Ceramic membrane filtration of natural and synthetic fibers in laundry wastewater

Abstract

The clothes washing industry generates large volumes of laundry wastewater that, in principle, can be well treated by ceramic membrane filtration. However, the fouling of ceramic membranes by fibers/fragments from laundry wastewater could result in a decrease of the water permeance across the membranes. In this study, synthetic wastewater containing cotton, linen, polyester, and nylon fibers and real wastewater were characterized and prepared for the filtration experiments, which were conducted at a flux of 70 Lm−2 h−1 using an alumina (Al2O3) membrane and a silicon carbide (SiC)-coated Al2O3 membrane. Results revealed that natural fabrics, particularly cotton and linen, released higher chemical oxygen demand (COD) loads than synthetic fibers when tested at equal mass, which was further supported by microscopic and SEM imaging. The SiC-coated membrane exhibited a relatively lower reversible and irreversible fouling, attributed to its highly negatively charged surface, which repels the fibers that are negatively charged by negatively charged surfactants. The observed fouling among different fibers corresponded well with the COD levels of the synthetic laundry wastewater containing those fibers. Laser direct infrared imaging (LDIR) analysis confirmed that natural fibers dominate in real laundry wastewater. Treating hot laundry wastewater was more effective in reducing both reversible and irreversible membrane fouling than treating it at room temperature. Moreover, the filtration of hot laundry wastewater could facilitate the recovery and reuse of water, surfactants, and heat, offering a sustainable solution to reduce both water consumption and energy costs. This study underscores the importance of paying closer attention to natural fibers, as they tend to cause more severe membrane fouling compared to synthetic fibers in ceramic membrane-based water treatment systems.