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Cake layer 3D structure regulation to optimize water channels during Al-based coagulation-ultrafiltration process.
Siqi Wu1, Baiwen Ma2, Chengzhi Hu1
1Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Water Research
|April 13, 2023
Summary
Coagulation pretreatment with high aluminum (Al) concentrations improves ultrafiltration (UF) efficiency by creating uniform cake layers and enhancing water transport. This optimization is key for effective water purification.
Area of Science:
- Water Treatment Technologies
- Membrane Science and Engineering
- Colloid and Surface Chemistry
Background:
- Ultrafiltration (UF) efficiency is often limited by cake layer formation and complex water channel characteristics.
- Understanding how coagulation pretreatment affects cake layer structure is crucial for improving UF performance in water purification.
Purpose of the Study:
- To analyze the regulation of cake layer three-dimensional (3D) structures by Al-based coagulation pretreatment at the micro/nanoscale.
- To investigate the impact of coagulant dosage and Al13 concentration on cake layer isotropy and water channel characteristics.
- To elucidate the mechanisms behind coagulation-enhanced UF efficiency.
Main Methods:
- Micro/nanoscale analysis of cake layer 3D structures formed by humic acids and sodium alginate.
- Evaluation of Al-based coagulation pretreatment with varying coagulant dosages and types (AlCl3 at different pH, polyaluminum chloride).
- Molecular dynamics simulations to assess water channel connectivity and transport coefficients within the cake layer.
Main Results:
- Coagulation pretreatment disrupted the sandwich-like cake layer, leading to more uniform foulant distribution and isotropic structures with increasing coagulant dosage.
- High Al13 concentrations (e.g., AlCl3 at pH 6, polyaluminum chloride) promoted a more isotropic foulant-floc layer compared to AlCl3 at pH 8.
- Specific membrane flux increased by 48.4% with high Al13 concentrations, and water transport coefficient improved by up to 54.1% due to enlarged and connected water channels.
Conclusions:
- Facilitating an isotropic foulant-floc layer with highly connected water channels via coagulation pretreatment is essential for optimizing UF efficiency.
- High-Al13-concentration coagulants effectively complex organic foulants, enhancing water transport and UF performance.
- The findings provide insights into coagulation-enhanced UF mechanisms and guide the precise design of pretreatment strategies for efficient water purification.
