Intermittent aeration to improve wastewater treatment efficiency in pilot-scale constructed wetland

Iron-enhanced microscale laboratory aerated filters in the treatment of artificial mariculture wastewater: A study on nitrogen removal performance and the impact on microbial community structure

This study investigates the nitrogen removal efficacy and microbial community dynamics in seawater aquaculture effluent treatment using three different substrate combinations of microscale laboratory aerated filters (MFs) - MF1 (LECA), MF2 (LECA/Fe-C), and MF3 (LECA/Pyrite). The findings indicated that the COD removal exceeded 95% across all MFs, with higher removal efficiencies in MF2 and MF3. In terms of nitrogen removal performance, MF2 exhibited the highest average nitrogen removal of 93.17%, achieving a 12.35% and 3.56% increase compared to MF1 (80.82%) and MF3 (89.61%), respectively. High-throughput sequencing analysis revealed that the Fe-C substrate significantly enhanced the diversity of the microbial community. Notably, in MF2, the salinophilic denitrifying bacterium Halomonas was significantly enriched, accounting for 42.6% of the total microbial community, which was beneficial for nitrogen removal. Moreover, an in-depth analysis of nitrogen metabolic pathways and microbial enzymes indicated that MF2 and MF3 possessed a high abundance of nitrification and denitrification enzymes, related to the high removal rates of NH4+-N and NO3--N. Therefore, the combination of LECA with iron-based materials significantly enhances the nitrogen removal efficiency from mariculture wastewater.

Water treatment and reclamation by implementing electrochemical systems with constructed wetlands

Seasonal or permanent water scarcity in off-grid communities can be alleviated by recycling water in decentralized wastewater treatment systems. Nature-based solutions, such as constructed wetlands (CWs), have become popular solutions for sanitation in remote locations. Although typical CWs can efficiently remove solids and organics to meet water reuse standards, polishing remains necessary for other parameters, such as pathogens, nutrients, and recalcitrant pollutants. Different CW designs and CWs coupled with electrochemical technologies have been proposed to improve treatment efficiency. Electrochemical systems (ECs) have been either implemented within the CW bed (ECin-CW) or as a stage in a sequential treatment (CW + EC). A large body of literature has focused on ECin-CW, and multiple scaled-up systems have recently been successfully implemented, primarily to remove recalcitrant organics. Conversely, only a few reports have explored the opportunity to polish CW effluents in a downstream electrochemical module for the electro-oxidation of micropollutants or electro-disinfection of pathogens to meet more stringent water reuse standards. This paper aims to critically review the opportunities, challenges, and future research directions of the different couplings of CW with EC as a decentralized technology for water treatment and recovery.

Assessment of the properties of aging biochar used as a substrate in constructed wetlands

Biochar has gained global recognition as an effective tool for environmental remediation, and is increasingly being used as an alternative substrate in constructed wetlands (CWs). While, most studies have focused on the positive effects of biochar for the pollutant removal in CWs, less is known about aging and longevity of the embedded biochar. This study investigated the aging and stability of biochar embedded in CWs post-treating the effluent of a municipal and an industrial wastewater treatment plant. Litter bags containing biochar were inserted into two aerated horizontal subsurface flow CWs (350 m² each), and retrieved on several dates (8-775 days after burial) for assessment of weight loss/gain and changes in biochar characteristics. Additionally, a 525-day laboratory incubation test was conducted to analyze biochar mineralization. The results showed that there was no significant biochar weight loss over time, but a slight increase in weight (2.3-3.0%) was observed at the end, likely due to mineral sorption. Biochar pH remained stable except for a sudden drop at the beginning (8.6-8.1), while the electrical conductivity continued to increase (96-256 μS cm^-1) throughout the experiment. The sorption capacity of the aged biochar for methylene blue significantly increased (1.0-1.7 mg g^-1), and a change in the biochar's elemental composition was also noted, with O-content increasing by 13-61% and C content decreasing by 4-7%. Despite these changes, the biochar remained stable according to the criteria of the European Biochar Foundation and International Biochar Initiative. The incubation test also showed negligible biochar mass loss (<0.02%), further validating the stability of the biochar. This study provides important insights into the evolution of biochar characteristics in CWs.

Organic media-based two-stage traditional and electrode-integrated tidal flow wetlands to treat landfill leachate: Influence of aeration strategy and plants

Landfill leachate treatment employing normal and electrode-integrated constructed wetlands is difficult due to the presence of significant amounts of organic compounds, which frequently impede the progression of microbial-based aerobic pollutant removal pathways. As a result, this study examines the effect of supplementary air availability via intermittent and continuous aeration strategies in improving organic, nutrient, and coliform removals of the unplanted, planted (normal and electrode-integrated) two-stage tidal flow constructed wetlands designed to treat landfill leachate. The constructed wetlands were filled with coal and biochar media and planted with Canna indica. Mean chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and coliform removal percentages of the externally aerated two-stage unplanted, only planted, planted-microbial fuel cell integrated constructed wetland systems ranged between 96 and 99%, 82 and 93%, 91 and 98%, 86 and 96%, respectively, throughout the experimental campaign. External aeration inhibited the development of a dominant anaerobic environment within the media of the wetland systems and improved overall pollutant removal. The electrode-integrated planted tidal flow wetlands produced better effluent quality than the unplanted or only planted tidal flow systems without electrode assistance. The first stages of the three wetland systems achieved an additional 5-7% COD, 7-12% TN, and 15-22% coliform removal during the continuous aeration period compared to the corresponding performance of the intermittent aeration phase. The pollutant removal performance of the second-stage wetlands decreased during the continuous aeration phase. The media composition supported electrochemically active and inactive microbial-based pollutant removal routes and the chemical adsorption of pollutants. Nitrogen and phosphorus accumulation percentage in plant tissues was low, i.e., 0.4-2.2% and 0.04-0.8%, respectively. During the continuous aeration period, the electrode-integrated tidal flow constructed wetlands achieved higher power density production, i.e., between 859 and 1432 mW (mW)/meter³(m³). This study demonstrates that external aeration might improve pollutant removal performance of the normal, electrodes integrated tidal flow-based constructed wetlands when employed for high organic-strength wastewater treatment such as landfill leachate.

Enhancement of nitrogen removal by a modular design of vertical flow constructed wetlands with a plant carbon source: Optimization of carbon dosage for nitrogen removal, practicability evaluation and strategy exploration for water quality control

The requirement of artificial aeration for increasing nitrogen removal in vertical flow constructed wetlands (VFCWs) brings extra energy consumption and complex maintenance. The feasibility of a modular design to replace artificial aeration for partially saturated VFCWs with palm bark as a carbon source (PSVFCW-pb) to achieve water quality control, especially nitrogen removal was evaluated. The PSVFCW-pb with a spatially separate structure and perforated peripheries for better oxygen diffusion had a promising total nitrogen removal (e.g., 66.4% at a dosage of 1.435 g/L of palm bark pretreated at 120 °C for 40 min) without additional aeration, while organic carbon removal was nearly unaffected. An appropriate increase of the palm bark dosage (≤1.435 g/L) resulted in higher nitrogen removal; however, a more palm bark (1.875 g/L) could not further increase nitrogen removal but caused color pollution. In addition, the removal of nitrogen by the modularized PSVFCW-pb was more sensitive to the ambient temperature than the removal of organic carbon and phosphorus, and the higher temperature was preferable. Notably, the more attractive property of the modular design is its great potential to improve nitrogen removal by conveniently altering the number and/or scale of oxic and oxygen-free modules. Finally, the relationships between the hydraulic load and inflow concentration were explored, by which the suitable hydraulic load could be flexibly adjusted based on real-time water quality to meet the specified surface water quality criteria in different seasons. This study provides a reliable CW design for controlling nutrient pollution in surface waters.

An innovative reuse of bottom ash from municipal solid waste incinerators as substrates of constructed wetlands

The incineration of municipal solid waste has been important in waste management, but it raises another environmental issue concerning residue treatment. This study describes an innovative use of naturally aged incineration bottom ash (AIBA) as an alternative substrate for horizontal subsurface flow (HSSF) constructed wetlands (CW). Although experimental results from a period lasting for 396 days only revealed slightly higher removal ratios in HSSF with AIBA (HSSF-E) than in HSSF-traditional pebble beds (HSSF-C), increasing from 67% to 76% for BOD, 44%-51% for TKN, 47%-54% for NH₃-N, and 44%-52% for TN. The data indicate that the use of AIBA in HSSF CW can achieves a certain removal efficiency of BOD and nitrogen species. Interestingly, the total phosphorus removal rates also increased significantly from 20% in HSSF-C to 36% in HSSF-E. These observations on the use of AIBA in HSSF CW confirmed that AIBA is a suitable alternative for use as a substrate for HSSF CWs and identified an additional way to reuse incineration bottom ash. Design criteria for a CW using AIBA as a partial substrate is proposed to improve the pollutant removal performance of HSSF CWs.

Fate of resistome components and characteristics of microbial communities in constructed wetlands and their receiving river

Currently, most researches focus on that constructed wetlands (CWs) achieve desirable removal of antibiotics, antibiotic resistance genes (ARGs) and human pathogens. However, few studies have assessed the fate of resistome components, especially the behavior and cooccurrence of ARGs, mobile genetic elements (MGEs) and virulence factors (VFs). Therefore, characteristics of microbial communities (MCs) in CWs and their receiving rivers also deserve attention. These factors are critical to water ecological security. This study used two CWs to explore the fate of resistome components and characteristics of MCs in the CWs and their receiving river. Eleven samples were collected from the two CWs and their receiving river. High-throughput profiles of ARGs and microbial taxa in the samples were characterized. 31 ARG types consisting of 400 subtypes with total relative abundance 42.63-84.94× /Gb of sequence were detected in CWs, and 62.07-88.08× /Gb of sequence in river, evidencing that ARG pollution covered CWs and the river, and implying huge potential risks from ARGs. MGEs and VFs were detected, and tnpA, IS91 and intI1 were the three dominant MGEs, while Flagella. Type IV pili and peritrichous flagella were main VFs. Both CWs can remove ARGs, MGEs and VFs efficiently. However, some ARGs were difficult to remove, such as sul1 and sul2, and certain ARGs remained in the effluent of the CWs. The co-occurrence of ARGs, MGEs, and VFs implies the risk of antibiotic resistance and dissemination of ARGs. Eighty-five types of human pathogen were detected in the river samples, particularly Pseudomonas aeruginosa, Bordetella bronchiseptica, Aeromonas hydrophila and Helicobacter pylori. Correlation analysis indicated that MCs had significant effects on the profiles of ARGs in the water environment. This study reveals potential risks of the reuse of reclaimed water, and illustrates the removal ability of ARGs and related elements by CWs. This study will be helpful for monitoring and managing resistomes in water environments.

Demonstration study of bypass multipond wetland system to enhance river water quality

This study focused on the water quality of a river in Wuhan City, China, which is surrounded by ponds that were transformed into a bypass multipond wetland system to improve river water quality. The bypass multipond wetland system included surface-flow artificial wetlands, modified partition ponds, aeration reoxygenation ponds, ecological ponds, and other processes. After the stable operation of the process, the water transparency was higher than 60 cm and the dissolved oxygen (DO) was higher than 5 mg/L, while the ammonia nitrogen (NH₃-N) concentration was less than 1.0 mg/L, total phosphorus (TP) was lower than 0.2 mg/L, and chemical oxygen demand (COD) was lower than 20 mg/L, achieving the treatment target. After monitoring the results of each process, the process which best enhanced the water transparency enhancement was the surface-flow of the artificial wetlands and ecological ponds. The aeration reoxygenation pond had the best effect on DO enhancement. The processes that most affected NH₃-N and TP removal were the surface-flow artificial wetlands and ecological ponds. The modified parthenogenic pond had the greatest effect on COD removal. The bypass multipond wetland system not only improved the river water quality but also enhanced the river landscape, and can act as a reference for similar river water quality improvement actions.

Assessment of the effectiveness of a field-scale combined ecological treatment system at removing water pollutants, after optimization using a system dynamic model: a case study of rural inland ponds in China

Field-scale combined ecological treatment systems (FCETS) are designed to remove nutrients from aquaculture wastewater in ponds according to the characteristics of the nutrients present. We designed and established a numerical model based on the system dynamic (SD) method, to optimize the parameters of FCETS. Results showed that the mean removal rates of TSS, TN, NO₃^--N, NH₄⁺-N, TP, DP, and COD_Mn ranged from 83.3 to 125.8%, 41.1 to 49.1%, 44.8 to 56.2%, 49.3 to 55.6%, 80.0 to 88.2%, 52.6 to 65.0%, and 52.0 to 61.5%, respectively. The SD model provided satisfactory estimates of water quality at the outlet throughout both the validation and calibration periods. In addition, we conducted a sensitivity analysis to determine the key parameters of the SD model. This also involved optimization of the N and P removal capacity of FCETS, and their corresponding discharge (Q), and concentration (C) at the inlet. This made it possible to use R and MATLAB to simulate seasonal differences in the removal of N and P. Our results indicate that a FCETS can be used to efficiently remove nutrients from rural wastewater in ponds. In addition, we demonstrated that the SD-based numerical model is a useful management support tool to ensure that decisions are made which result in the stable operation of a FCETS. This illustrates that contamination-free aquaculture from rural inland ponds is a feasible goal.

Developing a new approach for design support of subsurface constructed wetland using machine learning algorithms

Knowing the effluent quality of treatment systems in advance to enable the design of treatment systems that comply with environmental standards is a realistic strategy. This study aims to develop machine learning - based predictive models for designing the subsurface constructed wetlands (SCW). Data from the SCW literature during the period of 2009-2020 included 618 sets and 10 features. Five algorithms namely, Random forest, Classification and Regression trees, Support vector machines, K-nearest neighbors, and Cubist were compared to determine an optimal algorithm. All nine input features including the influent concentrations, C:N ratio, hydraulic loading rate, height, aeration, flow type, feeding, and filter type were confirmed as relevant features for the predictive algorithms. The comparative result revealed that Cubist is the best algorithm with the lowest RMSE (7.77 and 21.77 mg.L^-1 for NH₄-N and COD, respectively) corresponding to 84% of the variance in the effluents explained. The coefficient of determination of the Cubist algorithm obtained for NH₄-N and COD prediction from the test data were 0.92 and 0.93, respectively. Five case studies of the application of SCW design were also exercised and verified by the prediction model. Finally, a fully developed Cubist algorithm-based design tool for SCW was proposed.

Remediation of algal cells, PO43-, and NO3- from eutrophic wastewater using Echinodorus cordifolius in zigzag-horizontal subsurface constructed wetlands

The pollutant removal efficiency of traditionally constructed wetlands (CWs) is often limited due to low interaction time between wastewater and the CW matrix (plants, microbes, and substrates). A zigzag-horizontal subsurface flow constructed wetland with effluent recirculation (Z-HSSF + ER) was developed to improve removal efficiency. Echinodorus cordifolius plants were used in this study. The efficiency of the systems was evaluated using eutrophic wastewater. The results showed that the developed systems exhibited the high removal efficiency of algal cells, PO₄^3-, and NO₃^- (97%, 70%, and 100%, respectively), within 5 days. Algal cells were removed by the interception mechanism of gravel and zigzag baffles. PO₄^3- and NO₃^- in the eutrophic wastewater was mainly removed by E. cordifolius including rhizobacteria and other microorganisms. The long flow pathway created by the installation of zigzag baffles combined with effluent recirculation provides high dissolved oxygen (DO) in the systems and increases the interaction time between wastewater and the CW matrix, thus improving the pollutant removal efficiency of CWs.

Enhancing nitrogen removal from anaerobically-digested swine wastewater through integration of Myriophyllum aquaticum and free nitrous acid-based technology in a constructed wetland

Despite of low operation costs and convenient maintenance, the application of natural systems for swine wastewater treatment has been limited by large construction area and unsatisfactory effluent quality. Introducing ammonium high uptake aquatic plants and shifting nitrogen removal pathway from nitrate to nitrite in constructed wetlands (CWs) has been regarded as promising approach to promote their performances. This study aimed to establish nitrite pathway and enhance N removal via free nitrous acid (FNA)-sediment treatment and Myriophyllum aquaticum vegetation in the CWs treating anaerobically digested swine wastewater. Nitrite pathway was successfully and stably achieved in the M. aquaticum CW with FNA-treated sediment. The overall removal efficiencies of ammonium nitrogen and total nitrogen were 42.3 ± 10.2% and 37.7 ± 9.3% in the planted CWs with FNA-treated sediment, which were 76.3% and 65.4% higher than those in the conventional oxidation pond system, respectively. Microbial community analysis (qPCR and metagenomics) suggested that the nitrite pathway established through FNA-sediment treatment was based on the inactivation of nitrite oxidizing bacteria (lower nxrA gene abundance) and the reduction of relative abundances of NOB (especially Nitrobacter and Nitrospira). During the denitrification processes, the integration of M. aquaticum vegetation with FNA-sediment treatment can lower the nitrate reduction by decreasing narG gene abundances and decreasing the relative abundances of napA affiliated bacteria (especially Bradyrhizobium), while strengthening reduction of nitrite and nitrous oxide by increasing nirK and nosZ gene abundances and enriching the corresponding affiliated microbial taxa, Mycobacterium and Bacillus, respectively. Our findings suggest that applying FNA-based technology in CW systems is technically and economically feasible, which holds promise for upgrading current CW systems treating swine wastewater to meet future water quality requirements.

Boosting pharmaceutical removal through aeration in constructed wetlands

This work evaluated the removal efficiency of 13 wastewater-borne pharmaceuticals in a pilot constructed wetland (CW) operated under different aeration strategies (no aeration, intermittent and continuous). Aeration improved the removal of conventional wastewater parameters and the targeted micropollutants, compared to the non-aerated treatment. Reduction of chemical oxygen demand (COD) and total nitrogen (TN) was slightly higher applying intermittent aeration than applying continuous aeration, the opposite was observed for the investigated pharmaceuticals. Seven targeted compounds were found in influent wastewater, and five of them (acetaminophen, diclofenac, ketoprofen, bezafibrate and gemfibrozil) were efficiently removed (> 83%) in the aerated systems. The overall risk of the investigated samples against aquatic ecosystems was moderate, decreasing in the order influent > no aeration > intermittent aeration > continuous aeration, based on the hazard quotient approach. Lorazepam, diclofenac and ketoprofen were the pharmaceuticals that could contribute the most to this potential environmental impact of the CW effluents after discharge. To the authors' knowledge this is the first sound study on the removal and fate of ketoprofen, bezafibrate, and lorazepam in aerated CWs, and provides additional evidence on the removal and fate of acetaminophen, diclofenac, gemfibrozil, and carbamazepine in this type of bioremediation systems at pilot plant scale.

A review of emerging organic contaminants (EOCs), antibiotic resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in the environment: Increasing removal with wetlands and reducing environmental impacts

Emerging organic contaminants (EOCs) include a diverse group of chemical compounds, such as pharmaceuticals and personal care products (PPCPs), pesticides, hormones, surfactants, flame retardants and plasticizers. Many of these compounds are not significantly removed in conventional wastewater treatment plants and are discharged to the environment, presenting an increasing threat to both humans and natural ecosystems. Recently, antibiotics have received considerable attention due to growing microbial antibiotic-resistance in the environment. Constructed wetlands (CWs) have proven effective in removing many EOCs, including different antibiotics, before discharge of treated wastewater into the environment. Wastewater treatment systems that couple conventional treatment plants with constructed and natural wetlands offer a strategy to remove EOCs and reduce antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) far more efficiently than conventional treatment alone. This review presents as overview of the current knowledge on the efficiency of different wetland systems in reducing EOCs and antibiotic resistance.

Recent Advances in the Application, Design, and Operations & Maintenance of Aerated Treatment Wetlands

This paper outlines recent advances in the design, application, and operations and maintenance (O&M) of aerated treatment wetland systems as well as current research trends. We provide the first-ever comprehensive estimate of the number and geographical distribution of aerated treatment wetlands worldwide and review new developments in aerated wetland design and application. This paper also presents and discusses first-hand experiences and challenges with the O&M of full-scale aerated treatment wetland systems, which is an important aspect that is currently not well reported in the literature. Knowledge gaps and suggestions for future research on aerated treatment wetlands are provided.

Combined biochar vertical flow and free-water surface constructed wetland system for dormitory sewage treatment and reuse

A two-stage treatment system that included vertical flow (VF) and free-water surface (FWS) constructed wetlands was investigated for the dual purposes of sewage treatment and reuse. The VF included four layers (biochar, sand, gravel, and sandy soil), and the FWS was installed after the VF and used as a polishing tank. Two types of local plants, namely Colocasia esculenta and Canna indica, were planted in the VF and FWS, respectively. The system operated for approximately six months, and the experimental period was categorized into four stages that corresponded to changes in the hydraulic loading rate (HLR) (0.02-0.12 m/d). The removal efficiencies for total suspended solids (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD₅), ammonia (NH₄-N), and total coliform (Tcol) were 71 ± 11%, 73 ± 13%, 79 ± 11%, 91 ± 3%, and 70 ± 20%, respectively. At HLRs of 0.04-0.06 m/d, the COD and BOD₅ levels satisfied Vietnam's irrigation standards, with removable rates of 64% and 88%, respectively, and the TSS and Tcol levels satisfied Vietnam's standards for potable water. Furthermore, the NO₃-N levels satisfied the reuse limits, whereas the NH₄-N levels exceeded the reuse standards. At high HLRs (e.g., 0.12 m/d), all the effluent parameters, except Tcol and NO₃-N, exceeded the standards.

Application of an innovative front aeration and internal recirculation strategy to improve the removal of pollutants in subsurface flow constructed wetlands

The pollutant removal performance of traditional horizontal subsurface flow (HSSF) constructed wetlands (CWs) is limited because of the dissolved oxygen (DO) supply is insufficient. The aeration of HSSF CWs usually improves their pollutant removal performance, but a high DO induces the accumulation of nitrate-nitrogen (NO₃^--N) and suppresses the improvement of total nitrogen (TN) removal. In this study, an integrated solution that involved in-tank front aeration and internal recirculation (FAIR) was used to improve the pollutant removal performance of HSSF CWs. Based on the experimental results, the FAIR system significantly increased the removal efficiencies of biochemical oxygen demand (BOD) from 53.8-76.0% to 82.0-91.7% and reduced the BOD concentration in the effluent to below 10 mg L^-1. The removal efficiency of ammonia-nitrogen (NH₃-N) increased from 15.1-78.3% to 98.5-98.6% while the removal efficiencies of the total Kjeldahl nitrogen (TKN) of the control and FAIR HSSF CWs were 18.2-77.1% and 93.5-94.3%, respectively. HSSF CWs with FAIR outperformed aerated HSSF CWs in the removal of NH₃-N and TKN. The effects of two recirculation flow ratios (Rr = recirculation flow rate/influent flow rate), 14.3 and 3.0, on the improvement of pollutant removal performance were investigated. The lower Rr did not significantly affect the improvement of BOD, NH₃-N, and TKN, but a higher Rr resulted in more severe accumulation of NO₃^--N. The removal efficiency of TN in control HSSF CWs ranged from 20.4% to 75.5%, and in the FAIR HSSF CW was 71.6% for Rr = 14.3 and 81.3% for Rr = 3.0. However, the FAIR system did not enhance the removal performance of total phosphorus, suggesting that the DO level and internal recirculation were not dominant mechanisms for the removal of phosphorous. The easy maintenance of the FAIR system made it a superior modification for improving the pollutant removal performance of HSSF CWs.

The configuration, purification effect and mechanism of intensified constructed wetland for wastewater treatment from the aspect of nitrogen removal: A review

Constructed wetland (CW) for wastewater treatment has attracted increasing attention. In this review, the system configuration optimization, purification effect and general mechanisms of nitrogen removal in CW are systematically summarized and discussed. Ammonia oxidation is a crucial and primary process for total nitrogen (TN) removal in domestic or livestock wastewater treatment. Aeration, waterdrop influent and tidal operation are three main methods to strengthen the oxygen supplement and nitrification process in CW. Aeration significantly increases the ammonia removal rate (almost 100%), followed by the removal of chemical oxygen demand (COD) and TN. Solid carbon source, iron and anode material can be filled as electron donor for the denitrification process. The co-adjustment of oxygen and carbon/electron donor can form different conditions for different nitrogen removal pathways (e.g. the simultaneous nitrification-denitrification, the partial nitrification-denitrification and the anammox process), and achieve the optimal removal of nitrogen.

Shift of Sediments Bacterial Community in the Black-Odor Urban River during In Situ Remediation by Comprehensive Measures

The phenomenon of black-odor urban rivers with rapid urbanization has attracted extensive attention. In this study, we investigated the water quality and composition of sediment-associated bacteria communities in three remediation stages (before remediation, 30 days after remediation, and 90 days after remediation) based on the in situ remediation using comprehensive measures (physical, chemical, and biological measures). The results show that the overlying water quality was notably improved after in situ remediation, while the diversity and richness of sediment-associated bacterial communities decreased. A growing trend of some dominant genus was observed following the remediation of a black-odor river, such as Halomonas, Pseudomonas, Decarbonamis, Leptolina, Longilina, Caldiseericum, Smithella, Mesotoga, Truepera, and Ralstonia, which play an important role in the removal of nitrogen, organic pollutants and hydrogen sulfide (H2S) during the sediment remediation. Redundancy analysis (RDA) showed that the bacterial community succession may accelerate the transformation of organic pollutants into inorganic salts in the sediment after in situ remediation. In a word, the water quality of the black-odor river was obviously improved after in situ remediation, and the bacterial community in the sediment notably changed, which determines the nutrients environment in the sediment.

An Enhanced System with Macrophytes and Polyurethane Sponge as an Eco-Technology for Restoring Eutrophic Water: A Pilot Test

Water eutrophication is one of the most serious environmental problems in urban lakes and ponds due to the excessive nutrients. To deal with this problem, the development of methods for supporting ecological rehabilitation has been undertaken. Meanwhile, the trophic interactions during rehabilitation also have been analyzed. In this study, a new technique was employed to solve the water eutrophication problems in an urban pond. To evaluate the water eutrophication at a pilot scale, an enhanced artificial floating-type biological treatment system (FBTS) composed of a floating bed, macrophyte, artificial biofilm carrier (polyurethane sponge) and aerator could be used as equipment for urban pond remediation. In addition, FBTS was employed to decrease the total nitrogen (TN), ammonia-nitrogen (NH3-N), total phosphorus (TP) and chemical oxygen demand (COD) in water. Meanwhile, the changes of water qualities were monitored in the remediation process, and differences in phytoplankton functional group diversity were also registered. Cyanobacteria would decrease after the removal of P, and the diatom assemblage composition changed. The dominant species Cyanophyta were transformed to co-existed with Bacillariophyta, Pyrrophyta and Chlorophyta due to the improvement of water quality. Consequently, this new FBTS could be a promising eco-technology for the removal of nitrogen and phosphorus from eutrophic water, and even could promote the phytoplankton succession.

Vertical flow constructed wetlands for decentralized wastewater treatment in Jordan: Optimization of total nitrogen removal

The baseline performance of two full-scale vertical flow (VF) constructed wetlands operating in the arid climate of Jordan is presented in this study, within the context of the Jordanian Standards for reuse of treated wastewater. One system was a recirculating VF wetland, and the other was a single-pass two-stage VF wetland. Operational modifications were made to each treatment system, with the aim of improving Total Nitrogen (TN) removal. For the recirculating VF system, attached-growth media was added to the recirculation tank to provide increased surface area for growth of denitrifying bacteria. The modification showed a small but significant improvement in TN removal (8 mg/L less than the baseline phase; p = 0.004). Statistical analysis showed that 30% and 4.5% of the increase in compliance with the TN limits (Class A and Class B/C, respectively) could be attributed to the modification. The two-stage VF wetland was modified with a step-feeding line that introduced carbon-rich raw wastewater to the intermediate pump shaft just upstream of the second-stage filter. The modification also resulted in a small but significant improvement in TN removal (13 mg/L less than the baseline phase; p = 0.005). The increase in compliance with the TN standard due to the modification was estimated at 20% and 22% for Class A and B/C, respectively. The simple operational modifications proved to be effective for improving total nitrogen removal in arid climate VF wetland systems.

Modeling the relationship of aeration, oxygen transfer and treatment performance in aerated horizontal flow treatment wetlands

Mechanical aeration is commonly used to improve the overall treatment efficacy of constructed wetlands. However, the quantitative relationships of air flow rate (AFR), water temperature, field oxygen transfer and treatment performance have not been analyzed in detail until today. In this study, a reactive transport model based on dual-permeability flow and biokinetic formulations of the Constructed Wetland Model No. 1 (CWM1) was developed and extented to 1) simulate oxygen transfer and treatment performance for organic carbon and nitrogen of two pilot-scale horizontal flow (HF) aerated wetlands (Test and Control) treating domestic sewage, and, 2) to investigate the dependence of oxygen transfer and treatment performance on AFR and water temperature. Both pilot-scale wetlands exhibited preferential flow patters and high treatment performance for chemical oxygen demand (COD) and NH₄-N at AFRs of 128-700 L m^-2 h^-1. A reduction of the AFR in the Test system from 128 to 72 L h^-1 m^-2 substantially inhibited NH₄-N removal. Conservative tracer transport as well as reactive transport of dissolved oxygen (DO), soluble and total chemical oxygen demand (COD_s, COD_t), NH₄-N and NO_x-N measured in pilot-scale experiments were simulated with acceptable accuracy (E₁¯=0.39±0.26). An equation to estimate the volumetric oxygen transfer coefficient was found to be: k_La,20=0.511ln(AFR). Simulated treatment performance depended on k_La,20 in a non-linear manner. A local sensitivity analysis of the calibrated parameters revealed porosity, hydraulic permeability and dispersion length of the fast flow field as well as k_La,20 as most important. An optimal AFR for a spatially and temporally continuous aeration pattern for treatment wetlands treating similar influent was estimated to 150-200 L h^-1 m^-2. This study provides insights into aeration mechanisms of aerated treatment wetlands and highlights the benefits of process modeling for in-depth system analysis.

Comparative study about the performance of three types of modified natural treatment systems for rice noodle wastewater

In this study, three semi-pilot scale systems (vertical flow constructed wetland, multi-soil layering, and integrated hybrid systems) for treating real rice noodle wastewater were operated parallelly for the first time in a tropical climate at a loading rate of 50 L/(m²·d) for more than 7 months to determine the optimal conditions and to compare their treatment performance. The results demonstrated that these systems were appropriate for the removal of organics, suspended solids, and total coliform (Tcol). The highest reductions in chemical oxygen demand (COD_Cr, 73.2%), phosphorus (PO₄-P, 54%), and Tcol (4.78 log MPN/100 mL inactivation) were obtained by the integrated hybrid system, while the highest removal efficiencies of ammonium (NH₄-N, 60.64%) and suspended solids (80.49%) were achieved in the vertical-flow-constructed wetland and multi-soil layering systems respectively.

Effect of calcium peroxide on the water quality and bacterium community of sediment in black-odor water

This study investigated how efficiently CaO₂ could treat black-odor landscape water caused by low dissolved oxygen (DO) in a field experiment of 600 m². The study demonstrated that CaO₂ could significantly elevate the DO concentration in waters and the oxidation-reduction potential (ORP) level in sediments (p = 0.003 and p = 0), which is conducive to improving the anoxic environment of landscape water. The concentrations of total chemical oxygen demand (TCOD) and S^2- in overlying and interstitial waters were considerably decreased. The average concentrations of TCOD in the overlying and interstitial waters of the test zone (TZ) were 52.98% and 66.05% of those of the control zone (CZ), and the average concentrations of S^2- in the overlying and interstitial waters of TZ were 29.63% and 39.79% of those of CZ. Meanwhile, CaO₂ could obviously reduce turbidity but increase the transparency in the overlying water. The mean value of turbidity in the overlying water of TZ was 39.46% of that of CZ, whereas the transparency in the overlying water of TZ was 2.07 times that of CZ. Furthermore, CaO₂ changed the microbial community structure in the sediments, where the relative abundance of anaerobic bacteria was decreased but that of the aerobic bacteria was increased with some functional bacteria. In summary, CaO₂ could significantly increase the DO and ORP in black-odor landscape water, obviously inhibit the release of pollutants from sediment, and increase the diversity of microbial strains. Consequently, the black-odor phenomenon of landscape water could be alleviated effectively by adding CaO₂.

Study on the purification effect of aeration-enhanced horizontal subsurface-flow constructed wetland on polluted urban river water

The issue of urban river pollution has attracted great attention due to high concentrations of ammonia nitrogen (NH₄⁺-N) and low concentrations of dissolved oxygen (DO) in polluted water bodies. In order to investigate the effects of aeration-enhanced horizontal subsurface-flow constructed wetlands on polluted river water, unaerated aeration (NA), continuous aeration (CA), and intermittent aeration (IA) constructed wetlands were established. The purification effects of the wetland on various pollutants and the form of effluent nitrogen, influences of temperature on the removal rates of pollutants, the change of redox potential-oxidation reduction potential (ORP)-and the difference of dissolved oxygen (DO) between influent and effluent were investigated. The results indicated that aeration enhancement can improve the purification efficiencies of chemical oxygen demand (COD) and NH₄⁺-N in constructed wetlands. The purification efficiencies of TN in IA and CA constructed wetlands were 91.9% and 53.7%, respectively, indicating that IA is the optimized aeration method for removal of various pollutants in wetlands. Changes of DO and ORP in effluent under IA and CA suggested improvement of aeration on the water environment. Meanwhile, DO was more sensitive to temperature compared with ORP. Additionally, a study of the nitrogen content in effluent suggested that the aeration method had a significant influence on the nitrogen content in effluent. The removal rates of both NH₄⁺-N and TN degraded as the temperature dropped. The results also demonstrated that the removal rate of NH₄⁺-N under aeration condition was more sensitive to temperature than that under NA condition and the effect of temperature on the removal rate of NH₄⁺-N was greater than that of TN.

Side-by-side comparison of 15 pilot-scale conventional and intensified subsurface flow wetlands for treatment of domestic wastewater

This study reports a systematic assessment of treatment efficacy for 15 pilot-scale subsurface flow constructed wetlands of different designs for CBOD₅, TSS, TOC, TN, NH₄-N, NO₃-N, NO₂-N, and E. coli over the course of one year in an outdoor study to evaluate the effects of design and plants. The systems consisted of a range of designs: horizontal flow (HF) with 50 and 25 cm depth, unsaturated vertical flow (VF) with sand or fine gravel, and intensified systems (horizontal and saturated vertical flow with aeration, and reciprocating fill and drain). Each system was built in duplicate: one was planted with Phragmites and one was left unplanted (with the exception of the reciprocating system, of which there was only one and it was unplanted). All systems were fed with the same primary-treated domestic wastewater. Effluent concentrations, areal and volumetric mass removal rates, and percent mass removal for the 15 systems are discussed. HF wetlands removed CBOD₅, TSS, TN, NH₄-N and E. coli by 73-83%, 93-95%, 17-41%, 0-27% and 1.5 log units, respectively. Unsaturated VF and aerated VF wetlands removed CBOD₅, TSS, TN, NH₄-N and E. coli by 69-99%, 76-99%, 17-40%, 69-99% and 0.9-2.4 log units, respectively. The aerated HF and reciprocating systems removed CBOD₅, TSS, TN, NH₄-N and E. coli by 99%, 99%, 43-70%, 94-99% and 3.0-3.8 log units, respectively. The aerated HF and reciprocating systems achieved the highest TN removal rate of all of the designs. Design complexity clearly enhanced treatment efficacy (HF < VF < Intensified, p < 0.001) during the first two years of plant growth while the presence of plants had minor effects on TN and NH₄-N removal in the shallow HF design only.

Purification of leachate from sludge treatment beds by subsurface flow constructed wetlands: effects of plants and hydraulic retention time

Sludge treatment beds (STBs) have been used widely in many countries due to low energy consumption, low operating and maintenance costs, and better environmental compatibility. Penetration, evaporation, and transpiration are the main processes for sludge dewatering in STBs. However, the leachate quality from STBs usually cannot meet discharge limits. Moreover, such leachate has very low COD/N ratio, which makes it difficult to treat. In the present study, two subsurface flow (SSF) constructed wetlands (CWs) were investigated for the treatment of leachate from STBs under three different hydraulic retention time (HRT) (3 days, 4 days, 6 days), aiming for evaluating the effects of plants and HRT on treatment performance, as well as the potential of SSF CWs to treat sludge leachate with low COD/N ration. The results showed that plants play an important role in leachate treatment. The best treatment performance was achieved with HRT of 4 days. In this condition, the mean removal efficiencies of COD (chemical oxygen demand), NH₄⁺-N, TN (total nitrogen), and TP (total phosphorus) in the planted and the unplanted CWs were 61.6% (unplanted - 3.7%), 76.6% (unplanted 43.5%), 70% (unplanted 41%), and 65.6% (unplanted 6%), respectively. Heavy metal concentrations were below the Chinese integrated wastewater discharge standard during the experimental period in the planted CW, and the removal efficiencies in the planted CW system were higher than in the unplanted CW system. In all, planted SSF CWs can be an effective approach in removing leachate from sludge treatment beds. Furthermore, considering to temperature and seasonal variation, the leachate from STBs needs to be further studied in pilot- and full-scale condition.

Lessons learnt from a pilot study on residual dye removal by an aerated treatment wetland

Treatment wetlands (TWs) have shown good capacity in dye removal from textile wastewater. However, the high hydraulic retention times (HRTs) required by these solutions and the connected high area requirements, remain a big drawback towards the application of TWs for dye treatment at full scale. Aerated TWs are interesting intensified solutions that attempt to reduce the TW required area. Therefore, an aerated CW pilot plant, composed of a 20 m² horizontal subsurface flow TW (HF) and a 21 m² Free Water System (FWS), equipped with aeration pipelines, was built and monitored to investigate the potential reduction of required area for dye removal from the effluent wastewater of a centralized wastewater treatment plant (WWTP). During a 8 months long study, experimenting with different hydraulic retention times (HRTs - 1.2, 2.6 and 3.5 days) and aeration modes (intermittent and continuous), the pilot plant has shown a normal biological degradation for organic matter and nutrients, while the residual dye removal has been very low, as demonstrated by the absorbance measure at three wavelengths: at 426 nm (blue) the removal varies from -55% at influent absorbance of 0.010 to 41% at 0.060; at 558 nm (yellow) the removal is negative at 0.005 (-58%) and high at higher influent concentrations (72% at 0.035 of absorbance for the inlet); at 660 nm (red) -82% of removal efficiency was obtained at influent absorbance of 0.002 and 74% at 0.010. These results are a consequence of the biological oxidation processes taking place in the WWTP, so that the residual dye seems to be resistant to further aerobic degradation. Therefore, TWs enhanced by aeration can provide only a buffer effect on peak dye concentrations.

Effect of climate change on humic substances and associated impacts on the quality of surface water and groundwater: A review

Humic substances (HS), a highly transformed part of non-living natural organic matter (NOM), comprise up to 70% of the soil organic matter (SOM), 50-80% of dissolved organic matter (DOM) in surface water, and 25% of DOM in groundwater. They considerably contribute to climate change (CC) by generating greenhouse gases (GHG). On the other hand, CC affects HS, their structure and reactivity. HS important role in global warming has been recognized and extensively studied. However, much less attention has been paid so far to effects on the freshwater quality, which may result from the climate induced impact on HS, and HS interactions with contaminants in soil, surface water and groundwater. It is expected that an increased temperature and enhanced biodegradation of SOM will lead to an increase in the production of DOM, while the flooding and runoff will export it from soil to rivers, lakes, and groundwater. Microbial growth will be stimulated and biodegradation of pollutants in water can be enhanced. However, there may be also negative effects, including an inhibition of solar disinfection in brown lakes. The CC induced desorption from soil and sediments, as well as re-mobilization of metals and organic pollutants are anticipated. In-situ treatment of surface water and groundwater may be affected. Quality of the source freshwater is expected to deteriorate and drinking water production may become more expensive. Many of the possible effects of CC described in this article have yet to be explored and understood. Enormous potential for interesting, multidisciplinary studies in the important research areas has been presented.

Effect of Aeration Modes and COD/N Ratios on Organic Matter and Nitrogen Removal in Horizontal Subsurface Flow Constructed Wetland Mesocosms

A series of mesocosm-scale horizontal subsurface flow constructed wetlands (HSSF-CWs) were established. In Experiment 1, four artificial aeration (AA) modes, including pre-aeration at 24 h before the input of influent water (PA), aeration at 6 h (6AA) and 12 h (12AA) after the input of influent water and non-aeration (NA), were tested to obtain an optimal aeration mode for chemical oxygen demand (CODCr) and nitrogen removal. The results showed that aeration after the input of influent water could improve the removal efficiencies of CODCr and ammonia-nitrogen (NH4⁺-N), but lead to an accumulation of nitrate-nitrogen (NO3−-N). The above observation demonstrated that a single aeration cannot create an ideal alternation of aerobic and anaerobic conditions for simultaneous nitrification and denitrification. Therefore, HSSF-CWs with intermittent aeration (IA), after the input of influent water and NA were established to evaluate the combined effects of IA and influent COD/N ratios on pollutant removal in Experiment 2. The HSSF-CW with IA exhibited a better performance in CODCr and nitrogen removal compared to HSSF-CW with NA. The highest removal percentages of CODCr (90.1%), NH4+-N (99.8%) and total nitrogen (TN, 99.5%) were achieved at a COD/N ratio of 9.3 in HSSF-CW with IA.

Intermittent micro-aeration control of methane emissions from an integrated vertical-flow constructed wetland during agricultural domestic wastewater treatment

It is very important to control methane emissions to mitigate global warming. An intermittent micro-aeration control system was used to control methane emissions from an integrated vertical-flow constructed wetland (IVCW) to treat agricultural domestic wastewater pollution in this study. The optimized intermittent micro-aeration conditions were a 20-min aeration time and 340-min non-aeration time, 3.9 m³ h^-1 aeration intensity, evenly distributed micro-aeration diffusers at the tank bottom, and an aeration period of every 6 h. Methane flux emission by intermittent micro-aeration was decreased by 60.7% under the optimized conditions. The average oxygen transfer efficiency was 26.73%. The control of CH₄ emission from IVCWs was most strongly influenced by the intermittent micro-aeration diffuser distribution, followed by aeration intensity, aeration time, and water depth. Scaling up of IVCWs is feasible in rural areas by using intermittent micro-aeration control as a mitigation measure for methane gas emissions for climate change.

New approaches to enhance pollutant removal in artificially aerated wastewater treatment systems

Freshwater ecosystems sustain human society through the provision of a range of services. However, the status of these ecosystems is threatened by a multitude of pressures, including point sources of wastewater. Future treatment of wastewater will increasingly require new forms of decentralised infrastructure. The research reported here sought to enhance pollutant removal within a novel wastewater treatment technology, based on un-planted, artificially aerated, horizontal subsurface flow constructed wetlands. The potential for these systems to treat de-icer contaminated runoff from airports, a source of wastewater that is likely to grow in importance alongside the expansion of air travel and under future climate scenarios, was evaluated. A new configuration for the delivery of air to aerated treatment systems was developed and tested, based on a phased-aeration approach. This new aeration approach significantly improved pollutant removal efficiency compared to alternative aeration configurations, achieving >90% removal of influent load for COD, BOD₅ and TOC. Optimised operating conditions under phased aeration were also determined. Based on a hydraulic retention time of 1.5 d and a pollutant mass loading rate of 0.10 kg d^-1 m^-2 BOD₅, >95% BOD₅ removal, alongside final effluent BOD₅ concentrations <21 mg L^-1, could be achieved from an influent characterised by a BOD₅ concentration > 800 mg L^-1. Key controls on oxygen transfer efficiency within the aerated treatment system were also determined, revealing that standard oxygen transfer efficiency was inversely related to aeration rate between 1 L and 3 L min^-1 and positively related to bed media depth between 1500 mm and 3000 mm. The research reported here highlights the potential for optimisation and subsequent widespread application of the aerated wetland technology, in order to protect and restore freshwater ecosystems and the services that they provide to human society.

Resilience of carbon and nitrogen removal due to aeration interruption in aerated treatment wetlands

Treatment wetlands have long been used for domestic and industrial wastewater treatment. In recent decades, treatment wetland technology has evolved and now includes intensified designs such as aerated treatment wetlands. Aerated treatment wetlands are particularly dependent on aeration, which requires reliable air pumps and, in most cases, electricity. Whether aerated treatment wetlands are resilient to disturbances such as an aeration interruption is currently not well known. In order to investigate this knowledge gap, we carried out a pilot-scale experiment on one aerated horizontal flow wetland and one aerated vertical flow wetland under warm (T_water>17°C) and cold (T_water<10°C) weather conditions. Both wetlands were monitored before, during and after an aeration interruption of 6d by taking grab samples of the influent and effluent, as well as pore water. The resilience of organic carbon and nitrogen removal processes in the aerated treatment wetlands depended on system design (horizontal or vertical flow) and water temperature. Organic carbon and nitrogen removal for both systems severely deteriorated after 4-5d of aeration interruption, resulting in effluent water quality similar to that expected from a conventional horizontal sub-surface flow treatment wetland. Both experimental aerated treatment wetlands recovered their initial treatment performance within 3-4d at T_water>17°C (warm weather) and within 6-8d (horizontal flow system) and 4-5d (vertical flow system) at T_water<10°C (cold weather). In the vertical flow system, DOC, DN and NH₄-N removal were less affected by low water temperatures, however, the decrease of DN removal in the vertical flow aerated wetland at T_water>17°C was twice as high as in the horizontal flow aerated wetland. The quick recovery of treatment performance highlights the benefits of aerated treatment wetlands as resilient wastewater treatment technologies.

A novel aerated surface flow constructed wetland using exhaust gas from biological wastewater treatment: Performance and mechanisms

In this study, a novel aerated surface flow constructed wetland (SFCW) using exhaust gas from biological wastewater treatment was investigated. Compared with un-aerated SFCW, the introduction of exhaust gas into SFCW significantly improved NH₄⁺-N, TN and COD removal efficiencies by 68.30 ± 2.06%, 24.92 ± 1.13% and 73.92 ± 2.36%, respectively. The pollutants removal mechanism was related to the microbial abundance and the highest microbial abundance was observed in the SFCW with exhaust gas because of the introduction of exhaust gas from sequencing batch reactor (SBR), and thereby optimizing nitrogen transformation processes. Moreover, SFCW would significantly mitigate the risk of exhaust gas pollution. SFCW removed 20.00 ± 1.23%, 34.78 ± 1.39%, and 59.50 ± 2.33% of H₂S, NH₃ and N₂O in the exhaust gas, respectively. And 31.32 ± 2.23% and 32.02 ± 2.86% of bacterial and fungal aerosols in exhaust gas were also removed through passing SFCW, respectively.

The performance of the intensified constructed wetlands for organic matter and nitrogen removal: A review

The effects of different aeration strategies including tidal flow (TF), effluent recirculation (ER) and artificial aeration (AA) on performance of vertical flow constructed wetland (VFCW), horizontal flow constructed wetland (HFCW) and hybrid constructed wetland (HCW) are comprehensively and critically reviewed in this paper. The removal efficiencies of nine types of intensified constructed wetlands (CWs) were examined in detail and their mean and standard deviation were estimated at 89 ± 11%, 84 ± 12%, 81 ± 17% and 63 ± 20% for total suspended solids (TSS), chemical oxygen demand (COD), ammonium-nitrogen (NH₄⁺N) and total nitrogen (TN), respectively. From the studied CWs, ER-HCW, TF-HCW, AA-VFCW and ER-VFCW emerged as the four best performing systems. The overall removal efficiency of TSS, COD, NH₄⁺N and TN by ER-HCW was 98 ± 2%, 85 ± 11%, 83 ± 15% and 73 ± 11%, respectively. Specifically, the ER enhances the interactions between pollutants and micro-organisms, consequently, the efficient removal of NH₄⁺N and TN has been achieved in ER-HCW. The TF has a positive effect in refreshing the wetland with fresh air to enhance the dissolved oxygen (DO) in the system. In case of AA, intermittent aeration is more effective than continuous aeration, as it facilitates the establishment of aerobic and anaerobic conditions suitable for nitrification and denitrification. Statistical analysis shows that DO, organic loading rate and specific surface area requirement are the most significant factors that influence the performance of intensified CWs.

A mechanistic review on vermifiltration of wastewater: Design, operation and performance

With global population explosion, the available water resources are slowly being polluted due to the excessive human interference. To encounter this, it is the need of this hour to find out sustainable pollution remediating technologies to meet the stringent discharge standards for domestic as well as industrial wastewaters. In addition, those techniques should have the capabilities for effective implementation even in developing countries. Based on the available literatures, one such technique, named vermifilter, has been identified which takes care of almost all the sustainable and economical criteria for its effective implementation even in developing countries. The aim of this meta-analysis is to provide a comprehensive review on assessment mechanisms involved, factors affecting the process and performance of vermifiltration under different scenarios. The present review envisages the current state of the knowledge regarding physical, chemical and biological aspects related to the treatment mechanisms and effective functioning of earthworms. This review has also proposed several suggestive plans on its application at any proposed site.

Achieving short-cut nitrification and denitrification in modified intermittently aerated constructed wetland

This study aim to enhance nitrogen removal performance via shifting nitrogen removal pathway from nitrate to nitrite pathway. It was demonstrated that nitrite pathway was successfully and stably achieved in CWs by using modified intermittent aeration control with aeration 20min/non-aeration 100min and reducing DO concentration during aeration, nitrite in the effluent could accumulate to over 70% of the total oxidized nitrogen. Q-PCR analysis showed that nitrifying microbial communities were optimized under the alternating anoxic and aerobic conditions, ammonia oxidizing bacteria increased from 7.15×10⁶ to 8.99×10⁶copies/g, while nitrite oxidizing bacteria decreased approximately threefold after 234days operation. Most importantly, high nitrogen removal efficiency with ammonium removal efficiency of 94.6%, and total nitrogen removal efficiency of 82.6% could be achieved via nitrite pathway even under carbon limiting conditions. In comparison to the nitrate pathway, the nitrite pathway could improve the TN removal by about 55%.

Intensification of constructed wetlands for land area reduction: a review

The large land area requirement of constructed wetlands (CWs) is a major limitation of its application especially in densely populated and mountainous areas. This review paper provides insights on different strategies applied for the reduction of land area including stack design and intensification of CWs with different aeration methods. The impacts of different aeration methods on the performance and land area reduction were extensively and critically evaluated for nine wetland systems under three aeration strategies such as tidal flow (TF), effluent recirculation (ER), and artificial aeration (AA) applied on three types of CWs including vertical flow constructed wetland (VFCW), horizontal flow constructed wetland (HFCW), and hybrid constructed wetland (HCW). The area reduction and pollutant removal efficiency showed substantial variation among different types of CWs and aeration strategies. The ER-VFCW designated the smallest footprint of 1.1 ± 0.5 m² PE^-1 (population equivalent) followed by TF-VFCW with the footprint of 2.1 ± 1.8 m² PE^-1, and the large footprint was of AA-HFCW (7.8 ± 4.7 m² PE^-1). When footprint and removal efficiency both are the major indicators for the selection of wetland type, the best options for practical application could be TF-VFCW, ER-HCW, and AA-HCW. The data and results outlined in this review could be instructive for futures studies and practical applications of CWs for wastewater treatment, especially in land-limited regions.

Enhanced long-term organics and nitrogen removal and associated microbial community in intermittently aerated subsurface flow constructed wetlands

The long-term enhanced removal efficiency of organics and nitrogen in subsurface flow constructed wetlands (SSF CWs) with and without intermittent aeration for decentralized domestic wastewater was evaluated, and the function of intermittent aeration on microbial community was also investigated in this study. The high and long-term 95.6% COD, 96.1% NH4(+)-N and 85.8% TN removal efficiencies were achieved in experimental intermittently aerated SSF CW compared with non-aerated SSF CW. Aerated SSF CWs also exhibited the excellent removal performance when comparatively comparing with other strategies and techniques applied in CWs. In addition, fluorescence in situ hybridization (FISH) analysis revealed that associated microbial abundance significantly increased owing to intermittent aeration. These results indicated intermittent aeration CWs might be an effective and sustainable strategy for wastewater treatment in rural areas, but require further full-scale investigation in future.