Distribution, mobilization, risk assessment and source identification of heavy metals and nutrients in surface sediments of three urban-rural rivers after long-term water pollution treatment.

Sediments are critical pollution carriers in urban-rural rivers, which can threaten the water quality of the river and downstream lakes for a long time. However, it is still not clear whether conventional water pollution treatments could abate sediment pollution or not. In this study, heavy metals (HMs) and nutrient salts in the surface sediments and overlying water were investigated after decades' water pollution treatment in three urban-rural rivers. HM speciation was determined by the sequential extraction; diffusion fluxes were estimated using Fick's first law; HM ecological risk and nutrient pollution were evaluated; and pollution sources were identified by statistical analysis and GIS. The results showed that the HMs and nutrients were extremely serious in the urban regions. The accumulation level of Pb, Cu and Cd in the sediments of the three rivers were all much higher than the soil background value, and the labile fractions accounted for high proportions (57 % for Pb, 55 % for Cu and 43 % for Cd), which could be easily eluate from the sediments and caused hazards to the aquatic environment. The sediment diffusion fluxes of HMs and ammonia nitrogen were mostly positive, which indicated these sites currently released these pollutants from sediment to overlying water. Cd, Pb, Cu and Cr may mainly originate from industrial discharge and domestic sewage, while Cr was also greatly affected by crustal weathering; nutrient pollution may originate from agricultural activities and domestic sewage. Our study demonstrated that after decades' conventional water treatment in these rivers, the sediment pollution was still in a serious level with high ecological risk, and Cd was the dominant pollutant. At present, the external point source pollution has been effectively controlled, thus, the in-depth understanding of the sediment pollution characteristics after long-term water treatment could provide a scientific basis for the accurate elimination of river pollution.

One-Step Fabrication of Coconut-Like Capsules via Competitive Reactions at an All-Aqueous Interface for Enzyme Immobilization.

A concept of interfacial competitive reaction between biomineralization and alginate gelation at an all-aqueous single-emulsion droplet interface to prepare robust coconut-like capsules (inner hard wall and outer soft wall) is developed. The concept is further applied for enzyme immobilization with high encapsulation efficiency, enzyme loading, mass transfer coefficient, and recyclability. The thickness and swelling properties of the shell are simply tunable by a competitive reaction. Our platform may open a green, facile, and efficient way to prepare organic-inorganic hybrid sustainable materials with tailored compositions and structures.

Monodisperse Alginate Microcapsules with Spatially Confined Bioactive Molecules via Microfluid-Generated W/W/O Emulsions.

A simple process is developed for the one-step preparation of dual-compartment alginate microcapsules with controlled size and structure from microfluid-generated water-in-water-in-oil (W/W/O) emulsion droplet. Unlike other methods that rely on transient W/W/O emulsion droplet, we introduce an aqueous two-phase system (ATPS) to form a stable W/W/O emulsion droplet as a template for preparing dual-compartment alginate microcapsules. Two different bioactive molecules are able to be spatially confined encapsulated in the shell and core of alginate microcapsules due to the partitioning effect of ATPS and the high viscosity of alginate solution. Moreover, an enzyme cascade reaction with a spatial confined glucose oxidase and horseradish peroxidase in the shell and core of alginate microcapsules confirms its excellent biocompatibility and high activity. This method provides a green platform for enzyme-catalyzed tandem reactions and controlled sequential release of multiple drugs based on alginate microcapsules.

Aqueous Two-Phase Droplet-Templated Colloidosomes Composed of Self-Formed Particles via Spatial Confined Biomineralization.

A facile and green approach is developed for fabricating colloidosomes with well-controlled size and structure from the microfluidic-generated aqueous two-phase system (ATPS) emulsion droplet. Unlike other methods that rely on self-assembly of externally added colloidal particles at the emulsion interface, urease-mediated biomineralization induced by "drainage" is introduced to form CaCO3 particles at the alginate emulsion interface for preparing Ca-alg@CaCO3 colloidosomes. Two types of bioactive molecules (bovine serum albumin and catalase) can be encapsulated with high efficiency (>85%) because of the partitioning effect of the ATPS and high viscosity of alginate solution. The encapsulated bioactive molecules can be controllably released by regulating the compactness of colloidosomes. Moreover, after being freeze-dried or dried at 37 °C, the activity of catalase in colloidosomes is obviously higher than that in alginate hydrogels, which confirms that the Ca-alg@CaCO3 structure has strong protection for inclusions. We believe that the biocompatible and controllable Ca-alg@CaCO3 colloidosomes possess great potential applications in bioencapsulation for foods, daily chemicals, and synthetic protocell formation.