Seasonal variation of nutrient removal in a full-scale horizontal constructed wetland

Nitrate and ammonium removal in constructed wetlands: Experimental insights and zero-dimensional numerical modeling

Constructed wetlands (CWs) have emerged as effective wastewater treatment systems, mimicked natural wetland processes but engineered for enhanced pollutant removal efficiency. Ammonium (NH4+) and nitrate (NO3-) are among common pollutants in wastewater, posing significant environmental and health risks. The primary objective of this study is to compares the performance of CWs using gravel and three sizes of natural pumice, along with phragmites australis, in horizontal and horizontal-vertical CWs for nitrate and ammonium removal in the complementary treatment of domestic wastewater. Additionally, the study aims to develop and validate a numerical model using MATLAB software to predict the removal efficiency of these pollutants, thereby contributing to the optimization of CW design and operation. The model operates as a zero-dimensional model based on the law of mass conservation, treating the wetland as a completely mixed reactor, thus avoiding complexities associated with solute movement in porous media. It accurately could predict removal efficiency of chemical, biochemical, and biological indicators while considering active and passive absorption mechanisms by plant uptake. Notably, the determination of coefficients in the model equation does not rely on potentially error-prone laboratory measurements due to sampling issues. Instead, optimization techniques alongside field data robustly estimate these coefficients, ensuring reliability and practicality. Results indicate that higher pollutant concentrations increase reaction rates, particularly enhancing CW efficiency in ammonium removal. Pumice, especially in larger sizes, exhibits superior absorption due to increased porosity and surface area. Overall, the model accurately predicts nitrates concentrations, demonstrating its potential for CW performance optimization and confirming the significance of effective pollutant removal strategies in wastewater treatment.

Purification of the secondary treatment tail water for wastewater reclamation by integrated subsurface-constructed wetlands

A whole-year investigation of full-scale integrated subsurface-constructed wetlands (ISCWs) was carried out to purify the tail water from a wastewater treatment plant (WWTP) for wastewater reclamation under four plant species, four hydraulic loading rates (HLRs), and four seasons. The results showed that ISCWs were effective for the purification of WWTP discharge, with the average removal efficiencies of COD, NH4+-N, TN, and TP being 48%, 49%, 9%, and 30%, respectively. Typical pollutant concentrations in the treated effluent of ISCWs were 8.19 mg/L COD, 1.76 mg/L NH4+-N, 11.57 mg/L TN, and 0.36 mg/L TP, which met most of the water quality standards for reusing recycling water. Emergent plants with well-developed root systems may be capable of promoting the decontamination of ISCWs. Seasonal change played an important role in the treatment process: the removal of phosphorus by plant uptake and microbial utilization was more active in the warm season and the co-occurrence of organic degradation and nitrification, whereas the cold season is conducive to exothermic adsorption process of pollutants to substrates. Properly increasing the HLRs may improve the availability of ISCWs according to the requirement of effluent quality. Furthermore, the C/N ratio might be the key factor for the purification effect of ISCWs, because the COD level of WWTP discharge may change the process of NH4+-N biotransformation.

Long-term performance of a deep oxidation pond with horizontal subsurface flow constructed wetland for purification of rural polluted river water

A full-scale deep oxidation pond with horizontal subsurface flow constructed wetland (DOP-HSCWs) was constructed and used to investigate the nutrient removal and establish a practical inversion prediction model. The high long-term performances of nearly 7 years were obtained with the average removal efficiencies of 76.48 ± 10.11% (chemical oxygen demand, COD), 60.61 ± 29.21% (ammonia nitrogen, NH4+-N), 54.04 ± 21.92% (total phosphorus, TP) and 88.44 ± 6.86% (suspended solids, SS), respectively. The removal efficiency actually increased after 2016 with outflow concentrations lower as compared to initial phase of operation. The effluent concentration in autumn were obviously higher than that in other seasons because of high influent loadings. The Flaml model achieved good performance demonstrating the ability to predict water quality of DOP-HSCWs without human intervention. In addition, COD, NH4+-N, TP concentration of effluent can be significantly affected by SS concentration of influent according to the generalized additive model (p < 0.001). Compared with HSCWs, the DOPs was mainly contributed to pollutant removal. In summer, Cyanobacteria, Cyanobacteria and Proteobacteria were dominated in DOPs, while Proteobacteria was dominated in winter. Although the relative abundance of Proteobacteria in anaerobic zone decreased by 14.99%, the relative abundance of Firmicutes and Chloroflexi increased by nearly 10%, which ensured decontamination effect of the DOPs. Proteobacteria was also dominated in HSCWs, but it was lower than that in DOPs. This study indicated that DOP-HSCWs can achieve a sustainably excellent purification of rural polluted river water during the long period of operation.

Remediation and characterization of emerging and environmental pollutants from residential wastewater using a nature-based system

The nature-based systems (NBS) are nature inspired, unflagging, efficient, and budget friendly ideas that evolved as ideal technologies for wastewater treatment. The present study deals with the purification of residential wastewater through the NBS, covering three seasons. The NBS embedded with the Canna lily effectively eliminated organic matter, nutrients, and heavy metals. Nearly 57.2-75.2% COD, 69.9-83.2% BOD, 73.4-90.6% TSS, 51.1-71.6% PO₄^3--P, 66.3-84.8% NH₄⁺-N, 52-61.5% NO₃^--N, and 68-70.6% NO₂^--N removal were achieved. Heavy metals like Al, Cr, Mn, Fe, Ni, Cu, Zn, Mo, and Pb were removed, with a 98.25% reduction in the total bacterial count. The pollutant removal's kinetics was calculated using first-order kinetics. The mass removal rate of BOD was high in monsoon (22.3 g/m²/d), and COD was high in summer (36.4 g/m²/d). Organic compound removal (65.2%), including emerging pollutants, was observed by gas chromatography-mass spectrometry (GCMS) analysis of water and Canna samples. Wavelength dispersive X-ray fluorescence spectrometer (WDXRF) studied the elements and oxides retention by media and accumulation by the plant. The CHN content of the Canna and its morphological study was checked using the carbon CHNS analyzer and scanning electron microscope-energy dispersive X-ray (SEM-EDX), respectively. The performance of the NBS was validated using variance, correlation, and principal component analysis (PCA). This study shows the NBS effects on the remediation of environmental and emerging contaminants from residential wastewater and further use it for horticultural activities, thereby achieving sustainable development goals.

High Strength Wastewater Reclamation Capacity of Vetiver Grass in Tropics: The Case of Ethiopia

It is generally accepted that industrial wastewater like tannery effluent is high strength wastewater. The aim of this study was to examine the capacity of Vetiver grass for the treatment of high strength wastewater in a constructed wetland. Two constructed wetland beds were designed and one of them was not planted used as a control group. The grass was planted with 20 cm by 20 cm distance from each seedling. The biometric characteristics of Vetiver grass was evaluated by taking randomly selected clusters of the grass. The concentration of chromium in the extract of parts of the grass was determined by atomic absorption spectrophotometer. The Chromium bioaccumulation and Translocation factor was estimated. Composite samples before and after treatment of 4 different hydraulic retention time was collected. The physiochemical analysis of the wastewater has been carried out. The constructed wetland bed with Vetiver grass performed that, BOD, COD, NH₄-N, NO₃-N, TN, PO₄-P, and TP were reduced at the retention time of 9 days by 91.9%, 96.3%, 62%, 86%, 88.7%, 96.3%, and 92.2% respectively. Chromium was also reduced by 97% at retention time of both 7 and 9 days over the planted bed. The bed with plant performs significantly better than without plant at P-value <.01. Therefore, Vetiver grass has a capacity to reclaim high strength industrial wastewater in tropical areas.

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

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

Changes in the nitrification-denitrification capacity of pilot-scale partially saturated vertical flow wetlands (with corncob in the free-drainage zone) after two years of operation

This six-month study aimed to evaluate the removal of total nitrogen (TN) in two duplicated partially saturated (PS) vertical flow (VF) wetlands added with corncob in two different heights of the free-drainage zone (FDZ) after two years in operation. Both PS VF wetlands efficiently removed organic matter measured as biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD) as well as total suspended solids (TSS) achieving average mass removal efficiencies of 95.3%, 83.2% and 92.9%, respectively, in system I (SI) and 96.3%, 84.0% and 94.9%, respectively, in system II (SII); with no significant differences (p > 0.05) between the systems. Measurements of oxidation-reduction potential (ORP), dissolved oxygen (DO), pH and electrical conductivity (EC) showed suitable conditions in the saturated zone (SZ) of the systems for denitrification process. TN removal was similar in both systems (p > 0.05) (51.5% and 52.9% in SI and SII), and decreased in 15% with respect to the first year. This decrease was due to the lower denitrification capacity of the FDZ as a result of the reduction in the supply of biodegradable carbon by corncob. Denitrification occurred in the SZ, but not at a sufficient level to increase TN removal. NoveltyFirst, the use of lignocellulosic residues in partially saturated vertical wetlands to promote total nitrogen removal is very recent. Furthermore, to the best of our knowledge, this is the first study evaluating TN removal after two years of operation in this type of wetland. Therefore, this study allows us to better understand the function of these systems, in a relatively long term. Thanks to this study: it is possible to confirm that the main process of TN elimination is through the simultaneous nitrification-denitrification process in the free drainage zone (denitrification in the saturated zone is irrelevant) and that TN elimination decreases due to the reduction in carbon supply from the corn, in this area.

Enhanced nitrogen removal in filled-and-drained vertical flow constructed wetlands: microbial responses to aeration mode and carbon source

For the purpose of enhancing the removal rate of nitrogen (N) and organic matters, intermittent aeration and carbon source were used in filled-and-drained vertical flow constructed wetlands (VFCWs). The results showed that the best removal of COD (74.16%), NH₄⁺-N (93.56%), TN (86.88%), and NO₃^--N (79.65%) was achieved in VFCW1 (aerated with carbon source system). Illumina MiSeq300 high-throughput sequencing showed that carbon source aerated system increases the diversity and richness of the microbial community. The copy numbers of nitrification functional genes (nxrA, amoA), denitrification functional genes (nirS, nirK, nosZ), and anammox functional gene (anammox 16S rRNA) displayed various changes when applied different aeration modes and additional carbon source to each system. An increase of the DO concentration and carbon source facilitated the absolute abundance of microbial nitrification and denitrification functional genes, respectively. All in all, these results demonstrate that carbon source combined with intermittent aeration is valid to improve the pollutant treatment performance in these systems.

Multistage Horizontal Subsurface Flow vs. Hybrid Constructed Wetlands for the Treatment of Raw Urban Wastewater

In this study, pilot-scale hybrid constructed wetlands (CWs) and multistage horizontal subsurface flow CWs (HF CWs) have been studied and compared for the treatment of raw urban wastewater. In the hybrid CWs, the first stage was a mulch-based horizontal subsurface flow CW and the second stage was a vertical subsurface flow CW (VF CW). The VF CWs were used to determine if sand could improve the performance of the hybrid CW with respect to the mulch. In the multistage HFs, mulch, gravel and sand were used as substrates. The effect of water height (HF10: 10 cm vs. HF40: 40 cm) and surface loading rate (SLR: 12 vs. 24 g Chemical Oxygen Demand (COD)/m2d) has been studied. The results show that the use of sand in the vertical flow stage of the hybrid CW did not improve the average performance. Additionally, the sand became clogged, while the mulch did not. The effect of water height on average pollutant removal was not determined but HF10 performed better regarding compliance with legal regulations. With a SLR of 12 g COD/m2d, removals of HF10 were: 79% for COD, 75% for NH4+-N, 53% for dissolved molybdate-reactive phosphate-P (DRP), 99% for turbidity and 99.998% for E. coli and total coliforms. When SLR was doubled, removals decreased for NH4+-N: 49%, DRP: −20%, E coli and total coliforms: 99.5–99.9%, but not for COD (85%) and turbidity (99%). Considering the obtained results and the simplicity of the construction and operation of HFs, HF10 would be the most suitable choice for the treatment of raw urban wastewater without clogging problems.

New insights for enhancing the performance of constructed wetlands at low temperatures

Constructed wetlands (CWs) have been widely utilized for various types of wastewater treatment due to their merits, including high cost-effectiveness and easy operation. However, a few intrinsic drawbacks have always restricted their application and long-term stability, especially their weak performance at temperatures under 10 °C (low temperatures) due to the deterioration of microbial assimilation and plant uptake processes. The existing modifications to improve CWs performance from the direct optimization of internal components to the indirect adjunction of external resources promoted the wastewater treatment efficiency to a certain degree, but the sustainability and sufficiency of pollutants removal remains a challenge. With the goal of optimizing CW components, the integrity of the CW ecosystem and the removal of emerging pollutants, future directions for research should include radiation plant breeding, improvements to CW ecosystems, and the combination or integration of certain treatment processes with CWs to enhance wastewater treatment effects at low temperatures.

Removal of nitrogen from low pollution water by long-term operation of an integrated vertical-flow constructed wetland: Performance and mechanism

The efficiency of nitrogen removal and its mechanism, aquatic organism distribution characteristics and regeneration capability of zeolite from an integrated vertical-flow constructed wetland (IVFCW) for low pollution water treatment were evaluated after steady and continuous operation for eight years. After running for eight years, better than average COD and NH₄⁺-N removal were observed in the IVFCW. The NH₄⁺-N removal rate in this system was controlled by ammoxidation and adsorption and ion exchange of zeolite. The low total nitrogen (TN) removal efficiency was due to NO₃^--N accumulation and zeolite desorption. In addition, this phenomenon indicated that because of poor organic carbon sources, nitrification was stronger than denitrification, consistent with the distribution of the functional genes for nitrification and denitrification. The biological activity in this system was abundant, especially that of spirogyra and navicula. The saturated adsorption capacity of zeolite was as high as 1.35 mg g^-1 with a desorption rate of <20%. There were no obvious differences among the effects of aeration, water cleaning, drained reoxygenation and steam stripping for zeolite regeneration (adsorption capacity of >50%). However, the drained reoxygenation performance of was better due to zero energy consumption and regeneration in situ.