College of Environmental Science and Engineering, Hunan University, Changsha, 410082, PR China; Key Laboratory of Environment Biology and Pollution Control, Hunan University, Ministry of Education, Changsha, 410082, PR China.
College of Environmental Science and Engineering, Hunan University, Changsha, 410082, PR China; Key Laboratory of Environment Biology and Pollution Control, Hunan University, Ministry of Education, Changsha, 410082, PR China.
Water Res. 2019 Oct 15;163:114912. doi: 10.1016/j.watres.2019.114912. Epub 2019 Jul 23.
Zero valent iron (ZVI) activating peroxydisulfate (PDS) was demonstrated to be effective in improving the dewaterability of anaerobically digested sludge (ADS). However, details of how ZVI/PDS enhances the dewaterability remain largely unknown. This work therefore aims to reveal the facts of what happen in ZVI/PDS involved ADS systems. Experimental results showed that ZVI/PDS treatment remarkably improved the dewaterability of ADS, with the minimal normalized capillary suction time of 8.6 ± 0.5 s L/g·VSS being obtained at the dosages of 2 g/g TSS ZVI and 0.5 g/g TSS PDS, which was 42.5% of that in the control. In this case, 71.2% ± 1.8% of water content (press filtration) was measured, which was 16.9% lower than that determined in the control. The mechanism investigations showed that ZVI activating PDS produced substantially reactive species, i.e., SO and •OH, and these strong oxidative radicals decreased surface negative charges of ADS flocs, caused disruption of extracellular polymeric substances (EPS) and release of intracellular substances, and changed the secondary structure of proteins. Additionally, the products of ZVI oxidation, i.e., Fe and Fe, were effective flocculants, thus their generation benefited the coagulation of ADS flocs through compressing double electric layers and neutralizing negative charges of sludge colloidal particles. As a result, the flocculability, hydrophobicity, and flowability of ADS were enhanced, but the bound water content, fractal dimension, and viscosity of ADS were decreased, which were responsible for the improvement of dewaterability. Further analyses exhibited that the contributions of these major contributors were different, and their contributions to the dewaterability improvement were in the order of SO > ·OH > Fe/Fe. It was also found that ZVI/PDS treatment enhanced the degradation of recalcitrant organics, inactivation of the fecal coliforms, and mitigation of the toxicity of heavy metals in the dewatered sludge, which were beneficial to its land application.
零价铁（ZVI）激活过二硫酸盐（PDS）已被证明可有效提高厌氧消化污泥（ADS）的脱水性能。然而，ZVI/PDS 提高脱水性能的详细机制在很大程度上仍不清楚。因此，本工作旨在揭示 ZVI/PDS 处理 ADS 系统中发生的情况。实验结果表明，ZVI/PDS 处理可显著提高 ADS 的脱水性能，在 ZVI 和 PDS 的投加量分别为 2 g/g TSS 和 0.5 g/g TSS 时，获得的最小归一化毛细吸水时间为 8.6±0.5 s/L/g·VSS，为对照组的 42.5%。在这种情况下，测量到的水含量（压滤）为 71.2%±1.8%，比对照组低 16.9%。机理研究表明，ZVI 激活 PDS 产生了大量的活性物质，即 SO 和•OH，这些强氧化性自由基降低了 ADS 絮体的表面负电荷，导致细胞外聚合物物质（EPS）的破坏和细胞内物质的释放，并改变了蛋白质的二级结构。此外，ZVI 氧化的产物，即 Fe 和 Fe，是有效的絮凝剂，因此它们的生成有利于通过压缩双层和中和污泥胶体颗粒的负电荷来促进 ADS 絮体的凝聚。结果，ADS 的絮凝性、疏水性和流动性得到了提高，但其结合水含量、分形维数和粘度降低，这是提高脱水性能的原因。进一步的分析表明，这些主要贡献者的贡献不同，它们对脱水性能提高的贡献顺序为 SO＞·OH＞Fe/Fe。还发现，ZVI/PDS 处理增强了难降解有机物的降解、粪大肠菌群的失活以及脱水污泥中重金属毒性的缓解，这有利于其土地应用。
