An Insight into Dissolved Organic Matter Removal Characteristics of Recycling Filter Backwash Water: A Comparative Study

<div><p>It is necessary to put all aspects,,namely raw water characteristics, corresponding FBWW, and coagulation mechanisms, i.e., charge neutralization and sweep flocculation together to make clear the dissolved organic matter (DOM) removal characteristics and the fate of fractionations in recycle design. The DOM characteristics of molecular weight (MW) distribution, hydrophobicity, and fluorescence in source water W1 (synthesized water) and W2 (“Longtan” lake water), FBWW and treated water samples therefore are identified, and three recycling ratios of 2%, 5%, and 8% as compared to control (0%) are conducted. It is found that DOM within FBWW becomes more hydrophilic and lower MW as compared to corresponding source water. Recycling trials indicate that higher DOM concentrations and more low-MW fractions are not of any benefit to enhance UV<sub>254</sub> and DOC removal. Hydrophobic acid can be further eliminated in case recycling particles mainly produced by sweep flocculation, while weakly hydrophobic acid and hydrophilic fraction can be enhanced and removed under recycling particles mainly formed by charge neutralization. Higher molecular weight fraction (>30 kDa) exhibits potentially enhanced removal at preferred recycling ratio of 5%. Fluorescent characteristics analysis demonstrate that recycling FBWW can effectively improve humic-like substances removal, but the protein-like matters are resistant to be eliminated with unvaried structure.</p></div>