Removal of silver nanoparticles in aqueous solution by activated sludge: Mechanism and characteristics

Nanoparticles in drinking water: Assessing health risks and regulatory challenges

Nanoparticles (NPs) pose a significant concern in drinking water due to their potential health risks and environmental impact. This review provides a comprehensive analysis of the current understanding of NP sources and contamination in drinking water, focusing on health concerns, mitigation strategies, regulatory frameworks, and future perspectives. This review highlights the importance of nano-specific pathways, fate processes, health risks & toxicity, and the need for realistic toxicity assessments. Different NPs like titanium dioxide, silver, nanoplastics, nanoscale liquid crystal monomers, copper oxide, and others pose potential health risks through ingestion, inhalation, or dermal exposure, impacting organs and potentially leading to oxidative stress, inflammatory responses, DNA damage, cytotoxicity, disrupt intracellular energetic mechanisms, reactive oxygen species generation, respiratory and immune toxicity, and genotoxicity in humans. Utilizing case studies and literature reviews, we investigate the health risks associated with NPs in freshwater environments, emphasizing their relevance to drinking water quality. Various mitigation and treatment strategies, including filtration systems (e.g., reverse osmosis, and ultra/nano-filtration), adsorption processes, coagulation/flocculation, electrocoagulation, advanced oxidation processes, membrane distillation, and ultraviolet treatment, all of which demonstrate high removal efficiencies for NPs from drinking water. Regulatory frameworks and challenges for the production, applications, and disposal of NPs at both national and international levels are discussed, emphasizing the need for tailored regulations to address NP contamination and standardize safety testing and risk assessment practices. Looking ahead, this review underscores the necessity of advancing detection methods and nanomaterial-based treatment technologies while stressing the pivotal role of public awareness and tailored regulatory guidelines in upholding drinking water quality standards. This review emphasizes the urgency of addressing NP contamination in drinking water and provides insights into potential solutions and future research directions. Lastly, this review worth concluded with future recommendations on advanced analytical techniques and sensitive sensors for NP detection for safeguarding public health and policy implementations.

Remediation of preservative ethylparaben in water using natural sphalerite: Kinetics and mechanisms

As a typical class of emerging organic contaminants (EOCs), the environmental transformation and abatement of preservative parabens have raised certain environmental concerns. However, the remediation of parabens-contaminated water using natural matrixes (such as, naturally abundant minerals) is not reported extensively in literature. In this study, the transformation kinetics and the mechanism of ethylparaben using natural sphalerite (NS) were investigated. The results show that around 63% of ethylparaben could be absorbed onto NS within 38 hr, whereas the maximum adsorption capacity was 0.45 mg/g under room temperature. High temperature could improve the adsorption performance of ethylparaben using NS. In particular, for the temperature of 313 K, the adsorption turned spontaneous. The well-fitted adsorption kinetics indicated that both the surface adsorption and intra-particle diffusion contribute to the overall adsorption process. The monolayer adsorption on the surface of NS was primarily responsible for the elimination of ethylparaben. The adsorption mechanism showed that hydrophobic partitioning into organic matter could largely govern the adsorption process, rather than the ZnS that was the main component of NS. Furthermore, the ethylparaben adsorbed on the surface of NS was stable, as only less than 2% was desorbed and photochemically degraded under irradiation of simulated sunlight for 5 days. This study revealed that NS might serve as a potential natural remediation agent for some hydrophobic EOCs including parabens, and emphasized the significant role of naturally abundant minerals on the remediation of EOCs-contaminated water bodies.

Recent developments in the removal of metal-based engineered nanoparticles from the aquatic environments by adsorption

Nowadays, metal-based engineered nanoparticles (m-ENPs) are ubiquitous in aquatic environments for their wide applications in all walks of life. m-ENPs have been demonstrated to exert ecotoxicity, cytotoxicity and genotoxicity towards organisms and even humans. Therefore, the removal of m-ENPs from water has recently become a hot global concerned issue. Adsorption is widely investigated for this purpose, owing to its advantages of low cost, easy operation, high removal efficiency and potential recycling use of both the adsorbents and adsorbates. As the adsorption and related technologies were hardly comprehensively overviewed for the removal of m-ENPs, herein, the present review particularly focuses on this topic. The fundamentals to the technology, including adsorption isotherm, adsorption dynamics, the adsorption process with the special emphasis on the relationship between surface area and porosity of the adsorbent and the adsorption capacity, etc., are fully discussed. As the kernel of the adsorption method, adsorbents with diversified chemical and physical properties in different types are comprehensively elaborated. The primary factors affecting the adsorption, and adsorption mechanisms are well summarized. Particularly, the regeneration of the adsorbents and the reuse of adsorbed m-ENPs are highlighted for the sustainability. Finally, challenges and prospects in this field are outlined. Overall, this review aims to provide valuable references for the development of new adsorbents with more efficient and practical applications to remove m-ENPs and direct the future study.

Effect of Engineered Biomaterials and Magnetite on Wastewater Treatment: Biogas and Kinetic Evaluation

In this study, the principle of sustaining circular economy is presented as a way of recovering valuable resources from wastewater and utilizing its energy potential via anaerobic digestion (AD) of municipality wastewater. Biostimulation of the AD process was investigated to improve its treatability efficiency, biogas production, and kinetic stability. Addressing this together with agricultural waste such as eggshells (CE), banana peel (PB), and calcined banana peels (BI) were employed and compared to magnetite (Fe₃O₄) as biostimulation additives via 1 L biochemical methane potential tests. With a working volume of 0.8 L (charge with inoculum to substrate ratio of 3:5 v/v) and 1.5 g of the additives, each bioreactor was operated at a mesophilic temperature of 40 °C for 30 days while being compared to a control bioreactor. Scanning electron microscopy and energy dispersive X-ray (SEM/EDX) analysis was used to reveal the absorbent’s morphology at high magnification of 10 kx and surface pore size of 20.8 µm. The results showed over 70% biodegradation efficiency in removing the organic contaminants (chemical oxygen demand, color, and turbidity) as well as enhancing the biogas production. Among the setups, the bioreactor with Fe₃O₄ additives was found to be the most efficient, with an average daily biogas production of 40 mL/day and a cumulative yield of 1117 mL/day. The kinetic dynamics were evaluated with the cumulative biogas produced by each bioreactor via the first order modified Gompertz and Chen and Hashimoto kinetic models. The modified Gompertz model was found to be the most reliable, with good predictability.

Known data on the effectiveness of silver nano particles on root canal disinfection

The goal of endodontic treatment is the debridement and removal of the microbial ecosystem associated with the disease process. The need for root canal disinfectants increases especially in those cases where infection is resistant to the regular treatment and the outcome of endodontic therapy is often compromised. Therefore, it is of interest to document the known effectiveness of silver nanoparticle based root canal disinfectants with other root canal disinfectants on microbial load reduction during root canal disinfection. Known data shows that the overall risk of bias for the selected studies was moderate. Silver nanoparticle based root canal disinfectants showed superior reduction of microbial counts in majority of the studies. This data is limited to vitro studies with no clinical information to validate the use of antimicrobial properties of silver nanoparticles used as root canal disinfectant.

Understanding the interaction between triclocarban and denitrifiers

The widespread use of triclocarban (TCC) has led to its substantial release into aquatic environment. As an important microbial community in wastewater treatment, denitrifying cultures likely remove TCC and also may be affected by TCC which has not been revealed. This work therefore aims to add knowledge to these questions. Experimental results showed that 71.2 %-79.4 % of TCC was removed by denitrifying sludge in stable operation when TCC concentration was 1∼20 mg/L. Mass balance analyses revealed that TCC was dominantly removed by adsorption rather than biodegradation, and non-homogeneous multilayer adsorption was responsible for this removal, with hydroxyl groups, amides and polysaccharides acting as the possible adsorption sites. Although the physicochemical properties of denitrifying cultures were unaffected after short-term exposure, long-term exposure to TCC deteriorated the settleability, dewaterability, flocculability and hydrophobicity of denitrifying biomass. It was observed that 20 mg/L TCC decreased denitrification efficiency by 70 % in long-term operation. Mechanism studies revealed that long-term exposure to TCC resulted in the increase of extracellular polymeric substances especially proteins, and the decrease of denitrifiers' activities. High-throughput sequencing revealed that TCC decreased the diversity of microbial community and the abundances of denitrifier genera such as Hyphomicrobium, Paracoccus, Saprospiraceae and unclassified-f-Rhodocyclaceae.

Long-term accumulation, depth distribution, and speciation of silver nanoparticles in biosolids-amended soils

Biosolids can be a source of metals and metal nanoparticles. The objective of this study was to quantify and characterize the accumulation and transport of silver (Ag) in a natural soil that has received agronomically recommended rates of biosolids as fertilizer from 1994 to 2017. Total Ag concentrations were measured in biosolids and soil samples collected from 0 to 10 cm between 1996 and 2017. The depth distribution of Ag in soil to 60-cm depth was measured in 2017. Electron microscopy, in combination with X-ray spectroscopy, and X-ray absorption spectroscopy were used to characterize the Ag. The Ag concentrations in the biosolids-amended soil increased steadily from 1996 until 2007, after which the concentrations leveled off at about 1.25 mg Ag kg^-1 soil. This corresponded with a decrease of Ag concentrations in biosolids over time. The majority of the Ag (82%) was confined to the top 10 cm of the soil, small amounts (14%) were detected at 10-to-20-cm depth, and trace amounts (4%) were detected at 30-to-40-cm depth. The Ag in the biosolids was identified as S-containing nanoparticles (Ag₂ S) with a diameter of 10-12 nm; however, in soil, the Ag concentrations were too low to allow identification of Ag speciation. This study shows that in a real-world field scenario, biosolids applied at agronomic rates represent a long-term, economically viable source of crop nutrients without increasing the concentration of total Ag in soil above a maximum of 1.5 mg Ag kg^-1 . This concentration is below estimated ecotoxicity limits for Ag₂ S in soil.

Insight into formation and biological characteristics of Aspergillus tubingensis-based aerobic granular sludge (AT-AGS) in wastewater treatment

The long start-up time and facile biomass loss of aerobic granular sludge (AGS) impede its application for actual wastewater treatment. The present study investigates a novel assist-aggregation strategy based on Aspergillus tubingensis (AT) mycelium pellets to accelerate sludge granulation, and engineered Fe₃O₄ nanoparticles (NPs) were used to further enhance flocculent sludge (FS) aggregation. The AT mycelium pellets, modified by 0.5 g/L Fe₃O₄@SiO₂-QC NPs (AT-V), had a more compact internal structure than the unmodified group (AT-I). The content of extracellular polymeric substances (EPS) and the zeta potential values were observed to increase from 39.86 mg/gVSS and -9.19 mv for AT-I to 69.64 mg/gVSS and 2.35 mv for AT-V, respectively. In optimized cultivation conditions, the aggregated sludge biomass of AT-V reached 1.54 g/g. An original AT-based AGS (AT-AGS) with a high biological activity (64.45 mgO₂/gVSS·h as specific oxygen uptake rate) and enhanced velocity (58.22 m/h) was developed in only 9 days. The removal efficiencies of total nitrogen (TN) and total phosphorus (TP) of the AT-AGS were 12.24% and 16.29% higher than those of the inoculated FS under high feeding load. Additionally, the analysis of cyclic diguanylate (c-di-GMP) and con-focal microscope images implied that polysaccharide (PS) of EPS played an important role in maintaining the stability of the AT-AGS. Finally, the dominant functional species contributing to sludge aggregation and pollutants removal of the AT-AGS showed a larger richness and diversity than those of the inoculated FS. This study might provide a novel high-efficiency strategy for the fast formation of AGS.