Generation Of Trihalomethanes Research Articles

지표수에서 이산화염소 및 염소 복합소독에 의한 트리할로메탄 생성 평가

Due to its synergistic effects, sequential disinfection is considered a viable treatment option for the effective inactivation of pathogenic microorganisms that cannot be treated using the single-step application of chlorine-based disinfectants. This study systematically demonstrated the applicability of sequential disinfection with chlorine dioxide followed by chlorine to control disinfection byproducts. At pH 7,chlorine dioxide/chlorine treatment suppressed the formation of trihalomethanes (THMs) by 10.0% and 25.0% at temperatures of 10℃ and 20℃, respectively, compared to chlorine only. In addition, when using chlorine oxide/chlorine disinfection, a higher pH led to amore significant suppression of THMs production. It was also found that THMs production was lower as the chlorine dioxide dosage increased; in particular, the use of 1.2 mg/L and 5.0 mg/L chlorine dioxide at pH 9 had a substantial suppressive effect on THMs formation, with a reduction of 25.8% compared to chlorine only. Higher temperatures and a higher dissolved organic carbon concentration suppressed the generation of THMs in the chlorine dioxide/chlorine disinfection system compared with the chlorination alone.

Chlorine decay and disinfection by-products transformation under booster chlorination conditions: A pilot-scale study

Booster chlorination was usually employed in water distribution systems with a long hydraulic retention time. The free chlorine decay and disinfection by-products (DBPs) transformation under booster chlorination conditions were investigated within a pilot-scale water distribution system (WDS). Compared with the initial chlorination in water plants, the loss of chlorine was relatively slow and could be described with first-order kinetic model. The rate of chlorine decay and the generation of DBPs in WDS were much greater than those in beaker. High flow rate and the hydraulic transients both promoted chlorine decay and DBPs formation, especially for dichloroacetonitrile (DCAN). The formation of trihalomethanes (THMs) and haloacetic acids (HAAs) was higher in the ductile iron pipe than in the steel pipe. After booster chlorination, THMs, HAAs, and DCAN all climbed up and then declined continuously, but the peak times were different during the reaction process. The results showed the generation period of DBPs followed the order: THMs (27 h) > HAAs (22 h) > DCAN (5 h). DCAN was not stable in WDS and could be decomposed for a long hydraulic retention time (HRT). The decrease of dichloroacetic acid (DCAA) and increase of trichloroacetic acid (TCAA) indicated that DCAA may turn into TCAA. Linear relationships between the free chlorine demand (FCD) and the generation of THMs that considered both buck water and the pipe wall, as well as the different hydraulic conditions, were established to predict the formation of DBPs in WDS after booster chlorination.

Pilot-scale electrochemical disinfection of surface water: assessing disinfection by-product and free chlorine formation

Electrochemical disinfection of surface water using mixed metal oxide anodes was evaluated in a pilot-scale demonstration. Disinfection rates, chlorine generation, energy demand, and generation of disinfection by-products were monitored over the 190-day study. Particular attention was given to the generation of trihalomethanes (THMs) and haloacetic acids (HAAs) during the electrochemical treatment cycle. In addition, the potential for generation of THMs and HAAs during post-treatment storage of the water was assessed. The electrochemical treatment system resulted in a 2- to 3-log removal of total heterotrophic bacteria, with values below detection (<1 CFU/mL) often observed. Disinfection occurred with only very low levels of observed chlorine generation (<0.1 mg/L), suggesting that alternate disinfection mechanisms likely played a significant role in the observed removal of bacteria. THM and HAA concentrations after treatment were consistently well below regulatory levels. Results also showed that electrochemical treatment significantly reduced the formation of bromoform when the water received subsequent exposure to hypochlorite. Removal of naturally occurring bromide in the water by the electrochemical system may have been the cause (in part) for this observed mitigation of bromoform formation. The formation of calcium scale on the cathode surface over time was the primary operational challenge.

Ternary Model of the Speciation of I-/Br-/Cl-Trihalomethanes Formed in Chloraminated Surface Waters.

This study examined the effects of the iodide concentration and pH on yields and speciation of the entire group of 10 species of iodine-, bromine-, and chlorine-containing trihalomethanes (THMs) formed at pH values from 6.5 to 8.5 in chloraminated surface waters in the presence of bromide and iodide. Pathways of iodine, bromine, and chlorine incorporation in the active sites in dissolved organic matter (DOM) were examined on the basis of a ternary halogenation/THM speciation model. The model assumed the occurrence of sequential three-step halogenation of the active site and competition of iodine, bromine, and chlorine species at each node of the halogenation sequence. A comparison of experimentally measured and modeled speciation coefficients and also iodine and bromine incorporation factors calculated for 10 THM species showed that the developed approach was sufficient to closely model the observed trends. Interpretation of preferred iodine incorporation pathways associated with the generation of THMs in all examined conditions showed that the susceptibility of the halogenated intermediates to iodine incorporation increases rapidly with the number of iodine atoms that have already been incorporated into the reaction site. In contrast, the incorporation of bromine and chlorine atoms in the intermediates involved in the generation of THMs makes them largely inactive in iodine incorporation reactions. The presented approach allows for a further understanding of the mechanisms of DOM/halogen interactions and prediction of the speciation of THMs formed at varying pH values, iodide concentrations, and other system conditions.

Pilot-scale spiral wound membrane assessment for THM precursor rejection from upland waters

ABSTRACTThe outcomes of a pilot-scale study of the rejection of trihalomethanes (THMs) precursors by commercial ultrafiltration/nanofiltration (UF/NF) spiral-wound membrane elements are presented based on a single surface water source in Scotland. The study revealed the expected trend of increased flux and permeability with increasing pore size for the UF membranes; the NF membranes provided similar fluxes despite the lower nominal pore size. The dissolved organic carbon (DOC) passage decreased with decreasing molecular weight cut-off, with a less than one-third the passage recorded for the NF membranes than for the UF ones.The yield (weight % total THMs per DOC) varied between 2.5% and 8% across all membranes tested, in reasonable agreement with the literature, with the aromatic polyamide membrane providing both the lowest yield and lowest DOC passage. The proportion of the hydrophobic (HPO) fraction removed was found to increase with decreasing membrane selectivity (increasing pore size), and THM generation correlated closely (R2 = 0.98) with the permeate HPO fractional concentration.

Evaluation of drinking water quality produced by ultrafiltration membranes in distribution systems

The final quality of the drinking water in the consumers’ tap depends on the purification treatment applied, but also on its route through the drinking water distribution system (DWDS). This study assesses the quality of water treated by ultrafiltration membranes in a DWDS at a pilot scale in order to determine how possible network fouling affects drinking water quality, with special interest in natural organic matter, trihalomethanes (THM) and biofilm. Two different configurations were tested: an initial stage with an ultrafiltration (UF) system and a subsequent stage with coagulation-hydraulic flocculation (CF) pretreatment coupled to the UF. Although CF pretreatment helped reduce the dissolved organic matter (DOM) of the effluent that passed through the UF system, the high concentration of DOM promoted the fouling of the DWDS by organic matter deposits. This, together with the increase in water temperature in DWDS, allowed the adhesion of bacteria on the inner pipeline surface, encouraging the formation of a biofilm. Finally, despite the high concentration of DOM, THM generation was negligible throughout the study.

The Trihalomethanes Formation Potential in Treated Waters Exposed to Ozone and Chlorine

The present study was implemented to investigate the trihalomethanes formation potential (THMFP) in drinking water treatment and to determine the impact of preozonation on the reduction of Trihalomethanes (THMs). The full-scale examination was carried out, using Luan River as the raw water. Two different preoxidation methods, prechlorination and preozonation were performed. THMFP and THM species were analyzed. The investigation indicated that 18.72% of THMFP was removed during preozonation. Further study on the distribution of THM species showed a significant reduction of Chloroform and bromodichloromethane, 20.62% and 17.39% during preozonation, respectively. The result suggested that the application of preozonation process is an effective method for reducing THMs generation in drinking water treatment. In the final effluent, the total removal rates of THMFP were 47.49% after preozonation and 55.67% after prechlorination.

Cross-contamination of Escherichia coli O157:H7 is inhibited by electrolyzed water combined with salt under dynamic conditions of increasing organic matter

Water can be a vector for foodborne pathogen cross-contamination during washing of vegetables if an efficient method of water disinfection is not used. Chlorination is the disinfection method most widely used, but it generates disinfection by-products such as trihalomethanes (THMs). Therefore, alternative disinfection methods are sought. In this study, a dynamic system was used to simulate the commercial conditions of a washing tank. Organic matter and the inoculum of Escherichia coli O157:H7 were progressively added to the wash water in the washing tank. We evaluated the effectiveness of the electrolyzed water (EW) when combining with the addition of salt (1, 0.5 and 0.15 g/L NaCl) on the pathogenic inactivation, organic matter depletion and THM generation. Results indicated that electrolysis of vegetable wash water with addition of salt (0.5 g/L NaCl) was able to eliminate E. coli O157:H7 population build-up and decrease COD accumulation while low levels of THMs were produced.

Minimum free chlorine residual level required for the inactivation of Escherichia coli O157:H7 and trihalomethane generation during dynamic washing of fresh-cut spinach

Abstract Even though chlorination of wash water in the fresh-cut industry is a common practice, little is known about the minimum free chlorine residual level required to keep water free from foodborne pathogens and its concomitant generation of disinfection by-products. This work aimed to provide insight to these issues. Two kinds of tests were performed to simulate a fresh-cut industry washing tank of spinach. In the first, a washing tank containing clean water was continuously filled with concentrated process wash water with high organic matter obtained from spinach and inoculated with an Escherichia coli O157:H7 cocktail (5 log CFU/ml). A peristaltic pump dosed a chlorinated solution to the washing tank during the test in order to adjust free chlorine (FC) concentration to 1 and 3 mg/l. In the second test, the washing tank already contained process wash water from the beginning of the experiments and the FC concentration was adjusted to 3 and 5 mg/l. Results showed that the maintenance of a FC concentration of ca. 5 mg/l (until a maximum of 7 mg/l) during washing of fresh-cut spinach kept the wash water free from the pathogen during one hour although trihalomethane levels > 1000 μg/l were generated. Results indicate that a minimum residual level of ca. 7 mg/l FC is an effective treatment to inactivate E. coli O157:H7 under industrial conditions. Validation of sanitizer efficacy by using a dynamic system might facilitate the implementation of selected treatments in the food industry.

Electrochemical treatment of reverse osmosis concentrate generated by the leather industry using a Cu–graphite electrode

Electrochemical treatment of reverse osmosis concentrate (ROC) generated by the leather industry was evaluated using a copper coated graphite (Cu–graphite) electrode for the elimination of refractory organic pollutants. The effect of dilution of the ROC and applied current density on the performance of electrochemical oxidation was investigated. The presence of chloride ions in the ROC favoured the complete elimination of TKN and COD removal by 98% at optimum conditions: current density, 100 mA cm−2 and electrolysis period, 6 h. The increase in ROC dilution slightly decreased the percentage removal of COD from 98% to 96%. The effect of current density on the removal of COD and TKN in raw ROC was found to be lower than in more diluted ROC. It was concluded that electrochemical treatment was more favourable for ROC samples without dilution. The generation of trihalomethanes during the electrochemical oxidation of ROC was effectively removed in an activated carbon packed bed column.

Generation of trihalomethanes with chlorine-based sanitizers and impact on microbial, nutritional and sensory quality of baby spinach

The potential generation of trihalomethanes (THMs) during washing of vegetable products as a consequence of the use of chlorine has become one of the main concerns for researchers, industry and regulatory agencies. However, only scarce information is known about the actual THM formation in process wash water and in the final product to establish the real risks associated with it. The aim of this work was to evaluate the THM formation in process wash water after washing baby spinach with chlorine-based sanitizers such as sodium hypochlorite and electrolyzed oxidizing water with and without the addition of salt (EOW+NaCl and EOW, respectively). Additionally, the impact of these chlorine-based sanitizers on the microbial, nutritional and sensory quality of baby spinach was compared with a non-chlorine based sanitizer such as peroxyacetic acid. The total THM levels of the process wash water treated with sodium hypochlorite and EOW+NaCl were over the authorized limit fixed by the European legislation and USEPA (100 and 80μgL−1, respectively) for drinking water. However, the THM levels after treatment with EOW did not exceed these established limits. In baby spinach, THMs were detected in low levels in sodium hypochlorite and EOW washed samples because the rinsing step reduced them to levels below the detection limit. Chlorine and non-chlorine based sanitizers such as peroxyacetic acid, did not affect the quality and shelf-life of the product. After washing and during storage in modified atmosphere packaging, similar headspace gas concentrations, microbial and sensory quality, instrumental texture and colour measures and electrolyte leakage were observed for all sanitizers. The results provide evidence that, under these specific experimental conditions, chlorine-based sanitizers do not represent a risk for THM formation during baby spinach leaf processing. In our opinion, current experimental data does not support banning the use of chlorine-based sanitizers in the fresh-cut vegetable industry because of THM generation in commodities such as spinach.

A Simple and Semi-Empirical Model to Predict THMs Generation in Water Facilities Including pH Effects

Abstract This work presents a study focused on the development of a simple useful tool to predict the generation of trihalomethanes in drinking water purification systems, using two precursors and trichloromethane as model compounds through a simple chlorine decay model. This work proposed a semiempirical model without adjustable power parameters where fast and slow stages and the effect of pH were included. Despite that the model is not based in a complete kinetic scheme, using the proposed equations it is possible to predict the simultaneous evolution of chlorine and TCM with a set of linear kinetics parameters which characterize the system and will be obtained using simple routine laboratory measurements. The results show that both TCM formation and chlorine decay are strongly dependent on the chemical nature of the model precursor. Although resorcinol and phenol have different reactivity with chlorine and represent different functional groups which are present in natural compounds, the TCM generation appears to be properly described in both cases by the total chlorine consumption. Considering that during the potabilization processes the pH changes, the study of the effects of this variable is very important to achieve the minimization of THMs generation. The pH has a significant effect on the time evolution of chlorine-substituted hydroxybenzene intermediates and therefore on the TCM formation, since the properties of the reacting species are directly affected by the reaction medium for their participation in the different reaction paths. The study of the distribution and selectivity of the intermediate species allowed explaining the results obtained for the kinetics of formation of TCM. The results suggest that in order to understand the effect of pH, the nature of oxidation of HOCl and ClO‒, should be considered simultaneously with the electronegative nature of the precursor compounds. Finally, in terms of minimizing the generation of THM it is important to consider the potential impact of pH changes within the water treatment process and supply and the stages where chlorination may be carried out.

Significant decrease of THMs generated during chlorination of river water by previous photo-Fenton treatment at near neutral pH

► THMs generation decrease by reducing NOM concentration prior to the chlorination step. ► Photo-Fenton process at neutral pH is effective system for the NOM degradation. ► Solar photo-Fenton process can be used to obtain at low cost drinking water safe. An important issue in chlorine drinking water disinfection is the generation from natural organic matter (NOM) of disinfection by-products (DBPs), especially trihalomethanes (THMs). The THMs generation can be limited by reducing the levels of NOM prior to the chlorination step. Herein, photo-Fenton system under solar simulator degraded humic acid solutions (as NOM model compounds), as well as NOM contained in river water (Pance River, Cali-Colombia), and dramatically reduced THMs formation during the subsequent chlorination step. In both cases the initial pH of treated water was near to 7. In no pre-treated river water 100–160 μg/L of THMs are formed during chlorination while values of 20–60 μg/L were reached in water previously treated for 4 h by neutral photo-Fenton under solar simulator. The decrease in the generated THMs/total organic carbon ratio suggests that mainly the NOM fraction sensitive to THMs formation was photo-degraded. Therefore, the neutral photo-Fenton reagent could be implemented as a technological option for NOM removal for limiting THMs formation during a subsequent chlorination step.

Humic acids removal by aerated spiral-wound ultrafiltration membrane combined with coagulation–hydraulic flocculation

An aerated spiral-wound ultrafiltration membrane system (ASWUF) combined with coagulation–hydraulic flocculation was tested with a view to evaluating its efficiency as a system for removing humic acids (HA). The tests were carried out at pilot scale, using FeCl 3 as a coagulant. The ASWUF was equipped with polyethersulphone membranes (molecular weight cut-off of 50 kDa). The system was fed with reservoir water, to which different concentrations of HA (1–30 mg/l) were added. HA removal capacity of the ASWUF varied according to the molecular weight (MW) of the HA, and performance never exceeded 41% as dissolved organic carbon (DOC). However, coagulation–flocculation combined with ASWUF achieved results of approximately 90% for HA concentrations of up to 30 mg/l. Coagulation–flocculation as pretreatment for ASWUF makes it possible to remove HA with a low MW, without having to modify the pH of the water. This efficiency led to a decline in the specific UV absorbance (SUVA) of the effluent, which therefore presented a lower risk of trihalomethane (THM) generation after post-chlorination. Final effluent HA concentration was the main conditioning factor for THM generation. However, it was noted that the fraction of HA persisting after treatment generated a higher concentration of THM per unit of DOC.

Factorial analysis of the trihalomethane formation in the reaction of colloidal, hydrophobic, and transphilic fractions of DOM with free chlorine

This study focuses on the factors that affect trihalomethane (THMs) formation when dissolved organic matter (DOM) fractions (colloidal, hydrophobic, and transphilic fractions) in aqueous solutions were disinfected with chlorine. DOM fractions were isolated and fractionated from filtered lake water and were characterized by elemental analysis. The investigation involved a screening Placket-Burman factorial analysis design of five factors (DOM concentration, chlorine dose, temperature, pH, and bromide concentration) and a Box-Behnken design for a detailed assessment of the three most important factor effects (DOM concentration, chlorine dose, and temperature). The results showed that colloidal fraction has a relatively low contribution to THM formation; transphilic fraction was responsible for about 50% of the chloroform generation, and the hydrophobic fraction was the most important to the brominated THM formation. When colloidal and hydrophobic fraction solutions were disinfected, the most significant factors were the following: higher DOM fraction concentration led to higher THM concentration, an increase of pH corresponded to higher concentration levels of chloroform and reduced bromoform, higher levels of chlorine dose and temperature produced a rise in the total THM formation, especially of the chlorinated THMs; higher bromide concentration generates higher concentrations of brominated THMs. Moreover, linear models were implemented and response surface plots were obtained for the four THM concentrations and their total sum in the disinfection solution as a function of the DOM concentration, chlorine dose, and temperature. Overall, results indicated that THM formation models were very complex due to individual factor effects and significant interactions among the factors. In order to reduce the concentration of THMs in drinking water, DOM concentrations must be reduced in the water prior to the disinfection. Fractionation of DOM, together with an elemental analysis of the fractions, is important issue in the revealing of the quality and quantity characteristics of DOM. Systematic study composed from DOM fraction investigation and factorial analysis of the responsible parameters in the THM formation reaction can, after an evaluation of the adjustment of the models with the reality, serves well for the evaluation of the spatial and temporal variability in the THM formation in dependence of DOM. However, taking into consideration the natural complexity of DOM, different operations and a strict control of them (like coagulation/flocculation and filtration) has to be used to quantitatively remove DOM from the raw water. Assuming that this study represents a local case study, similar experiments can be easily applied and will supply with relevant information every local water treatment plant meeting problems with THM formation. The coagulation/flocculation and the filtration stages are the main mechanisms to remove DOM, particularly the colloidal DOM fraction. With the objective to minimize THMs generation, different unit operation designed to quantitatively remove DOM from water must be optimized.

Survey Study of Trihalomethane Generation and Fate at 25 Municipal Wastewater Treatment Plants in North Carolina

Survey Study of Trihalomethane Generation and Fate at 25 Municipal Wastewater Treatment Plants in North Carolina

An analysis of stay-in-pipe time in water distribution network for an estimation of THM generation

This paper presents a mathematical approach for the analysis of trihalomethane (THM) generation and its spread in water distribution network. THM is a carcinogenic substance, which is produced principally from chlorine and some THM precursors, whereas chlorination of water in purification plants is an indispensable process. Therefore it is important to know when, where and how much THM will be generated in distribution network that has an exceedingly complex structure. In this paper, we propose a mathematically analyzing system of THM generation and its spread that consists of four functional componets, which are a pipe network analysis, an analysis of stay-in-pipe time of water, an estimation of THM generation, and an analysis of THM spreading. We describe in detail the new algorithm to calculate stay-in-pipe time of water, which is needed in the estimation of THM generation, and show a numerical experiment for the proposing algorithm.

Formation of Trihalomethanes during Production of Bean-Curd.

Trihalomethanes such as chloroform, dichlorobromomethane, dibromochloromethane and bromoform in food, which might be produced by the treatment of foods with sodium hypochlorite, were determined by the distillation method. The distillation method was modified for the extraction of trihalomethanes from foods containing lipids and/or proteins. Trihalomethanes in the commercially available bean-curd were determined in the range of 19.8 to 53.5 ppb, although they were not detected in ice candy and pickles. The amount of chloroform in the bean-curd increased with an increase in concentration of sodium hypochlorite used for treatment and in storage temperature. The amount of chloroform produced in the Kinu bean-curd was greater than that produced in the Momen bean-curd. In the bean-curd treated with hypochlorite a large amount of trihalomethanes was generated. On the other hand, in the bean-curd treated with chlorine dioxide or chlorite trihalomethanes were hardly generated. This fact recommends the use of chlorine dioxide or chlorite instead of sodium hypochlorite for the disinfection of food. The use of hypochlorite should be prohibited, because the hypochlorite treatment caused the generation of trihalomethanes in food.

Health risks for infants caused by trihalomethane generation during chemical disinfection of feeding utensils†

A simple pouring out of “baby‐bottles” after disinfection with hypochlorite solution results in an average residual volume of about 2 ml per bottle. Subsequent preparation of baby food in the contaminated bottles leads to the generation of halogenated organic compounds. The volatile fraction of these compounds was analyzed by gas chromatography in various baby foods after the disinfection procedure. The generated volatile halogenated organic compounds mainly consisted of trihalomethanes. An estimate of the dose ingested by infants is given and the resulting health risk is discussed. Alternatives to chemical disinfection are proposed.