The performance and mechanism of iron-modified aluminum sludge substrate tidal flow constructed wetlands for simultaneous nitrogen and phosphorus removal in the effluent of wastewater treatment plants

Iron-carbon enhanced constructed wetland microbial fuel cells for tetracycline wastewater treatment: Efficacy, power generation, and the role of iron-carbon

Tetracycline (TC) antibiotics wastewater is a serious threat to human health and environment. In this study, four groups of laboratory-scale constructed wetlands (CWs) with different configurations were constructed to evaluate the removal efficiency of iron-carbon (Ic) coupled constructed wetland microbial fuel cells (CW-MFC) system for different pollutants removal and bioelectricity production. The results showed that the addition of Ic significantly promoted the removal of contaminants. The maximum removal rates of COD, TN, NH4+-N, and TP were 86.13 %, 81.60 %, 79.07 %, and 97.35 %, respectively. In particular, the removal rates of TC reached 100 %. 3D-EEM analysis further confirmed the role of Ic in promoting organic degradation. The Ic-CW-MFC system also showed superiority in power generation performance with peak power density of 7.90 mW/m2 (internal resistance is 10 Ω), 88.07 % higher than the traditional CW-MFC, while the internal resistance was 68.21 % lower. Therefore, when Ic is used as the substrate of CW-MFC system, its decontamination and electricity generation performance is the best. Analysis of RDA was used to elucidate the relationship of four CWs, dominant strains and environmental factors (pH, ORP and DO). The performance of traditional CWs decreased significantly after TC addition (5-20 mg/L), but Ic-CW-MFC could effectively alleviate the inhibition effect caused by high-concentration TC wastewater. The working mechanism of Ic-CW-MFC in TC wastewater was further analyzed through typical cycle experiment and characterization. The results showed that Ic-CW-MFC is an efficient and economical wastewater treatment technology, which has great potential application value in the treatment of wastewater containing TC.

Iron-carbon micro-electrolysis coupled to heterotrophic nitrification aerobic denitrification treating low carbon/nitrogen mariculture wastewater

Considering the unsatisfied nitrogen (N) and phosphorus (P) treatment performance of mariculture wastewater caused by low carbon/nitrogen (C/N), a novel iron-carbon (Fe-C) micro-electrolysis coupled to heterotrophic nitrification aerobic denitrification (HNAD) process was proposed to enhance the N and P elimination. Results revealed that total nitrogen (TN) removal and total phosphorus (TP) removal efficiencies in Fe-C filter with HNAD (R-Fe) increased by 76.1% and 113.3% compared to filter packed with ceramsite (R-C). Fe-C micro-electrolysis reaction led to the decrease of microbial diversity and richness, the enrichment of heterotrophic nitrification aerobic denitrification bacteria (HNADB) and HNAD genes (napA and napB) by 7.3 times and 56.3%. Besides, a synergistic effect existed that Fe-C substances not only further accumulated main functional genes associated with the transformation of N, carbon (C) and iron (Fe), but also indirectly enhanced electron transport system activity and ATP generation, thus resulting in elevating TN removal.

Ecological restoration orientated application and modification of constructed wetland substrates

Constructed wetlands (CWs) have gained recognition as an environmentally friendly and cost-efficient option for treating municipal, industrial, and agricultural wastewater. They treat wastewater by harnessing the combined action of physical, chemical, and biological processes within substrates, plants, and microorganisms, with substrates exerting the greatest influence on the life cycle and purification efficiency of the system. This review provides an in-depth discussion on the development and performance of various substrate types used in CWs, including natural materials, ore-based materials, biomass materials, waste materials, and modified and novel materials. Key substrate modification techniques are summarized in detail, such as acid-base treatment, metal doping, compound modification, and heat treatment, which enhance structural and functional properties to improve pollutant removal. The paper also systematically explores the mechanisms of introducing methods like inorganic electronic enhancement and describes their applications in improving pollutant removal in CW systems. This review provides a holistic evaluation of substrate classification and optimization strategies and a prospective discussion of their challenges and opportunities in practical applications. It contributes to the creation of more efficient and sustainable materials for CW systems and provides theoretical support for selecting and optimizing substrates, thereby driving progress in wastewater treatment technology.

Alum sludge-driven electro-phytoremediation in constructed wetlands: a novel approach for sustainable nutrient removal

In addition to their advantages as promising methods for wastewater treatment, CWs exhibit poor performance in terms of N and P removal efficiency in the effluent of wastewater treatment plants. By focusing on this issue, we designed CWs integrated with a biochar-doped activated carbon cloth (ACC) electrode and alum sludge from water treatment plants as a substrate to achieve concomitant organic matter and nutrient removal efficiency. Compared with the use of one layer of alum sludge in CWs (CWs-C3) with ACC electrodes inserted in two layers, which uses one layer of alum sludge, a significant improvement in removal efficiency was achieved (96% for COD; 89% for TN; and 77% for TP). The findings revealed that the application of potential accompanied by the insertion of a cathode ACC electrode into the first layer of alum sludge was beneficial for completing nitrification and facilitating denitrification in the cathode and anode regions, respectively, resulting in increased removal of organic matter and nutrients. Further evaluation revealed that the TN-TP synergetic removal mechanism was influenced by the use of Fe2+ as an electron donor and as a driving force for the development of autotrophic denitrifying bacteria to increase nitrate reduction. Additionally, the formation of FePO4 and AlPO4 and their adsorption through the interaction of FeOOH and AlOOH with phosphate constitute the main removal mechanism for TP in wastewater. Another reason for the increased removal efficiency in the CW-C3 reactor was the greater abundance and microbial diversity effectuated by the application of potential in the anode and cathode regions. In summary, a promising strategy for simultaneously promoting organic matter and nutrients and utilizing CWs on a large scale and in practical applications was proposed.

A comprehensive review on iron‒carbon microelectrolysis constructed wetlands: Efficiency, mechanism and prospects

The traditional constructed wetlands (CWs) face challenges such as significant seasonal fluctuations in decontamination performance and susceptibility to clogging, with the bottlenecks in advanced wastewater treatment becoming increasingly prominent. The iron‒carbon microelectrolysis coupled with constructed wetlands (ICME‒CWs) represents a promising new type of CWs, capable of removing typical and emerging pollutants in water through various mechanisms including adsorption, precipitation, oxidation‒reduction, microelectrolysis, and plant‒microbial synergy. Therefore, this review summarizes the sources, preparation, and basic properties of the ICME substrate commonly used in ICME‒CWs in recent years. It systematically outlines the decontamination mechanisms of ICME‒CWs and their removal performance for pollutants. Additionally, the potential ecological effects of ICME on wetland organisms (microorganisms and plants) are discussed. Finally, the prospects and challenges of ICME‒CWs in applications such as greenhouse gas reduction, groundwater remediation, and the removal of emerging pollutants are proposed. This review aims to advance the development of ICME‒CWs technology for efficient wastewater treatment and provide prospects and guidance for the sustainable and environmentally friendly development of CWs.

Nutrient removal in floating and vertical flow constructed wetlands using aluminium dross: An innovative approach to mitigate eutrophication

On global scale, eutrophication is one of the most prevalent environmental threats to water quality, primarily caused by elevated concentration of nutrients in wastewater. This study utilizes aluminum dross (AD), an industrial waste, to create a value-added material by improving its operational feasibility and application for removing phosphate and ammonium from water. The operational challenges of AD such as its powdered nature and effective operation under only extreme pH conditions were addressed by immobilizing in calcium alginate to form calcium alginate aluminium dross (Ca-Alg-Al dross) beads. These Ca-Alg-Al dross beads were further tested for phosphate and ammonium removal from natural wastewater in two different aqueous environment systems: (i) vertical flow constructed wetlands (VF-CWs) followed by Ca-Alg-Al dross beads fixed bed system and (ii) Ca-Alg-Al dross beads mounted floating constructed wetlands (FCW) for remediating polluted lentic ecosystems. Our results show maximum phosphate and ammonium removal of 85 ± 0.41 % and 93.44 %, respectively, in VF-CWs followed by Ca-Alg-Al dross beads fixed bed system. The Ca-Alg-Al dross beads mounted FCW system achieved maximum phosphate removal of 79.18 ± 8.56 % and ammonium removal of 65.45 ± 21.04 %. Furthermore, the treated water from the FCW system was assessed for its potential to inhibit algal growth by artificially inoculating treated water with natural algae to simulate eutrophic conditions. Interestingly, treated water from the FCW system was found capable of arresting the algal growth. Besides, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and Fourier transform infrared (FTIR) spectroscopy confirmed the functional groups and surface properties and probable participation of multiple mechanisms including ion exchange, electrostatic attraction, and ligand complexation for phosphate and ammonium removal. Overall, these results offer a promising way to utilize AD for high-end applications in wastewater treatment.

N-methyl pyrrolidone manufacturing wastewater as the electron donor for denitrification: From bench to pilot scale

Actual wastewater generated from N-methylpyrrolidone (NMP) manufacture was used as electron donor for tertiary denitrification. The organic components of NMP wastewater were mainly NMP and monomethylamine (CH3NH2), and their biodegradation released ammonium that was nitrified to nitrate that also had to be denitrified. Bench-scale experiments documented that alternating denitrification and nitrification realized effective total‑nitrogen removal. Ammonium released from NMP was nitrified in the aerobic reactor and then denitrified when actual NMP wastewater was used as the electron donor for endogenous and exogenous nitrate. Whereas TN and NMP removals occurred in the denitrification step, dissolved organic carbon (DOC) and CH3NH2 removals occurred in the denitrification and nitrification stages. The genera Thauera and Paracoccus were important for NMP biodegradation and denitrification in the denitrification reactor; in the nitrification stage, Amaricoccus and Sphingobium played key roles for biodegrading intermediates of NMP, while Nitrospira was responsible for NH4+ oxidation to NO3-. Pilot-scale demonstration was achieved in a two-stage vertical baffled bioreactor (VBBR) in which total‑nitrogen removal was realized sequential anoxic-oxic treatment without biomass recycle. Although the bench-scale reactors and the VBBR had different configurations, both effectively removed total nitrogen through the same mechanisms. Thus, an N-containing organic compound in an industrial wastewater could be used to drive total-N removal in a tertiary-treatment scenario.

Performance and mechanism of sacrificed iron anode coupled with constructed wetlands (E-Fe) for simultaneous nitrogen and phosphorus removal

Three anodic biofilm electrode coupled CWs (BECWs) with graphite (E-C), aluminum (E-Al), and iron (E-Fe), respectively, and a control system (CK) were constructed to evaluate the removal performance of N and P in the secondary effluent of wastewater treatment plants (WWTPs) under different hydraulic retention time (HRT), electrified time (ET), and current density (CD). Microbial communities, and different P speciation, were analyzed to reveal the potential removal pathways and mechanism of N and P in BECWs. Results showed that the optimal average TN and TP removal rates of CK (34.10% and 55.66%), E-C (66.77% and 71.33%), E-Al (63.46% and 84.93%), and E-Fe (74.93% and 91.22%) were obtained under the optimum conditions (HRT 10 h, ET 4 h, CD 0.13 mA/cm²), which demonstrated that the biofilm electrode could significantly improve N and P removal. Microbial community analysis showed that E-Fe owned the highest abundance of chemotrophic Fe(II) (Dechloromonas) and hydrogen autotrophic denitrifying bacteria (Hydrogenophaga). N was mainly removed by hydrogen and iron autotrophic denitrification in E-Fe. Moreover, the highest TP removal rate of E-Fe was attributed to the iron ion formed on the anode, causing co-precipitation of Fe(II) or Fe(III) with PO₄^3--P. The Fe released from the anode acted as carriers for electron transport and accelerated the efficiency of biological and chemical reactions to enhance the simultaneous removal of N and P. Thus, BECWs provide a new perspective for the treatment of the secondary effluent from WWTPs.

Towards Effective, Sustainable Solution for Hospital Wastewater Treatment to Cope with the Post-Pandemic Era

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has spread across the globe since the end of 2019, posing significant challenges for global medical facilities and human health. Treatment of hospital wastewater is vitally important under this special circumstance. However, there is a shortage of studies on the sustainable wastewater treatment processes utilized by hospitals. Based on a review of the research trends regarding hospital wastewater treatment in the past three years of the COVID-19 outbreak, this review overviews the existing hospital wastewater treatment processes. It is clear that activated sludge processes (ASPs) and the use of membrane bioreactors (MBRs) are the major and effective treatment techniques applied to hospital wastewater. Advanced technology (such as Fenton oxidation, electrocoagulation, etc.) has also achieved good results, but the use of such technology remains small scale for the moment and poses some side effects, including increased cost. More interestingly, this review reveals the increased use of constructed wetlands (CWs) as an eco-solution for hospital wastewater treatment and then focuses in slightly more detail on examining the roles and mechanisms of CWs' components with respect to purifying hospital wastewater and compares their removal efficiency with other treatment processes. It is believed that a multi-stage CW system with various intensifications or CWs incorporated with other treatment processes constitute an effective, sustainable solution for hospital wastewater treatment in order to cope with the post-pandemic era.