Key Laboratory for Environment and Disaster Monitoring and Evaluation, Hubei, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan, 430077, China; Department of Chemical and Environmental Engineering, University of California, Riverside, CA, 92521, USA.
Department of Chemical and Environmental Engineering, University of California, Riverside, CA, 92521, USA.
Water Res. 2019 Aug 1;159:30-37. doi: 10.1016/j.watres.2019.04.051. Epub 2019 May 1.
Nitrilotris-methylenephosphonic acid (NTMP) has been widely used as an antiscalant in reverse osmosis (RO) desalination and other industrial processes to inhibit scaling from calcium and other hardness ions. Removal of NTMP from RO concentrate can induce the precipitation of oversaturated scale-forming substances, enable additional water recovery from RO concentrate, and reduce the risk of eutrophication after brine disposal. This study investigated the kinetics and mechanisms of oxidative degradation of NTMP by UV photolysis of persulfate at 254 nm. Results showed that NTMP was effectively degraded by persulfate photolysis and the reaction followed pseudo first-order kinetics. The degradation of NTMP was favorable at circumneutral pHs but significantly inhibited in highly alkaline conditions (e.g., pH of 11.5), mainly due to the reduced concentration of SO. Using a competition reaction kinetics approach, the second-order rate constants of NTMP with SO and HO were determined to be (2.9 ± 0.6) × 10 Ms and (1.1 ± 0.1) × 10 Ms, respectively. SO had a predominant contribution to NTMP degradation (62%-95%), because the steady-state concentration of SO was 11-54 times higher than that of HO at pHs between 4 and 11.5. NTMP degradation rate increased with an increase in persulfate dosage and a decrease in NTMP concentration. In the real RO concentrate, NTMP degradation rate was impacted by the presence of chloride and bicarbonate. The degradation of NTMP started with the cleavage of C-N bonds, and then generated intermediates including iminodi(methylene)phosphonate, hydroxymethylphosphonic acid and aminotris(methylenephosphonic acid), which were eventually mineralized into ammonia, phosphate and carbon dioxide. This study demonstrated that UV/persulfate is a promising technology to remove phosphonate antiscalants from RO concentrate.
亚甲基膦酸（NTMP）作为一种阻垢剂被广泛应用于反渗透（RO）脱盐和其他工业过程中，以抑制钙和其他硬度离子的结垢。从 RO 浓缩液中去除 NTMP 可以诱导过饱和成垢物质的沉淀，实现 RO 浓缩液的额外水回收，并减少盐水处置后的富营养化风险。本研究采用 254nm 紫外光解过硫酸盐的方法，考察了 NTMP 的氧化降解动力学和机制。结果表明，NTMP 可被过硫酸盐光解有效降解，反应遵循准一级动力学。在中性 pH 值条件下，NTMP 的降解效果良好，但在高碱性条件（例如 pH 值为 11.5）下，降解明显受到抑制，主要是由于 SO 的浓度降低。通过竞争反应动力学方法，确定了 NTMP 与 SO 和 HO 的二级速率常数分别为（2.9±0.6）×10 M s 和（1.1±0.1）×10 M s。SO 对 NTMP 降解的贡献占主导地位（62%-95%），因为在 pH 值为 4-11.5 之间，SO 的稳态浓度比 HO 高 11-54 倍。随着过硫酸盐剂量的增加和 NTMP 浓度的降低，NTMP 的降解速率增加。在实际的 RO 浓缩液中，氯离子和碳酸氢根的存在会影响 NTMP 的降解。NTMP 的降解首先从 C-N 键的断裂开始，然后生成包括亚氨基二（亚甲基）膦酸、羟甲基膦酸和氨三（亚甲基膦酸）在内的中间产物，最终矿化为氨、磷酸盐和二氧化碳。本研究表明，UV/过硫酸盐是一种从 RO 浓缩液中去除膦酸盐阻垢剂的有前途的技术。
