Aggregation behavior of polystyrene nanoplastics: Role of surface functional groups and protein and electrolyte variation

Aggregation kinetics of plastics are affected by the surface functional groups and exposure orders (electrolyte and protein) with kinds of mechanisms in aquatic environment. This study investigates the aggregation of polystyrene nanoplastics (PSNPs) with varying surface functional groups in the presence of common electrolytes (NaCl, CaCl2, Na2SO4) and bovine serum albumin (BSA). It also examines the impact of different exposure orders, namely BSA + NaCl (adding them together), BSA → NaCl (adding BSA firstly and then NaCl), and NaCl → BSA (adding NaCl firstly and then BSA), on PSNPs aggregation. The presence of BSA decreased the critical coagulation concentration in NaCl (CCCNa+) of the non-modified PS-Bare from 222.17 to 142.81 mM (35.72%), but increased that of the carboxyl-modified PS-COOH from 157.34 to 160.03 mM (1.71%). This might be ascribed to the thicker absorbed layer of BSA onto the PS-Bare surface, known from Ohshima's soft particle theory. Their aggregation in CaCl2 was both increased because of Ca2+ bridging. Different from the monotonous effects of BSA on PS-Bare and PS-COOH, BSA initially facilitated PS-NH2 aggregation via patch-charge attraction, then inhibited it at higher salt levels through steric repulsion. Furthermore, exposure orders had no significant effect on PS-Bare and PS-COOH, but had a NaCl concentration-dependent impact on PS-NH2. At the low NaCl concentrations (10 and 100 mM), no obvious influence could be observed. While, at 300 mM NaCl, the high concentrations of BSA could not totally stabilize the salt-induced aggregates in NaCl → BSA, but could achieve it in the other two orders. These might be attributed to the electrical double layer compression by NaCl, "patch-charge" force and steric hindrance by BSA. These experimental findings shed light on the potential fate and transport of nanoparticles in aquatic environments.

Adsorption of SARS-CoV-2 onto granular activated carbon (GAC) in wastewater: Implications for improvements in passive sampling

Based on recent studies, passive sampling is a promising method for detecting SARS-CoV-2 in wastewater surveillance (WWS) applications. Passive sampling has many advantages over conventional sampling approaches. However, the potential benefits of passive sampling are also coupled with apparent limitations. We established a passive sampling technique for detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in wastewater using electronegative filters. Though, it was evident that the adsorption capacity of the filters constrained their use. This work intends to demonstrate an optimized passive sampling technique for SARS-CoV-2 in wastewater using granular activated carbon (GAC). Through bench-scale batch-adsorption studies and sewershed deployments, we established the adsorption characteristics of SARS-CoV-2 and two human feacal viruses (PMMoV and CrAssphage) onto GAC. A pseudo-second-order model best-described adsorption kinetics for SARS-CoV-2 in either deionized (DI) water and SARS-CoV-2, CrAssphage, and PMMoV in wastewater. In both laboratory batch-adsorption experiments and in-situ sewershed deployments, the maximum amount of SARS-CoV-2 adsorbed by GAC occurred at ~60 h in wastewater. In wastewater, the maximum adsorption of PMMoV and CrAssphage by GAC occurred at ~60 h. In contrast, the adsorption capacity was reached in DI water seeded with SARS-CoV-2 after ~35 h. The equilibrium assay modeled the maximum adsorption quantity (q_max) in wastewater with spiked SARS-CoV-2 concentrations using a Hybrid Langmuir-Freundlich equation, a q_max of 2.5 × 10⁹ GU/g was calculated. In paired sewershed deployments, it was found that GAC adsorbs SARS-CoV-2 in wastewater more effectively than electronegative filters. Based on the anticipated viral loading in wastewater, bi-weekly sampling intervals with deployments up to ~96 h are highly feasible without reaching adsorption capacity with GAC. GAC offers improved sensitivity and reproducibility to capture SARS-CoV-2 RNA in wastewater, promoting a scalable and convenient alternative for capturing viral pathogens in wastewater.

Phosphate functionalized layered double hydroxides (phos-LDH) for ultrafast and efficient U(VI) uptake from polluted solutions

Elimination of U(VI) from polluted solutions is important for human health and environmental safety. In this work, a relatively low-cost 3D flower-like phosphate-functionalized layered double hydroxides (phos-LDH) was fabricated by a one-pot hydrothermal method. The prepared phos-LDH inherited the structure of 3D flower-like layered double hydroxides (LDH), and had a higher specific surface area (∼203.4 m²⋅g^-1) than that of LDH. The kinetic process indicated that U(VI) adsorption onto phos-LDH achieved equilibrium within 15 min and obeyed general order model. The adsorption isotherms of phos-LDH illustrated that the U(VI) adsorption obeyed Langmuir model, the adsorption capability of phos-LDH can reach 923.1 mg⋅g^-1 at 298 K. The U(VI) adsorption was a spontaneous and endothermic process according to the thermodynamic data. There was the electrostatic attraction between U(VI) and phos-LDH at pH = 5.0. FTIR and XPS analyses educed that the hydroxyl and phosphate groups played a very useful role for the complexation between U(VI) and phos-LDH. In addition, the excellent selective adsorption capability for U(VI) in competitive cation and anion solutions further confirmed the practical application of phos-LDH in real wastewater treatment.

Exogenous Calcium Ions Enhance Patulin Adsorption Capability of Saccharomyces cerevisiae

Patulin contamination is a serious issue that restricts the development of the global fruit processing industry. Yeasts adsorb patulin more effectively than other microbial adsorbents, and this adsorption process depends mainly on the function of the cell wall. The present study examined the effect of exogenous calcium, in concentrations ranging from 0 to 1 mol/L, on Saccharomyces cerevisiae cell wall structure and on patulin adsorption capability; the patulin adsorption capability of yeast was found to strengthen with an increase in exogenous calcium concentrations from 1 × 10^-4 to 1 × 10^-2 mol/L. Moreover, yeast cell wall thickness, β-1,3-glucan content, and the activities of the key catalytic enzymes β-1,3-glucanase and β-1,3-glycosyl transferase were all increased within this range. The results indicate that exogenous calcium activates key enzymes that are crucial for cell wall network formation and patulin adsorption capability.