Changes in Dissolved Organic Matter during the Treatment Processes of a Drinking Water Plant in Sweden and Formation of Previously Unknown Disinfection Byproducts

Abstract

The changes in dissolved organic matter (DOM) throughout the treatment processes in a drinking water treatment plant in Sweden and the formation of disinfection byproducts (DBPs) were evaluated by using ultra-high-resolution mass spectrometry (resolution of ∼500,000 at m/z 400) and nuclear magnetic resonance (NMR). Mass spectrometric results revealed that flocculation induced substantial changes in the DOM and caused quantitative removal of DOM constituents that usually are associated with DBP formation. While half of the chromophoric DOM (CDOM) was removed by flocculation, ∼4-5 mg L(-1) total organic carbon remained in the finished water. A conservative approach revealed the formation of ∼800 mass spectrometry ions with unambiguous molecular formula assignments that contained at least one halogen atom. These molecules likely represented new DBPs, which could not be prevented by the flocculation process. The most abundant m/z peaks, associated with formed DBPs, could be assigned to C5HO3Cl3, C5HO3Cl2Br, and C5HO3ClBr2 using isotope simulation patterns. Other halogen-containing formulas suggested the presence of halogenated polyphenolic and aromatic acid-type structures, which was supported by possible structures that matched the lower molecular mass range (maximum of 10 carbon atoms) of these DBPs. 1H NMR before and after disinfection revealed an ∼2% change in the overall 1H NMR signals supporting a significant change in the DOM caused by disinfection. This study underlines the fact that a large and increasing number of people are exposed to a very diverse pool of organohalogens through water, by both drinking and uptake through the skin upon contact. Nontarget analytical approaches are indispensable for revealing the magnitude of this exposure and to test alternative ways to reduce it.

Depth-dependent photodegradation of marine dissolved organic matter

“…However, the region of the van Krevelen with O/C ratios between 0.5 and 0.8 and H/C ratios between 0.5 and 1.2 was much more occupied (Figure 8, CHO plot). This region in the van Krevelen diagram has been previously suggested to be highly correlated with CDOM that can be flocculated by aluminum sulfate in a drinking water treatment plant (Gonsior et al, 2014b).…”

Waterworks-specific composition of drinking water disinfection by-products

“…[24][25][26] Electrospray ionization FT-ICR MS operated in negative mode has already been shown to successfully determine new DBPs. 16,[19][20][21] Importantly, due to selectivity in sample preparation and susceptibility of ionization, the compounds observed with this approach typically include nonvolatile, hydrophobic to semi polar, oxygen containing compounds, 27,28 e.g. containing carboxyl or hydroxyl groups.…”

“…In previous DBP studies based on FT-ICR MS, CHOCl 2 molecular formulae were frequently found at waterworks using NaOCl disinfection and not at those using chloramine, supporting this interpretation. [19][20][21] Overall, few CHOCl 3 molecular formulae were found, even at LIN and NOR. For activated aromatic structures, such as phenolic compounds, that undergo electrophilic aromatic substitution reactions, the chlorination reaction rate decreases after each chlorine incorporation, which means that the conditions required for chlorine incorporation change during the continuous chlorination.…”

“…13 A number of studies have been carried out to analyze the non-volatile fraction of DBPs using nontarget approaches, where some have focused on lab experiments, [14][15][16][17][18] and a few on real waterworks. [19][20][21] Previous studies indicate that there is variation and overlap of nonvolatile DBPs formed at different waterworks. [19][20][21] However, sampling in those studies was restricted to a single occasion, and the degree of similarity or variability between water treatment plants and treatment methods remains inconclusive.…”

“…[19][20][21] Previous studies indicate that there is variation and overlap of nonvolatile DBPs formed at different waterworks. [19][20][21] However, sampling in those studies was restricted to a single occasion, and the degree of similarity or variability between water treatment plants and treatment methods remains inconclusive. Expanding the knowledge about compositional variability of non-volatile DBPs is important to link DBP formation to water treatment conditions and evaluating remaining toxicity caused by DBPs.…”