As eco-friendly adsorption material, hydroxyapatite (Ca₅(PO₄)₃OH, HA) has been extensively applied to the removal of heavy metal ions. However, separating and recovering of HA powder after the adsorption process limits their application. Alginate-based composite beads (HCA) encapsulated with HA and cellulose were designed to remove Cu(II) from aqueous solution. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used for characteristic analysis. An extensive discussion in terms of HCA adsorption capacity, effect of various Cu(II) concentration, and analysis of the involved mechanisms of Cu(II) removal on the biosorption. HCA beads showed that the maximum adsorption capacity for Cu(II) of 64.14 mg/g at pH = 5 with 8 h contact time. The Langmuir adsorption isotherm and second-order kinetic model gave the closest fit. HCA beads display good regeneration ability after four cycles and offer potentiality for practical application.

Heteroatom-doped carbons are emerging candidates for metal-free catalysis, photocatalysis, and pollutant removal. Herein, we report the synthesis of N-doped solid (CS) and hollow carbon spheres (CNB) via a modified Stöber’s method. TEM, Raman, and XPS characterization techniques demonstrated a well-constructed N-doped sp²/sp³ hybridized carbons scaffold. Both CNB and CS nanospherical carbons have shown a high surface area of 360 and 400 m²/g, respectively, making them ideal candidates for the adsorption of pharmaceutical pollutants (ciprofloxacin and ibuprofen) and heavy metals (Pb and Cr) from wastewater. These materials have good interfacial interaction with the adsorbate and generate the proper medium to facilitate fast and efficient remediation. The highest surface adsorption (96% in 30 min) was observed for ibuprofen by CS. Interestingly, CNB was more selective for heavy metals at lower concentrations, while CS showed high surface adsorption at higher concentrations.

E-waste (EW) from discarded electrical and electronic devices is a potential source of rare earth elements (REEs) that might be recovered from urban and industrial wastes. REEs are essential raw materials for emerging and high technologies. China currently dominates global REE production with a proportion of 97%. To increase the independence of REE supply and eliminate the environmental impacts related to REE mining, methods for an efficient REE recovery from secondary sources like EW are needed. In this work, we examine improvements in pre-treatment and acidic leaching processes to recover REEs and other valuable metals. EW was crushed and ground prior to the sieving. The materials obtained were then subjected to acid leaching. The parameters used to optimize the conditions for leaching were as follows: acid type (HCl, HNO₃, and aqua regia), particle size, and waste-to-acid ratio. The maximum leaching efficiency was obtained from the ground, sieved, and undersized part of e-waste by using HCl with a W:A of 12.5 mg/mL. The total REE concentration was 435 mg/kg. Several treatment scenarios are identified with promise for improving REE recovery at full scale in EW recovery plants and thereby advancing goals for a sustainable, circular economy.

Phosphorus is an essential mineral for the growth of plants which is supplied in the form of fertilizers. Phosphorus remains an inseparable part of developing agrarian economics. Phosphorus enters waterways through three different sources: domestic, agricultural, and industrial sources. Rainfall is the main cause for washing away a large amount of phosphates from farm soils into nearby waterways. The surplus of phosphorus in the water sources cause eutrophication and degradation of the habitat with an adverse effect on aquatic life and plants. Phosphate elimination is necessary to control eutrophication in water sources. Among the different methods reported for the removal and recovery of phosphorus: ion exchange, precipitation, crystallization, and others, adsorption standout as a sustainable solution. The current review offers a comparative assessment of the literature on novel materials and techniques for the removal of phosphorus. Herein, different adsorbents, their behaviors, mechanisms, and capacity of materials are discussed in detail. The adsorbents are categorized under different heads: iron-based, silica-alumina-based, calcium-based, biochar-based wherein the metal and metal oxides are employed in phosphorus removal. The ideal attribute of adsorbent will be the utilization of spent adsorbents as a phosphate plant food and a soil conditioner in agriculture. The review provides the perspective on the current research with potential challenges and directives for possible research in the field.

Ecosystem services provided by river ecosystems rely on healthy ecosystem structure and ecological processes. The Beijing-Tianjin-Hebei urban is a typical water-deficient area. As an important part of the urban–rural integration construction, evaluating the health status of the Beiyun River Basin and discovering the weak links in the water environment are the basis for improving the health of the basin. In this study, analytic hierarchy process (AHP) was used to establish an evaluation index system for the Beiyun River Basin from 5 aspects including water quality, biology, ecology, hydrology, and social functions, and the principal component analysis (PCA) was then used to assign weights to the index layer. The evaluation results showed that the health evaluation results of the Beiyun River Basin in 2019 are “sub-healthy,” and the overall health status is getting worse from northwest to southeast. In the middle reaches of the region, the evaluation result is “healthy,” followed by the upstream, and the downstream is the worst. The results showed that areas with less human interference or orderly intervention are in better health. High eutrophication level, low bio-diversity, and low vegetation coverage are the main indicators that leads to poor ecosystem health in the Beiyun River Basin. For the comprehensive management of the Beiyun River, the improvement of water quality and habitat ecological restoration are key actions to the health of the upstream ecosystem. The improvement of the health status of the downstream should focus on equal emphasis on water quality and quantity, restoration of biodiversity, and improvement of the quality of the riparian ecological environment.

In this study, the alginate/hydroxyapatite/graphene oxide (AHGO) nanocomposite hydrogel beads (nhb) were designed, synthesized by an ionotropic gelation technique, and studied as an efficient, environment-friendly adsorbent for cationic dyes. The adsorptive capacities of AHGO nanocomposite toward methylene blue (MB) as a model dye solution were investigated through batch adsorption experiments in which the effects of initial dye concentration, adsorbent dosage, pH, temperature, ionic strength, and contact time on MB removal efficiency were examined. To explore the adsorption mechanisms, adsorption kinetics, isotherm analyses, XRD, FTIR, SEM–EDS, and point of zero charge (pHPZC) were performed. The results showed that AHGO-nhb had a maximum adsorption capacity of 311.81 mg/g for MB. This suggests that AHGO could be a good adsorbent for getting dyes out of water. Adsorption kinetics measurements proved to be closely correlated with both first and pseudo-second order (PSO) kinetics at the start, with the PSO taking control after 75 min, whereas the Sips model best described the MB adsorption isotherm process on AHGO. Based on the thermodynamic values ΔG°, ΔS°, and ΔH°, the process was spontaneous and exothermic in nature for cationic dyes. The mechanism underlying MB removal by AHGO is primarily a surface phenomenon involving electrostatic interaction, n-π interaction, and π-π interaction without intercalation. The process was shown to be a sequence of film diffusion followed by intra-particle diffusion, as demonstrated by the Weber-Moris and Boyed models. The adsorbent still maintains its adsorption ability for up to five cycles and could be a good alternative for treating wastewater.

A full-scale three-dimensional CFD study is done to determine the optimum position and size of lamella packet for an industrial wastewater sedimentation tank. The Euler–Lagrange method is adopted for this study by utilising the discrete phase model (DPM). Validation of the model is done by comparing the settling efficiency obtained from this study with that of the experimental settling efficiency from a published paper. A huge amount of wall-clock time for the study is saved without compromising on the final result by performing preliminary 2-D simulations before the actual 3-D study. Out of the three positions studied, namely inlet-biased, outlet-biased, and centre-biased, the outlet-biased position is found to be the most effective in improving the settling efficiency of the sedimentation tank. It is also observed that the settling efficiency increases with an increase in the number of inclined plates, but, only up to a certain extent after which there is a rapid fall in the settling efficiency. The total settling efficiency is found to be highest when only 39 inclined plates are installed with an outlet-biased position. Short-circuiting between inlet and outlet is found to be the most prominent problem deterring the complete filling up of the sedimentation tank with inclined plates. ARTICLE HIGHLIGHTS: • The first study about the optimum position of inclined plates. • A comprehensive study on the optimum number of inclined plates using the discrete phase model. • Key findings especially about the paradox of ‘increase in settling efficiency with increase in the settleable area due to addition of incline plates’.

This study analyzed the nutrients and metals concentrations of the surrounding soils and sclerophyllous vegetation of a tailing at the CODELCO–El Teniente copper mine in Central Chile. The content of metal, macro-, and micronutrients were analyzed in the soils outward from the tailing till 60-m distance at depths of 30, 60, and 90 cm, and in the foliage and stems of the native vegetation associated to the tailing. At plant level, we measured height, diameter, level of damage, and physiological attributes. Cu, Ni, Cr, and As were higher in the tailing, whereas soil Mn and Fe were higher at 60 m from the tailing. Soil K was higher at 30-cm depth, whereas Na was higher at 90-cm depth. Foliar Cu was higher in Acacia caven (40.5 mg kg⁻¹), whereas the levels of Cu and Zn in stems were higher in Quillaja saponaria (6.5 mg kg⁻¹ for Cu and 13.1 mg kg⁻¹ for Zn). As the values of water potential and quantum efficiency of the photosystem II averaged − 1.1 MPa and 0.73, respectively, these two species exhibited no physiological stress. Only Q. saponaria tended to increase the level of damage at higher distances from the tailing. A. caven and Q. saponaria exhibited foliar contents of Cu and Fe considered toxic (Cu from 18.5 to 40.5 and Fe from 298 to 407 mg kg⁻¹); however, both species were able to prosper at the limit of the tailing.

The 2019 outbreak of corona virus disease began from Wuhan (China), transforming into a leading pandemic, posing an immense threat to the global population. The WHO coined the term nCOVID-19 for the disease on 11th February, 2020 and the International Committee of Taxonomy of Viruses named it SARS-CoV-2, on account of its similarity with SARS-CoV-1 of 2003. The infection is associated with fever, cough, pneumonia, lung damage, and ARDS along with clinical implications of lung opacities. Brief understanding of the entry target of virus, i.e., ACE2 receptors has enabled numerous treatment options as discussed in this review. The manuscript provides a holistic picture of treatment options in COVID-19, such as non-specific anti-viral drugs, immunosuppressive agents, anti-inflammatory candidates, anti-HCV, nucleotide inhibitors, antibodies and anti-parasitic, RNA-dependent RNA polymerase inhibitors, anti-retroviral, vitamins and hormones, JAK inhibitors, and blood plasma therapy. The text targets to enlist the investigations conducted on all the above categories of drugs, with respect to the COVID-19 pandemic, to accelerate their significance in hindering the disease progression. The data collected primarily targets recently published articles and most recent records of clinical trials, focusing on the last 10-year database. The current review provides a comprehensive view on the critical need of finding a suitable treatment for the currently prevalent COVID-19 disease, and an opportunity for the researchers to investigate the varying possibilities to find and optimized treatment approach to mitigate and ameliorate the chaos created by the pandemic worldwide.

In the dye removal application, regeneration of hydrogen titanate nanotubes (HTN, H₂Ti₃O₇) has been achieved via thermal activation of persulfate anion (PS, S₂O₈²⁻) by using the conventional hot plate technique which has limitations from the commercial perspective since it does not provide any precise control over the thermal generation process typically during the scale-up operation. To overcome this drawback, HTN have been synthesized via hydrothermal process which exhibit the methylene blue (MB) adsorption of 93% at the initial dye concentration and solution pH of 90 µM and 10 respectively. HTN have been regenerated via the thermal activation of PS by varying its initial concentration and regeneration temperature, within the range of 0.27–1 wt% and 40–80 °C, under the thermal conditions set by the autoclave and pulsed ultrasound (US) cavitation process. The results of recycling experiments suggest that the optimum values of initial PS concentration and temperature, for the regeneration of HTN under the autoclave conditions, are 1 wt% and 70 °C with the maximum MB adsorption of 92%, while, the corresponding values for the pulsed US cavitation process are 1 wt%, 80 °C, and 91% respectively. Thus, the regeneration and recycling of HTN have been successfully demonstrated by using the autoclave and pulsed US cavitation process. Under the optimum conditions, MB degradation involves the generation and attack of SO₄•⁻ for both the thermal generation techniques. The regeneration techniques developed here may be utilized in future during the scale-up operation and also for the regeneration of adsorbents besides HTN.