coli isolates. Five plasmid replicons were confined to the Enterobacter cloacae isolate and two were confined to the Klebsiella pneumoniae isolate. Virulence genes associated with functions including stress, survival, regulation, iron uptake secretion systems, invasion, adherence and toxin production were identified. Our study showed that antimicrobial resistant organisms (AROs) can persist even following wastewater treatment and could transmit AMR of clinical relevance to the environment and ultimately pose a risk to human or animal health.

Pesticide degradation in an integrated constructed wetland: Insights from compound-specific isotope analysis and 16S rDNA sequencing

Carbon isotope analysis and the 16S rDNA sequencing were adopted to investigate the degradation process of chlorpyrifos during its transport in the integrated constructed wetland (ICW). Firstly, the extent of concentration decrease of chlorpyrifos was examined, and the removal efficiency in the first 36 h was found to be the highest. The removal rate reached 96.83 % after 96 h, and this process fit to the first-order kinetic model, with a kinetic constant (k) of 0.066 h−1. A significant carbon isotope fractionation was observed, with a change of the δ13C values from −26.54 ± 0.07 ‰ to −25.41 ± 0.08 ‰. The average chlorpyrifos biodegradation proportion reached 71.23 % (60.42 %–85.04 %), and it was predicted that about 11.79 %–36.41 % of chlorpyrifos removal in the ICW was attributed to abiotic factors. The outlet of the subsurface flow constructed wetland saw the highest D∗/B∗ value (1.38–3.88), indicating that the remaining fraction of dilution was much more significant than that of degradation in this period. The top 20 phyla of microbial community were identified in the ICW. Proteobacteria was the most dominant phylum, accounting for >40 % of the bacterial communities in all sampling locations. Acidobacteria and Bacteroidetes were the second and third dominant phyla. At the genus level, the microbial community composition differed more greatly in every stage of the ICW, and the spatial distribution difference was quite significant in the ICW. This study is important to figure out the migration and transformation of chlorpyrifos when the ICW was adopted as a removal tool for organic micro-pollutants, and more similar studies could be carried out in the future to promote the evaluation of pollutant removal capacity of the ICWs, and to further develop the application of stable isotope analysis of compounds in the natural environment.

Efficacy of a large-scale integrated constructed wetland for pesticide removal in tail water from a sewage treatment plant

The higher and higher detection frequencies of micro-pollutants such as pesticides in water are nowadays intensifying the investigation for strategies to provide effective engineering methods that could mitigate such substances. Traditional sewage treatment plants (STP) do not design specific processes for micro-pollutants removal in water. As an environmentally-friendly measure, some laboratory-scale wetlands have been proved to be effective in the removal of pesticides in water, but such studies are rarely carried out in large-scale wetlands, especially when they are adopted as a polishing step of STPs. Therefore, the further removals of micro-pollutants in tail water of STPs through the large-scale wetlands and the relevant removal mechanism are still knowledge gaps. In this study, 44 target pesticides were detected in the water of a large-scale integrated constructed wetland (ICW) for four seasons. The ICW was established to further process the tail water from a STP, whose drainage was from domestic sewage of local residents. There were 19, 16, 17, and 19 pesticides detected in spring, summer, autumn, and winter, respectively. The removal values for Σ19 pesticides ranged from 49.99% to 84.96% during the study period, and the removal of these pesticides followed significant seasonal trends, which was likely because the microorganisms responsible for biotic degradation were markedly influenced by seasonal temperature fluctuations. Proteobacteria, Chloroflexi, Acidobacteria, Planctomycetes, and Bacteroidetes were the dominant phyla, and might be associated with the biodegradation of organic pollutants in the ICW. Removal of pesticides by the ICW resulted in overall toxicity reductions in water, but butachlor and chlorpyrifos were still at non-ignorable ecological risks. This study highlights the potential of constructed wetlands for micro-pollutants removal in water as a polishing step in STPs.

Wetland Construction, Restoration, and Integration: A Comparative Review

In response to the global loss and degradation of wetland ecosystems, extensive efforts have been made to reestablish wetland habitat and function in landscapes where they once existed. The reintroduction of wetland ecosystem services has largely occurred in two categories: constructed wetlands (CW) for wastewater treatment, and restored wetlands (RW) for the renewal or creation of multiple ecosystem services. This is the first review to compare the objectives, design, performance, and management of CW and RW, and to assess the status of efforts to combine CW and RW as Integrated Constructed Wetlands (ICW). These wetland systems are assessed for their ecological attributes and their relative contribution to ecosystem services. CW are designed to process a wide variety of wastewaters using surface, subsurface, or hybrid treatment systems. Designed and maintained within narrow hydrologic parameters, CW can be highly effective at contaminant transformation, remediation, and sequestration. The ecosystem services provided by CW are limited by their status as high-stress, successionally arrested systems with low landscape connectivity and an effective lifespan. RW are typically situated and designed for a greater degree of connection with regional ecosystems. After construction, revegetation, and early successional management, RW are intended as self-maintaining ecosystems. This affords RW a broader range of ecosystem services than CW, though RW system performance can be highly variable and subject to invasive species and landscape-level stressors. Where the spatial and biogeochemical contexts are favorable, ICW present the opportunity to couple CW and RW functions, thereby enhancing the replacement of wetland services on the landscape.

Critically important antimicrobial resistant Enterobacteriaceae in Irish farm effluent and their removal in integrated constructed wetlands

This study investigated the ability of Integrated Constructed Wetlands (ICWs) to remove critically important antimicrobial resistant organisms (AROs) from farm wastewater. Influent samples from the untreated farm waste and effluent samples taken at the end of the ICW system were collected monthly from four ICWs, serving four different farm types (suckler, dairy, dairy & poultry and pig). Using selective media to screen for the presence of carbapenemase resistant organisms, plasmid mediated and AmpC β-Lactamase producing organisms (ESBL/pAmpC) and fluoroquinolone resistant organisms, a total of 82 AROs were obtained with the majority being E. coli (n = 79). Statistically significant were the differences on the number of AROs isolated from influent (higher) compared to effluent, as well as a seasonal effect, with less AROs recovered during winter in comparison to other seasons (P < 0.05). On the other hand, there was no significant differences in the recovery of AROs on different farms. The majority of isolates from each of the farms (99%) were multi drug resistant, with 65% resistant to seven or more antimicrobials. A high incidence of tetracycline, trimethoprim/sulfamethoxazole, and ampicillin resistance was common to the isolates from all four farms but there were differences in ESBL levels with 63% of the isolates recovered from Farm 4 (piggery) being ESBLs compared to 18%, 36% and 4.5% recovered from Farms 1 (suckler), 2 (dairy) and 3 (dairy & poultry), respectively. No carbapenemase producing organisms were isolated. Our results showed that ICWs are effective in removing critically important AROs from farm wastewater on all four farm types.

Performance efficiency of a large-scale integrated constructed wetland

Introduction: Wastewater treatment plants are used to reduce pollution depending upon their effectiveness, treatment-efficiency, available-land, energy-sources, topography, climate and prevailing-winds, seasonal and climatic variations, and principal-cost. Integrated constructed wetlands (ICWs) are diversely used for wastewater treatment because of their increased treatment efficiency. Purpose of the study: This study comprises of large-scale-ICW located at NUST Islamabad, Pakistan. Purpose of study was to monitor and identify the nutrient removal over the period of six month from October 2018 to March 2019. Material and methods: Samples were taken from each compartment of HSSF-CW (Horizontal Sub-Surface Flow Constructed Wetland) and FILTER technology (Filtration and Irrigated cropping for Land Treatment and Effluent Reuse) of treatment system. Different parameters including EC(Electrical conductivity), NO3 (Nitrate), NO2 (Nitrite), TKN (Total Kjeldahl Nitrogen), PO43- (Phosphate) were measured. Results: Removal efficiency of above discrice parameters was recorded 3, 0, 43, 43 and 27% of HSSF-CW respectively, while FILTER- technology contribute in removal by 6, 75, 19, 23 and 37% respectively. Conclusion: Spatial, temporal and plantation variation was calculated and results showed that effluent concentrations were significantly varied. TKN and Phosphate showed significant spatial and temporal variation, and also significantly varied due to presence and absence of plantation while no significant spatial variation was recorded in EC and Nitrite. Correlation was observed between physicochemical and weather parameters.

Assessing the environmental and economic efficacy of two integrated constructed wetlands at mitigating eutrophication risk from sewage effluent

AbstractThe nutrient removal efficiency of two integrated constructed wetlands (ICWs) installed at commercial wastewater treatment plants (WWTPs) in Norfolk, UK, is assessed – the River Ingol ICW (1 year old) and the River Mun ICW (5 years old). Analysing water samples collected across the ICWs between February and September 2019, significant reductions in both effluent nutrient concentration and load were recorded. At the River Mun ICW, mean nitrate and phosphate concentrations were reduced by ~63% across the wetland, whilst nutrient loadings were reduced by ~57%. At the River Ingol ICW, mean nitrate and phosphate concentrations were reduced by ~30%, whilst nutrient loadings were reduced by ~70%. Economically, the total capital cost of both ICWs was comparable at £31‐39 per person served. Overall, this study demonstrates ICWs can significantly reduce the eutrophication risk associated with WWTP discharges and can do so whilst providing a cost‐effective alternative to conventional tertiary wastewater treatment.

Application of 15N tracing for estimating nitrogen cycle processes in soils of a constructed wetland

Integrated Constructed Wetlands (ICW) area technology for the attenuation of contaminants such as organic carbon (C), nitrogen (N), phosphorous (P) and sulphur (S) in water coming from point or diffuse sources. Currently there is a lack of knowledge on the rates of gross N transformations in soils of the ICW bed leading to losses of reactive N to the environment. In addition, the kinetics of these processes need to be studied thoroughly for the sustainable use of ICW for removal of excessive N in the treatment of waste waters. Gross N transformation processes were quantified at two soil depths (0–15 and 30–45 cm) in the bed of a surface flow ICW using a 15N tracing approach. The ICW, located in Dunhill village at Waterford in Southeastern Ireland, receives 500 person equivalent waste waters containing large quantities of organic pollutants (ca. mean annual C, N, P and S contents of 240, 60, 5 and 73 mg L−1). Soil was removed from these depths in December 2014 and incubated anaerobically in the laboratory, with either 15N labeled ammonium (NH4+) or nitrate (NO3−), differentially labeled with 14NH415NO3 and 15NH414NO3 in parallel setups, enriched to 50 atm% 15N. Results showed that at both soil depths, NO3− production rates were small, which may have resulted in lower NO3− reduction by either denitrification or dissimilatory NO3− reduction to ammonium (DNRA). However, despite being low, the DNRA rates were greater than denitrification rates. Direct transformation of organic N to NO3−, without mineralization to NH4+, was a prevalent pathway of NO3− production accounting for 28–33% of the total NO3− production. Relative contribution of this process to the total N mineralization was negligible at depth 1 (0.01%) but dominant at depth 2 (99.7%). Total NO3−production to total immobilization of NH4+ and NO3− was very small (<0.50%) suggesting that ICW soils are not a source of NO3−. Despite a large potential of N immobilization existed at both the layers, relative N immobilization to the total N conversion was higher at depth 2 (ca. 2.2) than at depth 1 (ca. 1.5). The NH4+ desorption rate at 30–45 cm was high. However, immobilization in the recalcitrant and labile organic N pools was higher. Mineralization and immobilization of NH4+ processes showed that recalcitrant organic N was the predominant source in ICW soils whereas the labile organic N was comparatively small. Source apportionment of N2O production showed that the majority of the N2O produced through denitrification (ca. 92.5%) followed by heterotrophic nitrification (ca. 5.5%), co-denitrification (ca. 1.90%) and nitrification (0.20%). These results revealed that application of a detailed 15N tracing method can provide insights on the underlying processes of ecosystem based abundances of reactive N. A key finding of this study was that both investigated ICW layers were characterised by large N immobilization which restricts production of NO3− and further gaseous N losses.

Can an Integrated Constructed Wetland in Norfolk Reduce Nutrient Concentrations and Promote In Situ Bird Species Richness?

Integrated Constructed Wetlands (ICWs) are potentially effective tools in the effort to restore aquatic ecosystems, and also they incorporate multiple co-benefits. An ICW was constructed in Norfolk, UK, to address the degradation of a stream and lake receiving treated effluent from a small Sewage Treatment Works (STW). Results demonstrated that: (1) nutrient concentrations significantly reduced from the ICW influent to the effluent (percentage reductions: total phosphorus [TP]: 78%, orthophosphate: 80%, total oxidised nitrogen [TON]: 65%, nitrate: 65%, nitrite: 67%, ammoniacal nitrogen: 62%), and mean dissolved oxygen concentrations increased (influent mean: 6.4 ± 1.4 mg l−1 effluent mean: 17.8 ± 3.3 mg l−1), (2) there were non-significant reductions in nutrient concentrations in the receiving stream (percentage reductions: TP: 23%, orthophosphate: 23%, TON: 26%, nitrate: 26%), with the exception of ammoniacal nitrogen (127% increase) and nitrite (76%) after ICW commissioning, and (3) mean in situ avian species richness increased from 10 to 27 species. Thus, the ICW substantially reduced nutrient concentrations, and had in situ conservation benefits. It is recommended that appropriately designed ICWs should be implemented widely and statutory authorities should ensure: 1) best-practice maintenance and 2) final effluent monitoring at both the STW and at the ICW outflows.

The Removal of Antibiotics in Relation to a Microbial Community in an Integrated Constructed Wetland for Tail Water Decontamination

An integrated constructed wetland (ICW) with six subsystems has been operated for six years (60,000 Ton day−1) and exhibited strong stability and high efficiency for removing conventional pollutants in tail water. This study was aimed to characterize the removal efficiency of antibiotics in relation to bacterial community structure and composition in this integrated constructed wetland. Water samples were taken from different ICW sites in two distinct seasons (i.e. winter and summer). The results showed that concentrations of antibiotics in ICW decreased from influent to effluent with varying removal rates among the different antibiotics (quinolones, ulfonamides and macrolides). The pyrosequencing of 16S ribosomal DNA revealed that the composition of dominant phyla could be grouped into four bacterial clusters and the key discriminant phyla, family or genera from each cluster was strongly associated with the specific physicochemical parameters of water or type of antibiotics. Members of the key phyla (Proteobacteria, Bacteroidetes, Parcubacteria, and Actinobacteria) appeared to play an important role in antibiotics removal. In general, both the concentration of antibiotics and physicochemical parameters of water shaped the bacterial communities. These results improve our understanding of the interactions between antibiotics or water physiochemical parameters and bacterial communities in the integrated constructed wetland.

Removal of steroid hormones and biocides from rural wastewater by an integrated constructed wetland

Steroid hormones and biocides are regarded as emerging contaminants in rural wastewater in China, owing to their widespread occurrence and adverse effects on both aquatic organisms and humans. Constructed wetlands (CWs) are an alternative technology for cost-effective and efficient decentralized rural sewage treatment. In this study, an integrated constructed wetland (ICW) system was built and used to treat a typical rural wastewater mixture composed of domestic sewage and livestock wastewater from a small village. As expected, five steroid hormones (ADD, AED, 19-NTD, T, and P) and four biocides (DEET, TCS, CBD, and MP) were detected in the influent in concentrations ranging from 30.5 ± 1.25 ng/L to 105 ± 5.14 ng/L and from 63.4 ± 2.85 ng/L to 515 ± 19.7 ng/L, respectively. The ICW system effectively removed the detected steroid hormones (97.4 ± 0.09%) and biocides (92.4 ± 0.54%). Based on the measured concentrations, the total pollution loadings of the detected steroid hormones and biocides in the influent were calculated to be 2330 ± 26.5 μg/day and 5710 ± 196 μg/day, which decreased to 60.8 ± 1.44 μg/day and 433 ± 25.6 μg/day in the final effluent. The risk quotients for these steroid hormones and biocides in the effluent from the ICW system were lower than those from reported wastewater treatment plants, indicating that CWs are a promising technology for removing contaminants including steroid hormones and biocides in rural wastewater, although additional efforts are required to optimize and improve the design of CWs before the steroid hormones and biocides present in the effluent can be safely and directly discharged into the environment.

Reactive carbon and nitrogen concentrations and dynamics in groundwater beneath an earthen-lined integrated constructed wetland

Using earthen liners at the base of an integrated constructed wetland (ICW) maintains a hydraulic continuum between the ICW and the underlying groundwater body. This may enable migration of reactive carbon (dissolved organic and inorganic carbon (DOC, DIC)) and reactive nitrogen (Nr) across this liner to groundwater along this continuum to groundwater. Therefore, in terms of a holistic assessment of ICWs, quantification of these losses is important and indeed from an environmental perspective comparing such losses to other ICW dis-connected areas within the same groundwater body is critical. The main objective of the present study on an ICW site in SE Ireland was to compare reactive forms of C and N in groundwater (three piezometer nests) representing the continuum end point of ICW Cell 2 and 3 with that of groundwater dis-connected to the ICW system. For this purpose two control planes consisting of shallow and deep groundwater piezometer nests were installed and monitored at 1 and 4 m depths, respectively underneath the earthen liners at 0.2 m adjacent to the ICW cells. Fieldwork was conducted between Nov 2013 and Nov 2014 and results showed that groundwater beneath the ICW liner had a highly reduced signal with C and N concentrations being significantly higher to those of the disconnected up-gradient groundwater. The DOC, DIC and dissolved CO2 and CH4 concentrations in groundwater beneath the ICW cells were significantly higher than the up-gradient groundwater. All the reactive forms of C were higher in Cell 2 than in Cell 3. With respect to depth, all forms of reactive C were higher in deeper groundwater than the shallow equivalents except for DOC. Equally, Nr concentrations (NH4+, DON, NO3−-N and N2O) were higher in groundwater beneath the ICW cells than the up-gradient groundwater. They were higher in Cell 2 than in Cell 3 and higher in shallow rather than deep groundwater. The fate of the reactive C and N is unknown. Typically DOC delivery from groundwater to surface water drives many biogeochemical processes as an electron donor to microbes or can be converted to CO2 and CH4 emissions and the dissolved CO2 and CH4 can be indirectly exchanged to the atmosphere. The results suggest that nutrient delivery from the ICW cells to the underlying groundwater needs to be evaluated and the design of earthen-lined ICWs should consider this nutrient loss continuum across the liner.

Assessing the Integration of Wetlands along Small European Waterways to Address Diffuse Nitrate Pollution

Nitrate concentrations in numerous European fresh watercourses have decreased due to end-of-pipe measures towards manure and fertilization management, but fail to meet the environmental objectives. The implementation of complementary measures to attenuate diffuse nitrate pollution in densely populated regions characterised by limited available area has been barely studied. To tackle this issue, this study evaluates the feasibility of integrating Constructed Wetlands (CWs) along waterways as a promising tool to facilitate compliance with the nitrate regulations. The aim is to calculate the required area of land alongside a specific watercourse to integrate CWs to reduce nitrate concentrations consistently below the 11.3 and 5.65 mgNO3-N/L levels, according to the Nitrates Directive and the Flemish Environmental Regulations. Nitrate-nitrogen removal efficiencies achieved at case study CWs were compared and validated with reported values to estimate the needed wetland areas. In addition, the removal efficiencies and areas needed to meet the standards were calculated via the kinetic model by Kadlec and Knight. The predicted areas by both methods indicated that CWs of 1.4–3.4 ha could be implemented in certain regions, such as Flanders (Belgium), with restricted available land. To conclude, three designs for ICWs (Integrated Constructed Wetlands) are proposed and evaluated, assessing the feasibility of their implementation.

Nitrogen removal and distribution of ammonia-oxidizing and denitrifying genes in an integrated constructed wetland for swine wastewater treatment

This study investigated nitrogen (N) removal process and microbial community distribution in a full-scale integrated constructed wetland (ICW), which was constructed with a bioreactor (R) and three wetland units (W1, W2, and W3) arranged successively along the flow path. For swine wastewater treatment, ICW showed high N removal efficiency with average removal rate of 98% for NH4+-N and 96% for total nitrogen (TN) from August 2012 to July 2014. In ICW sediments, abundance of amoA gene of ammonia-oxidizing archaea (AOA) was 1 order of magnitude greater than ammonia-oxidizing oxidizing bacteria (AOB), and narG gene was 2 orders of magnitude greater than nosZ. The highest amoA gene abundance of AOA and AOB in R were consistent with the most efficient NH4+-N and TN removal compared to W1, W2, and W3. Both W1 and W3 vegetated with Myriophyllum aquaticum had significantly higher AOA abundance than W2 vegetated with Ipomoea aquatica, Zizania latifolia, and Nasturtium officinale (p<0.05). Responding to the increasing NO3−-N concentrations along the flow path, higher narG and nosZ abundance were observed in W2 and W3 than in R and W1. Principal component analysis revealed that there were clear differences in the relative abundance of terminal restriction fragments. These findings demonstrated that environmental factors such as wetland plants and NH4+-N and NO3−-N concentrations had effects on the distri bution of microbial ammonia oxidizers and denitrifiers. Therefore, the responsible development of functional microbial communities could contribute to efficient N removal in the ICW.

Phosphorus Sorption Capacities of Steel Slag in Pilot-Scale Constructed Wetlands for Treating Urban Runoff: Saturation Potential and Longevity

Two parallel pilot-scale integrated constructed wetland (ICW) systems were constructed on the bank of Nanfeihe River. The phosphate (PO43-) isothermal adsorption properties of the upper substrate steel furnace slag (SFS) in up-flow chamber was investigated during one-year operation period. The maximum phosphorus (P) adsorption capacity of SFS 9, 11, 13, 15, 17, 19 months service time were 848.9 mg/kg, 968.1 mg/kg, 824.5 mg/kg, 788.7 mg/kg, 864.7 mg/kg and 960.3 mg/kg, respectively. The saturated adsorption amount of SFS had not decreased with the service time prolonging in ICW. The longevity of a full-scale system could not be reliably estimated only based on the theoretical saturated adsorption capacity from laboratory experiments.

Multicriteria decision analysis for the evaluation of water quality improvement and ecosystem service provision

AbstractWater and land management decisions require consideration of multiple factors. Multicriteria decision analysis (MCDA) provides a structured, auditable and transparent tool that helps inform and add rigour to multioption decisions. MCDA was used in a payment for ecosystem services (PES) project to evaluate options for delivering good ecological status in Tortworth Brook, Gloucestershire, UK. Following a process of stakeholder engagement, final options considered were: (1) doing nothing; (2) modifying existing sewage treatment works; (3) a single integrated constructed wetland (ICW) targeting multiple ecosystem service outcomes; and (4) catchment wide multiple ICWs. The analysis concluded that the ‘do nothing’ option and modifying the existing works are both likely to provide poor utility and value for money. Both ICW options offered the greatest utility in terms of optimising the benefits to all stakeholders.

Performance Evaluation of Integrated Constructed Wetland for Domestic Wastewater Treatment

Simple, budget friendly, laboratory-scale integrated constructed wetland (ICW) was designed to assess domestic wastewater treatment performance at a loading rate of 75 mm/d, planted with native plant species: Veronica-angallis aquatica and compared with non-vegetative control system at various residence times of 4, 8, 12, 16, 20, 24, and 28 days. Results revealed that the vegetated ICW demonstrated superior performance over non-vegetated control: 69.12 vs 17.12%, 67.77 vs 16.04%, 68 vs 16.48%, 71.19 vs 6.56%, 71.54 vs 14.80%, and 72.04 vs 11.41% for total dissolved solids, total suspended solids, phosphates (PO4(-)), sulfate (SO4(-)), nitrate (NO3(-)), and nitrite (NO2(-)), respectively, at 20 days residence times. Reduction in bacterial counts (2.79 × 10(4) CFU/mL) and fecal pathogens (345.5 MPN index/100 mL) was observed in V. aquatica at 20 days residence time. Therefore, the present study highlights not only the presence of vegetation but also appropriate residence time in constructed wetlands for better performances.

Phosphorus retention and mass balance in an integrated constructed wetland treating domestic wastewater

This study quantified the contributions of different P removal pathways in an integrated constructed wetland (ICW) treating domestic wastewater. Findings over the study period (February 2008 to March 2012) showed average P retention rates of 31 ± 2 mg/m2/day for molybdate reactive phosphate (MRP) and 40 ± 3 mg/m2/day for total P. Near complete P removal was achieved during the first 2 years of operation. Thereafter, effluent concentrations increased slightly. According to the mass balance estimation, assimilation by plants accounted for approximately 16% of the total P retained, while sediment storage contributed nearly 60%. Sediment storage was the major P removal pathway in the ICW. Thus, high effluent concentrations recorded during high effluent flow volumes was due to remobilisation of P from the sediment. Management of ICW systems may therefore require implementing sediment removal schemes. The combination of plants with high biomass production can be beneficial for improving ICW performance.