The spatial variability of disinfection by-products relative to regional chemical gradients

摘要

Background and Problem Statement- A spatial analysis of disinfection by-products(DBPs) in public water supplies in Maine showed a progressive prevalence oftrihalomethanes (THM) over haloacetic acids (HAA) with increasing distance from theocean, as well as a parallel increase in total DBPs. Since proximity to the ocean controlsthe deposition of salt from marine aerosols, background chloride was suspected as animportant factor in DBP formation. The character of dissolved organic carbon (DOC) isknown to be related to landscape factors that also vary from coastal to inland areas.Project Description and Setup- The experimental approach involved an analysis of theinfluences of chloride and DOC on the formation of different types of DBPs using rawand finished water samples (lakes or rivers) collected from 21 public water supplies inMaine. Sample locations ranged along a 300 km transect from coastal to inland areas.Water samples were analyzed for general water chemistry, specific UV absorbance(SUVA), and DBPs. Additional raw water samples were collected for salt (NaCl)addition experiments while monitoring DBP formation. The character of the DBPsformed was analyzed using chromatography coupled to a novel ultra-high resolutionFourier transform ion cyclotron resonance mass spectrometer (GC/FT-ICR MS).Results- Field data exhibited an inverse relationship between dissolved organic carbon(DOC) and chloride concentrations. There was also a positive relationship betweenSUVA, DOC, and DBPs that probably relates to DOC precursors of DBPs. However,paired samples of raw and finished water showed no correlation between the type of DBPformed and chloride concentrations.Significance to the Industry and Recommendations- The types and quantities of DBPsformed are controlled in part by the raw water chemistry. Chloride has been considered tobe relatively inert but its presence is correlated with different types of DBPs. Thepotential exists for DBP precursors to be formed in source watersheds under naturalbiogeochemical conditions. Water utilities may be able to gain additional DBP reductionthrough understanding and managing these conditions in source watersheds.