Formation of chlorination by-products in drinking water treatment plants using breakpoint chlorination

A group of emerging heterocyclic nitrogenous disinfection byproducts: Formation and cytotoxicity of halopyridinols in drinking water

Recently, a new group of halopyridinol disinfection byproducts (DBPs) was reported in drinking water. The in vivo developmental and acute toxicity assays have shown that they were more toxic than a few commonly known aliphatic DBPs such as bromoform and iodoacetic acid. However, many pyridinol DBPs with the same main structures but different halogen substitutions were still unknown due to complicated water quality conditions and various disinfection methods applied in drinking water treatment plants. Studies on their transformation mechanisms in drinking water disinfection were quite limited. In this study, comprehensive detection and identification of halopyridinols were conducted, and five new halopyridinols were first reported, including 2-chloro-3-pyridinol, 2,6-dichloro-3-pyridinol, 2-bromo-5-chloro-3-pyridinol, 2,4,6-trichloro-3-pyridinol and 2,5,6-trichloro-3-pyridinol. Formation conditions and mechanisms of the halopyridinols were explored, and results showed that chlorination promoted their formation compared with chloramination. Halopyridinols were intermediate DBPs that could undergo further transformation/degradation with increasing contact time, disinfectant dose, bromide concentration, and pH. The in vitro cytotoxicity of the halopyridinols was evaluated using human hepatocellular carcinoma cells. Results showed that the cytotoxicity of 3,5,6-trichloro-2-pyridinol was the highest (EC50 = 474.3 μM), which was 13.0 and 1.6 times higher than that of 2-bromo-3-pyridinol (EC50 = 6214.5 μM) and tribromomethane (EC50 = 753.6 μM), respectively.

Formation potential of disinfection byproducts during chlorination of petroleum hydrocarbon-contaminated drinking water

Recent leaks of underground fuel storage tanks in the Pearl Harbor region have led to direct release of un-weathered petroleum hydrocarbons (PHCs) into drinking water sources, which then directly underwent chlorination disinfection treatment. Since the control of disinfection byproducts (DBPs) traditionally focuses natural organic matters (NOM) from source water and little is known about the interactions between free chlorine and un-weathered PHCs, laboratory chlorination experiments in batch reactors were conducted to determine the formation potential of DBPs during chlorination of PHC-contaminated drinking water. Quantitative analysis of regulated DBPs showed that significant quantities of THM4 (average 3,498 μg/L) and HAA5 (average 355.4 μg/L) compounds were formed as the result of chlorination of un-weathered PHCs. Amongst the regulated DBPs, THM4, which were comprised primarily of chloroform and bromodichloromethane, were more abundant than HAA5. Numerous unregulated DBPs and a large diversity of unidentified potentially halogenated organic compounds were also produced, with the most abundant being 1,1-dichloroacetone, 1,2-dibromo-3-chloropropane, chloropicrin, dichloroacetonitrile, and trichloracetonitrile. Together, the results demonstrated the DBP formation potential when PHC-contaminated water undergoes chlorination treatment. Further studies are needed to confirm the regulated DBP production and health risks under field relevant conditions.

Temporal and spatial variations of disinfection by-products in South Taihu's drinking water, Zhejiang Province, China

Some disinfection by-products (DBPs) in drinking water present a potential safety concern. This study focuses on the elements influencing DBPs formation. A total of 120 water samples were collected from 10 different drinking water facilities spanning 5 counties within Huzhou, Zhejiang Province, China. Concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) were observed to be 14.5 and 27.4 μg/L, respectively, constituting 34 and 64% of the total DBPs. Seasonal fluctuations demonstrated that HAAs, THMs, halonitromethanes (HNMs), and haloacetonitriles (HANs) followed a similar pattern with higher levels in summer or autumn compared to spring. Importantly, the concentrations of HAAs and THMs were markedly higher in Taihu-sourced water compared to other sources. Geographically, Nanxun exhibited the highest levels of total DBPs, HAAs, and THMs, while Deqing and Changxing demonstrated significantly lower levels. Correlation studies between water quality parameters and DBPs revealed that factors such as chloride content, temperature, and residual chlorine positively influenced DBPs formation, whereas turbidity negatively affected it. Principal component analysis suggested similar formation processes for HANs, haloketones (HKs), HNMs, and THMs. Factors such as temperature, chemical oxygen demand (COD), and residual chlorine were identified as significant contributors to the prevalence of HAAs.

Perchlorate and chlorate assessment in drinking water in northern Chilean cities

Perchlorate and chlorate are endocrine disruptors considered emerging contaminants (ECs). Both oxyanions are commonly associated with anthropogenic contamination from fertilizers, pesticides, explosives, and disinfection byproducts. However, the soils of the Atacama Desert are the most extensive natural reservoirs of perchlorate in the world, compromising drinking water sources in northern Chile. Field campaigns were carried (2014-2018) to assess the presence of these ECs in the water supply networks of twelve Chilean cities. Additionally, the occurrence of perchlorate, chlorate and other anions typically observed in drinking water matrices of the Atacama Desert (i.e., nitrate, chloride, sulfate) was evaluated using a Spearman correlation analysis to determine predictors for perchlorate and chlorate. High concentrations of perchlorate (up to 114.48 μg L-1) and chlorate (up to 9650 μg L-1) were found in three northern cities. Spatial heterogeneities were observed in the physicochemical properties and anion concentrations of the water supply network. Spearman correlation analysis indicated that nitrate, chloride, and sulfate were not useful predictors for the presence of perchlorate and chlorate in drinking water in Chile. Hence, this study highlights the need to establish systematic monitoring, regulation, and treatment for these EC of drinking water sources in northern Chilean cities for public health protection.

Status of disinfection byproducts research in India

India faces high incidents of waterborne disease outbreaks owing to their limited access to safe drinking water. In many ways, the effort to improve the quality of drinking water is performed, and it has been keenly monitored. Among those, the disinfection of drinking water is considered a necessary and important step as it controls the microbial population. Chlorination is the most practiced (greater than 80%) disinfection process in India, and it is known to generate various disinfection byproducts (DBPs). Although the toxicity and trend of DBPs are regularly monitored and investigated in most countries, still in India, the research is at the toddler level. This review summarizes i) the status of drinking water disinfection in India, ii) types of disinfection processes in centralized water treatment plants, iii) concentrations and occurrence patterns of DBPs in a different region of India, iv) a literature survey on the toxicity of DBPs, and v) removal methodologies or alternative technologies to mitigate the DBPs formation. Overall, this review may act as a roadmap to understand the trend of disinfection practices in India and their impacts on securing the goal of safe drinking water for all.

Carbon dots electrochemically prepared from dopamine and epigallocatechin gallate for hypochlorite detection with high selectivity via a dynamic quenching mechanism

Monitoring hypochlorite levels in water is of great importance because of its high toxicity and wide applications as water disinfectants. In this manuscript, carbon dot (CD) was electrochemically prepared by using dopamine and epigallocatechin gallate (molar ratio 1:1) as the carbon source for efficient hypochlorite determination. By electrolyzing the solution at 10 V for 12 min with PBS as an electrolyte, dopamine would react with epigallocatechin at the anode, and through polymerization, dehydration, and carbonization, strong blue-fluorescent CDs were obtained. CDs were characterized by UV-Vis spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy, FT-IR, etc. These CDs have an excitation wavelength at 372 nm and an emission wavelength at 462 nm, owing an average particle size of 5.5 nm. The presence of hypochlorites can quench the fluorescence of CDs, and its reduction in intensity is linear with hypochlorite concentration over the range of 0.5-50 μM, ΔF/F₀ = 0.0056 + 0.0194C_ClO^-, R²=0.997. The detection limit achieved 0.23 μM (S/N = 3). The mechanism for fluorescence quenching is via a dynamic process. Different from many other fluorescence methods based on the strong oxidizing ability of hypochlorites, our method shows strong selectivity toward hypochlorites over other oxidizing agents such as H₂O₂. The assay was validated by the detection of hypochlorites in water samples, with recoveries between 98.2% and 104.3%.

Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective

With the extensive development of industrial livestock and poultry production, a considerable part of agricultural wastewater containing tremendous ammonium and antibiotics have been indiscriminately released into the aquatic systems, causing serious harms to ecosystem and human health. In this review, ammonium detection technologies, including spectroscopy and fluorescence methods, and sensors were systematically summarized. Antibiotics analysis methodologies were critically reviewed, including chromatographic methods coupled with mass spectrometry, electrochemical sensors, fluorescence sensors, and biosensors. Current progress in remediation methods for ammonium removal were discussed and analyzed, including chemical precipitation, breakpoint chlorination, air stripping, reverse osmosis, adsorption, advanced oxidation processes (AOPs), and biological methods. Antibiotics removal approaches were comprehensively reviewed, including physical, AOPs, and biological processes. Furthermore, the simultaneous removal strategies for ammonium and antibiotics were reviewed and discussed, including physical adsorption processes, AOPs, biological processes. Finally, research gaps and the future perspectives were discussed. Through conducting comprehensive review, future research priorities include: (1) to improve the stabilities and adaptabilities of detection and analysis techniques for ammonium and antibiotics, (2) to develop innovative, efficient, and low cost approaches for simultaneous removal of ammonium and antibiotics, and (3) to explore the underlying mechanisms that governs the simultaneous removal of ammonium and antibiotics. This review could facilitate the evolution of innovative and efficient technologies for ammonium and antibiotics treatment in agricultural wastewater.

Effective removal of ammonia from aqueous solution through struvite synthesis and breakpoint chlorination: Insights into the synergistic effects of the hybrid system

The ever-growing contamination of surface water due to various catchment activities poses threats and stress to downstream water treatment entities. Specifically, the presence of ammonia, microbial contaminants, organic matter, and heavy metals has been an issue of paramount concern to water treatment entities since stringent regulatory frameworks require these pollutants to be removed prior to water consumption. Herein, a hybrid approach that integrates struvite crystallization (precipitation) and breakpoint chlorination (stripping) for the removal of ammonia from aqueous solution was evaluated. To fulfil the goals of this study, batch experimental studies were pursued through the adoption of the well-known one-factor-at-a-time (AFAAT) method, specifically the effects of time, concentration/dosage, and mixing speed. The fate of chemical species was underpinned using the state-of-the-art analytical instruments and accredited standard methods. Cryptocrystalline magnesium oxide nanoparticles (MgO-NPs) were used as the magnesium source while the high-test hypochlorite (HTH) was used as the source of chlorine. From the experimental results, the optimum conditions were observed to be, i.e., Stage 1 - struvite synthesis, 110 mg/L of Mg and P dosage (concentration), 150 rpm of mixing speed, 60 min of contact time, and lastly, 120 min of sedimentation while optimum condition for the breakpoint chlorination (Stage 2) were 30 min of mixing and 8:1 Cl₂:NH₃ weight ratio. Specifically, in Stage 1, i.e., MgO-NPs, the pH increased from 6.7 to ≥9.6, while the turbidity was reduced from 9.1 to ≤1.3 NTU. Mn removal efficacy attained ≥97.70% (reduced from 174 μg/L to 4 μg/L) and Fe attained ≥96.64% (reduced from 11 mg/L to 0.37 mg/L). Elevated pH also led to the deactivation of bacteria. In Stage 2, i.e. breakpoint chlorination, the product water was further polished by eliminating residual ammonia and TPC at 8:1 Cl₂-NH₃ weight ratio. Interestingly, ammonia was reduced from 6.51 to 2.1 mg/L in Stage 1 (67.74% removal) and then from 2.1 to 0.002 mg/L post breakpoint chlorination (99.96% removal), i.e., stage 2. Overall, synergistic and complementary effects of integrating struvite synthesis and breakpoint chlorination hold great promise for the removal of ammonia from aqueous solutions thus confirming that this technology could potentially be used to curtail the effects of ammonia in the receiving environments and drinking water.

Occurrence and fate of an emerging drug pollutant and its by-products during conventional and advanced wastewater treatment: Case study of furosemide

Conventional wastewater treatment systems are not designed to remove pharmaceutical compounds from wastewater. These compounds can be degraded into many other transformation products which are hardly, if at all, studied. In this context, we studied the occurrence and degradation of furosemide, a very frequently detected diuretic, along with its known degradation products in several types of wastewater. Influent and effluent from the Seine-Centre Wastewater Treatment Plant (WWTP) (Paris, France) as well as outlet of residential care homes (Dordogne, France) were analyzed by Ultra-Performance Liquid Chromatography-tandem Mass Spectrometry (UPLC-MS/MS) to quantify furosemide and its known degradation products, saluamine and pyridinium of furosemide. Oxidation experiments (chlorination, ozonation and UV photolysis with hydrogen peroxide) were then performed on furosemide solutions and on water from residential care facilities to study the degradation of furosemide by potential advanced processes, and also to identify unknown oxidation products by high-resolution mass spectrometry. Furosemide was well degraded in Seine-Centre WWTP (>75%) but did not increase the concentrations of its main degradation products. Saluamine and pyridinium of furosemide were already present at similar concentrations to furosemide in the raw wastewater (∼2.5-3.5 μg.L^-1), and their removal in the WWTPs were very high (>80%). Despite their removal, the three compounds remained present in treated wastewater effluents at concentrations of hundreds of nanograms per liter. Chlorination degraded furosemide without pyridinium production unlike the other two processes. Chlorination and ozonation were also effective for the removal of furosemide and pyridinium in residential care home water, but they resulted in the production of saluamine. To our knowledge this is the first evidence of saluamine and pyridinium of furosemide in real water samples in either the particulate or dissolved phase.

Removal of ammonium and manganese from surface water using a MeOx filter system as a pretreatment process

Residual aluminium from the coagulation-sedimentation process in the treatment of surface water can decrease the catalytic activity of a manganese co-oxide filter film (MeO_x) used for ammonium and manganese removal. To solve this problem, a MeO_x filter was used as a pretreatment process to filtrate source water directly before the coagulation and sedimentation treatment. The removal performance and the mechanism of change in the activity of MeO_x were investigated. The experimental results indicated that the MeO_x filter removed ammonium and manganese from surface water sources effectively, and its manganese removal activity was enhanced. The characteristics of MeO_x were investigated via SEM, EDS, XPS, and the BET surface area. Analysis of the experimental results showed that the increase in the content of Al under this condition was much lower than that under treatment with the coagulation-sedimentation process. After long-term operation, the amount and surface area of MeO_x coated on the filter sand increased significantly, leading to an increase in the catalytic activity. However, in cold water, the catalytic activity of MeO_x decreased, and more Mn(II) was obtained on the surface of MeO_x. Thus, the morphology of MeO_x changed. Fortunately, when water temperature increases, the removal activity can recover immediately. By inactivating microorganisms and comparing the removal performance with that under other conditions, the MeO_x activity of the pretreatment process is preserved effectively and no strengthening measures are required. This study will provide a new strategy for the use of the MeO_x catalytic technology.

Effects of graphitic carbon nitride in the formation of disinfection byproducts

Graphitic carbon nitride (CN) was a promising candidate for efficient environmental remediation in the advanced oxidation processes (AOPs). However, whether CN itself had some potential environmental risks, such as affecting the production of disinfection byproducts (DBPs) was still unknown. This study investigated the formation potential of DBPs in the presence of CN. The experimental data revealed that CN had a high potential to form DBPs, and dichloroacetonitrile (DCAN) was the most produced species during the chlorination and chloramination processes. Moreover, the effects of chlorine time, chlorine dosage, pH, and CN dosage during the chlorination process were evaluated to understand the formation pattern of DBPs. The possible mechanism of DBPs formation was deduced by analyzing the results of FTIR, Raman, and XPS before and after chlorination. Finally, the DBPs formation potential and cytotoxicity of the CN leaching solution were investigated, indicating CN could leach the precursors of DBPs and that the potential toxicity of the leaching solution increased with the extension of CN immersion time. In general, this research adds an understanding of the DBP formation of CN in water treatment systems and sheds light on CN's environmental potential risks.

Synthesis of NaA zeolite from foundry dust and its adsorption capacity of ammonia

Eutrophication of water bodies due to excess ammonia nitrogen (NH₄⁺-N) is harmful to aquatic organisms and human health. In this study, foundry dust (FD) from foundry industry was used to synthesize NaA zeolite to use as an adsorbent to remove NH₄⁺-N from wastewater. Results demonstrate that FD could be successfully synthesized to form a foundry dust-based NaA zeolite (FZA) through adjustment of the silica-alumina ratio of n (SiO₂)/n (Al₂O₃) at 2 at 95 °C. Specific surface area, total pore volume, and cation exchange capacity (CEC), and maximum adsorption NH₄⁺-N of FZA was respectively 43.185 cm²/g, 0.0364 cm³/g, 212.35 mmol/100 g and 37.81 mg/g, which was 4.74, 1.54, 1.52 and 1.62 times as much as the NaA zeolite (SZA). FZA with higher adsorption NH₄⁺-N capacity was related to higher specific surface area and CEC. The NH₄⁺-N adsorption amount of 28.57 mg/g by FZA was obtained after the fourth regeneration, which was notably higher than that of SZA (23.27 mg/g). The desorption rate of NH₄⁺-N from FZA was 87% by the fourth regeneration. FZA effectively removed NH₄⁺-N from swine wastewater containing 153.32 mg/L NH₄⁺-N. Results suggest that FZA could be used as absorbent to removal NH₄⁺-N from wastewater.

The occurrence, formation and transformation of disinfection byproducts in the water distribution system: A review

Disinfection is an effective process to inactivate pathogens in drinking water treatment. However, disinfection byproducts (DBPs) will inevitably form and may cause severe health concerns. Previous research has mainly focused on DBPs formation during the disinfection in water treatment plants. But few studies paid attention to the formation and transformation of DBPs in the water distribution system (WDS). The complex environment in WDS will affect the reaction between residual chlorine and organic matter to form new DBPs. This paper provides an overall review of DBPs formation and transformation in the WDS. Firstly, the occurrence of DBPs in the WDS around the world was cataloged. Secondly, the primary factors affecting the formation of DBPs in WDS have also been summarized, including secondary chlorination, pipe materials, biofilm, deposits and coexisting anions. Secondary chlorination and biofilm increased the concentration of regular DBPs (e.g., trihalomethanes (THMs) and haloacetic acids (HAAs)) in the WDS, while Br^- and I^- increased the formation of brominated DBPs (Br-DBPs) and iodinated DBPs (I-DBPs), respectively. The mechanism of DBPs formation and transformation in the WDS was systematically described. Aromatic DBPs could be directly or indirectly converted to aliphatic DBPs, including ring opening, side chain breaking, chlorination, etc. Finally, the toxicity of drinking water in the WDS caused by DBPs transformation was examined. This review is conducive to improving the knowledge gap about DBPs formation and transformation in WDS to better solve water supply security problems in the future.

Drinking water treatment and associated toxic byproducts: Concurrence and urgence

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.

Large-scale study on groundwater dissolved organic matter reveals a strong heterogeneity and a complex microbial footprint

Dissolved organic matter (DOM) in terrestrial groundwater is generally low in concentration compared to inland surface waters. However, the overall amount of groundwater DOM is huge, as there is 100 times more fresh groundwater than fresh surface water. To date, research on groundwater DOM has merely focused on specific threats to humans such as e.g. DOM and heavy metal complexations and DOM from hydrocarbon contamination. A comprehensive, large-scale study of groundwater is still missing. Here, we examine DOM properties in a large-scale approach with regards to surface characteristics such as land use and altitude, aquifer characteristics as well as microbial features. We analyzed 1600 water samples from 100 groundwater bodies all over Austria with regards to their DOM quantity, quality and bacterial abundance (BA). DOM quality was evaluated with self-organizing maps on fluorescence excitation-emission-matrices (EEMs) combined with Ward clustering and subsequent parallel factor analysis to describe DOM properties of each cluster. We evaluated how these clusters differed among each other, based on DOC and nitrate concentrations, BA and selected environmental characteristics. Our results show that fluorescence components in groundwater resemble components found in other groundwater studies, in studies from forest streams, the dark ocean, agricultural catchments and wastewater treatment plants. The latter fluorescence components were associated with a cluster that is characterized by agricultural and urban land use, as well as by high nitrate concentrations. Clusters with an increased abundance of high-molecular weight and humic components, commonly associated with vascular plant and soil origin, correlated with a higher bacterial abundance. This observation provides evidence that elevated numbers of suspended bacteria mainly originate from the surface. Our study shows that DOM fluorescence can be a fast monitoring tool to identify aquifers under anthropogenic stress and delineate sensitive recharge areas with high surface-groundwater interaction.

Efficient Removal of Ammonia Nitrogen by an Electrochemical Process for Spent Caustic Wastewater Treatment

Spent caustic wastewater produced in a soda plant has a high concentration of ammonia nitrogen (NH4+-N). As excessive NH4+-N discharging into water bodies would cause eutrophication as well as destruction to the ecology balance, developing an efficient technology for NH4+-N removal from the spent caustic wastewater is imperative in the current society. In this study, an electrochemical process with graphene electrodes was designed for the NH4+-N removal in the spent caustic wastewater. The removal efficiency of the NH4+-N during the electrochemical process could reach 98.7% at 4 A in a short treatment time (within 120 s) with an acceptable energy consumption (6.1 kWh/m3-order). NO3− and NO2− were not detected during the electrochemical process. An insignificant amount of NH2Cl, NHCl2, and NCl3 produced in the treatment suggested that little of the NH4+-N reacted with chlorine, that is, chlorination played a negligible role in the NH4+-N removal. By electron equilibrium and nitrogen conversion analysis, we think that NH4+-N was primarily converted to NH2(ads) on the surface of a graphene electrode by one-electron transfer during the direct oxidation of the electrochemical process. Due to the high calcium ion (Ca2+) in the spent caustic wastewater, the electrode scale significantly increased to 1.4 g after treatment of 240 s at 4 A. By X-ray diffraction (XRD) analysis, the composition of the electrode scale is portlandite Ca(OH)2. Although the electrode scale was obvious during the electrochemical treatment, it could be alleviated by alternating the electrode polarity. As a result, the life and efficiency of the graphene electrode for NH4+-N removal could remain stable for a long time. These results suggest that the electrochemical process with a graphene electrode may provide a competitive technology for NH4+-N removal in spent caustic wastewater treatment.

Controlling the formation of halogenated byproducts in the chlorination of source waters by oxidative pre-treatment with the Fe(II)/Fe(III)-S(IV)-air system

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 SO₄^2-) by the end of the process.

Trichloramine and Hydroxyl Radical Contributions to Dichloroacetonitrile Formation Following Breakpoint Chlorination

Breakpoint chlorination is applied to remove ammonia in water treatment. Trichloramine (NCl₃) and transient reactive species can be present, but how they affect the formation of nitrogenous disinfection byproducts is unknown. In this study, the dichloroacetonitrile (DCAN) formation mechanisms and pathways involved during breakpoint chlorination (i.e., free chlorine to ammonia molar ratio ≥2.0) were investigated. DCAN formation during breakpoint chlorination of natural organic matter (NOM) isolates was 14.3-20.3 μg/L, which was 2-10 times that in chlorination without ammonia at similar free chlorine residual conditions (2.1-2.9 mg/L as Cl₂). The probe tests and electron paramagnetic resonance spectra supported the presence of ^•OH, ^•NO, and NCl₃ besides free chlorine in breakpoint chlorination. ¹⁵N-labeled ammonium-N tests indicated the incorporation of ammonium-N in DCAN formation though ammonia was eliminated during breakpoint chlorination. Aromatic non-nitrogenous moieties, such as phenols (i.e., none DCAN precursors in the free-chlorine-only system), became DCAN precursors during breakpoint chlorination. The reactions involved in reactive nitrogen species, such as ^•NO/^•NO₂ and NCl₃, led to additional nitrogen sources in DCAN formation, accounting for 36-84% of total nitrogen sources in DCAN formation from NOM isolates and real water samples. Scavenging ^•OH by tert-butanol reduced DCAN formation by 40-56%, indicating an important role of ^•OH in transforming DCAN precursors. This study improves the understanding of breakpoint chlorination chemistry.

Enhanced removal of ammonia nitrogen from rare earth wastewater by NaCl modified vermiculite: Performance and mechanism

Wastewater from rare earth mining (WREM) is very harmful to environment and human health due to its high concentration of ammonia nitrogen (NH₃-N). It is therefore necessary and urgent to find a low-cost and convenient technique to remove high concentration of NH₃-N from WREM. In this study, Natural powdered vermiculite (NV) was modified with seven sodium chloride (NaCl) solutions, and seven kinds of sodium chloride modified vermiculite (Na-V) were obtained. The NH₃-N adsorption performance of Na-V is greatly improved compared with NV. Among them, vermiculite modified with 180 g/L NaCl yielded the highest ammonium adsorption capacity (Q_m, 11.569 mg/g), which was 63.43% higher than NZ (Q_m, 7.079 mg/g). The characterizations of 180-Na-V confirmed the removal mechanism of NH₃-N that the improved capacity of modified vermiculite was attributed to its higher mesoporous volume and ion-exchange capacity, which are the result of sodium-ion exchange and Interlayer effect from high concentration of NaCl. The adsorption isotherms and kinetics were respectively best consistent with Langmuir model and the pseudo-second-order (PSO) model. The adsorption capacity (3.808 mg/g) of vermiculite after 5 cycles could still maintain 75.09% of the initial adsorption capacity (5.071 mg/g). A large amount of Na-V had little effect on pH of water, which meet the requirements of practical application. Including pH, dosage, coexisting ions, the effects of other factors on ammonium adsorption were also determined. This study provides a new method for vermiculite to remove high concentration of NH₃-N.

Feel the Burn: Disinfection Byproduct Formation and Cytotoxicity during Chlorine Burn Events

Nitrification and biofilm growth within distribution systems remain major issues for drinking water treatment plants utilizing chloramine disinfection. Many chloraminated plants periodically switch to chlorine disinfection for several weeks to mitigate these issues, known as "chlorine burns". The evaluation of disinfection byproduct (DBP) formation during chlorine burns beyond regulated DBPs is scarce. Here, we quantified an extensive suite of 80 regulated and emerging, unregulated DBPs from 10 DBP classes in drinking water from two U.S. drinking water plants during chlorine burn and chloramination treatments. Total organic halogen (TOX), including total organic chlorine, total organic bromine, and total organic iodine, was also quantified, and mammalian cell cytotoxicity of whole water mixtures was assessed in chlorine burn waters for the first time. TOX and most DBPs increased in concentration during chlorine burns, and one emerging DBP, trichloroacetaldehyde, reached 99 μg/L. THMs and HAAs reached concentrations of 249 and 271 μg/L, respectively. Two highly cytotoxic nitrogenous DBP classes, haloacetamides and haloacetonitriles, increased during chlorine burns, reaching up to 14.2 and 19.3 μg/L, respectively. Cytotoxicity did not always increase from chloramine treatment to chlorine burn, but a 100% increase in cytotoxicity was observed for one plant. These data highlight that consumer DBP exposure during chlorine burns can be substantial.

Comparison of Disinfection By-Product Formation and Distribution during Breakpoint Chlorination and Chlorine-Based Disinfection in Drinking Water

Breakpoint chlorination (BC) and disinfection with chlorine-based disinfectant are widely used procedures in drinking water production. Both involve dosing chlorine into the raw water, where it can react with organic compounds, forming disinfection by-products (DBPs) of health concern. However, technological parameters (e.g., contact time, chlorine dosage, and bromide to residual free chlorine ratio) of the two chlorination procedures are different, which can lead to differences in DBP formation. To better understand this, a year-long sampling campaign was carried out at three waterworks in Hungary, where both BC and chlorine disinfection are used. To confirm the results of the field sampling, bench-scale experiments were carried out, investigating the impact of (a) bromide concentration in raw water, (b) residual free chlorine (bromide to residual chlorine ratio), and (c) contact time on DBP formation. The measured DBPs were trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and chlorate. During BC, the DBPs were formed in higher concentration, with the exception of one waterwork having elevated bromide content in the raw water. Bromine substitution factors (BSFs) were significantly higher during disinfection than BC in both field and laboratory experiments. After BC, the chlorate concentration range was 0.15–1.1 mg/L, and 96% of the samples exceeded the European Union (EU) parametric value (0.25 mg/L), whereas disinfection contributed only slightly. Granular activated carbon (GAC) filters used to remove DBPs in waterworks were exhausted after 6–8 months of use, first for those chlorinated THMs, which are generated predominantly during BC. The biological activity of the filters started to increase after 3–6 months of operation. This activity helps to remove the biodegradable compounds, such as disubstituted haloacetic acid (DHAAs) and HANs, even if the adsorption capacity of the GAC filters are low.

Ammonium and hydroxylamine can be preferentially removed during simultaneous nitrification and denitrification by Pseudomonas taiwanensis EN-F2

To overcome a large amount of nitrite accumulation and poor removal rate for hydroxylamine, a simultaneous nitrification and denitrification (SND) bacterium was isolated and identified as Pseudomonas taiwanensis EN-F2 by DNA sequencing. Strain EN-F2 could remove 100% of ammonium (52.90 mg/L), 100% of hydroxylamine (23.32 mg/L), 86.99% of nitrite (56.32 mg/L) and 89.21% of nitrate (56.18 mg/L) with a maximum removal rate of 8.72, 2.12, 4.55 and 5.80 mg/L/h, respectively. Ammonium and hydroxylamine could be preferentially removed during the SND process. The nitrite removal rate and cell growth were substantially enhanced by 2.10 mg/L/h and 0.45 after supplementation of hydroxylamine. The specific activities of ammonia monooxygenase (AMO), hydroxylamine oxidoreductase (HAO), nitrate reductase (NR), nitrite reductase (NIR) were successfully detected as 0.95, 0.31, 0.42 and 0.03 U/mg protein, respectively. All results demonstrated that strain EN-F2 could perform SND to remove multiple nitrogen sources from wastewater.

Advanced bioelectrochemical system for nitrogen removal in wastewater

Nitrogen (N) pollution in water has become a serious issue that cannot be ignored due to the harm posed by excessive nitrogen to environmental safety and human health; as such, N concentrations in water are strictly limited. The bioelectrochemical system (BES) is a new method to remove excessive N from water, and has attracted considerable attention. Compared with other methods, it is highly efficient and has low energy consumption. However, the BES has not been applied for N removal in practice due to lack of in-depth research on the mechanism and construction of high-performance electrodes, separators, and reactor configurations; this highlights a need to review and examine the efforts in this field. This paper provides a comprehensive review on the current BES research for N removal focusing on the reaction principles, reactor configurations, electrodes and separators, and treatment of actual wastewater; the corresponding performances in these realms are also discussed. Finally, the prospects for N removal in water using the BES are presented.

Study on performance and mechanism of enhanced low-concentration ammonia nitrogen removal from low-temperature wastewater by iron-loaded biological activated carbon filter

In order to strengthen the treatment of low-concentration ammonia nitrogen wastewater at low temperature, iron-loaded activated carbon (Fe-AC) with ultrasonic impregnation method was used as the filter material of biofilter process. The performance and mechanism of ammonia nitrogen removal from simulated secondary wastewater by iron-loaded biological activated carbon filter (Fe-BACF) were studied at 10 °C. The characterization results showed that iron was loaded on the surface of AC in the form of Fe₂O₃, and the specific surface area, total pore volume, pore size and alkaline functional group content of Fe-AC were obviously increased. After the formation of biofilm on the surface of filter media, the average removal rate of ammonia nitrogen by Fe-BACF (97.9%) was significantly higher than that of conventional BACF (87.8%). The improved surface properties increased the number and metabolic activity of microorganisms, and promoted the secretion of EPS on the surface of Fe-BAC. The results of high-throughput sequencing showed that the existence of Fe optimized the bacterial community structure on the surface of Fe-BAC, with the increase of the abundances of psychrophilic bacteria and ammonia nitrogen removal bacteria. The mechanism of enhanced ammonia nitrogen removal by Fe-BACF was the joint action of many factors, among which the main causal relationship was that modification of iron could optimize the number and category of microorganisms on Fe-BAC surface by improving the surface properties, thus improving the biological nitrogen removal ability. Results of this study provided a practical way for the treatment of low ammonia nitrogen wastewater in cold regions.

A novel and efficient strategy mediated with calcium carbonate-rich sources to remove ammonium sulfate from rare earth wastewater by heterotrophic Chlorella species

This work was the first time to establish the desired approach with two heterotrophic Chlorella species for ammonium sulfate (AS)-rich rare earth elements (REEs) wastewater treatment by heterotrophic cultivation. The results showed that these two Chlorella species treated by 6 g/L CaCO₃ performed the best ability to remove NH₄⁺-N and SO₄^2- of REEs wastewater. Moreover, the established process performed similar features in REEs wastewater treatment by replacing CaCO₃ with eggshell powder (ESP) and oyster shell powder (OSP) enriched in CaCO₃. Furthermore, microalgae treated by ESP/OSP in a 10-L fermenter showed 837.39 mg/(L·d) NH₄⁺-N and 1,820 mg/(L·d) SO₄^2- removal rates. The developed kinetic models could be well fitted to the experimental data obtained by the 10-L fermenter. Taken together, the established process mediated with two Chlorella species and ESP/OSP by heterotrophic cultivation was the great potential for AS-rich REEs wastewater treatment in a cost-effective manner.

Assessment of the di- and tri-chlorinated haloacetic acids during broiler prechilling

Sodium hypochlorite (NaClO) has been widely used at 100 ppm concentration during poultry slaughter to reduce carcass microorganism loads. However, its use in poultry processing is restricted owing to the potential risks of disinfection by-products (DBPs) that can be produced by the reaction of NaClO with poultry meat components. This study assessed whether dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), as primary DBP representatives, were produced when NaClO was used as a disinfectant in various methods during broiler prechilling. Headspace gas chromatography-mass spectrometry for the quantitative determination of DCAA and TCAA in 180 prechilling water samples and 30 broiler meat samples, obtained from large standard slaughterhouses equipped with an online monitoring system to control the NaClO concentration between 50 and 100 ppm, showed that neither DCAA nor TCAA were detected. In simulation assays, haloacetic acids (HAAs) were not detected when the concentration of the NaClO solution was less than 200 ppm with low frequency addition; however, more than 0.1 mg/L of DCAA and TCAA were detected on applying 200, 300, 400, 500, and 1000 ppm NaClO at high frequency. These findings indicated that adding high concentrations of NaClO and frequently adding low levels pose a potential risk of DBP formation. This investigation provides a basis for the establishment of food risk and the scientific use of NaClO in poultry processing, and contributes to the evaluation of DBPs in poultry slaughter. PRACTICAL APPLICATION: This study confirmed the occurrences of DCAA and TCAA during broiler chilling processing, indicating that formation of HAAs in simulation systems was correlated with NaClO levels and validated the absence of DCAA and TCAA with less than 200 ppm, providing a basic study for food safety standards and regulations on the disinfectants used in food processing.

Exploring applicability of end member mixing approach for predicting environmental reactivity of dissolved organic matter

Despite the wide applications of end member mixing analysis (EMMA) for assigning the sources of dissolved organic matter (DOM) in aquatic environment, there was no study attempting to test the applicability of EMMA for predicting environmental reactivity of DOM. This study aimed to explore the feasibility of EMMA, or the concept of ideal mixing behavior of end members, for describing several well-known DOM reactivities using two DOM end member sources (i.e., soil and algae) at varying mixing ratios. The selected DOM reactivities were trihalomethane formation potential (THMFP), mineral adsorption amount, pyrene binding, membrane resistance, and biodegradation potential. Among the tested DOM functions, all were found to follow the ideal mixing behavior, presenting the linear relationships between the source mixing ratios and the tested reactivity with the R² value of >0.80. The ideal mixing behavior of the DOM functions was more pronounced than that based on several spectroscopic indicators derived from UV absorption and fluorescence spectroscopy. This study provided insight into potential applicability and limitation of EMMA approach in monitoring and predicting environmental functions of DOM in aquatic systems where identified DOM sources are mixed and vary dynamically with the mixing ratios.

Optimization and Modeling of Ammonia Nitrogen Removal from High Strength Synthetic Wastewater Using Vacuum Thermal Stripping

Waste streams with high ammonia nitrogen (NH3-N) concentrations are very commonly produced due to human intervention and often end up in waterbodies with effluent discharge. The removal of NH3-N from wastewater is therefore of utmost importance to alleviate water quality issues including eutrophication and fouling. In the present study, vacuum thermal stripping of NH3-N from high strength synthetic wastewater was conducted using a rotary evaporator and the process was optimized and modeled using response surface methodology (RSM) and RSM–artificial neural network (ANN) approaches. RSM was first employed to evaluate the process performance using three independent variables, namely pH, temperature (°C) and stripping time (min), and the optimal conditions for NH3-N removal (response) were determined. Later, the obtained data from the designed experiments of RSM were used to train the ANN for predicting the responses. NH3-N removal was found to be 97.84 ± 1.86% under the optimal conditions (pH: 9.6, temperature: 65.5 °C, and stripping time: 59.6 min) and was in good agreement with the values predicted by RSM and RSM–ANN models. A statistical comparison between the models revealed the better predictability of RSM–ANN than that of the RSM. To the best of our knowledge, this is the first attempt comparing the RSM and RSM–ANN in vacuum thermal stripping of NH3-N from wastewater. The findings of this study can therefore be useful in designing and carrying out the vacuum thermal stripping process for efficient removal of NH3-N from wastewater under different operating conditions.

Fate of ammonia and implications for distribution system water quality at four ion exchange softening plants with elevated source water ammonia

Hard water and elevated ammonia are problems for many United States groundwater drinking water utilities, and some utilities, particularly those in the Midwest, face both challenges. Ion (cation) exchange (IX) is a common treatment technique for hardness reduction (i.e., softening) and may be used to remove ammonia as well, but these constituents may compete in IX and impact overall treatment performance. Few data have been reported on the impact on ammonia concentrations when using IX for softening in full-scale systems. This study investigated four full-scale groundwater treatment plants in Illinois that practice IX for softening (raw water hardness > 220 mg/L as CaCO₃) and have elevated groundwater ammonia concentrations (> 2 mg N/L). Sampling throughout the year revealed consistent finished water hardness levels but variable ammonia concentrations. Ammonia removal varied and depended on how much water had been treated since the last regeneration. High ammonia removal (sometimes > 90%) occurred in the first half of the IX service cycle, while effluent ammonia concentrations increased compared to the influent (sometimes > 200%) towards the end of the IX cycle (total length 50,000-92,000 gallons [190-350 m³]). Ammonia removal efficiency varied among the plants, but the overall trends were similar. Because variable ammonia concentrations may make it difficult to produce a consistent total chlorine residual, they can negatively impact disinfection and water quality in the distribution system. Ammonia concentrations should be considered when designing softening systems to determine regeneration frequency, develop blending strategies, or include an alternative ammonia treatment process before IX softening to produce a more stable and consistent finished water.

Occurrence, influencing factors, toxicity, regulations, and abatement approaches for disinfection by-products in chlorinated drinking water: A comprehensive review

Disinfection is considered as a vital step to ensure the supply of clean and safe drinking water. Various approaches are adopted for this purpose; however, chlorination is highly preferred all over the world. This method is opted owing to its several advantages. However, it leads to the formation of certain by-products. These chlorination disinfection by-products (DBPs) are genotoxic, carcinogenic and mutagenic. Still chlorination is being practiced worldwide. Present review gives insights into the occurrence, toxicity and factors affecting the formation of regulated (THMs, HAAs) and emerging DBPs (N-DBPs, HKs, HAs and aromatic DBPs) found in drinking water. Furthermore, remediation techniques used to control DBPs have also been summarized here. Key findings are: (i) concentration of regulated DBPs surpassed the permissible limit in most of the regions, (ii) high chlorine dose, high NOM, more reaction time (up to 3 h) and high temperature (up to 30 °C) enhance the formation of THMs and HAAs, (iii) high pH favors the formation of THMs while low pH is suitable of the formation of HAAs, (iv) high NOM, low temperature, low chlorine dose and moderate pH favors the formation of unstable DBPs (N-DBPs, HKs and HAs), (v) DBPs are toxic not only for humans but for aquatic fauna as well, (vi) membrane technologies, enhanced coagulation and AOPs remove NOM, (vii) adsorption, air stripping and other physical and chemical methods are post-formation approaches (viii) step-wise chlorination is assumed to be an efficient method to reduce DBPs formation without any treatment. Toxicity data revealed that N-DBPs are found to be more toxic than C-DBPs and aromatic DBPs than aliphatic DBPs. In majority of the studies, merely THMs and HAAs have been studied and USEPA has regulated just these two groups. Future studies should focus on emerging DBPs and provide information regarding their regulation.

The Influence of Photocatalytic Reactors Design and Operating Parameters on the Wastewater Organic Pollutants Removal—A Mini-Review

The organic pollutants removal by conventional methods (adsorption, coagulation, filtration, microorganism and enzymes) showed important limitation due to the reluctance of these molecules. An alternative to this issue is represented by the photocatalytic technology considered as an advanced oxidation process (AOP). The photoreactors design and concepts vary based on the working regime (static or dynamic), photocatalyst morphology (powders or bulk) and volume. This mini-review aims to provide specific guidelines on the correlations between the photoreactor concept characteristics (working regime, volume and flow rate), irradiation scenarios (light spectra, irradiation period and intensity) and the photocatalytic process parameters (photocatalyst materials and dosage, pollutant type and concentration, pollutant removal efficiency and constant rate). The paper considers two main photoreactor geometries (cylindrical and rectangular) and analyses the influence of parameters optimization on the overall photocatalytic efficiency. Based on the systematic evaluation of the input data reported in the scientific papers, several perspectives regarding the photocatalytic reactors’ optimization were included.

Modeling and Optimizing of NH4+ Removal from Stormwater by Coal-Based Granular Activated Carbon Using RSM and ANN Coupled with GA

As a key parameter in the adsorption process, removal rate is not available under most operating conditions due to the time and cost of experimental testing. To address this issue, evaluation of the efficiency of NH4+ removal from stormwater by coal-based granular activated carbon (CB-GAC), a novel approach, the response surface methodology (RSM), back-propagation artificial neural network (BP-ANN) coupled with genetic algorithm (GA), has been applied in this research. The sorption process was modeled based on Box-Behnben design (BBD) RSM method for independent variables: Contact time, initial concentration, temperature, and pH; suggesting a quadratic polynomial model with p-value < 0.001, R2 = 0.9762. The BP-ANN with a structure of 4-8-1 gave the best performance. Compared with the BBD-RSM model, the BP-ANN model indicated better prediction of the response with R2 = 0.9959. The weights derived from BP-ANN was further analyzed by Garson equation, and the results showed that the order of the variables’ effectiveness is as follow: Contact time (31.23%) > pH (24.68%) > temperature (22.93%) > initial concentration (21.16%). The process parameters were optimized via RSM optimization tools and GA. The results of validation experiments showed that the optimization results of GA-ANN are more accurate than BBD-RSM, with contact time = 899.41 min, initial concentration = 17.35 mg/L, temperature = 15 °C, pH = 6.98, NH4+ removal rate = 63.74%, and relative error = 0.87%. Furthermore, the CB-GAC has been characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET). The isotherm and kinetic studies of the adsorption process illustrated that adsorption of NH4+ onto CB-GAC corresponded Langmuir isotherm and pseudo-second-order kinetic models. The calculated maximum adsorption capacity was 0.2821 mg/g.

Study on adsorption of ammonia nitrogen by iron-loaded activated carbon from low temperature wastewater

In order to improve the adsorption efficiency of ammonia nitrogen in low temperature wastewater, the modified activated carbon (Fe-AC) was prepared by impregnation-calcination modification of Fe(NO₃)₃. The characterization results indicated that the total pore volume, specific surface area and the point of zero charge of activated carbon increased after modification. A better adsorption effect was achieved under neutral condition than under alkaline or acidic condition. The effect of Ca²⁺ on competitive adsorption of NH₄⁺ was greater than that of Na⁺ when both cations were present. Pseudo-first-order kinetic model was confirmed to be consistent with Fe-AC adsorption kinetic data, and Langmuir model was consistent with adsorption isotherm data. The adsorption thermodynamics demonstrated that the ammonia nitrogen adsorption process by Fe-AC was spontaneous and low-temperature was helpful to improve the adsorption capacity. The mechanism of adsorption of ammonia nitrogen by Fe-AC was the comprehensive effect of physical adsorption and chemical adsorption, which was the essential reason for improving the adsorption efficiency of ammonia nitrogen by Fe-AC at a low temperature. This research offered a new way for the modification of activated carbon and a new method for the removal of ammonia nitrogen at a low temperature.

Disinfection of Bacteria in Water by Capacitive Deionization

Clean water is one of the primary UN sustainable development goals for 2,030 and sustainable water deionization and disinfection is the backbone of that goal. Capacitive deionization (CDI) is an upcoming technique for water deionization and has shown substantial promise for large scale commercialization. In this study, activated carbon cloth (ACC) electrode based CDI devices are used to study the removal of ionic contaminants in water and the effect of ion concentrations on the electrosorption and disinfection functions of the CDI device for mixed microbial communities in groundwater and a model bacterial strain Escherichia coli. Up to 75 % of microbial cells could be removed in a single pass through the CDI unit for both synthetic and groundwater, while maintaining the salt removal activity. Mortality of the microbial cells were also observed during the CDI cell regeneration and correlated with the chloride ion concentrations. The power consumption and salt removal capacity in the presence and absence of salt were mapped and shown to be as low as 0.1 kWh m⁻³ and 9.5 mg g⁻¹, respectively. The results indicate that CDI could be a viable option for single step deionization and microbial disinfection of brackish water.

LLDPE Composites with Nanosized Copper and Copper Oxides for Water Disinfection

Consumption of contaminated water may lead to dangerous and even fatal water-borne diseases. Disinfection of drinking water is the most effective solution for this problem. The most common water treatment methods are based on the use of toxic disinfectants. Composites of polymers with nanosized metals and their oxides may become a good alternative to the existing methods. Expanding the scope of our previous publication, copper, cuprous, and copper oxide nanoparticles were immobilized onto linear low-density polyethylene by a simple thermal adhesion method. The antibacterial efficiency of the immobilized nanoparticles was tested against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus in batch experiments and for the first time the efficiency of these composites is reported for continuous flow regime. Immobilized copper and cuprous oxide nanoparticles demonstrated a high ability to eradicate bacteria after 30 min. These composites showed no or very limited leaching of copper ions into the aqueous phase both in the presence and in the absence of a bacterial suspension. Immobilized copper and cuprous oxide nanoparticles can be used for batch or continuous disinfection of water.