Treatment of disinfection by-product precursors

Abstract

Natural organic matter (NOM) in drinking water forms disinfection byproducts (DBPs) through reactions with disinfectants, typically chlorine. Many DBPs are harmful to human health. Potentially the most effective means of controlling DBPs is to remove NOM precursors before disinfection. However, both DBP formation and removal of precursors in natural waters are variable and unpredictable, reflecting the diverse and variable nature of NOM. To better understand the relationships between DBP formation, compound character and treatment, experiments were undertaken with a range of NOM surrogates, assessing both DBP formation and treatability. Activated aromatics, β-dicarbonyls, masked β-dicarbonyls and amino acids were indentified as reactive precursor categories. No correlations were found between compound physicochemical properties and DBP formation. This indicates reliable bulk predictors of DBP formation are unlikely to exist in natural waters. In contrast, treatability was explicable in terms of compound physicochemical properties. Levels of removal by coagulation and anion exchange were controlled by amount of anionic charge, while molecular weight and hydrophobicity also affect removal by activated carbon and nanofiltration. Advanced oxidation processes (AOPs) at high doses was able to completely mineralise all NOM surrogates, however at lower doses DBP formation can be increased, dramatically in the case of two amino acids. Biotreatment is effective in removing amino acids but can cause moderate increases in DBP levels. A DBP control strategy is outlined based on this information. Where a high proportion of DBP precursors are highly-anionic aromatic compounds, coagulation may be sufficient for DBP control. Where reactive precursors are moderately-anionic carboxylic acids, ion exchange should be considered. In waters where less-treatable NOM has a high DBPgenerating capacity, activated carbon should be investigated for removal of neutral or weakly-charged aromatic precursors and a (hydrophobic) nanofiltration membrane for neutral or weakly-charged amino acids or carbohydrates.