Immobilization of heavy metals in tannery sludge by the formation of tobermorite in subcritical water treatment with rice husk silica.

Tannery sludge, heavy metals (HMs) enriched hazardous solid waste, is produced extensively in many regions of the world. Even though the sludge is hazardous, it can be considered a material resource, if organic matter and HMs in the sludge can be stabilized to minimize its negative environmental impacts. This research aimed to evaluate the efficacy of using subcritical water (SCW) treatment for tannery sludge treatment through immobilization and thus reduction of HMs to mitigate their potential environmental risk and toxicity. HMs in the tannery sludge were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and the average concentration of HMs (mg kg-1) was found in the following decreasing order of Cr (12 950) > Fe (1265) > Cu (76) > Mn (44) > Zn (36) > Pb (14) with very high Cr concentration. The result of toxicity characteristics leaching procedure and sequential extraction procedure tests revealed that the raw tannery sludge leachate contained 11.24 mg L-1 Cr, which classified the raw tannery sludge into a very high-risk category. After SCW treatment, the concentration of Cr in leachate was reduced to 1.6 mg L-1 indicating risk reduction to a low-risk category. The eco-toxicity levels of other HMs also decreased considerably after SCW treatment. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) analysis were employed to identify the effective immobilizing substances formed in the SCW treatment process. The favorable formation of immobilizing orthorhombic tobermorite (Ca5Si6O16(OH)2·4H2O) at 240 °C in the SCW treatment process was confirmed by XRD and SEM analysis. The results confirmed that the formation of 11 Å tobermorite is capable of strongly immobilizing HMs in the SCW treatment process. Further, both orthorhombic 11 Å tobermorite and 9 Å tobermorite were successfully synthesized by SCW treatment on a mixture of tannery sludge including rice husk silica and Ca(OH)2 with water under rather mild conditions. Hence, it can be concluded that SCW treatment of tannery sludge with supplementary silica from rice husk can effectively immobilize the HMs and significantly reduce their environmental risk through tobermorite formation.

Personal protective equipment (PPE) disposal during COVID-19: An emerging source of microplastic and microfiber pollution in the environment.

Waste generated by healthcare facilities during the COVID-19 pandemic has become a new source of pollution, particularly with the widespread use of single-use personal protective equipment (PPE). Releasing microplastics (MPs) and microfibers (MFs) from discarded PPE becomes an emerging threat to environmental sustainability. MPs/MFs have recently been reported in a variety of aquatic and terrestrial ecosystems, including water, deep-sea sediments, air, and soil. As COVID-19 spreads, the use of plastic-made PPE in healthcare facilities has increased significantly worldwide, resulting in massive amounts of plastic waste entering the terrestrial and marine environments. High loads of MPs/MFs emitted into the environment due to excessive PPE consumption are easily consumed by aquatic organisms, disrupting the food chain, and potentially causing chronic health problems in humans. Thus, proper management of PPE waste is critical for ensuring a post-COVID sustainable environment, which has recently attracted the attention of the scientific community. The current study aims to review the global consumption and sustainable management of discarded PPE in the context of COVID-19. The severe impacts of PPE-emitted MPs/MFs on human health and other environmental segments are briefly addressed. Despite extensive research progress in the area, many questions about MP/MF contamination in the context of COVID-19 remain unanswered. Therefore, in response to the post-COVID environmental remediation concerns, future research directions and recommendations are highlighted considering the current MP/MF research progress from COVID-related PPE waste.

Isotherm models for adsorption of heavy metals from water - A review.

Adsorption is a widely used technology for removing and separating heavy metal from water, attributed to its eco-friendly, cost-effective, and high efficiency. Adsorption isotherm modeling has been used for many years to predict the adsorption equilibrium mechanism, adsorption capacity, and the inherent characteristics of the adsorption process, all of which are substantial in evaluating the performance of adsorbents. This review summarizes the development history, fundamental characteristics, and mathematical derivations of various isotherm models, along with their applicable conditions and application scenarios in heavy metal adsorption. The latest progress in applying isotherm models with a one-parameter, two-parameter, and three-parameter in heavy metal adsorption using carbon-based materials, which has gained much attention in recent years as low-cost adsorbents, is critically reviewed and discussed. Several experimental factors affecting the adsorption equilibrium, such as solution pH, temperature, ionic strength, adsorbent dose, and initial heavy metal concentration, are briefly discussed. The criteria for selecting the optimum isotherm for heavy metal adsorption are proposed by comparing various adsorption models and analyzing mathematical error functions. Finally, the relative performance of different isotherm models for heavy metal adsorption is compared, and the future research gaps are identified.

A review of atmospheric microplastics pollution: In-depth sighting of sources, analytical methods, physiognomies, transport and risks.

Micro-sized plastics were first examined for atmospheric environment in 2016. From then on, they have been detected in both indoor and outdoor atmospheric samples, with indoor environments demonstrated as containing a big proportion of these particles. The sparse distribution of these particles, is attributed to their swift and long distance transportation that is mainly eased by their tiny size (1 µm to 5 mm) and low density. Due to ongoing limitation on detectable size, analysis methods together with a lack of standardized sampling and analytical procedures, few studies were conducted on airborne microplastics (MPs). Thus, the facts regarding the occurrence, global spatial distribution, fate, and threats to ecosystem and human health of airborne MPs, are still far from being fully clarified. This literature review is a broad depiction of a state of knowledge on atmospheric MPs. Within it, robust and concise information on the sources, inspection, transport, and threats pertaining to airborne MPs are presented. Particularly, the paper entails some information concerning traffic-generated MPs pollution, which has not been frequently discussed within previously published reports. In addition, this paper has widely unveiled sectors and aspects in need of further attention, with the gaps to be filled pinpointed.

Removal of organic pollutants from aqueous solution using metal organic frameworks (MOFs)-based adsorbents: A review.

The development of metal organic frameworks (MOFs) has recently drawn a lot of scientific interest in water treatment due to the unique properties such as tunable porosities, large pore volumes, hierarchical structures, excellent adsorption and regeneration performances. MOFs represent an eco-friendly alternative to conventional adsorbents especially for the adsorptive removal of noxious organic pollutants from aqueous solution. Advanced MOFs' performances are justified by the introduction of functional groups, magnetic moieties, and specific foreign materials onto MOFs. This however leads to increase in the manufacturing costs of MOFs and consequently possess a huge challenge in large-scale applications. This review hence critically discusses the recent progresses in the development of MOFs-based adsorbents for the removal of selected organic pollutants (e.g., dyes, antibiotics and pesticides) from aqueous solution. Furthermore, major interaction mechanisms between MOFs and organic pollutants in response to numerous experimental conditions, such as pH, temperature, coexisting ions are put forward. Finally, some recommendations in support for designing MOFs with improved adsorption performances are also highlighted.

Lead immobilization in soil using new hydroxyapatite-like compounds derived from oyster shell and its uptake by plant.

Protecting the natural environment and ecological systems from the inorganic pollutants such as lead (Pb) has highlighted the urgent need to develop new and effective approaches for this substance's immobilization in soil. In this study, new, low-cost, and eco-friendly hydroxyapatite (HAp)-like compounds were prepared by reacting oyster shell (Oys) with diammonium phosphate ((NH4)2HPO4) (DAP) and calcium hydroxide (Ca(OH)2) at 25-28 °C (OyOHr) and 100 °C (OyOHh). Furthermore, OyOHr and OyOHh were assessed for their effectiveness to immobilize Pb in soil and suppress Pb uptake by Indian spinach (Basella Alba L.). Application of 0.5% OyOHr and OyOHh to soil (by weight) reduced Pb concentration in the shoots by 76.9-78.0% compared to control (CK), to a level that was slightly higher (by 15.5-21.5%) than the recommended food safety level (2 mg kg-1) suggested by WHO. The changes in Pb fractions revealed that the total contents of oxidizable and residual forms in OyOHr or OyOHh after harvest was >415.0 mg kg-1, which indicated that >92% of Pb when added to the soil, was immobilized and not able to be taken up by plants. The proposed Pb immobilization mechanism might be the dissolution of OyOHr or OyOHh followed by hydroxypyromorphite (Pb10(PO4)6(OH)2) (HP) formation. Due to their facile preparation and eco-friendly and excellent Pb immobilizing characteristics, OyOHr or OyOHh could be readily integrated into current farming systems to mitigate the risk of Pb transferring to plants. However, OyOHr seemed a better immobilizing agent correspond to OyOHh in terms of cost and efficiency.