Improved (and Singular) Disinfectant Protocol for Indirectly Assessing Organic Precursor Concentrations of Trihalomethanes and Dihaloacetonitriles

Abstract

Measurements of disinfection byproduct (DBP) organic precursor concentrations (OPCs) are crucial to assess and improve DBP control processes. Typically, formation potential tests - specified in Standard Methods (SM) 5710-B/D - are used to measure OPCs. Here, we highlight several limitations of this protocol for dihaloacetonitriles and trihalomethanes and validate a novel Alternative Method (AM). The effects of pH, disinfectant type (free chlorine and monochloramine), and chlor(am)ine residual (CR) were examined on DBP formation in a suite of waters. Using the SM, DHAN decreased 43-47% as the CR increased from 3 to 5 mg L(-1) as Cl2, compromising OPC assessments. In contrast, a high monochloramine dose (250 mg L(-1) as Cl2) at pH 7.0 (the AM) accurately reflected OPCs. The two methods were compared for assessing DBP precursor removal through three granular activated carbon (GAC) columns in series. Breakthrough profiles assessed using the AM only showed DBP precursor sorption occurred in each column that decreased over time (p = 0.0001). Similarly, the AM facilitated ranking of three types of GAC compared in parallel columns, whereas the SM produced ambiguous results. Fluorescence intensity of a humic-like fluorophore (i.e., I345/425) correlated strongly to precursor removal in the GAC columns. The practical implications of the results are discussed.

Trihalomethane, dihaloacetonitrile, and total N-nitrosamine precursor adsorption by carbon nanotubes: the importance of surface oxides and pore volume

“…27 The WS-EFF samples were passed through prerinsed 0.7 μm glass fiber filters prior to 0.45 μm PES filtration, as direct filtration with the PES membranes was impractically slow. In both cases, filtration removed all CNTs from the water samples, which was confirmed by the lower chlorine residuals (or higher demand) of the blank relative to the CNT-treated waters (Table S4 † 16 was used to assess the DBPFP of untreated waters (i.e., samples not exposed to CNTs) and CNT-treated waters and is detailed in the ESI. † EPA method 551.1 with modifications 28 was used to extract TTHMs and DHANs into n-pentane.…”

“…Nine commercially available CNTs were selected with a variety of characteristics and used in batch isotherm tests with two diverse water sourcesa wellcharacterized lake water 24 that serves as a drinking water source and an effluent from a conventional WWTP. The TTHM-, DHAN-, and TONO-precursor concentrations in the raw and CNT-treated waters were indirectly measured using a recently verified DBP formation potential (DBPFP) test, 16 modified from Standard Methods 5710-B and D. 25 Each CNT type was characterized physically by gas adsorption isotherms to determine their specific surface area and pore volume distributions, and chemically by X-ray photoelectron spectroscopy (XPS) to determine the relative composition of surface functional groups. These physicochemical properties were used as primary variables in models to assess the adsorption of TTHM-, DHAN-, and TONO-precursors.…”

Review: Natural organic matter in aquatic systems – a South African perspective

“…Various alternative approaches have been suggested and tested to be effective in one way or the other compared to the use of chlorine as a disinfectant (Gopal et al, 2007). One such way of reducing DBPs is to reduce the chlorine dosages and/or to remove as much NOM as possible before the disinfection step (Bond et al, 2014;Do et al, 2015). Other researchers prefer the use of chloramine as a disinfectant instead of chlorine (Pifer and Fairey, 2012).…”

Disinfection Processes

“…Sorption of THM precursors by activated carbon was found to depend on the composition of humic substances and the chemical nature of the activated carbon used, both of which were influenced by pH (Abouleish et al, 2015). A new method was used to evaluated organic precursor removal and breakthrough curves through granular activated carbon columns; fluorescence intensity of a humic-like fluorophore correlated strongly with Water Environment Research, Volume 88, Number 10-Copyright © 2016 Water Environment Federation precursor removal (Do et al, 2015). In laboratory tests, granular activated carbon removed 60% of soluble microbial products (SMPs) and 70% of DBP formation potential (DBPFP); in contrast, enhanced coagulation with alum removed far less SMPs and ozone removed SMPs but did not change DBPFP .…”