Recent advancements in antimony (Sb) removal from water and wastewater by carbon-based materials: a systematic review.

Antimony (Sb) has been classified as a high-priority contaminant in the environment. Sb contamination resulting from the use of antimony-containing compounds in industry necessitates the development of efficient methods to remove it from water and wastewater. Adsorption is a highly efficient and reliable method for pollutants removal owing to its availability, recyclability, and low cost. Recently, carbonaceous materials and their applications for the removal of Sb from the aqueous matrices have received special attention worldwide. Herein, this review systematically summarizes the occurrence and exposure of Sb in the environment and on human health, respectively. Different carbon-based adsorbents have been classified for the adsorptive removal of Sb and their adsorption characteristics have been delineated. Recent development in the adsorption performance of the adsorbent materials for improving the Sb removal from the aqueous medium has been outlined. Further, to develop an understanding of the effect of different parameters like pH, competitive ions, and dissolved ions for Sb adsorption and subsequent removal have been discussed. A retrospective analysis of literature was conducted to present the adsorption behavior and underlying mechanisms involved in the removal of Sb using various adsorbents. Moreover, this study has identified emerging research gaps and emphasized the need for developing modified/engineered carbonaceous adsorbents to enhance Sb adsorption from various aqueous matrices.

Smart Adsorbents for Aquatic Environmental Remediation.

A noticeable interest and steady rise in research studies reporting the design and assessment of smart adsorbents for sequestering aqueous metal ions and xenobiotics has occurred in the last decade. This motivates compiling and reviewing the characteristics, potentials, and performances of this new adsorbent generation's metal ion and xenobiotics sequestration. Herein, stimuli-responsive adsorbents that respond to its media (as internal triggers; e.g., pH and temperature) or external triggers (e.g., magnetic field and light) are highlighted. Readers are then introduced to selective adsorbents that selectively capture materials of interest. This is followed by a discussion of self-healing and self-cleaning adsorbents. Finally, the review ends with research gaps in material designs.

Pharmaceuticals of Emerging Concern in Aquatic Systems: Chemistry, Occurrence, Effects, and Removal Methods.

In the last few decades, pharmaceuticals, credited with saving millions of lives, have emerged as a new class of environmental contaminant. These compounds can have both chronic and acute harmful effects on natural flora and fauna. The presence of pharmaceutical contaminants in ground waters, surface waters (lakes, rivers, and streams), sea water, wastewater treatment plants (influents and effluents), soils, and sludges has been well doccumented. A range of methods including oxidation, photolysis, UV-degradation, nanofiltration, reverse osmosis, and adsorption has been used for their remediation from aqueous systems. Many methods have been commercially limited by toxic sludge generation, incomplete removal, high capital and operating costs, and the need for skilled operating and maintenance personnel. Adsorption technologies are a low-cost alternative, easily used in developing countries where there is a dearth of advanced technologies, skilled personnel, and available capital, and adsorption appears to be the most broadly feasible pharmaceutical removal method. Adsorption remediation methods are easily integrated with wastewater treatment plants (WWTPs). Herein, we have reviewed the literature (1990-2018) illustrating the rising environmental pharmaceutical contamination concerns as well as remediation efforts emphasizing adsorption.

Ciprofloxacin and acetaminophen sorption onto banana peel biochars: Environmental and process parameter influences.

Environmental (pH, temperature ionic strength, cations, anions) and process (pyrolysis temperature, particle size, adsorbent dosage, initial concentration) parameters were evaluated for ciprofloxacin and acetaminophen sorption onto a series of sustainable banana peel biochars. Ciprofloxacin and acetaminophen were chosen as model pharmaceuticals for removal owing to their worldwide presence in aquatic systems. After pyrolytic preparation from 450 to 750 °C, the biochars were qualitatively and quantitatively characterized by physicochemical, morphological, mineralogical and elemental analyses. Batch sorption studies were employed to evaluate the pH effects from 2 to 10, biochar pyrolysis temperatures (450, 550, 650, and 750 °C), particle sizes (30-50, 50-100, 100-150 BSS mesh), adsorbent dosages (0.5, 1.0, 2.0 g/L), adsorbate concentrations (0.5-200 ppm) and uptake temperatures (10, 25, 40 °C) on sorption efficiency. Maximum pharmaceutical sorption is achieved by the biochar prepared at 750 °C. Sorption rate increased with decrease in biochar particle size from 30 to 50 to 100-150 BSS mesh. Relationships between biochar properties and their sorptive potential showed positive correlations with surface area, total pore volume, %C, %ash and C/N molar ratios. Sorption data was modelled using different isotherm models and both kinetic and thermodynamic equations. Maximum Langmuir capacities of ciprofloxacin and acetaminophen on BPBC750 were 23.3 and 40.8 mg/g at 10 °C; 21.0 and 49.93 mg/g at 25 °C and 20.42 and 57.3 mg/g at 45 °C, respectively. Langmuir isotherm fittings and thermodynamic parameters confirmed the exothermic sorption (for ciprofloxacin) and endothermic sorption (for acetaminophen). The role of ionic strength, cations and anions on pharmaceuticals sorption were evaluated. H-bonding, π-π-interactions and pore diffusion were major contributors to pharmaceutical sorption.

Definitive Review of Nanobiochar.

Nanobiochar is an advanced nanosized biochar with enhanced properties and wide applicability for a variety of modern-day applications. Nanobiochar can be developed easily from bulk biochar through top-down approaches including ball-milling, centrifugation, sonication, and hydrothermal synthesis. Nanobiochar can also be modified or engineered to obtain "engineered nanobiochar" or biochar nanocomposites with enhanced properties and applications. Nanobiochar provides many fold enhancements in surface area (0.4-97-times), pore size (0.1-5.3-times), total pore volume (0.5-48.5-times), and surface functionalities over bulk biochars. These enhancements have given increased contaminant sorption in both aqueous and soil media. Further, nanobiochar has also shown catalytic properties and applications in sensors, additive/fillers, targeted drug delivery, enzyme immobilization, polymer production, etc. The advantages and disadvantages of nanobiochar over bulk biochar are summarized herein, in detail. The processes and mechanisms involved in nanobiochar synthesis and contaminants sorption over nanobiochar are summarized. Finally, future directions and recommendations are suggested.

Coronavirus (SARS-CoV-2) in the environment: Occurrence, persistence, analysis in aquatic systems and possible management.

The year 2020 brought the news of the emergence of a new respiratory disease (COVID-19) from Wuhan, China. The disease is now a global pandemic and is caused by a virus named SARS-CoV-2 by international bodies. Important viral transmission sources include human contact, respiratory droplets and aerosols, and through contact with contaminated objects. However, viral shedding in feces and urine by COVID-19-afflicted patients raises concerns about SARS-CoV-2 entering aquatic systems. Recently, targeted SARS-CoV-2 genome fragments have been successfully detected in wastewater, sewage sludge and river waters around the world. Wastewater-based epidemiology (WBE) studies can provide early detection and assessment of COVID-19 transmission and the growth of active cases within given wastewater catchment areas. WBE surveillance's ability to detect the growth of cases was demonstrated. Was this science applied throughout the world as this pandemic spread throughout the globe? Wastewater treatment efficacy for SARS-CoV-2 removal and risk assessments associated with treated water are reported. Disinfection strategies using chemical disinfectants, heat and radiation for deactivating and destroying SARS-CoV-2 are explained. Analytical methods of SARS-CoV-2 detection are covered. This review provides a more complete overview of the present status of SARS-CoV-2 and its consequences in aquatic systems. So far, WBE programs have not yet served to provide the early alerts to authorities that they have the potential to achieve. This would be desirable in order to activate broad public health measures at earlier stages of local and regional stages of transmission.

Batch and Continuous Fixed-Bed Lead Removal Using Himalayan Pine Needle Biochar: Isotherm and Kinetic Studies.

Pine needle litter in Himalayan forests leads to forest fires, ground water recharge inhibition, soil acidification and contamination, and stops the growth of grass and plants. This study provides a possible solution for pine needle litter problem by converting it to biochar. Pine needle litter lying on the ground for approximately a month was collected from the Himalayan region. The pine needle litter biochars were generated using slow pyrolysis (residence time, 30 min; heating rate, 10 °C/min) at 350, 450, 550, 650, and 750 °C. Finally, pine needle litter biochar prepared at 550 °C (PNBC550) was selected for sorptive removal of aqueous lead both in batch and column studies. The PNBC550 was characterized for proximate and elemental compositions, crystallinity, surface area, morphology, and functional groups. A BET surface area of 230.9 m2/g was obtained for PNBC550. Batch sorption studies were carried out to study (1) the adsorption versus pH studies (at pH 2 to 7), (2) isotherms (at 10, 25, and 35 °C) to evaluate the temperature effect on the sorption efficiency, and (3) kinetics to reveal the effect of time, adsorbent dose, and initial concentration on the reaction rate. Increasing pyrolysis temperature raised lead sorption up to 550 °C. Lead adsorption increased considerably as pH rose from 2 to a maximum adsorption around pH 5 and above. The sorption data were fitted using different isotherm models and kinetic equations. The Langmuir adsorption capacity increased from 22.93 mg/g at 10 °C to 40.43 mg/g at 35 °C, showing that adsorption was endothermic. Fixed-bed studies were conducted at room temperature with an initial lead concentration of 7.85 mg/L and 4.0 g of PNBC550 at initial pH 5.0 and a flow rate of 3 mL/min. Desorption studies conducted under the same experimental conditions found about 90-93% lead recovery. Development of high-efficiency biochars for lead remediation provides a sustainable solution for the Himalayan pine needle litter problem. The biochars also possess the possible potential for aqueous removal of other metal cations.

Aqueous carbofuran removal using slow pyrolyzed sugarcane bagasse biochar: equilibrium and fixed-bed studies.

Herein, biochar was produced by the slow pyrolysis of sugarcane bagasse at 500 °C in absence of oxygen. The resulting sugarcane bagasse biochar (SB500) was characterized and used for aqueous carbofuran sorptive removal. Batch carbofuran sorption studies were accomplished to ascertain the influence of solution pH, contact time, temperature (25, 35 and 45 °C) and adsorbate/adsorbent concentration. SB500 adsorbed more carbofuran at low pH values and less carbofuran at high pH values. The necessary sorption equilibrium, kinetic and thermodynamic parameters were determined. The equilibrium isotherm data were fitted to the Freundlich, Langmuir and Temkin models. The Langmuir equation best fitted the experimental sorption data. The maximum Langmuir adsorption capacity of 18.9 mg g-1 was obtained at pH 6.0 and 45 °C. The enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy (ΔG°) were evaluated. The fixed-bed carbofuran sorption studies were carried out using the optimum parameters determined via the batch studies. The necessary fixed-bed design parameters were obtained. Carbofuran desorption and SB500 regeneration were successfully achieved. About 96% of the total carbofuran was successfully desorbed from the exhausted biochar using 20 mL ethanol in 10 mL increments. Moreover, a possible carbofuran adsorption mechanism has been proposed. A number of interactions including (1) hydrogen bonding of the protonated and neutral carbofuran to biochar, (2) carbofuran sorption onto biochar via π-π electron donor-acceptor interactions and (3) carbofuran diffusion into the biochar pores were considered to explain the sorption mechanism. The batch and fixed-bed sorption results demonstrate that the sugarcane bagasse biochar (SB500) can be effectively used for the sustainable removal and recovery of carbofuran from water.

Simplified Batch and Fixed-Bed Design System for Efficient and Sustainable Fluoride Removal from Water Using Slow Pyrolyzed Okra Stem and Black Gram Straw Biochars.

Okra stem biochar (OSBC) and black gram straw biochar (BGSBC) were prepared by slow pyrolysis at 500 and 600 °C, respectively. OSBC and BGSBC were characterized using S BET, Fourier transform infrared, X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, SEM-energy dispersive X-ray, and energy dispersive X-ray fluorescence. High carbon contents (dry basis) of 66.2 and 67.3% were recorded in OSBC and BGSBC, respectively. The OSBC surface area (23.52 m2/g) was higher than BGSBC (9.27 m2/g). The developed biochars successfully remediate fluoride contaminated water. Fluoride sorption experiments were accomplished at 25, 35, and 45 °C. Biochar-fluoride adsorption equilibrium data were fitted to Langmuir, Freundlich, Sips, Temkin, Koble-Corrigan, Radke and Prausnitz, Redlich-Peterson, and Toth isotherm models. The sorption dynamic data was better fitted to the pseudo-second order rate equation versus the pseudo-first order rate equation. The Langmuir sorption capacities of Q OSBC 0 = 20 mg/g and Q BGSBC 0 = 16 mg/g were obtained. Biochar fixed-bed dynamic studies were accomplished to ascertain the design parameters for developing an efficient and sustainable fluoride water treatment system. A column capacity of 6.0 mg/g for OSBC was achieved. OSBC and BGSBC satisfactorily remediated fluoride from contaminated ground water and may be considered as a sustainable solution for drinking water purification.

Emerging technologies for arsenic removal from drinking water in rural and peri-urban areas: Methods, experience from, and options for Latin America.

Providing drinking water with safe arsenic levels in Latin American (LA) countries (a total of 22 countries) is a major current challenge. Arsenic's presence in water has been neglected for many decades since it was first reported ~100 years ago in Argentina. The major arsenic source in this region is geogenic. So far, arsenic has been reported in 15 LA countries. Arsenic concentrations in drinking water have been reported up to >200 fold (2000 µg/L) the WHO limit of 10 µg/L. About 14 million people in the arsenic affected LA countries depend on contaminated water characterized by >10 µg/L of arsenic. Low-cost, easy to use, efficient, and sustainable solutions are needed to supply arsenic safe water to the rural and peri-urban population in the affected areas. In the present study, >250 research articles published on various emerging technologies used for arsenic remediation in rural and peri-urban areas of LA countries are critically reviewed. Special attention has been given to arsenic adsorption methods. The manuscript focuses on providing insights into low cost emergent adsorbents with an implementation potential in Latin America. Natural, modified and synthetic adsorbents used for arsenic decontamination were reviewed and compared. Advantages and disadvantages of treatment methods are summarized. Adsorbent selection criteria are developed. Recommendations concerning emerging adsorbents for aqueous arsenic removal in LA countries have also been made.