Disinfectant Dose Research Articles

An Analytical Model for the Decontamination of Water Distribution Systems Using Slug‐Feed Method of Disinfection

AbstractThe increasing risk of intentional, negligent, or accidental intrusion of biological, chemical, or radioactive contaminants in water distribution systems is becoming a major concern that has significant and adverse impacts on public health. As such, it is important to have an effective, robust, and flexible plan that can be readily implemented to minimize the impact of these contamination events. However, limited research has been focused on the strategic planning of the decontamination process of the contaminated infrastructure. This paper proposes an analytical method for modeling the slug‐feed method of disinfection given the drainage and disinfectant dosage profiles. The efficacy of the proposed method has been demonstrated by using it as the evaluation function in a genetic algorithm optimization of two case studies. Results show the proposed method exhibits higher robustness compared to the procedures defined in the current standard and literature. The main contributions of this study are to (1) provide a robust and accurate model to describe the slug‐feed method of disinfection, (2) offer additional resource utilization flexibility for water authorities, and (3) providing additional levels of district metered areas prioritization.

Використання гіпохлориту натрію при знезаражуванні води басейну спортивного комплексу національного технічного університету (СК НТУ)

This article is about the importance of sanitary and hygienic examination of water complexes, in particular, swimming pools and water parks. There is an increasing demand for visiting such water complexes in Ukraine, both for sports activities and for leisure activities. The focus of this article is on the sanitary and hygienic examination and survey of pool water, which is treated with sodium hypochlorite (obtained by chemical way). Material and methods. The studies were carried out for 10 weeks, including a series of water samples, which were taken during the quarantine period, when swimmers were prohibited from visiting the pool. This situation made possible to make a comparative hygienic assessment of the effect of workload on the water condition in the pool and the effectiveness of disinfection. There was also a short review and characteristics of hypochlorite A, which was obtained in chemical way, its advantages and disadvantages as a disinfectant. The article analyzes the data obtained during the sanitary and hygienic survey of the pool of the swimming pool of the national technical university, their statistical processing, and comparison with the current regulatory documents of Ukraine and some other states. The data obtained in the course of a series of studies indicated a significant human influence on the state of water in the pool, which once again indicates the importance of health education of the population and visitors in swimming pools and water parks, in particular, the need to take a shower before swimming, after using the toilet, etc.; the need for training the right culture of visiting different water objects. Particular attention should be paid to swimming pools frequented by children, as they often do not have sufficient hygiene skills, or due to age cannot constantly monitor urination, so, as a rule, it`s an acute issue of large amounts of chloramines in swimming pools for children. Conclusion. In particular, a statistically significant difference was obtained in terms of ammonia and ammonium ions (in total), which indicated a significant influence of visitors on this parameter. And, as you know, organic impurities (sweat, urine, cosmetics remains etc.) that get into the water together with the swimmers, react with chlorine and form chloramines, which can negatively affect the health of both the visitors and the staff. This must be taken into account while changing the workload on the pool and choosing the dose of disinfectant

Electrochemical Disinfection in Water and Wastewater Treatment: Identifying Impacts of Water Quality and Operating Conditions on Performance.

Electrochemical disinfection—a method in which chemical oxidants are generated in situ via redox reactions on the surface of an electrode—has attracted increased attention in recent years as an alternative to traditional chemical dosing disinfection methods. Because electrochemical disinfection does not entail the transport and storage of hazardous materials and can be scaled across centralized and distributed treatment contexts, it shows promise for use both in resource limited settings and as a supplement for aging centralized systems. In this Critical Review, we explore the significance of treatment context, oxidant selection, and operating practice on electrochemical disinfection system performance. We analyze the impacts of water composition on oxidant demand and required disinfectant dose across drinking water, centralized wastewater, and distributed wastewater treatment contexts for both free chlorine- and hydroxyl-radical-based systems. Drivers of energy consumption during oxidant generation are identified, and the energetic performance of experimentally reported electrochemical disinfection systems are evaluated against optimal modeled performance. We also highlight promising applications and operational strategies for electrochemical disinfection and propose reporting standards for future work.

Soft sensor predictor of E. coli concentration based on conventional monitoring parameters for wastewater disinfection control

Real-time acquisition of indicator bacteria concentration at the inlet of disinfection unit is a fundamental support to the control of chemical and ultraviolet wastewater disinfection. Culture-based enumeration methods need time-consuming laboratory analyses, which give results after several hours or days, while newest biosensors rarely provide information about specific strains and outputs are not directly comparable with regulatory limits as a consequence of measurement principles.In this work, a novel soft sensor approach for virtual real-time monitoring of E. coli concentration is proposed. Conventional wastewater physical and chemical indicators (chemical oxygen demand, total nitrogen, nitrate, ammonia, total suspended solids, conductivity, pH, turbidity and absorbance at 254 nm) and flowrate were studied as potential predictors of E. coli concentration relying on data collected from three full-scale wastewater treatment plants. Different methods were compared: (i) linear modeling via ordinary least squares; (ii) ridge regression; (iii) principal component regression and partial least squares; (iv) non-linear modeling through artificial neural networks.Linear soft sensors reached some degree of accuracy, but performances of the artificial neural network based models were by far superior. Sensitivity analysis allowed to prioritize the importance of each predictor and to highlight the site-specific nature of the approach, because of the site-specific nature of relationships between predictors and E. coli concentration. In one case study, pH and conductivity worked as good proxy variables when the occurrence of intense rain events caused sharp increases in E. coli concentration. Differently, in other case studies, chemical oxygen demand, total suspended solids, turbidity and absorbance at 254 nm accounted for the positive correlation between low wastewater quality and E. coli concentration. Moreover, sensitivity analysis of artificial neural network models highlighted the importance of interactions among predictors, contributing to 25 to 30% of the model output variance. This evidence, along with performance results, supported the idea that nonlinear families of models should be preferred in the estimation of E. coli concentration.The artificial neural network based soft sensor deployment for control of peracetic acid disinfectant dosage was simulated over a realistic scenario of wastewater quality recorded by on-line sensors over 2 months. The scenario simulations highlighted the significant benefit of an E. coli soft sensor, which provided up to 57% of disinfectant saving.

Water Stagnation and Flow Obstruction Reduces the Quality of Potable Water and Increases the Risk of Legionelloses

Legionella is an opportunistic waterborne pathogen associated with Legionnaires' disease and Pontiac fever. Despite improved public awareness, the incidence of Legionella associated infections has been increasing. Aerosols generated from engineered potable water systems are a demonstrated cause of both nosocomial and community-acquired legionellosis. The ecology of Legionella in these systems is complex with multiple factors impacting their colonization and persistence. Flow dynamics has been identified as an important factor and stagnation in cooling towers is an accepted risk for increased Legionella growth; however, less is known about the impact of flow dynamic on Legionella in potable water systems. This is especially complex due to the inherent intermittent and variable usage observed within outlets of a potable water system. This systematic literature review examines the role of fluid dynamics and stagnation on the colonization and growth of Legionella in potable water systems. Twenty two of 24 identified studies show a positive association between stagnation zones and increased colonization of Legionella. These zones included dead legs, dead ends, storage tanks, and obstructed water flow (such as intermittent usage or flow restriction). Prolonged stagnation in building plumbing systems also deteriorates the quality of thermally or chemically treated potable water. This stimulates the colonization of Legionella established biofilms. Such biofilms are intrinsically resistant to disinfection procedures and accelerate the rate of decay of chemical disinfectants. Sub-lethal doses of disinfectants and the presence of protozoan hosts in stationary water promote generation of viable but non-culturable Legionella cells. This results in false negatives in surveillance methods that use culture methodology. In conclusion, elimination of temporal and permanent stagnation points can improve the quality of potable water, efficacy of disinfectants, and reduce the risk of legionellosis. Current guidelines and water safety plans recognize the risks associated with permanent stagnation point (dead ends and dead legs); however, there is a need for greater emphasis on controlling temporal stagnation arising from intermittent usage.

Efficient synergistic disinfection by ozone, ultraviolet irradiation and chlorine in secondary effluents

Disinfection of secondary effluents is vital to provide a sustainable aquatic environment, minimize microbial risks and guarantee public and environmental safety. This study investigated the effectiveness of six treatment trains including single and combined disinfection processes (i.e., ozone alone, ultraviolet (UV) irradiation alone, chlorine alone, sequential ozone-UV, sequential ozone-chlorine and sequential ozone-UV-chlorine) on bacterial inactivation, as well as bulk water quality parameters such as color, turbidity, absorbance at 254 nm (UV254), dissolved organic carbon (DOC) and fluorescence based on samples collected from an actual water reclamation plant (WRP). For the single disinfection processes, when the ozone, UV and chlorine doses reached 5 mg/L, 15 mJ/cm2 and 4 mg/L, respectively, the log removal of Escherichia coli (E. coli) reached 5 log. A trailing phenomenon was observed with further increases in the disinfectant dosage. Under the combined treatment scenarios, ozone pretreatment resulted in substantial removal of color, turbidity, UV254, fluorescence excitation-emission matrix (FEEM) and chlorine consuming organics, thus enhancing the efficiency of subsequent UV irradiation or chlorine treatments. In the sequential ozone-UV-chlorine experiments, E. coli inactivation reached 7 log with ozone, UV and available chlorine of 3 mg/L, 5 or 10 mJ/cm2 and 2.5 mg/L, respectively. On the basis of the results from the actual WRP, the estimated operating cost per unit for the disinfection systems is 0.065 CNY/t, which is economical for long-term operation.

Tetracycline antibiotics as precursors of dichloroacetamide and other disinfection byproducts during chlorination and chloramination

Pollution of natural water and even source water with pharmaceuticals is problematic worldwide and raises concern about the possibility of disinfection byproduct (DBP) formation during subsequent water treatment. In this study, the formation of DBPs, especially dichloroacetamide (DCAcAm), was investigated during chlorination and chloramination of tetracyclines, which are a class of broad-spectrum antibiotics. DBPs including DCAcAm were formed during chlorination and chloramination of tetracycline (TC). Although the concentrations and theoretical cytotoxicity of the DBPs formed from TC were affected by the contact time, disinfectant dose, and pH, DCAcAm was the main contributor determining the yields and cytotoxicity of the measured DBPs. The DCAcAm yields from four tetracycline antibiotics ranged from 0.43% to 54.26% for chlorination. For chloramination, the DCAcAm yields reached 44.57%, and the nitrogen in DCAcAm mainly came from tetracycline antibiotics rather than chloramines. ClO2 pre-oxidation and UV photolysis decreased DCAcAm formation during chlorination and chloramination of TC. The high yields observed in this study suggest that tetracycline antibiotics are possible precursors of DCAcAm.

SARS-CoV-2 coronavirus in water and wastewater: A critical review about presence and concern

The presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in water and wastewater has recently been reported. According to the updated literature, the stools and masks of the patients diagnosed with coronavirus disease (COVID-19) were considered as the primary route of coronavirus transmission into water and wastewater. Most coronavirus types which attack human (possible for SARS-CoV-2) are often inactivated rapidly in water (i.e., the survival of human coronavirus 229E in water being 7 day at 23 °C). However, the survival period of coronavirus in water environments strongly depends on temperature, property of water, concentration of suspended solids and organic matter, solution pH, and dose of disinfectant used. The World Health Organization has stated that the current disinfection process of drinking water could effectively inactivate most of the bacterial and viral communities present in water, especially SARS-CoV-2 (more sensitive to disinfectant like free chlorine). A recent study confirmed that SARS-CoV-2 RNA was detected in inflow wastewater (but not detected in outflow one). Although the existence of SARS-CoV-2 in water influents has been confirmed, an important question is whether it can survive or infect after the disinfection process of drinking water. To date, only one study confirmed that the infectivity of SARS-CoV-2 in water for people was null based on the absence of cytopathic effect (CPE) in infectivity tests. Therefore, further studies should focus on the survival of SARS-CoV-2 in water and wastewater under different operational conditions (i.e., temperature and water matrix) and whether the transmission from COVID-19-contaminated water to human is an emerging concern. Although paper-based devices have been suggested for detecting the traces of SARS-CoV-2 in water, the protocols and appropriate devices should be developed soon. Wastewater and sewage workers should follow the procedures for safety precaution against SARS-CoV-2 exposure.

Optimization of disinfectant dosage for simultaneous control of lead and disinfection-byproducts in water distribution networks

Drinking water utilities are increasingly facing the challenges of maintaining water quality, and simultaneously complying with conflicting regulatory standards. One such challenge is the dosage of chlorine-based disinfectants which is typically regulated to prevent microbial growth in the water distribution systems, while limiting disinfection by-products (DBPs). On the other hand, chlorine residuals also influence the dissolution of lead into drinking water from corrosion scales in the pipe internals, as has been shown by previous studies. Hence, it is important to consider water lead levels (WLLs) while determining the appropriate chlorine dosage. This study proposes a multi-objective optimization framework to understand and balance the trade-offs between (i) minimizing total disinfectant dosage to reduce DBPs formation potential, and (ii) maximizing the volume of safe drinking water supply with respect to both WLLs and residual free chlorine concentrations. The approach comprises of the development of a dynamic simulation-optimization framework to account for the impact of spatial and temporal variations of network hydraulics and water chemistry on WLLs and residual free chlorine. The framework couples dynamic multi-species water quality simulations (pH, residual free chlorine, dissolved inorganic carbon, and orthophosphate concentration) with a multi-objective genetic optimization algorithm in an integrated MATLAB-EPANET-MSX platform. The application of the optimization formulation is demonstrated on a real-world distribution network case study. The resulting optimal solution set on pareto-plots are discussed for sensitivity of the trade-offs between the two objective functions, under various water chemistry conditions that have been suggested in earlier studies for minimizing lead release from plattnerite (PbO2) corrosion scales in lead service lines. The resulting optimal disinfectant dosage schedule, for pumping and booster station nodes in each case, provided insights on maintaining disinfectant residuals throughout the distribution system so as to prevent microbial growth as well as lead contamination events while limiting DBPs formation. Further, environmental implications related to the use of the proposed framework are also discussed.

Inactivation Dynamics of Gram-negative and Gram-positive Microbes in Drinking Water: a Comparative Study of Chlorine and Monochloramine Disinfection

To assure the prevention of microbial contamination and the provision of safe potable water to consumers, efficient disinfection is the final barrier. Chlorine, once a widely applied disinfectant, has essentially been re-considered by many water treatment practitioners. Since the research unveiled chlorine-associated health repercussions, the investigation shifted to more viable disinfection options such as the use of monochloramines, that remains active in the system for relatively long periods. Keeping in view, the present study compared the biocidal competence of chlorine and monochloramine to inactivate the gram-negative Klebsiella pneumoniae and Pseudomonas aeruginosa along with the gram-positive Staphylococcus aureus. A lab-scale testing batch was set up in carefully monitored conditions to investigate the response of these bacterial species to the applied disinfection dosages of 1 and 2 mg/L. Moreover, a referenced batch of control evidenced the accuracy of results. A significant difference in the response to chlorine and monochloramine was recorded both in mixed and mono-cultures of bacteria. The bench-scale inactivation experiments revealed that chlorine and monochloramine greatly damaged K. pneumoniae and S. aureus in monocultures. Whereas these bacterial species revealed greater tolerance when acted together in a mixed-cultures and, hence, an overall lower degree of disinfection was achieved. P. aeruginosa exhibited reduced vulnerability to disinfectants in mixed-cultures, marking K. pneumoniae tolerant to chlorine. Most significant correlation between disinfectant species was found at 30 min of exposure with notable logremoval of K. pneumoniae (p = 0.01), P. aeruginosa (p = 0.003) and S. aureus (p = 0.0001). In conclusion, for prolonged exposures, monochloramine is advisable owing to its immediate microbial inactivation upon contact as well as enhanced stability in drinking water networks. The results could predict the pattern of bacterial inactivation in drinking water distribution networks and fill a major gap in the water sector.

Comparison of chlorination and chloramination practices on microbial inactivation efficiencies within a scaled‐up water distribution network using central composite design

AbstractDisinfection practices reduce the incidence of water‐borne diseases but may result in formation of disinfection byproducts (DBPs) in raw water that are reported to be carcinogenic. Central composite design (CCD) was employed in the present study for optimization of disinfectant dose and contact time with the rationale to evaluate if an optimal balance could be achieved between minimal DBPs formation and effective microbial inactivation with either free or combined chlorine in treated water within a lab‐scale prototype network to simulate real water distribution network conditions. After a series of experimental runs based upon design of experiments (DoE) by CCD, dose was found to be the most significant factor (P < 0.01) in determining DBPs formation in both disinfectant’s applications. Where, contact time significantly (P < 0.01) affected bacterial inactivation in chlorination experiments, in contrast, dose was effective in chloramination experiments. Thus, it was concluded that the optimal balance may be achieved in the water networks with the help of multifactorial optimization when disinfectant dose was maintained near 3 mg/L as applied chlorine dose in both disinfection cases, while contact time was 62 and 155 min for chlorine and chloramine, respectively.

THMs, HAAs and NAs production from culturable microorganisms in pipeline network by ozonation, chlorination, chloramination and joint disinfection strategies

Disinfection is an indispensable process to inactivate pathogens, while unexpected disinfection by-products (DBPs) would also be formed between the reaction of residual disinfectants and microorganisms in the water distribution system (WDS). However, there are few studies referring to the formation of DBPs and DBPs-associated toxicity under various disinfection methods based on microorganisms in the real WDS. In addition, the main contributors of bacterial communities or components that generate DBPs are unclear. In this study, the formation of trihalomethanes (THMs), halo-acetic acids (HAAs), nitrosamines (NAs) from culturable microorganisms in pipeline network by ozonation(O3), chlorination (Cl2), chloramination (NH2Cl) and joint disinfection methods were compared, meanwhile, their calculated toxicities under different oxidation scenarios were also discussed. Moreover, 16S ribosomal ribonucleic acid (rRNA) gene sequencing was used to identify the main microbial communities. The results demonstrated that THMs and HAAs increased with increasing disinfectant dosages, while the quantity of NAs (mainly nitroso dimethylamine (NDMA)) was not significantly related to disinfectant dosages for each disinfection strategy. Chloroform (TCM) and dichloroacetic acid (DCAA) were the dominant THMs and HAAs species, respectively. NDMA existed in the samples before disinfections, which may due to the metabolic activity of microorganisms. Pre-O3 increased THMs formation during subsequent Cl2 and NH2Cl treatment. However, pre-O3 effectively reduced HAAs produced by subsequent chlorination. O3/Cl2 disinfection had the highest DBPs formation potential (DBPFP) (883.6 nM), while its calculated toxicity was similar to that in Cl2 disinfection treatment. Pseudomonas was the most abundant bacterial genus in biofilm of WDS pipeline. This study can aid in an optimal disinfection strategy for water treatment plants to reduce the toxicity of DBPs caused by biomass in pipelines and ensure water quality safety.

Wastewater disinfection: long-term laboratory and full-scale studies on performic acid in comparison with peracetic acid and chlorine

Chemical disinfection of municipal wastewater to preserve the microbiological quality of discharges has traditionally relied on chlorine, and more recently on peracetic acid (PAA). A more recent option is performic acid (PFA). This work uses laboratory and full-scale studies over a span of 15 years and five wastewater treatment plants (WWTPs) in Italy, to compare the efficacy of these three disinfectants and identify the differences among peracids in a context where both can be an alternative to chlorine. The investigations focused on treatment effectiveness and bacterial inactivation kinetics using E. coli and the more resistant enterococci, as well as on PFA and PAA decomposition as the residuals may affect the downstream microenvironment. Furthermore, the potential for the two peracids to oxidize organic substances and create troublesome byproducts was also studied. Chlorine, applied as hypochlorite (“HYP”) and here essentially functioning as chloramines, was used as a baseline comparison for the two peracids. Appropriate statistical tests were applied to the data from different WWTPs to account for potential interferences and compounding effects of the different matrices. Average doses of 0.8, 2.9 and 1.4 mg/L and contact times of 18, 21 and 31 min, respectively for PFA, chlorine and PAA guaranteed with a high level of assurance the 5000 CFU/100 mL E. coli limit; the order of effectiveness was PFA > HYP > PAA, refined as PFA > HYP ≈ PAA against E. coli and PFA ≈ HYP > PAA with enterococci. Similar bacterial reductions for the peracids were found at higher disinfectant doses used for the kinetic tests. PFA decayed more quickly than PAA. The first-order decay constants were 0.031 and 0.007 min−1, respectively, suggesting that disinfection residuals when PFA is used may be less of a concern than with PAA. This faster decomposition did not affect the PFA oxidation power on estrone, which was as weak as that of PAA.

Biocidal potential of electrochemically activated solutions (ECAS) against Aeromonas sp. Enterobacter sp. and Escherichia coli in tap water

The biocidal efficiency of electrochemically activated solutions (ECAS) against isolated bacterial species from the water distribution network was analyzed. Predominant microbial consortia (identified using 16S rRNA gene sequencing as Aeromonas sp. Enterobacter sp. and Escherichia. coli) with a mean count of 1.15 × 106 CFU/mL was inoculated in 100 L tap water in a prototype network to simulate real conditions. The physico-chemical quality of tap water of subsurface origin was assessed before experimentation. The contact times of 10 s, 10 min and 1 h were selected against the ECAS dosages of 1%, 5% and 10% (v/v), respectively. Each test organism showed an independent response at varying dosages. A 10% disinfectant dosage corresponding to a contact time of 1 h showed the highest Log reduction as 4.11 > 3.50 > 2.74 for Enterobacter sp. >E. coli >Aeromonas sp., respectively. The results revealed that due to varying physico-chemical composition and carbon content of test water, complete inhibition of test organism (1.15 × 106 CFU/mL) was not achieved at 10% ECAS dosing for 1 h. The study concludes that adequate pretreatment could further enhance the removal efficacy and reduce the minimum inhibitory concentration of ECAS.

Systematic Review and Meta-Analysis of the Persistence and Disinfection of Human Coronaviruses and Their Viral Surrogates in Water and Wastewater.

A systematic review and meta-analysis was conducted to identify decay rate constants (k) of human coronaviruses and their viral surrogates (i.e., animal coronaviruses and the enveloped bacteriophage Phi6) in water and wastewater and disinfection rates with exposure to free chlorine and germicidal ultraviolet light (UV254). Here, 73 k were identified, with only 12 for human coronaviruses, as opposed to animal coronaviruses or Phi6. In the absence of disinfectants, k increased with temperature. Between 22 and 25 °C, mean k for coronaviruses ranged from 0.19 ± 0.06 d–1 in laboratory buffer (n = 4) to 2.9 ± 0.03 d–1 in sterilized wastewater (n = 3), which are within the ranges observed for Phi6 and nonenveloped viruses. No free chlorine or UV254 disinfection studies for coronaviruses were identified that met the systematic review inclusion criteria, although evidence from the literature suggests that coronaviruses would be inactivated if disinfectant doses recommended for nonenveloped viruses were applied. Three disinfection experiments were identified for Phi6. However, given different genome compositions and virion structures between coronaviruses and Phi6, it is not clear whether Phi6 should be used as a surrogate for evaluating free chlorine or UV254k. Therefore, there is a critical need for additional studies that specifically evaluate disinfection kinetics of coronaviruses in the aqueous environment.

604 Comparing Disinfection of Different Dosages of Vaporized Hydrogen Peroxide in Burn Ward

Abstract Introduction The objective of this study is to compare the disinfection effects using the vaporized hydrogen peroxide disinfection method in critical burn ward. Methods A 110m3 empty ward of the burn center was selected as the experimental site. The Bacillus subtilis var. niger spores were opened and placed in 15 unprepared positions (with 0 m, 1 m, 2 m, 3 m, and 4 m from the disinfection machine, each of which was divided into upper, middle, and The lower 3 planes), as well as the 15 points of the cloth (the same position as before), are fixed with hydrogen peroxide indicating tape. The amount of hydrogen peroxide was calculated according to the size of the ward (8 g/m3, 12 g/m3, respectively), and disinfected at a rate of 10 g/min of hydrogen peroxide release flow. After 5 hours of disinfection, the chemical indicator tape and the bacteria pieces were taken out. Observe the discoloration of the chemical indicating tape. The bacteria pieces were placed in a test tube containing the broth culture medium, and the results were observed after incubation in a 37 ° C incubator for 7*24 hours. Results (1) Under the condition of no cover, the two disinfecting dose chemical indicating tapes are all discolored, and in the case of obstruction, they cannot be completely discolored; (2) When the amount of hydrogen peroxide disinfection is 8g/m3 and 12g/m3 respectively, The positive rates of unobstructed specimens were 6.67% and 2.67%, respectively, no significant difference (P= >0.05), and there was no difference in disinfection effect between the positions (P >0.05); (3) 8g/m3 disinfection dose The peak concentration is 255.9g, the peak concentration is 1h48min; the peak concentration is 337.6g at 12g/m3 disinfection, and the peak concentration is 2h26min. When the two disinfection doses were disinfected for 8 hours, the peak concentrations of the chambers were basically the same(1) Under the condition of no cover, the two disinfecting dose chemical indicating tapes are all discolored, and in the case of obstruction, they cannot be completely discolored; (2) When the amount of hydrogen peroxide disinfection is 8g/m3 and 12g/m3 respectively, The positive rates of unobstructed specimens were 6.67% and 2.67%, respectively, no significant difference (P= >0.05), and there was no difference in disinfection effect between the positions (P >0.05); (3) 8g/m3 disinfection dose The peak concentration is 255.9g, the peak concentration is 1h48min; the peak concentration is 337.6g at 12g/m3 disinfection, and the peak concentration is 2h26min. When the two disinfection doses were disinfected for 8 hours, the peak concentrations of the chambers were basically the same. Conclusions The use of vaporized hydrogen peroxide for terminal disinfection should be as full as possible to expose the items to be disinfected. Applicability of Research to Practice Disinfection.

Elucidating sulfate radical-mediated disinfection profiles and mechanisms of Escherichia coli and Enterococcus faecalis in municipal wastewater

Practical applications of disinfection technologies for engineered waters require an in‒depth understanding of disinfection profiles and mechanisms of pathogenic bacteria in a complex matrix. This study investigated the inactivation of E. coli and E. faecalis by SO4•−, an emerging advanced disinfectant, in ultrapure water (UPW) and wastewater effluent (WE). Based on the bacterial inactivation kinetics in UPW in a zerovalent iron/peroxydisulfate system, the second order rate constants (k) for SO4•− reacting with E. coli and E. faecalis were measured to be (1.39 ± 0.1) × 109 M−1 s−1 and (6.71 ± 0.1) × 109 M−1 s−1, respectively. The morphological images of both bacteria by the scanning electron microscope indicated that SO4•− initiates oxidative reactions on the wall/membranes, causing their irreversible damage, ultimately affecting membrane permeability and physiological functions. To profile the inactivation kinetics of two strains of bacteria in WE matrix, a mechanistic process‒based model with the obtained k values was developed. Sensitivity and uncertainty analyses indicated that the key parameters for the model predictions were the concentrations of halide ions (i.e., Br− and Cl−) in WE and their k values reacting with SO4•− accounting for >80% of uncertainty or variance expected in predicted bacterial inactivation. This model allows precise estimation of required disinfectant dose even in complex water matrices, shedding lights on the extension of application of SO4•−‒based technology in wastewater treatments.

Control of Lead Contamination in Water Distribution Networks: A Dynamic Optimization Framework

This study investigates the optimization of free chlorine-based disinfectant dosage for controlling the dissolution of lead (Pb) while limiting disinfection by-products (DBPs) formation in water distribution networks. A dynamic optimization framework is developed in this study to account for the impact of spatial and temporal variations of network hydraulics and water chemistry on dissolved lead concentrations. Accordingly, a dynamic schedule of disinfectant dosage is proposed to minimize water lead levels and two-point chlorine residual violations in the network. The results suggest that optimization of water chemistry parameters such as pH and orthophosphate dosage provide an additional degree of freedom to be explored in the problem of optimizing disinfectant dosage for compliance with conflicting mandates regulating lead levels and DBPs concentration in drinking water.

Integral model of a reacting chlorine jet in ammonia nitrogen and treated primary effluent

Chlorine is extensively used in disinfection processes in water and wastewater treatment processes. The chlorine is typically dosed by jet mixing, and yet no systematic study of chlorine jets has been conducted. In the Stonecutters Island Sewage Treatment Works (SCISTW) of the Hong Kong Harbour Area Treatment Scheme (HATS), concentrated chlorine solution (in sodium hypochlorite form) is injected into primary treated effluent in the form of turbulent dense jets. In view of the importance of sewage disinfection to the environmental impact, it is essential to understand the mixing and reaction of chlorine with ammonia nitrogen for disinfection dosage optimization. In this study, an integral buoyant jet model is developed for a chlorine jet reacting with ammonia nitrogen in CEPT sewage. The jet mixing and chlorine demand is studied by accounting for the stoichiometric reaction of chlorine and ammonia including breakpoint chlorination. Based on experiments of chlorine jet in ammonia solution, the stoichiometric mass ratio of chlorine to ammonia under dynamic mixing process is found to be 7.48. The chlorination kinetics model is then incorporated in a general model of a chlorine jet discharging into a coflowing primary treated sewage effluent, with the reaction ratio calibrated based on experimental measurements for the stagnant case. Significant chlorine demand can occur within a short distance (in the order of 0.1 m, or 1 s or less of travel time) from the dosing point due to the turbulent mixing and reaction with ammonia nitrogen and organic impurities. The chlorine demand of CEPT effluent increases with jet dosing total residual chlorine (TRC) concentration. At TRC < 2000 mg/L, the chlorine demand of sewage is mainly due to ammonia nitrogen (>60%), while for TRC ≫ 2000 mg/L, up to two thirds of chlorine demand can be induced by the oxidation of organic debris. Model predictions of chlorine demand and concentration agree well with laboratory experiments and field data.

Oxidation of Citalopram with Sodium Hypochlorite and Chlorine Dioxide: Influencing Factors and NDMA Formation Kinetics.

The highly prescribed antidepressant, citalopram, as one of newly emerging pollutants, has been frequently detected in the aquatic environment. Citalopram oxidation was examined during sodium hypochlorite (NaOCl) and chlorine dioxide (ClO2) chlorination processes since conventional wastewater treatment plants cannot remove citalopram effectively. Citalopram has been demonstrated to form N-nitrosodimethylamine (NDMA) during chlorination in our previous study. Further investigation on NDMA formation kinetics was conducted in the present study. Influences of operational variables (disinfectant dose, pH value) and water matrix on citalopram degradation, as well as NDMA generation, were evaluated. The results indicated high reactivity of citalopram with NaOCl and ClO2. NDMA formation included two stages during CIT oxidation, which were linear related with reaction time. NaOCl was more beneficial to remove CIT, but it caused more NDMA formation. Increasing disinfectant dosage promoted citalopram removal and NDMA formation. However, no consistent correlation was found between citalopram removal and pH. Contrary to the situation of citalopram removal, NDMA generation was enhanced when citalopram was present in actual water matrices, especially in secondary effluent. DMA, as an intermediate of citalopram chlorination, contributed to NDMA formation, but not the only way.