Comparative removal of emerging contaminants from aqueous solution by adsorption on an activated carbon

Temperature effects and molecular insights towards the optimization of polyvinyl alcohol as adsorbent of organic pollutants from aqueous solution

One of the easier methods of wastewater treatment is adsorption due to its simplicity in implementation, environmental friendliness, and economic feasibility. Polyvinyl alcohol (PVA) looks promising as an adsorbent due to its biocompatible, non-toxic, water-soluble and eco-friendly nature. The investigation of PVA for its potential in the adsorption of pollutants has been reported in many studies but the mechanistic understanding of the adsorption is poor. The present study used a theoretical approach through density functional theory and Monte Carlo with molecular dynamics simulations to investigate the adsorption mechanism behaviors of model organic molecules (bromothymol blue (BTB), methylene blue (MB), metronidazole (MNZ) and tetracycline (TC)) on PVA surface. The quantum chemical calculations result showed that with the increase in PVA chains (2, 4, 8, 16, and 32 units), the zero-point energy decreases (from -308.79 to -4922.93 kcal/mol) while the dipole moment increases (from 4.37 to 87.52 Debye). Temperature effect on the PVA chain structures showed the same trends for all the chain units and with the increase in temperature (50-600 K), there are no appreciable changes in zero-point energy, enthalpy energy increases while Gibbs free energy decreases. Considering PVA-pollutant complexes, the effects of temperature on the structures showed that there are no appreciable changes in the zero-point energy, Gibbs free and thermal energies increase with an increase in temperature while the kinetic rate of reactions decreases with an increase in temperature. The enthalpy of the reaction showed different trends with antibiotic and dye complexes. In all the thermodynamic properties investigated and the rate of reaction, the order of affinity of the pollutants with PVA followed TC > MNZ > MB > BTB. Monte Carlo simulation was used to investigate the adsorption behavior of the pollutants on the surface of PVA. The negative adsorption energies (-366.56 to -2266.81 kcal/mol) in terms of affinity towards the pollutants on the surface of PVA followed the sequence TC > MNZ > BTB > MB and the molecular dynamic simulation results followed the same order. The obtained results give valuable insights into the mechanism and performance of PVA as an adsorbent. Most of these computational observations are in good agreement with the available experimental results.

Hydrophilic magnetic Ti3C2Tx-based nanocomposite as an efficient boron adsorbent: Synthesis, characterization, and application

It is widely recognized that wastewater containing boron is an environmental issue. Therefore, the development of adsorbents with excellent adsorption capacity, stability, and recyclability is essential in water treatment applications. A Fe3O4/PDA/Ti3C2Tx/PEI/DHHA nanocomposite has been prepared that can be used to separate and recover boric acid by adjusting the pH of the solution, based on the affinity theory of boric acid and cis-diol. Through series characterization, it was determined that the adsorbent possessed good magnetic properties, high hydrophilicity and high loading capacities. In this study, 4-formylphenylboronic acid (FPBA) was selected as the model compound. The nanocomposite exhibited an adsorption equilibrium time of 10 h and an adsorption capacity of 98.99 mg/g at pH = 8.5 and 25 °C. The Langmuir isothermal model and the quasi-secondary kinetic model are both appropriate for describing the adsorption process. Thermodynamic results suggest that adsorption is a spontaneous chemisorption process. Furthermore, the nanocomposite retains good regeneration performance after five adsorption-desorption cycles.

Adsorption of aqueous phase contaminants of emerging concern by activated carbon: Comparative fixed-bed column study and in situ regeneration methods

This work investigated the adsorption of five model contaminants of emerging concern (CECs) that are released daily in domestic effluents (caffeine, hydrochlorothiazide, saccharin, sulfamethoxazole and sucralose) onto two activated carbons (ACs), in fixed-bed column experiments with different aqueous matrices (ultrapure water, wastewater treatment plant (WWTP) effluent and WWTP effluent pretreated by reverse osmosis and photoperoxidation (reuse water)). The ACs were chemically similar, but AC1 had smaller particles (0.7-1.7 mm) and lower surface area (551 m2 g-1) than AC2 (1.2-2.4 mm and 716 m2 g-1). AC1 had a higher adsorption capacity (qads) for the CECs in the downflow mode. Overall, the qads values of the CECs followed the order: caffeine > sulfamethoxazole > hydrochlorothiazide = saccharin > sucralose. In the downflow mode, preferential pathways reduced the hydraulic retention time (HRT) of the fixed-bed column loaded with AC, which reduced the useful lifetime of column and the adsorption capacity. Nevertheless, the adsorption capacity and useful lifetime of the fixed-bed columns remained similar in the upflow mode (no preferential pathways were observed) regardless of the AC used. Since the HRTs were also found to be similar, it was evident that the crucial factor influencing the adsorption of the CECs was the HRT, which played a pivotal role in the overall process becoming evident. Compared to ultrapure water, use of the WWTP effluent reduced qads for all the CECs by up to 4.1 times, while reuse water reduced qads by up to 1.2 times. The AC1 could be in-situ regenerated using ethanol, with a global efficiency of 97.2 %. The results showed the importance of pretreatment techniques and optimization of the operational parameters, such as HRT, for enhancing the useful lifetime and qads of fixed-bed columns.

Applications of Carbon-Based Materials in Activated Peroxymonosulfate for the Degradation of Organic Pollutants: A Review

In recent years, water pollution has posed a serious threat to aquatic organisms and humans. Advanced oxidation processes (AOPs) based on activated peroxymonosulfate (PMS) show high oxidation, good selectivity, wide pH range and no secondary pollution in the removal of organic pollutants in water. Carbon-based materials are emerging green catalysts that can effectively activate persulfates to generate radical and non-radical active species to degrade organic pollutants. Compared with transition metal catalysts, carbon-based materials are widely used in SR-AOPs because of their low cost, non-toxicity, acid and alkali resistance, large specific surface area, and scalable surface charge, which can be used for selective control of specific water pollutants. This paper mainly presents several carbon-based materials used to activate PMS, including raw carbon materials and modified carbon materials (heteroatom-doped and metal-doped), analyzes and summarizes the mechanism of activating PMS by carbon-based catalysts, and discusses the influencing factors (temperature, pH, PMS concentration, catalyst concentration, inorganic anions, inorganic cations and dissolved oxygen) in the activation process. Finally, the future challenges and prospects of carbon-based materials in water pollution control are also presented.

Insight into the adsorptive removal of ibuprofen using porous carbonaceous materials: A review

Over the last decade, the removal of pharmaceuticals from aquatic bodies has garnered substantial attention from the scientific community. Ibuprofen (IBP), a non-steroidal anti-inflammatory drug, is released into the environment in pharmaceutical waste as well as medical, hospital, and household effluents. Adsorption technology is a highly efficient approach to reduce the IBP in the aquatic environment, particularly at low IBP concentrations. Due to the exceptional surface properties of carbonaceous materials, they are considered ideal adsorbents for the IBP removal of, with high binding capacity. Given the importance of the topic, the adsorptive removal of IBP from effluent using various carbonaceous adsorbents, including activated carbon, biochar, graphene-based materials, and carbon nanostructures, has been compiled and critically reviewed. Furthermore, the adsorption behavior, binding mechanisms, the most effective parameters, thermodynamics, and regeneration methods as well as the cost analysis were comprehensively reviewed for modified and unmodified carbonaceous adsorbents. The compiled studies on the IBP adsorption shows that the IBP uptake of some carbon-based adsorbents is significantly than that of commercial activated carbons. In the future, much attention is needed for practical utilization and upscaling of the research findings to aid the management and sustainability of water resource.

Amazon raw clay as a precursor of a clay-based adsorbent: experimental study and DFT analysis for the adsorption of Basic Yellow 2 dye

A clay-based adsorbent (CBA) was purified from a sustainable precursor (raw clay, RC), which was obtained from the Amazon region in Brazil. The CBA was characterized using X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Brunauer-Emmet-Teller surface area (S_BET, RC = 23.386 m².g^-1, CBA = 33.020 m².g^-1), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), thermogravimetric analysis (TGA), cation exchange capacity (CEC, CBA = 44.75 cmol/kg), and point of zero charge analyses (pH_PZC, CBA = 2.20). Subsequently, CBA was used to adsorb basic yellow 2 (BY2) dye from aqueous solutions. A CBA dosage (1 g/L), initial concentration of dye (C₀ = 15 mg/L), and pH (5.6) were ideal conditions for the BY2 dye removal of ~ 98%. The BY2 kinetics was better represented by the pseudo-first-order (PFO) model while the BY2 equilibrium was well represented by the Sips model, with a maximum adsorption capacity of q_ms = 18.04 mg/g at 28 °C. The negative values of ΔG° and ΔH° showed that the studied process is spontaneous and exothermic, while the values of isosteric heat (∆H_st, -16 to -20 kJ/mol) suggest a predominance of physical interactions. The molecular chemical reactivity of BY2 was investigated using quantum chemical descriptors calculated based on Density Functional Theory (DFT) optimization of the dye molecule, and the results revealed a large energy gap value (4.3900 eV) and considerable chemical hardness (η = 2.1950 eV). Therefore, the correlation between DFT and experimental results consistently sustains that BY2 dye tends to be adsorbed on the CBA surface by electrostatic interactions, thus, this is the possible adsorption mechanism of this process.

Nitrogen Doped Porous Biochar/β-CD-MOFs Heterostructures: Bi-Functional Material for Highly Sensitive Electrochemical Detection and Removal of Acetaminophen

Acetaminophen (AC) is one of the most common over-the-counter drugs, and its pollutant in groundwater has attracted more attention due to its serious risk to human health. Currently, the research on AC is mainly focused on its detection, but few are concerned about its removal. In this work, for the first time, nitrogen-doped Soulangeana sepals derived biochar/β-cyclodextrin-Metal-organic frameworks (N-SC/β-CD-MOFs) composite was proposed for the simultaneous efficient removal and detection of AC. N-SC/β-CD-MOFs combined the properties of host-guest recognition of β-CD-MOFs and porous structure, high porosity, and large surface area of N-SC. Their synergies endowed N-SC/β-CD-MOFs with a high adsorption capacity toward AC, which was up to 66.43 mg/g. The adsorption type of AC on the surface of N-SC/β-CD-MOFs conformed to the Langmuir adsorption model, and the study of the adsorption mechanism showed that AC adsorption on N-SC was mainly achieved through hydrogen bonding. In addition, the high conductivity, large specific surface area and abundant active sites of N-SC/β-CD-MOFs were of great significance to the high-performance detection of AC. Accordingly, the sensor prepared with N-SC/β-CD-MOFs presented a wide linear range (1.0-30.0 μM) and a low limit of detection of 0.3 nM (S/N = 3). These excellent performances demonstrate that N-SC/β-CD-MOFs could act as an efficient dual-functional material for the detection and removal of AC.

Mechanism and behavior of caffeine sorption: affecting factors

Caffeine is one of the emerging pollutants with a diverse chemical composition. It is mixed with the hydrobiota as a result of its high consumption, and when certain dose intervals are exceeded, it re-enters the human body through indirect routes such as plants, animals, soil, water, and the food chain, causing health problems that are difficult or impossible to treat, and irreversible environmental problems. This situation raises concerns about the presence of pollutants emerging in water resources, igniting interest in water treatment processes and the development of alternative methods. Although there are several methods for removing caffeine from aqueous media, adsorption is the most popular because it is less expensive than other methods and has the highest removal efficiency. Furthermore, it has the benefit of selectively attaching the molecules in solution. In this article, studies on the caffeine adsorption process have been examined, and the caffeine adsorption efficiency of various adsorbents has been summarized by compiling information such as pH, contact time, temperature, and concentration of adsorbent and adsorbate, which are considered as optimum processing conditions. The binding mechanism was investigated, and it was clearly stated how caffeine adheres to the adsorbent surface. Among the equilibrium adsorption isotherms, the isotherm model with the best agreement with the experimental data was attempted to be determined. Many studies clearly show that the process of developing environmentally friendly and high-capacity adsorbents in sustainable processes and in harmony with the circular economy is increasing day by day.

Biological removal processes in aerobic granular sludge exposed to diclofenac

Diclofenac is a worldwide consumed drug included in the watch list of substances to be monitored according to the European Union Water Framework Directive (Directive 2013/39/EU). Aerobic granular sludge sequencing batch reactors (AGS-SBR) are increasingly used for wastewater treatment but there is scant information on the fate and effect of micropollutants to nutrient removal processes. An AGS-SBR fed with synthetic wastewater containing diclofenac was bioaugmented with a diclofenac degrading bacterial strain and performance and microbial community dynamics was analysed. Chemical oxygen demand, phosphate and ammonia removal were not affected by the micropollutant at 0.03 mM (9.54 mg L^-1). The AGS was able to retain the degrading strain, which was detected in the sludge throughout after augmentation. Nevertheless, besides some adsorption to the biomass, diclofenac was not degraded by the augmented sludge given the short operating cycles and even if batch degradation assays confirmed that the bioaugmented AGS was able to biodegrade the compound. The exposure to the pharmaceutical affected the microbial community of the sludge, separating the two first phases of reactor operation (acclimatization and granulation) from subsequent phases. The AGS was able to keep the bioaugmented strain and to maintain the main functions of nutrient removal even through the long exposure to the pharmaceutical, but combined strategies are needed to reduce the spread of micropollutants in the environment.

Maximizing Adsorption Involving Three Solutes on Enhanced Adsorbents Using the Mixture-Process Variable Design

Unmodified (UN), acid-treated (AT) and microwave-acid-treated (MAT) activated carbons were optimized for their solute removal efficacies by adjusting feed mixture compositions and process conditions. Acetaminophen, benzotriazole, and caffeine were used either individually or as binary/ternary mixtures in this study. The process conditions considered were the pH, adsorbent dosage, and type of adsorbent. Experimental responses such as total adsorbent loading (q _total) and total percentage removal (PR_total) were fitted with empirical models that had high adjusted R ² (>0.95), insignificant lack of fit (p-value > 0.22), and high model predictive R ² (>0.93). Mixture compositions of the feed were found to interact significantly not only among themselves but with process variables as well. Hence, adsorption optimization must simultaneously consider mixture as well as process variables. The conventional response surface methodology for mixtures, termed as ridge analysis, optimizes mixture compositions at specified values of process variables. An improved steepest ascent method which considers mixture and process variables simultaneously was developed in this work. This could track the path of steepest ascent toward globally optimal settings, from any arbitrary starting point within the design space. For the chosen adsorbent, optimal settings for feed mixture compositions and pH were found to change along this steepest ascent path. The feed compositions, pH, and adsorbent dosage identified for maximum adsorbent utilization were usually quite different from those identified for maximum total percentage removal. When both these objectives were optimized together, the most favorable compromise solutions for q _total and PR_total were, respectively, 264.1 mg/g and 43.4% for UN, 294.9 mg/g and 52.5% for AT, and 336.6 mg/g and 55.9% for MAT.

Diclofenac removal from the wastewater using activated sludge and analysis of multidrug resistant bacteria from the sludge

Diclofenac is an anti-inflammatory drug and has been frequently detected from the wastewater. In the present study, factors affecting diclofenac adsorption on sewage sludge was evaluated. At 1 mg/L initial diclofenac concentration, more than 80% diclofenac removal was achieved. Adsorption increased at higher concentration (100 mg/L concentration) and more than 99% diclofenac was adsorbed from the wastewater. Significant removal of diclofenac was observed after 5 min contact time. The adsorption efficacy was more than 98% after 50 and 60 min. Pseudo-first and second order kinetics revealed reasonable regression value (0.9) indicated that the model is best fitted. Diclofenac adsorption was extremely high at acidic pHs than alkaline range. The sludge samples showed the presence of multi drug resistant bacteria. Vancomycin-resistant enterococcus stains were 27%, Methicillin-resistant Staphylococcus aureus positive strains were 16.5% and Extended-spectrum betal-lactamase-harbouring Enterobacteriacea were 65.4% in the sludge. The drug resistance Enterobacteriaceae revealed 14 Klebsiella pneumonia strains, 11 strains from E. coli and two from the genus Enterobacter. To conclude, the activated sludge could be effectively utilized for the removal of diclofenac from wastewater.

Ultrasonic-assisted synthesis of zeolite/activated carbon@MnO2 composite as a novel adsorbent for treatment of wastewater containing methylene blue and brilliant blue

In this study, zeolite/activated carbon@MnO₂ composite was used as a novel adsorbent to eliminate methylene blue (MB) and brilliant blue (BB) dyes from aqueous media. To this end, activated carbon (AC) was produced by Ziziphus Spina-Christi leaves and then used to synthesize zeolite/AC@MnO₂ composite. Various analyses such as BET, SEM, EDX, Map, FTIR, and XRD were performed to determine the surface features of the above composite. BET analysis indicated that the aforementioned composite has a mesoporous structure. Also, the best conditions for the adsorption of MB and BB dyes were obtained at pH of 9 and 2, temperature of 25 °C, adsorbent dosage of 1 and 2 g/L, initial dye concentration of 10 mg/L, and contact time of 40 and 60 min, respectively. Under optimal conditions, the utmost removal efficiency of MB and BB dyes using the zeolite/AC@MnO₂ composite was 98.43% and 96.54%, respectively, indicating significant adsorption efficiencies. Moreover, the utmost adsorption capacity of MB and BB dyes was 67.56 and 66.22 mg/g, respectively. Furthermore, intraparticle and film diffusion mechanisms were very important in the adsorption process. Besides, thermodynamic and equilibrium studies indicated that the adsorption process is exothermic, physical, and spontaneous. Generally, the aforementioned composite has a significant adsorption capacity and can be a suitable adsorbent to eliminate cationic dyes from industrial effluents.

Kinetic and isotherm insights of Diclofenac removal by sludge derived hydrochar

Recently, hydrothermal carbonization emerges as the most viable option for the management of solid waste with high moisture content. Sludge derived hydrochar is used as an adsorbent for emerging contaminants or micro-pollutants in the domain of sustainability. Current study demonstrates the KOH activation of hydrochar produced from paper board mill sludge and evaluates its removal potential of a Non-steroidal anti-inflammatory drug, Diclofenac from aqueous solution. The activated hydrochars exhibited porous, spherical micro-structures with higher fraction of oxygenated functional groups paving way for the efficient adsorption of Diclofenac. The effect of initial Diclofenac concentration and contact time was ascertained using adsorption kinetics and isotherms. The adsorption kinetics exhibited second-order reaction for all adsorbents indicating higher coefficient of determination (R² > 0.9). The Diclofenac adsorption on hydrochars followed Langmuir isotherm model with the post-activated hydrochar recording a highest adsorption capacity of 37.23 mg g⁻¹ in 40 mg L⁻¹ initial Diclofenac concentration at 15 h equilibrium time.

3,5-Dinitrosalicylic Acid Adsorption Using Granulated and Powdered Activated Carbons

Some nitroaromatic compounds are found in wastewater from industries such as the weapons industry or the wine industry. One of these compounds is 3,5-dinitrosalicylic acid (DNS), widely used in various tests and frequently found as an emerging pollutant in wastewater and to which the required attention has not been given, even though it may cause serious diseases due to its high toxicity. This study investigated the adsorption of DNS using granulated activated carbon (GAC) and powdered activated carbon (PAC) at different temperatures. The results show that in equilibrium, the adsorption takes place in more than one layer and is favorable for the removal of DNS in both GAC and PAC; The maximum adsorption capacity was obtained at 45 °C, with values of 6.97 mg/g and 11.57 mg/g, respectively. The process is spontaneous and exothermic. In addition, there was a greater disorder in the solid-liquid interface during the desorption process. The predominant kinetics using GAC (7.14 mg/g) as an adsorbent is Elovich, indicating that there are heterogeneous active sites, and when PAC (10.72 mg/g) is used, Pseudo-second order kinetics predominate, requiring two active sites for DNS removal. External mass transfer limitations are only significant in GAC, and ATR-FTIR studies in PAC demonstrated the participation of functional groups present on the adsorbent surface for DNS adsorption.

Solketal Removal from Aqueous Solutions Using Activated Carbon and a Metal-Organic Framework as Adsorbents

The worldwide rise in biodiesel production has generated an excess of glycerol, a byproduct of the process. One of the most interesting alternative uses of glycerol is the production of solketal, a bioadditive that can improve the properties of both diesel and gasoline fuels. Even with its promising future, not much research has been performed on its toxicity in aqueous environments. In this work, solketal adsorption has been tested with two different commercial adsorbents: an activated carbon (Hydrodarco 3000) and a metal-organic framework (MIL-53). Diclofenac and caffeine were also chosen as emerging contaminants for comparison purposes. The effect of various parameters, such as the adsorbent mass or initial concentration of pollutants, has been studied. Adsorption kinetics with a better fit to a pseudo-second-order model, intraparticle diffusion, and effective diffusion coefficient were studied as well. Various isotherm equation models were employed to study the equilibrium process. The results obtained indicate that activated carbon is more effective in removing solketal from aqueous solutions than the metal-organic framework.

A Review of Caffeine Adsorption Studies onto Various Types of Adsorbents

A systematic literature review of publications from 2000 to 2020 was carried out to identify research trends on adsorbent materials for the removal of caffeine from aqueous solutions. Publications were retrieved from three databases (Scopus, Web of Science, and Google Scholar). Words "adsorption AND caffeine" were examined into titles, abstracts, and keywords. A brief bibliometric analysis was performed with emphasis on the type of publication and of most cited articles. Materials for the removal of caffeine were classified according to the type of material into three main groups: organic, inorganic, and composites, each of them subdivided into different subgroups consistent with their origin or production. Tables resume for each subgroup of adsorbents the key information: specific surface area, dose, pH, maximum adsorption capacity, and isotherm models for the removal of caffeine. The highest adsorption capacities were achieved by organic adsorbents, specifically those with granular activated carbon (1961.3 mg/g) and grape stalk activated carbon (916.7 mg/g). Phenyl-phosphate-based porous organic polymer (301 mg/g), natural sandy loam sediment (221.2 mg/g), composites of MCM-48 encapsulated graphene oxide (153.8 mg/g), and organically modified clay (143.7 mg/g) showed adsorption capacities lower than those of activated carbons. In some activated carbons, a relation between the specific surface area (SSA) and the maximum adsorption capacity (Q max) was found.

Application of adsorption process for effective removal of emerging contaminants from water and wastewater

Emerging pollutants in the marine ecosystem, as well as their possible impact on live species, have become a rising cause of worry. A traditional wastewater treatment plants alone are not successful in eliminating such massive contaminant groups and therefore additional water treatment is required which is to be cost effective. Since standard primary and secondary treatment plants are unsuccessful at eliminating or degrading these harmful chemicals, a cost-effective tertiary treatment approach is proposed. Adsorption is a successful approach for Contaminants removal globally, because it is low installation expense, high performance and has easy operational design. Emerging pollutants have been removed from wastewaters using various adsorbents like activated carbons, improved bio chars, Nano adsorbents, hybrid adsorbents, and others. The purpose of this paper is to review the source of contaminants and the concept of adsorption when separating emerging contaminants. The present study aims to examine the adsorption mechanism as an effective approach for treating emerging contaminants. Then, the analysis of natural and man-made adsorbents for the separation of contaminants is examined along with its comparison. Also, future view on emerging contaminants and adsorbents in modern generation has been discussed.

Adsorption onto ACFC of mixture of pharmaceutical residues in water - experimental studies and modelling

The presence of pharmaceutical residues in water resources is a critical issue for the production of drinking water, even though trace concentrations are mostly encountered. The adsorption of eight micropollutants, in mixture, onto a microporous activated carbon fibre cloth was investigated. For each compound, the kinetics and isotherms of adsorption were studied in batch reactors with ultrapure water, groundwater and half-diluted groundwater. Experimental data were generated and compared to values calculated by the association of Ideal Adsorbed Solution Theory (IAST) model and the Homogeneous Surface Diffusion Model (HSDM). The impact of the nature and the content of Natural Organic Matter (NOM) was modelled considering an Equivalent Background Compound (EBC). The presence of NOM in the groundwater is largely detrimental for the adsorption of trace micropollutants.

Comparative overview of advanced oxidation processes and biological approaches for the removal pharmaceuticals

Nowadays, pharmaceuticals are the center of significant environmental research due to their complex and highly stable bioactivity, increasing concentration in the water streams and high persistence in aquatic environments. Conventional wastewater treatment techniques are generally inadequate to remove these pollutants. Aiming to tackle this issue effectively, various methods have been developed and investigated on the light of chemical, physical and biological procedures. Increasing attention has recently been paid to the advanced oxidation processes (AOPs) as efficient methods for the complete mineralization of pharmaceuticals. Their high operating costs compared to other processes, however, remain a challenge. Hence, this review summarizes the current and state of art related to AOPs, biological treatment and their effective exploitation for the degradation of various pharmaceuticals and other emerging molecules present in wastewater. The review covers the last decade with a particular focus on the previous five years. It is further envisioned that this review of advanced oxidation methods and biological treatments, discussed herein, will help readers to better understand the mechanisms and limitations of these methods for the removal of pharmaceuticals from the environment. In addition, we compared AOPs and biological treatments for the disposal of pharmaceuticals from the point of view of cost, effectiveness, and popularity of their use. The exploitation of coupling AOPs and biological procedures for the degradation of pharmaceuticals in wastewater was also presented. It is worthy of note that an integrated AOPs/biological system is essential to reach the complete degradation of pharmaceuticals; other advantages of this hybrid technique involve low energy cost, an efficient degradation process and generation of non-toxic by-products.

Facile Synthesis of g-C3N4/MoO3 Nanohybrid for Efficient Removal of Aqueous Diclofenac Sodium

Graphitic carbon nitride modified by molybdenum trioxide (g-C₃N_4/MoO₃) as a nanohybrid was synthesized by co-precipitation method. Here, g-C₃N₄/MoO₃ nanohybrid was used for the first time as an adsorbent for the pharmaceutical drug, diclofenac, (an aqueous micropollutant) from water to mitigate its possible environmental toxic effects. Compared to pristine components, the nanohybrid exhibited better adsorptive removal of diclofenac. Adsorption was enhanced with increment in MoO₃ content from 1 to 3 wt %; however further increment in MoO₃ content resulted in lower adsorption capacity due to agglomeration of MoO₃ particles over g-C₃N₄. 162 mg g⁻¹ adsorption capacity was achieved for 300 mg L⁻¹ diclofenac in solution with 1 g L⁻¹ adsorbent at pH = 6. Adsorption of diclofenac over g-C₃N₄ /MoO₃ followed pseudo 2nd order kinetics. Temkin, Langmuir, Dubinin Radushkevich and Freundlich isotherm models were applied on the experimental results concluding that diclofenac adsorption over g-C₃N₄/MoO₃ followed the Langmuir isotherm. The adsorption mechanism could be explained by the π–π interaction between aromatic rings of diclofenac and g-C₃N₄/MoO₃ (3%) nanohybrid, which is also evident by the FTIR results. This study presents the facile fabrication of a 2nd generation adsorbent for the treatment of diclofenac contaminated water that may as well help achieve the removal of other micropollutants form water.

Emerging pharmaceutical and organic contaminants removal using carbonaceous waste from oil refineries

The occurrence of emerging organic contaminants (EOCs) such as chemicals in personal care products, pharmaceuticals, plasticizers, etc. in surface waters is a growing global concern. The discharge of most EOCs is not regulated, and EOCs have been shown to be toxic to both human and aquatic life even at low concentrations. In this work, acid-leached carbon black waste (LCBW), a carbonaceous residue from petroleum refineries, was investigated as a potential waste-derived adsorbent for the removal of EOCs. Ciprofloxacin hydrochloride, (CIPRO, antibiotic), sulfamethoxazole (SULFA, antibiotic), acetaminophen (ACET, pharmaceutical), bisphenol A (BPA, plasticizer) and N,N-diethyl-3-methylbenzamide (DEET, insect repellent) were chosen as the target EOCs owing to their presence in relatively high concentrations in surface waters as well as in the influent and effluent of wastewater treatment plants. LCBW, with a specific surface area of 409 m²/g, demonstrated 90-99% removal of 10 ppm CIPRO, BPA, and ACET and 70-80% removal of 10 ppm SULFA and DEET in tap water. Adsorption was rapid, particularly for CIPRO, BPA, and ACET, wherein >85% of the adsorption occurred within 1 h of contact time. To illustrate the potential of LCBW as an adsorbent in different physical forms, ∼3 mm spherical beads of LCBW encapsulated within carboxymethyl cellulose matrix were prepared by a facile ionic gelation method and their adsorption performance was demonstrated.

Ecotoxicological assessment of micropollutant Diclofenac biosorption on magnetic sawdust: Phyto, Microbial and Fish toxicity studies

Diclofenac (DCF), a persistent pharmaceutical micropollutant which occurs in the ecosystems causing adverse effects on aquatic as well as terrestrial organisms. In this study, magnetic sawdust (MSD) was prepared using co-precipitation method for biosorptive removal of DCF from water. The MSD was characterized using various analytical techniques like microscopic and spectroscopic analysis. Magnetometer study confirms the ferromagnetic behavior of the biosorbent which is a key advantage in the separation of MSD after biosorption. The effect of experimental parameters was optimized in batch mode with evaluated maximum efficiency of 86.12 % at pH 6, biosorbent dosage 25 mg for 50 mg/L of DCF. Ecotoxicological assessment has been performed for the treated and untreated sample using plant seeds, microbes and zebra fish to check the adverse effects of DCF on these organisms. Evaluation of toxicity studies revealed that inhibition concentration of DCF for various seeds (60.91 mg/L to 43.11 mg/L), E. coli (48.82 μg/mL) and B. subtilis (31.55 μg/mL). The lethal concentration of DCF on the Danio rerio was found to be 156.99 mg/L. In contrast, significant increase in both the concentration measures of DCF after biosorption was observed making this biosorbent a potent alternative to other available treatment measures.

Optimization of the adsorption of diclofenac by activated carbon and the acidic regeneration of spent activated carbon

Diclofenac sodium (DCF) is a non-steroidal anti-inflammatory drug. It has been classified as ecotoxic even at low concentrations. In this study, adsorption of DCF on coconut shell-based granular activated carbon (GAC) and regeneration of spent GAC with hydrochloric acid (HCl) were investigated. The results showed that GAC with heterogeneous surface structure adsorbs DCF endothermically with both chemical and physical forces. Adsorption and regeneration processes were optimized with Taguchi Experimental Design. The effects of all parameters affecting the adsorption and regeneration processes were determined by analysis of variance and Pareto analyses. DCF removal of 79.80% was obtained at optimum conditions and the most effective parameter was evaluated as GAC size. At optimum regeneration conditions, 6.85 mg DCF/g GAC adsorption capacity was found with an operating cost of €0.05 g GAC. The amount of HCl was the most effective parameter. It was determined that the regenerated GAC had an adsorptive capacity higher than the adsorptive capacity of the raw GAC during at least three regeneration cycles. Raw, spent and regenerated GACs were characterized by Fourier transform infrared spectrometry and scanning electron microscopy analysis.

Membrane Removal of Emerging Contaminants from Water: Which Kind of Membranes Should We Use?

Membrane technologies are nowadays widely used; especially various types of filtration or reverse osmosis in households, desalination plants, pharmaceutical applications etc. Facing water pollution, they are also applied to eliminate emerging contaminants from water. Incomplete knowledge directs the composition of membranes towards more and more dense materials known for their higher selectivity compared to porous constituents. This paper evaluates advantages and disadvantages of well-known membrane materials that separate on the basis of particle size, usually exposed to a large amount of water, versus dense hydrophobic membranes with target transport of emerging contaminants through a selective barrier. In addition, the authors present several membrane processes employing the second type of membrane.

Emerging pollutants-Part II: Treatment

Emerging pollutants (EPs) refer to a class of pollutants, which are emerging in the environment or recently attracted attention. EPs mainly include pharmaceutical and personal care products (PPCPs), endocrine-disrupting chemicals (EDCs), and antibiotic resistance genes (ARGs). EPs have potential threats to human health and ecological environment. In recent years, the continuous detections of EPs in surface and ground water have brought huge challenges to water treatment and also made the treatment of EPs become an international research hotspot. This paper summarizes some research results on EPs treatment published in 2019. This paper may be helpful to understand the current situations and development trends of EP treatment technologies.

A novel robust adsorbent for efficient oil/water separation: Magnetic carbon nanospheres/graphene composite aerogel

Recently, graphene aerogels (GAs) have attracted considerable research attention in oil/water separation owing to their remarkable properties. However, the serious stacking of graphene oxide nanosheets (GO) would lead to low adsorption capacity and poor recyclability. For the first time, with alkaline ammonium citrate as reducing agent and nitrogen source, the point-to-face contact between magnetic carbon nanospheres (MCNS) and graphene sheets was adopted to effectively inhibit the aggregation of graphene sheets. Nitrogen-doped magnetic carbon nanospheres/graphene composite aerogels (MCNS/NGA) were fabricated under weakly alkaline conditions by one-step hydrothermal in-situ electrostatic self-assembling strategy. The aerogels have low density, super-elasticity (up to 95 % compression), high specific surface area (787.92 m² g^-1) and good magnetic properties. Therefore, they exhibit adsorption capacity in the range of 187-537 g g^-1 towards various organic solvents and oils, superior to most reported materials to date. In addition, thanks to their good mechanical properties, excellent thermal stability and flame retardancy, they can be regenerated by squeezing, distillation and combustion. More importantly, magnetic control technology can be adopted to realize oriented adsorption and facilitate recycling of organic solvents and oils in extreme environments.

Removal of pharmaceutical compounds from aqueous solution by novel activated carbon synthesized from lovegrass (Poaceae)

In this work, lovegrass (Cpa), an abundant grass of the Poaceae family, was employed as feedstock for the production of activated carbon in a conventional furnace using ZnCl₂ as a chemical activator. The prepared material (Cpa-AC) was characterized by pH of the point of zero charges (pH_pzc), Boehm's titration method, CHN/O elemental analysis, ATR-FTIR, N₂ adsorption/desorption curves, and SEM. This carbon material was used for adsorption of acetylsalicylic acid (ASA) and sodium diclofenac (DFC). FTIR analysis identified the presence of O-H, N-H, O-C=O), C-O, and aromatic ring bulk and surface of (Cpa-AC) adsorbent. The quantification of the surface functional groups showed the presence of a large amount of acidic functional groups on the surface of the carbon material. The isotherms of adsorption and desorption of N₂ confirm that the Cpa-AC adsorbent is mesopore material with a large surface area of 1040 m² g^-1. SEM results showed that the surface of Cpa-AC is rugous. The kinetic study indicates that the system followed the pseudo-second-order model (pH 4.0). The equilibrium time was achieved at 45 (ASA) and 60 min (DCF). The Liu isotherm model best fitted the experimental data. The maxima sorption capacities (Q_max) for ASA and DFC at 25 °C were 221.7 mg g^-1 and 312.4 mg g^-1, respectively. The primary mechanism of ASA and DFC adsorption was justified considering electrostatic interactions and π-π interactions between the Cpa-AC and the adsorbate from the solution.

Effect of the preparation method and metal content on the synthesis of metal modified titanium oxide used for the removal of salicylic acid under UV light

Titanium dioxide modified with Ag and Fe was synthesized using two preparation methods, characterized and applied to the photocatalytic degradation of salicylic acid in aqueous solution. The modified TiO₂ samples were prepared by the sol-gel and wet impregnation methods starting from titanium(IV) isopropoxide and using AgNO₃ and Fe(NO₃)₃·9H₂O as precursors of the modifiers, with their content varying between 0 and 5 wt.%. Catalysts characterization was based on powder X-ray diffraction (PXRD), nitrogen physisorption at 77 K, temperature programmed reduction (H₂-TPR), chemisorption of NH₃ at 343 K and X-ray photoelectron spectroscopy (XPS). The photocatalytic degradation of salicylic acid by modified TiO₂ was investigated under ultraviolet irradiation at 298 K considering various concentrations of the catalyst, between 100 and 1000 mg_catalyst/dm³, and of the organic molecule, between 0 and 15 mg/dm³. The catalysts most active in the degradation of salicylic acid were those having the highest Fe content.

Adsorptive removal of gallic acid from aqueous solution onto magnetic ion exchange resin

Finding an appropriate adsorbent with high adsorption capacity, quick adsorption kinetics and easy regeneration was crucial to the removal of gallic acid (GA) from water and wastewater. Our aims were to investigate whether a magnetic ion exchange (MIEX) resin had the three merits mentioned above, and investigate the feasibility of GA adsorption on MIEX resin, and the adsorption kinetics, equilibrium, thermodynamics, regeneration and mechanism using batch tests. The uptake of GA increased with increasing GA concentration. The GA concentration influenced the time needed to reach equilibrium, but the adsorption could be completed within 120 min. Elevating temperature facilitated the GA removal. The removal percent remained above 95.0% at pH 5.0-11.0. Carbonate and bicarbonate promoted the GA removal; conversely chloride, sulfate and nitrate restrained the GA removal significantly. The adsorption kinetics could be fitted well with the pseudo second-order model, and the film diffusion governed the whole adsorption rate. The equilibrium data followed the Redlich-Peterson isotherm model. The adsorption was a spontaneous, endothermic and entropy driven process. The ion exchange dominated the removal mechanism. The spent MIEX resin was well regenerated by sodium chloride. Therefore, MIEX resin is a potential adsorbent for removing GA quickly and efficiently from water and wastewater.

Efficient removal of anti-inflammatory from solution by Fe-containing activated carbon: Adsorption kinetics, isotherms, and thermodynamics

This work developed an innovative activated carbon (ICAC) derived from orange peels (OP) through chemical activation using FeCl₃. The traditional activated carbon (PCAC) that was prepared through K₂CO₃ activation served as a comparison. Three adsorbents (ICAC, PCAC, and OP) were characterized by various techniques, these being: Brunauer-Emmett-Teller (BET) surface area analysis, thermo-gravimetric analysis, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. They were applied to remove diclofenac from aqueous solution applying batch experiments, in order to investigate the characteristics of adsorptive kinetics, isotherms, and thermodynamics. Results indicated that the S_BET values were in the following order: 457 m²/g (PCAC) > 184 m²/g (ICAC) > 3.56 m²/g (OP). The adsorption process reached a fast equilibrium, with activating energies being 27.6 kJ/mol (ICAC), 16.0 kJ/mol (OP), and 11.2 kJ/mol (PCAC). The Langmuir adsorption capacities at 30 °C exhibited the decreasing order: 144 mg/g (ICAC) > 6.44 mg/g (OP) > 5.61 mg/g (PCAC). The thermodynamic parameters demonstrated a signal dissimilarity between biosorbent (ΔG° <0, ΔH° <0, and ΔS° <0) and activated carbon samples (ΔG° <0, ΔH° >0, and ΔS° >0). The presence of iron (FeOCl, γ-Fe₂O₃, and FeOOH) on the surface of ICAC played a determining role in efficiently removing diclofenac from solution. The excellent adsorption capacity of ICAC toward diclofenac resulted presumably from the contribution of complicated adsorption mechanisms, such as hydrogen bonding, ion-dipole interaction, π-π interaction, pore filling, and possible Fenton-like degradation. Therefore, FeCl₃ can serve as a promising activating agent for AC preparation with excellent efficiency in removing diclofenac.

Nanocellulose-Block Copolymer Films for the Removal of Emerging Organic Contaminants from Aqueous Solutions

The prevalence of emerging organic contaminants (EOCs) in ground and surface water has sparked the search for more effective methods to remove EOCs from the environment. In pursuit of a solution for this environmental concern, herein we present the development of reusable films based on cellulose nanofibers (CNFs) and the block copolymer, poly(4-vinylpyridine-b-ethylene oxide) (P4VP-PEO) to adsorb sulfamethoxazole (SMX) as an EOC model compound. We hypothesize that the adsorption of SMX was achieved mainly by π-π interactions between the pyridine functionalities of the block copolymer and the electron deficient phenyl group of the SMX. Preceding preparation of the films, CNFs were modified with the alkoxysilane trimethoxy(2-phenylethyl)silane (TMPES) to increase their stability in aqueous solution. After the addition of P4VP-PEO, the process was completed by filtration followed by oven-drying. XPS and FTIR were employed to confirm the addition of TMPES and P4VP-PEO, respectively. Adsorption batch experiments were performed in aqueous solutions of SMX at a neutral pH, obtaining adsorptions of up to 0.014 mmol/g in a moderate time of 60 min. For the reusability tests, films were immersed in ethanol 95 wt.% to elude the adsorbed SMX, rinsed with deionized (DI) water, and dried at room temperature to be reused in a new adsorption cycle. We found that this new composite material could be reused several times with negligible loss of adsorption capacity. The films presented have been shown to be of substantial importance for water remediation as they find direct application in the adsorption of electron deficient aromatic compounds and are reusable.

Application of Industrial Wastes from Chemically Treated Aluminum Saline Slags as Adsorbents

In this study, industrial wastes, which remain after aluminum extraction from saline slags, were used as adsorbents. The aluminum saline slags were treated under reflux with 2 mol/dm³ aqueous solutions of NaOH, H₂SO₄, and HCl for 2 h. After separation by filtration, aqueous solutions containing the extracted aluminum and residual wastes were obtained. The wastes were characterized by nitrogen adsorption at -196 °C, X-ray diffraction, scanning electron microscopy, and ammonia pulse chemisorption. The chemical treatment reduced the specific surface area, from 84 to 23 m²/g, and the pore volume, from 0.136 to 0.052 cm³/g, of the saline slag and increased the ammonia-adsorption capacity from 2.84 to 5.22 cm³/g, in the case of acid-treated solids. The materials were applied for the removal of Acid Orange 7 and Acid Blue 80 from aqueous solutions, considering both single and binary systems. The results showed interesting differences in the adsorption capacity between the samples. The saline slag treated with HCl rapidly adsorbed all of the dyes present in solution, whereas the other materials retained between 50 and 70% of the molecules present in solution. The amount of Acid Orange 7 removed by the nontreated material and by the material treated with NaOH increased in the presence of Acid Blue 80, which can be considered as a synergistic behavior. The CO₂ adsorption of the solids at several temperatures up to 200 °C was also evaluated under dry conditions. The aluminum saline slag presented an adsorption capacity higher than the rest of treated samples, a behavior that can be explained by the specific sites of adsorption and the textural properties of the solids. The isosteric heats of CO₂ adsorption, determined from the Clausius-Clapeyron equation, varied between 1.7 and 26.8 kJ/mol. The wastes should be used as adsorbents for the selective removal of organic contaminants in wastewater treatment.

Aquatic photodegradation of clofibric acid under simulated sunlight irradiation: kinetics and mechanism analysis

Clofibric acid is one of the most frequently detected pharmaceuticals in various aquatic environments.