DBPs Formation Research Articles

Revisiting iodide species transformation in peracetic acid oxidation: unexpected role of radicals in micropollutants decontamination and iodate formation

Peracetic acid (PAA) is an alternative disinfectant for saline wastewaters, and hypohalous acids are typically regarded as the reactive species for oxidation and disinfection. However, new results herein strongly suggest that reactive radicals instead of HOI primarily contributed to decontamination during PAA treatment of iodine-containing wastewater. The presence of I- could greatly accelerate the micropollutants (e.g., sulfamethoxazole (SMX)) transformation by PAA. Chemical probes experiments and electron paramagnetic resonance analysis demonstrate acetylperoxyl radical rather than reactive iodine species primarily responsible for SMX degradation. The kinetic model was developed to further distinguish and quantify the contribution of radicals and iodine species, as well as to elucidate the transformation pathways of iodine species. Density functional theory calculations indicated that the nucleophilic attack of I- on the peroxide bond of PAA could form unstable O−I bond, with the transition state energy barrier for radical generation lower than that for HOI formation. The transformation of iodine species was regulated by acetylperoxyl radical to generate nontoxic IO3-, greatly alleviating the iodinated DBPs formation in saline wastewaters. This work provides mechanistic insights in radical-regulated iodine species transformation during PAA oxidation, paving the way for the development of viable and eco-friendly technology for iodide containing water treatment.

Comparison of UV/PS and VUV/PS as ultrafiltration pretreatment: Performance, mechanisms, DBPs formation and toxicity assessment

Ultrafiltration (UF) is widely used in drinking water plants, nevertheless, it still encounters challenges stemming from inevitable membrane fouling caused by natural organic matter (NOM). Herein, this work applied VUV/PS as UF membrane pretreatment and used UV/PS for comparison. VUV/PS system exhibited superior ability in removing NOM compared to UV/PS system. HO and SO4− played crucial roles in the degradation. [SO4−]ss was notably higher than [HO]ss in the systems, yet HO was of greater significance. [HO]ss and [SO4−]ss in the VUV/PS process were remarkably higher than those in the UV/PS process, due to the function of 185 nm photons. VUV/PS pretreatment basically recovered flux and effectively reduced fouling resistance, with better performance than UV/PS. Fouling mechanism was dominated by multiple mechanisms after UV/PS pretreatment, whereas it was transformed into pore blockage after VUV/PS pretreatment. Moreover, the UF effluent quality after VUV/PS pretreatment outperformed that of UV/PS but fell short of that without pretreatment, possibly due to the generation of abundant low MW substances under the action of HO and SO4−. After chlorine disinfection, UV/PS and VUV/PS pretreatments increased the DBPs production and cytotoxicity. Specifically, oxidant PS affected the membrane surface morphology and fouling behaviors, and had no obvious effect on interception performance and mechanical properties. In actual water treatment, VUV/PS and UV/PS pretreatments exhibited excellent performance in alleviating membrane fouling, improving water quality, and reducing DBPs formation and acute toxicity.

Reclamation of impacted urban phreatic water through nanofiltration technology: Insight on natural organic matter removal by fluorescence spectroscopy

Nanofiltration (NF) is a promising technology called to play a relevant role in water reclamation, which lies in the core of circular economy in the water sector. The aim of this study was to assess two aromatic polyamide-based NF membranes (the looser NF270 and the tighter NF90 ones) for the treatment of urban impacted phreatic water. The focus was centred on the removal of dissolved inorganic and organic solutes and on the differences observed between solutes. Membrane ions rejection was modelled by the Solution-Electro-Diffusion Film Model (SEDFM). DOC was tracked by Fluorescence Excitation-Emission Matrices (FEEM) coupled to Parallel Factor Analysis (PARAFAC) to get insight into the character of DOC rejected by or permeated through the membranes. Results showed that the NF90 membrane systematically achieved upper values in the rejection of ions than the looser NF270 one. Variations between ions could be interpreted by the mechanisms ruling their rejection, i.e. Donnan and dielectric exclusion phenomena. Experimental rejections were also satisfactorily fit by the SEDFM, indicating that that the presence of DOC in the phreatic water did affect modelling of ions transport through the membranes. DOC was rejected at very high percentages (>90%) by both membranes, but FEEM-PARAFAC analysis revealed that humic- and tryptophan- like components were more rejected (>90% for both membranes) than tyrosine-like compounds (45% for NF270 and 57% for NF90). The finding is of relevance from a point of view of disinfection practices, as it has been observed that humic-like substances are strongly correlated with DBPs formation.

Oxidative abatement of saccharin by ozone and its influence on DBPs formation during postchlorination

As one of artificial sweeteners, saccharin (SAC) is widely used in food, personal care products and animal feed industry. SAC cannot be effectively metabolized by organisms and most of them are discharged into the water environment through multiple channels, leading to general detection in water source. In this study, the fate of SAC in the advanced ozone treatment of drinking water and subsequent chlorination disinfection was investigated. The results showed ozone could effectively degrade SAC and >99 % of 20 mg/L SAC could be removed under 7.10 mg/min ozone flow within 60 min. While, the mineralization was comparably low by 80 %, which indicated that ozone converted SAC into organic intermediate products. Therefore, SAC characterized with anti-chlorination property was changed to disinfection by-product precursor. Disinfection by-products including trichloromethane (TCM), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA) and dichloroacetonitrile (DCAN) were found during subsequent chlorination. The yields of TCM, DCAA, TCAA and DCAN were found to be 8.1, 0.4, 1.2 and 0.1 μg/mg SAC, respectively, 3, 39, 41 and 178 times of those produced by direct chlorination. In addition, the increase of ozone flux promoted the formation of disinfection by-products. Meta-alkalescence was conducive to the formation of DCAA, TCAA and DCAN in pH range of 6 to 8. The presence of anions including Cl−, NO3− and CO32− reduced the formation of TCM, DCAA and DCAN.

Effective control of DBPs formation and membrane fouling in catalytic ozonation membrane reactor for municipal wastewater reclamation

This study aimed to evaluate the performance of different ceramic membranes, namely CuMn2O4 (CMO), g-C3N4 (CN), and CuMn2O4/g-C3N4 (CMO/CN) ceramic membrane (CM), in a catalytic ozonation membrane reactor (COMR) for municipal wastewater reclamation. The results demonstrated that CMO/CM and CMO/CN/CM used in the COMR exhibited high performance in terms of flux, removal efficiency of effluent organic matter (EfOM), control of disinfection by-products formation potential (DBPs-FP), and mitigation of membrane fouling. Notably, catalytic ozonation by CMO/CM showed superior reduction in DBPs formation (40.6 % of nitrogenous DBPs, 83.4 % of halogenated hydrocarbons, 36.6 % of haloacetic acids). Furthermore, significant inhibition of both organic fouling and biofouling was observed in the COMR. The addition of O3 altered the membrane fouling mechanism from gel layer formation to intermediate blocking. Ozonation primarily reduced the physically reversible fouling while catalytic ozonation additionally mitigated physically irreversible fouling. In addition to the almost complete removal of total cells and proteins, catalytic ozonation by CMO/CM further cleaned the α-polysaccharides and β-polysaccharides on the membrane surface, resulting in a 55.3 % reduction in biofilm thickness and demonstrating strong self-cleaning properties. These findings have important implications for enhancing the overall performance and durability of COMR systems in municipal wastewater reclamation.

Accelerated degradation of micro-pollutant by combined UV and chlorine dioxide: Unexpected inhibition of chlorite formation

UV/chlorine dioxide (ClO2) process can be intentionally or accidently conducted and is potentially effective in micro-pollutants degradation. UV irradiation can promote ClO2 decay and subsequently result in the formation of reactive radicals. Hence, the co-exposure of ClO2 and UV exhibited a synergetic effect on metribuzin (MET) degradation. The MET degradation was promoted by UV/ClO2 with a rate of 0.089 min−1 at pH 7.5, which was around 2.4 folds the total of rates caused by single ClO2 (0.004 min−1) and single UV (0.033 min−1). Reactive radicals mainly HO• and reactive chlorine species were involved in the acceleration effect, and contributed to 59%–67% of the total degradation rate of MET during UV/ClO2 under pHs 5.5–7.5. Among them, HO• was the predominant contributor and the contribution rate gradually rose under higher pH. Chlorite (ClO2−) and chlorate (ClO3−) formation has been the major concern of ClO2 oxidation. However, a comparison of their formation during UV/ClO2 and ClO2 oxidation is rarely reported. Herein, during MET degradation by ClO2, only ClO2− was identified with the highest amount of 1.17 mg L−1. Conversely, during MET degradation by UV/ClO2, only ClO3− was identified with the highest amount of 0.68 mg L−1, showing an upward trend with prolonging treatment time. Furthermore, organic halogenated DBPs formation after 24 h post-chlorination with UV/ClO2 and ClO2 pre-treatments was comparatively evaluated. Organic DBPs formation after post-chlorination was higher with UV/ClO2 pre-treatment compared to ClO2 pre-treatment. The overall concentration of DBPs produced with 30 min UV/ClO2 pre-treatment was about 4.5 times that with 1min UV/ClO2 pre-treatment. This study provided useful reference for the application of UV/ClO2 in micro-pollutants degradation.

Photodegradation of halogenated organic disinfection by-products: Decomposition and reformation

In this study, the photodegradation of 33 different DBPs (trihalomethanes, haloacetic acids, haloacetaldehydes, and haloacetonitriles) and TOX with low pressure UV light and the subsequent reformation of DBPs with chlorine and monochloramine were investigated. Results indicated that photodegradation followed the order of TOI > TOBr > TOCl, and treated surface water with low SUVA254 background did not impact the photodegradation of highly UV susceptible DBPs such as triiodomethane (TIM), diiodobromomethane (DIBM), tribromomethane (TBM). The mass balance results of chloride, bromide and iodide showed that the main photodegradation mechanism of TOBr and TOI was dehalogenation supported by halide releases (i.e., Cl−, Br− and/or I− ion). In addition, the photodegradation removal effect was higher, when brominated DBPs formation was high. Although low pressure UV light effectively removed halogenated organic DBPs, subsequent use of disinfectants (Cl2 and NH2Cl) reformed photodegraded DBPs, and the overall DBPs concentrations were increased, which suggested that the released Br− and I− ions will reform DBPs in distribution systems, with oxidants present or added (e.g., booster chlorination) in distribution systems. This study showed that although UV photodegradation will reduce halogenated organic DBPs in distribution systems, especially more toxic iodinated and brominated DBPs, it will be a more effective technology towards the end of the distribution system or a point of entry solution rather than in distribution system with post-disinfection and residence time.

Characteristics of dissolved organic matter in two alternative water sources: A comparative study between reclaimed water and stormwater

Reclaimed water and stormwater are two important alternative water sources to mitigate water resource shortage. They can be reused by discharging into drinking water sources. Due to different sources, characteristics of dissolved organic matter (DOM, a precursor of disinfection by-products, DBPs) present in reclaimed water and stormwater would be different. This study selected reclaimed water to compare with stormwater (including both stormwater runoff and rainwater) by investigating their DOM characteristics, including concentrations, aromaticity, molecular weight, hydrophobicity/hydrophilicity, composition and DBPs formation potential. The results showed that reclaimed water had higher dissolved organic carbon (DOC) concentrations (6.02–10.8 mg/L) than stormwater (3.62–5.48 mg/L) while SUVA254 values of stormwater runoff (1.92–2.53 L/(mg-C·m)) were higher than reclaimed water (1.11–1.24 L/(mg-C·m)). Additionally, reclaimed water is more hydrophobic while stormwater runoff and rainwater are more hydrophilic. Although all water types included the highest fraction of DOM with molecular weight <1 kDa (43.0 %–77.5 %), reclaimed water primarily contained soluble microbial products (SMPs)-like and humic acid-like substances while stormwater runoff primarily contained humic acid-like DOM. In terms of DBPs, reclaimed water showed relatively higher formation potential than stormwater runoff while rainwater had the lowest DBPs formation potential. These results can contribute to effective water resource management. Particularly, when reclaimed water or/and stormwater are discharged into drinking water sources, these outcomes can help on efficient drinking water treatment.

Degradation of tetracycline by UV/Fe3+/persulfate process: Kinetics, mechanism, DBPs yield, toxicity evaluation and bacterial community analysis

As a widely produced and used antibiotic, tetracycline (TC) has been frequently found in rivers, soil and drinking water. In this study, the degradation of TC was investigated by UV/Fe3+/persulfate (PS) coupled process. The degradation behavior was well fitted with pseudo-first-order model. Hydroxyl radicals (·OH), sulfate radicals (SO4−·) and superoxide radical (O2−·) were identified as the primary reactive oxygen species (ROS) in UV/Fe3+/PS process, the contribution to TC degradation were found to be 41.94%, 33.94% and 17.44% at pH 3.0, respectively. Fe(IV) generated from the system also played a crucial role in TC removal. The effects of process parameters (PS/Fe3+ dosages, pH, humic acid, Cl−, HCO3−, NO3− and CO32−) on degradation were investigated. It was found that the degradation of TC was highly pH-dependent, and the optimal performance was obtained at pH 3.0. Except for Cl−, the presence of HA, HCO3−, NO3− and CO32− inhibited TC degradation. The possible transformation pathway involving the hydroxylation, N-demethylation, hydrogenation and dehydroxylation was proposed. Furthermore, the toxicity and mutagenicity of TC and transformation products (TPs) were estimated using ECOSAR and TEST softwares, demonstrating that the toxicity level of most TPs was lower/equal to their precursors. The evaluation of DBPs showed that UV/Fe3+/PS process could reduce the potential of DBPs formation, especially for TCAA and TCM. Microbial community composition was analyzed by 16 S rDNA sequencing, and the relative abundance of ARG-carrying opportunistic pathogens was significantly declined after UV/Fe3+/PS treatment. In general, this study provides an economical, efficient and safe strategy for TC removal.

Comparative investigation of diclofenac degradation by Fe2+/chlorine and Fe2+/PMS processes

The degradation of diclofenac (DCF), a commonly used nonsteroidal anti-inflammatory drug, by Fe2+/chlorine and Fe2+/PMS processes was comparatively investigated. The influencing factors of pH, Fe2+ and oxidant dosage on DCF degradation efficiency were evaluated and optimized. Typically, with an initial solution pH of 5, an Fe2+ dosage of 70 μM, and a chlorine or PMS dosage of 70 μM, the degradation efficiency of DCF using the Fe2+/chlorine and Fe2+/PMS processes reached 94.2% and 79.7%, respectively, within 10 min. Quenching tests indicated the coexistence of •OH and RCS in the Fe2+/chlorine system, and both SO4●– and •OH were identified in the Fe2+/PMS system. In addition, Fe(IV) was also identified to participate in DCF degradation in two systems based on the oxidation of PMSO to PMSO2. The degradation products and pathways of DCF were elucidated by LC/TOF/MS analysis and DFT calculations. It was assumed that the degradation pathway of DCF involves hydroxylation, dechlorination, decarboxylation, cleavage of the C-N bond, and chlorine substitution. In addition, trichloromethane (TCM), dichloroacetaldehyde (DCAL), dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM) were also detected in the Fe2+/chlorine process, and these chlorinated DBPs initially increased and then decreased with prolonged reaction time, indicating that Fe2+/chlorine is capable of controlling DBPs formation. Finally, the acute and chronic toxicity of DCF and its degradation products were evaluated by the ECOSAR program.

Improvement of Fe(Vi) Oxidation by Naclo on Degrading Phenolic Substances and Reducing Dbps Formation Potential

Improvement of Fe(Vi) Oxidation by Naclo on Degrading Phenolic Substances and Reducing Dbps Formation Potential

Removal of saccharin by UV/persulfate process: Degradation kinetics, mechanism and DBPs formation

As a widely used artificial sweetener, saccharin (SAC) has received extensive attention due to its widespread detection in aquatic environment and potential risk to human health. In this study, the SAC removal by UV-activated persulfate (PS) was comprehensively examined. The results demonstrated that SAC could be eliminated effectively through UV/PS oxidation and its removal behavior can be well described by pseudo-first-order kinetic model. The introduction of different scavengers manifested that sulfate radicals (SO4−∙) were identified to be the major reactive radicals under acidic and neutral conditions, while hydroxyl radicals (HO∙) were determined to be the dominant species under alkaline environments. The reaction rates of SAC with SO4−∙ and HO∙ were calculated to be 1.48 × 108 and 1.56 × 109 M−1 s−1, respectively. The degradation rate constant was positively related to PS dosage (0.21–2.52 mM). The degradation decelerated with the increase of pH from 4.0 to 8.0 and slightly accelerated at pH 9.0. The introduction of Cl− posed a positive impact, while the presence of HCO3−, Br− and humic acid overall retarded SAC removal. Low concentrations of NO3− promoted the degradation, whereas the high levels of NO3− exerted a negative effect. The SAC degradation by UV/PS was mainly initiated through the hydroxylation of the benzene ring, cleavage of C-N bonds, decarboxylation and denitrogenation. The SAC removal in real water matrices by UV/PS treatment was still relatively efficient. Of note, the increased yield of trichloromethane, dichloroacetic acid, trichloroacetic acid and dichloroacetonitrile was found due to chlorination after UV/PS pretreatment.

Comparison of fleroxacin oxidation by chlorine and chlorine dioxide: Kinetics, mechanism and halogenated DBPs formation

Fleroxacin (FLE) is a widely used fluoroquinolones to cure urinary tract infections and respiratory disease, which has been frequently detected in the aquatic environment. The reactivity kinetics of FLE by chlorine and chlorine dioxide (ClO2) and transformation mechanism were investigated in this study. The results showed that FLE was degraded efficiently by chlorine and ClO2, and both reactions followed second-order kinetics overall. The increase of disinfectant dosage and temperature would enhance the degradation of FLE. The highest removal of FLE by chlorine was achieved at a neutral condition (pH 7.4), whereas ClO2 reaction rates increased dramatically with the increasing pH in this study condition. The number of intermediates identified in FLE chlorination and ClO2 oxidation was seven and ten, respectively. The piperazine ring cleavage was the principal and initial reaction in both above reactions. Then, the removal of the piperazine group was predominantly in FLE removal by chlorine, while the decarboxylation mainly occurred in FLE removal by ClO2. The intermediates increased first and then decreased with time, while three kinds of halogenated DBPs increased with time, indicating the above-identified intermediates were further transformed to the halogenated DBPs. Additionally, compared to chlorine reaction, the reaction of ClO2 with FLE reduced the formation of halogenated DBPs, but it also induced the formation of chlorite. The analysis of toxicity showed that compared with chlorination, the oxidation of ClO2 was more suitable for FLE removal.

Degradation of p-arsanilic acid by pre-magnetized Fe0/persulfate system: Kinetics, mechanism, degradation pathways and DBPs formation during subsequent chlorination

Pre-magnetized Fe0/persulfate (pre-Fe0/PS) process was innovatively employed for controlling the pollution of p-arsanilic acid (p-ASA). This process showed favorable removal performance, achieving almost complete elimination of 10 mg/L p-ASA within 30 min at the reaction conditions of 0.2 g/L pre-Fe0 and 1 mM PS. The increase of PS concentration and pre-Fe0 dosage was conducive to the degradation. The coexistence of Cl−, NO3− and SO42− accelerated the removal, however the presence of HCO3− and HA presented the opposite trend. The p-ASA degradation decelerated gradually with increasing pH from 5 to 9. Its removal was caused by the attack of reactive oxygen species (i.e., SO4−, OH, O2−), which could be continuously formed via the Fe2+/Fe3+ cycle in solution and on pre-Fe0 surface. In pre-Fe0/PS system, SO4− in solution, surface-bound SO4−, OH, OH in solution, O2− in solution and Fe(IV) contributed to the p-ASA degradation. A plausible transformation route related to the break of C-N and As-C bonds, the substitution of OH group was put forward. More importantly, the released inorganic arsenic during p-ASA decomposition could be effectively controlled through multiple functions including the precipitation, co-precipitation and sorption, which was well confirmed by XPS, FTIR and XRD analysis. Pre-Fe0/PS and Fe0/PS pretreatments both reduced the generation of C-DBPs except for chloral hydrate, while increased the formation of N-DBPs except for trichloroacetamide.

Tracing TOC concentration and SUVA254 in surface water, treated water and wasted aluminum sludge

Safe water production is the world's primary concern; however, organic pollution is a continuous threat to it. Egypt depends primarily on the Nile River to supply potable water. Organic pollution threatens freshwater, and it is reduced through effective conventional treatment, but using disinfectants generates harmful byproducts. This study aims to the evaluation of conventional treatment in eight WTPs in Cairo. Water Treatment Plants (WTPs) were chosen in greater Cairo to perform this study throughout the year 2018. Raw, tap water and sludge TOC was measured. Raw and tap waters SUVA254 is calculated to determine the WTP's efficiencies to reduce DBPs formation probability. The maximum and minimum TOC obtained in winter and summer, respectively. SUVA254 increased in Mostorod WTP and reduced in other WTPs. In conclusion, the Nile river organic matter is natural with a minimum amount of industrial origin, but the Ismailia canal suffers from industrial spills.

Developing a restricted chlorine-dosing strategy for UV/chlorine and post-chlorination under different pH and UV irradiation wavelength conditions

UV/chlorine and chlorination processes have drawn great interests of water treatment utilities for oxidation and disinfection purposes. This work proposed a restricted chlorine-dosing strategy for UV/chlorine and post-chlorination under different pH and UV irradiation conditions by comprehensively assessing the oxidation of natural organic matter (NOM), formation of 9 haloacetic acids (HAA9) and bromate, and alteration of toxicity. During UV/chlorine with restricted chlorine doses, the oxidation of NOM chromophores (i.e., ΔUVA254) showed an apparent dependence on cumulative exposures of free available chlorine (CTFAC); Meanwhile, HAA9 formation was determined by CTFAC values and could be linearly correlated with ΔUVA254 irrespective of pH and UV irradiation wavelength. Irradiated by 254 nm LP-Hg lamp, the faster chlorine photolysis produced relatively higher steady-state concentrations of Cl• and HO• species but resulted in lower CTFAC. Reducing CTFAC values by operation parameters (pH, UV wavelength and irradiation fluence) could mitigate HAA9 formation during UV/chlorine at a specific chlorine dose. Additionally, high bromide concentration and acidic pH promoted more bromo-HAAs formation, and the presence of NOM significantly suppressed bromate formation. Analogous to ozonation, the UV/chlorine pre-oxidation could reduce the HAA9 formation potentials during post-chlorination at mildly alkaline pH. The photobacterium bioassay further demonstrated that although the UV/chlorine treatment might have increased the acute toxicity, the post-chlorination treatment could polish the acute toxicity to the level of chlorination alone. These results suggest that with the restricted chlorine-dosing strategy, the trade-off between oxidation/disinfection efficiency and DBPs formation can be controlled by monitoring CTFAC and ΔUVA254 values during UV/chlorine treatment.

Degradation of tetracycline by UV activated monochloramine process: Kinetics, degradation pathway, DBPs formation and toxicity assessment

The combination of UV and monochloramine (UV/NH2Cl) was investigated to eliminate tetracycline (TC) in water. The results indicated that TC degradation by UV/NH2Cl oxidation far exceeded that by UV photolysis and dark chloramination and these processes well fitted pseudo-first-order kinetics. With the increase of NH2Cl dosage, the pseudo-first-order rate constant (kobs) value increased linearly during TC chloramination, while the growth rate of kobs presented a gradual downward trend in UV/NH2Cl process. TC degradation by UV photolysis, dark chloramination and UV/NH2Cl oxidation displayed highly pH-dependent. As solution pH increased from 5.0 to 9.0, the TC removal increased during UV photolysis, while decreased during dark chloramination. For UV/NH2Cl process, the TC degradation showed a decreasing trend with increasing pH from 5.0 to 7.0, but further increasing pH to 9.0 presented an increasing trend. Reactive chlorine species acted as the major contributors to TC degradation in pH range of 6.0–8.0. TC degradation was not apparently affected after the introduction of HA and chloride, but was substantially accelerated in the presence of HCO3−. The proposed degradation pathways involved the hydroxylation, demethylation, dehydration and chlorine substitution processes. Compared with dark chloramination, the N-Nitrosodimethylamine (NDMA) generation was enhanced during TC oxidation by UV/NH2Cl process. The NDMA concentration increased with increasing solution pH from 6.0 to 8.0 and also elevated in the presences of humic acid (HA), nitrite, nitrate and ammonium during TC oxidation by chloramination and UV/NH2Cl. The results of acute toxicity test demonstrated that the toxicity of the reacted solution exhibited similar trends during dark chloramination and UV/NH2Cl treatment and was found to be obviously higher than UV photolysis.

The influence of bromide on the degradation of sulfonamides in UV/free chlorine treatment: Degradation mechanism, DBPs formation and toxicity assessment

The degradation of sulfonamides (SAs) in the presence of bromide during the UV/free chlorine process was investigated in this study. The reactions followed pseudo first-order kinetics. With increasing bromide concentrations of 1, 5, 10–20 µM, the degradation rate was gradually raised. The contribution of different reactive species has been calculated. The degradation products and DBPs formed by SAs were determined. The mechanisms of the degradation of SAs in the presence of bromide included hydroxylation, cleavage of the pyrimidinyl group, and bromine and chlorine electrophilic addition. The concentration of brominated disinfection by-products, including DBCM, TBM and DBAN, increased with increasing bromide dosage and degradation time, while 1, 1, 1-TCP and 1, 1-DCP decreased. In an acute toxicity test, the inhibition rate decreased in the first 5–10 min then increased after 10 min degradation when 10 µM Br− was added to the system. The initial decrease may due to the formation of low toxicity substances after the cleavage of the pyrimidinyl group, while the subsequent increase may be attributable to the increased formation of DBPs.

Eutrophication: a threat to freshwater reservoirs and human health

Eutrophication is an environmental problem that results from the increment of chemical nutrients (Phosphorous and Nitrogen) in a water body, transforming from oligotrophic into eutrophic, and in worst cases a hypertrophic stage. This process can occur naturally or due to human action. When the occurrence is natural, this phenomenon occurs slowly due to increase of organic matter by natural runoff from the soil and rock sediments. The anthropic actions generate punctual and diffuse pollution, this phenomenon favor aggravation of eutrophication process. The increment chemical induces a quickly increase of primary production of photosynthetic organisms in the aquatic systems, like phytoplankton and cyanobacteria, decreasing the light availability by increase of organic matter and consequently depletion of oxygen, resulting in loss of biodiversity. Eutrophication causes loss of water quality that is essential for human survival and development of social and economic activities. The eutrophic reservoirs usually present toxins, undesirable taste and odor, and DBPs formation in drinking water, the purification of the contaminated water might be complex and require long-term measures, turning the process quite costly. Therefore, actions to prevent the eutrophication of ecosystems are preferable. Sometimes the restoration of a disturbed environment is necessary, although expensive and complex, for which we present some methods of treatment of some chemical substances.

A comparison of trichloromethane formation from two algae species during two pre-oxidation-coagulation-chlorination processes

Microcystis aeruginosa (M. aeruginosa) commonly blooms in summer while Cyclotella meneghiniana (C. meneghiniana) outbreaks in fall in water reservoirs of Southeast China. Pre-oxidation has been demonstrated to enhance the algae removal from chemical coagulation processes. However, excessive dosage of pre-oxidant can increase the disinfection by-products formation potential (DBPsFP). Additionally, the DBPs formation mechanisms from algae during the pre-oxidation-coagulation-chlorination processes have not well elucidated. In this study, the objectives were to investigate the trichloromethane (TCM) formation, the changes of water quality indexes, and the morphology changes of algal cells from M. aeruginosa or C. meneghiniana contaminated water during potassium permanganate (KMnO4) or chlorine (Cl2) pre-oxidation-coagulation-chlorination disinfection. The results showed that the TCM yield for two algal species decreased with the dosage increase of KMnO4 pre-oxidation, but increased with the dosage increase of pre-chlorination. Therefore, the 2.0 mg/L KMnO4 or 0.5 mg/L Cl2 was proposed as the optimal dosage for preventing both M. aeruginosa blooms in summer and for C. meneghiniana outbreaks in fall. M. aeruginosa exhibited a slightly higher TCM yield than C. meneghiniana in these treatment processes. Based on the release of potassium (K) ion and SEM analysis, KMnO4 had less damage on cell integrity than Cl2 at the dosage ≤2.0 mg/L. In addition, C. meneghiniana was easier to be disrupted by both pre-oxidants than M. aeruginosa, combining with subsequent coagulation led to different value of dissolved organic carbon (DOC), UV–visible absorbance (UV254) and turbidity.