Although there are numerous studies concerning the occurrence of microplastics (MP) in the environment and its impact on the ecosystem, dissolved organic matter (DOM) leached from MP (MP-DOM) has ...received little attention, and its characteristics have been rarely examined. It is presumed that the DOM leaching from plastics could be accelerated when plastics lost their protective additives during their transport and weathering processes in aquatic systems. In this study, two additive-free MPs (or micro-sized plastic polymers) were leached in artificial freshwater under UV irradiation and dark conditions. The leached DOM was characterized by typical analyses for naturally occurring DOM (N-DOM) such as dissolved organic carbon (DOC), size exclusion chromatography (SEC), and Fourier-transform infrared spectroscopy (FTIR). The potential to generate trihalomethanes (THMs), a well-known environmental impact of N-DOM, was also explored for the DOM with plastic origins for the first time. The leaching results demonstrated that UV irradiation promoted the leaching of DOM from the plastic polymers with an amount corresponding to ∼3% of the total mass of the polymers. The leached amounts were much greater than those previously reported using commercial plastics which presumably contained protective additives. The SEC results revealed that, different from typical aquatic N-DOM, MP-DOM is mostly composed of low molecular weight fractions <350 Da. For the two polymer types (polyethylene and polypropylene), the MP-DOM exhibited a high potential to form THMs upon chlorination, which was comparable to those of typical aquatic N-DOM. This study highlighted an overlooked contribution of UV irradiation to the DOM leaching from additive-free plastics and the potential risk of MP-DOM to produce toxic disinfection byproducts (DBPs) upon chlorination.
Display omitted
•This is the first report on THM formation by MP-DOM upon chlorination.•UV irradiation accelerates DOM leaching from additive-free MPs or MP polymers.•Different from aquatic NOM, low molecular weight fraction is predominant in MP-DOM.•THM formation potentials of MP-DOM are comparable to those of aquatic NOM.
Reclaimed water is highly required for environmental sustainability and to meet sustainable development goals (SDGs). Chemical processes are frequently associated with highly hazardous and toxic ...by-products, like nitrosamines, trihalomethanes, haloaldehydes, haloketones, and haloacetic acids. In this context, we aim to summarize the formation of various commonly produced disinfection by-products (DBPs) during wastewater treatment and their treatment approaches. Owing to DBPs formation, we discussed permissible limits, concentrations in various water systems reported globally, and their consequences on humans. While most reviews focus on DBPs detection methods, this review discusses factors affecting DBPs formation and critically reviews various remediation approaches, such as adsorption, reverse osmosis, nano/micro-filtration, UV treatment, ozonation, and advanced oxidation process. However, research in the detection of hazardous DBPs and their removal is quite at an early and initial stage, and therefore, numerous advancements are required prior to scale-up at commercial level. DBPs abatement in wastewater treatment approach should be considered. This review provides the baseline for optimizing DBPs formation and advancements in the remediation process, efficiently reducing their production and providing safe, clean drinking water. Future studies should focus on a more efficient and rigorous understanding of DBPs properties and degradation of hazardous pollutants using low-cost techniques in wastewater treatment.
Display omitted
•Disinfection is highly required but mostly associated with byproduct formation.•Raw water reported high disinfection byproducts (DBPs) levels than treated water.•UV/Cl2 was reported to be an effective disinfectant for DBPs formation.•Technique to remove nitrosamine precursors from WWTPs is urgently needed.
Trihalomethanes (THMs) and haloacetonitriles (HANs), most common disinfection by-products in drinking water, pose adverse environmental impacts and potential risks to human health. There is a ...pressing need to develop innovative, economically feasible, and environmentally benign processes to control these persistent contaminants. In this paper, visible-light-responsive graphitic carbon nitride (g-C3N4) samples were synthesized to degrade the THMs and HANs and the photocatalytic degradation mechanism was explored. The results indicated that a carbon-doped g-C3N4 with an optimum dopant content (MCB0.07) displayed the best photocatalytic activity for the total trihalomethanes (TTHM) and total haloacetonitriles (THAN), with the reaction rate constant of 11.6 and 10.4 (10−3 min−1), respectively. MCB0.07 demonstrated a high THMs and HANs removal efficiency under visible light irradiation and could be reused. According to scavenger tests of the selected reactive species and X-ray photoelectron spectroscopy, holes play a dominant role for both THMs and HANs degradation on the MCB0.07. The degradation of HANs by holes proceeded mainly through breakage of the CC bond in the CCN group. The THMs degradation was achieved through hydrogen abstraction or/and dehalogenation. The brominated-THMs/HANs were more photosensitive than their chlorinated analogous and were less stable than bromo-chloro-THMs/HANs. This study sheds light on the mechanism of the photocatalytic degradation of THMs and HANs under visible light irradiation by carbon-doped g-C3N4. Furthermore, it could provide insights for engineering applications and contaminant control in drinking water purification.
Display omitted
•A carbon-doped g-C3N4 displayed high photocatalytic activity for TTHM and THAN.•Holes played dominant roles for THMs and HANs degradation.•THMs degradation was achieved through hydrogen abstraction or/and dehalogenation.•The photocatalysis removed HANs mainly through CC bond breakage.
•Bayesian network is an alternative approach for predictive trihalomethane formation•The interrelationship between disinfection by-products influencing factors is shown•A higher pH could mitigate ...monochloramine decay and trihalomethane formation•Conductivity and total dissolve solids can be surrogate measure for bromide ions.
Controlling disinfection by-products formation while ensuring effective drinking water disinfection is important for protecting public health. However, understanding and predicting disinfection by-product formation under a variety of conditions in drinking water distribution systems remains challenging as disinfection by-product formation is a multifactorial phenomenon. This study aimed to assess the application of Bayesian Network models to predict the concentration of trihalomethanes, the dominant halogenated disinfection by-product class, using various water quality parameters. Naïve Bayesian and semi-naïve Bayesian models were constructed from Sydney and South East Queensland datasets across 15 drinking water distribution systems in Australia. The targeted variable, total trihalomethanes concentration, was discretised into 3 bins (<0.1 mg L−1, 0.1 – 0.2 mg L−1 and >0.2 mg L−1). The Bayesian network structures were built using water quality parameters including concentrations of individual and total trihalomethanes, disinfectant species (free chlorine, monochloramine, dichloramine, total chlorine), nitrogen species (free ammonia, total ammonia, nitrate, nitrite), and other physical/chemical parameters (temperature, pH, dissolved organic carbon, total dissolved solids, conductivity and turbidity). Seven performance parameters, including predictive accuracy and the rates of true and false positive and negative results, were used to assess the accuracy and precision of the Bayesian network models. After evaluating the model performance, the optimum models were selected to be Bayesian network augmented naïve models. These were observed to have the highest predictive accuracies for Sydney (78%) and South East Queensland (94%). Although disinfectant residuals are among the key variables that lead to trihalomethanes formation, potential concentrations of trihalomethanes in distribution systems can be more confidently predicted, in terms of probability associated with a wider range of water quality variables, using Bayesian networks. The modelling procedure developed in this work can now be applied to develop system-specific Bayesian network models for trihalomethanes prediction in other drinking water distribution systems.
Display omitted
Breakpoint chlorination is a generally accepted method for removing ammonium ion from source waters in drinking water treatment technologies. This process is often accompanied by the formation of ...halogenated organic byproducts. The presence of these compounds in potable water is of primary concern. In this paper, we demonstrate that the concentration of the precursors of the halogenated species can sufficiently be decreased by oxidizing the organic pollutants with the Fe(II)/Fe(III) – S(IV) – air system. Pre-oxidative treatment of the source waters results in a substantial reduction of chemical oxygen demand, while the ammonium ion concentration remains unaffected. The breakpoint chlorination produces substantially less trihalomethanes (THMs) and adsorbable halogenated organic compounds (AOXs) in oxidatively pre-treated source waters than in raw waters. These results offer a possibility to improve drinking water treatment technologies for better controlling the formation of antagonistic byproducts. It is demonstrated that reaching the regulated concentration levels of THMs is feasible with this method even in source waters containing organic pollutants at relatively high concentration levels. The main advantage of the procedure is that the reagents used for the oxidative pre-treatment are converted into non-toxic products (Fe(III) and SO42−) by the end of the process.
Display omitted
•The oxygen demand of source waters was decreased by an oxidative treatment.•The concentration of ammonium ion is not affected by the oxidative process.•Breakpoint chlorination yields less halogenated compounds after the treatment.•The regulated concentration levels of trihalomethanes are easily maintained.
Display omitted
•The chlorination disinfection by-products water is from a local municipal water supply plant.•The dispersion of modified nanoscale zero-valent iron (NZVI) was enhanced.•The removal ...rate increased with the increase of bromine atoms in trihalomethanes (THMs).•Change of pH during the process of removal of THMs was measured.•The composites (NZVI/AC) were highly effective for low concentration THMs.
Trihalomethanes (THMs) in drinking water are difficult to remove with conventional methods. In this study, activated carbon supported nanoscale zero-valent iron (NZVI/AC) was synthesized by liquid-phase reduction and used to treat THMs in actual drinking water, including chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3). The as-prepared NZVI/AC composites were characterized in terms of specific surface area, pore size distribution, morphological properties and structural features. The effects of NZVI dosage, initial pH and contact time on removal efficiency were also studied. Scanning electron microscopy showed uniformly dispersed NZVI particles with diameters of 30–100nm on average on the surface or inside the pores of AC. The removal efficiency was enhanced with the increasing amount of NZVI/AC, and the optimum dosage was 1.8g/L and the optimal was 7. The kinetics of the removal of THMs was in agreement with a pseudo-first-order model. NZVI/AC accelerated removal rate of THMs over NZVI alone by both its higher reactivity and greater adsorption. The degradation products were analyzed using gas chromatography–mass spectrometry which showed that dehalogenation of THMs by NZVI/AC followed the order of CHBr3>CHBr2Cl>CHBrCl2>CHCl3. AC-supported nanoscale zero-valent iron particles is a promising sustainable material for potential application in elimination of THMs from actual drinking water.
Present study aimed to generate multiple regression models to estimate the formation of trihalomethanes (THMs), haloacetonitriles (HANs) and haloacetic acids (HAAs) during chloramination of source ...water obtained from Yangtze River Delta Region, China. The results showed that the regression models for trichloromethane (TCM), dichloroacetonitrile (DCAN), dichloroacetic acid (DCAA), dihaloacetic acids (DHAAs), 5 HAAs species regulated by U.S. EPA (HAA5) and total haloacetic acids (HAA9) have good evaluation ability (prediction accuracy reached 81–94%), while the models for total haloacetonitriles (HAN4), trichloroacetic acid (TCAA), trihaloacetic acids (THAAs) and total trihalomethanes (THM4), they appeared relative low prediction accuracy (58–72%). For THMs, dissolved organic nitrogen (DON) was their key organic precursor, yet for HAN, DHAAs and THAAs, UVA254 played the dominant role. The other key factors influencing DBP formation included the bromide (THM4, DHAAs and HAA9), reaction time (DCAN, HAN4), chloramine dose (TCM, DCAA, TCAA, HAA5 and THAAs). These results provided important information for water works to optimize the water treatment process to control DBPs, and give an evaluating method for DBPs levels when estimating the health risks related with DBP exposure during chloramination.
Display omitted
•Regression models can well describe the DBPs formation during chloramination.•For THMs, dissolved organic nitrogen (DON) was their key organic precursor.•For HAN, DHAA and THAA, UVA254 played the dominant role.•Control of DON, UV254, Br- and NH2Cl dose may be effective to control DBPs.
The formations of THMs, HAAs, and HNMs from chlorination and chloramination of water from Jinlan Reservoir were investigated in this study. Results showed that monochloramine rather than chlorine ...generally resulted in lower concentration of DBPs, and the DBPs formation varied greatly as the treatment conditions changed. Specifically, the yields of THMs, HAAs and HNMs all increased with the high bromide level and high disinfectant dose both during chlorination and chloramination. The longer reaction time had a positive effect on the formation of THMs, HAAs and HNMs during chlorination and HNMs during chloramination. However, no time effect was observed on the formation of THMs and HAAs during chloramination. An increase in pH enhanced the levels of THMs and HNMs upon chlorination but reduced levels of HNMs upon chloramination. As for the THMs in chloramination and HAAs in chlorination and chloramination, no obvious pH effect was observed. The elevated temperature significantly increased the yields of THMs during chlorination and HNMs during chloramination, but has no effect on THMs and HAAs yields during chloramination. In the same temperature range, the formation of HAAs and HNMs in chlorination showed a first increasing and then a decreasing trend. In chloramination study, addition of nitrite markedly increased the formation of HNMs but had little impact on the formation of THMs and HAAs. While in chlorination study, the presence of high nitrite levels significantly reduced the yields of THMs, HAAs and HNMs. Range analysis revealed that the bromide and disinfectant levels were the major factors affecting THMs, HAAs and HNMs formation, in both chlorination and chloramination. Finally, comparisons of the speciation of mono-halogenated, di-halogenated, tri-halogenated HAAs and HNMs between chlorination and monochloramination were also conducted, and factors influencing the speciation pattern were identified.
► NH2Cl generally produced lower THMs, HAAs and HNMs yields than Cl2. ► Bromide level and disinfectant dose are two most important factors affecting THMs, HAAs and HNMs formation. ► Addition of nitrite significantly increased HNMs formation during chloramination, but was not necessary in the chlorination. ► The factors affect the speciation of mono-halogenated, dihalogenated, and trihalogenated HAAs and HNMs were assessed.
Display omitted
•THM formation was generally higher during UV-chlorination.•HAN and HNM formation was generally higher during UV-chloramination.•Increasing UV dose enhanced the formation of DBPs ...during both processes.•Increasing bromide concentration shifted DBPs to more brominated species.•LP UV irradiation produced less DBPs compared to MP UV during both processes.
This study investigated the effect of several factors on the formation of disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetonitriles (HANs) and halonitromethanes (HNMs) during UV-chlor(am)ination of the water collected after filtration unit in a drinking water treatment plant. In general, THM formation was higher during UV-chlorination while HAN and HNM formation were higher during UV-chloramination. Higher Medium pressure (MP) UV dose resulted in more DBP formation. The value of pH affected DBP formation differently. THMs decreased with increasing pH during UV-chlorination but remained stable during UV-chloramination. HNMs increased as pH increased from 5 to 7 but decreased as pH further increased to 9 during UV-chlorination. On the other hand, HNM formation decreased with increasing pH during UV-chloramination. However, pH had little impact on HAN formation. The nitrate concentration had negligible impact on the formation of THM, HAN and HNM during both UV-chlor(am)ination. Increasing bromide concentration improved THM and HAN formation, decreased HNM formation, and shifted DBPs to more brominated species in the three categories. MP UV irradiation enhanced the formation of DBPs compared to low pressure UV during both UV-chlor(am)ination, especially for nitrogenated DBPs.
