Removal of norfloxacin in deionized, municipal water and urine using rice (Oryza sativa) and coffee (Coffea arabica) husk wastes as natural adsorbents

Azithromycin removal using pine bark, oak ash and mussel shell

Adsorption is considered an interesting option for removing antibiotics from the environment because of its simple design, low cost, and potential efficiency. In this work we evaluated three by-products (pine bark, oak ash, and mussel shell) as bio-adsorbents for the antibiotic azithromycin (AZM). Furthermore, they were added at doses of 48 t ha-1 to four different soils, then comparing AZM removal for soils with and without bio-adsorbents. Batch-type experiments were used, adding AZM concentrations between 2.5 and 600 μmol L-1 to the different bio-adsorbents and soil + bio-adsorbent mixtures. Regarding the bio-adsorbents, oak ash showed the best adsorption scores (9600 μmol kg-1, meaning >80% retention), followed by pine bark (8280 μmol kg-1, 69%) and mussel shell (between 3000 and 6000 μmol kg-1, 25-50% retention). Adsorption data were adjusted to different models (Linear, Freundlich and Langmuir), showing that just mussel shell presented an acceptable fitting to the Freundlich equation, while pine bark and oak ash did not present a good adjustment to any of the three models. Regarding desorption, the values were always below the detection limit, indicating a rather irreversible adsorption of AZM onto these three by-products. Furthermore, the results showed that when the lowest concentrations of AZM were added to the not amended soils they adsorbed 100% of the antibiotic, whereas when the highest concentrations of AZM were spread, the adsorption decreased to 55%. However, when any of the three bio-adsorbents was added to the soils, AZM adsorption reached 100% for all the antibiotic concentrations used. Desorption was null in all cases for both soils with and without bio-adsorbents. These results, corresponding to an investigation carried out for the first time for the antibiotic AZM, can be seen as relevant in the search of low-cost alternative treatments to face environmental pollution caused by this emerging contaminant.

Efficient adsorption of chloroquine phosphate by a novel sodium alginate/tannic acid double-network hydrogel in a wide pH range

In this work, a novel double-network composite hydrogel (SA/TA), composed of sodium alginate (SA) and tannic acid (TA), was designed and fabricated by a successive cross-linking method using Ti(IV) and Ca(II) as crosslinkers. SA/TA exhibited reinforced mechanical strength and anti-swelling properties because of the double-network structure. SA/TA was used as an adsorbent for removal of a popular antiviral drug, chloroquine phosphate (CQ), in water. The adsorption performance of SA/TA was systematically investigated, to study various effects including those of TA mass content, solution pH, adsorption time, and initial CQ concentration. Adsorption was also examined in presence of inorganic and organic coexisting substances commonly found in wastewater, and under different actual water samples. Batch experimental results indicated that SA/TA could maintain higher and more stable CQ uptakes within a wide solution pH range from 3.0 to 10.0, compared to its precursor, SA hydrogel, owing to the addition of TA-Ti(IV) coordination network. The maximum experimental CQ uptake exhibited by the 1:1 (by wt) SA/TA (SA/TA2) was as high as 0.699 mmol/g at the initial pH of 9.0. A high concentration of coexisting NaCl evidently reduced the CQ uptakes of SA/TA2 due to the electrostatic shielding effect, moreover, divalent cations including Ca(II) and Mg(II) also inhibited the adsorption of CQ due to competitive adsorption. However, humic acid had little effect on this adsorption. Considering the apparent adsorption performance, the aforementioned effects of various factors and the spectroscopic characterizations, multi-interactions are suggested for adsorption including chelation, electrostatic interactions, π-π electron donor-acceptor interaction and hydrogen bonding. SA/TA showed a slight loss in adsorption capacity toward CQ and sustained physicochemical structural stability, even after six adsorption-desorption cycles. In addition to CQ, SA/TA could be efficiently used for adsorption of two other antivirus drugs, namely, hydroxychloroquine sulfate and oseltamivir phosphate. This work provides an effective strategy for the design and fabrication of novel adsorbents that can effectively adsorb antiviral drugs over a wide pH range.

The structural transformation reversibility of biogas slurry derived dissolved organic matter and its binding properties with norfloxacin under temperature fluctuation

The widespread use of biogas slurry could potentially raise the environmental risk of antibiotics. Dissolved organic matter (DOM), as the most active part of biogas slurry, was able to interact with antibiotics and play a crucial role in the structure and function of soil and aquatic ecosystems. The recent shifts in global climate patterns have garnered significant attention due to their substantial impact on temperature, thereby exerting a direct influence on the characteristics of DOM and subsequently on the environmental behavior of antibiotics. However, there is limited research concerning the impact of temperature on the binding of DOM and antibiotics. Thus, this study aimed to explore the temperature-dependent structural transformation and driving factors of biogas slurry-derived DOM (BSDOM). Additionally, the binding characteristics between BSDOM and the commonly used antibiotic norfloxacin (NOR) at different temperatures were studied by using multi spectroscopic methods and two-dimensional correlation spectroscopy (2D-COS) analysis. The results suggested that the temperature-dependent structural transformation of BSDOM was reversible, with a slight lag in the transition temperature under cooling (13 °C for heating and 17 °C for cooling). Heating promoted the conversion of protein-like to humic-like substances while cooling favored the decomposition of humic-like substances. BSDOM and NOR were static quenching, with oxygen-containing functional groups such as C-O and -OH playing an important role. Temperature influenced the order of binding, the activity of the protein fraction, and its associated functional groups. At temperatures of 25 °C and 40 °C, the fluorescent components were observed to exhibit consistent binding preferences, whereby the humic-like component demonstrated a greater affinity for NOR compared to the protein-like component. However, the functional group binding order exhibited an opposite trend. At 10 °C, a new protein-like component appeared and bound preferentially to NOR, when no C-O stretch corresponding to the amide was observed. The finding will contribute to a comprehensive understanding of the interaction mechanisms between DOM and antibiotics under climate change, as well as providing a theoretical basis to reduce the environmental risks of biogas slurry and antibiotics.

High reusability and adsorption capacity of acid washed calcium alginate/chitosan composite hydrogel spheres in the removal of norfloxacin

Calcium alginate (CA) hydrogel spheres were widely used as adsorbents to remove organics, but their adsorption capacities and reusability to some antibiotics are unsatisfactory. In this study, calcium alginate/chitosan (CA/CTS) hydrogel spheres were prepared as precursors. Acid-washed CA/CTS (CA/CTS-M) hydrogel spheres (310.6 mg/g) behaved much better adsorption capacity of norfloxacin (NOR) than CA (69.5 mg/g) and CA/CTS (87.7 mg/g) hydrogel spheres. Astonishingly, after being reused for 15 cycles, CA/CTS-M has no loss of NOR adsorption capacity. In the original idea, acid wash was expected to remove the chitosan in CA/CTS hydrogel spheres for obtaining a larger specific surface area. Both scanning electron microscopy and Brunauer-Emmett-Teller test showed that acid wash can remove CTS from CA/CTS hydrogel spheres to increase the specific surface area. However, part of the chitosan remained in CA/CTS-M, having a role to enhance the structural stability of the material, because the acid-washed CA (about 2 mm) has a significantly smaller diameter than CA/CTS-M (about 3 mm). According to the influence of pH and density functional theory calculations, electrostatic attraction is the key driving force of NOR adsorption. Importantly, acid wash led to more negative-charged surface characterized by Zeta potential, which is the main reason of the significantly enhanced adsorption capacity of CA/CTS-M in removal of NOR. In short, CA/CTS-M hydrogel spheres are environment friendly and highly stable adsorbents with high adsorption capacity in the removal of NOR.

Trends in removal of pharmaceuticals in contaminated water using waste coffee and tea-based materials with their derivatives

The introduction of large amounts of pharmaceuticals into the environmental waters is well-documented in literature with their occurrence reported in all different water matrices accessible to humans and animals. At the same time, the increasing consumption of coffee and tea-based beverages results in the generation of solid waste, which is mostly disposed-off in the environment. To minimize environmental pollution, coffee and tea-based materials have been proposed as suitable options to remove pharmaceuticals in environmental waters. Therefore, this article provides a critical review on the preparation and applications of coffee and tea-based materials in removing pharmaceuticals from contaminated water. In this context, most studies in literature focused on the applications of these materials as adsorbents, while only limited work on their role in degradation of pharmaceuticals is discussed. The successful application in adsorption studies is attributed to high surface areas of adsorbents and the ability to easily modify the adsorbent surfaces by incorporating functional groups that provide additional oxygen atoms, which promote easy interactions with pharmaceuticals. Hence, the adsorption mechanisms are mostly described by hydrogen bonding, electrostatic and π-π interactions with sample pH playing a dominant role in the adsorption process. Overall, the present article focused on the developments, trends and future research direction on the preparations and applications of coffee and tea-based materials for efficient removal of pharmaceuticals in water. PRACTITIONER POINTS: Review of tea and coffee wastes application for removal of pharmaceuticals in water Key applications in adsorption and degradation of pharmaceuticals in water Removal mostly explained by hydrogen bonding, electrostatic, and π-π interactions Trends, gaps, and future research to be explored are reviewed and highlighted.

Non-toxic and biodegradable κ-carrageenan/ZnO hydrogel for adsorptive removal of norfloxacin: Optimization using response surface methodology

Antibiotic resistance is increasing globally due to increased prescription and easy dispensing of antibiotic drugs universally. Hence, to mitigate this effect, efficient, biodegradable, and non-toxic adsorbents are required to be developed. Carrageenan (CG), a natural polymer, having multiple functional groups, provides a backbone for crosslinking with borax and incorporation of ZnO nanoparticles that formed borax-cross-linked κ-carrageenan (CG/Bx/ZnO) hydrogel which is used for efficient adsorption of norfloxacin from water. Surface morphology of as-synthesized hydrogel revealed the rough surface, which was determined by FESEM. Surface area of CG/Bx/ZnO hydrogel was found to be 22.90 m²/g with 3.41 nm pore radius. Systematic batch adsorption studies revealed that 99.4 % removal efficiency could be achieved at a dosage level of 20 mg/L of norfloxacin with 10 mg of hydrogel at pH of 4 in 8 h at room temperature. Experimentally optimized key parameters affecting the overall efficiency of adsorption matched well with the results assessed from ANOVA using Box-Behnken composite design model. The adsorption process was well fitted with the pseudo-second-order model and Langmuir isotherm with 1282.05 mg/g adsorption capacity. Thermodynamic study results show that adsorption is spontaneous and endothermic. The CG/Bx/ZnO hydrogel demonstrated excellent repeatability with minimal loss in norfloxacin adsorption for seven cycles.

A review of the adsorption method for norfloxacin reduction from aqueous media

Norfloxacin (NRFX) is one of a class of antibiotics known as broad-spectrum fluoroquinolone antibiotic that is frequently used to treat infectious disorders in both animals and humans. NRFX is considered an emergent pharmaceutical contaminate. This review's objective is to evaluate empirical data on NRFX's removal from aqueous medium. The environmental danger of NRFX in the aquatic environment was validated by an initial ecotoxicological study. Graphene oxide/Metal Organic Framework (MOF) based composite, followed by Magnesium oxide/Chitosan/Graphene oxide composite gave the highest NRFX adsorption capacities (Qmax) of 1114.8 and 1000 mg/g, respectively. The main adsorption mechanisms for NRFX uptake include electrostatic interactions, H-bonds, π-π interactions, electron donor-acceptor interactions, hydrophobic interactions, and pore diffusion. The adsorptive uptake of NRFX were most suitably described by Langmuir isotherm and pseudo-second order implying adsorbate-to-adsorbent electron transfer on a monolayer surface. The thermodynamics of NRFX uptake is heavily dependent on the makeup of the adsorbent, and the selection of the eluent for desorption from the solid phase is equally important. There were detected knowledge gaps in column studies and adsorbent disposal method. There's great interest in scale-up and industrial applications of research results that will aid in management of water resources for sustainability.

Biochar from palm fiber wastes as an activator of different oxidants for the elimination of pharmaceuticals from diverse classes in aqueous samples

Biochar (BP) obtained from palm fiber wastes was combined with H₂O₂, peroxymonosulfate (PMS), or persulfate (PDS) to treat valsartan, acetaminophen, and cephalexin in water. BP activated PMS and PDS but no H₂O₂. Computational calculations indicated that interactions of PMS and PDS with BP are more favored than those with HP. The highest synergistic effect was obtained for the removal of valsartan by BP + PMS. This carbocatalytic process was optimized, evaluating the effects of pH, BP dose, and peroxymonosulfate concentration, and minimizing the oxidant quantity to decrease costs and environmental impacts of the process. SO₄•^-, HO•, ¹O₂, and O₂•^- were the agents involved in the degradation of the pharmaceuticals. The reusability of BP was tested, showing that the carbocatalytic process removed ∼80% of target pollutants after 120 min of treatment even at the fourth reuse cycle. Also, the process decreased the phytotoxicity of the treated sample. Simulated hospital wastewater was treated and its components induced competing effects, but the system achieved the target pharmaceuticals removal in this matrix. Additionally, the analysis of environmental impact using a life cycle assessment unraveled that the carbocatalytic process had a carbon footprint of 2.87 Kg CO₂-Eq, with the biochar preparation (which involves the use of ZnCl₂ and electric energy consumption) as the main hotspot in the process.

Outstanding Enrofloxacin Removal Using an Unmodified Low-Cost Sorbent Prepared from the Leaves of Pyracantha koidzumii

Increasing discharges of synthetic antimicrobial agents from industrial and municipal sewage, as well as from agricultural runoffs into water bodies, is still a global challenge. Here, an unmodified low-cost sorbent was prepared in an ecofriendly manner from Pyracantha koidzumii leaves for the removal of enrofloxacin (ENR). Sorbent characterization was accomplished using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), BET surface area, zeta potential, and point of zero charge. Biosorption assays were carried out via batch mode concerning the impact of adsorbent dosage, contact time, solution pH, solution ionic strength, adsorbate concentration, and temperature. In general, ENR adsorption was significantly correlated with pH and ionic strength. At a neutral pH, the sorbent had a theoretical maximal ENR uptake of 138.89 mg/g. However, the adsorption capacity was significantly affected by the presence of high concentrations of divalent cations (Ca2+ and Mg2+). The findings from the kinetics and isotherms showed that the pseudo-second-order kinetic and Langmuir isotherm models best fit the experimental data. Electrostatic interactions, hydrogen bonding, and π-π stacking were the most important mechanisms of adsorption of ENR onto the P. koidzumii sorbent. Overall, this study suggests the promising application of this agricultural residue for the efficient removal of ENR from water.

Emerging pharma residue contaminants: Occurrence, monitoring, risk and fate assessment - A challenge to water resource management

Water is one of the important gifts to mankind. In recent days the accessibility of pharmaceuticals in the environment is progressively a worldwide concern. The significant wellspring of these contaminations in water assets is drugs for human use or veterinary medications. Intermediates, active metabolites and raw materials present in water from pharmaceutical industry waste because of incomplete sewage treatment systems. Various pharmaceutical components such as analgesic/antipyretics such as Ibuprofen (57.9-104 ng/L), Diclofenac (17-129 ng/L), antibiotics such as Sulfamethoxazole (28.7-124.5 ng/L), Sulfamethazine (29.2-83.9 ng/L), Azithromycin (10-68 ng/L), psychiatric drug such as Carbamazepine (9.3-92.4 ng/L), stimulants such as caffeine greater than 55 ng/L, antidepressants, antihypertensive, contraceptives etc., are present in water resources and have been detected in mg/L to μg/L range. The synergic effects and ecotoxicological hazard assessment must be developed. Studies demonstrate that these drugs might cause morphological, metabolic and sex alterations on sea-going species, and interruption of biodegradation activities. Hazard analysis and assessments are in progress. However, the conventional effluent treatment methods are not sufficient to remove API (active pharmaceutical ingredients) from this water effectively. There is necessitate for continuous monitoring of the pharmaceutical compounds in aquatic ecosystem to save the environment and living form of lives from health hazards. This work highlights the hazards, environmental assessment and the mitigation measures of pharmaceutical pollutants.

Development and Characterization of Bioadsorbents Derived from Different Agricultural Wastes for Water Reclamation: A Review

The presence of dangerous pollutants in different water sources has restricted the availability of this natural resource. Thus, the development of new low-cost and environmentally-friendly technologies is currently required to ensure access to clean water. Various approaches to the recovery of contaminated water have been considered, including the generation of biomaterials with adsorption capacity for dangerous compounds. Research on bioadsorbents has boomed in recent years, as they constitute one of the most sustainable options for water treatment thanks to their abundance and high cellulose content. Thanks to the vast amount of information published to date, the present review addresses the current status of different biosorbents and the principal processes and characterization methods involved, focusing on base biomaterials such as fruits and vegetables, grains and seeds, and herbage and forage. In comparison to other reviews, this work reports more than 60 adsorbents obtained from agricultural wastes. The removal efficiencies and/or maximum adsorption capacities for heavy metals, industrial contaminants, nutrients and pharmaceuticals are presented as well. In addition to the valuable information provided in the literature investigation, challenges and perspectives concerning the implementation of bioadsorbents are discussed in order to comprehensively guide selection of the most suitable biomaterials according to the target contaminant and the available biowastes.

Removal of diclofenac and oxytetracycline from synthetic urine by furfuryl alcohol-derived mesoporous carbon

In this study, using furfuryl alcohol as the precursor carbon and mesoporous silica as the template, and furfuryl alcohol-derived mesoporous carbon (FMC) was prepared. The specific surface area of FMC was 1022.61 m²/g, the pore volume was 1.71 cm³/g, and the mesoporous volume was 98.8%. Based on the adsorption kinetics of pharmaceuticals onto the FMC in synthetic urine, equilibrium adsorption was reached in 120 min, and it followed a pseudo-second-order model. The adsorption isotherms were well-fitted by the Sips isotherm model, and the saturated adsorption capacities of diclofenac and oxytetracycline in fresh urine were 411.8 mg/g and 465.9 mg/g, respectively. Batch experiment results showed that pharmaceutical removal was strongly influenced by urine components such as sodium chloride, urea, and ammonium hydroxide. The adsorption of diclofenac and oxytetracycline was influenced by many factors including π-π interactions, hydrogen bonds, and electrostatic forces. FMC exhibited excellent reusability and retained urine nutrients during pharmaceutical adsorption.

Conversion of scrap iron into ultrafine α-Fe2O3 nanorods for the efficient visible light photodegradation of ciprofloxacin

The present study illustrates a feasible approach of utilizing scrap iron for the synthesis of iron(ii) oxide.

State of the art of urine treatment technologies: A critical review

Over the last 15 years, urine treatment technologies have developed from lab studies of a few pioneers to an interesting innovation, attracting attention from a growing number of process engineers. In this broad review, we present literature from more than a decade on biological, physical-chemical and electrochemical urine treatment processes. Like in the first review on urine treatment from 2006, we categorize the technologies according to the following objectives: stabilization, volume reduction, targeted N-recovery, targeted P-recovery, nutrient removal, sanitization, and handling of organic micropollutants. We add energy recovery as a new objective, because extensive work has been done on electrochemical energy harvesting, especially with bio-electrochemical systems. Our review reveals that biological processes are a good choice for urine stabilization. They have the advantage of little demand for chemicals and energy. Due to instabilities, however, they are not suited for bathroom applications and they cannot provide the desired volume reduction on their own. A number of physical-chemical treatment technologies are applicable at bathroom scale and can provide the necessary volume reduction, but only with a steady supply of chemicals and often with high demand for energy and maintenance. Electrochemical processes is a recent, but rapidly growing field, which could give rise to exciting technologies at bathroom scale, although energy production might only be interesting for niche applications. The review includes a qualitative assessment of all unit processes. A quantitative comparison of treatment performance was not the goal of the study and could anyway only be done for complete treatment trains. An important next step in urine technology research and development will be the combination of unit processes to set up and test robust treatment trains. We hope that the present review will help guide these efforts to accelerate the development towards a mature technology with pilot scale and eventually full-scale implementations.

Biochars produced from various agro-industrial by-products applied in Cr(VI) adsorption-reduction processes

This study aimed to reuse different agro-industrial by-products (poultry litter, pig manure, sewage sludge and coffee husk) for biochar production and to evaluate their Cr(VI) removal capacities in aqueous medium. The biochars showed different morphologies with porous structures. The percentages of Cr(VI) removal from solution were higher in acid medium (pH = 2), reaching values up to 87%. For all biochars, Cr(VI) removal occurs via both adsorption and reduction, being a rapid (30 min) process, which fits best to the pseudo-second order kinetic model. The biochars, especially from coffee husk, were able to reduce up to 20% of Cr(VI) to Cr(III). The maximum Cr(VI) removal capacities ranged from 10.86 mg g^-1 (sewage sludge biochar) to 18.52 mg g^-1 (coffee husk biochar). Therefore, the production of biochars from the agro-industrial by-products using the same experimental conditions in one single study is important to compare the Cr(VI) removal capacities from different biomasses. Thus, this study explored the corresponding raw material without the need of further treatment. Biochars showed potential for environmental applications considering Cr(VI)-polluted environments. It is hoped to provide basis to future studies using real wastewater samples.

Evaluating the Removal of the Antibiotic Cephalexin from Aqueous Solutions Using an Adsorbent Obtained from Palm Oil Fiber

This study aimed to understand the adsorption process of cephalexin (CPX) from aqueous solution by a biochar produced from the fiber residue of palm oil. Scanning electron microscopy, Fourier transform infrared spectroscopy, Boehm titration, and the point of zero charge were used to characterize the morphology and surface functional groups of the adsorbent. Batch tests were carried out to evaluate the effects of the solution pH, temperature, and antibiotic structure. The adsorption behavior followed the Langmuir model and pseudo-second-order model with a maximum CPX adsorption capacity of 57.47 mg g^-1. Tests on the thermodynamic behavior suggested that chemisorption occurs with an activation energy of 91.6 kJ mol^-1 through a spontaneous endothermic process. Electrostatic interactions and hydrogen bonding represent the most likely adsorption mechanisms, although π-π interactions also appear to contribute. Finally, the CPX removal efficiency of the adsorbent was evaluated for synthetic matrices of municipal wastewater and urine. Promising results were obtained, indicating that this adsorbent can potentially be applied to purifying wastewater that contains trace antibiotics.

Highly efficient removal of imidacloprid using potassium hydroxide activated magnetic microporous loofah sponge biochar

Extensive application of imidacloprid (IMI) in pest control and its undesirable removal efficiency enabled it to be a critical global challenge. Low cost, efficient, sustainable and environment-friendly technologies are urgently needed to be developed to remove IMI from water. A novel adsorbent of potassium hydroxide activated magnetic microporous loofah sponge biochar (KOH+Fe/Zn-LBC) was synthesized, as well as its adsorption capacity and mechanisms for IMI were investigated in this study. KOH+Fe/Zn-LBC had the superior pore structure (surface area and pore volume) and its maximum adsorption capacity for IMI could reach 738 mg g^-1 at 298 K. Kinetics, isotherms, thermodynamics and characterization analysis suggested that pore filling, hydrogen bonding and π-π conjugation were its main adsorption mechanisms. Additionally, the thermodynamic parameters described that IMI adsorption was a spontaneous, endothermic and less random process. Particularly, the magnetic separation of KOH+Fe/Zn-LBC was beneficial for its reuse. Ultrasound and ethanol co-processing could effectively regenerate the used KOH+Fe/Zn-LBC and maintain its stable sustainable adsorption capacity (99.4% of its fresh adsorption capacity after five reuse cycles). Besides, KOH+Fe/Zn-LBC exhibited a stable adsorption capacity and environmental safety in a wide pH range. Therefore, KOH+Fe/Zn-LBC has the potential to be an efficient, green and sustainable adsorbent for neonicotinoids removal.

Norfloxacin adsorption on montmorillonite and carbon/montmorillonite hybrids: pH effects on the adsorption mechanism, and column assays

The presence of norfloxacin antibiotic (NFX) in drinking water raises significant scientific concern due to the health and environmental problems that may cause. This study aimed to evaluate the NFX removal: 1) in batch adsorption at different pH values on montmorillonite (M) and montmorillonite-carbon hybrids (M-HC); 2) in continuous columns experiments, to assess the technological application of these hybrids as domestic filters, using one M-HC as adsorbent material ranging from 1% to 5%. Batch experiments showed that adsorption occurred in all the samples, being M the material with the highest adsorption capacity (95% of adsorption for cationic NFX). For the M-HC the adsorption seemed to be not strongly dependent of the pH (20%- 41% of adsorption). The characterization of adsorbents and NFX adsorption products (FTIR, XRD, and zeta potential analysis) disclosed that adsorption occurs at both the external surface and the interlayer space of M. For the M-HC synthesized without activation, the interlayer space seemed to be predominantly responsible; while for the activated M-HC the adsorption occurred at the external surface (its interlayer was destroyed). The column experiments revealed that the best adsorption capacity and highest flow were attained using 1% of adsorbent material in the column packing.

Adsorptive removal of azithromycin from aqueous solutions using raw and saponin-modified nano diatomite

This study aims to investigate the performance and mechanism of raw (R-ND) and saponin-modified nano diatomite (M-ND) in the removal of azithromycin from aqueous solutions. Adsorbent characterization was performed using X-ray fluorescence, Brunauer-Emmett-Teller (BET), scanning electron spectroscopy, dynamic light scattering and energy-dispersive X-ray analyses. It was shown that the specific surface area of R-ND was 119.5 m²/g, 14-fold higher than that for raw diatomite, and for M-ND it was 90.1 m²/g. Various adsorption conditions, i.e. adsorbent dosage, pH, initial concentration and contact time were investigated. According to the results, despite reducing the specific surface area by 25%, modification of nano diatomite by saponin markedly enhanced its performance in the removal of azithromycin. The maximum adsorption capacity of R-ND and M-ND in the removal of azithromycin was 68 and 91.7 mg/g, respectively. Fourier transform infrared spectroscopy results revealed that azithromycin was adsorbed by O-H groups on the diatomite surface. Weber-Morris intra-particle diffusion (IPD) model suggested that while IPD is not the rate-controlling step in high concentrations of azithromycin, it is the only step that controls the rate of adsorption in low concentrations. In comparison to R-ND, M-ND showed a higher efficiency in the removal of azithromycin and, therefore, it can be used as a promising low-cost adsorbent to remove azithromycin from aqueous solutions.

Use of biotechnological approaches to add value to rice hulls

One of the most common agricultural wastes generated in rice producing countries, rice hull (RH) is considered an environmental problem due to increased rice production and RH accumulation, especially because natural degradation in the environment is very difficult and time-consuming. Currently, RH is mostly used as bed for broiler chickens or burned for energy generation, two processes that prevent environmental accumulation in a sustainable way, without adding value to the RH. To diversificate its use and effectively add some value to the RH, a pretreatment is frequently needed, allowing the application of several biotechnological approaches. In this review, we gather information about biotechnological uses of crude and processed RH, including their use as fertilizers, filler material in natural rubber and incorporation in cement for civil construction purposes, along with their use in processes as silica extraction and adsorption/removal of environmental contaminants as heavy metals and dyes. Finally, we critically evaluate the data published in the literature, and based on our own findings, we point future directions related to RH biodegradation and further methane production.

Efficient cephalexin degradation using active chlorine produced on ruthenium and iridium oxide anodes: Role of bath composition, analysis of degradation pathways and degradation extent

The elimination of cephalexin (CPX) using electro-generated Cl₂-active on Ti/RuO₂-IrO₂ anode was assessed in different effluents: deionized water (DW), municipal wastewater (MWW) and urine. Single Ti/RuO₂ and Ti/IrO₂ catalysts were prepared to compare their morphologies and electrochemical behavior against the binary DSA. XRD and profile refinement suggest that Ti/RuO₂-IrO₂ forms a solid solution, where RuO₂ and IrO₂ growths are oriented by the TiO₂ substrate through substitution of Ir by Ru atoms within its rutile-type structure. SEM reveals mud-cracked structures with flat areas for all catalysts, while EDS analysis indicates atomic ratios in the range of the oxide stoichiometries in the nominal concentrations used during synthesis. A considerably higher CPX degradation is achieved in the presence of NaCl than in Na₂SO₄ or Na₃PO₄ media due to the active chlorine generation. A faster CPX degradation is reached when the current density is increased or the pH value is lowered. This last behavior may be ascribed to an acid-catalyzed reaction between HClO and CPX. Degradation rates of 22.5, 3.96, and 0.576 μmol L^-1 min^-1 were observed for DW, MWW and urine, respectively. The lower efficiency measured in these last two effluents was related to the presence of organic matter and urea in the matrix. A degradation pathway is proposed based on HPLC-DAD and HPLC-MS analysis, indicating the fast formation (5 min) of CPX-(S)-sulfoxide and CPX-(R)-sulfoxide, generated due the Cl₂-active attack at the CPX thioether. Furthermore, antimicrobial activity elimination of the treated solution is reached once CPX, and the initial by-products are considerably eliminated. Finally, even if only 16% of initial TOC is removed, BOD₅ tests prove the ability of electro-generated Cl₂-active to transform the antibiotic into biodegradable compounds. A similar strategy can be used for the abatement of other recalcitrant compounds contained in real water matrices such as urine and municipal wastewaters.

Use of chemically activated termite feces a low-cost adsorbent for the adsorption of norfloxacin from aqueous solution

Antibiotics, as emerging contaminants, are of global concern due to the development of antibiotic resistant microorganisms. Current wastewater treatment technology cannot efficiently remove sewage antibiotics and therefore new low-cost technologies are needed. Adsorption is a widely used process for removal of substances, and the search for efficient, low-cost adsorbents is ongoing. In this work, termite feces treated with H₂SO₄ (FT/H₂SO₄) were used as a low-cost adsorbent for removal of norfloxacin (NOR) present in aqueous medium. Termite feces were treated with H₂SO₄ at a ratio of 1:1 for 24 h, at 100 °C. The parameters contact time, initial NOR concentration, medium pH and temperature were evaluated. The optimum adsorption pH was 8.0. The pseudo-second-order model was found to best represent the kinetics of NOR adsorption. The maximum adsorption capacity, calculated from the Sips isotherm model, was 104.4 mg/g at 55 °C. The positive values of ΔH⁰ (change in enthalpy) confirm the endothermic nature of the adsorption. The results show that FT/H₂SO₄ is an efficient adsorbent for removal of NOR present in aqueous medium. The adsorption capacity is higher than those reported in the literature for other low-cost adsorbents.

The synergetic effect of a structure-engineered mesoporous SiO2–ZnO composite for doxycycline adsorption

The design and synthesis of an efficient adsorbent for antibiotics-based pollutants is challenging due to the unique physicochemical properties of antibiotics. The development of a mesoporous SiO₂–ZnO composite is a novel way to achieve excellent adsorption efficiency for doxycycline hydrochloride (DOX) in aqueous solutions due to the engineered highly open mesoporous structure and the ZnO-modified framework. Unlike the traditional method of obtaining mesoporous composites by post-synthesis techniques, the novel one-step method developed in this study is both effective and environment-friendly. The adsorption mechanism based on the novel synergetic effect between SiO₂ and ZnO was demonstrated through several experiments. SiO₂ led to the creation of a 3D open framework structure that provides sufficient space and rapid transport channels for adsorption, ensuring rapid adsorption kinetics. A higher number of active sites and enhanced affinity of the contaminants are provided by ZnO, ensuring high adsorption capacity. The mesoporous SiO₂–ZnO could be easily regenerated without a significant decrease in its adsorption efficiency. These results indicate that the developed strategy afforded a simple approach for synthesizing the novel mesoporous composites, and that mesoporous SiO₂–ZnO is a possible alternative adsorbent for the removal of DOX from wastewater.

The design and synthesis of an efficient adsorbent for antibiotics-based pollutants is challenging due to the unique physicochemical properties of antibiotics.