Formation of disinfection byproducts from chlorinated soluble microbial products: Effect of carbon sources in wastewater denitrification processes

Abstract

Carbon sources are crucial for biological denitrification in wastewater treatment that significantly affects the production of soluble microbial products (SMPs), thereby affecting the formation of disinfection byproducts (DBPs) during subsequent chlorination. However, the effect of carbon sources on DBPs formation has not been studied. In this work, sodium acetate, sodium lactate, and glucose were used as carbon sources, and denitrifying SMPs derived from different carbon sources were used as DBPs precursors to investigate the formation potential (FP) of 16 carbonaceous DBPs and 19 nitrogenous DBPs. Results showed that the carbonaceous DBPs FP of SMPs derived from acetate, lactate, and glucose were 502.1–584.3, 250.3–288.9, and 374.7–439.1 μg/L, respectively, and the nitrogenous DBPs FP were 19.1–45.6, 12.8–21.9, and 7.9–9.0 μg/L, respectively. After chlorination, the genotoxicity of SMPs measured by the SOS/umu test was also evaluated with 364 ng 4-NQO/L for acetate, 212 ng 4-NQO/L for lactate, and 138 ng 4-NQO/L for glucose. Based on X-ray photoelectron spectroscopy, chemical structures of SMPs were characterized, and their relationship with DBPs FP was investigated to explain the mechanism of DBPs formation. Aromatic C and C-O were found to be the major precursor structures to form carbonaceous DBPs, and their lowest proportions in lactate-derived SMPs caused the lowest carbonaceous DBPs FP. Organic nitrogen, including aromatic N, amide/peptide N, and primary amine N, was the precursor of nitrogenous DBPs. The lowest concentration of dissolved organic nitrogen for glucose-derived SMPs caused the lowest nitrogenous DBPs FP and genotoxicity. Glucose may be a better choice among the three carbon sources in terms of reducing genotoxicity.