[Organic Matter Removal and Membrane Fouling Control of Secondary Effluents Using a Combined Nanofiltration Process]

For cities and various types of constructions, the recycling and reuse of wastewater can be an important and unconventional water source. However, water quality must meet relevant standards, especially with respect to organic matter. In this study, secondary effluents from a large sewage plant in a northern city in China were analyzed. The removal efficiencies for soluble organic matter and the characteristics of nanofiltration (NF) membrane fouling of UV-TiO₂ photocatalysis and GAC adsorption were studied, and a combined UV-TiO₂/GAC/NF process was developed. The removal of organic matter and the controlling effect of membrane fouling in the combined UV-TiO₂/GAC/NF process was evaluated. The types and molecular weights of organic matter, which influenced the degree of membrane fouling, were analyzed. The results indicated that both the UV-TiO₂ and GAC techniques can alleviate irreversible NF membrane fouling and reduce the attenuation rate of membrane flux to some extent. Compared to individual UV-TiO₂ or GAC processes, the degree of irreversible membrane fouling in the combined UV-TiO₂/GAC process was reduced by 48.7% and 61.4%, respectively. Protein-like and humus-like components were dominant in the irreversible membrane fouling, and organic components with relative molecular mass of less than 3×10³ and between 30×10³ and 100×10³ were dominant in causing a decrease in NF membrane flux. Organic content was efficiently removed using UV-TiO₂/GAC/NF combined process, achieving a removal rate for COD, DOC, and UV₂₅₄ of 45.7%, 74.5%, and 89.2%, respectively. This study provides technical support for the advanced treatment and multi-path reuse of unconventional water sources for cities and various types of constructions.