Enhanced Cloth Washing by Combining Alkaline Electrolyzed Water and Ultra-Fine Bubble Water Under Alternating-Flow Conditions

The development of detergent-free washing technologies has become increasingly important due to growing environmental concerns associated with synthetic surfactants. This study investigated the washing performance obtained by combining alkaline electrolyzed water (AlEW) with ultra-fine bubble (UFB) water within a two-stage washing process consisting of immersion pre-washing and alternating-flow main washing. During immersion washing, AlEW exhibited a pronounced cleaning effect, attributable to alkaline hydrolysis and saponification reactions as well as enhanced electrostatic repulsion between soils and fibers. In contrast, acidic electrolyzed water caused coagulation of proteinaceous soils and did not facilitate subsequent cleaning. When AlEW pre-washing was followed by alternating-flow washing using UFB water, a significant improvement in washing rate was obtained compared with deionized water. This enhancement was interpreted as the result of combined effects among chemical soil weakening, strong mechanical forces generated by alternating flow, and UFB-related physicochemical processes. Increasing the immersion time in AlEW further improved washing performance, demonstrating the time-dependent progression of the chemical pre-treatment. Overall, the optimal washing sequence consisted of AlEW immersion followed by UFB-assisted alternating-flow washing, which yielded the highest washing efficiency among all tested conditions. These findings highlight the potential of integrating electrolyzed water and ultra-fine bubble technologies to develop high-performance, low-environmental-load, and detergent-free washing systems suitable for developing environmentally benign washing approaches.