Effect of bromide on the formation of disinfection by-products during wastewater chlorination

Halogenated aliphatic and phenolic disinfection byproducts in chlorinated and chloraminated dairy wastewater: Occurrence and ecological risk evaluation

The increasing demand for dairy products has led to the production of a large amount of wastewater in dairy plants, and disinfection is an essential treatment process before wastewater discharge. Disinfection byproducts (DBPs) in disinfected dairy wastewater may negatively influence the aquatic organisms in receiving water. During chlorine and chloramine disinfection of dairy wastewater, the concentrations of aliphatic DBPs increased from below the detection limits to 485.1 μg/L and 26.6 μg/L, respectively. Brominated and iodinated phenolic DBPs produced during chlor(am)ination could further react with chlorine/chloramine to be transformed. High level of bromide in dairy wastewater (12.9 mg/L) could be oxidized to active bromine species by chlorine/chloramine, promoting the formation of highly toxic brominated DBPs (Br-DBPs), and they accounted for 80.3% and 71.1% of the total content of DBPs in chlorinated and chloraminated dairy wastewater, respectively. Moreover, Br-DBPs contributed 49.9-75.9% and 34.2-96.4% to the cumulative risk quotient of DBPs in chlorinated and chloraminated wastewater, respectively. The cumulative risk quotient of DBPs on green algae, daphnid, and fish in chlorinated wastewater was 2.8-11.4 times higher than that in chloraminated wastewater. Shortening disinfection time or adopting chloramine disinfection can reduce the ecological risks of DBPs.

Analyzing disinfection by-products yield and mechanisms in UV/Cl2 using response surface methodology and quantitative structure-activity relationship models

The study aimed to investigate the formation of halogenated disinfection byproducts (DBPs) during applying UV/chlorine (UV/Cl2) and unravel the interactive impacts of critical operational parameters and the mechanisms behind DBPs formation. Response surface methodology and quantitative structure-activity relationship models were developed to evaluate the contribution of electrophilic, nucleophilic, and free radical reactions to the formation of DBPs in UV/Cl2. The study found that Cl2 and its interactions dominated the total DBPs and non-Br-DBPs formation, while Br- and the Cl2-Br- interaction played a decisive role in the Br-DBPs formation. The study also observed significant interactions of Br, Cl2, and pH on chloroform, bromodichloromethane, dichloroacetonitrile, 1,1-dichloro-2-propanone, trichloroactic acid, and chlorodibromoacetic acid formations, while no evident interaction on chloral hydrate, dibromochloromethane, trichloroacetone, dibromoacetic acid, and bromodichloroacetic acid formations. The electrophilic substitution of HOBr mainly controlled the formation of trihalomethanes, and the contribution of nucleophilic, electrophilic, and free radical (•OH, Cl•, Cl2•- and ClO•) reactions depended on the molar ratio of Cl2 to Br, and pH-determined hydrolysis rate constants of DBPs and the types of free radicals. Overall, the response surface methodology and quantitative structure-activity relationship models provided a reference for revealing DBPs formation mechanisms in other disinfection processes.

Continuous flow operation of solar photo-Fenton fused with NaOCl as a novel tertiary treatment

A novel strategy based on solar photo-Fenton mediated by ferric nitrilotriacetate (Fe3+-NTA) combined with NaOCl in continuous flow mode for wastewater reclamation has been studied. Escherichia coli (E. coli) inactivation attained ≥ 5 log10-units, meeting the most restrictive EU 2020/741 target (10 CFU/100 mL), and 75% of organic microcontaminant total load was removed. As a remarkable finding, trihalomethanes (THMs) concentration was insignificant, complying by far with the Italian legislation limit. To attain these results, first the effect of liquid depth on E. coli inactivation and imidacloprid (IMD) removal from spiked municipal effluents was evaluated in continuous flow pilot-scale raceway pond reactors at 60-min hydraulic residence time with low reagent concentrations (0.10 mM Fe3+-NTA, 0.73 mM H2O2 and 0.13 mM NaOCl). Disinfection was due to the bactericidal effect of chlorine. In contrast, liquid depth notably influenced microcontaminant removal, highlighting that operation at 10-cm liquid depth allows achieving treatment capacities higher than at 5 cm (16.50 vs 28.20 mg IMD/m2∙day). Next, the monitoring of THMs was carried out to evaluate the generation and degradation of disinfection by-products, along with the removal of actual microcontaminants. These promising results draw attention to the treatment potential and open the way for its commercial application.

Formation and speciation of hazardous trihalomethanes and haloacetic acids during chlorinated washing of brined kimchi cabbage in the presence of bromide

Brominated disinfection byproducts (Br-DBPs) may be generated in high concentrations during the chlorinated washing of brined kimchi cabbage (BKC) in kimchi manufacturing. However, the generation of these DBPs is not sufficiently understood. Therefore, in this study, we investigated the formation and speciation of the DBPs trihalomethanes (THMs) and haloacetic acids (HAAs) during the chlorinated washing process. The average bromide content in 22 salt products sourced from various regions of Korea was 1600 ± 468 mg/kg. Increasing bromide content shifted the speciation of DBPs from chlorinated to mixed bromochloro to brominated species, which would be more harmful than their chlorinated analogs. DBP formation during the washing of BKC at average bromide levels changed based on the brine salinity, salting temperature, and disinfectant type. Based on our findings, we recommend that low salinity and low temperature should be maintained during the salting of KC and that NaOCl should be used as the disinfectant rather than slightly acidic electrolyzed water during the chlorinated washing of KC to alleviate the formation of Br-DBPs. Moreover, we recommend the use of salts with low bromide levels for the salting of KC and the addition of a rinse step after chlorinated washing.

A Critical Review on Chemical Speciation of Chlorine-Produced Oxidants (CPOs) in Seawater. Part 1: Chlorine Chemistry in Seawater and Its Consequences in Terms of Biocidal Effectiveness and Environmental Impact

Seawater chlorination has three main industrial uses: disinfection of water and installations, control of biofouling, and preventing the transport of aquatic invasive species. Once in contact with seawater, chlorine reacts rapidly with water constituents (e.g. bromide ions, ammonia, and nitrogen-containing compounds) to form a range of oxidative species (e.g. bromine and N-haloamines), termed "chlorine-produced oxidants" (CPOs) or "total residual oxidants" (TRO). The chemical nature of CPOs and their concentration are a function of two categories of parameters related to treatment modality (e.g. chlorine dose) and water quality (e.g. temperature, pH, ammonia concentration, and organic constituents). The chlorination process may result in continuous or intermittent releases of CPOs in seawater. The reactivity and potential ecotoxicity of CPO species largely depend on their physical and chemical properties. Therefore, evaluation of the biocidal effectiveness of chlorination and its potential impacts requires not only determining the sum of CPOs (via a bulk parameter), but also their chemical speciation. The aim of this article - which is the first of a trilogy dedicated to the chemical speciation of CPOs in seawater - is to provide an overview of current knowledge about chlorine chemistry in seawater and to discuss the biocidal efficacy and the environmental fate of resulting CPOs. The 2nd and 3rd articles delineate a comprehensive and critical review of analytical methods and approaches for the determination of CPOs in seawater.

Effects of ultrasonication on the DBP formation and toxicity during chlorination of saline wastewater effluents

Chlorine disinfection of saline wastewater effluents rich in bromide and iodide forms relatively toxic brominated and iodinated disinfection byproducts (DBPs). Ultrasonication is a relatively new water treatment technology, and it is less sensitive to suspended solids in wastewaters. In this study, we examined the effects of ultrasonication (in terms of reactor type and combination mode with chlorination) on the DBP formation and toxicity in chlorinated primary and secondary saline wastewater effluents. Compared with the chlorinated wastewater effluent samples without ultrasonication, ultrasonic horn pretreatment of the wastewater effluent samples reduced the total organic halogen (TOX) levels in chlorination by ∼30%, but ultrasonic bath pretreatment of the wastewater samples did not significantly change the TOX levels in chlorination, which might be attributed to the higher energy utilization and decomposition extent of organic DBP precursors in the ultrasonic horn reactor. Moreover, the TOX levels in the chlorinated samples with ultrasonic horn pretreatment (USH-chlorination), simultaneous treatment (chlorination+USH) and subsequent treatment (chlorination-USH) were also significantly reduced, with the maximum TOX reductions occurring in the samples with ultrasonic horn pretreatment. A toxicity index was calculated by weighting and summing the levels of total organic chlorine, total organic bromine and total organic iodine in each treated sample. The calculated toxicity index values of the chlorinated wastewater effluent samples followed a descending rank order of "chlorination" > "chlorination+USH" > "chlorination-USH" > "USH-chlorination", with the lowest toxicity occurring in the samples with ultrasonic horn pretreatment. Then, a developmental toxicity bioassay was conducted for each treated sample. The measured toxicity index values of the chlorinated wastewater samples followed the same descending rank order.

Inputs of disinfection by-products to the marine environment from various industrial activities: Comparison to natural production

Oxidative treatment of seawater in coastal and shipboard installations is applied to control biofouling and/or minimize the input of noxious or invasive species into the marine environment. This treatment allows a safe and efficient operation of industrial installations and helps to protect human health from infectious diseases and to maintain the biodiversity in the marine environment. On the downside, the application of chemical oxidants generates undesired organic compounds, so-called disinfection by-products (DBPs), which are discharged into the marine environment. This article provides an overview on sources and quantities of DBP inputs, which could serve as basis for hazard analysis for the marine environment, human health and the atmosphere. During oxidation of marine water, mainly brominated DBPs are generated with bromoform (CHBr₃) being the major DBP. CHBr₃ has been used as an indicator to compare inputs from different sources. Total global annual volumes of treated seawater inputs resulting from cooling processes of coastal power stations, from desalination plants and from ballast water treatment in ships are estimated to be 470-800 × 10⁹ m³, 46 × 10⁹ m³ and 3.5 × 10⁹ m³, respectively. Overall, the total estimated anthropogenic bromoform production and discharge adds up to 13.5-21.8 × 10⁶ kg/a (kg per year) with contributions of 11.8-20.1 × 10⁶ kg/a from cooling water treatment, 0.89 × 10⁶ kg/a from desalination and 0.86 × 10⁶ kg/a from ballast water treatment. This equals approximately 2-6% of the natural bromoform emissions from marine water, which is estimated to be 385-870 × 10⁶ kg/a.

Halogen substitution reactions of halobenzenes during water disinfection

Although being successfully applied all over the world for more than 100 years water disinfection by means of chlorination possesses certain drawbacks, first of all formation of hazardous disinfection by-products (DBP). Aromatic halogenated DBPs significantly contribute to the total organic halogen and developmental toxicity of chlorinated water. The present study deals with investigation of possible substitution of one halogen for another in aromatic substrates in conditions of aqueous chlorination/bromination. The reaction showed high yields especially in case of substrates with proper position of an activating group in the aromatic ring. Thus, ipso-substitution of iodine by chlorine is the main process of aqueous chlorination of para-iodoanisole. Oxidation of the eliminating I⁺ ions into non-reactive IO₃^- species facilitates the substitution. Oxidation of eliminating Br⁺ is not so easy while being highly reactive it attacks initial substrates forming polybrominated products. Substitution of iodine and bromine by chlorine may also involve migration of electrophilic species inside the aromatic ring resulting in larger number of isomeric DBPs. Substitution of chlorine by bromine in aromatic substrates during aqueous bromination is not so pronounced as substitution of bromine by chlorine in aqueous chlorination due to higher electronegativity of chlorine atom. However, formation of some chlorine-free polybrominated products proves possibility of that process.

Structural effects on the bromination rate and selectivity of alkylbenzenes and alkoxybenzenes in aqueous solution

Aqueous free bromine species (e.g., HOBr, BrCl, Br2, BrOCl, Br2O, and H2OBr+) can react with activated aromatic compounds via electrophilic aromatic substitution to generate products with industrial applications, environmental consequences, and potentially adverse biological effects. The relative contributions of these brominating agents to overall bromination rates can be calculated via nonlinear regression analyses of kinetic data collected under a variety of solution conditions, including variations in parameters (e.g., [Cl-], [Br-], and pH) known to influence free bromine speciation. Herein, kinetic experiments conducted in batch reactors were employed to evaluate the contributions of steric and electronic effects on bromination of monosubstituted alkylbenzenes (ethyl, isopropyl, tert-butyl) and alkoxybenzenes (ethoxy, isopropoxy, tert-butoxy) and to elucidate the inherent reactivities of aqueous brominating agents towards these aromatic compounds. For bromination at the para position of alkylbenzenes, overall reactivity increased from tert-butyl < ethyl ≈ isopropyl. For bromination at the para position of alkoxybenzenes, reactivity increased from tert-butoxy < ethoxy < isopropoxy. In going from ethyl to tert-butyl and ethoxy to isopropoxy, unfavorable steric effects attenuated the favorable electronic effects imparted by the substituents. When comparing unsubstituted benzene, alkyl-, and alkoxybenzenes, the structure of the substituent has a significant effect on bromination rates, nucleophile regioselectivity, and electrophile chemoselectivity. Hirshfeld charges were useful predictors of reactivity and regioselectivity. The experimental results were also modeled using Taft equations. Collectively, these findings indicate that steric effects, electronic effects, and brominating agents other than HOBr can influence aromatic compound bromination in solutions of free bromine.

Monitoring and Statistical Analysis of Formation of Organochlorine and Organobromine Compounds in Drinking Water of Different Water Intakes

The main drawback of drinking water chlorination involves the formation of quite hazardous disinfection by-products (DBPs), represented mainly by halogenated species. Based on the authors’ monitoring data since 2002, the prevalence of chlorine over bromine in the composition of volatile DBPs was shown for the drinking water in Ufa (Russia). However, the situation was completely reversed in the case of semi-volatile DBPs. The principal goal of the present study involved rationalization of the results of the long-term monitoring. Gas chromatography–mass spectrometry (GC-MS) was used for the qualitative and quantitative analysis of volatile DBPs. Identification of semi-volatile compounds was carried out with GC-MS, while gas chromatography with an atomic emission detector (GC-AED) was used for their quantification. A significant contribution of oxygen to the composition of semi-volatile compounds proves the decisive role of the dissolved organic matter oxidative destructive processes. Statistical analysis revealed notable linear correlations for trihalomethane and haloacetic acid formation vs. chlorine dose. On the contrary, halogenated semi-volatile products do not demonstrate any correlations with the water quality parameters or chlorine dose. Principal component analysis (PCA) placed them into separate groups. The results allow for proposing that formation of the organohalogenated species involved the fast penetration of bromine into the humic matter molecules and, further, their oxidative destruction by active chlorine.

Determination of environmental properties and toxicity of octyl-dimethyl-para-aminobenzoic acid and its degradation products

Octyl-dimethyl-para-aminobenzoic acid (ODPABA) is one of compounds of emerging concern. It undergoes transformations under the influence of oxidizing or chlorinating agents and UV radiation forming products with different properties. There is very little experimental data concerning the environmental fate of ODPABA and its transformation products. Therefore, the purpose of the studies was to determine environmental parameters: water solubility, soil - water partition coefficient, octanol - air partition coefficient, bioconcentration factor as well as half-life in air, water and soil. Based on the results obtained, the persistence and migration possibilities of ODPABA and its transformation products in the aquatic environment were estimated. Moreover, the ecological toxicity of oxidation and chlorination products was investigated. Microtox®, Daphtoxkit F® and Artoxkit M® tests were used to determine toxicity. LC₅₀ for Fish and Daphnia magna was calculated by Ecosar module. Studies have shown that as a result of ODPABA transformations, chloroorganic products are formed, which are lipophilic, are bioconcentrated in organic matter, are characterized by significant environmental persistence, can spread over considerable distances and are toxic. Oxidation products have significantly smaller impact on the environment. They are characterized by higher water solubility, lower bioconcentration factor and are less toxic.

DBP formation and toxicity alteration during UV/chlorine treatment of wastewater and the effects of ammonia and bromide

The UV/chlorine process is efficient for the abatement of micropollutants; yet, the formation of disinfection by-products (DBPs) and the toxicity can be altered during the treatment. This study investigated effluent organic matter characterization, DBP formation and toxicity alteration after the UV/chlorine treatment of wastewater; particularly, typical water matrix components in wastewater, namely, ammonia and bromide, were studied. The raw wastewater contained low levels of ammonia (3 µM) and bromide (0.5 µM). The UV/chlorine treatment efficiently eliminated 90 - 94% of fluorescent components. Compared with chlorination alone, a 20 min UV/chlorine treatment increased the formation of trihalomethanes (THMs), haloacetic acids (HAAs), chloral hydrate (CH), haloacetonitriles (HANs), trichloronitromethane (TCNM) and haloacetamides (HAcAms) by 90 - 508%. In post-chlorination after the UV/chlorine treatment, the formation of CH, HANs, TCNM and HAcAms increased by 77 - 274%, whereas the formation of both THMs and HAAs increased slightly by 11%. Meanwhile, the calculated cytotoxicity and genotoxicity of DBPs increased considerably after the UV/chlorine treatment and in post-chlorination, primarily due to the increased formation of HAAs and nitrogenous DBPs (N-DBPs). However, the acute toxicity of the wastewater to Vibrio fischeri and genotoxicity determined by the umu test decreased by 19% and 76%, respectively, after the 20 min UV/chlorine treatment. An additional 200 µM ammonia decreased the formation of all detected DBPs during the UV/chlorine treatment and 24 h post-chlorination, except that TCNM formation increased by 11% during post-chlorination. The acute toxicity of wastewater spiked with 200 µM ammonia was 32% lower than that of raw wastewater after the UV/chlorine treatment, but the genotoxicity was 58% higher. The addition of 1 mg/L bromide to the UV/chlorine process dramatically increased the formation of brominated DBPs and the overall calculated cytotoxicity and genotoxicity of DBPs. However, the acute toxicity and genotoxicity of the wastewater decreased by 7% and 100%, respectively, when bromide was added to the UV/chlorine treatment. This study illuminated that UV/chlorine treatment can decrease acute and geno- toxicities of wastewater efficiently.

The effect of operational conditions on the disinfection by-products formation potential of exopolymeric substances from biofilms in drinking water

Biofilms are ubiquitous in drinking water systems due to their external matrix of exopolymeric substances (EPS) that provide them protection and adaptability. They are even more common in low flow conditions where hydraulics favor their growth. EPS are organic substances (i.e., proteins, carbohydrates and humic substances) that can react with disinfectant, forming disinfection byproducts (DBP), some of which are controlled by water regulation. However, there is little information available on biofilm-disinfectant interaction and the effect of operational conditions such as biofilm age, water velocity, chlorine and pipeline length on the DBP formation potential of EPS (DBP_fpEPS). Using experimental setup and studies of two different biofilms: Biofilm 1 (2.6 ± 0.8 mg Cl/L) and Biofilm 2 (0.7 ± 0.2 mg Cl/L), the DBP_fpEPS was studied and compared to the DBP_fp of filtered water (FW). The DBP studied were trihalomethanes (THM), haloacetic acids (HAA), haloacetonitriles (HAN), chloropropanones (CP) and chloropicrin (CPK). The DBP concentration trend in both EPS and FW was HAA > THM > CP > HAN > CPK. Biofilm age only increased chloroform (CF)_fpEPS in Biofilm 1, while other DBP_fpEPS decreased. A direct relationship between water velocity and CF_fp in Biofilm 1 was found, probably related to higher chlorine diffusion and the production of a more reactive matrix. Chlorine positively affected DBP_fpEPS, increasing Cl-HAA, Cl-THM, CPK and Br-HAN. Biofilm 2 produced higher quantities of EPS per meter of pipeline, this constituting a precursor of intermediary DBP 1,1 dichloropropanone (1,1, DCP). The study compared DBP in chlorinated water in contact with biofilm (BCW) and without (CW). Biofilm 1 increased levels of Cl-HAA, Cl-CP and dichloro-acetonitrile, while Biofilm 2 diminished Cl-HAA and Cl-HAN. Biofilm 1 reduced some Br-HAA in BCW, whereas Biofilm 2 promoted Br-HAA and 1,1, DCP in BCW. EPS and biofilms were significant in terms of their effect on DBP formation.

Low water treatability efficiency of wildfire-induced dissolved organic matter and disinfection by-product precursors

Wildfire could alter both the quantity and composition of terrestrial organic matter exported into source water, and water treatability of fire-impacted dissolved organic matter (DOM) could be different from its unburned counterpart. Currently, there is no standard protocol to treat wildfire-impacted source water. To identify the best treatment practices in handling post-fire runoffs, we conducted a systematic controlled study using leachates of unburned white fir (Abies concolor) and Ponderosa pine (Pinus ponderosa) and black and white ashes (collected immediately and one year after the 2013 Rim Fire, California) to evaluate coagulation and oxidation strategies for controlling disinfection byproducts (DBPs) formation. Results showed that the efficiency (%) of alum coagulation in removing dissolved organic carbon and nitrogen followed the order of litter > ash immediately after the fire > ash one year after the fire. Alum coagulation was less effectiveness in removing DOM and DBP precursors in ash leachates, compared to litter leachates. This may be attributed to the loss of side chains and the decrease of DOM molecular weight during the wildfire, thus inducing lower removal efficiency of the DOM and DBP precursors during the alum coagulation. Considering use of brominated flame retardants by firefighters, the addition of bromide (Br^-) (100 μg/L) greatly increased the formation of haloacetonitriles by chlorine, and this increase was relatively lower in ash leachates. The influence of reaction time and pH on DOM reactivity was similar among the leachates of litter and ash samples. Our results show that alum coagulation followed by chloramination at alkaline pH is an effective strategy for reducing post-fire DBP formation in drinking water.

Novel Disinfection Byproducts Formed from the Pharmaceutical Gemfibrozil Are Bioaccumulative and Elicit Increased Toxicity Relative to the Parent Compound in Marine Polychaetes (Neanthes arenaceodentata)

Formation of halogenated disinfection byproducts (DBPs) from pharmaceutically active compounds has been observed in water supply systems following wastewater chlorination. Although research has been limited thus far, several studies have shown that halogenated DBPs may elicit increased toxicity compared to their parent compounds. For example, the lipid regulator gemfibrozil has been shown to form chlorogemfibrozil (Cl-gemfibrozil) and bromogemfibrozil (Br-gemfibrozil) following chlorination, which are more potent antiandrogens in male Japanese medaka (Oryzias latipes) compared to their parent compounds. In the present study, we aimed to characterize the bioaccumulative ability of halogenated gemfibrozil DBPs in marine polychaetes via chronic sediment exposures and, consequently, to assess the chronic and acute toxicity of halogenated gemfibrozil DBPs through sediment (in vivo) and aqueous (in vivo and in silico) toxicity evaluations. Following 28 day sediment exposures, Cl-gemfibrozil and Br-gemfibrozil bioaccumulated within Neanthes arenaceodentata, with both compounds reducing survival and growth. The biota-sediment accumulation factors determined for Cl-gemfibrozil and Br-gemfibrozil were 2.59 and 6.86, respectively. Furthermore, aqueous 96 h toxicity tests with N. arenaceodentata indicated that gemfibrozil DBPs elicited increased toxicity compared to the parent compound. While gemfibrozil had an acute LC50 value of 469.85 ± 0.096 mg/L, Cl-gemfibrozil and Br-gemfibrozil had LC50 values of 12.34 ± 0.085 and 9.54 ± 0.086 mg/L, respectively. Although acute toxicity is relatively low, our results indicate that halogenated gemfibrozil DBPs are bioaccumulative and may elicit effects in apex food web organisms prone to accumulation following lifelong exposures.

Use of spectroscopic indicators for the monitoring of bromate generation in ozonated wastewater containing variable concentrations of bromide

Time-resolved monitoring of bromate and other by-products formed into effluents treated with ozone or advanced oxidation processes in wastewater treatment plants (WWTPs) is time-consuming and expensive. This study examined whether concentrations of bromate formed in wastewater after ozonation in the presence of widely varying bromide levels (from ca. 0.7-21.2 mg/L) can be quantified based on measurements of changes in optical properties (differential UV absorbance (ΔUVA), spectral slopes, total or regional fluorescence) of the ozonated samples. Batch ozonation was carried out using a secondary effluent produced at a major wastewater treatment plant located in the Metropolitan Seattle Area. The tests involved raw and bromide-spiked samples treated with ozone doses from 0.1 to 1 mg O₃/mg DOC. Measurements of the absorbance at 254 nm (UVA254), fluorescence and bromate concentrations were performed on the treated samples. In the ozonated wastewater the concentration of bromate increased approximately linearly, from <10 ppb to ca. 200 ppb, without showing the lag phase characteristic for lower ozone doses (<0.4 mg O₃/mg DOC) that was observed in previous studies carried out with concentrations of bromide in the range of 0.05-0.5 mg/L. The highest bromide concentrations used in this study (>10 mg/L) tended to inhibit the generation of bromate. Relative reduction of UVA254 and total fluorescence (TF) were found to be good predictors of bromate generation. Specifically, exponential curves could adequately fit the non-linear relationships found to exist between the concentrations of bromate and the relative reductions of the UV254 and TF, for any initial bromide concentrations used in this study. Little formation of bromate was found to occur for reduction ranges for UVA254 and TF of 30-40% and 70-80% respectively. Conversely, rapid increases in bromate generation were observed when the decrease of UVA254 or TF exceeded these threshold values.

Volatile DBPs contributed marginally to the developmental toxicity of drinking water DBP mixtures against Platynereis dumerilii

Halogenated disinfection byproducts (DBPs) are formed during chlorine disinfection of drinking water. The complicated natural organic matter in source water causes the formation of an even more complicated mixture of DBPs. To evaluate the toxicity of a DBP mixture in a disinfected water sample, the sample needs to be pretreated in order to attain an observable acute adverse effect in the toxicity test. During sample pretreatment, volatile DBPs including trihalomethanes, haloacetonitriles and haloketones may be lost, which could affect the toxicity evaluation of the DBP mixture. In this study, we intentionally prepared "concentrated" simulated drinking water samples, which contained sufficiently high levels of volatile and nonvolatile DBPs and thus enabled directly evaluating the toxicity of the DBP mixtures without sample pretreatment. Specifically, the natural organic matter and bromide concentrations and the chlorine dose in the concentrated water samples were 250 times higher than those in a typical drinking water sample. Each concentrated water sample was divided into two aliquots, and one of them was nitrogen sparged to eliminate volatile DBPs; then, both aliquots were used directly in a well-established developmental toxicity test. No significant difference (p > 0.10) was found between the developmental toxicity indexes of each concentrated water sample without and with nitrogen sparging, indicating that the contribution of volatile DBPs to the developmental toxicity of the DBP mixture might be marginal. A reasonable interpretation is that nonvolatile halogenated DBPs (especially the aromatic ones) in the DBP mixture could be the major developmental toxicity contributor that warrants more attention.

Orthophosphate vs. bicarbonate used as a buffering substance for optimizing the bromide-enhanced ozonation process for ammonia nitrogen removal

Bromide-enhanced ozonation (BEO) process can be a fast and effective solution for the complete removal of total nitrogen (TN) from wastewaters containing from moderate to high concentrations of ammonia nitrogen (AN). Like the traditional biological process of AN oxidation, even BEO requires the presence of buffering agents, in order to oppose the progressive acidification induced by the reaction. This study compares the effect of two buffering substances (namely bicarbonate and mixtures of orthophosphates) in hindering the acidification caused by AN oxidation and, consequently, optimizing the overall efficiency of the process. Tests were carried out with on-purpose made solutions containing concentrations of AN of 5-10 mM. The range of [Br^-]/[O₃] ratio values was from 12 to 18, so as to make ozone the limiting factor in HOBr generation. The results of this study proved that, in the absence of natural buffering agents, mixtures of orthophosphates must be preferred to the more traditionally employed bicarbonate to control the pH evolution of BEO process. In fact, orthophosphates proved to be capable to guarantee an initial pH of the wastewater in the order of 7.5, thus making the zero-order AN removal rates 15% faster than those observed in the presence of bicarbonate. Furthermore, in the presence of mixtures of orthophosphates, the generation of ozonation byproducts in the oxidized form (nitrate, bromate) was reduced by over 70%. Finally, the fine control of pH obtained with orthophosphates in the BEO of AN makes that process an attractive solution for the treatment of effluents containing AN, thus preventing the discharge of residual nitrogen into aquatic environments and avoiding eutrophication of receiving water bodies.

Use of multiple regression models for predicting the formation of bromoform and dibromochloromethane during ballast water treatment based on an advanced oxidation process

Disinfection byproducts (DBPs) generated by ballast water treatment have become a concern worldwide because of their potential threat to the marine environment. Predicting the relative DBP concentrations after disinfection could enable better control of DBP formation. However, there is no appropriate method of evaluating DBP formation in a full-scale ballast water treatment system (BWTS). In this study, multiple regression models were developed for predicting the dibromochloromethane (DBCM) and bromoform (TBM) concentrations produced by an emergency BWTS using field experimental data from ballast water treatments conducted at Dalian Port, China. Six combinations of independent variables [including several water parameters and/or the total residual oxidant (TRO) concentration] were evaluated to construct mathematical prediction formulas based on a polynomial linear model and logarithmic regression model. Further, statistical analyses were performed to verify and determine the appropriate mathematical models for DBCM and TBM formation, which were ultimately validated using additional field experimental data. The polynomial linear model with four variables (temperature, salinity, chlorophyll, and TRO) and the logarithmic regression model with seven variables (temperature, salinity, dissolved oxygen, pH, turbidity, chlorophyll, and TRO) exhibited good reproducibility and could be used to predict the DBCM and TBM concentrations, respectively. The validation results indicated that the developed models could accurately predict DBP concentrations, with no significant statistical difference from the measured values. The results of this work could provide a theoretical basis and data reference for ballast water treatment control in engineering applications of emergency BWTSs.

Occurrence of disinfection by-products in sewage treatment plants and the marine environment in Hong Kong

Disinfection byproducts (DBPs) are generated by disinfectants reacting with organic matters. Previous studies have focused on DBPs in drinking water, but they have not paid sufficient attention to DBPs in sewage treatment plants (STPs), where the sources and compositions of DBPs are much more complicated, and there is a likelihood of more toxic DBPs being formed. In this study, the occurrence of DBPs in six STPs in Hong Kong and the potential impact of the effluents from the STPs on the marine environment were investigated. In STPs, the mean concentrations of the total DBPs ranged from 1160 to 17,019 ng/L, 1562 to 20,795 ng/L, and 289 to 1037 ng/L in the influent, effluent, and seawater, respectively. Trihalomethanes, haloacetonitriles, and trihalophenols were the most commonly detected DBPs, whereas hexachloro-1,3-butadiene and halocarbazoles were not detected in the STPs and in the marine environment in Hong Kong. Secondary treatment efficiently removed DBPs and DBP precursors. Regarding disinfection techniques, UV irradiation showed little effect on the concentrations of DBPs, whereas sodium hypochlorite significantly elevated the levels of both traditional and emerging DBPs. The effluents from two selected STPs that use chlorination have an obvious impact on the marine environment. This work presents the potential sources of DBPs in sewage, the influence of the treatment processes and disinfection techniques employed in STPs on the removal/formation of DBPs, and the impact of the effluents from the STPs on the marine environment. This work also highlights the need for investigating the emerging DBPs generated in STPs and their related environmental concerns.

Ballast water management system: Assessment of chemical quality status of several ports in Adriatic Sea

Oxidant treatment of ballast water (BW) is commonly used in BW systems in order to minimize the transport of alien species. The release of disinfection by-products (DBPs) associated to the treatment of BW and cross-contamination of butyltin (BT) compounds through BW discharge is a topic of environmental concern. A chemical port baseline survey has been conducted in seven ports of the Adriatic Sea. Analysis have been performed on transplanted mussels, surface sediment, seawater, BW. Results showed an evidence of BT contamination, particularly in sediments, probably related to their illegal usage or to intensive shipping activities. Therefore, BW may act as a vector and contribute to re-buildup of BT contamination in the coastal regions. A baseline set of data concerning DBPs is provided, showing the preferential distribution of these compounds in the marine environment that will be useful for future considerations on monitoring and assessment of chemical contamination associated with BW.

Disinfection byproducts and their toxicity in wastewater effluents treated by the mixing oxidant of ClO2/Cl2

Mixing oxidant of chlorine dioxide (ClO₂) and chlorine (Cl₂) often applied in water disinfection. Two secondary wastewater effluents at different ammonium-N levels (0.1 and 1.6 mg N L^-1) were treated with the mixing oxidant (ClO₂/Cl2) to evaluate the formation of disinfection byproducts (DBPs) and the associated cytotoxicity of treated wastewaters. The total chlorine concentrations of ClO₂ and Cl₂ were maintained at 10 mg L^-1 as Cl₂ with varied mixing ratios of ClO₂ to Cl₂. The formation of 37 halogenated DBPs, including nitrogenous, brominated and iodinated analogues, and 2 inorganic DBPs (chlorite and chlorate) was examined. The sum concentrations of the halogenated DBPs were reduced remarkably with decreasing Cl₂ percentages, but each individual DBP group had distinct features. The regulated trihalomethanes reduced the most when ClO₂ was present in chlorination, but decreasing Cl₂ percentage from 70% to 30% was not quite effective to reduce the formation of iodinated trihalomethanes, haloacetic acids and haloacetontriles in low ammonium-N wastewater. The bromine and iodine substitution factors tend to increase with decreasing Cl₂ percentages, indicating that destruction of DBP precursors by ClO₂ favored bromine and iodine incorporation. Additionally, decreasing Cl₂ percentages in the mixing oxidant (ClO₂/Cl₂) was often accompanied with lower chlorate formation but higher chlorite formation. The toxicity of treated wastewaters was evaluated through two approaches: the calculated cytotoxicity based on the concentrations of detected DBPs and the experimental cytotoxicity using the Chinese hamster ovary (CHO) cells. The calculated cytotoxicity decreased with decreasing Cl₂ percentages, with haloacetonitriles and haloacetaldehydes as predominate contributors. However, the experimental cytotoxicity tests showed that treatment of high ammonium-N wastewater with ClO₂/Cl₂ exhibited considerable higher (> 3 times) cytotoxicity potency than using single disinfectant.

Monitoring chlorine residual and trihalomethanes in the chlorinated seawater effluent of a nuclear power plant

Periodic sampling of the discharged seawater effluent from Madras Atomic Power Station (Kalpakkam, Tamil Nadu, India) was carried out during 2013-2017 to assess the residual chlorine and trihalomethanes content in the outfall discharge water. The variations in dissolved oxygen, temperature, and pH were correlated with the residual chlorine and trihalomethanes content in the discharged effluent. The difference in temperature (ΔT) between influent and effluent seawater samples ranged from 1.95 to 11.0 °C (6.47 ± 1.87). More than 95% of the ΔT values were within the guideline value of 7 °C. The discharge water was associated with a marginal reduction in dissolved oxygen and a marginal increase in conductivity values. The total residual chlorine content in the discharged seawater at outfall ranged from 0.06 to 0.42 (0.16 ± 0.08) mg/L, which was within the stipulated values of 0.5 mg/L. Trihalomethanes values ranged from 0.04 to 65.03 (13.06 ± 14.38) μg/L. In addition to bromoform as the major constituent, occurrence of significant amount chloroform of was occasionally observed in the discharge water.

Transformation of norfloxacin during the chlorination of marine culture water in the presence of iodide ions

The antibacterial agent norfloxacin (NOR) and sodium hypochlorite (NaClO), which are both widely used in marine culture, react with each other to form the halogenated disinfection byproducts (X-DBPs). The effects of the water characteristics and iodide concentration on the reaction kinetics were investigated. The results showed that the reaction rate of NOR with NaClO increases from 0.0586 min^-1 to 0.1075 min^-1 when the iodide concentration was changed from 0 μg^-1 to 50 μg^-1. This demonstrated the enhancement of NOR oxidation in the presence of iodide ions. Four novel iodinated DBPs (I-DBPs) were identified in the marine culture water. Iodine substitutions occurred at the C3 and C8 positions of NOR. The formation mechanisms of X-DBPs in the marine culture water were proposed based on the intermediate and final products. NOR may undergo a ring-opening reaction, a de-carbonyl reaction and substitution to form intermediates and finally generate the X-DBPs. Furthermore, the predicted logK_OW and logBCF values of the I-DBPs were higher than that of the Br-DBPs and Cl-DBPs. The AOX concentration in the synthetic water samples decreased in the following order: seawater (8.49 mg L^-1) > marine culture water (4.05 mg L^-1) > fresh water (1.89 mg L^-1). The amount of AOX also increased with the increase in iodide concentration. These results indicated that the I-DBPs were more toxic than their brominated and chlorinated analogues.

Removal of disinfection byproduct precursors and reduction in additive toxicity of chlorinated and chloraminated waters by ozonation and up-flow biological activated carbon process

The variations of disinfection byproduct (DBP) precursors and DBPs-associated toxic potencies were evaluated by ozonation, followed by a up-flow biological activated carbon (O₃/UBAC) filter treating two reconstituted water samples, featuring either high bromide (105.3 μg/L) or dissolved organic nitrogen (0.73 mg N/L) concentration, respectively. Ozonation contributed to ∼20% decrease in dissolved organic carbon (DOC) concentration at a dosage of 0.7 mg of O₃/mg of DOC, but no further reduction in DOC level was observed with an increased dose of 1.0 mg of O₃/mg of DOC. When chlorine or preformed monochloramine was used as a disinfectant, UBAC process led to ∼40% reduction in the sum of detected DBP formation potential (FP) due to the removal of precursors at a feasible empty bed contact time of 15 min. The integrated effect of ozonation and UBAC biofiltration decreased the sum of DBP FP by ∼50% including halonitromethanes (THNMs), N-nitrosamines (NAs), and bromate, which increased in the effluent of ozonation. Chloramination produced less DBPs by weight as well as DBPs-associated additive toxic potencies than chlorination. The reduction in additive toxic potencies was generally lower than the removal efficiency of DBP FP after chlor(am)ination of treated waters by O₃/UBAC, indicating that the removal of DBPs-associated additive toxic potencies should be focused to better understand on the residual risk to public health in controlling DBP precursors.

Dopamine crosslinked graphene oxide membrane for simultaneous removal of organic pollutants and trace heavy metals from aqueous solution

A graphene oxide-polydopamine-(β-cyclodextrin) (GPC) ultrafiltration membrane was fabricated by using the method of drop-coating combined with vacuum filtration. The prepared GPC membrane was characterized with FTIR and XPS spectrophotometry and evaluated for its performances for the rejection of organic molecules (methylene blue) and adsorption of trace heavy metals (Pb²⁺) from aqueous solutions. The membrane exhibited an excellent rejection coefficient of 99.2% for methylene blue and the permeation flux was 12 L m^-2 h^-1 at 0.1 bar. The membrane also exhibited fast adsorption kinetics for Pb²⁺ and the adsorption capacity was 101.6 mg g^-1 at a solution pH of 6. The performance of the membrane could almost be completely recovered after a simple clean and regeneration process. These results indicate that the GPC membrane has potential applications in treatment of complex industrial wastewater streams.

Impacts of shale gas production wastewater on disinfection byproduct formation: An investigation from a non-bromide perspective

The rapid rise of shale gas development has triggered environmental and human health concerns due to its impacts on water resources, especially on disinfection byproduct (DBP) formation upon chlorination. Despite the recently reported results on bromide, the effects of non-bromide ions in production wastewater at extremely high levels are vaguely defined. In this study, we investigated the effects of production wastewater, with bromide and non-bromide species, on the formation of DBPs when production wastewater was spiked into surface waters at various percentages. Results showed that the introduction of debrominated production wastewater led to increased formation of some chlorinated DBP species in selected surface water and wastewater. As the spiking percentage of debrominated production wastewater increased, the chlorinated DBP species increased. The contributions of individual cations to DBP formation followed a sequence of magnesium > calcium > barium at 0.10% spiking percentage due to the different catalytic effects of their chelates with organic precursors. The study of anions suggested that the discharge of treated production wastewater containing elevated sulfate may further enhance DBP formation. The significance of this study lies in the fact that in addition to bromide concerns from production wastewater, non-bromide species also contributed to DBP formation. The gas production wastewater management decision should consider the negative impacts from both bromide and non-bromide species to better protect the receiving water resources.

17β-estradiol as precursors of Cl/Br-DBPs in the disinfection process of different water samples

During chlorine disinfection process, reactions between the disinfectant and 17β-estradiol (E2) lead to the formation of halogenated disinfection byproducts (DBPs) which can be a risk to both ecosystem and human health. The degradation and transformation products of E2 in sodium hypochlorite (NaClO) disinfection processes of different water samples were investigated. The reaction kinetics research showed that the degradation rates of E2 were considerably dependent on the initial pH value and the types of water samples. In fresh water, synthetic marine aquaculture water and seawater, the reaction rate constant was 0.133 min^-1, 2.067 min^-1 and 2.592 min^-1, respectively. The reasons for the above phenomena may be due to the different concentrations of bromide ions (Br^-) in these three water samples which could promote the reaction between NaClO and E2. Furthermore, Br^- could also cause the formation of brominated DBPs (Br-DBPs). The main DBPs, reaction centers and conceivable reaction pathways were explored. Seven halogenated DBPs have been observed including three chlorinated DBPs (Cl-DBPs) and four Br-DBPs. The active sites of E2 were found to be the pentabasic cyclic ring and the ortho position of the phenol moiety as well as C9-C10 position. The identified Cl/Br-DBPs were also confirmed in actual marine aquaculture water from a shrimp pond. The comparison of bio-concentration factors (BCF) values based on calculation of EPI-suite showed that the toxicities of the Br-DBPs were stronger than that of their chloride analogues. The absorbable organic halogens (AOX) analysis also suggested that the DBPs produced in the marine aquaculture water were more toxic than that in the fresh water system.

Validation of a robust LLE-GC-MS method for determination of trihalomethanes in environmental samples

An analytical liquid-liquid extraction-gas chromatography-mass spectrometry (LLE-GC-MS) method was developed and validated for the determination of trihalomethanes (THMs) in environmental samples. The compounds studied were trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and tribromomethane (TBM). The calibration curves for the THMs showed high linearity in the range of 1-1000 μg L^-1. Studies of intra-day and inter-day precision, limit of detection (LOD), limit of quantification (LOQ), accuracy, and recovery were performed with low (10 μg L^-1), medium (40 μg L^-1), and high (200 μg L^-1) concentrations of THMs. The intra-day and inter-day precision RSD varied in the ranges of 0.17-6.95% and 0.26-15.70%, respectively. No statistical differences were observed between the analysis of the concentration of certified reference materials (CRM 4M8140-U) and the values reported by CRM, indicating the good accuracy of the proposed method. The recovery was 88.75-119.21%. The LOD and LOQ were smaller than 0.13 and 0.40 μg L^-1. Compared with reported LLE-GC-MS methods, the validated method had similar LOD and enhanced LOQ, precision, accuracy, and recovery. Also, the method is robust, selective to THMs, and the total time for the extraction and GC separation of THMs is about 18 min. The method was useful for detecting and quantifying low concentrations of TCM (40-80 μg L^-1) formed by water chlorination in the presence of Microcystis aeruginosa cyanobacteria, thus demonstrating its applicability for monitoring THMs in real samples.

Effects of bromide on the formation and transformation of disinfection by-products during chlorination and chloramination

The presence of bromide ion (Br^-) complicates the formation of disinfection by-products (DBPs) during chlorination and chloramination greatly. To better illustrate the role of Br^-, Br^- was introduced at different time intervals, i.e., 0min, 5min, 30min, and 24h, after dosing with chlorine (Cl₂) or chloramine (NH₂Cl), and the formation of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles, and haloacetones was investigated during these two disinfection scenarios. Ammonia rapidly reacts with chlorine and forms low-reactivity NH₂Cl, and this effect inhibits the formation of these DBPs greatly. Br^- promotes the formation of THMs, HAAs, and dichloroacetone (DCP) during chlorination, and the later bromide is introduced, i.e., the higher T_Cl2→Br^- is, the more significant the formation of THMs and HAAs observed. Bromide incorporation factors (BIF) increase upon the introduction of Br^-, and lower T_Cl2→Br^- is related to higher BIF values. Additionally, Br^- inhibits the formation of dichloroacetonitrile (DCAN) and trichloroacetone (TCP), owing to its catalytic degradation effect towards them. In the chloramination process, Br^- shows similar effects towards the formation of THMs and HAAs, except that higher T_NH2Cl→Br^- inhibits their formation. Br^- greatly inhibits the formation of DCP, TCP, and DCAN, and the formed haloacetones rapidly degrade upon the introduction of Br^-. The results of UV and EEM spectral analysis indicate that the reducing Br^- may improve rather than inhibit the oxidation of both the reactive components (DOC₁) and the slowly reactive sites (DOC₂) within HA, possibly owing to its buffering effect towards chlorine. In chlorination of source water with Br^- present, Br^- promotes the formation of most DBPs and enhances the incorporation of Br atoms therein, and in this case, DBP formation may be remarkably decreased by dosing with ammonia to transform chlorination to chloramination.

Carbonaceous and nitrogenous disinfection byproduct precursor variation during the reversed anaerobic-anoxic-oxic process of a sewage treatment plant

Disinfection byproduct (DBP) precursors in wastewater during the reversed anaerobic-anoxic-oxic (A²/O) process, as well as their molecular weight (MW) and polarity-based fractions, were characterized with UV scanning, fluorescence excitation emission matrix, Fourier transform infrared and nuclear magnetic resonance spectroscopy. Their DBP formation potentials (DBPFPs) after chlorination were further tested. Results indicated that the reversed A²/O process could not only effectively remove the dissolved organic carbon (DOC) and dissolved total nitrogen in the wastewater, but also affect the MW distribution and hydrophilic-hydrophobic properties of dissolved organic matter (DOM). The accumulation of low MW and hydrophobic (HPO) DOM was possibly due to the formation of soluble microbial product-like (SMP-like) matters in the reversed A²/O treatment, especially in the anoxic and aerobic processes. Moreover, DOM in the wastewater displayed a high carbonaceous disinfection byproduct formation potential (C-DBPFP) in the fractions of MW>100kDa and MW<5kDa, and revealed an increasing tendency of nitrogenous disinfection byproduct formation potential (N-DBPFP) with decrease of MW. For polarity-based fractions, the HPO fraction of wastewater showed significantly higher C-DBPFP and N-DBPFP than hydrophilic and transphilic fractions. Therefore, although the reversed A²/O process could remove most DBP precursors by DOC reduction, it led to the enhancement of DBPFP with the formation and accumulation of low MW and HPO DOM. In addition, strong correlations between C-DBPFPs and SUVA, and between N-DBPFPs and DON/DOC, were observed in the wastewater, which might be helpful for DBPFP prediction in wastewater and reclaimed water chlorination.

Chlorine decay and trihalomethane formation following ferrate(VI) preoxidation and chlorination of drinking water

This paper presents the effect of preoxidation with ferrate(VI) (Fe^VIO₄^2-, Fe(VI)) prior to chlorination on chlorine decay and formation of disinfection by-products in filtered raw water from a full-scale drinking water treatment plant. The rate of chlorine decay became significantly faster as the concentration of ferrate(VI) increased. Chlorine degradation followed two first-order decay reactions with rate constants k₁ and k₂ for fast and slow decay, respectively. Kinetic modeling established the relationships between k₁ and k₂ and varying dosages of chlorine and ferrate(VI). When ferrate(VI) was used as a pre-oxidant, the levels of trihalomethanes (trichloromethane (TCM), dichlorobromomethane (DCBM), dibromochloromethane (DBCM), and tribromomethane (TBM)) in water samples decreased as the ferrate(VI) concentration increased. The concentrations of these trihalomethanes followed the order TCM > DCBM ≈ DBCM > TBM.

Removal of disinfection byproduct (DBP) precursors in water by two-stage biofiltration treatment

The removal of precursors of 36 disinfection byproducts (DBPs) in effluents from flocculation/sedimentation process was evaluated across a pilot-scale two-stage biofiltration process, i.e., a sand/anthracite (SA) biofilter (empty bed contact time (EBCT) of 7.5 min) coupled with a biologically-active granular activated carbon (GAC) contactor (EBCT of 15 min). The biofiltration process exhibited a good capacity for removal of the total DBP formation potential (DBPFP) (by 25.90 ± 2.63%), and GAC contactors contributed most to the DBPFP removal (accounting for 60.63 ± 16.64% of the total removal). The removal percentage of DBPFPs of different structure types was in the following order: halonitroalkanes (58.50%) > haloaldehydes (33.62%) > haloacetic acids (HAAs, 28.13%) > haloalkanes (20.46%) > haloketones (13.46%) > nitrosamines (10.23%) > halonitriles (-8.82%) > haloalkenes (-9.84%). The precursors of bromo-DBPs (containing only bromine atoms) and maximal halogenated DBPs (containing 3 & 4 halo atoms) were removed largely compared to other DBPs. Among the total DBPFP, trihalomethanes (THMs), HAAs, and chloral hydrate were the dominant DBPs, and they accounted for >92% of the total targeted DBPs by weight. Pearson correlation analysis (CA) and principal components analysis (PCA) indicated a significant association among these dominant DBPs. Canonical correspondence analysis (CCA) revealed specific ultraviolet absorbance (SUVA₂₅₄) could serve as a good surrogate parameter for DBPFP. Pre-chlorination upstream of the biofilters may not greatly impact the overall removal of DBPFP by SA/GAC biofiltration. In addition, results showed that SA/GAC biofiltration was a useful procedure to remove the inorganic DBP chlorite.

Chemical fingerprinting of saline water intrusion into sewage lines

High salinity in sewage sludge can affect not only the operation of wastewater treatment plants (WWTPs) but also the quality of treated water generated, thereby limiting its downstream reuse. Using data on geochemical parameters, both for the central WWTP in Abu Dhabi, UAE, and literature values for potential regional saline water sources (e.g., shallow groundwater and regional Arabian Gulf seawater), a variety of chemical fingerprinting diagnostic ratios were calculated and plotted in order to determine the source of salinity in the municipal sewage. Data were compared with data from a regional WWTP that was not impacted by salinity. Monitoring data demonstrated persistently elevated levels of salinity in the municipal wastewater arriving at the central WWTP from the city. Dilution/concentration analysis using a conductivity vs. chloride plot showed both potential sources, i.e. Arabian Gulf seawater and coastal hypersaline groundwater, as feasible sources of wastewater salinization. Further diagnostic analysis using a Panno Plot indicated that coastal groundwater was the only likely source of salinization of municipal sewage. Additional confirmation of the identity of the source and the extent of mixing using different lines of evidence like stable isotope ratios is recommended for future study.

Toxicity of Wastewater with Elevated Bromide and Iodide after Chlorination, Chloramination, or Ozonation Disinfection

Water reuse is receiving unprecedented attention as many areas around the globe attempt to better-manage their fresh water resources. Wastewaters in coastal regions may contain elevated levels of bromide (Br^-) and iodide (I^-) from seawater intrusion or high mineral content in the source waters. Disinfection of such wastewater is essential to prevent the spread of pathogens; however, little is known about the toxicity of the treated wastewater. In this study, we evaluated the genotoxicity to Chinese hamster ovary (CHO) cells induced by municipal secondary wastewater effluent amended with elevated Br^- and I^- after disinfection by chlorine, chloramines, or ozone. We calibrated and applied an N-acetylcysteine (NAC) thiol reactivity assay as a surrogate for thiol reactivity with biological proteins (glutathione) of wastewater samples. Chlorination of wastewaters produced CHO cell genotoxicity comparable to chloramination, 3.9 times more genotoxic than the nondisinfected controls. Ozonated wastewater was at least 3 times less genotoxic than the samples treated with chlorine-based disinfectants and was not significantly different compared with the nondisinfected controls. Positive and significant correlations were observed among genotoxicity, cytotoxicity, and NAC thiol reactivity for all disinfected samples. These results indicate that the ozonation of wastewater with high Br^- and I^- levels may yield organics with lower genotoxicity to CHO cells than chlorine-based disinfection. NAC thiol reactivity, although excluding the possible effect of bromate from ozonation in this work, could be used as a rapid in chemico screen for potential genotoxicity and cytotoxicity in mammalian cells exposed to disinfected wastewaters.

Comparative mammalian cell cytotoxicity of wastewater with elevated bromide and iodide after chlorination, chloramination, or ozonation

Recycling wastewater is becoming more common as communities around the world try to better control their water resources against an increased frequency of either prolonged droughts or intense flooding. For communities in coastal areas, wastewaters may contain elevated levels of bromide (Br^-) and iodide (I^-) from seawater intrusion or high mineral content of source waters. Disinfection of such wastewater is mandatory to prevent the spread of pathogens, however little is known about the toxicity of wastewater after disinfection in the presence of Br^- and I^-. In this study we compared the induction of chronic cytotoxicity in mammalian cells in samples of municipal secondary wastewater effluent amended with elevated levels of Br^-/I^- after disinfection by chlorine, chloramines or ozone to identify which disinfection process generated wastewater with the lowest level of adverse biological response. Chlorination increased mammalian cell cytotoxicity by 5 times as compared to non-disinfected controls. Chloramination produced disinfected wastewater that expressed 6.3 times more cytotoxicity than the non-disinfected controls and was 1.3 times more cytotoxic than the chlorinated samples. Ozonation produced wastewater with cytotoxicity comparable to the non-disinfected controls and was at least 4 times less cytotoxic than the chlorine disinfected wastewaters. These results indicate that compared to chlorination and chloramination, ozonation of wastewater with high Br^-/I^- levels yielded the lowest mammalian cell cytotoxicity, suggesting its potential as a more favorable method to disinfect wastewater with minimizing the biological toxicity in mind.

Bromine incorporation into five DBP classes upon chlorination of water with extremely low SUVA values

The main objective of this study was to assess the effects of disinfection conditions on bromine incorporation into disinfection by-products (DBPs) during chlorination of water with low specific UV absorbance (SUVA). Five classes of DBPs were included: trihalomethanes (THMs), dihaloacetic acids (di-HAAs), trihaloacetic acids (tri-HAAs), dihaloacetonitriles (DHANs) and trihalonitromethanes (THNMs). Results showed that the bromine utilization in DBPs formation was positive related with reaction time, pH and temperature. On the other hand, the bromine substitution factors (BSFs) of DBPs were generally increased with pH (except tri-HAAs) and bromide concentration, but decreased with the reaction time, temperature and chlorine dose. Moreover, the BSFs values varied with DBP classes with the ranking being as following: THNMs≫DHANs≫tri-HAAs>THM≈di-HAAs. These results were mostly similar with the references, yet the pH effect on BSFs as well as the rank of BSFs for different DBP classes may differ with the specific UV absorbance of organic matter.

Effect of Ozonation and Biological Activated Carbon Treatment of Wastewater Effluents on Formation of N-nitrosamines and Halogenated Disinfection Byproducts

Ozonation followed by biological activated carbon (O₃/BAC) is being considered as a key component of reverse osmosis-free advanced treatment trains for potable wastewater reuse. Using a laboratory-scale O₃/BAC system treating two nitrified wastewater effluents, this study characterized the effect of different ozone dosages (0-1.0 mg O₃/mg dissolved organic carbon) and BAC empty bed contact times (EBCT; 15-60 min) on the formation after chlorination or chloramination of 35 regulated and unregulated halogenated disinfection byproducts (DBPs), 8 N-nitrosamines, and bromate. DBP concentrations were remarkably similar between the two wastewaters across O₃/BAC conditions. Ozonation increased bromate, TCNM, and N-nitrosodimethylamine, but ozonation was less significant for other DBPs. DBP formation generally decreased significantly with BAC treatment at 15 min EBCT, but little further reduction was observed at higher EBCT where low dissolved oxygen concentrations may have limited biological activity. The O₃/BAC-treated wastewaters met regulatory levels for trihalomethanes (THMs), haloacetic acids (HAAs), and bromate, although N-nitrosodimethylamine exceeded the California Notification Level in one case. Regulated THMs and HAAs dominated by mass. When DBP concentrations were weighted by measures of their toxic potencies, unregulated haloacetonitriles, haloacetaldehydes, and haloacetamides dominated. Assuming toxicity is additive, the calculated DBP-associated toxicity of the O₃/BAC-treated chloraminated effluents were comparable or slightly higher than those calculated in a recent evaluation of Full Advanced Treatment trains incorporating reverse osmosis.

Three-step effluent chlorination increases disinfection efficiency and reduces DBP formation and toxicity

Chlorination is extensively applied for disinfecting sewage effluents, but it unintentionally generates disinfection byproducts (DBPs). Using seawater for toilet flushing introduces a high level of bromide into domestic sewage. Chlorination of sewage effluent rich in bromide causes the formation of brominated DBPs. The objectives of achieving a disinfection goal, reducing disinfectant consumption and operational costs, as well as diminishing adverse effects to aquatic organisms in receiving water body remain a challenge in sewage treatment. In this study, we have demonstrated that, with the same total chlorine dosage, a three-step chlorination (dosing chlorine by splitting it into three equal portions with a 5-min time interval for each portion) was significantly more efficient in disinfecting a primary saline sewage effluent than a one-step chlorination (dosing chlorine at one time). Compared to one-step chlorination, three-step chlorination enhanced the disinfection efficiency by up to 0.73-log reduction of Escherichia coli. The overall DBP formation resulting from one-step and three-step chlorination was quantified by total organic halogen measurement. Compared to one-step chlorination, the DBP formation in three-step chlorination was decreased by up to 23.4%. The comparative toxicity of one-step and three-step chlorination was evaluated in terms of the development of embryo-larva of a marine polychaete Platynereis dumerilii. The results revealed that the primary sewage effluent with three-step chlorination was less toxic than that with one-step chlorination, indicating that three-step chlorination could reduce the potential adverse effects of disinfected sewage effluents to aquatic organisms in the receiving marine water.

Characterization of trihalomethane, haloacetic acid, and haloacetonitrile precursors in a seawater reverse osmosis system

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.

Governing factors affecting the impacts of silver nanoparticles on wastewater treatment

Silver nanoparticles (nanosilver or AgNPs) enter municipal wastewater from various sources, raising concerns about their potential adverse effects on wastewater treatment processes. We argue that the biological effects of silver nanoparticles at environmentally realistic concentrations (μgL^-1 or lower) on the performance of a full-scale municipal water resource recovery facility (WRRF) are minimal. Reactor configuration is a critical factor that reduces or even mutes the toxicity of silver nanoparticles towards wastewater microbes in a full-scale WRRF. Municipal sewage collection networks transform silver nanoparticles into silver(I)-complexes/precipitates with low ecotoxicity, and preliminary/primary treatment processes in front of biological treatment utilities partially remove silver nanoparticles to sludge. Microbial functional redundancy and microbial adaptability to silver nanoparticles also greatly alleviate the adverse effects of silver nanoparticles on the performance of a full-scale WRRF. Silver nanoparticles in a lab-scale bioreactor without a sewage collection system and/or a preliminary/primary treatment process, in contrast to being in a full scale system, may deteriorate the reactor performance at relatively high concentrations (e.g., mgL^-1 levels or higher). However, in many cases, silver nanoparticles have minimal impacts on lab-scale bioreactors, such as sequencing batch bioreactors (SBRs), especially when at relatively low concentrations (e.g., less than 1mgL^-1). The susceptibility of wastewater microbes to silver nanoparticles is species-specific. In general, silver nanoparticles have higher toxicity towards nitrifying bacteria than heterotrophic bacteria.

Bromide Sources and Loads in Swiss Surface Waters and Their Relevance for Bromate Formation during Wastewater Ozonation

Bromide measurements and mass balances in the catchments of major Swiss rivers revealed that chemical industry and municipal waste incinerators are the most important bromide sources and account for ∼50% and ∼20%, respectively, of the ∼2000 tons of bromide discharged in the Rhine river in 2014 in Switzerland. About 100 wastewater treatment plants (WWTPs) will upgrade their treatment for micropollutant abatement in the future to comply with Swiss regulations. An upgrade with ozonation may lead to unintended bromate formation in bromide-containing wastewaters. Measured bromide concentrations were <0.05 mg L(-1) in ∼75% of 69 WWTPs, while they ranged from 0.4 to ∼50 mg L(-1) in WWTPs with specific bromide sources (e.g., municipal waste incinerators, landfill leachate, and chemical industry). Wastewater ozonation formed little bromate at specific ozone doses of ≤0.4 mg O3/mg DOC, while the bromate yields were almost linearly correlated to the specific ozone dose for higher ozone doses. Molar bromate yields for typical specific ozone doses in wastewater treatment (0.4-0.6 mg O3/mg DOC) are ≤3%. In a modeled extreme scenario (in which all upgraded WWTPs release 10 μg L(-1) of bromate), bromate concentrations increased by <0.4 μg L(-1) in major Swiss rivers and by several micrograms per liter in receiving water bodies with a high fraction of municipal wastewater.

Comparative study on DBPs formation profiles of intermediate organics from hydroxyl radicals oxidation of microbial cells

This study assessed the characteristics of disinfection byproducts (DBPs) formation from intermediate organics during UV/H2O2 treatment of activated sludge and algae cells under various reaction conditions. The DBPs including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs) and haloacetonitriles (HANs) in UV/H2O2-treated and chlorinated water were measured. The results showed that both dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) increased during the initial stage of UV/H2O2 treatment due to the lysis of sludge and algae cells, which enhanced the formation of both C- and N-DBPs; however, both DOC and DON decreased after longer reaction times. During the UV/H2O2 treatments, THMs formation potential (THMFP) peaked earlier than did HAAs formation potential (HAAFP). This shows that the dissolved organics released from lysis of microbial cells in the early stages of oxidation favor the production of THMs over HAAs; however, HAAs precursors increased with the oxidation time. Chlorination with bromide increased the formation of THMs and HAAs but less HKs and HANs were produced. Comparisons of normalized DBP formation potential (DBPFP) of samples collected during UV/H2O2 treatments of four different types of organic matter showed that the highest DBPFP occurred in filtered treated wastewater effluent, followed by samples of activated sludge, filtered eutrophicated pond water, and samples of algae cells. With increasing oxidation time, the dominant DBP species shifted from THMs to HAAs in the samples of activated sludge and algae cells. The DBPFP tests also showed that more HAAs were formed in biologically treated wastewater effluent, while the eutrophicated source water produced more THMs.

Combination of UV absorbance and electron donating capacity to assess degradation of micropollutants and formation of bromate during ozonation of wastewater effluents

In this study, the changes in UV absorbance at 254 nm (UVA254) and electron donating capacity (EDC) were investigated as surrogate indicators for assessing removal of micropollutants and bromate formation during ozonation of wastewater effluents. To measure the EDC, a novel method based on size exclusion chromatography followed by a post-column reaction was developed and calibrated against an existing electrochemical method. Low specific ozone doses led to a more efficient abatement of EDC than of UVA254. This was attributed to the abatement of phenolic moieties in the dissolved organic matter (DOM), which lose their EDC upon oxidation, but are partially transformed into quinones, which still absorb in the measured UV range. For higher specific ozone doses, the relative EDC abatement was lower than the relative UVA abatement, which can be explained by the oxidation of UV absorbing moieties (e.g. non-activated aromatic compounds), which contribute less to EDC. The abatement of the selected micropollutants (i.e., 17α-ethinylestradiol (EE2), carbamazepine (CBZ), atenolol (ATE), bezafibrate (BZF), ibuprofen (IBU), and p-chlorobenzoic acid (pCBA)) varied significantly depending on their reactivity with ozone in the examined specific ozone dose range of 0-1.45 mgO3/mgDOC. The decrease of EE2 and CBZ with high ozone reactivity was linearly proportional to the reduction of the relative residuals of UVA254 and EDC. The abatement of ATE, BZF, IBU, and pCBA with intermediate to low ozone reactivities was not significant in a first phase (UVA254/UVA254,0 = 1.00-0.70; EDC/EDC0 = 1.00-0.56) while their abatement was more efficient than the degradation of the relative residual UVA254 and much more noticeable than the degradation of the relative residual EDC in a second phase (UVA254/UVA254,0 = 0.70-0.25; EDC/EDC0 = 0.56-0.25) because the partially destroyed UV absorbing and electron donating DOM moieties become recalcitrant to ozone attack. Bromate formation was pronounced for specific ozone doses >0.25 mgO3/mgDOC. At these ozone doses, the residual DOM competes less with bromide for ozone as the electron-rich DOM moieties are almost completely degraded. Overall, these results imply that a combination of the relative residual UVA254 and EDC more truly reflects the intrinsic reactivity of DOM associated with the removal of micropollutants and bromate formation than the single use of the UV absorbance-based surrogate indicators.

Dissolved effluent organic matter: Characteristics and potential implications in wastewater treatment and reuse applications

Wastewater reuse is currently considered globally as the most critical element of sustainable water management. The dissolved effluent organic matter (dEfOM) present in biologically treated urban wastewater, consists of a heterogeneous mixture of refractory organic compounds with diverse structures and varying origin, including dissolved natural organic matter, soluble microbial products, endocrine disrupting compounds, pharmaceuticals and personal care products residues, disinfection by-products, metabolites/transformation products and others, which can reach the aquatic environment through discharge and reuse applications. dEfOM constitutes the major fraction of the effluent organic matter (EfOM) and due to its chemical complexity, it is necessary to utilize a battery of complementary techniques to adequately describe its structural and functional character. dEfOM has been shown to exhibit contrasting effects towards various aquatic organisms. It decreases metal uptake, thus potentially reducing their bioavailability to exposed organisms. On the other hand, dEfOM can be adsorbed on cell membranes inducing toxic effects. This review paper evaluates the performance of various advanced treatment processes (i.e., membrane filtration and separation processes, activated carbon adsorption, ion-exchange resin process, and advanced chemical oxidation processes) in removing dEfOM from wastewater effluents. In general, the literature findings reveal that dEfOM removal by advanced treatment processes depends on the type and the amount of organic compounds present in the aqueous matrix, as well as the operational parameters and the removal mechanisms taking place during the application of each treatment technology.