Effect of ozonation on the characteristics of effluent organic matter fractions and subsequent associations with disinfection by-products formation

Abstract

Ozonation could be used in advanced wastewater treatment plants to reduce the precursors of disinfection by-products (DBPs), or for disinfection and oxidation of trace organic compounds. Detailed analysis of effluent organic matter (EfOM) is intrinsic to the understanding of impact of ozonation on the characterization variation of EfOM, which is closely related with DBPs formation during subsequent chlorination. In this study, the raw as well as oxidized EfOM with ozone were fractionated into hydrophobic acids, neutrals and bases, and hydrophilic acids, neutrals and bases. Results indicated that ozonation increased the proportion of hydrophilic fractions in EfOM, especially of hydrophilic acids, which resulted in increased specific haloacetic acids formation potential (HAAFP) in the subsequent chlorination. Although ozonation decreased the total organic carbon and SUVA254 of EfOM and most isolated fractions, further ozonation increased the SUVA of hydrophilic acids after the initial decrease. This was in accordance with the chemical structures analysis with FTIR, which showed the relative abundance of unsaturated structures such as CO bonds in hydrophilic fractions increased with further ozonation. Furthermore, specific trihalomethanes formation potential (THMFP) of each fraction decreased after initial pre-ozonation but increased with different extent with further ozonation. While for HAAs, pre-ozonation of hydrophilic acids significantly increased the dichloroacetic acid (DCAA) formation potential. In brief, EfOM containing a relatively high content of aromatic structures i.e. SUVA254 and aliphatic structures yielded a remarkably high specific DBPFP. Further mineralization of organic fractions and specific increased formation of aliphatic CH structures by further ozonation caused the increased DBPFPs especially DCAAFP during subsequent chlorination.