All-in-one integrated coagulation–flotation–nanofiltration (iCFN) process for complex textile wastewater treatment

Complex industrial wastewater such as textile wastewater containing textile auxiliaries, dyes, and inorganic salts often demands multi-step treatment processes, suffering lengthy route and compromise of separation efficiency. A highly integrated coagulation–flotation–hollow fiber nanofiltration (iCFN) process is developed to cope with the complex wastewater. By synergizing microbubble flotation with coagulant-formed flocs, the iCFN system simultaneously enriches pollutants into the foam phase and enhances nanofiltration performance by improving selectivity and mitigating membrane fouling. The effects of coagulant dosage and dissolved-air pressure on membrane selectivity, fouling dynamics, fouling composition, and foam characteristics were systematically investigated. Pollutant concentrations in the flotation foam markedly increased. Mechanistic analysis based on floc size distribution and zeta potential reveals that tuning floc surface charge governs the partitioning of contaminants between the membrane and foam phases. The normalized flux ( J/J₀ ) rose from 0.5 to 0.8, accompanied by a significant reduction in irreversible fouling resistance. Under optimized conditions, dye rejection increased from <70% to >99% while salt rejection remained low (< 10%), yielding an over 80-fold improvement in salt/dye selectivity. These investigations provide a rational basis for optimizing the iCFN process toward practical application. The developed iCFN process gives insights into the treatment of complex industrial wastewater with high efficiency and shortened process.