微塑料是一种新兴污染物，广泛分布在水体当中，可通过饮用水进入人体并造成危害。混凝是去除微米及纳米级塑料的主要方法之一，但水厂混凝过程中该类污染物的 去除过程、机理研究相对较少。本研究选用单体态和聚合态 Al（AlCl₃ 和 Al₁₃）和 Fe(FeCl₃ 和 Fe₁₃） 为混凝药剂，以在日常生活中的广泛应用微米级和纳米级聚苯乙烯塑 料为典型微塑料污染物， 探究了单体态和聚合态铝基、铁基混凝剂对微纳米塑料的去除效果， 解析了聚合态和单体铝铁絮凝剂对微米级（MP） 和纳米级（NP） 塑料的混凝去除机理。 主要结果如下：

(1) 无论是微米还是纳米塑料污染物， 单体和聚合态铁混凝性能均优于铝基混凝剂。Al₁₃ 和 Fe₁₃ 比 AlCl₃ 和 FeCl₃ 具有更高的去除稳定性和效率。对于 AlCl₃ ; FeCl₃; Al13 和 Fe13 四种混凝剂， 微米塑料的最高去除率分为 88.81%; 95.83%; 91.52%; 95.80%; 而纳米塑料去除率最高分别是 84.20%; 91.47%; 65.74%; 85.28%。 在微米塑性去除上; 四种混凝剂最佳混凝剂投加量均在 70μM/L 和 100μM/L 之间。 AlCl₃; FeCl₃; Al₁₃ 和 Fe₁₃ 对纳米塑料去除的最佳剂量则分别为 70-100μM/L; 100-200μM/L; 70μM/L; 和 500 μM/L。

(2) 与纳米塑料去除相比，溶液 pH 值对微米塑料的去除影响相对较小。 微米塑料在碱性条件（pH=10） 下的去除效果优于酸性条件（pH=4） 。纳米塑料在酸性和碱性条件下的去除率均低于微米塑料。离子强度对纳米塑料的去除有较大影响。 在 6 mM NaCl 溶液条件下， Alm-MP 和 Al13-MP 体系中微米塑料的去除率最高为 80%， Fe_m-MP 和 Fe₁₃-MP 体系中去除率超过 90%。 在 6 mM 和 9 mM NaCl 溶液条件下， AlCl₃和 Al₁₃ 混凝剂对纳米塑料的去除率分别达到 65.41%; 和 73.37%; 而 FeCl₃和 Fe₁₃混凝剂对纳米 塑料的去除率则较低（>50%）。 在颗粒浓度的影响探究中; MP 的去除率在 10 NTU, 15 NTU 和 20 NTU 条件下均高于 NP。 在 10 NTU 溶液体系中， 纳米微塑料去除率效果 较差， Fe₁₃ 不利于 NP 的去除。 高浊度体系中（15 NTU 和 20 NTU）; 各种混凝剂对 MP的去除率相对稳定。 与微米塑料相比; 腐殖酸共存会对纳米塑料的去除产生影响。在腐殖酸共存条件下，随着混凝剂投加量增加， MP的去除率最高达 90%以上; 而纳米塑料的去除率最高达 70%以上。

(3) 微纳米塑料的去除过程可用两种不同的机理进行解释。 AlCl₃ 和 Al₁₃ 混凝剂的阳离子水解产物对带负电的微米塑料和纳米塑料产生电中和与吸附作用; FeCl₃ 和 Fe₁₃则通过快速水解形成无定型氢氧化物沉淀（即‘网捕卷扫’） 完成污染物的去除。研究成果系统阐释了单体态和聚合态铝和铁盐混凝剂对微米塑料和纳米塑料的混凝去除效果; 影响因素和机理; 未来研究可针对微纳米塑料在混凝过程中的行为过程开展深入探究; 并进一步评估其他因子对混凝效率的影响。

Micro – and Nano – plastics are new form of emerging contaminant widely distributed in water and can contact humans via drinking water. Coagulation is one of the main strategy in water treatment processes and the removal behavior of these contaminants in water treatment plant, coagulation is lack of studies. However, Al – and Fe – based salts are commonly used for coagulation via electrostatic interaction between metal ions and micro – and Nano – plastics. Therefore, monomeric and polymeric Al (AlCl₃ and Al₁₃) and Fe (FeCl₃ and Fe₁₃) coagulants were used in this study because of their wide application in water treatment coagulation-flocculation. Poly (methyl methacrylate) micro-plastic and Polystyrene Nanoplastic was used because of its wide usage in daily life applications. This study investigated the removal efficiency and evaluated the mechanism of micro – and Nano – plastic by monomeric and polymeric Al – and Fe – based coagulants.

The major findings of the study are as follows:

(1) To remove micro and Nano-plastic, monomeric and polymeric Fe coagulants outperformed Al-based coagulants. Al₁₃ and Fe₁₃ demonstrated greater removal stability and efficiency than AlCl₃ and FeCl₃. The highest removal efficiency of micro-plastic achieved was 88.81%, 95.83%, 91.52%, 95.80%, and 84.20%, 91.47%, 65.74%, and 85.28% of Nano – plastic AlCl3, FeCl3, Al13, and Fe13, respectively. The optimal coagulant dosage was discovered to be between 70 μM/L and 100 μM/L for micro-plastic removal by the studied coagulants. The optimum dose for Nano-plastic removal was 70-100 μM/L, 100-200 μM, 70 μM/L and 500 μM/L for AlCl₃, FeCl₃, Al₁₃ and Fe₁₃ respectively.

(2) In comparison to Nano-plastic, the pH of the solution had little impact on the removal of micro-plastic. At pH value of 10.0, micro-plastic was removed more effectively  than that at pH value of 4.0. Nano-plastic had a lower removal performance in both acidic and alkaline conditions than micro-plastic. In the presence of NaCl, the effects of ions on the removal of micro-and Nano-plastics were investigated. Ionic strength had a significant impact on Nano-plastic removal. In the presence of both 6 mM and 9 mMNaCl, the highest removal efficiency of micro-plastic was > 80% in Al_m-MP, Al₁₃-MP, Fe_m-MP, Fe₁₃-MP systems, while more than 90 % in Fe_m-MP, Fe₁₃-MP systems in the presence of 6 mM NaCl. In the presence of 6 and 9 mM NaCl, AlCl₃ and Al₁₃ coagulants reached 65.41% and 73.37% for Nano-plastic removal, while FeCl₃ and Fe₁₃ coagulants, on the other hand, have a lower removal performance of Nano plastic (> 50%), respectively. The removal efficiency of micro-plastic was higher under the effect of particle concentration than Nano-plastic in terms of 10 NTU, 15 NTU, and 20 NTU, respectively. At a particle concentration of 10 NTU, the removal of NP was lower, and Fe₁₃ was found to be less efficient in Nano-plastic removal. The removal of MP remained stable under the effect of particle concentrations of 15 NTU and 20 NTU. The addition of HA affected the removal efficiency of Nano-plastic as compared to Micro-plastic. Higher removal > 90 % of micro-plastic was observed at higher coagulant dosage, while above 70 % for Nano-plastic removal.

(3) The removal behaviour of micro – and Nano – plastic is explained in two distinctive mechanisms. Charge neutralization and adsorption of negatively charged micro – and Nano – plastic by cationic hydrolysis products of AlCl₃ and Al₁₃ coagulants and incorporation of impurities in an amorphous hydroxide precipitate (‘sweep flocculation’) was induced by FeCl₃ and Fe₁₃, respectively. 

Overall, this study provided significant insight into removing micro – and Nano –plastic by monomeric and polymeric Al – and Fe – coagulants. Moreover, future studies are warranted to understand micro – and Nano – plastic behaviour during coagulation-flocculation and evaluate the coagulant's efficiency associated with other experimental conditions.