Presence Of Residual Chlorine Research Articles

Ru/TiO2 Catalyzed High‐Yield Synthesis of Furanic Diols by 5‐Hydroxymethylfurfural Hydrogenation with Switchable Selectivity

Abstract5‐Hydroxymethylfurfural (HMF) is a versatile platform molecule that can be derived from biomass feedstocks and catalytically converted into various value‐added chemicals. In this work, selective hydrogenation of HMF is investigated to produce valuable furan‐based diols, namely 2,5‐bis‐hydroxymethylfuran (BHMF) and 2,5‐bis‐hydroxymethyltetrahydrofuran (BHMTHF), using TiO2 supported Ru catalysts. The catalyst performance was fine‐tuned to achieve over 98% yield to BHMF and BHMTHF under optimized reaction conditions with very good recyclability. We pointed out several key factors allowing to maximize the yield towards the respective diols. Features such as the Ru nanoparticle size, the strength of metal‐support interactions and the presence of residual chlorine were found to significantly influence the reaction. A characteristic volcano‐shaped relationship was obtained between the particle size and the catalytic activity giving the highest diol yield for an optimum Ru nanoparticle size of 1.6 nm. Further, metal‐support interactions were found to be responsible for providing optimum Ru‐TiOx interfacial surface sites and chlorine was affecting the electronic properties of Ru nanoparticles, potentially benefiting to the selective formation of BHMF. The reaction time was shown to control the hydrogenation of the furan ring and the selectivity of the reaction, that can be directed optimally towards BHMF or BHMTHF.

Chloro- and bromo-benzoquinone formation and transformation mechanisms in a drinking water-distribution system

Halogenated benzoquinones (HBQs) are frequently detected in tap water. HBQ levels are correlated with water age. As the water–transmission distance (water age) increases, the levels of bromo-benzoquinones (Br-BQs) decreased and those of chloro-benzoquinones (Cl-BQs) remained relatively stable in drinking water–distribution system in the presence of residual chlorine. 2,3,5,6-Tetrachloro-1,4-benzoquinone (TCBQ) and 2,6-dibromo-1,4-benzoquinone (DBBQ) were the most abundant Cl-BQ and Br-BQ, with maximum concentrations of 60.2 and 181.4 ng/L, respectively. TCBQ and DBBQ were chosen as representatives of HBQs to investigate their reactions with chlorine, including kinetics, pathways, and changes in toxicity. The hydrolysis and chlorination rates of HBQs were significantly pH-dependent, and the kinetic rates of DBBQ were faster than TCBQ in the pH range of 5–10. Chlorination converted highly toxic TCBQ and DBBQ to less-toxic chlorinated/brominated aliphatic disinfection by-products (DBPs), thereby reducing the overall toxicity of water bodies. This study provides comprehensive insights into the distinct life cycles of TCBQ and DBBQ in drinking water, covering formation, transformation, and toxicity. These findings provide a nuanced understanding of the risks posed by HBQs at various locations within the drinking water distribution system, offering valuable guidance for improving the control of DBPs in drinking water.

Substantial lifetime enhancement for Si-based photoanodes enabled by amorphous TiO2 coating with improved stoichiometry

Amorphous titanium dioxide (TiO2) film coating by atomic layer deposition (ALD) is a promising strategy to extend the photoelectrode lifetime to meet the industrial standard for solar fuel generation. To realize this promise, the essential structure-property relationship that dictates the protection lifetime needs to be uncovered. In this work, we reveal that in addition to the imbedded crystalline phase, the presence of residual chlorine (Cl) ligands is detrimental to the silicon (Si) photoanode lifetime. We further demonstrate that post-ALD in-situ water treatment can effectively decouple the ALD reaction completeness from crystallization. The as-processed TiO2 film has a much lower residual Cl concentration and thus an improved film stoichiometry, while its uniform amorphous phase is well preserved. As a result, the protected Si photoanode exhibits a substantially improved lifetime to ~600 h at a photocurrent density of more than 30 mA/cm2. This study demonstrates a significant advancement toward sustainable hydrogen generation.

English

This research investigates the microbial and physicochemical characteristics of five local hand dug wells used for drinking and agricultural activities in Blama, Small-Bo Chiefdom, in the Kenema District, Eastern Province of Sierra Leone. These five local hand-dug wells were randomly selected based on the availability of water in them throughout the year. The physical characteristics examined are: pH, turbidity, conductivity, temperature, total dissolve solid (TDS); and the chemical characteristics, such as: Residual chlorine (R. Chorine), magnesium, potassium, nitrite, iron, fluoride, ammonia, copper; and the microbial characteristics include: Total coliforms, fecal coliform and non-fecal coliform. Samples were collected in 500 ml sterilized plastic containers and transported to the laboratory, within 30 min. The results analysed indicate that the physical and chemical characteristic are within the WHO guideline limits for safe drinking water. However, a large amount of non-Faecal coliform was recorded in all the water samples analysed which exceed the World Health Organization standard for non-faecal coliform ((<10), and with no presence of residual chlorine. It can therefore be concluded that the water sample analyzed was potable and fit for drinking and agricultural activities. Key words: Hand-dug, well, local, safe and sample.

CFD based analysis of chlorination contact tank design

Chlorination is the most widely used technique for disinfecting water. Disinfection by chlorination inactivates pathogenic micro-organisms, preventing water-borne diseases. The design of a chlorination contact tank (CCT) requires precise residence time during which the chlorine passes through the tank and the consumption of a substantial quantity of chlorine during the disinfection process. The arrangements of baffles, as well as the inlet–outlet configurations, are also important which leads to the formation of a complex flow pattern causing the short-circuiting of the fluid flow and dead zone formation inside the CCT. Short-circuiting results in inefficient mixing, whereas, dead zones indicate the presence of residual chlorine in the tank. The objective of the present work is to report the preliminary results of the Computational Fluid Dynamics (CFD) analysis undertaken to investigate the hydrodynamics, turbulent transport and mixing inside the chlorination tank. Two different types of CCT geometry (rectangular and spiral) are considered for comparing the hydraulic and mixing efficiencies. Two-dimensional steady-state and time-variable numerical simulations are carried out. Species Transport modelling provides the distribution of residence time as well as chlorine concentration inside the tank. The presence of recirculation and dead zones in the chlorination tank are analysed from the velocity contour using image analysis. It was observed that amount of dead zones is significantly higher in the case of a rectangular tank when compared to a spiral one. Different hydraulic and mixing indexes were analysed in this study to compare the disinfection efficiency of the two tanks. The presence of secondary flow due to the centrifugal force facilitates the mixing process in spiral tanks.

Influence Mechanism of Cyanobacterial Extracellular Polymeric Substances on the Water Quality in Dynamic Water Supply System

As a kind of high-organic-content contamination source, extracellular polymeric substances (EPS) secreted by cyanobacteria have become an important factor restricting the safety of supply water. In the dynamic batch mode water supply system, cyanobacterial EPS accelerated the decay rate of residual chlorine, resulting in a 21–26 times increase of the total viable bacteria count within 72 h. The water turbidity exceeded upper limit of the standards for drinking water quality within 4 h, with an increase of 306–332% within 72 h. The biological stability was reduced with BDOC and AOC increased by 41.4–43.8% and 331–396%, respectively. The main cause is that cyanobacterial EPS act as nutrients and metabolic energy for microorganisms, promoting their metabolic activity and secretion of extracellular organic components. This leads to the metabolic accumulation of tryptophan, fulvic acids and humic acids in the pipeline, thus further promoting the regeneration of bacteria. Compared with the influence of biofilm on pipe wall caused by long-term use of water supply network, the contribution of cyanobacterial EPS to the water contamination of pipe network is increased several times. Therefore, even in the presence of residual chlorine, the secondary contamination caused by cyanobacterial EPS in the water supply system could not be neglected.

Effect of residual chlorine on iron particle formation considering drinking water conditions

In drinking water, residual chlorine is very likely to coexist with iron particles. However, the understanding of the effect of residual chlorine on iron particle formation in relation to different drinking water conditions is limited. Here, we found a significant competitive relationship between residual chlorine and dissolved oxygen (DO) during iron particle formation. Composition gave a good indicator of the extent of oxidation; with DO being the sole oxidant, the most abundant iron crystal in the particles formed was FeOOH (79.12%) followed by Fe3O4 (20.88%); in the presence of residual chlorine, however, the oxidation states of the iron crystals shifted upwards; the composition became as follows: FeOOH (50.64%), Fe3O4 (27.96%) and Fe2O3 (21.40%). The morphology of the particles formed showed interesting trends. In the presence of residual chlorine, the iron particles became denser and the specific surface area decreased. Particle size also exhibited a positive correlation with the chlorine concentration. The iron particle's specific surface areas formed with and without residual chlorine were 41.11m2/g and 61.30 m2/g, respectively. Linear regression also showed a good linear relationship between concentrations of iron ion and residual chlorine and the turbidity of the resulting water sample. Residual chlorine affects iron particle formation through different aspects, especially so when considering the interaction between residual chlorine with other oxidants and the resulting change in morphology. Runs of solutions with a high chlorine concentration through the pipe network could potentially act as a maintenance treatment.

A randomized, double-blind water taste test to evaluate the equivalence of taste between tap water and filtered water in the Taipei metropolis

High water quality and sufficient water availability are the main concerns of water users. Promoting the efficient use of tap water can contribute to sustainable drinking water management and progress towards Sustainable Development Goals. In many metropolises, water suppliers treat municipal water with appropriate treatment processes and well-maintained distribution infrastructure. Under this circumstance, it is acceptable that municipal water can be a source of drinking water. The presence of residual chlorine in tap water, connected to municipal water supply, inactivates pathogenic microorganisms and prevents recontamination. However, adding chlorine to tap water may affect the organoleptic properties of drinking water. On the other hand, the use of point-of-use (POU) water dispensers, which provides an additional treatment step on tap water, is not energy-efficient. A randomized, double-blind water taste test was conducted in the Taipei metropolis to assess whether tap water from public drinking fountains and filtered water from POU water dispensers have similar organoleptic properties. An odds ratio (OR) and the area under the receiver operating characteristic curve (AUC) were used to measure the participants’ ability to distinguish between the two water varieties. A five-region hypothesis test was conducted to test the OR, and a 95% bootstrap confidence interval of the AUC was calculated. The results of the study showed that the 95% five-region confidence interval of OR equal to (0.5, 1.49), and the 95% bootstrap confidence interval of AUC equal to (0.42, 0.56). These results implied that people in the Taipei metropolis could not distinguish between tap water and filtered water. It is recommended that more drinking fountains be installed and maintained fully functional and clean to achieve excellence in tap water access.

Bacterial community dynamics and disinfection impact in cooling water systems

Understanding the bacterial dynamics in cooling towers is imperative for the assessment of disinfection efficiency and management of microbial risks linked to aerosol formation. The objective of this study was to evaluate the impact of feed water on the cooling water bacterial microbiome and investigate the survival ability of its members when exposed to continuous chlorine disinfection. Water from an industrial cooling water system (2600 m3/h) was collected over a 5-month period at 3 locations along the feed water line and 3 locations in the cooling tower. ATP measurements suggested that the average ATP-per-cell in the cooling tower evolved independently from the average ATP-per-cell in the feed water. Flow cytometry and 16S rRNA gene amplicon sequencing were then combined to quantify the bacterial dynamics in the whole system. A mass balance based equation was established to determine net growth and net decay of the cooling tower bacterial communities in order to evaluate the impact of continuous chlorination (0.35–0.41 mg Cl2/L residual chlorine). The results indicated that cooling tower main community members were determined by the input feed water microbiome and the bacterial community structure was further shaped by varying decay rates of the microorganisms. Notably, the order Obscuribacterales showed to be growing in the cooling tower in the presence of residual chlorine up to 0.4 mg Cl2/L, with a recurrent net growth of 260 ± 95%, taking into account the impact of the concentration factor. This conclusion was only possible thanks to the systematic analysis described in this paper and generates discussion about the resistance of Obscuribacterales to residual chlorine. The described mass balance approach provides a high level of understanding on bacterial dynamics and should be considered for future characterization studies of cooling towers in which accurate investigation of microbiome changes is essential.

Understanding the impact of water distribution system conditions on the biodegradation of haloacetic acids and expression of bacterial dehalogenase genes

The objective of this study is to evaluate the influence of water distribution system conditions (pH, total organic carbon, residual chlorine, and phosphate) on haloacetic acids (HAAs) biodegradation. A series of batch microcosm tests were conducted to determine biodegradation kinetics and collected biomass was used for real time quantitative reverse transcription polymerase chain reaction analyses to monitor how these drinking water distribution system conditions affect the relative expression of bacterial dehalogenase genes. It was observed that tested water distribution system conditions affected HAA biodegradation with different removal efficiencies (0–100%). HAA biodegradation was improved in tested samples with TOC (3 mg/L) and pH 8.5 compared to those of TOC (0 mg/L) and pH 7, respectively. However, slight improvement was observed with the increased PO4 concentration (3.5 mg/L), and the presence of residual chlorine even at low concentration prohibited biodegradation of HAAs. The observed trend in the relative expression of dehII genes was compatible with the HAA biodegradation trend. Overall relative expression ratio of dehII genes was lower at pH 7, phosphate (0.5 mg/L), and TOC (0 mg/L) in comparison with pH 8.5, phosphate (3.5 mg/L), and TOC (3 mg/L) in the same experimental conditions.

Identification and characterization of phenylacetonitrile as a nitrogenous disinfection byproduct derived from chlorination of phenylalanine in drinking water

Unregulated disinfection byproducts (DBPs), including nitrogenous disinfection byproducts (N-DBPs), originating from chlorination of the precursor amino acid phenylalanine in aqueous systems, were identified in laboratory reactions and distributed tap. The major N-DBP identified was phenylacetonitrile, and minor DBPs of benzyl chloride, phenylacetaldehyde, 2-chlorobenzyl cyanide, and 2, 6-diphenylpyridine were also formed. Phenylacetonitrile was generated through decarboxylation, dechlorination and/or hydrolysis processes. With an aromatic structure, phenylacetonitrile has an unpleasant odor of various descriptors and an odor threshold concentration of 0.2 ppt-v as measured through gas chromatography-olfactometry. The half-life of phenylacetonitrile in reagent water and chlorinated water at 19 °C were 121 h and 792 h, respectively. The occurrence of phenylacetonitrile as an N-DBP in tap water was investigated for the first time; the results revealed that μg/L concentrations were present in nine different distributed drinking waters in China and the United States. Phenylacetonitrile deteriorates the aesthetic quality of drinking water and may present risk due to its prolonged existence in drinking water, especially in the presence of residual chlorine.

残留塩素共存下における亜硝酸態窒素の吸光光度定量

残留塩素共存下における亜硝酸態窒素の吸光光度定量

The Influence of Bromate Formation by Chlorination in Drinking Water

In order to prove the effect of bromate formation by chlorination in drinking water treatment process, by carrying out laboratory chlorination test in simulated water, Harbin drinking water and the Songhua River raw water samples, the influences of bromine ion be oxidated into bromate by chlorine were investigated. The results showed that when chlorine quantity was 5 mg/L, the conversion rate of bromide ion to bromate was less than 1.3%. On a large amount of chlorine (5 mg/L), significant bromate generation changes could not cause by the long-term existence of chlorine in the water, and the bromate concentration did not change significantly for a long period of time. In the conditions of high concentration of organic matter in water, the risk of bromate formation was low. When chlorine content reached 5 mg/L, a very small amount of bromate was detected in the raw water. New excessive risk caused by the presence of residual chlorine would not exist in the process of water supply.

Autocalibration of dynamic bacterial growth model for water distribution system using GA

The presence of residual chlorine and organic matter govern the bacterial regrowth within a water distribution system. The bacterial growth model is essential to predict the spatial and temporal variation of all these substances throughout the system. The parameters governing the bacterial growth and biodegradable dissolved organic carbon (BDOC) utilization are difficult to determine by experimentation. In the present study, the estimation of these parameters is addressed by using simulation-optimization procedure. The optimal solution by genetic algorithm (GA) has indicated that the proper combination of parameter values are significant rather than correct individual values. The applicability of the model is illustrated using synthetic data generated by introducing noise in to the error-free measurements. The GA was found to be a potential tool in estimating the parameters controlling the bacterial growth and BDOC utilization. Further, the GA was also used for evaluating the sensitivity issues relating parameter values and objective function. It was observed that mu and k(cl) are more significant and dominating compared to the other parameters. But the magnitude of the parameters is also an important issue in deciding the dominance of a particular parameter. GA is found to be a useful tool in autocalibration of bacterial growth model and a sensitivity study of parameters.

Supported Ru catalysts prepared by two sonication-assisted methods for preferential oxidation of CO in H2

The preferential oxidation (PROX) of CO in the presence of H(2) is an important step in the production of pure H(2) for industrial applications. In this report, two sonochemical methods (S1 and S2) were used to prepare highly dispersed Ru catalysts supported on mesoporous TiO(2) (TiO(2)(MSP)) for the PROX reaction, in which a reaction gas mixture containing 1% CO + 1% O(2) + 18% CO(2) + 78% H(2) was used. The supported Ru catalysts performed better than the supported Au and Pt catalysts, and the S1 and S2 methods are superior to the impregnation method. The Ru/TiO(2)(MSP) catalysts were active for the PROX reaction below 200 °C and good for the methanation reactions of CO and CO(2) above 200 °C. The presence of residual chlorine in the catalysts severely suppressed their PROX reaction activity, and a higher dispersion of Ru particles led to better catalytic performances. The addition of Au in the Ru/TiO(2)(MSP) catalyst also caused a poorer catalytic activity for both the PROX and the methanation reactions. TPR results showed that in the active catalysts prepared by the S1 and S2 methods, the well dispersed Ru particles, after calcination in air, had a stronger interaction with the support than those in the catalyst prepared by the impregnation method and in the Au-Ru/TiO(2)(MSP) catalyst. In situ CO absorption experiments performed with the diffusion reflectance Fourier transform infra red (DRIFT) method showed that the bridged adsorbed CO species on isolated Ru(0) sites correlated with the catalytic performances, indicating that these isolated Ru(0) sites are the most active sites of the Ru/TiO(2)(MSP) catalysts in the PROX reaction.

Factors influencing structure and catalytic activity of Au/Ce1−xZrxO2 catalysts in CO oxidation

The Au/Ce1−xZrxO2 (x=0, 0.25, 0.5, 0.75, 1) catalysts were synthesized by the direct anionic exchange (DAE) method, characterized by BET, SEM–EDS, XRD, TPR-CO, HRTEM, AAS, ToF-SIMS and tested in CO oxidation. The correlations between structural, redox and catalytic properties of Au/Ce1−xZrxO2 catalysts prepared using different synthesis procedures have been studied. The poisoning effect of residual chlorine on their catalytic performance was found. The agglomeration of Au particles during the calcination step in the presence of residual chlorine was observed. Its removal through the washing treatment both inhibited the sintering process and led to the increase in activity of the studied systems. The sequence of increasing activity was followed by the sequence of increasing reducibility of the catalysts. This shows the role of the support redox properties in the creation of the catalytic performance of supported Au nanoparticles in CO oxidation.

New electrophilic coupling reagents for spectrophotometric determination of residual chlorine in drinking water and environmental samples in micellar medium of cetylpyridinium chloride

Simple, sensitive and rapid spectrophotometric methods were developed for the determination of residual chlorine (RSC) in drinking water and environmental samples using phenoxazine (PNZ), an anticancer drug, as a chromogen and 4-nitro-2-(trifluoromethyl)aniline (NTA) or 2-chloro-4-(trifluoromethyl)aniline (CTA) as new electrophilic coupling reagents. In this method NTA or CTA is oxidized in the presence of RSC and subsequently coupled with PNZ to produce the red color dyestuff having λ max 520 nm. The formation of colored derivatives with the coupling agents is almost instantaneous and stable for 2 h. The methods are easy to operate and permit the determination of RSC with detection limits of 0.060 and 0.065 μg mL −1. The results indicated that by this method the fundamental interferences caused by non-target ions can be eliminated and the use of cetylpyridinium chloride as surfactant improved solubilization of red dyestuff and enhanced the selectivity and sensitivity of the methods. The methods were applicable to the determination of RSC in drinking, sewage, lake and well water samples up to nanogram level.

Formation of disinfection by-products and applicability of differential absorbance spectroscopy to monitor halogenation in chlorinated coastal and deep ocean seawater

Formation of disinfection by-products (DBPs) in chlorinated coastal (CS) and deep ocean (sampled at a 1500-m depth) seawater (DO) was explored using conventional chromatographic methods and differential absorbance spectroscopy. It was determined that trihalomethanes (THMs) predominated by bromoform, haloacetonitriles and haloacetic acids (HAA) form in chlorinated seawater. The yield of identified DBPs, especially THMs, was higher in CS, while in DO seawater the relative contribution of HAAs was almost four times higher than that of THMs. The fraction of consumed chlorine incorporated into the identified DBPs in DO natural organic matter (NOM) was much lower than that for coastal marine NOM, which was also more active in forming brominated DBPs. The kinetics of seawater chlorination was relatively rapid, and high levels of DBPs were released within the first 20–30 min of reaction. The kinetics of THMs and HAAs release could be approximated using a logarithmic function of reaction time. Absorbance measurements showed that chlorination caused the absorbance of DO and CS to decrease at wavelengths >250 nm. The features of the differential absorbance spectra of chlorinated seawater were close to those reported for drinking water, but their intensity was lower. The concentrations of CHBr 3, CHBr 2Cl and CHBrCl 2 formed in CS and DO chlorinated at varying chlorine doses and reaction times were well correlated with the corresponding — ΔA 272 and/or — ΔA 405 values. (The differential absorbance at 405 nm can be measured in the presence of residual chlorine). These results show that differential absorbance provides a number of sensitive surrogate parameters that can be used to monitor and quantify the formation of halogen-containing DBPs in seawater.

Gas-phase hydrogenation of o-xylene over Pt/alumina catalyst, activity, and stereoselectivity

The kinetics of the gas-phase hydrogenation of o-xylene over Pt/alumina catalysts was studied at 430–520 K, a hydrogen partial pressure of 0.19–0.36, and an o-xylene partial pressure of 0.04–0.10. The catalysts were characterized by H 2/ o-xylene TPD, H 2 chemisorption, energy-dispersive X-ray analysis, and XPS. The stereoisomers, cis- and trans-1,2-dimethylcyclohexane, were the only reaction products. A reversible maximum in the o-xylene hydrogenation activity vs temperature was observed; it was explained by a decrease in the surface concentration of o-xylene at higher temperatures. The hydrogenation rate was independent of the o-xylene concentration, whereas the reaction orders with respect to hydrogen varied from 0.9 to 3 in the temperature range investigated. The stereoselectivity of the products was found to depend on temperature, reactant concentrations, and platinum precursor. The catalyst prepared from a chlorine-containing precursor exhibited a lower hydrogenation activity and selectivity toward the trans isomer. Chlorine remained on the catalyst surface, even after reduction at 673 K. Dehydrogenation and configurational isomerization of cis- to trans-1,2-dimethylcyclohexane took place at the same time as hydrogenation. Dehydrogenation and configurational isomerization reactions are enhanced by the presence of residual chlorine on the catalyst surface. The reaction pathway is proposed.

Pseudomonas aeruginosa as an indicator of health risk in water for human consumption

During an outbreak of gastroenteritis in 28 children living in a small neighbourhood of Cuernavaca city (Mexico), a survey was performed to evaluate the confidence in coliform bacteria as sole indicators of potability of drinking waters. A primary infection by E. coli and a secondary by Pseudomonas aeruginosa was diagnosed in five of the children and the drinking water provided by a well was suspected as a transmission source. General and household distribution systems, household filters and bottled waters were evaluated for total and faecal coliforms, family Enterobacteriaceae, P aeruginosa and residual chlorine. In every sample, pathogenic/opportunistic bacteria were isolated even in the absence of coliforms and in the presence of residual chlorine. Arbitrarily assigned "pollution/risk levels" indicated that the most elevated risk was most frequently associated with storage in tanks and with bacterial colonisation in the pipeline system and commercial household filters where high levels of P aeruginosa were determined. A probability of correspondence between the presence of this bacterium and the secondary gastrointestinal infection diagnosed was found pointing towards a need for the inclusion of other microorganisms, one of which may be P aeruginosa, as indicators of health risk associated with drinking waters in Mexico.