Comparison between integrated MIEX/UF and PAC/UF in long-term irreversible membrane fouling reduction: Effectiveness and mechanism analysis

Abstract

In an integrated adsorption/ultrafiltration process, the choice of adsorbent is key as it affects the effluent water quality in addition to providing membrane fouling control. Magnetic ion-exchange resin (MIEX) and powdered activated carbon (PAC), two of the most used adsorbents in water treatment processes, have similar organic matter removal abilities. However, the corresponding integrated processes exhibited significant differences in terms of irreversible membrane fouling mitigation. Long-term filtration experimental results suggested that the chemical cleaning interval of the MIEX/UF process was 134% longer than that of the PAC/UF process. In addition, MIEX/UF had a 28.8% reduction for the chemically irreversible fouling rate compared to that of PAC/UF. Hydraulically irreversible fouling was effectively alleviated in the MIEX/UF process throughout long-term operation, whereas fouling was exacerbated in the PAC/UF process under the condition of timed chemical cleaning. Further analysis indicated that in the PAC/UF process, irreversible fouling control depended on adsorption; however, fouling mitigation in the MIEX/UF process mainly relied on the enhancement of backwashing by the MIEX dynamic layer. The significant difference in the interfacial forces between the MIEX-pollutants and PAC-pollutants was the fundamental cause for this phenomenon. Therefore, the mitigation of membrane fouling in an integrated adsorption/UF process depends more on the adhesion force between the adsorbent and pollutants than on the adsorption capacity of the adsorbent.