Control of ultrafiltration membrane fouling during the recycling of sludge water based on Fe(II)-activated peroxymonosulfate pretreatment

Abstract

Sludge water was recycled using an ultrafiltration (UF) system. In order to control membrane fouling, three typical Fe(II)-activated peroxymonosulfate (PMS) processes: Fe(II)/PMS-UF (FPUF), 1/4Fe(II) × 4/PMS-UF (F⁴PUF) (adding Fe(II) in small increments four times), and Fe(II)/thiosulfate/PMS-UF (FTPUF) (adding Fe(II) after complexing with thiosulfate), were employed as UF pretreatments. Their mitigating effects of UF membrane fouling caused by sludge water are systematically discussed and compared. The results showed that FTPUF system had the best membrane fouling control effect. The F⁴PUF system was more suitable for long-term operation than FPUF due to its lower irreversible resistance. The pretreatments can effectively remove contaminants from sludge water through the dual effects of coagulation and oxidation. Specifically, coagulation removed most of the particles and macromolecular organic matter. Oxidation effectively decomposed fluorescent and UV-absorbing organic components, and reduced bacterial proliferation on the membrane surface. Concentrations of 2-methylisoborneol and geosmin in FPUF permeate were dramatically increased, which was mainly due to the rupture of algal cells in sludge water. Both adhesion force date and extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the pretreatments significantly reduced interactions between the membrane-organic colloid and cake layer-organic colloid. In contrast, the stronger membrane-organic colloid interaction was a major contributor to membrane fouling. The mitigation of irreversible fouling was mainly attributed to the fact that oxidation enhanced the hydrophilicity of the organic colloids, thereby reducing the Lewis acid-base interaction energy. The results demonstrated the potential application of different Fe(II)-activated PMS processes as pretreatments for membrane fouling control during sludge water treatment.

Keywords: Fe(II)-activated peroxymonosulfate; Membrane fouling; Sludge water; Thiosulfate; Ultrafiltration.