Encapsulating solid carbon source and zero-valent iron (ZVI) within hydrogel can prevent direct contact with groundwater, thereby extending the lifespan of their released active substrates. It is currently unclear whether solid carbon source and ZVI will mutually influence each other’s active substrate release process and the corresponding denitrification patterns, necessitating further investigation. This study synthesized hydrogel encapsulates with different weight ratios of micron-sized zero-valent iron (mZVI, as ZVI) and polyhydroxybutyrate (PHB, as solid carbon source). The aim was to investigate the influence of PHB on the release of dissolved iron from mZVI and denitrification mechanism. Results indicate that PHB was consumed at a higher rate than mZVI, and the pores remaining after PHB consumption exposed more active sites of mZVI. Meanwhile, PHB increased the porosity of the hydrogel, also exposing more active sites of mZVI. These exposed active sites led to a higher release of dissolved iron. Furthermore, PHB enhanced the rate of microbial corrosion of mZVI, leading to an increased release of dissolved iron. Higher PHB content in the hydrogel reduces the released dissolved iron oxidation, 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 laying the foundation for its further practical application in groundwater.

中文翻译：

---

水凝胶固定铁/固体碳源增强地下水反硝化：对反硝化和底物释放性能的影响

将固体碳源和零价铁（ZVI）封装在水凝胶中可以防止与地下水直接接触，从而延长其释放的活性底物的寿命。目前尚不清楚固体碳源和ZVI是否会相互影响彼此的活性底物释放过程和相应的反硝化模式，需要进一步研究。本研究合成了具有不同重量比的微米级零价铁（mZVI，作为ZVI）和聚羟基丁酸酯（PHB，作为固体碳源）的水凝胶胶囊。目的是研究PHB对mZVI释放溶解铁的影响和反硝化机制。结果表明，PHB 的消耗速度高于 mZVI，并且 PHB 消耗后剩余的孔暴露出更多的 mZVI 活性位点。同时，PHB增加了水凝胶的孔隙率，也暴露了更多的mZVI活性位点。这些暴露的活性位点导致溶解铁的释放量更高。此外，PHB 提高了 mZVI 的微生物腐蚀速率，导致溶解铁的释放增加。水凝胶中较高的 PHB 含量减少了释放的溶解铁氧化，从而形成以异养微生物为主的微生物群落。相反，较低的 PHB 含量会导致 Fe(II) 显着氧化，并导致微生物群落中混合营养微生物相对丰富。还检测到具有铁还原潜力的微生物。该研究为基于水凝胶固定化的混合营养盐反硝化的精确控制提供了理论支撑，并为其进一步在地下水中的实际应用奠定了基础。