Influence of the flooded time on the performance of a tidal flow constructed wetland treating urban stream water

Advancements in constructed wetland technology: a state-of-the-art review on bio-electrochemical processes, tidal flow dynamics, and resilience to shock loads

This research article presents a comprehensive examination of recent advancements in constructed wetland technology, with a primary focus on bio-electrochemical processes, including electrolysis and microbial fuel cells, as well as the impact of tidal flow and shock loads on the constructed wetland performance. To date, extensive studies and in-depth analyses in these aspects are limited, highlighting a significant research gap. Electrolysis is explored for its efficacy in dephosphorization and denitrification, particularly under conditions of low carbon availability. Additionally, microbial fuel cell technology is investigated for its dual benefits of bioenergy generation and climate change mitigation. The tidal flow component is highlighted for its ability to create anaerobic, anoxic, and aerobic environments within and between cells, crucial for effective nitrogen removal. The study emphasizes the importance of constructed wetland resilience to shock loads, whether from increased discharge due to rainfall or heightened contaminant levels. The research employs bibliographic analysis and microbial community profiling and investigates factors such as nutrient removal, polarization curves, and the effects of flood/rest and flood/drain in tidal flow. Furthermore, the article delves into the impacts of hydraulic and organic shock loads on constructed wetland systems, providing a comprehensive overview of the current state of the field.

Intensifying intermittent aeration for optimizing nutrient and hormone removal in vertical-flow constructed wetlands filled with aerated concrete

Operational strategies have been applied in constructed wetlands to optimize the removal of nutrients and hormones that are still a concern in wastewater treatment. The strategy of intensifying intermittent aeration was investigated in two microcosm-scale vertical-flow constructed wetlands (VFCWs) planted with Eichhornia crassipes onto autoclaved aerated concrete (AC) in the removal of nutrients, estrone (E1), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2). CW-1 (2.4 LO2 min-1) and CW-2 (1.4 LO2 min-1) were fed with synthetic wastewater in sequencing-batch mode (cycles 48-48-72 h) and intermittently aerated for 1 h, followed by 7 h without aeration for 377 days. Combined with the intensification strategy, the use of planted free-floating macrophytes and concrete-based material (emergent) as filtering media stand out as the innovation and originality aspects of this study. Despite the hormone addition, intensifying aeration enhanced the efficiencies since CW-1 achieved the highest removals with 91% COD, 77% TN, 74% TAN, 60% nitrate, and 97% TP in Stage I (no hormone addition) and 90% COD, 80% TN, 93% TAN, 63% nitrate, and 82% TP in Stage II (with hormone addition). CW-1 achieved the highest removal efficiencies of E1 (84%), E2 (95%), and EE2 (73%). Conversely, the efficiencies decreased under the lower aeration rate (in CW-2) for all parameters. Macrophyte uptake and adsorption stood out for TN (>60.25%) and TP (>27.6%) removal as the main mechanisms in the VFCWs. The characteristics of AC favored ion exchange and precipitation, reinforcing the potential of this material as filtering media in VFCWs. Intensification of intermittent aeration combined with hormone addition diverse and riched the microbial community with the presence of Thauera, Lentimicrobium (denitrification), Candidatus Accumulibacter (phosphorus removal), Pseudomonas, Fusibacter, and Azoarcus (EE2 degradation). Intensifying intermittent aeration was an important strategy to enhance the simultaneous removal of nutrients and hormones in the VFCWs under the evaluated operational conditions.

A review of interconnected challenges in the water-energy-food nexus: Urban pollution perspective towards sustainable development

The swift growth of cities worldwide poses significant challenges in ensuring a sufficient water, energy, and food supply. The Nexus has innovated valuable systems to address these challenges. However, a crucial issue is the potential for pollution resulting from these systems, which directly and indirectly impacts public health and the overall quality of urban living. This study comprehensively reviews the interconnected challenges of the water-energy-food (WEF) nexus and various forms of pollution in cities. The primary focus of this review article is to showcase the findings of WEF nexus studies regarding various pollutions across different geographical regions and spatial scales. It aims to examine the problems resulting from these pollutions, specifically their effects on human health and urban life. It also delves into the sources of pollution as identified in these studies. Furthermore, the article will highlight the proposed solutions from the research aimed at effectively mitigating pollution in each sector studied. This article is a systematic review which analyses research sources from the Scopus database. It extensively reviewed 2463 peer-reviewed published articles and focused explicitly on articles related to the WEF nexus that discussed pollution. Our study emphasizes, firstly, raising awareness about the crucial link between the WEF nexus, pollution, urban environments, and human health among policymakers and key stakeholders, including urban planners, industry partners and municipalities. This is to promote the development of policies that encourage sustainable practices and key stakeholders. Secondly, it evaluates WEF nexus and pollution research methods and findings, aiding in identifying research gaps technological innovation and potential, as well as enhancing decision-making. Lastly, it outlines future research challenges, providing a roadmap for researchers and policymakers to advance understanding in this domain and identify opportunities for resource efficiency and collaboration between different sectors.

Biodegradation and sorption of nutrients and endocrine disruptors in a novel concrete-based substrate in vertical-flow constructed wetlands

Removing phosphorus and endocrine-disruptors (EDC) is still challenging for low-cost sewage treatment systems. This study investigated the efficiency of three vertical-flow constructed wetlands (VFCW) vegetated with Eichhornia crassipes onto red clay (CW-RC), autoclaved aerated concrete (CW-AC), and composite from the chemical activation of autoclaved aerated concrete with white cement (CW-AAC) in the removal of organic matter, nutrients, and estrone, 17β-estradiol, and 17α-ethinylestradiol. The novelty aspect of this study is related to selecting these clay and cementitious-based materials in removing endocrine disruptors and nutrients in VFCW. The subsurface VFCW were operated in sequencing-batch mode (cycles of 48-48-72 h), treating synthetic wastewater for 308 days. The operation consisted of Stages I and II, different by adding EDC in Stage II. The presence of EDC increased the competition for dissolved oxygen (DO) and reduced the active sites available for adsorption, diminishing the removal efficiencies of TKN and TAN and total phosphorus in the systems. CW-RC showed a significant increase in COD removal from 65% to 91%, while CW-AC and CW-AAC maintained stable COD removal (84%-82% and 78%-81%, respectively). Overall, the substrates proved effective in removing EDC, with CW-AC and CW-AAC achieving >60% of removal. Bacteria Candidatus Brocadia and Candidatus Jettenia, responsible for carrying out the Anammox process, were identified in assessing the microbial community structure. According to the mass balance analysis, adsorption is the main mechanism for removing TP in CW-AC and CW-AAC, while other losses were predominant in CW-RC. Conversely, for TN removal, the adsorption is more representative in CW-RC, and the different metabolic routes of microorganisms, biofilm assimilation, and partial ammonia volatilization in CW-AC and CW-AAC. The results suggest that the composite AAC is the most suitable material for enhancing the simultaneous removal of organic matter, nutrients, and EDC in VFCW under the evaluated operational conditions.

Effect of steel slag on ammonia removal and ammonia-oxidizing microorganisms in zeolite-based tidal flow constructed wetlands

The ammonia removal performance of tidal flow constructed wetlands (TFCWs) requires to be improved under high hydraulic loading rates (HLRs). The pH decrease caused by nitrification may adversely affect the NH₄⁺-N removal and ammonia-oxidizing microorganisms (AOMs) of TFCWs. Herein, TFCWs with zeolite (TFCW_Z) and a mixture of zeolite and steel slag (TFCW_S) were built to investigate the influence of steel slag on NH₄⁺-N removal and AOMs. Both TFCWs were operated under short flooding/drying (F/D) cycles and high HLRs (3.13 and 4.69 m³/(m² d)). The results revealed that a neutral effluent pH (6.98-7.82) was achieved in TFCW_S owing to the CaO dissolution of steel slag. The NH₄⁺-N removal efficiencies in TFCW_S (91.2 ± 5.1%) were much higher than those in TFCW_Z (73.2 ± 7.1%). Total nitrogen (TN) removal was poor in both TFCWs mainly due to the low influent COD/TN. Phosphorus removal in TFCW_S was unsatisfactory because of the short hydraulic retention time. The addition of steel slag stimulated the flourishing AOMs, including Nitrosomonas (ammonia-oxidizing bacteria, AOB), Candidatus_Nitrocosmicus (ammonia-oxidizing archaea, AOA), and comammox Nitrospira, which may be responsible for the better ammonia removal performance in TFCW_S. PICRUSt2 showed that steel slag also enriched the relative abundance of functional genes involved in nitrification (amoCAB, hao, and nxrAB) but inhibited genes related to denitrification (nirK, norB, and nosZ). Quantitative polymerase chain reaction (qPCR) revealed that complete AOB (CAOB) and AOB contributed more to the amoA genes in TFCW_S and TFCW_Z, respectively. Therefore, this study revealed that the dominant AOMs could be significantly changed in zeolite-based TFCW by adding steel slag to regulate the pH in situ, resulting in a more efficient NH₄⁺-N removal performance.

Removal of micropollutants by UASB reactor and post-treatment by Fenton and photo-Fenton: Matrix effect and toxicity responses

Literature is scarce on the performance of Fenton-based processes as post-treatment of municipal wastewater treated by upflow anaerobic sludge blanket (UASB) reactor. This study aims to perform Fenton and photo-Fenton from UASB influent and effluent matrices to remove micropollutants (MPs) models: atrazine (ATZ), rifampicin (RIF), and 17α-ethynylestradiol (EE2). A UASB reactor at bench-scale (14 L) was operated with these MPs, and the AOPs experiments at bench-scale were performed on a conventional photochemical reactor (1 L). A high-pressure vapor mercury lamp was used for photo-Fenton process (UVA-Vis) as a radiation source. Microcrustacean Daphnia magna (acute toxicity) and seeds of Lactuca sativa (phytotoxicity) were indicator organisms for toxicity monitoring. The UASB reactor showed stability removing 90% of the mean chemical oxygen demand, and removal efficiencies for ATZ, RIF, and EE2 were 16.5%, 45.9%, and 15.7%, respectively. A matrix effect was noted regarding the application of both Fenton and photo-Fenton in UASB influent and effluent to remove MPs and toxicity responses. The pesticide ATZ was the most recalcitrant compound, yet the processes carried out from UASB effluent achieved removal >99.99%. The post-treatment of the UASB reactor by photo-Fenton removed acute toxicity in D. magna for all treatment times. However, only the photo-Fenton conducted for 90 min did not result in a phytotoxic effect in L. sativa.

Study of the effect of pyrite and alkali-modified rice husk substrates on enhancing nitrogen and phosphorus removals in constructed wetlands

The combined effects and respective advantages of using pyrite and alkali-modified rice husk (RH) were studied as substrates for nitrogen and phosphorus removal from constructed wetlands, and the effects of the carbon to nitrogen (C/N) ratio and the tidal flow mode on system performance were explored. The results showed that alkali-modified RH, which enhances heterotrophic denitrification, had far more advantages than pyrite, which enhances autotrophic denitrification, and alkali-modified RH can be used for the treatment of sewage containing low C/N ratios. At a C/N ratio of 1.5, the total nitrogen (TN) removal rates exceeded 95%. However, the removal efficiency of the system with only pyrite only reached 76.90% when the influent C/N ratio was 6. Pyrite achieved a total phosphorus (TP) removal 10-20% higher than that of the control group. The tidal flow CWs showed enhanced nitrification, and the NH₄⁺-N removal rates increased by approximately 10%, but the increase in dissolved oxygen (DO) was still insufficient to meet the needs of the systems, leading to limited TP removal. The combination of pyrite and alkali-modified RH was optimal for improving the ability of constructed wetlands to treat wastewaters, simultaneously removing nitrogen and phosphorus from sewage containing low C/N ratios. Combined with the tidal flow mode strategy, the use of pyrite and alkali-modified RH as substrates showed substantial advantages for improving water quality.

Knowledge Atlas on the Relationship between Water Management and Constructed Wetlands—A Bibliometric Analysis Based on CiteSpace

Water management is a crucial resource conservation challenge that mankind faces, and encouraging the creation of manmade wetlands with the goal of achieving long-term water management is the key to long-term urban development. To summarise and analyse the status of the research on the relationship between water management and constructed wetlands, this paper makes use of the advantages of the bibliometric visualization of CiteSpace to generate country/region maps and author-collaboration maps, and to analyse research hotspots and research dynamics by using keywords and literature co-citations based on 1248 pieces of related literature in the core collection in the Web of Science (WoS) database. The existing research shows that the research content and methods in the field of constructed-wetland and water-management research are constantly being enriched and deepened, including the research methods frequently used in constructed wetlands in water management and in the research content under concern, the functions and roles of constructed wetlands, the relevant measurement indicators of the purification impact of constructed wetlands on water bodies, and the types of water bodies treated by constructed wetlands in water management. We summarise the impact pathways of constructed wetlands on water management, as well as the impact factors of constructed wetlands under water-management objectives, by analysing the future concerns in the research field to provide references for research.

Functional genera for efficient nitrogen removal under low C/N ratio influent at low temperatures in a two-stage tidal flow constructed wetland

A two-stage tidal flow constructed wetland (referred to as TFCW-A and TFCW-B) was used to treat low chemical oxygen demand/total nitrogen (COD/TN or simply C/N) ratio influent at low temperatures (<15 °C). The influence of the flooding-resting time (A: 8 h-4 h, B: 4 h-8 h) and effluent recirculation on nitrogen removal and microbial community characteristics were explored. TFCW-B achieved optimal average nitrogen removal efficiency with effluent recirculation (96.05% ammonium nitrogen (NH₄⁺-N); 78.43% TN) and led to nitrate nitrogen (NO₃^--N) accumulation due to the lack of a carbon source and longer resting time. Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were inhibited at low temperatures. Except for nrfA, AOA, AOB, narG and nirS were separated by the flooding-resting time rather than by spatial position. Furthermore, the dominant genera in TFCW-A were Arthrobacter, Rhodobacter, Pseudomonas, and Solitalea, whereas prolonging resting time promoted the growth of Thauera and Zoogloea in TFCW-B. Spearman correlation analysis showed that Zoogloea and Rhodobacter had the strongest correlations with other genera. Moreover, the NH₄⁺-N concentration was significantly positively influenced by Arthrobacter, Rhodobacter, Pseudomonas, and Solitalea but negatively influenced by Thauera and Zoogloea. There was no significant correlation between TN and the dominant genera. This study not only provides a practicable system for wastewater treatment with a low C/N ratio but also presents a theoretical basis for the regulation of microbial communities in nitrogen removal systems at low temperatures.