Generation Of Disinfection By-products Research Articles

Study on the efficiency of the preoxidation–coagulation process in removing disinfection by-product precursors from micropolluted water

The efficiency of preoxidation–coagulation technology in removing disinfection by-product precursors and organic compounds from polluted surface water and the effect of this technology on the generation of disinfection by-products are explored.

Effect of pure oxygen aeration on soluble microbial products production in activated sludge system under the toxic condition of phenol

Soluble microbial products (SMP) contribute most of effluent organic matter (EfOM) in biological treatment processes. These products cause membrane fouling and generate disinfection by-products. This study investigated the effect of pure oxygen aeration on the production and characteristics of SMP under the toxic condition of phenol. Two sequencing batch reactors with pure oxygen (O-SBR) and air (A-SBR) aeration were used in the experiments. Results showed that the effluent chemical oxygen demand values of O- and A-SBR were 36.11 ± 1.54 and 42.44 ± 1.42 mg/L, respectively. SMP was the dominant component of EfOM. The various aeration types caused differences in the contents of extracellular polymeric substances (EPS) and SMP in the two SBRs. The content of loosely bound EPS (LB-EPS) in A-SBR was higher than that in O-SBR by 25%, whereas the tightly bound EPS content in A-SBR was lower than that in O-SBR by 19%. Pure oxygen aeration decreased 15% of humic acids, 42% of polysaccharides, and 29% of protein contents of SMP compared with air aeration, but it did not change the functional groups of SMP. SMP concentration was positively correlated with LB-EPS. Pure oxygen aeration caused the low contents of LB-EPS and SMP. This study showed the effect of pure oxygen aeration on SMP reduction, which can be useful for toxic industrial-wastewater biological treatment.

Novel UV-LED-driven photocatalysis-chlorine activation for carbamazepine degradation by sulfur-doped NH2-MIL 53 (Fe) composites: Electronic modulation effect and the dual role of chlorine

Chlorine activation-inefficient and the generation of disinfection by-products (DBPs) has indeed limited the application of UV/chlorine process. In this study, the typical metal-organic frameworks (MOFs) NH2-MIL53(Fe) were successfully modified with organic ligands containing sulfur functional groups and applied to construct a novel UV-LED-driven heterogeneous chlorine activation system. The generation of intermediate energy levels and the charge redistribution effect on Fe-S bond facilitated the excitation of electrons and realized the effective separation of photohole (hvb+) and photoelectron (ecb-). The involvement of S-NH2-MIL53(Fe) improved the efficiency of UV-LED/chlorine process by 6 times. The effective activation of HOCl/OCl- by hvb+ and ecb- significantly enhanced the yield of HO· and Cl·. More importantly, HOCl/OCl- played a dual role in UV-LED/chlorine/S-NH2-MIL53(Fe) process as a precursor for the generation of free radicals and a catalyst for the enhancement of HO· yield, which could achieve efficient removal of the target pollutants at lower chlorine doses. In addition, the presence of low-valent sulfur species and ecb- accelerated the cycle of Fe(II)/Fe(III) and in-situ generation of HO· and Cl·. The known generation of DBPs in UV-LED/chlorine/S-NH2-MIL53(Fe) process decreased by 37.9% compared to UV-LED/chlorine process. Developing novel UV-LED/chlorine/S-NH2-MIL53(Fe) processes provided a reliable strategy to efficiently purify actual micro-polluted water bodies.

Electro-oxidation and UV irradiation coupled method for in-site removing pollutants from human body fluids in swimming pool

A comprehensive study was conducted to investigate how ultraviolet (UV) irradiation combined with electrochemistry (EC) can efficiently remove human body fluids (HBFs) related pollutants, such as urea/creatinine/hippuric acid, from swimming pool water (SPW). In comparison with the chlorination, UV, EC, and UV/chlorine treatments, the EC/UV treatment exhibited the highest removal rates for these typical pollutants (TPs) from HBFs in synthetic SPW. Specifically, increasing the operating current of the EC/UV process from 20 to 60 mA, as well as NaCl content from 0.5 to 3.0 g/L, improved urea and creatinine degradation while having no influence on hippuric acid. In contrast, EC/UV process was resilient to changes in water parameters (pH, HCO3-, and actual water matrix). Urea removal was primarily attributable to reactive chlorine species (RCS), whereas creatinine and hippuric acid removal were primarily related to hydroxyl radical, UV photolysis, and RCS. In addition, the EC/UV procedure can lessen the propensity for creatinine and hippuric acid to generate disinfection by-products. We can therefore draw the conclusion that the EC/UV process is a green and efficient in-situ technology for removing HBFs related TPs from SPW with the benefits of needless chlorine-based chemical additive, easy operation, continuous disinfection efficiency, and fewer byproducts production.

A UVA light-emitting diode microreactor for the photocatalytic degradation of humic acids and the control of disinfection by-products formation potential

Chlorination is one of the most applied technologies for drinking water disinfection. However, the generation of disinfection by-products (DBPs) in the chlorination process is threatening drinking water safety, especially when the concentration of natural organic matter (NOM) is high in source water. Climate change increases the fluctuation of NOM in source water, which further challenges water safety in small and rural communities. In this study, environmental microfluidics was introduced to a UVA-LED photocatalytic oxidation system for a rapid oxidation of NOM. The results showed that HA adsorption and degradation, and DOC degradation were more favored in low pH. At pH 5, 56.9% of HA and 58.1% of dissolved organic carbon (DOC) were removed in 3.4 min by the microreactor. DBP formation potential was efficiently reduced, with the highest reduction of THM and HAA formation potentials by 76% and 70.7%, respectively. Compared with the bottle reactor, the degradation rate constants of HA and DOC by UVA-LED microreactor were increased by 2.99 – 15.8 times, and 6.8 – 170.2 times, respectively. Homogenous irradiation and rapid mass transfer in the microreactor accelerated the inhibited oxidation of HA in acidic and base solutions and increased the apparent quantum yields of photocatalysis. Further, the microfluidic photocatalytic oxidation was much more efficient in the reduction of DPBs formation potential in a source water sample. The process was rapid and had low chemical and energy consumption. Approaches on system scale-up, system simplification, and energy conservation would increase potential of microfluidic photocatalytic oxidation in water purification for households and small communities.

Disinfection Effects and Disinfection by-products Generation Characteristics of a Continuous Hypochlorous Acid Water Producing Device Using Citric Acid as a pH Control Agent

The use of disinfectants and disinfecting devices is becoming increasingly common in homes as they prevent the development and spread of pathogens while improving hygiene. Common disinfectants include chlorine compounds, alcohol, and quaternary ammonium compounds. Among them, chlorine compounds are easily manufactured and commonly used in the form of sodium hypochlorite. When chlorine compounds are dissolved in water, free chlorine divides into hypochlorous acid and hypochlorite ions with different molar fractions depending on solution pHs. Maintaining a high hypochlorous acid fraction by adjusting the solution pH is crucial as hypochlorous acid is more than 100 times more effective as a disinfectant than hypochlorite ions. However, due to the chemical nature of its conversion to hypochlorite ions, hypochlorous acid is not very stable, making it more efficient to prepare and consume it at the time of use. In this study, we used citric acid as a pH adjuster to determine the optimal conditions required for producing electrolyzed water. We built a device capable of continuously producing electrolyzed water containing hypochlorous acid, and we analyzed the efficiency of the produced electrolyzed water using disinfection tests and measurements of disinfection by-products.

Algae removal characteristics of the ultrasonic radiation enhanced drinking water treatment process

Algal blooms have become a critical environmental problem and affect the water quality of drinking water treatment plants. This study investigated the effects of different ultrasonic methods on Microcystis aeruginosa and enhanced drinking water treatment processes. Results showed that the removal rate of algae cells increased with the extension of time and the removal effect of static ultrasound was better than that of dynamic ultrasound. However, the release of algae organics and algae toxins was less in dynamic ultrasound radiation. Scanning electron microscope (SEM) and transmission electron microscope (TEM) analyses showed that ultrasonic radiation destroyed parts of the cell structure but not the integrity of the algae cells' membrane and wall. The coagulation experiment found that short-time ultrasonic radiation can promote the coagulation effect and improve the removal efficiency of algae cells and organics. The 740 kHz ultrasonic enhanced water purification process significantly improves the removal efficiency of algae cells in the sedimentation tank, reduces the treatment pressure of the filter, and releases less algae cell substances, reducing the risk of disinfection by-products generation. This study provides a reference for the application of ultrasound in water purification technology and is of great significance in ensuring water quality safety.

Newly Discovered Irbesartan Disinfection Byproducts via Chlorination: Investigating Potential Environmental Toxicity

Irbesartan belongs to the Sartan family, whose members are used in the treatment of arterial hypertension and kidney disease among patients with hypertension and type 2 diabetes mellitus as part of a treatment based on antihypertensive drugs. This drug has reached surface waters, accumulating to the extent of being considered an emerging pollutant, along with other substances from the same class. Wastewater treatment plants, which constitute the main environmental source of this compound, fail to completely reduce its presence in wastewater and generate additional toxic byproducts through the chlorine-based disinfection process. This study provides a comprehensive investigation into the chlorination mechanisms of irbesartan, revealing the identity of twelve new byproducts, which were characterized using NMR and mass spectrometry (MS-TOF). The other six byproducts were published in a previous study, allowing for the confirmation of some aspects of the supposed mechanisms of degradation, along with the identification of those that had only been hypothesized. An ecotoxicological assessment of a mixture and isolated byproducts was performed using Raphidocelis subcapitata for algal growth inhibition, Daphnia magna for immobility, and Aliivibrio fischeri for luminescence inhibition. The results revealed the variable toxicity of irbesartan and its byproducts. Different organisms exhibited varying sensitivities to the byproducts, with Aliivibrio fischeri being the most sensitive. The coexistence of multiple byproducts in the environment, their high toxicity, and their potential interactions highlight the significant environmental risks associated with chlorination and its derivates. Our study highlights the ongoing debate surrounding the generation of disinfection byproducts.

UV-LED-driven photocatalytic chlorine activation with typical spinel ferrites for carbamazepine degradation: Critical role of superoxide radicals, disinfection by-product formation and toxicity evaluation

Chlorine activation-inefficiency and the generation of disinfection by-products (DBPs) have indeed limited the application of the UV/chlorine process. In this study, zinc ferrite nanorods (ZFO-R) with excellent photovoltaic properties were successfully prepared for the construction of a novel heterogeneous UV-LED-driven chlorine activation system. The addition of ZFO-R increased the first-order reaction rate constant for the degradation of carbamazepine (CBZ) by the UV-LED/chlorine process by 6 times. Mechanism investigation indicated that superoxide radicals (O2−) dominated the generation of hydroxyl radicals (HO) and chlorine radicals (Cl) in the system by promoting the activation of HClO/ClO−, and the increased yields of HO and Cl enhanced their contribution to the degradation of the target pollutants. Importantly, the efficient activation of chlorine not only promoted the generation of reactive species but also inhibited the formation of DBPs by shorting the contact time between chlorine and precursors, which effectively controlled the toxicity of the reaction system. This work proposes a reliable strategy for inhibiting DBPs formation in the UV/chlorine process and broadens the application of spinel ferrites in environmental remediation, achieving efficient and reliable purification of actual micropolluted water bodies.

Highly selective adsorption performance and mechanism of basic amino acids by modified cation resin: Batch experiments and DFT calculation

Basic amino acids have been a major concern due to poor removal and high generation potential for nitrogenous disinfection by-products in drinking water treatment. Conventional cation exchange resins struggle to effectively eliminate basic amino acids owing to their inferior selectivity. In this work, a novel magnetic cation exchange resin (noted as MCER resin) was designed for the selective adsorption of basic amino acids. Batch experiments were conducted to investigate the removal efficiency for basic amino acids (histidine, arginine) and influencing factors (pH, ionic strength). Notably, MCER resin was superior in the removal of histidine (68.5%) and arginine (90%), which significantly reduced the generation of disinfection by-products (DBPs). It exhibited higher resistance to the interference of cations (Na+, Ca2+) at different levels and displayed a promising application potential for simultaneous removal of hardness. The adsorption for histidine and arginine reached equilibrium within 140 min and was well defined by pseudo-first order and intra-particle diffusion kinetic models. Furthermore, the reusability of MCER resin was elucidated after five consecutive adsorption-desorption cycles and the selective adsorption mechanism was determined through various pathways such as electrostatic attraction, hydrogen bonding and ion exchange, as evidenced by XPS and DFT calculations.

Characterization and Disinfection by Product Formation of Dissolved Organic Matter in Anaerobic–Anoxic–Oxic Membrane Bioreactor (AAO-MBR) Process

In the process of sewage treatment, the characteristics of dissolved organic matter (DOM) are always changed during chemical and biological processes, affecting the generation of disinfection by-products (DBPs) compositions at the following disinfection stage. The present study systematically investigated the effect of DOM characterization on C- and N-DBPs formation at AAO-MBR reactor when treating wastewater. The results showed that the AAO-MBR treatment process could efficiently eliminate dissolved organic carbon (DOC) and ammonium nitrogen (NH4+-N) from wastewater with an elimination rate of 89% and 98%, respectively. Most of the precursors (i.e., 56.8% C-DBPs and 78.1% N-DBPs) were removed at the MBR unit, while AGC and AAO units promoted the formation of DBPs precursors. More specifically, soluble microbial products (SMPs) and humus acid were increased, which led to improved C- and N-DBPs via aerated grit chamber (AGC) treatment. At the AAO treatment unit, the content of low MW hydrophobic SMPs, humus acid, and polysaccharides was increased, indicating low MW and HPO fractions dominating the C- and N-DBPs. MBR treatment improved C-DBPs in high MW and HPO fractions and N-DBPs in low MW and HPO fractions, which is explained by higher MW hydrophobic SMPs and humus acids, compared to the AAO unit. The present study provided deep insight into the linkage of DOM characteristics and C- and N-DBPs formation at each treatment unit during the AAO-MBR process.

Integration of ozonation with water treatment for pharmaceuticals removal from Arroio Diluvio in southern Brazil.

Pharmaceutical compounds can reach water bodies through sewage systems. The process of water treatment is insufficient for the removal of these contaminants. The ozonation has great potential to be integrated into the treatment, since it promotes the reduction of pharmaceuticals, reduces the generation of disinfection byproducts and can reduce operational costs. In this work, the integration of the ozonation process with water treatment was studied. The ozone was applied in the pre-oxidation and intermediate ozonation stages, to evaluate the dependence of different variables. Water samples were collected from Arroio Diluvio, a river of the city of Porto Alegre (Brazil). The doses of ozone were maintained between 0.5 and 1.0 mgO3 L-1 while the coagulant was between 25 and 150 mg·L-1. Pre-ozonation resulted in a removal of pharmaceuticals at pH 10.0, time of 15 min and coagulant concentration of 52.5 mgL-1. The intermediate ozonation provided a removal with pH 10.0 and a time of 5 min of bubbling. Based on the results, it was confirmed that the synergy of the ozonation process with conventional water treatment is an effective, sensitive and fast method for the removal of pharmaceuticals from the aqueous medium.

Applying lysozyme, alkaline protease, and sodium hypochlorite to reduce bioclogging during managed aquifer recharge: A laboratory study

Alleviating bacterial-induced clogging is of great importance to improve the efficiency of managed aquifer recharge (MAR). Enzymes (lysozyme and alkaline protease) and sodium hypochlorite (NaClO) are common biological and chemical reagents for inhibiting bacterial growth and activity. To investigate the applicability of these reagents to reduce bioclogging, percolation experiments were performed to simulate a weak alkaline recharge water infiltration through laboratory-scale sand columns, with adding 10 mg/L lysozyme, alkaline protease, and NaClO, respectively. The results showed that, with the addition of lysozyme, alkaline protease, and NaClO, the average clogging rates (the reduced percentages of relative saturated hydraulic conductivity of the sand columns per hour during the percolation experiments) were 0.53%/h, 0.32%/h and 0.06%/h, respectively, which were much lower than that in the control group (0.99%/h). This implied that bioclogging could be alleviated to some extent following the treatments. For further analyzing the mechanisms of the regents on alleviating bioclogging, the bacterial cell amount and extracellular polymeric substances (EPS) concentration were also measured to study the effects of lysozyme, alkaline protease, and NaClO on bacterial growth and EPS secretion. Lysozyme and alkaline protease could disintegrate bacterial EPS by hydrolyzing polysaccharides and proteins, respectively, while they had little effect on the bacterial cell amount. The addition of NaClO significantly decreased the bacterial cell amount (P < 0.05) and thus greatly alleviated bioclogging. Although the lowest average clogging rate was achieved in the NaClO group, it can generate disinfection by-products that are potentially harmful to the environment and human health. Therefore, the biological-based method, i.e., enzyme treatment, could be a promising option for bioclogging control. Our results provide insights for understanding the mechanisms of lysozyme, alkaline protease, and NaClO to alleviate bioclogging, which is of great importance for addressing the clogging problem during MAR activities and achieving groundwater resources sustainable utilization.

Non targeted screening of nitrogen containing disinfection by-products in formation potential tests of river water and subsequent monitoring in tap water samples.

The generation of disinfection by-products during water chlorination is a major concern in water treatment, given the potential health risks that these substances may pose. In particular, nitrogen-containing DBPs are believed to have greater toxicological significance than carbon-based DBPs. Hence, high performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC-HRMS) in positive mode was employed to identify new non-volatile nitrogen containing disinfection by-products (DBPs) and to assess their presence in potable water. Nine water samples were taken in the Llobregat river, in the context of a water reuse trial, near the catchment of a drinking water treatment plant (DWTP) in 2019. River samples were disinfected with chlorine under controlled formation potential tests conditions and analysed with a non-target approach. The peak lists of raw and chlorinated samples were compared exhaustively, resulting in an extensive list of 495 DBPs that include bromine and/or chlorine atoms. 172 of these species were found frequently, in three or more chlorinated samples. The empirical formulae of these DBPs were unambiguously annotated on the basis of accurate m/z measurements, isotopic patterns and common heuristic rules. Most of the annotated species (310) contained bromide, which is consistent with the relatively high bromide content of the Llobregat basin (>0.3mg/l). Drinking water samples were taken at the outlet of the DWTP during the same sampling period. According to their analysis, a large portion of the DBPs detected after the formation potential tests do not reach real-life drinking water, which suggests that the treatment train successfully removes a significant fraction of DBP precursors. However, 131 DBPs could still be detected in the final product water. A larger sampling was carried in the Barcelona water distribution network, during six consecutive weeks, and it revealed the presence of 78 halogenated DBPs in end-consumer water, most of which were nitrogen-containing. MS/MS fragmentation and retention times were employed to tentatively suggest molecular structure for these recalcitrant DBPs.

Synthesis and characterization of a novel magnetic resin (m-MAR resin) and its removal performance for alkaline amino acids

Alkaline amino acids as dissolved organic nitrogen (DON) have raised much concern in drinking water treatment due to poor removal in conventional treatment process and high potential for nitrogenous disinfection by-products (N-DBPs). This work was intended to devise a new magnetic adsorption resin (noted as m-MAR resin) for the efficient reduction of alkaline amino acids and explore the application potential of combined MIEX and m-MAR resins. The distribution and composition of DON and amino acids was clarified for different water sources in Lake Taihu basin, in which alkaline amino acids accounted for a higher proportion. The removal of different nitrogenous organics by MIEX resin was also examined, where the resin was effective in removing phycocyanin (65.6%) and glutamic acid (74.2%), reducing the generation of disinfection by-products (DBPs). The m-MAR resin was manufactured and characterized to cope with alkaline amino acids, and batch experiments were undertaken to investigate its adsorption behaviors on histidine and arginine under different operating conditions. The maximal adsorption capacities of arginine and histidine onto m-MAR resin were 2.84 mg/g and 1.62 mg/g, respectively, which was better than MIEX resin. The removal mechanism of the two basic amino acids by m-MAR resin was mainly due to the hydrogen bonding and the acid-base reaction. Moreover, the reusability of the m-MAR resin was elucidated after six successive adsorption-desorption cycles. Finally, the effectiveness of combined MIEX and m-MAR resin in treating DON derived from Microcystis aeruginosa reached 35.2% and the DON concentration in Lake Taihu could be reduced from 0.56 to 0.16 mg/L, which simultaneously decreased the generation potential of N-DBPs. The enhancement of coagulation by the combined process of m-MIER and m-MAR as pretreatment was estimated.

Towards Selective Removal of Bromide from Drinking Water Resources using Electrochemical Desalination

Disinfection of drinking water is crucial in water treatment as it suppresses waterborne pathogenic diseases. However, as an unintended consequence, disinfection generates disinfection byproducts (DBP). DBPs are cytotoxic, carcinogenic, and nephrotoxic especially when they are brominated. Brominated DBP formation is governed by the interaction of reactive precursors such as natural organic matter (NOM), and Brˉ with oxidants that are added as disinfectants (e.g., chlorine, chloramines, ozone). Historically, the main strategy to control the formation of DBP was to remove NOM from water by coagulation, adsorption, bio-filtration, pre-oxidation, or membrane separation; however, processes that remove NOM do not necessarily remove Brˉ. Herein, we investigated the utilization of combined capacitive and faradaic ion removal in a flow cell to remove Brˉ as well as Clˉ concurrently with more selectivity towards the former. The effectiveness of the proposed technique was evaluated by determining the maximum salt adsorption capacity and measuring the specific ion concentration with ion chromatography. In a binary equimolar mixture of Brˉ and Clˉ, Brˉ was more selectively adsorbed over Clˉ at 1.2 V applied potential due to the contribution of bromine gas evolution to the capacitive deionization.

(Digital Presentation) Water Treatment through the Arc and Pulsed Spark Discharge

Water deterioration and depletion are accompanied by population growth and fast urbanization, posing major environmental problems. The prevalence of water-borne infections remains high, making it critical to discover effective ways of disinfecting water thoroughly. The main methods for inactivating a wide spectrum of harmful bacteria are chemical, physical, electrochemical, and radical. Conventional decontamination methods not only fail to completely disinfect water but also have several drawbacks, including the generation of disinfection byproducts; the complexity of disinfection reactor design; high energy consumption; and high running expenses. As a result, a versatile approach should be developed to overcome the limitations of current decontamination methods while also being efficient against a variety of diseases. Plasma-based water treatment has recently emerged as a possible alternative to traditional approaches. Plasma has proven to be more effective than conventional oxidants and disinfectants, both directly and indirectly. Plasma-related effects vary depending on the type of discharge, device settings, and process parameters. Electrical discharges are one of the most effective water treatment treatments. To this end, two plasma discharges, i.e., arc and pulsed spark discharge, are used for the treatment of synthetic contaminated water with microorganisms, which can be used for naturally contaminated surface water. Our results revealed that in comparison to arc discharge, pulse spark discharge produces more extreme acidic conditions by lowering the pH of water samples as well as a more reactive environment, which results in greater antibacterial efficacy. Furthermore, water samples treated with arc discharge had greater temperatures than water samples treated with pulse spark discharge, indicating that temperature was not a critical effector in the plasma-based sterilizing process.

Chlorination of L-tyrosine and metal complex: degradation kinetics and disinfection by-products generation

The presence of metal ions in drinking water treatment and distribution systems may affect the disinfection process of organic matter, which had aroused people's concern. L-tyrosine can complex with metal ions through carboxyl, carbonyl and amino groups and affected its chemical reactions. In this paper, the complexation of L-tyrosine with common metal ions was studied and the influence of complexation in chlorination with different experimental factors were investigated. It was inferred that L-tyrosine complexed with metal ions by single dentate ligand or double dentate chelation in a ratio of 2:1. The degradation of L-tyrosine-metal complex followed the pseudo-first-order reaction kinetic. TCM, DCAA and TCAA were the main species DBPs in chlorination of L-tyrosine. Compared with L-tyrosine, the reaction rate constants of complex increased by 5.6%, the formation of trihalomethane production decreased by 21.5% and the formation of haloacetic acids production increased by 26.9% at the state of metal complexation. The effect of metal complexation on chlorination was more obvious than that of metal coexistence. For different metal complexation, the order of inhibition on trihalomethane production was Ca2+> Fe3+> Mn2+ and the order of promotion on haloacetic acids production was Mn2+> Fe3+> Ca2+. Moreover, it was found that alkaline conditions were favorable to the formation of DBPs due to the hydroxyl radical. The combination of ultraviolet (UV) and chlorine disinfection promoted L-Tyr degradation and DBPs generation, and the promotion efficiency follow the order: UV/Cl2> UV-Cl2> Cl2.

A preliminary review on antimicrobial property of zinc-based nanoflakes and its impact on wastewater purification

Decreasing supply and increasing demand are among the factors causing global water scarcity. Existing water disinfection systems have limits, specifically the generation of disinfection by-products, prompting researchers to hunt for alternatives. Zinc oxide, an antibacterial compound used in the pharmaceutical and rubber industries, has aroused researchers' curiosity. Zinc oxide has indicated antimicrobial properties at the nanoscale, indicating broad application possibilities. This paper discusses zinc oxide, its antimicrobial properties, and its potential use in water disinfection.

Cumulative impact of swimmers on pool water quality: A full-scale study revealing seasonal and daily variabilities of disinfection by-products

Swimming pool water is continuously disinfected to control microbial safety. However, the disinfection processes also generate disinfection by-products (DBPs) that are created by the reaction between a disinfectant and organic matter. In this study, the water quality of two indoor pools with different characteristics was monitored at full scale. To assess the cumulative impact of swimmers, pools water quality was monitored for long term (2 months), after complete water renewal in pools. The daily impact of swimmers on water quality was also estimated by intensively sampling water quality during one high attendance day. Samples were analyzed for DBPs (Trihalomethanes-THMs, Haloacetic acids-HAAs, chlorites and chlorates) and their precursors (total organic carbon-TOC, UV 254 nm, water temperature, pH, free and total chlorine). Results showed that swimmers had a clear impact on the levels of organic matter indicators (TOC and UV 254 nm) and total nitrogen, whose variabilities were associated with the swimmers attendance. The highest levels of DBPs (THMs and HAAs) were detected in the pools during periods of maximum attendance and when there was a higher ratio of swimmers to pool-water volume. THM levels were also found to be influenced by parameters associated with pool operations (water temperature, water renewal, disinfection). Most notably HAAs accumulated in both pools due to their low volatility. Further studies should include nitrogenous DBPs, given their important toxicity, and should assess the impact of water quality and ventilation on the presence of volatile DBPs in air.