College of Civil Engineering, Zhejiang University of Technology, Hangzhou 310023, China.
School of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215009, China.
J Environ Manage. 2022 Sep 15;318:115646. doi: 10.1016/j.jenvman.2022.115646. Epub 2022 Jul 1.
The dewaterability of waste-activated sludge (WAS) has been extensively examined using zero-valent iron (ZVI)-based advanced oxidation processes (AOPs). However, the high dosage and low utilization efficiencies of ZVI cast doubt on the dependability and viability of ZVI-based AOPs. In this study, we successfully demonstrated pre-magnetization as an efficient, chemical-free, and ecological method for improving the efficiency of sludge dewatering by ZVI/persulfate (PS) process, in which the reduction ratios of capillary suction time (CST) and specific resistance to filtration (SRF) increased by 8.67% and 11.06% under optimal conditions, respectively. The highly active Fe released during ZVI corrosion may be more essential than ZVI itself during PS activation, which could be strengthened by pre-magnetization. Both homogeneous and heterogeneous Fe could react with PS to produce aqueous hydroxyl radicals (∙OH) and sulfate radicals (SO∙) as well as surface-bound ∙OH and SO∙, further decomposing bound-extracellular polymeric substances fractions, broking hydrophilic functional groups and compounds, altering protein secondary structure to expose more hydrophobic sites, and releasing abundant EPS-bound water. Due to the protection of tightly-bound extracellular polymeric substances (TB-EPS) and the competitive oxidation of organics released during the early disintegration stage, radical oxidation primarily occurs at extracellular levels, releasing a bit of intracellular water. Besides, polysaccharides in TB-EPS may function a more significant role in flocculation than proteins, and a porous structure favorable to drainage will be formed after the pre-magnetized ZVI/PS treatment. The cost-benefit analysis further reveals that the Pre-ZVI/PS process presents high reusability and utilization, making it potential for particle application in sludge dewatering.
利用零价铁（ZVI）基高级氧化工艺（AOPs）广泛研究了废活性污泥（WAS）的脱水性能。然而，ZVI 的高剂量和低利用率使人们对 ZVI 基 AOPs 的可靠性和可行性产生了怀疑。在本研究中，我们成功地证明了预磁化是一种有效、无化学试剂且生态友好的方法，可以提高 ZVI/过硫酸盐（PS）工艺的污泥脱水效率，在最佳条件下，毛细吸留时间（CST）和比过滤阻力（SRF）的还原率分别提高了 8.67%和 11.06%。ZVI 腐蚀过程中释放的高活性 Fe 可能比 PS 激活过程中的 ZVI 本身更为重要，而预磁化可以增强这种作用。均相和非均相 Fe 都可以与 PS 反应，生成水相羟基自由基（∙OH）和硫酸根自由基（SO∙）以及表面结合的∙OH 和 SO∙，进一步分解结合的胞外聚合物（EPS），打破亲水性官能团和化合物，改变蛋白质二级结构以暴露出更多的疏水性位点，并释放大量 EPS 结合水。由于紧密结合的胞外聚合物（TB-EPS）的保护和早期解体阶段释放的有机物的竞争氧化，自由基氧化主要在外层发生，仅释放少量胞内水。此外，TB-EPS 中的多糖在絮凝中可能比蛋白质发挥更重要的作用，并且经过预磁化的 ZVI/PS 处理后，将形成有利于排水的多孔结构。成本效益分析进一步表明，Pre-ZVI/PS 工艺具有高的可重复使用性和利用率，使其有可能在污泥脱水领域得到应用。
