Metal-based nanoparticles (NPs) can be found in wastewater streams, which are significant pathways for the release of NPs to the environment. Determination of the NPs concentration in wastewater streams is important for performing appropriate ecotoxicological evaluations. The aim of this work was to determine the incidence of NPs from 13 different elements throughout the wastewater treatment process by using single particle inductively coupled plasma mass spectrometry (spICP-MS). The incidence was determined in samples of the influent, post-primary treatment and effluent of the activated sludge process, as well as in the reclaimed water of a full-scale wastewater treatment plant (WWTP). In addition, concentration of NPs was determined in the waste activated sludge and in the anaerobic digester. The concentration of metal-based NPs in the influent wastewater were between 1,600 and 10,700 ng/L for elements such as Ti, Fe, Ce, Mg, Zn and Cu, while that for Ni, Al, Ag, Au, Co and Cd was below 100 ng/L. Concentrations in reclaimed water ranged between 0.6 and 721 ng/L, ranked as Mg > Ti > Fe > Cu > Ni > Ce > Zn > Mn > Al  > Co > Ag > Cd  > Au. Results indicated that the activated sludge process and reclaimed water system removed 84-99% of natural and engineered metal-based NPs from influent to reclaimed water, except for Mg, Ni and Cd where the removal ranged from 70 to 78%. The highest concentrations of NPs were found in the waste activated sludge and anaerobic sludge, ranging from 0.5 to 39,900 ng/L. The size distribution of NPs differed in different wastewater streams within the WWTP, resulting in smaller particles in the effluent (20-180 nm) than in the influent (23-233 nm) for most elements. Conversely, NPs were notably larger in the waste activated sludge samples than in the anaerobic sludge or wastewater, since conditions in the secondary treatment lead to precipitation of several metal-based NPs. The incidence of metal-based NPs from 13 elements in wastewater decreased significatively after the conventional wastewater treatment train. However, anaerobic digesters store high NPs concentrations. Hence, the disposal of sludge needs to take this into account to evaluate the risk of the release of NPs to the environment.

The concentration of silver nanoparticles (nano-Ag) in aqueous media influences the kinetics of ion release; hence, the transformation and stability of nano-Ag are also influenced. The stability, dissolution and further transformation of nano-Ag in aqueous media at predicted environmental concentrations (PECs) ≤ μg/L may differ from that reported at higher concentrations. Analytical techniques characterizing nanoparticles (NPs) at μg/L have advantages and limitations, including an inherent bias based on theoretical and analytical considerations, as well as the matrix effects. In this work, we applied nanoparticle tracking analysis (NTA), single particle ICP-MS (sp-ICP-MS), and localized surface plasmon resonance (LSPR) analysis to study the stability and dissolution of nano-Ag with different nominal sizes (20, 40, 80 and 100 nm) at PECs in synthetic wastewater (SWW). The influence of the main wastewater constituents, such as organic matter, Cl^-, S^2-, PO₄^3- and NH₄⁺, on the stability and dissolution of nano-Ag (40 nm) at PECs was also determined. Diagrams of the predominant species of silver exposed to major ligands were generated using MINTEQ. After 5 h in SWW, 20 nm nano-Ag dissolved 19.27% and 40 nm nano-Ag dissolved 14.8%. Aggregates of Ag particles were clearly noted for 80 and 100 nm nano-Ag after 5 h of exposure to SWW. Aggregates size also ranged very similar for both techniques, NTA and sp-ICP-MS, 29-211 nm and 38-241 for NTA and 48-210 and 50-220 nm, for sp-ICP-MS, respectively. Monodispersed size distribution (22-85 nm) and low dissolution (up to 5.1%) of nano-Ag at PECs were observed in presence of organic matter (5-800 μg/L) and PO₄^3- (9.5-47.5 mg/L), while precipitation and higher dissolution (up to 74.9%) were observed in media containing either Cl^- (0.07-10.64 g/L), S^2- (0.32-32.1 mg/L) or NH₄⁺ (36-90 mg/L), respectively. Speciation diagrams predict the formation of Ag₂S_(s) and AgCl_(s), and soluble species such as AgCl_x^(x-1)-, AgNH₃⁺ and Ag(NH₃)²⁺ when Ag⁺ at PECs in wastewater. The NTA and sp-ICP-MS were suitable techniques for sizing nano-Ag in wastewater at PECs at experimented nominal sizes. sp-ICP-MS was also useful to quantify the coexistence of Ag⁺ and nano-Ag. The LSPR analysis served to determine the relative persistence of original nano-Ag at PECs in the wastewater during the first 5 h after spiking.

Influence of nanoceria in anaerobic digestion of WAS.

While the predicted or observed concentrations of Ag NPs in wastewater treatment plants (WWTPs) have ranged from μg/L to ng/L, there is still uncertainty with regards to the realistic concentration range of Ag NPs in WWTPs. In addition, the persistence, removal, and size of Ag NPs throughout WWTP process is also not well investigated, particularly in real operating conditions. In this study, the incidence and persistence of Ag NPs in the wastewater process were studied by using single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The incidence of Ag NPs was determined in samples collected at the influent and effluent of the conventional process, as well as reclaimed and backwash waters of the ultrafiltration (UF) system in a WWTP (Santa Barbara, CA), showing a concentration of 13.5, 3.2, 0.5 and 9.8 ng/L, respectively, with relative standard deviations (RSDs) < 5%. Total Ag concentration (Ag NP and Ag⁺) ranged from 40 to 70 ng/L, in line with lower predicted values. Most of the Ag NPs detected were below 100 nm, with a few above 100 nm in the conventional effluent. Biological and physical processes in the secondary treatment removed 76.3% of the colloidal Ag fraction, while with the tertiary treatment (UF) the WWTP achieved a removal of 96.3% of the colloidal fraction. Persistence of Ag NPs in various water matrixes, including a synthetic wastewater (SWW), was determined by spiking 300 ng/L of Ag NPs (40 nm) and monitoring the concentrations and size change for 15 days. The persistence of Ag NPs in suspension was Influent > Effluent > Reclaimed > SWW. Partial dissolution of NPs in all waters was observed from time 0 h. Although the current concentrations in the outlet flows from WWTP (effluent and reclaimed waters) were low, the presence of small and stable Ag NPs may raise ecotoxicological concerns via bioaccumulation.

This review provides a current opinion on the most recent works that have been published toward the application of electrochemical advance oxidation processes (EAOPs) for the degradation of pharmaceutical and personal care products (PPCPs) in water streams. Advances in the application of anodic oxidation (AO)- and electro-Fenton (EF)-based processes are reported, including operational conditions, electrode performance, and removal. Although AO- and EF-based processes can easily reach 100% removal of PPCPs, mineralization is desirable to avoid the generation of potential toxic byproducts. The following section exploring some techno-economic aspects of the application of EAOPs is based on electrode selection, operational costs as well as their use as cotreatments, and their synergistic effects. Finally, this short review ends with perspectives about the emerging topics that are faced by these technologies applied for the degradation of PPCPs in research and practice.

Maize (Zea mays) is a staple crop globally, and the application of nanotechnology holds great promise in enhancing maize growth, resilience, and yield. While various studies have reported the effects of several metallic, metalloid, and non-metallic-based nanomaterials (NMs) in maize, the full extent of their benefits, risks, and influencing factors remains to be fully understood. This systematic review of the last decade adhered to the PRISMA methodology. It examined 74 cutting-edge studies on the impact of NMs used as nanofertilizers for germination, plant growth, and abiotic stress alleviation, as nanopesticides, and the risks of NMs as toxic agents. We observed that NM-effects can be limited by influencing factors such as size, chemical composition, oxidation state, shape, surface chemistry, delivery system, exposure time, and concentration. Concentration might interplay with the exposure time, which is a crucial factor influencing the hormetic behavior of NMs in maize. NMs based on Zn, Ti, Ag, Fe, Mg, Se, and HA enhance imbibition and nutrient uptake, promoting Reactive Oxygen Species (ROS) production, and stimulating metabolic activity. In growth, NMs can up-regulate genes associated with essential metabolic processes, and the mitigation of abiotic and biotic stress has also been observed. This provides crucial insights into the role of nanotechnology in optimizing maize production. However, it also highlights the need for further research to fully understand this role, identify research gaps, and suggest directions for future studies in this rapidly evolving field.

Wastewater-based epidemiology offers a time- and cost-effective way to monitor SARS-CoV-2 spread in communities and therefore represents a complement to clinical testing. WBE applicability has been demonstrated in a number of cases over short-term periods as a method for tracking the prevalence of SARS-CoV-2 and an early-warning tool for predicting outbreaks in the population. This study reports SARS-CoV-2 viral loads from wastewater treatment plants (WWTPs) and hospitals over a 6-month period (June to December 2020). Results show that the overall range of viral load in positive tested samples was between 1.2 × 10³ and 3.5 × 10⁶ gene copies/l, unveiling that secondary-treated wastewaters mirrored the viral load of influents. The interpretation suggests that the viral titers found in three out of four WWTPs were associated to clinical COVID-19 surveillance indicators preceding 2-7 days the rise of reported clinical cases. The median wastewater detection rate of SARS-CoV-2 was one out of 14,300 reported new cases. Preliminary model estimates of prevalence ranged from 0.02 to 4.6% for the studied period. This comprehensive statistical and epidemiological analysis demonstrates that the applied wastewater-based approach to COVID-19 surveillance is in general consistent and feasible, although there is room for improvements.