Anthracite Releases Aromatic Carbons and Reacts with Chlorine to Form Disinfection Byproducts in Drinking Water Production.

Anthracite is globally used as a filter material for water purification. Herein, it was found that up to 15 disinfection byproducts (DBPs) were formed in the chlorination of anthracite-filtered pure water, while the levels of DBPs were below the detection limit in the chlorination of zeolite-, quartz sand-, and porcelain sandstone-filtered pure water. In new-anthracite-filtered water, the levels of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and ammonia nitrogen (NH3-N) ranged from 266.3 to 305.4 µg/L, 37 to 61 µg/L, and 8.6 to 17.1 µg/L, respectively. In aged anthracite (collected from a filter at a DWTP after one year of operation) filtered water, the levels of the above substances ranged from 475.1 to 597.5 µg/L, 62.1 to 125.6 µg/L, and 14 to 28.9 µg/L, respectively. Anthracite would release dissolved substances into filtered water, and aged anthracite releases more substances than new anthracite. The released organics were partly (around 5%) composed by the µg/L level of toxic and carcinogenic aromatic carbons including pyridine, paraxylene, benzene, naphthalene, and phenanthrene, while over 95% of the released organics could not be identified. Organic carbon may be torn off from the carbon skeleton structure of anthracite due to hydrodynamic force in the water filtration process.

Formation of iodinated aromatic DBPs at different molar ratios of chlorine and nitrogen in iodide-containing water.

Variations in iodinated aromatic disinfection byproducts (DBPs) in the presence of I- and organic compounds as a function of reaction time in different molar ratios (MRs) of HOCl:NH3-N were investigated. Up to 17 kinds of iodinated aromatic DBPs were identified in the breakpoint chlorination of iodide (I-)/organic (phenol, bisphenol S (BPS) and p-nitrophenol (p-NP)) systems, and the possible pathways for the formation of iodinated aromatic DBPs were proposed. The reaction pathways include HOCl/HOI electrophilic substitution and oxidation, while the dominant iodinated DBPs were quantified. In the I-/phenol system (pH = 7.0), the sum of the concentrations of four iodinated aliphatic DBPs ranged from 0.32 to 1.04 µM (triiodomethane (TIM), dichloroiodomethane (DCIM), diiodochloromethane (DICM) and monoiodoacetic acid (MIAA)), while the concentration of 4-iodophenol ranged from 2.99 to 12.87 µM. The concentration of iodinated aromatic DBPs remained stable with an MR = 1:1. When the MR was 6:1, iodinated aromatic DBPs decreased with increasing reaction time, in which the main disinfectant in the system was active chlorine. This study proposed the formation mechanism of iodinated aromatic DBPs during the breakpoint chlorination of iodide-containing water. These results can be used to control the formation of hazardous iodinated aromatic DBPs in the disinfection of iodine containing water.