Effluents from wastewater treatment plants (WWTPs) contain disinfection byproducts (DBPs) of health concern when the water is utilized downstream as a potable water supply. The pattern of DBP formation was strongly affected by whether or not the WWTP achieved good nitrification. Chlorine addition to poorly nitrified effluents formed low levels of halogenated DBPs, except for (in some cases) dihalogenated acetic acids, but often substantial amounts of N-nitrosodimethyamine (NDMA). Chlorination of well-nitrified effluent typically resulted in substantial formation of halogenated DBPs but much less NDMA. For example, on a median basis after chlorine addition, the well-nitrified effluents had 57 microg/L of trihalomethanes [THMs] and 3 ng/L of NDMA, while the poorly nitrified effluents had 2 microg/L of THMs and 11 ng/L of NDMA. DBPs with amino acid precursors (haloacetonitriles, haloacetaldehydes) formed at substantial levels after chlorination of well-nitrified effluent. The formation of halogenated DBPs but not that of NDMA correlated with the formation of THMs in WWTP effluents disinfected with free chlorine. However, THM formation did not correlate with the formation of other DBPs in effluents disinfected with chloramines. Because of the relatively high levels of bromide in treated wastewater, bromine incorporation was observed in various classes of DBPs.

Unintentional, indirect wastewater reuse often occurs as wastewater treatment plant (WWTP) discharges contaminate receiving waters serving as drinking-water supplies. A survey was conducted at 23 WWTPs that utilized a range of treatment technologies. Samples were analyzed for typical wastewater and drinking-water constituents, chemical characteristics of the dissolved organic matter (DOM), and disinfection byproduct (DBP) precursors present in the effluent organic matter (EfOM). This was the first large-scale assessment of the critical water quality parameters that affect the formation of potential carcinogens during drinking water treatment relative to the discharge of upstream WWTPs. This study considered a large and wide range of variables, including emerging contaminants rarely studied at WWTPs and never before in one study. This paper emphasizesthe profound impact of nitrification on many measures of effluent water quality, from the obvious wastewater parameters (e.g., ammonia, biochemical oxygen demand) to the ones specific to downstream drinking water treatment plants (e.g., formation potentialsfor a diverse group of DBPs of health concern). Complete nitrification reduced the concentration of biodegradable dissolved organic carbon (BDOC) and changed the ratio of BDOC/DOC. Although nitrification reduced ultraviolet absorbance (UVA) at 254 nm, it resulted in an increase in specific UVA (UVA/DOC). This is attributed to preferential removal of the less UV-absorbing (nonhumic) fraction of the DOC during biological treatment. EfOM is composed of hydrophilic and biodegradable DOM, as well as hydrophobic and recalcitrant DOM, whose proportions change with advanced biological treatment. The onset of nitrification yielded lower precursor levels for haloacetic acids and nitrogenous DBPs (haloacetonitriles, N-nitrosodimethylamine). However, trihalomethane precursors were relatively unaffected by the level of wastewater treatment Thus, one design/operations parameter in wastewater treatment, the decision to have a long enough solids retention time to get reliable nitrification, affected much beyond its immediate goal of ammonium oxidation.

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Hydrogen peroxide (HO) is ubiquitous in the natural environment, and it is now widely used for pollutant control in water and wastewater treatment processes. However, current analytical methods for HO inevitably require reactions between HO and other reactants to yield signals and are thus likely subjective to the interferences of coexisting colored, oxidative, and reductive compounds. In order to overcome these barriers, we herein for the first time propose to analyze HO by ion chromatography (IC) using an ultraviolet (UV) detector. The proposal is based on two principles: first, that HO can deprotonate to hydroperoxyl ion (HO) when eluent pH is higher than the acid-dissociation coefficient of HO (pK = 11.6); and second, that after separation from other compounds via IC column, HO can be quantified by a UV detector. Under favorable operating conditions, this method has successfully achieved acceptable recoveries (>91%) of HO dosed to ultrapure and natural waters, a calibration curve with R > 0.99 for a wide range of HO concentrations from 0.1 to 50 mg/L and a method detection limit of 0.027 mg/L. In addition, this approach was shown to be capable of distinguishing HO from anions (e.g., fluoride and chloride) and organics (e.g., glycolate) and monochloramine, suggesting that it is insensitive to many neighboring compounds as long as they do not react quickly with HO. Hence, this study proves the combination of IC and UV detector a facile and reliable method for HO measurement.

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Hydroxyl radical (•OH) is an active species widely reported in studies across many scientific fields, and hence, its reliable analysis is vitally important. Currently, alcohols are commonly used as scavengers for •OH determination. However, the impacts of alcohols on the reliability of •OH detection remain unknown. In this study, we found that adding different types and different amounts of alcohols in water samples treated with ultraviolet irradiation undesirably produced substantial amounts of hydrogen peroxide (H2O2), which is a known •OH precursor. This means that the conventional •OH determination method using alcohols is likely unreliable or even misleading. Through careful investigation, we revealed an overlooked reaction pathway during H2O2 and •OH transformations. Varying oxygen concentrations, pHs, alcohol dosages, and types altered H2O2 formation, which can affect •OH determination accuracy. Among alcohols, n-butanol is the best scavenger because it quenches •OH rapidly but re-forms little H2O2.

Quantitative structure-activity relationship (QSAR) models are tools for linking chemical activities with molecular structures and compositions. Due to the concern about the proliferating number of disinfection byproducts (DBPs) in water and the associated financial and technical burden, researchers have recently begun to develop QSAR models to investigate the toxicity, formation, property, and removal of DBPs. However, there are no standard procedures or best practices regarding how to develop QSAR models, which potentially limit their wide acceptance. In order to facilitate more frequent use of QSAR models in future DBP research, this article reviews the processes required for QSAR model development, summarizes recent trends in QSAR-DBP studies, and shares some important resources for QSAR development (e.g., free databases and QSAR programs). The paper follows the four steps of QSAR model development, i.e., data collection, descriptor filtration, algorithm selection, and model validation; and finishes by highlighting several research needs. Because QSAR models may have an important role in progressing our understanding of DBP issues, it is hoped that this paper will encourage their future use for this application.