Understanding the influence of pre-ozonation on the formation of disinfection byproducts and cytotoxicity during post-chlorination of natural organic matter: UV absorbance and electron-donating-moiety of molecular weight fractions

Ferrate(VI) assists in reducing cytotoxicity and genotoxicity to mammalian cells and organic bromine formation in ozonated wastewater

Ozonation of wastewater containing bromide (Br-) forms highly toxic organic bromine. The effectiveness of ozonation in mitigating wastewater toxicity is minimal. Simultaneous application of ozone (O3) (5 mg/L) and ferrate(VI) (Fe(VI)) (10 mg-Fe/L) reduced cytotoxicity and genotoxicity towards mammalian cells by 39.8% and 71.1% (pH 7.0), respectively, when the wastewater has low levels of Br-. This enhanced reduction in toxicity can be attributed to increased production of reactive iron species Fe(IV)/Fe(V) and reactive oxygen species (•OH) that possess higher oxidizing ability. When wastewater contains 2 mg/L Br-, ozonation increased cytotoxicity and genotoxicity by 168%-180% and 150%-155%, respectively, primarily due to the formation of organic bromine. However, O3/Fe(VI) significantly (p < 0.05) suppressed both total organic bromine (TOBr), BrO3-, as well as their associated toxicity. Electron donating capacity (EDC) measurement and precursor inference using Orbitrap ultra-high resolution mass spectrometry found that Fe(IV)/Fe(V) and •OH enhanced EDC removal from precursors present in wastewater, inhibiting electrophilic substitution and electrophilic addition reactions that lead to organic bromine formation. Additionally, HOBr quenched by self-decomposition-produced H2O2 from Fe(VI) also inhibits TOBr formation along with its associated toxicity. The adsorption of Fe(III) flocs resulting from Fe(VI) decomposition contributes only minimally to reducing toxicity. Compared to ozonation alone, integration of Fe(VI) with O3 offers improved safety for treating wastewater with varying concentrations of Br-.

Effects of ozone dose on brominated DBPs in subsequent chlor(am)ination: A comprehensive study of aliphatic, alicyclic and aromatic DBPs

Ozone‒chlor(am)ine is a commonly used combination of disinfectants in drinking water treatment. Although there are quite a few studies on the formation of some individual DBPs in the ozone‒chlor(am)ine disinfection, an overall picture of the DBP formation in the combined disinfection is largely unavailable. In this study, the effects of ozone dose on the formation and speciation of organic brominated disinfection byproducts (DBPs) in subsequent chlorination, chloramination, or chlorination‒chloramination of simulated drinking water were investigated. High-molecular-weight, aliphatic, alicyclic and aromatic brominated DBPs were selectively detected and studied using a powerful precursor ion scan method with ultra performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (UPLC/ESI-tqMS). Two groups of unregulated yet relatively toxic DBPs, dihalonitromethanes and dihaloacetaldehydes, were detected by the UPLC/ESI-tqMS for the first time. With increasing ozone dose, the levels of high-molecular-weight (m/z 300-500) and alicyclic and aromatic brominated DBPs generally decreased, the levels of brominated aliphatic acids were slightly affected, and the levels of dihalonitromethanes and dihaloacetaldehydes generally increased in the subsequent disinfection processes. Despite different molecular compositions of the detected DBPs, increasing ozone dose generally shifted the formation of DBPs from chlorinated ones to brominated analogues in the subsequent disinfection processes. This study provided a comprehensive analysis of the impact of ozone dose on the DBP formation and speciation in subsequent chlor(am)ine disinfection.

Phototransformation of Brominated Disinfection Byproducts and Toxicity Elimination in Sunlit-Ozonated Reclaimed Water

Ozonation is universally used during water treatment but can form hazardous brominated disinfection byproducts (Br-DBPs). While sunlight exposure is advised to reduce the risk of Br-DBPs, their phototransformation pathways remain insufficiently understood. Here, sunlight irradiation was found to reduce adsorbable organic bromine by 63%. Applying high-resolution mass spectrometry, the study investigated transformations of dissolved organic matter in sunlit-ozonated reclaimed water, revealing the number and abundance of assigned formulas decreased after irradiation. The Br-DBPs with O/C < 0.6 and MW > 400 Da were decreased or removed after irradiation, with the majority being CHOBr compounds. The peak intensity reduction ratio of CHOBr compounds correlated positively with double bound equivalent minus oxygen ratios but negatively with O/C, suggesting that photo-susceptible CHOBr compounds were highly unsaturated. Mass difference analysis revealed that the photodegradation pathways were mainly oxidation aligned with debromination. Three typical CHOBr molecular structures were resolved, and their photoproducts were proposed. Toxicity estimates indicated decreased toxicity in these photoproducts compared to their parent compounds, in line with experimentally determined values. Our proposed phototransformation pathways for Br-DBPs enhance our comprehension of their degradation and irradiation-induced toxicity reduction in reclaimed water, further illuminating their transformation under sunlight in widespread environmental scenarios.

Adsorption on activated carbon combined with ozonation for the removal of contaminants of emerging concern in drinking water

The presence of Contaminants of Emerging Concern (CECs) in drinking water is raising concern for potential negative effects on human health. Ozonation and adsorption on activated carbon are the most suitable processes for CECs removal in drinking water treatment plants (DWTPs). This study aims at evaluating the performance of ozonation and adsorption as in-series processes compared to those of the stand-alone processes, focusing on 18 compounds representative of various CECs families. No CECs spike was performed to evaluate the effectiveness of these processes towards CECs at their environmental concentrations. Adsorption isotherms were performed on water samples collected before and after the full-scale ozonation in a DWTP, testing different combinations of ozone and activated carbon doses. Generally, the combination of the two processes was beneficial (83% average removal) compared to adsorption and ozonation alone (71% and 34% average removal respectively). The effect of ozonation on adsorption depends on CECs reactivity with ozone, since ozonation improves the adsorption performance of poorly-oxidizable CECs, but worsens that of well-oxidizable compounds. The removal of organic matter, investigated by absorbance at 254 nm and fluorescence, by ozonation reduces competition for the subsequent CECs removal by adsorption (up to 20% increase of total CECs adsorption). Finally, the removal of both absorbance and fluorescence seems to be a good proxy variables for total CECs adsorption, with different relationships depending on the presence of ozonation. Conversely, it is not effective for ozonation, since the relationship depends on the reactivity of the specific CEC with ozone.

Multi-endpoint assays reveal more severe toxicity induced by chloraminated effluent organic matter than chloraminated natural organic matter

Disinfection by chloramination produces toxic byproducts and the difference in toxicity of reclaimed and drinking water treated by chloramination remains unclear. This study investigated cytotoxic effects at the same concentrations of dissolved organic matter and showed that chloraminated effluent organic matter (EfOM) induced 1.7 times higher cytotoxicity than chloraminated natural organic matter (NOM) applied to simulate drinking water. Chloraminated EfOM induced more reactive nitrogen species than chloraminated NOM, and chloraminated EfOM and NOM induced similar and higher levels of reactive oxygen species than the negative control, respectively. Consequently, intracellular macromolecule damage indicated by DNA/RNA damage marker 8‑hydroxy-(deoxy)guanosine and the intracellular protein carbonyl concentration induced by chloraminated EfOM was higher and slightly more than that induced by chloraminated NOM, respectively. These data were consistent with the effects on cell physiological processes. Cell cycle arrest mainly occurred in G2 phase by chloraminated EfOM and NOM. Early apoptotic cells, which could return to normal, increased upon exposure to high concentrations of chloraminated EfOM and NOM. Moreover, necrotic cells were significantly increased from 0.5% to 2.5% when the concentration increased from 20- to 60-fold chloraminated EfOM, but were not obviously changed by chloraminated NOM. These results indicated that the comprehensive intracellular changes induced by toxic substances in chloraminated EfOM were more irreversible and induced more cell death than chloraminated NOM.

Reduction of byproduct formation and cytotoxicity to mammalian cells during post-chlorination by the combined pretreatment of ferrate(VI) and biochar

Ferrate [Fe(VI)] can efficiently degrade various pollutants in wastewater. Biochar application can reduce resource use and waste emission. This study investigated the performance of Fe(VI)/biochar pretreatment to reduce disinfection byproducts (DBPs) and cytotoxicity to mammalian cells of wastewater during post-chlorination. Fe(VI)/biochar was more effective at inhibiting the cytotoxicity formation than Fe(VI) alone, reducing the cytotoxicity from 12.7 to 7.6 mg-phenol/L. The concentrations of total organic chlorine and total organic bromine decreased from 277 to 130 μg/L and from 51 to 39 μg/L, compared to the samples without pretreatment. Orbitrap ultra-high resolution mass spectrometry revealed that the number of molecules of DBPs decreased substantially from 517 to 229 by Fe(VI)/biochar, with the greatest reduction for phenols and highly unsaturated aliphatic compounds. In combination with the substantial reduction of 1Cl-DBPs and 2Cl-DBPs, 1Br-DBPs and 2Br-DBPs were also reduced. Fluorescence excitation-emission matrix coupled with parallel factor analysis suggested that fulvic acid-like substances and aromatic amino acid was obviously reduce likely due to the enhanced oxidation of Fe(IV)/Fe(V) produced by Fe(VI)/biochar and adsorption of biochar. Furthermore, the DBPs generated by electrophilic addition and electrophilic substitution of precursors were reduced. This study shows that Fe(VI)/biochar pretreatment can effectively reduce cytotoxicity formation during post-chlorination by transforming DBPs and their precursors.

Chlorination disinfection by-products in Southeast Asia: A review on potential precursor, formation, toxicity assessment, and removal technologies

This review discusses disinfection by-products' (DBPs) potential precursors, formation, and toxicity, alongside available research on the treatment of DBPs in Southeast Asian countries' water sources. Although natural organic matter (NOM) in the form of humic and fulvic acids is the major precursor of DBPs formation, the presence of anthropogenic organic matter (AOM) also plays essential roles during disinfection using chlorine. NOM has been observed in water sources in Southeast Asian countries, with a relatively high concentration in peat-influenced water sources and a relatively low concentration in non-peat-influenced water sources. Similarly, AOMs, such as microplastics, pharmaceuticals, pesticides, and endocrine-disrupting chemicals (EDCs), have also been detected in water sources in Southeast Asian countries. Although studies regarding DBPs in Southeast Asian countries are available, they focus on regulated DBPs. Here, the formation potential of unregulated DBPs is also discussed. In addition, the toxicity associated with extreme DBPs' formation potential, as well as the effectiveness of treatments such as conventional coagulation, filtration, adsorption, and ozonation in reducing DBPs' formation potential in Southeast Asian sources of water, is also analyzed.

Changes in toxicity and adsorbable organic bromine concentrations in ozonated reclaimed water irradiated with sunlight

Disinfecting reclaimed water for safe reuse can produce toxic disinfection by-products such as adsorbable organic bromine (AOBr). Irradiating stored reclaimed water with sunlight is a "green" and free method for eliminating some toxic disinfection by-products, but the effects of irradiation with sunlight on ozonated reclaimed water containing bromide are not well understood. In this study, AOBr was found at concentrations of 171-180 (µg Br)/L in ozonated reclaimed water containing bromide at a concentration of 2 (mg Br)/L and dissolved organic carbon at a concentration of ∼5 (mg C)/L. Irradiation with sunlight degraded 53-74% of the AOBr in two reclaimed water samples in 8 h, and the pseudo-first-order rate constants (k) were 0.09-0.17 h^-1. The concentration of tribromomethane, a typical Br-containing disinfection by-product, was decreased by >96% by irradiation for 8 h (k = 0.42-0.47 h^-1). Irradiation with sunlight decreased the toxicity of ozonated reclaimed water to Chinese hamster ovary cells. Irradiation with sunlight decreased the degree of intracellular oxidative stress and oxidative damage caused by ozonated reclaimed water. Irradiation with sunlight for 8 h decreased cytotoxicity of the ozonated reclaimed water samples by 79% and 65%. The change in AOBr concentration correlated with the change in toxicity (R²=0.69, p<0.05). The relationships between sunlight wavelength and decreases in the AOBr concentration and toxicity were assessed, and it was found that UV in sunlight was predominantly responsible for decreasing the AOBr concentration and toxicity by reclaimed water. During irradiation for 8 h, UV was responsible for 65%-66% of the decrease in the AOBr concentration and 65-79% of the decrease in reclaimed water induced cytotoxicity. Irradiation with sunlight is a promising method for degrading AOBr and detoxifying ozonated reclaimed water during storage to allow the water to be reused.

Effect of bromide on molecular transformation of dissolved effluent organic matter during ozonation, UV/H2O2, UV/persulfate, and UV/chlorine treatments

Ozonation and ultraviolet-based advanced oxidation processes (UV-AOPs) play important roles in advanced treatment of municipal wastewater for water reuse. Bromide is widely present in wastewater at different concentration levels (ranging from μg/L to mg/L). However, the effect of bromide on molecular transformation of dissolved effluent organic matter (dEfOM) in real wastewater during ozonation and UV-AOPs treatments still remains unclear. Herein, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was utilized to characterize the overall molecular transformation of dEfOM and the formation of unknown halogenated byproducts (X-BPs) in ozonation, UV/H₂O₂, UV/persulfate (UV/PS), and UV/chlorine (UV/Cl) processes in the presence of additional bromide. Compared with the same oxidation processes without additional bromide, the degree of dEfOM oxygenation had some extent decrement with the effect of bromide. A slightly increment of the number of unknown brominated byproducts (Br-BPs) was observed during ozonation, UV/H₂O₂, and UV/PS treatments in the presence of additional bromide, and the largest increment of these compounds was found in UV/Cl process. A total of 82 chlorinated byproducts (Cl-BPs) and 183 Br-BPs were detected in all oxidation processes with the effect of bromide, and the number of Br-BPs was significantly higher than that of Cl-BPs. Based on mass difference analysis, 69 pairs of possible precursors/Br-BPs were identified. In addition, the additional bromide did not remarkably increase the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) in ozonation, UV/H₂O₂, and UV/PS treatments, while the production of THMs and HAAs significantly decreased by 68.06% and 54.55%, respectively, during UV/Cl treatment. The calculated cytotoxicity increased to some extent for each treatment, especially for UV/Cl treatment, and the compound with largest contribution to cytotoxicity was monobromoacetic acid. This study provides new insights into the formation and transformation of X-BPs during advanced treatment of real wastewater with the effect of bromide.