Integrated Fe-based floc-membrane process for alleviating ultrafiltration membrane fouling by humic acid and reservoir water

Integrated ultrafiltration (UF) membranes are a promising technology in water treatment. However, commonly used granular adsorbents are only injected into the membrane tank once, which not only results in serious membrane surface damage, but also severe membrane fouling due to the low utilization efficiency of adsorbents over time. To overcome these disadvantages, loose Fe-based flocs, which display better sludge discharge than Al-based flocs, were investigated to improve integrated UF membrane performance under different injection frequencies with humic acid (HA) and reservoir water. Results showed that multiple dynamic floc layers were formed with batch injections and a critical injection frequency existed. When the injection frequency was too low, membrane fouling was induced by the formation of a dense HA cake layer on the floc surface. In contrast, it was alleviated when the HA molecules entering the membrane tank did not exceed the adsorption ability of the flocs injected each time. HA removal efficiency also increased with increasing injection frequency due to the improvement of floc utilization efficiency. With changing floc characteristics, better membrane performance was induced, especially under acidic conditions, which was ascribed to the higher positive surface charge and specific surface area of flocs. Raw water experiments further confirmed the excellent membrane performance based on high pollutant removal efficiency and minor membrane fouling. According to the outstanding membrane performance, this novel integrated floc-membrane process has great application potential in water treatment.