Insights into Photo/Electrocatalysts for the Degradation of Per- and Polyfluoroalkyl Substances (PFAS) by Advanced Oxidation Processes

Per- and polyfluoroalkyl substances (PFASs) are an emerging group of persistent organic pollutants in aquatic environments with high levels of toxicity and bioaccumulation. The risks posed by PFASs to the environment and health have attracted increasing attention. To remove them from water, advanced oxidation processes (AOPs), with the merits of high efficiency and low cost, are mainly used. Photo/electrocatalytic heterogeneous AOPs, with the assistance of nanostructured catalysts and external energy in the form of light/electricity, have emerged as one of the most powerful techniques, overcoming the difficulty associated with defluorination and achieving the effective and complete degradation of PFASs in water. The structures of photo/electrocatalysts play a critical role in the production of reactive oxygen species, the electron transfer process, and the degradation pathway and its efficiency. Herein, to elucidate the structure–performance relationship, a review of photo/electrocatalysts for the enhanced degradation of PFASs in heterogeneous AOPs, organized according to their composition and nanostructure design, is provided. This review article is mainly focused on (1) the mechanisms and pathways of PFAS degradation by heterogeneous photo/electrocatalytic AOPs, and (2) the structural designs and modifications of photo/electrocatalysts for the enhanced degradation of PFASs by heterogeneous AOPs. Finally, the challenges and prospects for future research into photo/electrocatalysts of heterogeneous AOPs in the field of PFAS remediation are discussed

Disinfection Byproduct Formation During Drinking Water Treatment and Distribution: a Review of Unintended Effects of Engineering Agents and Materials

Unintended effects of engineering agents and materials on the formation of undesirable disinfection byproducts (DBPs)during drinking water treatment and distribution were comprehensively reviewed. Specially, coagulants, biologically active filtration biofilms, activated carbons, nanomaterials, ion-exchange resins, membrane materials in drinking water treatment and piping materials, deposits and biofilms within drinking water distribution systems were discussed, which may serve as DBP precursors, transform DBPs into more toxic species, and/or catalyze the formation of DBPs. Speciation and quantity of DBPs generated rely heavily on the material characteristics, solution chemistry conditions, and operating factors. For example, quaternary ammonium polymer coagulants can increase concentrations of N-nitrosodimethylamine (NDMA)to above the California notification level (10 ng/L). Meanwhile, the application of strong base ion-exchange resins has been associated with the formation of N-nitrosamines and trichloronitromethane up to concentrations of 400 ng/L and 9.0 μg/L, respectively. Organic compounds leaching from membranes and plastic and rubber pipes can generate high NDMA (180–450 ng/L)and chloral hydrate (∼12.4 μg/L)upon downstream disinfection. Activated carbon and membranes preferentially remove organic precursors over bromide, resulting in a higher proportion of brominated DBPs. Copper corrosion products (CCPs)accelerate the decay of disinfectants and increase the formation of halogenated DBPs. Chlorination of high bromide waters containing CCPs can form bromate at concentrations exceeding regulatory limits. Owing to the aforementioned concern for the drinking water quality, the application of these materials and reagents during drinking water treatment and distribution should be based on the removal of pollutants with consideration for balancing DBP formation during disinfection scenarios. Overall, this review highlights situations in which the use of engineering agents and materials in drinking water treatment and distribution needs balance against deleterious impacts on DBP formation

Disinfection byproduct formation during drinking water treatment and distribution: A review of unintended effects of engineering agents and materials

Unintended effects of engineering agents and materials on the formation of undesirable disinfection byproducts (DBPs) during drinking water treatment and distribution were comprehensively reviewed. Specially, coagulants, biologically active filtration biofilms, activated carbons, nanomaterials, ion-exchange resins, membrane materials in drinking water treatment and piping materials, deposits and biofilms within drinking water distribution systems were discussed, which may serve as DBP precursors, transform DBPs into more toxic species, and/or catalyze the formation of DBPs. Speciation and quantity of DBPs generated rely heavily on the material characteristics, solution chemistry conditions, and operating factors. For example, quaternary ammonium polymer coagulants can increase concentrations of N-nitrosodimethylamine (NDMA) to above the California notification level (10 ng/L). Meanwhile, the application of strong base ion-exchange resins has been associated with the formation of N-nitrosamines and trichloronitromethane up to concentrations of 400 ng/L and 9.0 μg/L, respectively. Organic compounds leaching from membranes and plastic and rubber pipes can generate high NDMA (180–450 ng/L) and chloral hydrate (∼12.4 μg/L) upon downstream disinfection. Activated carbon and membranes preferentially remove organic precursors over bromide, resulting in a higher proportion of brominated DBPs. Copper corrosion products (CCPs) accelerate the decay of disinfectants and increase the formation of halogenated DBPs. Chlorination of high bromide waters containing CCPs can form bromate at concentrations exceeding regulatory limits. Owing to the aforementioned concern for the drinking water quality, the application of these materials and reagents during drinking water treatment and distribution should be based on the removal of pollutants with consideration for balancing DBP formation during disinfection scenarios. Overall, this review highlights situations in which the use of engineering agents and materials in drinking water treatment and distribution needs balance against deleterious impacts on DBP formation

Contribution of amide-based coagulant polyacrylamide as precursors of haloacetamides and other disinfection by-products

Coagulation is a widespread method of drinking water treatment. Coagulation can mitigate the formation of disinfection by-products (DBPs) through removing their precursors. Here we report that the amide-based organic polymer coagulants polyacrylamide (PAM) and its monomer acrylamide (AM) can serve as a source of HAcAm and other DBPs including trihalomethanes (THMs) and haloacetonitriles (HANs) during chlor(am)ination. The impact of the key experimental parameters, including reaction time, Cl2 or NH2Cl dose, pH and initial bromide concentration on the formation of DBPs was investigated. Furthermore, the major reaction pathways for AM transformation and DBP formation during chlor(am)ination are proposed and include N-chlorination, addition, and substitution. Jar tests demonstrated that coagulation by alum coupled with PAM achieved greatest removal of DOC and UV254, compared with alum and PAM alone. Treatment with PAM didn’t significantly promote the formation of THMs and HANs during post-chlorination, indicating that the PAM residual hardly contributes to THM and HAN formation. However, coagulation by applying alum salt and PAM increased total HAcAm concentrations by 2.2–3.1 μg/L at the higher PAM dose (2.0 mg/L), compared with alum alone. Therefore, the contribution of PAM to the formation of HAcAm cannot be ignored. The results highlight that the generation of secondary pollutants from the amide-based engineered organic polymer coagulants in drinking water should be considered; that is, they can adversely affect water quality because of their ability to enhance DBPs generated during downstream disinfection. Accordingly, the understanding of the stability and reactivity of PAM in the presence of disinfectants could help to better evaluate their contribution to the formation of HAcAms, THMs, and HANs, which has important implications for their environmental fate, transport, and responsible applications

Formation and estimated toxicity of trihalomethanes, haloacetonitriles, and haloacetamides from the chlor(am)ination of acetaminophen

The occurrence of pharmaceuticals and personal care products (PPCPs) in natural waters, which act as drinking water sources, raises concerns. Moreover, those compounds incompletely removed by treatment have the chance to form toxic disinfection byproducts (DBPs) during subsequent disinfection. In this study, acetaminophen (Apap), commonly used to treat pain and fever, was selected as a model PPCP. The formation of carbonaceous and nitrogenous DBPs, namely trihalomethanes, haloacetonitriles, and haloacetamides, during chlor(am)ination of Apap was investigated. Yields of chloroform (CF), dichloroacetonitrile (DCAN), dicholoacetamide (DCAcAm), and tricholoacetamide (TCAcAm), during chlorination were all higher than from chloramination. The yields of CF continuously increased over 48 h during both chlorination and chloramination. During chlorination, as the chlorine/Apap molar ratios increased from 1 to 20, CF yields increased from 0.33 ± 0.02% to 2.52 ± 0.15%, while the yields of DCAN, DCAcAm and TCAcAm all increased then decreased. In contrast, during chloramination, increased chloramine doses enhanced the formation of all DBPs. Acidic conditions favored nitrogenous DBP formation, regardless of chlorination or chloramination, whereas alkaline conditions enhanced CF formation. Two proposed formation mechanisms are presented. The analysed DBPs formed during chlorination were 2 orders of magnitude more genotoxic and cytotoxicity than those from chloramination