Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong 999066, China.
Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong 999066, China.
J Environ Sci (China). 2022 Jul;117:119-128. doi: 10.1016/j.jes.2022.03.022. Epub 2022 Mar 25.
Drinking water utilities are interested in upgrading their treatment facilities to enhance micropollutant removal and byproduct control. Pre-oxidation by chlorine dioxide (ClO) followed by coagulation-flocculation-sedimentation and advanced oxidation processes (AOPs) is one of the promising solutions. However, the chlorite (ClO) formed from the ClO pre-oxidation stage cannot be removed by the conventional coagulation process using aluminum sulfate. ClO negatively affects the post-UV/chlorine process due to its strong radical scavenging effect, and it also enhances the formation of chlorate (ClO). In this study, dosing micromolar-level ferrous iron (Fe(II)) into aluminum-based coagulants was proposed to eliminate the ClO generated from ClO pre-oxidation and benefit the post-UV/chlorine process in radical production and ClO reduction. Results showed that the addition of 52.1-µmol/L FeSO effectively eliminated the ClO generated from the pre-oxidation using 1.0 mg/L (14.8 µmol/L) of ClO. Reduction of ClO increased the degradation rate constant of a model micropollutant (carbamazepine) by 55.0% in the post-UV/chlorine process. The enhanced degradation was verified to be attributed to the increased steady-state concentrations of HO and ClO by Fe(II) addition. Moreover, Fe(II) addition also decreased the ClO formation by 53.8% in the UV/chlorine process and its impact on the formation of chloro-organic byproducts was rather minor. The findings demonstrated a promising strategy to improve the drinking water quality and safety by adding low-level Fe(II) in coagulation in an advanced drinking water treatment train.
饮用水处理厂有兴趣升级其处理设施，以增强去除微污染物和控制副产物的能力。二氧化氯（ClO）预氧化，然后进行混凝-絮凝-沉淀和高级氧化工艺（AOPs）是一种很有前途的解决方案。然而，ClO 预氧化阶段形成的亚氯酸盐（ClO）不能通过使用硫酸铝的常规混凝工艺去除。ClO 会通过其强自由基清除作用对后续的 UV/氯工艺产生负面影响，并且还会增强氯酸盐（ClO）的形成。在这项研究中，提出向基于铝的混凝剂中投加亚微米级的二价铁（Fe(II)），以去除 ClO 预氧化产生的 ClO，并有益于后续的 UV/氯工艺中自由基的产生和 ClO 的还原。结果表明，添加 52.1µmol/L 的 FeSO 可以有效地消除 1.0mg/L（14.8µmol/L）ClO 预氧化产生的 ClO。ClO 的还原将模型微污染物（卡马西平）在后 UV/氯工艺中的降解速率常数提高了 55.0%。通过添加 Fe(II) 增强降解的效果归因于 Fe(II) 增加了 HO 和 ClO 的稳态浓度。此外，Fe(II) 的添加还降低了 UV/氯工艺中 53.8%的 ClO 形成，并且对氯代有机副产物的形成影响较小。这些发现证明了在先进饮用水处理过程中，在混凝过程中添加低浓度的 Fe(II)是提高饮用水质量和安全性的一种很有前途的策略。
