Ultrasonic-assisted acid cleaning of nanofiltration membranes fouled by inorganic scales in arsenic-rich brackish water

This work studied the feasibility of ultrasonic-assisted (US-assisted) chemical cleaning of nanofiltration (NF) membranes that fouled with inorganic scales. We carried out US-assisted acid cleaning experiments by filter arsenic-rich brackish water to investigate the influencing conditions of US-assisted cleaning technology. We first optimized the proper ultrasonic power intensity (1 W/cm2) in avoiding of membrane damage. US-assisted water flushing can recover the membrane water flux by around 75%, which suggested that the removal of inorganic scales was inadequate. However, US-assisted acid cleaning is efficient for removing the inorganic scales on membrane surface, and cleaning time was significantly shortened by 1/3 to 2/3 when compared with acid cleaning. It is worth to note that US-assisted acid cleaning can be carried out at a lower pH value of 3.0, while traditional acid cleaning usually conducted at pH of 2.0.This would reduce disposal amount of chemical contaminants by up to 90%. Additionally, our investigation suggests the optimal temperature for US-assisted acid cleaning was around 30 °C. This study revealed that the US-assisted acid cleaning method is an effective and environmental-friendly method for NF membrane cleaning.