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Occurrence and removal of dissolved organic nitrogen in US water treatment plants

Two seasonal sampling campaigns of raw and finished waters from 28 water treatment plants were conducted to investigate the occurrence and removal of dissolved organic nitrogen (DON). A new dialysis pretreatment technique was applied for accurate DON determination. The average DON concentration was 0.186 mg/L nitrogen (N) in raw waters and 0.148 mg/L N in finished waters. On average, total dissolved nitrogen in the raw waters consist of 10% DON and 90% dissolved inorganic nitrogen. The dissolved organic carbon (DOC)‐to‐DON ratio of raw waters averaged 18 mg DOC to 1 mg DON. DON removal during water treatment closely mirrored that of DOC removal. The molecular weight distribution of DON roughly parallels that of DOC, and higher‐molecular‐weight fractions (> 10,000 D) of both DON and DOC were preferentially removed across the full‐scale water treatment plants.