Special Issue "Adsorbents for Water and Wastewater Treatment and Resource Recovery"

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

Deadline for manuscript submissions: closed (30 November 2020).

Special Issue Editors

Dr. Sílvia Santos
E-Mail Website
Guest Editor
LSRE – Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE-LCM, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
Interests: wastewater treatment; natural adsorbents, adsorption and metal recovery
Special Issues and Collections in MDPI journals
Dr. Cidália Botelho
E-Mail Website
Guest Editor
Laboratory of Separation and Reaction Engineering – Laboratory of Catalysis and Materials (LSRE-LCM), Chemical Engineering Department, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
Interests: water chemistry; water treatment; adsorption
Special Issues and Collections in MDPI journals
Dr. Ariana Pintor
E-Mail Website
Guest Editor
Laboratory of Separation and Reaction Engineering – Associate Laboratory LSRELCM, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Porto, Portugal
Interests: water treatment; wastewater treatment; micropollutants; resource recovery; adsorption
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Adsorption is a well-established operation commonly used in water and wastewater treatment. In the last decade, the search for alternative adsorbents has rocketed up, which is partially explained by the increasingly demanding standards and discharge limits imposed by legislation, the recognition of new and emerging contaminants and by the interest to reuse treated water in multiple applications. Additionally, in the current context of promoting an efficient use of natural resources and energy, many adsorbents based on natural and waste materials and requiring minimal processing have been proposed as alternatives to the conventional ones. Now is also the time when the contribution of the adsorption to the circular economy has been stepping up, going beyond the removal of harmful contaminants from water, and going towards the recovery of substances of economic interest or in risk of scarcity.

This special issue invites the submission of original research papers or review papers covering the latest findings and progresses in this field. We are keen to receive contributions reporting results with different kinds of adsorbents/biosorbents and for different applications (drinking-water treatment, purification of irrigation water, wastewater decontamination, industrial wastewater treatment, among others), covering a wide range of adsorbates (heavy metals, toxic metalloids, surfactants, dyes, nutrients, pharmaceuticals, personal care products, pesticides, among others). Contributions related to the recovery of substances from aqueous solution (e.g.: phosphate, critical and precious metals) will be also highly welcomed.

Dr. Sílvia Santos
Prof. Dr. Cidália Botelho
Dr. Ariana Pintor
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 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

  • adsorption
  • biosorption
  • water
  • wastewater
  • water reuse
  • emerging contaminants
  • heavy metals
  • critical metals
  • phosphate recovery

Published Papers (21 papers)

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Research

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Article
Cd(II) and Pb(II) Adsorption Using a Composite Obtained from Moringa oleifera Lam. Cellulose Nanofibrils Impregnated with Iron Nanoparticles
Water 2021, 13(1), 89; https://doi.org/10.3390/w13010089 - 03 Jan 2021
Cited by 1 | Viewed by 1172
Abstract
This work informs on the green synthesis of a novel adsorbent and its adsorption capacity. The adsorbent was synthesized by the combination of iron nanoparticles and cellulose nanofibers (FeNPs/NFCs). Cellulose nanofibers (NFCs) were obtained from Moringa (Moringa oleifera Lam.) by a pulping [...] Read more.
This work informs on the green synthesis of a novel adsorbent and its adsorption capacity. The adsorbent was synthesized by the combination of iron nanoparticles and cellulose nanofibers (FeNPs/NFCs). Cellulose nanofibers (NFCs) were obtained from Moringa (Moringa oleifera Lam.) by a pulping Kraft process, acid hydrolysis, and ultrasonic methods. The adsorption method has advantages such as high heavy metal removal in water treatment. Therefore, cadmium (Cd) and lead (Pb) adsorption with FeNP/NFC from aqueous solutions in batch systems was investigated. The kinetic, isotherm, and thermodynamic parameters, as well as the adsorption capacities of FeNP/NFC in each system at different temperatures, were evaluated. The adsorption kinetic data were fitted to mathematical models, so the pseudo-second-order kinetic model described both Cd and Pb. The kinetic rate constant (K2), was higher for Cd than for Pb, indicating that the metal adsorption was very fast. The adsorption isotherm data were best described by the Langmuir–Freundlich model for Pb multilayer adsorption. The Langmuir model described Cd monolayer sorption. However, experimental maximum adsorption capacities (qe exp) for Cd (>12 mg/g) were lower than those for Pb (>80 mg/g). In conclusion, iron nanoparticles on the FeNP/NFC composite improved Cd and Pb selectivity during adsorption processes, indicating the process’ spontaneous and exothermic nature. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Adsorption by Granular Activated Carbon and Nano Zerovalent Iron from Wastewater: A Study on Removal of Selenomethionine and Selenocysteine
Water 2021, 13(1), 23; https://doi.org/10.3390/w13010023 - 25 Dec 2020
Cited by 3 | Viewed by 650
Abstract
Selenomethionine (SeMet) and selenocysteine (SeCys) are the most common forms of organic selenium, which is often found in the effluent of industrial wastewater. These organic selenium compounds are toxic, bioavailable and most likely to bioaccumulate in aquatic organisms. This study investigated the use [...] Read more.
Selenomethionine (SeMet) and selenocysteine (SeCys) are the most common forms of organic selenium, which is often found in the effluent of industrial wastewater. These organic selenium compounds are toxic, bioavailable and most likely to bioaccumulate in aquatic organisms. This study investigated the use of two adsorbent candidates (granular activated carbon (GAC) and nano zerovalent iron (nZVI)) as treatment technologies for SeMet and SeCys removal. Batch experiments were performed and inductively coupled plasma optical emission spectrometer (ICP-OES) was used for sample analysis. Experimental data showed GAC demonstrated a higher affinity towards the removal of SeMet and SeCys compared to nZVI. The removal efficiency of SeCys and SeMet by GAC was 96.1% and 86.7%, respectively. NZVI adsorption capacity for SeCys was 39.4% and SeMet < 1.1%. Irrespective of the adsorbent, SeMet is more refractory to be adsorbed compared to SeCys. Kinetics data of GAC and nZVI agreed well with the pseudo-second-order model (R2 > 0.990). The experimental data of SeCys was characterized by Langmuir model, indicating monolayer adsorption. The adsorption capacity of nZVI for SeCys increased significantly by about 35%, with a decrease in pH from 9.0 to 4.0, indicating that SeCy removal by nZVI is pH dependent. While electrostatic attraction is considered the driving mechanism for nZVI adsorption, GAC uptake capacity is controlled by weak van der Waal forces. The adsorption of binary adsorbates (SeMet and SeCys) exhibited an inhibitory effect due to the competitive interaction between contaminant molecules. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Removal of Diclofenac in Wastewater Using Biosorption and Advanced Oxidation Techniques: Comparative Results
Water 2020, 12(12), 3567; https://doi.org/10.3390/w12123567 - 19 Dec 2020
Cited by 3 | Viewed by 644
Abstract
Wastewater treatment is a topic of primary interest with regard to the environment. Diclofenac is a common analgesic drug often detected in wastewater and surface water. In this paper, three commonly available agrifood waste types (artichoke agrowaste, olive-mill residues, and citrus waste) were [...] Read more.
Wastewater treatment is a topic of primary interest with regard to the environment. Diclofenac is a common analgesic drug often detected in wastewater and surface water. In this paper, three commonly available agrifood waste types (artichoke agrowaste, olive-mill residues, and citrus waste) were reused as sorbents of diclofenac present in aqueous effluents. Citrus-waste biomass for a dose of 2 g·L−1 allowed for removing 99.7% of diclofenac present in the initial sample, with a sorption capacity of 9 mg of adsorbed diclofenac for each gram of used biomass. The respective values obtained for olive-mill residues and artichoke agrowaste were around 4.15 mg·g−1. Advanced oxidation processes with UV/H2O2 and UV/HOCl were shown to be effective treatments for the elimination of diclofenac. A significant reduction in chemical oxygen demand (COD; 40–48%) was also achieved with these oxidation treatments. Despite the lesser effectiveness of the sorption process, it should be considered that the reuse and valorization of these lignocellulosic agrifood residues would facilitate the fostering of a circular economy. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Removal of Phenolic Compounds from Olive Mill Wastewater by a Polydimethylsiloxane/oxMWCNTs Porous Nanocomposite
Water 2020, 12(12), 3471; https://doi.org/10.3390/w12123471 - 10 Dec 2020
Cited by 1 | Viewed by 1497
Abstract
User-friendly and energy-efficient methods able to work in noncontinuous mode for in situ purification of olive mill wastewater (OMW) are necessary. Herein we determined the potential of oxidized multiwalled carbon nanotubes entrapped in a microporous polymeric matrix of polydimethylsiloxane in the removal and [...] Read more.
User-friendly and energy-efficient methods able to work in noncontinuous mode for in situ purification of olive mill wastewater (OMW) are necessary. Herein we determined the potential of oxidized multiwalled carbon nanotubes entrapped in a microporous polymeric matrix of polydimethylsiloxane in the removal and recovery of phenolic compounds (PCs) from OMW. The fabrication of the nanocomposite materials was straightforward and evidenced good adsorption capacity. The adsorption process is influenced by the pH of the OMW. Thermodynamic parameters evidenced the good affinity of the entrapped nanomaterial towards phenols. Furthermore, the kinetics and adsorption isotherms are studied in detail. The presence of oil inside the OMW can speed up the uptake process in batch adsorption experiments with respect to standard aqueous solutions, suggesting a possible use of the nanocomposite for fast processing of OMW directly in the tank where they are stored. Moreover, the prepared nanocomposite is safe and can be easily handled and disposed of, thus avoiding the presence of specialized personnel. After the adsorption process the surface of the nanomaterial can be easily regenerated by mild treatments with diluted acetic acid, thus permitting both the recyclability of the nanomaterial and the recovery of phenolic compounds for a possible use as additives in food and nutraceutical industries and the recovery of OMW for fertirrigation. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Uptake and Recovery of Gold from Simulated Hydrometallurgical Liquors by Adsorption on Pine Bark Tannin Resin
Water 2020, 12(12), 3456; https://doi.org/10.3390/w12123456 - 09 Dec 2020
Cited by 1 | Viewed by 589
Abstract
The recovery of critical and precious metals from waste electrical and electronic equipment (WEEE) is an environmental and economic imperative. Biosorption has been considered a key technology for the selective extraction of gold from hydrometallurgical liquors obtained in the chemical leaching of e-waste. [...] Read more.
The recovery of critical and precious metals from waste electrical and electronic equipment (WEEE) is an environmental and economic imperative. Biosorption has been considered a key technology for the selective extraction of gold from hydrometallurgical liquors obtained in the chemical leaching of e-waste. In this work, the potential of tannin resins prepared from Pinus pinaster bark to sequester and recover gold(III) from hydrochloric acid and aqua regia solutions was assessed. Equilibrium isotherms were experimentally determined and maximum adsorption capacities of 343 ± 38 and 270 ± 19 mg g−1 were found for Au uptake from HCl and HCl/HNO3 (3:1 v/v) solutions containing 1.0 mol L−1 H+. Higher levels of acidity (and chloride ligands) significantly impaired the adsorption of gold from both kinds of leaching solutions, especially in the aqua regia system, in which the adsorbent underperformed. Pseudo-first and pseudo-second order models successfully described the kinetic data. The adsorbent presented high selectivity towards gold. Actually, in simulated aqua regia WEEE liquors, Au(III) was extensively adsorbed, compared to Cu(II), Fe(III), Ni(II), Pd(II), and Zn(II). In three adsorption–desorption cycles, the adsorption capacity of the regenerated adsorbent moderately decreased (19%), although the gold elution in acidic thiourea solution had been quite limited. Future research is needed to examine more closely the elution of gold from the exhausted adsorbents. The results obtained in this work show good perspectives as regards the application of pine bark tannin resins for the selective extraction of Au from electronic waste leach liquors. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Mechanistic Study of Pb2+ Removal from Aqueous Solutions Using Eggshells
Water 2020, 12(9), 2517; https://doi.org/10.3390/w12092517 - 09 Sep 2020
Viewed by 592
Abstract
This study investigates the impact of eggshell particle size and solid-to-water (s/w) ratio on lead (Pb2+) removal from aqueous solution. Collected raw eggshells were washed, crushed, and sieved into two particle sizes (<150 and 150–500 µm). Batch Pb2+ removal experiments [...] Read more.
This study investigates the impact of eggshell particle size and solid-to-water (s/w) ratio on lead (Pb2+) removal from aqueous solution. Collected raw eggshells were washed, crushed, and sieved into two particle sizes (<150 and 150–500 µm). Batch Pb2+ removal experiments were conducted at different s/w ratios with initial Pb2+ concentrations of up to 70 mg/L. The contribution of precipitation to Pb2+ removal was simulated by quantifying removal using eggshell water, whereas sorbed Pb2+ was quantified by acid digestion. Results indicated that eggshell particle sizes did not affect Pb2+ removal. High removal (up to 99%) of Pb2+ was achieved for low initial Pb2+ concentrations (<30 mg/L) across all s/w ratios studied. However, higher removal capacity was observed at lower s/w ratios. In addition, results confirmed that precipitation played a major role in the removal of Pb2+ by eggshells. Yet, this role decreased as the s/w ratio and initial concentration of Pb2+ increased. A predictive relationship that relates the normalized removal capacity of eggshells to the s/w ratio was developed to potentially facilitate the design of the reactor. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
A Biosorption-Pyrolysis Process for Removal of Pb from Aqueous Solution and Subsequent Immobilization of Pb in the Char
Water 2020, 12(9), 2381; https://doi.org/10.3390/w12092381 - 25 Aug 2020
Cited by 1 | Viewed by 633
Abstract
The application of biosorption in the removal of heavy metals from water faces a challenge of safe disposal of contaminated biomass. In this study, a potential solution for this problem was proposed by using a biosorption-pyrolysis process featured by pretreatment of biomass with [...] Read more.
The application of biosorption in the removal of heavy metals from water faces a challenge of safe disposal of contaminated biomass. In this study, a potential solution for this problem was proposed by using a biosorption-pyrolysis process featured by pretreatment of biomass with phosphoric acid (PA). The PA pretreatment of biomass increased the removal efficiency of heavy metal Pb from water by sorption, and subsequent pyrolysis helped immobilize Pb in the residual char. The results indicate that most (>95%) of the Pb adsorbed by the PA-pretreated biomass was retained in the char, and that the lower pyrolysis temperature (350 °C) is more favorable for Pb immobilization. In this way, the bioavailable Pb in the char was hardly detected, while the Pb leachable in acidic solution decreased to <3% of total Pb in the char. However, higher pyrolysis temperature (450 °C) is unfavorable for Pb immobilization, as both the leachable and bioavailable Pb increased to >28%. The reason should be related to the formation of elemental Pb and unstable Pb compounds during pyrolysis at 450 °C, according to the X-ray diffraction study. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Removal of Pb2+ from Aqueous Solutions Using K-Type Zeolite Synthesized from Coal Fly Ash
Water 2020, 12(9), 2375; https://doi.org/10.3390/w12092375 - 24 Aug 2020
Cited by 3 | Viewed by 573
Abstract
In this study, a novel zeolite (K-type zeolite) was synthesized from coal fly ash (FA), and adsorption capacity on Pb2+ was assessed. Six types of zeolite (FA1, FA3, FA6, FA12, FA24, and FA48) were prepared, and their physicochemical properties, such as surface [...] Read more.
In this study, a novel zeolite (K-type zeolite) was synthesized from coal fly ash (FA), and adsorption capacity on Pb2+ was assessed. Six types of zeolite (FA1, FA3, FA6, FA12, FA24, and FA48) were prepared, and their physicochemical properties, such as surface functional groups, cation exchange capacity, pHpzc, specific surface area, and pore volume, were evaluated. The quantity of Pb2+ adsorbed by the prepared zeolites followed the order FA < FA1 < FA3 < FA6 < FA12 < FA24 < FA48. Current results indicate that the level of Pb2+ adsorbed was strongly related to the surface characteristics of the adsorbent. Additionally, the correlation coefficient between the amounts of Pb2+ adsorbed and K+ released from FA48 was 0.958. Thus, ion exchange with K+ in the interlayer of FA48 is critical for the removal of Pb2+ from aqueous media. The new binding energies of Pb(4f) at 135 and 140 eV were detected after adsorption. Moreover, FA48 showed selectivity for Pb2+ adsorption in binary solution systems containing cations. The results revealed that FA48 could be useful for removing Pb2+ from aqueous media. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Adsorptive Behavior of an Activated Carbon for Bisphenol A Removal in Single and Binary (Bisphenol A—Heavy Metal) Solutions
Water 2020, 12(8), 2150; https://doi.org/10.3390/w12082150 - 30 Jul 2020
Cited by 8 | Viewed by 1001
Abstract
Bisphenol A (BPA) is an extensively produced and consumed chemical in the world. Due to its widespread use, contamination by this pollutant has increased in recent years, reaching a critical environmental point. This work investigates the feasibility of bisphenol A adsorption from industrial [...] Read more.
Bisphenol A (BPA) is an extensively produced and consumed chemical in the world. Due to its widespread use, contamination by this pollutant has increased in recent years, reaching a critical environmental point. This work investigates the feasibility of bisphenol A adsorption from industrial wastewater solutions, testing the reduction of bisphenol A in synthetic solutions by a commercial activated carbon, AC-40, in batch mode. Besides, mixtures of bisphenol A and different heavy metal cations were also studied. So far, no works have reported a complete study about bisphenol A removal by this activated carbon including the use of this material to remove BPA in the presence of metal cations. First, adsorption experiments were performed in batch changing pH, dose of adsorbent, initial bisphenol A concentration and contact time. Results showed greater retention of bisphenol A by increasing the acidity of the medium. Further, the percentage of bisphenol A adsorbed increased with increasing contact time. The selected conditions for the rest of the experiments were pH 5 and a contact time of 48 h. In addition, an increase in retention of bisphenol A when the dose of adsorbent increased was observed. Then, specific experiments were carried out to define the kinetics and the adsorption isotherm. Equilibrium data were adequately fitted to a Langmuir isotherm and the kinetics data fitted well to the pseudo-second-order model. The maximum adsorption capacity provided by Langmuir model was 94.34 mg/g. Finally, the effect of the presence of other heavy metals in water solution on the adsorption of bisphenol A was analyzed. Binary tests revealed competition between the adsorbates and a significant selectivity toward bisphenol A. Finally, the study of the adsorption performance in three consecutive adsorption–desorption cycles showed efficiencies higher than 90% in all cycles, indicating that the activated carbon has good reusability. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Adsorption Mechanisms and Characteristics of Hg2+ Removal by Different Fractions of Biochar
Water 2020, 12(8), 2105; https://doi.org/10.3390/w12082105 - 24 Jul 2020
Cited by 3 | Viewed by 634
Abstract
The adsorption mechanisms of mercury ion (Hg2+) by different fractions of biochar were studied, providing a theoretical basis and practical value for the use of biochar to remediate mercury contamination in water. Biochar (RC) was prepared using corn straw as the [...] Read more.
The adsorption mechanisms of mercury ion (Hg2+) by different fractions of biochar were studied, providing a theoretical basis and practical value for the use of biochar to remediate mercury contamination in water. Biochar (RC) was prepared using corn straw as the raw material. It was then fractionated, resulting in inorganic carbon (IC), organic carbon (OC), hydroxyl-blocked carbon (BHC), and carboxyl-blocked carbon (BCC). Before and after Hg2+ adsorption, the biochar fractions were characterized by several techniques, such as energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Obtained results indicate that the reaction mechanisms of RC for Hg2+ removal mainly include electrostatic adsorption, ion exchange, reduction, precipitation, and complexation. The equilibrium adsorption capacity of RC for Hg2+ is 75.56 mg/g, and the adsorption contribution rates of IC and OC are approximately 22.4% and 77.6%, respectively. Despite the lower rate, IC shows the largest adsorption capacity, of 92.63 mg/g. This is attributed to all the mechanisms involved in Hg2+ adsorption by IC, with ion exchange being the main reaction mechanism (accounting for 39.8%). The main adsorption mechanism of OC is the complexation of carboxyl and hydroxyl groups with Hg2+, accounting for 71.6% of the total OC contribution. BHC and BCC adsorb mercury mainly via the reduction–adsorption mechanism, accounting for 54.6% and 54.5%, respectively. Among all the adsorption mechanisms, the complexation reaction of carboxyl and hydroxyl groups with Hg2+ is the dominant effect. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Removal of Arsenic(III) Ion from Aqueous Media Using Complex Nickel-Aluminum and Nickel-Aluminum-Zirconium Hydroxides
Water 2020, 12(6), 1697; https://doi.org/10.3390/w12061697 - 14 Jun 2020
Cited by 5 | Viewed by 761
Abstract
The technology of wastewater treatment involving removal of heavy metals using complex metal hydroxides is reported. In this study, complex nickel-aluminum (NA11 and NA12) and nickel-aluminum-zirconium (NAZ1 and NAZ2) hydroxides were prepared for the removal of arsenite ions, As(III), from aqueous solution. The [...] Read more.
The technology of wastewater treatment involving removal of heavy metals using complex metal hydroxides is reported. In this study, complex nickel-aluminum (NA11 and NA12) and nickel-aluminum-zirconium (NAZ1 and NAZ2) hydroxides were prepared for the removal of arsenite ions, As(III), from aqueous solution. The characteristics of each adsorbent were evaluated, and the adsorption capacity and adsorption mechanism were determined. The adsorption capacity of As(III) on NAZ1 (15.3 mg g−1) was greater than that on NA11 (9.3 mg g−1). Coverage is directly related to the specific surface area with a correlation coefficient of 0.921. Ion exchange involving sulfate ions in the interlayer of the adsorbent also plays a role in the mechanism of As(III) adsorption as demonstrated by correlation coefficients of 0.797 and 0.944 for the NA11 and NAZ1, respectively. The results demonstrate the usefulness of NAZ1 in removing As(III) from aqueous media. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Use of Chemically Treated Human Hair Wastes for the Removal of Heavy Metal Ions from Water
Water 2020, 12(5), 1263; https://doi.org/10.3390/w12051263 - 29 Apr 2020
Cited by 1 | Viewed by 967
Abstract
Human hair is considered a ubiquitous waste product and its accumulation can cause environmental problems. Hence, the search for alternatives that take advantage of this waste as a new raw material is of interest, and contributes to the idea of the circular economy. [...] Read more.
Human hair is considered a ubiquitous waste product and its accumulation can cause environmental problems. Hence, the search for alternatives that take advantage of this waste as a new raw material is of interest, and contributes to the idea of the circular economy. In this study, chemically modified human hair was used as a low cost biosorbent for the removal of heavy metal ions from aqueous solutions. The effect of the contact time, the pH, and the biosorbent concentration on the biosorption process were investigated. Kinetic modeling indicated that the pseudo-second order kinetic equation fitted well with R2 > 0.999. Furthermore, the equilibrium data fitted the Langmuir adsorption isotherm at 295 K resulting in saturation concentrations of 9.47 × 10−5, 5.57 × 10−5, 3.77 × 10−5, and 3.61 × 10−5 mol/g for the sorption of Cr(III), Cu(II), Cd(II), and Pb(II), respectively. The biosorption process did not change the chemical structure and morphology of the hair, which was shown by FTIR and SEM. In addition, desorption experiments prove that 0.1 mol/L EDTA solution is an efficient eluent for the recovery of Pb(II) from the treated human hair. To summarize, treated human hair showed satisfactory biosorption capacity and can be considered as an effective biosorbent for the treatment of water with a low concentration of heavy metal ions. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Removal Efficiencies of Manganese and Iron Using Pristine and Phosphoric Acid Pre-Treated Biochars Made from Banana Peels
Water 2020, 12(4), 1173; https://doi.org/10.3390/w12041173 - 20 Apr 2020
Cited by 9 | Viewed by 1028
Abstract
The purpose of this study was to compare the removal efficiencies of manganese (Mn) and iron (Fe) using pristine banana peel biochar (BPB) and phosphoric acid pre-treated biochars (PBPB) derived from banana peels. The removal efficiencies of Mn and Fe were investigated under [...] Read more.
The purpose of this study was to compare the removal efficiencies of manganese (Mn) and iron (Fe) using pristine banana peel biochar (BPB) and phosphoric acid pre-treated biochars (PBPB) derived from banana peels. The removal efficiencies of Mn and Fe were investigated under different adsorbent dosages (0.4–2 g L−1), temperatures (15–45 °C), and ionic strengths (0–0.1 M), and were directly correlated to the differences in physicochemical properties of BPB and PBPB, to identify the removal mechanisms of heavy metals by adsorption processes. The removal of Mn by PBPB obeyed the Freundlich isotherm model while the removal of Mn and Fe by BPB followed the Langmuir isotherm model. However, the removal of Fe by PBPB followed both Freundlich and Langmuir isotherm models. The removal efficiencies of Mn and Fe by BPB and PBPB increased with increasing temperatures and decreased with increasing ionic strengths. PBPB more effectively removed Mn and Fe compared to BPB due to its higher content of oxygen-containing functional groups (O/C ratio of PBPB = 0.45; O/C ratio of BPB = 0.01), higher surface area (PBPB = 27.41 m2 g−1; BPB = 11.32 m2 g−1), and slightly greater pore volume (PBPB = 0.03 cm3 g−1; BPB = 0.027 cm3 g−1). These observations clearly show that phosphoric acid pre-treatment can improve the physicochemical properties of biochar prepared from banana peels, which is closely related to the removal of heavy metals by adsorption processes. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Removal of Aquatic Cadmium Ions Using Thiourea Modified Poplar Biochar
Water 2020, 12(4), 1117; https://doi.org/10.3390/w12041117 - 14 Apr 2020
Cited by 3 | Viewed by 959
Abstract
Removal of aquatic cadmium ions using biochar is a low-cost method, but the results are usually not satisfactory. Modified biochar, which can be a low-cost and efficient material, is urgently required for Cd-polluted water and soil remediation. Herein, poplar bark (SB) and poplar [...] Read more.
Removal of aquatic cadmium ions using biochar is a low-cost method, but the results are usually not satisfactory. Modified biochar, which can be a low-cost and efficient material, is urgently required for Cd-polluted water and soil remediation. Herein, poplar bark (SB) and poplar sawdust (MB) were used as raw materials to prepare modified biochar, which is rich in N- and S- containing groups, i.e., TSBC-600 and TMBC-600, using a co-pyrolysis method with thiourea. The adsorption characteristics of Cd2+ in simulated wastewater were explored. The results indicated that the modification optimized the surface structure of biochar, Cd2+ adsorption process by both TSBC-600 and TMBC-600 was mainly influenced by the initial pH, biochar dosage, and contact time, sthe TSBC-600 showed a higher adsorption capacity compared to TMBC-600 under different conditions. The Langmuir adsorption isotherm model and pseudo-second-order kinetic model were more consistent with the adsorption behavior of TSBC-600 and TMBC-600 to Cd2+, the maximum adsorption capacity of TSBC-600 and TMBC-600 calculated by the Langmuir adsorption isotherm model was 19.998 mg/g and 9.631 mg/g, respectively. The modification method for introducing N and S into biochar by the co-pyrolysis of biomass and thiourea enhanced the removal rate of aquatic cadmium ions by biochar. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Upcycling of Electroplating Sludge to Prepare Erdite-Bearing Nanorods for the Adsorption of Heavy Metals from Electroplating Wastewater Effluent
Water 2020, 12(4), 1027; https://doi.org/10.3390/w12041027 - 03 Apr 2020
Cited by 5 | Viewed by 1022
Abstract
Electroplating sludge is a hazardous waste produced in plating and metallurgical processes which is commonly disposed of in safety landfills. In this work, electroplating sludge containing 25.6% Fe and 5.5% Co (named S1) and another containing 36.8% Fe and 7.8% Cr (S2) were [...] Read more.
Electroplating sludge is a hazardous waste produced in plating and metallurgical processes which is commonly disposed of in safety landfills. In this work, electroplating sludge containing 25.6% Fe and 5.5% Co (named S1) and another containing 36.8% Fe and 7.8% Cr (S2) were recycled for the preparation of erdite-bearing particles via a facile hydrothermal route with only the addition of Na2S·9H2O. In the sludges, Fe-containing compounds were weakly crystallized and spontaneously converted to short rod-like erdite particles (SP1) in the presence of Co or long nanorod (SP2) particles with a diameter of 100 nm and length of 0.5–1.5 μm in the presence of Cr. The two products, SP1 and SP2, were applied in electroplating wastewater treatment, in which a small portion of Co in SP1 was released in wastewater, whereas Cr in SP2 was not. Adding 0.3 g/L SP2 resulted in the removal of 99.7% of Zn, 99.4% of Cu, 37.9% of Ni and 53.3% of Co in the electroplating wastewater, with residues at concentrations of 0.007, 0.003, 0.33, 0.09 and 0.002 mg/L, respectively. Thus, the treated electroplating wastewater met the discharge standard for electroplating wastewater in China. These removal efficiencies were higher than those achieved using powdered activated carbon, polyaluminum chloride, polyferric sulfate or pure Na2S·9H2O reagent. With the method, waste electroplating sludge was recycled as nanorod erdite-bearing particles which showed superior efficiency in electroplating wastewater treatment. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Adsorption of Mixed Dye System with Cetyltrimethylammonium Bromide Modified Sepiolite: Characterization, Performance, Kinetics and Thermodynamics
Water 2020, 12(4), 981; https://doi.org/10.3390/w12040981 - 30 Mar 2020
Cited by 2 | Viewed by 871
Abstract
In this study, sepiolite was modified by calcination (200 °C) and cetyltrimethylammonium bromide (CTMAB) treatment. Though the specific surface area sharply declined, the adsorption amount of Acid Orange II (AO), Reactive Blue (RB), Acid Fuchsin (AR) and their mixed solution were improved. The [...] Read more.
In this study, sepiolite was modified by calcination (200 °C) and cetyltrimethylammonium bromide (CTMAB) treatment. Though the specific surface area sharply declined, the adsorption amount of Acid Orange II (AO), Reactive Blue (RB), Acid Fuchsin (AR) and their mixed solution were improved. The morphology of modified sepiolite showed a better dispersibility and looser structure. The adsorption performance was highly impacted by the pH condition and adsorbent dosage. The electrostatic attraction of positively charged adsorption sites on the adsorbent surface and the negatively charged anionic dye could enhance the adsorption amount especially under acid condition. The order of preferentially adsorbed dye was AO > RB > AR. The adsorption process was much correlated to the quasi-second-order reaction kinetics. The adsorption amount and equilibrium amount of single dye system, as well as in the mixed system were in accordance with the Langmuir model and extended Langmuir isotherm. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Article
Adsorption of Methylene Blue in Water onto Activated Carbon by Surfactant Modification
Water 2020, 12(2), 587; https://doi.org/10.3390/w12020587 - 21 Feb 2020
Cited by 63 | Viewed by 2821
Abstract
In this paper, the enhanced adsorption of methylene blue (MB) dye ion on the activated carbon (AC) modified by three surfactants in aqueous solution was researched. Anionic surfactants—sodium lauryl sulfate (SLS) and sodium dodecyl sulfonate (SDS)—and cationic surfactant—hexadecyl trimethyl ammonium bromide (CTAB)—were used [...] Read more.
In this paper, the enhanced adsorption of methylene blue (MB) dye ion on the activated carbon (AC) modified by three surfactants in aqueous solution was researched. Anionic surfactants—sodium lauryl sulfate (SLS) and sodium dodecyl sulfonate (SDS)—and cationic surfactant—hexadecyl trimethyl ammonium bromide (CTAB)—were used for the modification of AC. This work showed that the adsorption performance of cationic dye by activated carbon modified by anionic surfactants (SLS) was significantly improved, whereas the adsorption performance of cationic dye by activated carbon modified by cationic surfactant (CTAB) was reduced. In addition, the effects of initial MB concentration, AC dosage, pH, reaction time, temperature, real water samples, and additive salts on the adsorption were studied. When Na+, K+, Ca2+, NH4+, and Mg2+ were present in the MB dye solution, the effect of these cations was negligible on the adsorption (<5%). The presence of NO2- improved the adsorption performance significantly, whereas the removal rate of MB was reduced in the presence of competitive cation (Fe2+). It was found that the isotherm data had a good correlation with the Langmuir isotherm through analyzing the experimental data by various models. The dynamics of adsorption were better described by the pseudo-second-order model and the adsorption process was endothermic and spontaneous. The results showed that AC modified by anionic surfactant was effective for the adsorption of MB dye in both modeling water and real water. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Review

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Review
Biochar as an Eco-Friendly and Economical Adsorbent for the Removal of Colorants (Dyes) from Aqueous Environment: A Review
Water 2020, 12(12), 3561; https://doi.org/10.3390/w12123561 - 18 Dec 2020
Cited by 7 | Viewed by 957
Abstract
Dyes (colorants) are used in many industrial applications, and effluents of several industries contain toxic dyes. Dyes exhibit toxicity to humans, aquatic organisms, and the environment. Therefore, dyes containing wastewater must be properly treated before discharging to the surrounding water bodies. Among several [...] Read more.
Dyes (colorants) are used in many industrial applications, and effluents of several industries contain toxic dyes. Dyes exhibit toxicity to humans, aquatic organisms, and the environment. Therefore, dyes containing wastewater must be properly treated before discharging to the surrounding water bodies. Among several water treatment technologies, adsorption is the most preferred technique to sequester dyes from water bodies. Many studies have reported the removal of dyes from wastewater using biochar produced from different biomass, e.g., algae and plant biomass, forest, and domestic residues, animal waste, sewage sludge, etc. The aim of this review is to provide an overview of the application of biochar as an eco-friendly and economical adsorbent to remove toxic colorants (dyes) from the aqueous environment. This review highlights the routes of biochar production, such as hydrothermal carbonization, pyrolysis, and hydrothermal liquefaction. Biochar as an adsorbent possesses numerous advantages, such as being eco-friendly, low-cost, and easy to use; various precursors are available in abundance to be converted into biochar, it also has recyclability potential and higher adsorption capacity than other conventional adsorbents. From the literature review, it is clear that biochar is a vital candidate for removal of dyes from wastewater with adsorption capacity of above 80%. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Review
An Overview and Evaluation of Highly Porous Adsorbent Materials for Polycyclic Aromatic Hydrocarbons and Phenols Removal from Wastewater
Water 2020, 12(10), 2921; https://doi.org/10.3390/w12102921 - 19 Oct 2020
Cited by 6 | Viewed by 902
Abstract
Polycyclic aromatic hydrocarbons (PAHs) and phenolic compounds had been widely recognized as priority organic pollutants in wastewater with toxic effects on both plants and animals. Thus, the remediation of these pollutants has been an active area of research in the field of environmental [...] Read more.
Polycyclic aromatic hydrocarbons (PAHs) and phenolic compounds had been widely recognized as priority organic pollutants in wastewater with toxic effects on both plants and animals. Thus, the remediation of these pollutants has been an active area of research in the field of environmental science and engineering. This review highlighted the advantage of adsorption technology in the removal of PAHs and phenols in wastewater. The literature presented on the applications of various porous carbon materials such as biochar, activated carbon (AC), carbon nanotubes (CNTs), and graphene as potential adsorbents for these pollutants has been critically reviewed and analyzed. Under similar conditions, the use of porous polymers such as Chitosan and molecularly imprinted polymers (MIPs) have been well presented. The high adsorption capacities of advanced porous materials such as mesoporous silica and metal-organic frameworks have been considered and evaluated. The preference of these materials, higher adsorption efficiencies, mechanism of adsorptions, and possible challenges have been discussed. Recommendations have been proposed for commercialization, pilot, and industrial-scale applications of the studied adsorbents towards persistent organic pollutants (POPs) removal from wastewater. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Review
The Use of Biochar and Pyrolysed Materials to Improve Water Quality through Microcystin Sorption Separation
Water 2020, 12(10), 2871; https://doi.org/10.3390/w12102871 - 15 Oct 2020
Cited by 1 | Viewed by 673
Abstract
Harmful algal blooms have increased globally with warming of aquatic environments and increased eutrophication. Proliferation of cyanobacteria (blue-green algae) and the subsequent flux of toxic extracellular microcystins present threats to public and ecosystem health and challenges for remediation and management. Although methods exist, [...] Read more.
Harmful algal blooms have increased globally with warming of aquatic environments and increased eutrophication. Proliferation of cyanobacteria (blue-green algae) and the subsequent flux of toxic extracellular microcystins present threats to public and ecosystem health and challenges for remediation and management. Although methods exist, there is currently a need for more environmentally friendly and economically and technologically feasible sorbents. Biochar has been proposed in this regard because of its high porosity, chemical stability, and notable sorption efficiency for removing of cyanotoxins. In light of worsening cyanobacterial blooms and recent research advances, this review provides a timely assessment of microcystin removal strategies focusing on the most pertinent chemical and physical sorbent properties responsible for effective removal of various pollutants from wastewater, liquid wastes, and aqueous solutions. The pyrolysis process is then evaluated for the first time as a method for sorbent production for microcystin removal, considering the suitability and sorption efficiencies of pyrolysed materials and biochar. Inefficiencies and high costs of conventional methods can be avoided through the use of pyrolysis. The significant potential of biochar for microcystin removal is determined by feedstock type, pyrolysis conditions, and the physiochemical properties produced. This review informs future research and development of pyrolysed materials for the treatment of microcystin contaminated aquatic environments. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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Review
Chemically Modified Biosorbents and Their Role in the Removal of Emerging Pharmaceutical Waste in the Water System
Water 2020, 12(6), 1551; https://doi.org/10.3390/w12061551 - 29 May 2020
Cited by 11 | Viewed by 1150
Abstract
Presence of pharmaceutically active compounds (PACs) as emerging contaminants in water is a major concern. Recent reports have confirmed the presence of PACs in natural and wastewater systems, which have caused several problems indicating the urgent need for their removal. The current review [...] Read more.
Presence of pharmaceutically active compounds (PACs) as emerging contaminants in water is a major concern. Recent reports have confirmed the presence of PACs in natural and wastewater systems, which have caused several problems indicating the urgent need for their removal. The current review evaluates the role of chemically modified biosorbents in the removal of PACs in water. Reported biosorbents include plant and animal solid waste, microorganisms and bio-composite. Bio-composites exhibited better prospects when compared with other biosorbents. Types of chemical treatment reported include acid, alkaline, solvent extraction, metal salt impregnation and surface grafting, with alkaline treatment exhibiting better results when compared with other treatments. The biosorption processes mostly obeyed the pseudo-second-order model and the Langmuir isotherm model in a process described mainly by ionic interaction. Desorption and regeneration capacity are very important in selecting an appropriate biosorbent for the biosorption process. Depending on the type of biosorbent, the cost of water treatment per million liters of water was estimated as US $10–US $200, which presents biosorption as a cheap process compared to other known water treatment processes. However, there is a need to conduct large-scale studies on the biosorption process for removing PACs in water. Full article
(This article belongs to the Special Issue Adsorbents for Water and Wastewater Treatment and Resource Recovery)
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