Effects of ozonation and biological filtration on the formation of nitrogenous disinfection byproducts during chloramination

This study investigates the formation potential (FP) of nitrogenous disinfection byproducts and haloacetic acids (HAAs) during ozonation and biofiltration. Ozonation of raw waters was performed in batches with 1 mg O₃/mg dissolved organic carbon (DOC). The ozonized waters were subsequently passed through a biofilter with 25 minutes of empty bed contact time. The results show that the increases of biodegradable DOC in hydrophobic fractions were higher than those in hydrophilic (HPI) or transphilic fractions. Ozonation reduced the DOC (<10%), and FPs of haloacetonitriles (HANs) and HAAs by 23–70%. Subsequent biofiltration removed up to 35% of DOC, whereas the additional removals of HAN and HAA FPs were negligible during biofiltration. Trichloronitromethane FPs tended to increase by a factor of 5–10 after ozonation and slightly decrease (15–20%) during biofiltration. In the two nitrogen-rich natural organic matters (NOMs), transphilics and HPIs constituted half of the organic carbons and contributed 64–70% of the total N-nitrosodimethylamine (NDMA) formation. Ozonation-biofiltration reduced NDMA precursors in these two water sources but significantly enhanced NDMA formation in Suwannee River NOM. The increase of NDMA formation was attributable to the alteration of NOM characteristics of the HPI fraction by ozonation; the NDMA FP increased 214% in the HPI fraction after ozonation.