Formation Of Chloramines Research Articles

Optimization of Secondary Chlorination in Water Distribution Systems for Enhanced Disinfection and Reduced Chlorine Odor Using Deep Belief Network and NSGA-II

This research explores the strategic optimization of secondary chlorination in water distribution systems (WDSs), in order to enhance the efficiency of disinfection while mitigating odor and operational costs and promoting sustainability in water quality management. The methodology integrates EPANET simulations for water hydraulic and quality modeling with a deep belief network (DBN) within the deep learning framework for accurate chloric odor prediction. Utilizing the non-dominated sorting genetic algorithm-II (NSGA-II), this methodology systematically balances the objectives of chloride dosage and chloramine formation. It combines a chloric odor intensity assessment, a multi-component kinetic model, and dual-objective optimization to conduct a comparative analysis of case studies on secondary chlorination strategies. The optimal configuration with five secondary chlorination stations reduced chloric odor intensity to 1.20 at a cost of USD 40,020.77 per year in Network A while, with eight stations, chloric odor intensity was reduced to 0.88 at a cost of USD 71,405.38 per year in Network B. The results demonstrate a balanced trade-off between odor intensity and operational cost on one hand and sustainability on the other hand, highlighting the importance of precise chlorine management to improve both the sensory and safety qualities of drinking water while ensuring the sustainable use and management of water resources.

Ammonia oxidation by in-situ chloride electrolysis in etching wastewater of semiconductor manufacturing using RuSnOx/Ti electrode: Effect of plating mode and metal ratio

The indirect chloride-mediated ammonia oxidation encounters challenges in maintaining the effectiveness of metal oxide anodes when treating wastewaters with complex compositions. This study aims to develop a highly stable anode with RuO2-SnO2 coatings for treating an etching effluent from semiconductor manufacturing, which majorly contains NH3 and organic compounds. The RuSnOx/Ti electrode was synthesized using wet impregnation and calcination processes. The metal oxide configuration on Ti plate substrate was tuned by varying the step-dipping process in RuCl3 and SnCl4 baths. A 10-day continuous-flow electrolysis was conducted for studying the ammonia removal and chlorine yield under variable conditions, including detention, pH, current density, and initial ammonia and chloride concentrations. In the RuSnOx coatings, the configuration comprising RuO2 nanorods as the surface layer and an intermediate layer of SnO2 crystallites (by plating Ru3+ for three times to cover one Sn4+ layer, denoted as the Ru3Sn/Ti electrode) exhibited the best durability for acid washing, along with relatively high Faradaic efficiency and low energy consumption. To further improve the treatability of real wastewater (NH3-N = 634 mg L−1, chemical oxygen demand (COD) = 6700 mg L−1, Cl- = 2000 mg L−1, pH 11), the duel-cell electrolyzers were constructed in series under a current density of 30 mA cm−2 and 45 min detention. Ultimately, removals of NH3 and COD reached 95.8% and 76.3%, respectively, with successful limitation of chloramine formation.

Pre-oxidation coupled with charged covalent organic framework membranes for highly efficient removal of organic chloramines precursors in algae-containing water treatment

Organic chloramines in water would pose both chemical and microbiological risks. It is essential to remove the precursors of organic chloramine (amino acids and decomposed peptides/proteins) to limit its formation in disinfection. In our work, nanofiltration was chosen to remove organic chloramines precursors. To solve the “trade-off” effect and low rejection of small molecules in algae organic matter, we synthesized a thin film composite (TFC) nanofiltration (NF) membrane with a crumpled polyamide (PA) layer via interfacial polymerization on polyacrylonitrile (PAN) composite support loaded with covalent organic framework (COF) nanoparticles (TpPa-SO3H). The obtained NF membrane (PA-TpPa-SO3H/PAN) increased the permeance from 10.2 to 28.2 L m−2 h−1 bar−1 and the amino acid rejection from 24% to 69% compared to the control NF membrane. The addition of TpPa-SO3H nanoparticles decreased the thickness of PA layers, increased the hydrophilicity of the membrane, and increased the transition energy barrier for amino acids transferring through the membrane, which was identified by scanning electron microscope, contact angle test, and density functional theory computations, respectively. Finally, pre-oxidation coupled with PA-TpPa-SO3H/PAN membrane nanofiltration on the limitation of organic chloramines formation was evaluated. We found that the combined application of KMnO4 pre-oxidation and PA-TpPa-SO3H/PAN membranes nanofiltration in algae-containing water treatment could minimize the formation of organic chloramines in subsequent chlorination and maintain a high flux during filtration. Our work provides an effective way for algae-containing water treatment and organic chloramines control.

Bleach Emissions Interact Substantially with Surgical and KN95 Mask Surfaces.

Mask wearing and bleach disinfectants became commonplace during the COVID-19 pandemic. Bleach generates toxic species including hypochlorous acid (HOCl), chlorine (Cl2), and chloramines. Their reaction with organic species can generate additional toxic compounds. To understand interactions between masks and bleach disinfection, bleach was injected into a ventilated chamber containing a manikin with a breathing system and wearing a surgical or KN95 mask. Concentrations inside the chamber and behind the mask were measured by a chemical ionization mass spectrometer (CIMS) and a Vocus proton transfer reaction mass spectrometer (Vocus PTRMS). HOCl, Cl2, and chloramines were observed during disinfection and concentrations inside the chamber are 2-20 times greater than those behind the mask, driven by losses to the mask surface. After bleach injection, many species decay more slowly behind the mask by a factor of 0.5-0.7 as they desorb or form on the mask. Mass transfer modeling confirms the transition of the mask from a sink during disinfection to a source persisting >4 h after disinfection. Humidifying the mask increases reactive formation of chloramines, likely related to uptake of ammonia and HOCl. These experiments indicate that masks are a source of chemical exposure after cleaning events occur.

Lysine and Arginine Reactivity and Transformation Products during Peptide Chlorination.

Chlorine reactions with peptide-bound amino acids form disinfection byproducts and contribute to pathogen inactivation by degrading protein structure and function. Peptide-bound lysine and arginine are two of the seven chlorine-reactive amino acids, but their reactions with chlorine are poorly characterized. Using N-acetylated lysine and arginine as models for peptide-bound amino acids and authentic small peptides, this study demonstrated conversion of the lysine side chain to mono- and dichloramines and the arginine side chain to mono-, di-, and trichloramines in ≤0.5 h. The lysine chloramines formed lysine nitrile and lysine aldehyde at ∼6% yield over ∼1 week. The arginine chloramines formed ornithine nitrile at ∼3% yield over ∼1 week but not the corresponding aldehyde. While researchers hypothesized that the protein aggregation observed during chlorination arises from covalent Schiff base cross-links between lysine aldehyde and lysine on different proteins, no evidence for Schiff base formation was observed. The rapid formation of chloramines and their slow decay indicate that they are more relevant than the aldehydes and nitriles to byproduct formation and pathogen inactivation over timescales relevant to drinking water distribution. Previous research has indicated that lysine chloramines are cytotoxic and genotoxic to human cells. The conversion of lysine and arginine cationic side chains to neutral chloramines should alter protein structure and function and enhance protein aggregation by hydrophobic interactions, contributing to pathogen inactivation.

Prevention of Phytotoxic Effects of Regenerative In Situ Electrochemical Hypochlorination in Recirculating Hydroponic Systems

Recirculating nutrient solutions were treated using dimensionally stable anode (DSA)-based regenerative in situ electrochemical hypochlorination (RisEHc) in a deep water culture hydroponic lettuce (Lactuca sativa) production system. Phytotoxic effects were noted and attributed to the formation of chloramines in treated nutrient solutions containing ammonium. The presence of chloramines resulted in a decrease in overhead biomass by 53% using 2.27 mA/cm2 and 83% with 4.55 mA/cm2. Adding ultraviolet light as a tertiary treatment stage allowed the photodecomposition of chloramines, which prevented phytotoxicity in crops and caused no significant differences in growth between treatments. Furthermore, using a nitrate-based fertilizer also served to prevent phytotoxic effects in crops and showed no significant differences in growth between the control and 4.55 mA/cm2. In addition, it was found that the electrochemical flow cell (EFC) treatment resulted in a 13% increase in shoot biomass using 2.27 mA/cm2. The study demonstrated that phytotoxic effects can be prevented with the use of regenerative in situ hypochlorination through proper management and monitoring techniques in recirculating hydroponic systems.

Synergistic removal of ammonia nitrogen by UV photo-electrocatalytic process: Heterogeneous reaction pathways and mechanism

UV photo-electrocatalytic process has emerged as a promising approach for the abatement of ammonia nitrogen in wastewater. However, the radical chemistry for ammonia nitrogen removal in this process requires further clarification. The heterogeneous reaction pathways and mechanism of ammonia nitrogen oxidation in the UV photo-electrocatalytic process were investigated in this study. Photocurrents of the Ti/RuO2-IrO2-TiO2 electrodes with good electrocatalytic behavior were enhanced by UV radiation. Compared with the electrocatalytic process, the removal rates of ammonia nitrogen were improved by 12.4%∼20% at the Cl− concentration of 50 mM in the photo-electrocatalytic process. The ammonia nitrogen was mainly transferred into N2, meanwhile, the formation of nitrogenous by-products, active chlorine, and chloramines was inhibited in the photo-electrocatalytic process. The contribution of UV radiation was to photo-decompose the active chlorine and chloramines, generating free radicals. The removal efficiency of ammonia nitrogen reached more than 64% after the elimination of free radicals. The electro-generated HOCl was the principal species for ammonia nitrogen removal, and the synergistic effect for the acceleration of ammonia nitrogen oxidation resulted from the photo-generated chlorine radicals. This investigation provides insight into the electrochemistry, photochemistry, and radical chemistry for the heterogeneous catalytic degradation of ammonia nitrogen by UV photo-electrocatalytic process.

Novel insights into formation mechanism of organic chloramines from pre-oxidized algae-laden water: Multiple roles of dissolved organic nitrogen.

Organic chloramines posed significant risks to drinking water safety. However, the formation mechanism of algae-derived organic chloramines remained unclear. In this study, it was observed that pre-oxidation of algal suspensions increased organic chloramine formation during chlorination. Compared to KMnO4 pre-oxidation, O3 significantly increased the organic chloramine formation potential of algal suspensions. Characterization was performed with size exclusion chromatography-multiple detectors (SEC-MDs) to better understand the organic chloramine formation mechanism. The results revealed that low molecular weight proteins (AMW ≤ 0.64 kDa) were the main precursors of organic chloramines after conventional water treatment processes. We then focused on 14 essential amino acids involved in protein formation. Their concentrations and organic chloramine formation potentials were determined, based on which the theoretical organic chloramine formation potentials of the studied samples were evaluated. However, dramatic gaps between theoretical and experimental organic chloramine formations were observed, which suggested that not all organic nitrogen could react with chlorine to form organic chloramine. The condensed dual descriptor (CDD) was calculated to predict the electrophilic substitution reaction sites on peptides. Furthermore, the activation barrier of each proposed reaction was computed to confirm that the reaction sites for chlorine were located on amino groups. This study clarified the formation mechanism of algal-derived organic chloramines, which could provide a powerful theoretical foundation for controlling organic chloramine formation in drinking water processes.

Development of fluorescent azapentalenes to study the reactivity of hypochlorous acid and chloramines in micellar systems

Hypochlorous acid (HClO) is an endogenous reactive oxygen species generated by the oxidation of chloride catalyzed by myeloperoxidase (MPO). This enzyme is abundant in polymorphonuclear cells and involved in the human innate immune function. This work presents the development of a fluorescent azapentalene (C1) able to be incorporated in micelles and susceptive to HClO due to its sulfide moiety. C1 is non-fluorescent in the aqueous medium but fluoresces when incorporated in micelles produced by surfactants such as sodium dodecyl sulfate (SDS), Triton X-100, and cetyltrimethylammonium chloride (CTAC). The addition of HClO promoted instantaneous fluorescence decay of C1 incorporated in SDS but not in Triton X-100 or CTAC, showing the higher accessibility of HClO to the SDS micelle core. The reactivity of C1 was also studied in the presence of amine compounds taurine, 4-aminobutanoic acid (GABA), and its ethyl ester (GABA-EE), leading to the formation of the respective chloramines. The reactivity increased with the GABA-EE, evidencing the higher accessibility to the micellar core due to the hydrophobic character of the ester derivative. The potentiality of the system to monitor the enzymatic production of HClO was demonstrated by using MPO and hydrogen peroxide (H2O2). Scavengers of HClO were applied to validate the method. In conclusion, applying C1 opens new possibilities for studying the biochemical properties of HClO and chloramines in micelles.

Structural Basis of Stereospecific Vanadium-Dependent Haloperoxidase Family Enzymes in Napyradiomycin Biosynthesis.

Vanadium-dependent haloperoxidases (VHPOs) from Streptomyces bacteria differ from their counterparts in fungi, macroalgae, and other bacteria by catalyzing organohalogenating reactions with strict regiochemical and stereochemical control. While this group of enzymes collectively uses hydrogen peroxide to oxidize halides for incorporation into electron-rich organic molecules, the mechanism for the controlled transfer of highly reactive chloronium ions in the biosynthesis of napyradiomycin and merochlorin antibiotics sets the Streptomyces vanadium-dependent chloroperoxidases apart. Here we report high-resolution crystal structures of two homologous VHPO family members associated with napyradiomycin biosynthesis, NapH1 and NapH3, that catalyze distinctive chemical reactions in the construction of meroterpenoid natural products. The structures, combined with site-directed mutagenesis and intact protein mass spectrometry studies, afforded a mechanistic model for the asymmetric alkene and arene chlorination reactions catalyzed by NapH1 and the isomerase activity catalyzed by NapH3. A key lysine residue in NapH1 situated between the coordinated vanadate and the putative substrate binding pocket was shown to be essential for catalysis. This observation suggested the involvement of the ε-NH2, possibly through formation of a transient chloramine, as the chlorinating species much as proposed in structurally distinct flavin-dependent halogenases. Unexpectedly, NapH3 is modified post-translationally by phosphorylation of an active site His (τ-pHis) consistent with its repurposed halogenation-independent, α-hydroxyketone isomerase activity. These structural studies deepen our understanding of the mechanistic underpinnings of VHPO enzymes and their evolution as enantioselective biocatalysts.

The altered effects of chloride on the treatment efficiency of SO4·−-based AOPs by other background water constituents

A significant loss of the treatment efficiency induced by Cl− is a well-recognized drawback of the SO4·−-based AOPs and various mathematical model have been established to achieve quantitative prediction of the treatment efficiency of SO4·−-based AOPs at different levels of Cl−. However, the background water constituents (e.g., ammonia and dissolved organic matter (DOM)) complicate the chemistry of Cl−/SO4·− system and disable these models. This study shows that the degradation of sulfamethoxazole and bisphenol A by Co2+/PMS process decreased with dosing Cl− at fresh water level, due to the shifted distribution of reactive species from SO4·− to Cl2·−, ClO· and HOCl. Besides quenching radicals, HOCl also contributed to pollutant degradation. Though ammonia alone negligibly influence the Co2+/PMS process, ammonia reacts with the in situ formed HOCl in the Cl−/SO4·− process rapidly along with the generation of chloramine which mainly severed as radical scavenger rather than oxidant. Consequently, more severe efficiency loss of the SO4·−-based AOPs occur in the copresence of ammonia and Cl−. Unexpectedly, the efficiency loss was alleviated after dosing DOM, which was attributed to the suppressed formation of chloramine. The occurrence of chlorate and disinfection by-products are not concerns in the Co2+/PMS process when Cl− coexists with ammonia and DOM, because of the decreased formation of HOCl. These results enhance our understanding of the complex chemistry of SO4·−-based AOPs in real water and promote the progress of SO4·−-based AOPs towards the niche applications in water treatment.

Factors controlling the effectiveness of rechlor(am)ination to recover chloramine from nitrification

The two most commonly adopted strategies, rechlorination (addition of chlorine) and rechloramination (addition of chlorine and ammonia), to recover and stabilise chloramine from nitrification were comprehensively evaluated in laboratory- and full-scale systems. Laboratory-scale batch experiments were conducted in a nitrifying sample (~0.05 mg-N/L). In the full-scale service reservoir, repeated rechlorination was ineffective in suppressing nitrification and microbial chloramine decay during warmer months (>20 °C), even when rechlorination was started at nitrite <0.005 mg-N/L. Measurement of decay rates through microbial chloramine decay factor method provides a deeper understanding of a water sample than traditional nitrification indicators. The method has the ability to provide an early warning (one month in advance), show the presence of microbial chloramine decay in non-nitrified water and that of chloramine decaying proteins in any samples. In the batch sample, nitrification and the production of chloramine-decaying proteins and bacterial regrowth had to be suppressed to recover chloramine. Rechloramination (~2.5 mg/L) outperformed rechlorination, as it maintained a relatively higher chloramine concentration. Microbes were killed within 30 min of dosing chlor(am)ine, likely due to shock or compounds formed during chloramine formation reactions; however, microbes regrew (or survive) to a different degree in all samples despite the prolonged presence of chloramine (large CxT), defying the CxT concept. The key to the recovery of chloramine appears to be consistently maintaining chloramine >1.7 mg/L and shocking with a high chloramine dose. The findings will assist water utilities in designing and assessing the effectiveness of nitrification remediation strategies in chloraminated water supply systems.

Organic chloramines formation from algal organic matters: Insights from Fourier transform-ion cyclotron resonance mass spectrometry

Release of algal organic matter (AOM) from algae poses great threats to drinking water safety. As organic nitrogen in AOM is relatively higher compared to natural organic matter (NOM), the organic chloramine formation during chlorination cause overestimation of effective chlorine, which may lead to a biological risk. This study compared the organic chloramine formation from AOM and NOM, and confirmed that AOM tend to form more organic chloramines during chlorination. Furthermore, it was found that hydrophilic fraction and high molecular weight (>100 kDa) fraction of AOM generated major organic chloramines due to a high content of protein. Based on the results of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), Spearman's rank correlation was used to analyze the relationship between molecular composition of AOM and organic chloramine formation. Notably, molecules with high correlation to organic chloramine formation located in a triangle region of van Krevelen diagram, which is a typical area of peptides. Therefore, it indicates that the precursors of organic chloramine in AOM are mainly proteins/peptides, and appropriate treatment processes (e.g., biological treatment or membrane filtration) should be addressed to effectively remove the precursors before chlorination.

Formation of organic chloramines during chlorination of 18 compounds

Organic chloramines have attracted considerable attention because of their potential toxicity and reactivity. However, the lack of suitable and effective analytical methods has limited the study of organic chloramines due to their volatile and unstable properties. In this study, membrane introduction mass spectrometry (MIMS) combined with DPD/FAS titration was used to monitor the formation of organic chloramines. N-chlorodimethylamine [(CH3)2NCl] and N-chlorodiethylamine [(C2H5)2NCl] were detected and identified as the dominant volatile DBPs during chlorination of 18 organic compounds with dimethylamine or diethylamine functional groups, with yields ranging from 0.3% to 51.1% at a chlorine to precursor (Cl/P) molar ratio of 8.0. (CH3)2NBr was formed in the presence of bromide, while the formation of (CH3)2NCl was decreased. The reaction of phenol with (CH3)2NCl combined with theoretical calculations confirmed that the reactivity of (CH3)2NCl was similar to that of monochloramine. Moreover, (CH3)2NCl and (C2H5)2NCl were observed at the ppb level during chlorination of actual water samples collected from different areas. The results suggest that (CH3)2NCl and (C2H5)2NCl are important organic chloramines during chlorination, which may lead to the occurrence of further oxidation reactions and promote the formation of other disinfection byproducts simultaneously and should be of concern.

Formation and control of organic chloramines and disinfection by-products during the degradation of pyrimidines and purines by UV/chlorine process in water

Pyrimidine and purine bases (adenine, cytosine, guanine and thymine) are important precursors of organic chloramines (OC) and disinfection by-products (DBPs) during chlor(am)ination. In this study, OC and DBP formation derived from pyrimidine and purine bases during chlor(am)ination, post-chlor(am)ination after pretreated by UV alone and UV/chlorination were systematically investigated with ultraviolet light-emitting diodes (UV-LEDs, 265 and 275 nm) and low pressure mercury lamp (LPUV, 254 nm). The results revealed that higher OC formation was observed during chlorination than that during chloramination of pyrimidine and purine bases. The degradation of pyrimidine and purine bases followed the pseudo-first-order kinetics. Both solution pH and UV wavelength played vital influence on the degradation of pyrimidine and purine bases. In terms of fluence-based rate constants (kobs), the degradation rates of pyrimidine and purine bases decreased in the order of 275 nm > 265 nm > 254 nm in alkaline conditions. The synergistic effects of kobs, chlorine,kobs, •OH and kobs, RCS contributed to the differences of pyrimidine and purine bases degradation at different pH values and UV wavelengths. A vital suppression of OC formation was observed during post-chlorination after pretreated by 275 nm UV-LED/chlorination. In addition, compared with LPUV (254 nm), less DBP formation was observed at UV-LED (275 nm), especially during the UV/chlorine process. The phenomena obtained in this study indicated that 275 nm UV-LED combined with chlorine could be a preferred method to promote pyrimidine and purine bases degradation and control OC and DBP formation in practical water treatment.

UV-induced activation of organic chloramine: Radicals generation, transformation pathway and DBP formation

Organic chloramines of little disinfection efficacy commonly exist in disinfection process (chlor(am)ination) due to the wide presence of organic amines in water, of which N-chlorodimethylamine (CDMA) is a typical one. For the first time, UV photolysis for the activation of CDMA was investigated. UV photolysis caused the cleavage of N-Cl bond in CDMA to form Cl• and subsequently HO•, both of which are dominant contributors to the destruction of model contaminant bisphenol A (BPA). Typical spectra of HO• were detected by electron paramagnetic resonance (EPR) experiments, while spectra of reactive nitrogen species (RNS) were not detected during UV photolysis of CDMA. The increase of pH (6.0–8.0), HCO3−/CO32−, Cl− and nature organic matter inhibited the degradation of BPA. We proposed pathways of CDMA and BPA degradation based on the identified transformation products. UV photolysis of CDMA and BPA reduced the formation of N-nitrosodimethylamine (NDMA) at pH 8.0, but increased the formation of trichloronitromethane (TCNM) at pH 7.0 and 8.0. The increasing toxicity and the formation of TCNM and NDMA gave us a hint that formation of organic chloramines should be concerned.

Implications of breakpoint chlorination on chloramines decay and disinfection by-products formation in brine solution

The effects of breakpoint chlorination on formation and decay of inorganic chloramines and disinfection by-products (DBPs) in chlorinated brine solutions is investigated. A correlation was established between the decay and speciation of chloramines with the environmental factors such as pH, temperature, chlorine to ammonia ratio and natural organic matter dosage. Results showed that acidic pH and high chlorine to ammonia ratio favored the formation of trichloramine (NCl3), however neutral and high pH favored the formation of monochloramine (NH2Cl) and dichloramine (NHCl2) species. Further, the presence of natural organic matter (NOM) and higher pH enhanced the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) in the chlorinated brine solution. Further, kinetics simulations were performed to study the chloramine formation and decay kinetics as a function of temperature using web-based application designed by US Environmental protection Agency (EPA). Based on comparisons between simulated and experimental datasets, a close similarity was observed between chloramine chemistry synthetic chlorine system and chlorinated brine solution. Moreover, the mechanism of chloramine formation and decay has been proposed based on the model simulations and N2, ammonia and NO3− being identified as the main products.

The role of chloramines on the electrodisinfection of Klebsiella pneumoniae in hospital urines

In this work, the electrochemical disinfection of synthetic hospital urines inoculated with Klebsiella pneumoniae (K. pneumoniae) as antibiotic resistant bacteria model was evaluated, paying special attention to the formation and contribution of chloramines on the disinfection performance. A novel microfluidic flow-through reactor and a conventional parallel flow reactor equipped with Mixed Metal Oxide (MMO) electrodes as anode material were also compared. The influence of the current density was assessed within the range 5–50 A m−2. Results show that the inactivation increases more than 5 log units when varying the current density from 5 to 50 A m−2, regardless the reactor layout tested. The complete disinfection (7-log reduction) is attained before 120 min (Q: 0.278 Ah dm−3) at 50 A m−2 using the flow-through reactor. Chemical disinfection tests confirm the influence on the K. pneumoniae inactivation of both, the concentration and the exposure time, using hypochlorite and chloramine disinfectants. Unless the presence of chloramines slows down the removal of bacteria in hospital urine, they may avoid the formation of undesirable chlorine by-products. This is more remarkable when working with the flow-through reactor because it induces the accumulation of 2 times higher concentration of chloramines respect to the parallel flow under the same applied electric charge values. Hence, these results point out the important role of chloramines on the electrodisinfection of hospital urines.

Removal of antibiotic resistant bacteria by electrolysis with diamond anodes: A pretreatment or a tertiary treatment?

In the present work, the influence of the water matrix on the removal of antibiotic resistant bacteria during the electro-disinfection with diamond anodes was studied, paying special attention to the disinfection efficiency and the prevention of the formation of hazardous disinfection by-products. This will allow to evaluate if electrolysis is more suitable as pretreatment of the main pollution source or as tertiary treatment of urban wastewater. To do this, electrolysis of synthetic wastewater rich in ammonium (simulating the effluent of an oxidation pond) and hospital urine intensified with three different bacteria (E. faecalis, K. pneumoniae, and E. coli) were carried out. Results show that the disinfection efficiency is higher in the synthetic wastewater for all the bacteria tested, but chlorate is formed as disinfection by-product. Electrogenerated hypochlorite and chloramines are the main responsible species for bacteria depletion. Presence of organics (urea, creatinine and uric acid) as additional ammonia precursors in hospital urine leads to the well-known breakpoint reaction with electrogenerated active chlorine, yielding an increasing concentration of chloramines. This helps to prevent the formation of chlorate in hospital urine because hypochlorite is mainly wasted in the oxidation of organics and the formation of chloramines. These results are of a great significance because they indicate that antibiotic resistant bacteria can be efficiently removed in complex matrixes without the formation of hazardous chlorine by-products if it is carried out as a pretreatment before discharge to WWTP.

Influence of treatment processes and disinfectants on bacterial community compositions and opportunistic pathogens in a full-scale recycled water distribution system

In this study, for the first time, a recycled water distribution system was analysed in which the inorganic nitrogen content in the recycled water was substantially minimised (<0.2 mg/L) while the total chlorine residual was maintained above 0.1 mg/L (regulatory standard). The chemical parameters and bacterial community composition of the unique full-scale recycled water treatment and distribution system were comprehensively evaluated. The application of chlorine eliminated Escherichia coli (E. coli) and largely reduced the bacterial diversity, richness, and the number of species, despite the formation of organic chloramines (>85%) having minimal disinfection abilities. The majority of the bacterial communities were proteobacteria comprising alpha-, beta-, and gamma-proteobacteria, similar to the drinking water distribution system. The gene copy numbers of total bacterial 16S ribosomal ribonucleic acid (16S rRNA) and opportunistic pathogens (OPs) were significantly decreased after the chlorination, but their populations increased with the decrease of total chlorine residual level in the distribution system. The total bacterial 16S rRNA significantly correlated with Legionella spp., Mycobacterium spp., and Pseudomonas aeruginosa. Similarly, significant correlations existed between OPs (particularly Legionella spp. and Pseudomonas aeruginosa) and iron-oxidising, manganese-oxidising, and sulphate-reducing bacterial genera. The detection of several OPs in the absence of E. coli shows that the traditional indicator used for compliance monitoring may not accurately represent the microbial water quality. This study suggests monochloramine as an alternative secondary disinfectant.