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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Wastewater Treatment and Reuse".

Deadline for manuscript submissions: closed (25 September 2025) | Viewed by 26177

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Special Issue Editors

Dr. Yuanfeng Qi

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Guest Editor

School of Future Membrane Technology, Fuzhou University, Fuzhou 350108, China
Interests: wastewater recycling and resource; byproduct analysis and remedy; development of SiC-based membrane and catalyst; wastewater reactors; construction of wastewater engineering
Special Issues, Collections and Topics in MDPI journals

Dr. Kai He

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Guest Editor

School of Civil Engineering, Sun Yat-sen University, No. 2 University Road, Zhuhai 519082, China
Interests: water and wastewater engineering; water quality; water and wastewater treatment; water analysis; drinking water quality; water chemistry; environmental analysis; environmental remediation; environmental biodegradation; viological effluent treatment processes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Water resource scarcity and water pollution are serious global problems. The supply of adequate freshwater is essential in order to guarantee the welfare of people and the development of the global economy. Continuous research on water and wastewater treatment has promoted the evolution of water purification science and technology, leading to greater accessibility and affordability of clean water. Emerging technologies have also been studied to further support sustainable water supply.

This Special Issue on “Science and Technology for Water Purification, 2nd Edition” invites contributions that explore promising water and wastewater treatment technologies, as well as related scientific topics. Solutions to renew the existing water purification technology, in terms of its pollutant removal efficiency, energy consumption, and resource recovery, are also welcome.

In this Special Issue, research areas may include (but are not limited to) the following topics:

The evaluation and performance of wastewater reactors and techniques;
The identification, analysis, and remedy of novel pollutants and by-products;
Wastewater eco-environmental damage and evaluation;
Novel materials for wastewater treatment;
Processing models and process management;
Eco-friendly wastewater engineering;
Wastewater recycling, reuse, and resource.

Authors are invited to submit their latest results; both original research articles and reviews are welcomed.

We look forward to receiving your contributions.

Dr. Yuanfeng Qi
Dr. Kai He
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Water is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

recycling and resources
pollutant removal
by-product remedy
process management
specific fillers and carriers
processing models
reactors
wastewater engineering
identification and analysis

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Related Special Issues

Science and Technology for Water Purification in Water (10 articles)
Science and Technology for Water Purification, 3rd Edition in Water (1 article)

Published Papers (11 papers)

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Research

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21 pages, 13748 KB

Open AccessArticle

Integrated Assessment of Anthropogenic Carbon, Nitrogen, and Phosphorus Inputs: A Panjin City Case Study

by Tianxiang Wang, Simiao Wang, Li Ye, Guangyu Su, Tianzi Wang, Rongyue Ma and Zipeng Zhang

Water 2025, 17(20), 2962; https://doi.org/10.3390/w17202962 - 15 Oct 2025

Cited by 1 | Viewed by 759

Abstract

Energy consumption and environmental pollution pose significant challenges to sustainable development. This study develops a comprehensive coupled framework model that advances the quantitative integration of carbon (C), nitrogen (N), and phosphorus (P) cycles driven by multiple anthropogenic pollution sources. This paper used Panjin city as a case study to analyze the dynamic changes and interconnections among C, N, and P. Results indicated that net anthropogenic carbon inputs (NAI_C) increased by 33% from 2016–2020, while net anthropogenic nitrogen inputs (NAI_N) and net anthropogenic phosphorus inputs (NAI_P) decreased by 14% and 28%, respectively. The primary driver of NAI_C was energy consumption, while wetlands were the dominant carbon sequestration sink. Agricultural production was identified as the primary source of NAI_N and NAI_P, and approximately 4.5% of NAI_N and 2.9% of NAI_P were discharged into receiving water bodies. We demonstrate that human activities and natural processes exhibit dual attributes, producing positive and negative environmental effects. The increase in carbon emissions drives economic growth and industrial restructuring; however, the enhanced economic capacity also strengthens the ability to mitigate pollution through environmental protection measures. Similarly, natural ecosystems, including forests and grasslands, contribute to carbon sequestration and the release of non-point source pollution. The comprehensive environmental impact assessment of C, N, and P revealed that the comprehensive environmental index for Panjin city exhibited an improved trend. The factors of energy structure, energy efficiency, and economic scale promoted NAI_C growth, with the economic scale factor alone accounting for 93% of the total increment. Environmental efficiency factor and population size factor were the primary drivers in reducing NAI_N and NAI_P discharges into the receiving water bodies. We propose a novel management model, ecological restoration, clean energy utilization, resource recycling, and pollution source reduction to achieve systemic governance of C, N, and P inputs. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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16 pages, 1739 KB

Open AccessArticle

Synthesis and Characterization of Visible-Light-Responsive TiO₂/LDHs Heterostructures for Enhanced Photocatalytic Degradation Performance

by Jing Wei and Liying Ren

Water 2025, 17(17), 2582; https://doi.org/10.3390/w17172582 - 1 Sep 2025

Cited by 1 | Viewed by 1778

Abstract

A novel composite material comprising titanium dioxide and layered double hydroxides (TiO₂/LDHs) was innovatively proposed and prepared using the co-precipitation method to overcome the shortcomings of titanium dioxide, such as low efficiency in separating electron–hole pairs induced by light and a low utilization rate of visible light. This material was used to study the visible-light-driven photocatalytic degradation of methylene blue. The experimental results show that by constructing efficient heterojunction structures through the alignment of interface band energies and regulating the interface charge transfer pathways, the recombination rate of photogenerated electron–hole pairs is significantly reduced, and the photocatalytic activity is greatly enhanced. Among the tested samples, the TiO₂/LDHs composite material with an aluminum-to-titanium molar ratio of 1:1 (AT11) demonstrated the best photocatalytic performance. Within 70 min of simulated sunlight exposure, the degradation rate of methylene blue reached 98.2%, and the optimal concentration of the catalyst was 1 g/L. The photocatalytic process follows a first-order kinetic model. After four cycles of use, the degradation efficiency of methylene blue by the AT11 composite material was 78.93%, demonstrating good stability. The free radical capture experiments indicated that the main active substances for the photocatalytic degradation of methylene blue were h⁺ and ·OH. The constructed TiO₂/LDHs heterostructure system significantly enhanced the photocatalytic performance of TiO₂ materials, which was conducive to the efficient utilization of solar energy. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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14 pages, 2098 KB

Open AccessArticle

Addition of Heterotrophic Nitrification and Aerobic Denitrification Bacterial Agents to Enhance Bio-Nests Treating Low Carbon-to-Nitrogen Ratio Municipal Wastewater

by Qingxin Diao, Chaolin Quan, Wanmeng Li, Xiangtong Zhou, Zhigang Liu, Xinshan Rong, Zhishui Liang, Xiao Wang and Zhiren Wu

Water 2025, 17(16), 2392; https://doi.org/10.3390/w17162392 - 13 Aug 2025

Viewed by 2060

Abstract

Municipal wastewater with a low carbon-to-nitrogen (C/N) ratio presents challenges for conventional nitrogen removal processes, often requiring costly external carbon sources. This study investigated the enhancement of nitrogen removal in a simultaneous nitrification and denitrification (SND) system by incorporating heterotrophic nitrification and aerobic denitrification (HN-AD) bacterial agents (Klebsiella variicola L3, Acinetobacter beijerinckii W4, and Acinetobacter sp. Z1) with modified basalt fiber carriers. Three reactors were compared: mixed HN-AD strains (M), mixed strains with activated sludge (A+M), and activated sludge alone (A). Results demonstrated that the A+M reactor achieved superior performance, with median removal efficiencies of 82.2% for NH₄⁺-N, 52.9% for total nitrogen (TN), and 51.6% for COD, outperforming the M reactor (75.2%, 43.6%, and 51.6%) and the A reactor (63.2%, 29.3%, and 44.8%). The A+M reactor also exhibited a 40% reduction in COD consumption per unit TN removed (2.55 ± 1.75) compared to the control reactor A (4.25 ± 3.99). Microbial analysis revealed Acinetobacter sp. Z1 (6.1%) and K. variicola L3 (1.1%) as dominant species, with the A+M reactor showing higher microbial diversity (56.4% Proteobacteria, 10.2% Bacteroidota) and biological viability (VSS/SS ratio of 0.70 ± 0.01). Extracellular polymeric substance (EPS) content in A+M reached 242.26 ± 15.52 mg/g-VSS, with a protein-to-polysaccharide ratio of 2.77 ± 0.00, indicating robust biofilm activity. These findings highlight the potential of HN-AD bacterial agents to enhance nitrogen removal in low C/N wastewater treatment, offering a cost-effective and sustainable alternative to traditional methods by reducing reliance on external carbon sources and improving system efficiency. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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18 pages, 3531 KB

Open AccessArticle

Influence Mechanism of Coexisting Ions on the Extraction Efficiency of Lithium from Oil and Gas Field Water

by Qiaoli Shan, Guocheng Zhu, Pengjun Fan, Mengyu Liang, Xin Zhang, Jie Liu and Guizhi Wu

Water 2025, 17(15), 2258; https://doi.org/10.3390/w17152258 - 29 Jul 2025

Cited by 1 | Viewed by 1150

Abstract

Oil and gas field water not only contains low concentrations of lithium but also a lot of suspended matter, inorganic salt, and organic matter. Both inorganic ions and organic substances influence the extraction of lithium. To improve the extraction efficiency of low-concentration lithium in oil and gas field water, the effects of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, Br⁻, SO₄²⁻, NO₃⁻, and organic substances on the extraction efficiency of lithium were studied. The results showed that Na⁺ can promote the extraction of lithium to a certain extent, and lithium ions competed with K+ for extraction; however, the separation coefficient remained more than 13. Ca²⁺ and Mg²⁺ have a significant influence on the extraction of lithium and should be removed prior to extraction. Cl⁻, SO₄²⁻, and NO₃⁻ have little influence on the extraction solution of lithium. Among the organic components, a high concentration of long-chain alkane has a certain effect on the extraction efficiency of lithium, while other substances have little effect. On this basis, the first step for precipitating impurity ions and the second step for solvent extraction of lithium were established. After removing the impurity ions, the extraction efficiency of lithium can reach over 90%. Taking 15L of oil and gas field water as the research object, after extraction, back extraction, concentration, depth impurities removal by extraction, and precipitation drying, the purity of the lithium carbonate product can be achieved at 99.28%. This study can provide technical support for the efficient extraction of low-concentration lithium from oil and gas field water. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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17 pages, 5118 KB

Open AccessArticle

Nickel-Modified Orange Peel Biochar for the Efficient Adsorptive Removal of Eriochrome Black T from Aqueous Solution

by Ayesha Kanwal, Jawaria Abid, Waqar-Un-Nisa, Seema Gul, Muhammad Nouman, Abubakr M Idris and Habib Ullah

Water 2025, 17(10), 1484; https://doi.org/10.3390/w17101484 - 14 May 2025

Cited by 4 | Viewed by 2197

Abstract

The widespread discharge of synthetic dyes such as Eriochrome Black T (EBT) into water bodies poses significant environmental and health concerns due to their toxicity, persistence, and resistance to degradation. In response to this issue, the removal of EBT dye from aqueous solutions using nickel-modified orange peel biochar (MOPB) was investigated in this study at various experimental conditions such as adsorbent dose, pH, concentration of dye, temperature, and contact time. Biochar was prepared from orange peels via pyrolysis, and structural characterization was performed using FTIR, XRD, and SEM to assess morphological changes, pore structure, and functional groups post-modification. MOPB exhibited significantly enhanced adsorption capacity compared to unmodified biochar. Optimal removal (at 0.1 g adsorbent dose, 25 ppm dye concentration, 90 min contact time, 35 °C, and pH 4) resulted in maximum EBT elimination. The equilibrium dataset was evaluated using Langmuir and Freundlich isotherm models. The Langmuir model (R² = 0.99) best described the uptake of EBT dye, which implies that the adsorption of EBT dye onto MOPB was monolayered. The kinetic data were also analyzed using pseudo-first-order and pseudo-second-order models. The pseudo-second-order kinetic model was found to be the best fit (R² = 0.99), indicating that it governs the rate-limiting step of the reaction. Thermodynamic parameters confirmed that the adsorption process is spontaneous and exothermic. These findings demonstrate the potential of MOPB as a low-cost, sustainable adsorbent for the efficient removal of EBT from industrial wastewater. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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10 pages, 3552 KB

Open AccessCommunication

Co/Al–Layered Double Hydroxide-Modified Silicon Carbide Membrane Filters as Persulphate Activator for Aniline Degradation

by Yunfei Zhang, Hongmei Shen, Wenzheng Zheng, Tong Wu, Xianjuan Pu, Diwen Zhou, Senyuan Shen and Yingchao Lin

Water 2025, 17(3), 355; https://doi.org/10.3390/w17030355 - 27 Jan 2025

Cited by 1 | Viewed by 1352

Abstract

Novel catalytic silicon carbide membrane filters (SCMFs) are synthesized with Co/Al–layered double hydroxide (Co/Al-LDH)-coated silicon carbide powder. After capsuled in a self-designed membrane shell, the SCMFs are utilized in activating persulphate for aniline degradation. Thermal analysis conducted via TG/DTG/DSC examination shows that the heating treatment is beneficial in elevating the activating ability of SCMFs, and the derived Co₃O₄ displays superior catalytical efficiency than Co/Al-LDHs precursor. The XRD patterns and SEM images indicate the sheet-like Co/Al-LDHs are uniformly coprecipitated throughout the surface of SCMFs. Within 20 min, around 95% of aniline is eliminated under 0.7 m of flow velocity and 8:1 of persulphate to aniline ratio. Three-dimensional fluorescence and GC chromatography reveal that distinct by-products exist in the early stage of the aniline degradation process between the sintered and non-sintered Co/Al-LDH-coated SCMFs. The integration strategy of Co/Al-LDH coatings and heating treatment endows traditional SCMFs with robust catalytic properties for engineering-oriented applications in wastewater treatment. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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19 pages, 5619 KB

Open AccessArticle

Graphitic Carbon Nitride/CeO₂ Nanocomposite for Photocatalytic Degradation of Methyl Red

by Khansaa Al-Essa, Ethar M. Al-Essa, Alaa Qarqaz, Suhad Al-Issa, Solhe F. Alshahateet and O’la Al-Fawares

Water 2025, 17(2), 158; https://doi.org/10.3390/w17020158 - 9 Jan 2025

Cited by 14 | Viewed by 3230

Abstract

Nanosized ceria (CeO₂) and a graphitic carbon nitride-loaded ceria (CeO₂/GCN) nanocomposite were synthesized using a straightforward and efficient method and characterized by XRD, FTIR, SEM, TEM, TGA, and BET analyses. These techniques confirmed that CeO₂ was effectively supported on the surface of GCN, with particle sizes of the CeO₂/GCN composite in the range of 10–15 nm and a pore size of 3.33 nm. The photocatalytic activity of the CeO₂/GCN nanocomposite and CeO₂ NPs in the degradation of methyl red dye under sunlight radiation was studied using UV–visible spectroscopy. A noticeable red shift in the CeO₂/GCN nanocomposite compared to pure CeO₂ NPs suggests a reduction in its band gap energy, calculated at 3.90 eV for CeO₂ NPs and 2.97 eV for the CeO₂/GCN nanocomposite. This band gap reduction enhances the photocatalytic degradation process, achieving a removal efficiency of 99.92% within a short irradiation time of 40 min for the CeO₂/GCN nanocomposite, compared to 69.47% for CeO₂ NPs. These findings indicate that graphitic carbon nitride significantly enhances the photocatalytic properties of CeO₂ NPs. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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17 pages, 5308 KB

Open AccessArticle

Optimising Salt Recovery—Four-Year Operational Insights into Na₂SO₄ Recovery from Saline Waters Using Pipe Freeze-Crystallization

by Kagiso S. More, Johannes P. Maree and Mlungisi Mahlangu

Water 2025, 17(1), 101; https://doi.org/10.3390/w17010101 - 2 Jan 2025

Cited by 6 | Viewed by 3281

Abstract

Managing high-salinity industrial wastewater poses environmental and operational challenges, particularly in recovering valuable salts like Na₂SO₄. Traditional methods such as evaporation and distillation are energy-intensive (2200 kJ/kg) and environmentally unsustainable. Addressing these limitations, this study investigates the application and optimisation of pipe freeze-crystallization (PFC), an innovative, energy efficient technology operating at 330 kJ/kg, to achieve zero-waste treatment objectives. This research used OLI ESP software to model the crystallization dynamics, accurately predicting Na₂SO₄ recovery and reductions in sulphate concentrations from 74.3 g/L to 6.9 g/L at temperatures below −2 °C. The recovered Na₂SO₄ was analysed using X-ray diffraction with its purity increasing over the years from 50% to 84.9%. Over a four-year operational period at a demonstration plant in Olifantsfontein, South Africa, modifications including extending pipe length from 90 m to 120 m and increasing pipe diameter from 20 mm to 25 mm improved salt recovery rates from 3.5 t/month to 9.1 t/month. Enhanced chiller performance sustained sub-zero temperatures, achieving a cooling capacity of 7 kW while enabling consistent salt and ice recovery. Results showed that feedwater composition substantially influenced crystallization dynamics, with high NaCl concentrations delaying Na₂SO₄ crystallization. The plant’s adaptability to diverse feedwaters and scalability for broader industrial applications highlights its potential as a cost-effective solution. These findings establish PFC as a transformative technology for sustainable saline wastewater treatment, offering industry compliance with environmental regulations, and economic benefits through resource recovery. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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12 pages, 6071 KB

Open AccessArticle

Coupled Electrolysis–Microfiltration System for Efficient Phosphorus Removal and Recovery in the Form of Iron Phosphate Compounds from Wastewater

by Hengfei Yan, Lifeng Wang, Weiping Liu, Xiaofeng Liu and Di Liu

Water 2024, 16(23), 3397; https://doi.org/10.3390/w16233397 - 26 Nov 2024

Viewed by 1770

Abstract

Electrochemical technology presents a promising approach for phosphorus recovery from wastewater. Nevertheless, its application in industry is hindered by relatively low phosphorus recovery efficiency, high energy consumption and complex reactor configurations. In this study, a coupled electrolysis and microfiltration system was designed for phosphorus recovery in the shape of iron phosphate compounds with the use of steel pickling wastewater as the iron source. In the electrolysis unit, the anode diffusion layer was extracted from the porous anode surface with the production of an acid effluent and an alkaline effluent. The alkaline effluent was mixed with the stainless steel acid washing wastewater generated from the steel pickling process and then introduced into the microfiltration unit to intercept the iron phosphate crystals. The filtered effluent was finally introduced into the air aeration unit to further reduce the phosphorus content in the water. And the extracted acid solution could be reused in the pickling step of the iron and steel manufacturing process. The experimental results show that the coupled system achieved phosphorus recovery of 42~80% at a current density of 5~20 mA cm⁻², accompanying energy consumption of 5.78~9.15 kWh (kg P)⁻¹ and current efficiency of 79~43%, when the phosphorus concentration was 3 mM and the iron–phosphorus molar ratio was 1.5. After the microfiltration treatment, the residual phosphorus could be further reduced to 0.5 mg L⁻¹ within 30 min at an aeration rate of 80 mL min⁻¹, which met the discharge standard. The presence of interfering ions (HCO₃⁻ and SiO₄²⁻) posed inhibited effects on phosphorus recovery. Generally, this study provides a green and environmentally friendly way to efficiently recover phosphorus resources from wastewater. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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17 pages, 3473 KB

Open AccessArticle

Pipeline Leak Identification and Prediction of Urban Water Supply Network System with Deep Learning Artificial Neural Network

by Fei Xi, Luyi Liu, Liyu Shan, Bingjun Liu and Yuanfeng Qi

Water 2024, 16(20), 2903; https://doi.org/10.3390/w16202903 - 12 Oct 2024

Cited by 2 | Viewed by 3979

Abstract

Pipeline leakage, which leads to water wastage, financial losses, and contamination, is a significant challenge in urban water supply networks. Leak detection and prediction is urgent to secure the safety of the water supply system. Relaying on deep learning artificial neural networks and a specific optimization algorithm, an intelligential detection approach in identifying the pipeline leaks is proposed. A hydraulic model is initially constructed on the simplified Net2 benchmark pipe network. The District Metering Area (DMA) algorithm and the Cuckoo Search (CS) algorithm are integrated as the DMA-CS algorithm, which is employed for the hydraulic model optimization. Attributing to the suspected leak area identification and the exact leak location, the DMA-CS algorithm possess higher accuracy for pipeline leakage (97.43%) than that of the DMA algorithm (92.67%). The identification pattern of leakage nodes is correlated to the maximum number of leakage points set with the participation of the DMA-CS algorithm, which provide a more accurate pathway for identifying and predicting the specific pipeline leaks. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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Review

Jump to: Research

20 pages, 1665 KB

Open AccessReview

The Utilization of Dissolved Organic Matter Spectral and Molecular Properties in Freshwater Eutrophication Studies: A Mini Review

by Wengang Yan, Junfeng Xing, Chunzhao Chen, Yihua Xiao and Changqing Liu

Water 2025, 17(2), 151; https://doi.org/10.3390/w17020151 - 8 Jan 2025

Cited by 4 | Viewed by 3134

Abstract

Eutrophication is a major environmental issue affecting freshwater ecosystems worldwide. While its impact on the composition of dissolved organic matter (DOM) is well recognized, the relationships between DOM’s optical and molecular properties across eutrophication gradients remain underexplored. This review synthesizes recent research on DOM’s optical properties (derived from UV-Vis absorption and fluorescence spectroscopy) and molecular characteristics (analyzed using Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR MS) in freshwater systems of varying trophic states. Generalized additive model (GAM) analysis was used to assess correlations between DOM’s properties and the trophic state index (TSI). The dissolved organic carbon (DOC), a₂₅₄, SUVA₂₅₄, S_R, HIX, BIX, and FI averaged 11.44 ± 11.97 mg/L, 23.23 ± 16.95 m⁻¹. 2.98 ± 0.99 L·mg⁻¹·m⁻¹, 1.42 ± 0.38, 2.38 ± 1.31, 1.08 ± 0.16, and 2.11 ± 0.44, respectively, from mesotrophic to middle-eutrophic sites. The GAM results revealed a significant linear correlation between DOC and DOM’s optical properties, including a₂₅₄, SUVA₂₅₄, and FI, with the TSI, suggesting that DOM accumulation intensifies with eutrophication. DOM’s molecular properties, such as O/C and H/C ratios, double bond equivalents (DBEs), and CHOS% content, exhibited nonlinear correlations with the TSI. These trends imply a shift in DOM sources from terrestrial and macrophyte-derived inputs to those dominated by algal- and sediment-derived sources as eutrophication progresses. We concluded that DOM’s molecular indices alone may not serve as a reliable indicator of freshwater trophic states; future studies should focus on integrating both optical and molecular indices to offer a more comprehensive assessment of freshwater trophic states. Given the limited number of molecular variables examined in this study, this work only offers a preliminary investigation into the relationship between DOM molecular changes and freshwater eutrophication. More systematic studies focusing on the molecular-level analyses of DOM across varying trophic states on a broader geographic scale are needed. Full article

(This article belongs to the Special Issue Science and Technology for Water Purification, 2nd Edition)

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