Significant increase of assimilable organic carbon (AOC) levels in MBR effluents followed by coagulation,ozonation and combined treatments: Implications for biostability control of reclaimed water

? Annual AOCs in MBR effluents were stable with small increase in warmer seasons. ? Significant increase in AOC levels of tertiary effluents were observed. ? Coagulation in prior to ozonation can reduce AOC formation in tertiary treatment. ? ?UV₂₅₄ and SUVA can be surrogates to predict the AOC changes during ozonation. As water reuse development has increased, biological stability issues associated with reclaimed water have gained attention. This study evaluated assimilable organic carbon (AOC) in effluents from a full-scale membrane biological reactor (MBR) plant and found that they were generally stable over one year (125–216 µg/L), with slight increases in warmer seasons. After additional tertiary treatments, the largest increases in absolute and specific AOCs were detected during ozonation, followed by coagulation-ozonation and coagulation. Moreover, UV₂₅₄ absorbance is known to be an effective surrogate to predict the AOC changes during ozonation. Applying coagulation prior to ozonation of MBR effluents for removal of large molecules was found to reduce the AOC formation compared with ozonation treatment alone. Finally, the results revealed that attention should be paid to seasonal variations in influent and organic fraction changes during treatment to enable sustainable water reuse.