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Separations, Volume 12, Issue 10 (October 2025) – 6 articles

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16 pages, 2238 KB

Open AccessArticle

Enhanced Electro-Dewatering of Sludge Through Inorganic Coagulant Pre-Conditioning

by Xiaoyin Yang, Song Huang, Yusong Zhang, Hanjun Wu, Yabin Ma and Bingdi Cao

Separations 2025, 12(10), 262; https://doi.org/10.3390/separations12100262 - 26 Sep 2025

Abstract

Sludge electro-dewatering technology is an attractive dewatering technology, but its application is limited by high energy consumption and filter cloth clogging caused by the dissolution of extracellular polymeric substances (EPSs). Thus, the addition of inorganic coagulants is expected to enhance the electro-dewatering efficiency of waste activated sludge (WAS). In this study, we evaluated the effects of the three typical inorganic coagulants (HPAC, PAC, and FeCl₃) on sludge electro-dewatering behavior. The results show that the electro-dewatering rate at the cathode was increased with the raising of the inorganic coagulants dosage, and FeCl₃ exhibited the best effect on the improvement of sludge electro-dewatering among the three inorganic coagulants. The zeta potential of the sludge flocs and the electro-osmotic effect were raised with the increasing of the inorganic coagulants dosage. The sludge floc conditioned by FeCl₃ is more compact than HPAC and PAC. Moreover, the dissolved EPS content reduced in the sludge electro-dewatering process when inorganic coagulant was added. In comparison to increasing ionic strength, the compression of extracellular polymeric substances (EPSs) plays a more critical role in enhancing the electro-dewatering process of sludge. The addition of inorganic coagulants also reduced the energy consumption during water removal in the electro-dewatering process. Full article

(This article belongs to the Special Issue Advanced Separation Technology for Sludge Wastewater Treatment and Resource Utilization)

14 pages, 1297 KB

Open AccessArticle

Optimizing Natural Organic Matter Removal from Water by UV/H₂O₂ Advanced Oxidation Using Central Composite Design

by Hrvoje Juretić, Darko Smoljan, Hrvoje Cajner and Draženka Stipaničev

Separations 2025, 12(10), 261; https://doi.org/10.3390/separations12100261 - 24 Sep 2025

Abstract

The inevitable ubiquity of natural organic matter (NOM) in all waters presents a challenge to the proper functioning of water treatment processes. Therefore, minimizing NOM in raw water is crucial to avoid operational issues in subsequent treatment steps. In this experimental study, we aimed to maximize the degradation of NOM using UV/H₂O₂ advanced oxidation, employing design of experiments (DoE) and response surface methodology (RSM) for process optimization. Experiments were carried out on synthetic water, and the effects of dissolved organic carbon (DOC) content and hydrogen peroxide concentration on DOC removal at neutral pH were examined. NOM isolated from the Suwannee River was used as a representative model. The process was modeled and optimized using Design-Expert 14.0.7.0 software. The highest DOC removal of approximately 34% was observed at a DOC level of ~8 mg L⁻¹ and an H₂O₂ concentration just below 250 mg L⁻¹. Degradation products were analyzed by ultra-high-performance liquid chromatography coupled with hybrid quadrupole time-of-flight mass spectrometry, revealing sixteen compounds, mostly long-chain saturated fatty acids. Finally, the energy efficiency of the experimental setup was assessed and discussed. Full article

(This article belongs to the Special Issue Eco-Friendly Innovations for Water Purification: Advanced Oxidation and Sustainable Cleanup Solutions)

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14 pages, 4132 KB

Open AccessArticle

Pore-Engineered Magnetic Biochar: Optimizing Pyrolysis and Fe₃O₄ Loading for Targeted Chlorinated Aliphatic Hydrocarbon (CAH) Adsorption

by Fengyuan Zhang, Zixuan Li, Xiaohan Dou, Zhengwei Liu, Yan Xie, Jingru Liu and Shucai Zhang

Separations 2025, 12(10), 260; https://doi.org/10.3390/separations12100260 - 24 Sep 2025

Abstract

Chlorinated aliphatic hydrocarbons (CAHs) are some of the most widely distributed organic pollutants in underground environments and have high biological toxicity. This research aims to prepare an effective adsorbent comprising biochar and magnetite (MBC) to remove CAH pollution from soil. Optimization of the preparation and adsorption performance of MBC was investigated. The results of the adsorption experiment, combined with scanning electron microscopy (SEM) observations, show that the best raw material and pyrolysis temperature were coconut shell and 500 °C respectively. The Fourier transform infrared (FTIR) and X-ray diffraction (XRD) pattern characterizations, as well as the adsorption results, demonstrated the successful synthesis and enhancement effect of MBC for CAHs. The adsorption of CAHs on Fe₃O₄-loaded biochar was improved by 34.40–222.25% during pyrolysis at 500–900 °C. Additionally, MBC with a 10% Fe₃O₄ content had the best effect on three types of CAHs at low concentrations. A comparative pore analysis of MBC with different doses of Fe₃O₄ was carried out to reveal the relationship between the pore characteristics and adsorption properties. Furthermore, competitive adsorption experiments demonstrated that 4 wt% MBC addition significantly reduced the soil-bound TCE by 48.6%. Overall, these results indicated that MBC was an effective adsorbent for CAH removal from the polluted underground environment. Full article

(This article belongs to the Special Issue Removal of Environmental Pollutants and Bioremediation Strategies)

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14 pages, 1653 KB

Open AccessArticle

Efficient Adsorptive Removal of Phosphonate Antiscalant HEDP by Mg-Al LDH

by Changjin Guo, Lejiaqi Zhang, Qi Zhang, Congcong Ni, Ning Deng and Xin Huang

Separations 2025, 12(10), 259; https://doi.org/10.3390/separations12100259 - 24 Sep 2025

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Abstract

Phosphonate-based antiscalants such as 1-hydroxyethane-1,1-diphosphonic acid (HEDP) are extensively employed in industrial water treatment but pose significant environmental challenges due to their persistence and phosphorus content. In this study, Mg-Al layered double hydroxide (Mg-Al LDH) was synthesized and evaluated for its capacity to adsorb and remove HEDP. Mg-Al LDH showed a pronounced adsorption affinity and an exceptionally high capacity of 276.0 mg g⁻¹ at pH 7.0. The adsorption process was remarkably fast, attaining 97% of equilibrium uptake within 45 min at 298 K. The adsorption data fit well to the Elovich kinetic model and the Langmuir isotherm, indicating that the adsorption process is dominated by chemisorption. Thermodynamic analysis further confirmed its spontaneous nature. Additionally, Mg-Al LDH demonstrated strong tolerance to environmental fluctuations. Characterization techniques, including XRD, FTIR, and zeta potential measurements, confirmed that HEDP adsorption onto Mg-Al LDH primarily occurs via surface complexation with metal sites and electrostatic attraction. These findings demonstrate that Mg-Al LDH is a highly effective adsorbent for removing persistent phosphonate pollutants from wastewater streams. Full article

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15 pages, 2291 KB

Open AccessArticle

Eco-Friendly Dye Removal: Black Cumin Seed Press Cake for Toluidine Blue Adsorption

by Galia Gentscheva, Paunka Vassileva, Christina Tzvetkova, Aleksandar Pashev, Ina Yotkovska, Metodi Mladenov and Tsvetan Vassilev

Separations 2025, 12(10), 258; https://doi.org/10.3390/separations12100258 - 23 Sep 2025

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Abstract

This research investigates the potential of Seed Press Cake of Nigella sativa (SPCN) as a low-cost, eco-friendly biosorbent for the removal of the cationic dye Toluidine Blue (TB) from aqueous solutions. The physicochemical properties of the material were characterized using Fourier-transform infrared (FTIR) spectroscopy, nitrogen adsorption–desorption isotherms, and scanning electron microscopy (SEM). Adsorption performance was evaluated under varying conditions, with the process best described by the pseudo-second-order kinetic model and the Langmuir isotherm, indicating monolayer adsorption. The maximum adsorption capacity was determined to be 305 mg·g⁻¹ at 20 °C. Thermodynamic analysis revealed that the adsorption is spontaneous, exothermic, and entropy-driven. FTIR analysis indicated that TB interacts with SPCN primarily via physical interactions, including electrostatic attraction, van der Waals forces, and hydrogen bonding, without strong chemical bonding. These findings demonstrate the high potential of black cumin seed waste as a sustainable and efficient biosorbent for dye removal in wastewater treatment. Full article

(This article belongs to the Special Issue Applications of Adsorbent Materials in Water and Wastewater Treatment)

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18 pages, 2919 KB

Open AccessArticle

Development of an Efficient HPLC-MS/MS Method for the Detection of a Broad Spectrum of Hydrophilic and Lipophilic Contaminants in Marine Waters: An Experimental Design Approach

by Daniel Bona, Marina Di Carro, Emanuele Magi and Barbara Benedetti

Separations 2025, 12(10), 257; https://doi.org/10.3390/separations12100257 - 23 Sep 2025

Viewed by 68

Abstract

The present study develops and optimizes a targeted chromatographic method coupled with mass spectrometry, employing design of experiments, for the determination of several emerging contaminants in environmental waters. Their widespread presence poses environmental and health risks due to their pseudo-persistence and unknown long-term effects. Therefore, sensitive and selective analytical methods are essential for their reliable environmental monitoring. This work focuses on 40 organic micro-contaminants with a wide range of polarities, including drugs, pesticides and UV-filters. Chromatographic separation was performed on a pentafluorophenyl column, and a Face-Centered Design was applied for multivariate optimization. Mobile phase flow and temperature were chosen as the study factors, and retention time and peak width as the responses, as indicators of analytical performance. Two optimized runs (for positive and negative electrospray ionization modes) were obtained, enabling the analysis of all 40 analytes in a total of 29 min. The final method was successfully applied to seawater samples from different sites of the Genoa harbor area. Several analytes were detected and quantified, down to the ng L⁻¹ level, with tracers and pharmaceuticals showing the highest concentrations. The method demonstrated satisfactory accuracy, precision and specificity and is suitable for routine monitoring of a broad range of emerging contaminants in seawater. Full article

(This article belongs to the Special Issue Optimization of Advanced Separation Technologies for the Analysis of Emerging Contaminants)

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