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Encapsulating a solid carbon source and zero-valent iron (ZVI) within a hydrogel can prevent direct contact with groundwater, thereby extending the lifespan of their released active substrates. It is currently unclear whether the solid carbon source and ZVI will mutually influence each other's active substrate release process and the corresponding denitrification patterns, necessitating further investigation. In this study a hydrogel encapsulating different weight ratios of micron-sized zero-valent iron (mZVI, as ZVI) and polyhydroxybutyrate (PHB, as a solid carbon source) was synthesized. The aim was to investigate the influence of PHB on the release of dissolved iron from mZVI and denitrification mechanism. Results indicated that PHB was consumed at a higher rate than mZVI, and more mZVI active sites could be exposed after PHB consumption. Meanwhile, PHB increased the porosity of the hydrogel, allowing more active sites of mZVI to be exposed and thus releasing more dissolved iron. Furthermore, PHB enhanced the rate of microbial corrosion of mZVI, which further increased the release of dissolved iron. Higher PHB content in the hydrogel reduced the oxidation of the released dissolved iron, resulting in a microbial community dominated by heterotrophic microorganisms. Conversely, lower PHB content led to significant Fe(II) oxidation and a considerable relative abundance of mixotrophic microorganisms in the microbial community. Microorganisms with iron reduction potential were also detected. This study provides theoretical support for the precise control of mixed nutrient denitrification based on hydrogel immobilization and lays the foundation for its further practical application in groundwater. [ABSTRACT FROM AUTHOR]

Cationic silica scale inhibitors are widely used, but are prone to precipitation and exhibit poor performance in geothermal systems. In this study, the cationic polymer polyethyleneimine ethoxylate (PEIE) was first found to have high silica scale inhibition efficiency. Three anionic polymers were added separately to PEIE solutions to alleviate the precipitation and scaling. The inhibition effect of PEIE alone and PEIE with anionic polymers were measured at 40°C without salt and 136.7°C with salt. Molecular dynamics simulation was used to investigate the inhibition mechanism. The results showed that PEIE exhibited good inhibition efficiency of 62% at 40°C without salt and 48% at 136.7°C with salt, while the addition of the anionic polymer acrylic acid‐2‐acrylamide‐2‐methylpropanesulfonic acid (AA/AMPS) to PEIE further improved to 71% and 62%. Compared with commercial inhibitors, the PEIE + AA/AMPS enhanced at least 15% scale inhibition efficiency. This is because the addition of AA/AMPS: (1) enhances the attraction of PEIE to silicic acid and inhibits the silicic acid condensation process; (2) chelates metal ions that promote condensation; and (3) enhances dispersion ability, stabilizing the colloid formed by PEIE and silicic acid. This study provides a promising new inhibitor and efficient strategy for inhibiting silica scale in geothermal systems. [ABSTRACT FROM AUTHOR]