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•Colorimetric method capable of quantifying trihalomethanes in drinking water.•A method that can be adapted for minimally equipped laboratories.•The method was validated according to ...validation protocols.•The detection and quantification limits were 13.41 and 40.65 μg L−1, respectively.•Recovery assays ranged from 86.1 to 90.7 % and precision was <14 %.
Chlorine is a common disinfectant used in water treatment. However, its reaction with organic matter can lead to the formation of harmful byproducts, such as trihalomethanes (THMs), which are potentially carcinogenic. To address this issue, the aim of this work was to enhance a colorimetric method capable of quantifying THMs in drinking water through UV/Vis Spectrophotometry, using cost-effective equipment, and validate this methodology for the first time according to established validation protocols. The method’s innovation involved replacing the solvent pentane with the more common hexane, along with adjusting the heating ramp, elucidating the mechanisms involved in the process. This method involves the reaction between THMs, pyridine, and NaOH to produce a colored compound, which is then monitored through molecular absorption spectroscopy in the visible region. The method was thoroughly validated, achieving a limit of detection of 13.41 μg L−1 and a limit of quantification of 40.65 μg L−1. Recovery assays ranged from 86.1 % to 90.7 %, demonstrating high accuracy. The quality of the linear fit for the analytical curve exceeded R2 > 0.98. The method was applied to real samples, revealing concentrations ranging from 13.58 to 55.46 μg L−1, all way below the legal limit in Brazil (Maximum Contaminant Levels (MCL) = 100 μg L−1). This cost-effective and straightforward method is suitable for integration into water treatment plant laboratories.
Tetrabromobisphenol A (TBBPA) is one of the most widely applied brominated flame retardants and has been widely detected in water environment, which might pose risks of brominated disinfection ...by-products formation in water treatment system. Ferrate(VI)-CaSO3 (Fe(VI)-CaSO3) system could effectively degrade TBBPA at pH 7.0–9.0 but the decomposition rate of TBBPA dropped with increasing pH. The presence of 0.5 mg C/L humic acid (HA) had negligible impact on TBBPA removal, but the removal of TBBPA decreased to ~87% and 80% at pH 7.0 and 8.0, respectively, in the presence of 5.0 mg C/L HA. The transformation products of TBBPA detected in Fe(VI)-CaSO3 process revealed that TBBPA degradation mainly proceeded via electron abstraction, debromination, and ring-opening pathways and Br− was released. In the presence of TBBPA, Fe(VI)-CaSO3 pre-oxidation decreased the generation of all determined DBPs during chlorination at pH 8.0 but it lessened the generation of some DBPs and slightly increased the formation of the other DBPs at pH 7.0. The toxic risk analysis showed that Fe(VI)-CaSO3 pre-oxidation of TBBPA could reduce the toxic risk of DBPs in both synthetic water and natural water at pH 8.0, indicating that Fe(VI)-CaSO3 process has the potential to be applied in practical water treatment.
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•TBBPA could be efficiently degraded by Fe(VI)-CaSO3 technology at pH 7.0–9.0.•TBBPA was degraded via electron abstraction, debromination, and ring-opening steps.•Two mg C/L HA inhibited Br− release during TBBPA removal in Fe(VI)-CaSO3 process.•With TBBPA, Fe(VI)-CaSO3 process inhibited DBPs formed in chlorination at pH 8.0.•With TBBPA, Fe(VI)-CaSO3 pre-oxidation reduced the toxic risk of DBPs at pH 8.0.
Combined processes of light-emitting diodes ultraviolet (LED UV) and chlorination (Cl2) are alternative disinfection technologies in drinking water, while the formation of disinfection by-products ...(DBPs) needs to be evaluated. This study investigated the impacts of critical water matrix factors on the DBP formation in the combined processes. Moreover, the correlation between the degraded natural organic matter (NOM) and the formed DBP was studied. Simultaneous UV/Cl2 outperformed single Cl2 and sequential combined processes in degrading humic acids (HA) and resulted in the highest DBP yield. Iodide at 5–20 μg/L and bromide at 0.05–0.2 mg/L slightly affected the degradation of organics, while increased the formation of brominated DBPs up to 36.6 μg/L. pH 6 was regarded as the optimum pH, achieving high efficiency of HA degradation and a lower level of total DBP formation than pH 7 and 8 by 11 % and 24 %, respectively. Compared to HA samples (46.8–103.9 μg/L per mg/L DOC), NOM in canal water were less aromatic and yielded fewer DBPs (19.6 and 21.2 μg/L per mg/L DOC). However, the extremely high bromide in site 1 samples (18.6 mg/L) shifted the chlorinated DBPs to their brominated analogues, posting around 1 order of magnitude higher levels of toxicities than HA samples. The reduction of absorbance at 254 nm (UV254) correlated with all DBP categories in HA samples, while the correlation coefficients were compromised when included in the canal samples. For the first time, this study found that parallel factor analysis (PARAFAC) would neglect the fluorescence change caused by iodide/bromide in UV/Cl2, while the changes could be captured by self-organising map (SOM) trained with full fluorescence spectra. Fluorescence Ex/Em pairs were proposed to predict DBP formation, suggesting a potential method to develop an online monitoring system for DBPs.
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•Simultaneous LED UV/Cl2 yielded more DBPs than Cl2 alone from humic acids.•0.05–0.2 mg/L Br− increased the yield of Br-DBP in LED UV/Cl2 up to 36.6 μg/L.•EEM change neglected by PARAFAC was highlighted in SOM trained by full spectra.•UV254 was less correlated with DBPs when included in canal water samples.•Ex/Em pairs in whole fluorescence spectra were suggested to predict DBPs.
Water disinfection involves the use of different types of disinfectants, which are oxidizing agents that react with natural organic matter (NOM) to form disinfection by-products (DBPs). The United ...States Environmental Protection Agency (USEPA) has established threshold limits on some DBPs, which are known as regulated DBPs (R-DBPs). The human health risks associated with R-DBPs in drinking water distribution systems (DWDSs) and application of stricter regulations have led water utilities to switch from conventional disinfectant (i.e., chlorination) to alternative disinfectants. However, the use of alternative disinfectants causes formation of a new suit of DBPs known as unregulated DBPs (UR-DBPs), which in many cases can be more toxic. There is a growing concern of UR-DBPs formation in drinking water. This review prioritizes some commonly occurring UR-DBP groups and species in DWDSs based on their concentration level, reported frequency, and toxicity using an indexing method. There are nine UR-DBPs group and 36 species that have been identified based on recent published peer-reviewed articles. Haloacetonitriles (HANs) and haloacetaldehydes (HALs) are identified as important UR-DBP groups. Dichloroacetonitrile (DCAN) and trichloroacetaldehye (TCAL) are identified as critical UR-DBPs species. The outcomes of this review can help water regulators to identify the most critical UR-DBPs species in the context of drinking water safety and provide them with useful information to develop guidelines or threshold limits for UR-DBPs. The outcomes can also help water utilities in selecting water treatment processes for the mitigation of human health risk posed by UR-DBPs through drinking water.
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•Unregulated disinfection by-products in drinking water were comprehensively reviewed.•Commonly occurred unregulated disinfection by-products were prioritized.•Haloacetonitriles were identified as the most important group.•Dichloroacetonitrile and trichloroacetaldehyde were the most critical species.
Seawater reverse osmosis (SWRO) has been extensively applied to replenish the limited freshwater resources. One concern of such technology is the formation of disinfection by-products (DBPs) during ...the pre-chlorination process. For the SWRO tested in this study, the concentrations of trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs) increased by 35.1, 23.7 and 4.9μg/L, respectively, after a seawater sample (with UV254/DOC of 3.7L/mg·m and Br− of 50.9mg/L) was pre-chlorinated (1–2mg-Cl2/L). The dissolved organic matter (DOM) with molecular weight (MW) <1kDa dominated the formation of total THMs, HAAs and HANs. To further investigate DBPs precursors in the seawater, the DOM with MW<1kDa was fractionated to hydrophobic acids (HOA), hydrophobic bases (HOB), hydrophobic neutrals (HON), and hydrophilic substances (HIS). The excitation emission matrix fluorescence spectra analysis showed that most aromatic protein and fulvic acid of the DOM with MW<1kDa were present in the HON and HIS fractions. The HON fraction was the dominant precursor to form THMs and HAAs, while HIS controlled the formation of HANs. Furthermore, bromo - DBPs dominated the total DBPs yields after the chlorination of HIS fraction.
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•A large amount of THMs, HAAs and HANs were formed in the seawater reverse osmosis.•The MW<1kDa was the dominant DOM of the seawater and contributed to DBP formation.•The hydrophilic substances of MW<1kDa were the dominant precursors to form HANs.•The hydrophobic neutrals of MW<1kDa were the major precursors for THMs and HAAs.
A detailed comparison of sand filtration (SF) and ultrafiltration (UF) was conducted in this study with the aim to provide systematic support for alternative UF and SF technologies. The results of ...natural organic matter (NOM) removal indicated that SF conferred a slightly higher removal rate for UV-absorbing compounds, humic-like substances and protein-like substances than UF, with removal efficiencies of 21.9%, 19.8% and 26.1%, respectively. In addition, SF and UF exhibited different removal performances for organic fractions: UF better removed high molecular-weight (MW) organics, while SF exhibited higher removal of medium-MW organics. Furthermore, chlorine and chlorine dioxide were used as disinfectants to compare the different influences of SF and UF on disinfection by-product (DBP) formation. Unexpectedly, SF exhibited a better capacity for reducing the formation of chlorite than the UF process, with concentrations of 0.57 mg/L and 0.69 mg/L, respectively. Importantly, for the emergency scenario, e.g. seasonal algae pollution, the UF process achieved significantly higher removal of algae cells (98.7%) than SF due to size exclusion, indicating substantial resistance to algae load shocks. Therefore, these findings are beneficial for making practical decisions to adopt SF or UF technology in drinking water treatment plants.
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•A direct comparison between UF and SF was conducted.•The disinfection was combined with traditional filtration and ultrafiltration.•The residual chlorine of UF was lower than that of SF.•SF outperformed UF in alleviating formation of DBPs.•UF conferred great resistance to the algae load shocks than SF.
Artificial sweeteners have raised emerging concern due to their potential threats to human health, which were frequently detected in aquatic environment with median concentrations. Although current ...researches have widely reported that ultraviolet light-activated persulfate process (UV/PS) was superior to UV/H2O2 process for the degradation of refractory organic contaminants, UV/H2O2 process presented a more satisfactory saccharin (SAC) removal efficiency than UV/PS process, completely degraded 20 mg/L SAC within 45 min. Hence, quenching and probe experiments were employed to investigate the difference between hydroxyl radical (OH)- and sulfate radical (SO4-)-mediated oxidation mechanisms, which revealed the higher reactivity of OH (1.37–1.56 × 109 M−1 s−1) toward SAC than SO4- (3.84–4.13 × 108 M−1 s−1). A combination of density functional theory calculation and transformation products identification disclosed that OH preferred to attack the benzene ring of SAC via hydrogen atom transfer pathway, whereas SO4- oxidation was conducive to the cleavage of -C-NH2 bond. Increasing oxidant concentration significantly accelerated SAC degradation in both processes, while UV/H2O2 process consumed lower electrical energy with respect to UV/PS process. Additionally, UV/H2O2 system presented excellent adaptability and stability under various water matrices parameters (e.g. pH, anions and humic acid). While both UV/H2O2 and UV/PS processes promoted the generation of disinfection by-products (DBPs) during subsequent chlorination, and prolonging pretreatment time posed positive effect on reducing the formation of DBPs. Overall, the results clearly demonstrate the high efficiency, economy and practicality of UV/H2O2 process in the remediation of SAC-contaminated water.
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•The SAC degradation efficiency in UV/H2O2 process was superior to that in UV/PS process.•The contributions of SAC degradation by UV/PS oxidation was in the order of OH > SO4−>UV photolysis.•OH and SO4− preferred to attack the benzene ring of SAC via HAT and RAF pathways, respectively.•SO4− oxidation was conducive to the loss of –NH2 in SAC to generate the N-DBP precursors.•DBPs transformation was better controlled by UV/H2O2 pretreatment than by UV/PS.
Algal blooms intensified operational problems in water treatment due to the increases of taste- and odor-causing compounds and natural organic matter (NOM). Effects of powdered activated carbon (PAC) ...addition during algal blooms on NOM removal was investigated in this study using an algal-rich water. Water quality analyses including dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254) and specific UV absorbance (SUVA) were performed to elucidate characteristics of NOM removal by PAC adsorption. Variations of MW distributions and emission/excitation matrix (EEM) spectra with increasing PAC dosages were also measured. In addition, formation potential (FP) of trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs) was evaluated with increasing PAC dosage. The correlations between disinfection by-products formation potential (DBPFP) and water qualities such as DOC, UV254, SUVA, and EEM spectra were also investigated to identify factors associated with DBPFP. The PAC addition was effective to remove NOM, especially low molecular weights NOM and proteinaceous substances with weak aromatics. The PAC addition showed the consistent reduction of THMFPs, HAAFPs, and HANFPs with increasing PAC dosage while the greater reduction of HAN precursors was eminent compared to the other two FPs. The close correlations between UV254 and the three DBPFPs were obtained. The low molecular weight (i.e., 1–700 Da) NOM and three fluorescence spectra peaks, i.e., T1, A and C peaks, also showed high correlation factors with the three DBPFPs. Those analyses with high correlations with DBPFPs would provide useful information to reduce DBPs during algal blooms.
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•Algal-rich water had high DOC, low SUVA and relatively high HANFPs.•PAC was effective to remove low MW NOM and fluorescence peaks of T1, A, and C.•PAC adsorbed selectively precursors in the order of HANFP, THMFP and HAAFP.•The precursor removal by PAC changed the speciation of DBPFPs.•DBPFP showed higher correlation with UV254, low MW NOM, and fluorescence spectra.
•Combination of chlorine and PMS accelerated ACT degradation.•PMS-catalytic chlorination of ACT was identified at neutral condition.•Kinetics for ACT degradation in the PMS/chlorine system was ...established.•Impacts of typical operational conditions were evaluated.•PMS increased the concentration of most selected DBPs in chlorination process.
With the fast development of peroxymonosulfate (PMS)-dominating processes in drinking water and wastewater treatment, residual PMS is easy to come across chlorine as these processes are usually followed by secondary chlorine disinfection. The synergistic effect of PMS and chlorine on the degradation of micro-organic pollutants is investigated by selecting acetaminophen (ACT) as a reference compound for the first time in this study. Unlike conventional PMS or chlorine activation which generates reactive species such as hydroxyl radical (HO•), sulfate radical (SO4•−), chlorine radical (Cl•), and singlet oxygen (1O2), the efficient ACT removal is attributed to the direct catalytic chlorination by PMS due to the significantly enhanced consumption of chlorine along with negligible change of PMS concentration at neutral condition, and the same reaction pathways in both PMS/chlorine and chlorine processes. The kinetic study demonstrates that ACT oxidation by PMS/chlorine follows second order reaction, and the degradation efficiency can be promoted at alkaline conditions with peak rate constants at pH 9.0−10.0. The presence of chloride can enhance the removal of ACT, while ammonium and humic acid significantly retard ACT degradation. Higher formation of selected disinfection by-products (DBPs) is observed in the PMS/chlorine process than in the sole chlorination. This study highlights the important role of PMS in organic pollutants degradation and DBPs formation during the chlorination process.
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