Many types of nanoparticles (NPs) have been reported to be toxic to organisms. Wastewater treatment plants are among the important pathways for the migration and transformation of NPs in the environment. Based on a summary of the toxicity of NPs to microorganisms, this review discusses the advances in the fate and transformation of NPs in wastewater treatment plants (WWTPs) and the impacts of NPs on the biological treatment of wastewater. These NPs primarily include Ag NPs, Cu NPs, CuO NPs, ZnO NPs, TiO₂ NPs, Al₂O₃ NPs, SiO₂ NPs, carbon nanotubes (CNTs) and magnetic NPs. This review observes that the different properties of these NPs result in significant differences in the fate, transformation, antimicrobial activities and effects on biological wastewater treatment. Although many studies have been undertaken in this field, more studies are needed to address the adverse effects of NPs on organic and nutrient removal, as well as their toxic mechanisms.

Herein, a chitosan film (CS) was modified using 2,3-epoxy-propyl trimethyl ammonium chloride (GTA) to flocculate granular pollutants in potato starch wastewater, aiming at the deficiencies of poor water solubility and weak electropositivity of the chitosan film. By examining the degree of substitution of chitosan film amino under different factors and different levels and response surface optimization tests, the optimum preparation conditions of chitosan film quaternary ammonium salt (HTCC) were obtained. Using scanning electron microscopy (SEM), Fourier infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and ¹H-nuclear magnetic spectroscopy, the nucleophilic substitution reaction of the GTA molecule with the hydrogen atoms in the chitosan film amino group successfully improved the water solubility and electropositivity of the chitosan film. HTCC was used to treat potato starch wastewater, and the optimal flocculation conditions were obtained. The flocculation product was recovered, and the composition analysis of the flocculation product demonstrated that HTCC-potato protein flocculation precipitate was rich in high protein, which is a good choice of feed and can realize sustainable utilization of resources.

This study addresses the challenge of chitosan (CS) being difficult to dissolve in water due to its highly ordered crystalline structure. Chitosan is modified with chloroacetic acid to reduce its crystallinity and enhance its water solubility. Through single-factor experiments, the optimal conditions for preparing carboxymethyl chitosan film (CMCS) were determined: under conditions of 50 °C, a cellulose substrate (CS) concentration of 18.75 g/L, a NaOH concentration of 112.5 g/L, and a chloroacetic acid concentration of 18.75 g/L, the reaction proceeded for 5 h. Under these conditions, the resulting carboxymethyl chitosan film exhibited the best flocculation effect, forming chitosan films in water that had flocculation activity toward mung bean starch protein wastewater. The successful introduction of carboxyl groups at the N and O positions of the chitosan molecular chain, which reduced the crystallinity of chitosan and enhanced its water solubility, was confirmed through analysis using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The prepared carboxymethyl chitosan film (CMCS) was applied in the flocculation recovery of protein. Through single-factor and response surface experiments, the optimal process conditions for flocculating and recovering protein with CMCS were determined: a CMCS dosage of 1.1 g/L, a reaction time of 39.6 min, a reaction temperature of 42.7 °C, and a pH of 5.2. Under these conditions, the protein recovery rate reached 56.97%. The composition and amino acid profile of the flocculated product were analyzed, revealing that the mung bean protein flocculated product contained 62.33% crude protein. The total essential amino acids (EAAs) accounted for 52.91%, non-essential amino acids (NEAAs) for 47.09%, hydrophobic amino acids for 39.56%, and hydrophilic amino acids for 12.67%. The ratio of aromatic to branched-chain amino acids was 0.31, and the ratio of basic to acidic amino acids was 1.68. These findings indicate that the recovered product has high surface activity and good protein stability, foaming ability, and emulsifying properties.

The treatment of polluted water and sediment often costs too much and has little benefit. In this study, we proposed a novel design using dredged sediment, shrub willow (Salix spp.) and recirculating hand pumps for the restoration of polluted river water in Changchun city, China. Sediment was filled as a matrix for plant growth, shrub willow was transplanted for the absorption of nutrients, and ten hand-pumped water wells were built for recycling the polluted water. During the 5-month experimental period, the shrub willow growth and nutrient contents, sediment nutrient concentration and water quality were measured. The results showed that this pond system could effectively decrease the sediment pollutant levels, and its removal efficiencies of organic matter (OM), total nitrogen (TN) and total phosphorus (TP) could respectively reach as high as 11%, 10% and 26%. The dissolved oxygen (DO) content increased by more than 90% in August, and the chemical oxygen demand (COD) and total nitrogen (TN) content decreased by 44.93% and 19.82%, respectively. This means that the treatment pond could efficiently work toward the purification of polluted river water. The benefits and feasibility of this system application were also analyzed, and we found that it could be widely used for the treatment of polluted water and sediment in urban areas.