Reduction Equivalent Dose Research Articles

A systematic simulation of disinfection for the flow-through UV reactors with staggered ring baffles under the Eulerian framework

An integrated UV disinfection model is presented to simulate the disinfection in the flow through UV reactors. The concentration of microorganisms, the mean residence time, and the mean dose are solved under the Eulerian framework. An unbaffled reactor and three baffled reactors with staggered baffles are simulated. The accuracy of the computation is validated against Sozzi's measurement and simulation in the unbaffled reactor. The staggered baffles improve the flow field and enhance the mixing. The mean residence time is significantly changed by baffles. The cumulative frequency distributions of the mean residence time in the outlet plane may become narrow and wide depending on the size of baffles. The radiation intensity is nearly the same for all reactors. The mean dose is significantly affected by the baffles. The area-averaged mean doses at the outlet are nearly the same for all reactors whereas the range of the mean dose in the outlet plane is narrowed by baffles. Better disinfection levels are obtained in the baffled reactors than the unbaffled reactor, which is determined by the narrower distribution of the mean dose in the outlet plane. The increasing flow rate decreases the disinfection level for all reactors. The reduction equivalent dose is proportional to the minimum mean dose Dmin in the outlet plane and the slope decreases as the inactivation constant increases, meaning a decreasing effect of Dmin on the reduction equivalent dose. Dmin in the outlet plane can be used to characterize the disinfection capability of the flow-through UV reactors.

Virtual prototyping and characterization of a point-of-entry UV-LED water disinfection reactor with the synergic effect of radiation, hydrodynamics, and inactivation kinetics

We developed and studied one of the first high-flow UV-LED water disinfection reactors applicable to point-of-entry (POE) water disinfection. A multiphysics computational model was created to predict the performance of UV reactor design concepts by modeling the synergic effect of radiation, hydrodynamics, and the inactivation kinetics of microorganisms. The geometrical optics that describe light propagation in terms of rays were employed to model the radiation profile of multiple UV-LEDs with optical components in complex reactor geometries, the first account of such an approach. The computational solution of the mass, momentum, and species equations was applied to model the hydrodynamics and kinetics. We designed a reactor through a detailed computational study of the optical and hydrodynamic performance of various design strategies. Highly efficient UV fluence distribution in the reactor was achieved by creating nearly collimated UV radiation beams across the reactor and managing the hydrodynamics using a flow distributor. We fabricated a prototype of the optimized reactor design for experimental studies. Biodosimetry tests were conducted for various flow rates and UV transmittances (UVTs), and the experimental results were compared with the model predictions. The design, which employed 14 UV-LEDs assembled over custom-made optical modules, resulted in a reduction equivalent dose (RED) of 65 mJ/cm2 at a flow rate of 20 liters per minute (LPM) while consuming about 50 W energy. This reactor design required only 0.05 W radiant power per LPM flow rate to achieve an NSF Class A UV dose equivalent of 40 mJ/cm2. The findings of this study provide insights into UV-LED reactor development strategies as well as the creation and application of reactor virtual prototyping tools for designing and optimizing highly efficient UV-LED reactors.

Computational analysis of three lamp close conduit water disinfection UV reactor

The purpose of ultraviolet (UV) disinfection is to bring to end the growth and procreation of microorganism. UV reactors are used for the UV disinfection of the drinking water. Our goal of the current research work was properly locating the positions of the UV lamps in a three-lamp close conduit water disinfection UV reactor. Three positions of UV lamps are based on vertices of the four basic types of triangles (Equilateral, Right angle, Scalene and Isosceles). The objective function for optimized lamp positioning was Reduction Equivalent Dose (RED). To ascertain efficient UV dose delivery to pathogen, water disinfection UV reactors was simulated with the aid of computational fluid dynamics. The computational investigation was achieved employing ANSYS® Fluent 15.0 academic version. The turbulent flow was modeled using standard k−e model, fluence rate (FR) was modeled using UVCalc3D model and pathogen transport was modeled using discrete phase model. The scalene lamp positioning results in highest RED value and isosceles lamp positioning results in lowest RED value. There is meager difference between the RED values of equilateral and scalene lamp positioning. Moreover, we found two lamps on the upstream side and one lamp on the downstream side results in better UV disinfection. The proposed methodology for the three-lamp model provides useful insights to the design and optimization of close conduit water disinfection UV reactor. This research work has evaluated, for the first time, a systematic methodology for three-lamp positioning to ameliorate the performance of UV reactor and has revitalized the comprehension about the contribution of FR distribution within the UV reactor.

Validation test on real scale UV reactor for ballast water treatment

Design of UV reactors for drinking water has been widely studied using computational fluid dynamics (CFD) modeling. When combined with collimated beam test (CBT), CFD becomes a powerful tool for verifying the performance of a UV reactor. However, the design of real scale UV reactor for ballast water treatment system (BWTS) has not been extensively studied due to their relatively short R&D history. For this reason, we have attempted to validate the UV reactor through the results of the biological efficacy (BE) test with Tetraselmis microorganism. Through BE tests, we found that 3-log <i>Tetraselmis</i> inactivation was satisfied when the reduction equivalent dose (RED) was higher than that of 1,500 J/m<sup>2</sup>.

Numerical and experimental studies of water disinfection in UV reactors.

Performance of UV reactors for water disinfection is investigated in this paper. Both experimental and numerical studies are performed on base reactor LP24. Enterobacteria phage MS2 is chosen as the challenge microorganism in the experiments. Experiments are conducted to evaluate the effect of different parameters, i.e. flow rate and UV transmission, on the reactor performance. Simulation is carried out based on the commercial software ANSYS FLUENT with user defined functions (UDFs) implemented. The UDF is programmed to calculate UV dose absorbed by different microorganisms along their flow trajectories. The effect with boundary layer mesh and without boundary layer mesh for LP24 is studied. The results show that the inclusion of boundary layer mesh does not have much effect on the reactor performance in terms of reduction equivalent dose (RED). The numerical results agree well with the experimental measurements, hence validating the numerical model. With this achieved, the numerical model is applied to study other scaled reactors: LP12, LP40, LP60 and LP80. Comparisons show that LP40 has the highest RED and log inactivation among all the reactors while LP80 has the lowest RED and log inactivation.

Biodosimetric Studies for Ballast Water Treatment

Ultraviolet (UV) reactor for ballast water treatment is investigated in this paper. Experimental and numerical simulations are performed for a base reactor named LBW850e. B. Pumilus is chosen as a challenge organism in the experiments. Simulation is carried out based on the commercial software ANSYS FLUENT with user defined functions implemented. The effects of water flow rate and UV transmittance (UVT) on the UV reactor performance in terms of reduction equivalent dose (RED) are studied. The results show that the increase of water flow rate reduces RED. While RED increases with the increase of UVT. The experimental and simulation results show reasonable agreement with each other. With this achieved, the numerical model developed in the current work can be applied to other reactors.

Efficacy of ultraviolet (UV‐C) light in reducing foodborne pathogens and model viruses in skim milk

The efficacy of low wavelength ultraviolet light (UV-C) as a disinfection process for a scattering fluid such as skim milk was investigated in this study. UV-C inactivation kinetics of two surrogate viruses (bacteriophages MS2 and T1UV) and three bacteria Escherichia coli ATCC 25922, S. Typhimurium ATCC 13311, Listeria monocytogenes ATCC 19115 in buffer and skim milk were investigated. UV-C irradiation was applied to stirred samples, using a collimated beam operating at 253.7 nm wavelength. A series of known UV-C doses (0–40 mJ·cm−2) were delivered to the samples except MS2 where higher doses (0–150 mJ·cm−2) were delivered. Biodosimetry, utilizing D values of viruses inactivated in buffer, was carried out to verify and calculate reduction equivalent dose. At the highest dose of 40 mJ·cm−2, the three pathogenic organisms were inactivated by more than 5 log10 (p < .05). Results provide evidence that UV-C irradiation effectively inactivated bacteriophage and pathogenic microbes in skim milk. The inactivation kinetics of microorganisms was well described by log linear and exponential models with a low root mean squared error and high coefficient of determination (r2 > 0.96). Models were validated and parameterized for predicting log reduction as a function of UV-C irradiation dose (p < .05). This study clearly demonstrated that high levels of inactivation of pathogens can be achieved in skim milk, and suggests significant potential for UV-C treatment of treating fluids that exhibit significant scattering. Practical application This research paper provides scientific evidence of the potential use of UV technology in inactivating pathogenic bacteria and model viruses in skim milk. UV-C doses were validated and verified using biodosimetry. UV-C irradiation is an attractive food preservation technology and offers opportunities for dairy and food processing industries to meet the growing demand from consumers for safer food products. This study clearly shows the potential for using UV-C treatment for treating highly scattering fluid such as skim milk. Results from this work will be used to further develop continuous flow-through UV-C systems based on dean or turbulent flow patterns.

Geometry Defeaturing Effects in CFD Model-Based Assessment of an Open-Channel-Type UV Wastewater Disinfection System

Computational fluid dynamics (CFD) is a popular tool in the water industry for assessing ultraviolet (UV) reactor performance. However, due to the size of open-channel-type UV reactor systems, the CFD model requires significant computational time. Thus, most evaluations have been conducted using very simplified models. In order to ensure the reliability of this simplified CFD model, precise numerical modeling and validation by measurements are necessary considering the geometry defeaturing level. Therefore, simplified geometries in four defeatured levels were prepared for the CFD model, and simulations were performed to determine the level of geometric simplicity required to derive reliable results. A bioassay test was also conducted for a pilot-scale open-channel-type UV reactor that has the same geometrical configuration as the CFD model. Good agreement was observed between the bioassay test and CFD model results. It was found that the reduction equivalent dose (RED) is not significantly affected by geometry defeaturing under the assumption that the inlet flow conditions are relatively uniform. In multiple bank operation, the addition of banks yields a linear increment of the RED in the CFD model, however, a lower RED than the measured value was presented, especially for serial bank addition. The related aspects of the detailed flow physics and disinfection characteristics were also presented. These results are expected to provide useful information for CFD modeling, reactor design, and the assessment of the open-channel-type UV reactors.

Impact of asymmetric lamp positioning on the performance of a closed-conduit UV reactor

Abstract Computational fluid dynamics (CFD) analyses for the performance improvement of a closed-conduit ultraviolet (UV) reactor were performed by changing the lamp positions from symmetric to asymmetric. The asymmetric lamp positioning can be useful for UV reactor design and optimization. This goal was achieved by incorporating the two performance factors, namely reduction equivalent dose (RED) and system dose performance. Four cases were carried out for asymmetric lamp positioning within the UV reactor chamber and each case consisted of four UV lamps that were simulated once symmetrically and four times asymmetrically. The results of the four asymmetric cases were compared with the symmetric one. Moreover, these results were evaluated by using CFD simulations of a closed-conduit UV reactor. The fluence rate model, UVCalc3D was employed to validate the simulations results. The simulation results provide detailed information about the dose distribution, pathogen track modeling and RED. The RED value was increased by approximately 15% by using UVCalc3D fluence rate model. Additionally, the asymmetric lamp positioning of the UV lamps had more than 50% of the pathogens received a better and a higher UV dose than in the symmetric case. Consequently, the system dose performance was improved by asymmetric lamp positioning. It was concluded that the performance parameters (higher RED and system dose performance) were improved by using asymmetric lamp positioning.

Configuration optimization of UV reactors for water disinfection with computational fluid dynamics: Feasibility of using particle minimum UV dose as a performance indicator

Computational fluid dynamics is a powerful tool for ultraviolet (UV) reactor performance evaluation, since it allows the reactor configuration optimization by comparing the performance indicator [e.g., reduction equivalent dose (RED)] of various UV reactors. In this study, a new performance indicator independent of the microbial UV dose-response curve, namely particle minimum UV dose (Dmin), was introduced, and its feasibility was evaluated in the configuration optimization of 3-lamp UV reactors for water disinfection. Results indicate that the Dmin could serve as an alternative to the RED in characterizing the UV reactor performance. In general, reactors with a normal (NOR) lamp position pattern (i.e., with one lamp on the top and two at the bottom) had larger Dmin values (110−193mWcm−2) than those with a reverse (REV) lamp position pattern (i.e., with two lamps on the top and one at the bottom) (98−160mWcm−2). The largest Dmin (193mWcm−2) was obtained in an UV reactor with a lamp relative distance (i.e., the ratio of the distance between the lamp and reactor axes to the reactor radius) of 0.4 and an inlet internal diameter of 75mm, which could be ascribed to a well-mixed flow resulting from an optimal dispersion of the influent flow by the lamp array. The maximum disinfection flow rate of the UV reactor with the optimal configuration was elevated by 47−100% compared to those of the non-optimally designed reactors, which led to an energy saving efficiency of 32−50%.

Numerical study of the effects of lamp configuration and reactor wall roughness in an open channel water disinfection UV reactor

This article describes the assessment of a numerical procedure used to determine the UV lamp configuration and surface roughness effects on an open channel water disinfection UV reactor. The performance of the open channel water disinfection UV reactor was numerically analyzed on the basis of the performance indictor reduction equivalent dose (RED). The RED values were calculated as a function of the Reynolds number to monitor the performance. The flow through the open channel UV reactor was modelled using a k-ε model with scalable wall function, a discrete ordinate (DO) model for fluence rate calculation, a volume of fluid (VOF) model to locate the unknown free surface, a discrete phase model (DPM) to track the pathogen transport, and a modified law of the wall to incorporate the reactor wall roughness effects. The performance analysis was carried out using commercial CFD software (ANSYS Fluent 15.0). Four case studies were analyzed based on open channel UV reactor type (horizontal and vertical) and lamp configuration (parallel and staggered). The results show that lamp configuration can play an important role in the performance of an open channel water disinfection UV reactor. The effects of the reactor wall roughness were Reynolds number dependent. The proposed methodology is useful for performance optimization of an open channel water disinfection UV reactor.

Optimization of lamp arrangement in a closed-conduit UV reactor based on a genetic algorithm

The choice for the arrangement of the UV lamps in a closed-conduit ultraviolet (CCUV) reactor significantly affects the performance. However, a systematic methodology for the optimal lamp arrangement within the chamber of the CCUV reactor is not well established in the literature. In this research work, we propose a viable systematic methodology for the lamp arrangement based on a genetic algorithm (GA). In addition, we analyze the impacts of the diameter, angle, and symmetry of the lamp arrangement on the reduction equivalent dose (RED). The results are compared based on the simulated RED values and evaluated using the computational fluid dynamics simulations software ANSYS FLUENT. The fluence rate was calculated using commercial software UVCalc3D, and the GA-based lamp arrangement optimization was achieved using MATLAB. The simulation results provide detailed information about the GA-based methodology for the lamp arrangement, the pathogen transport, and the simulated RED values. A significant increase in the RED values was achieved by using the GA-based lamp arrangement methodology. This increase in RED value was highest for the asymmetric lamp arrangement within the chamber of the CCUV reactor. These results demonstrate that the proposed GA-based methodology for symmetric and asymmetric lamp arrangement provides a viable technical solution to the design and optimization of the CCUV reactor.

Numerical study of the effects of surface roughness on water disinfection UV reactor

UV reactors are an emerging choice as a big barrier against the pathogens present in drinking water. However, the precise role of reactor's wall roughness for cross flow ultraviolet (CF-UV) and axial flow ultraviolet (AF-UV) water disinfection reactors are unknown. In this paper, the influences of reactor's wall roughness were investigated with a view to identify their role on the performance factors namely dose distribution and reduction equivalent dose (RED). Herein, the relative effects of reactor's wall roughness on the performance of CF-UV and AF-UV reactors were also highlighted. This numerical study is a first step towards the comprehensive analysis of the effects of reactor's wall roughness for UV reactor. A numerical analysis was performed using ANSYS Fluent 15 academic version. The reactor's wall roughness has a significant effect on the RED. We found that the increase in RED is Reynolds number dependent (at lower value of turbulent Reynolds number the effects are remarkable). The effects of reactor's roughness were more pronounced for AF-UV reactor. The simulation results suggest that the study of reactor's wall roughness provides valuable insight to fully understand the effects of reactor's wall roughness and its impact on the flow behavior and other features of CF-UV and AF-UV water disinfection reactors.

Methodology considering surface roughness in UV water disinfection reactors

AbstractWater disinfection making use of an ultraviolet (UV) reactor is an attractive procedure because it does not produce any by-products. In this work, the effects of pipe roughness on the performance of a closed-conduit water disinfection UV reactor were investigated. In order to incorporate the surface roughness effects, a simple, stable, highly accurate model, better than any iterative approximation, was adopted in the numerical simulations. The analysis was carried out on the basis of two performance indicators: reduction equivalent dose (RED) and system dose distribution. The analysis was performed using a commercial computational fluid dynamics (CFD) tool (ANSYS Fluent). The fluence rate within the UV reactor was calculated using UVCalc3D. The pipe surface roughness resulted in longer pathogen residence times and higher dose distribution among the pathogens. The effect of pipe surface roughness on RED depends on the Reynolds number and relative roughness. Pipe surface roughness plays an important role because UV reactors for water disinfection operate at moderate Reynolds numbers. In addition, the positioning of the UV lamp in the reactor plays an important role in determining the RED of the reactor. Search criteria for lamp-positioning are also proposed in the current work. The proposed CFD methodology can be used to analyse the performance of closed-conduit reactors for water disinfection by UV.

Theoretical Evaluation of UV Reactors in Series

AbstractA theoretical analysis is provided of the extent to which doses from ultraviolet (UV) reactors in series are additive. It is shown that UV reactors’ reduction equivalent dose (RED) depends on the sensitivity of the microbe, the limits of which are the minimum and average of the dose distribution for infinitely sensitive and infinitely resistant microbes. For complete interbank mixing between two reactors in series, the additivity of RED is preserved. For systems where there is a negative correlation between dose paths, the RED is greater than or equal to twice that of a single reactor. The converse occurs for positive correlation. It is proven that when a single reactor is validated with a microbe whose sensitivity is at least twice that of the target microbe, it is assured that two identical UV reactors in series will deliver a RED at least two times that of the single reactor.

Computational fluid dynamics simulation and parametric study of an open channel ultra-violet wastewater disinfection reactor

The disinfection characteristics of an open channel ultra-violet (UV) disinfection reactor is investigated numerically. The computational fluid dynamics (CFD) model used in this study is based on the volume of fluid (VOF) method to capture the water–air interface. The Lagrangian particle tracking method is used to calculate the microbial particle trajectory and the discrete ordinate (DO) model is used to calculate the UV intensity field inside the reactor. A commercial CFD software package ANSYS FLUENT is used to solve the governing equations. Custom user defined functions (UDFs) are developed to calculate the UV doses. A post-processor is developed in MATLAB to implement the inactivation kinetics of the microbes. The post-processor provides the probabilistic dose distribution and reduction equivalent dose (RED) values achievable in the reactor. The numerical predictions are compared with available experimental data to validate the CFD model. A parametric study is performed to understand the effects of different parameters on disinfection performance of the reactor. The low/high dosed particle trajectories, which can provide an insight for hydraulic and optical characteristics of the reactor for possible design improvements, are identified.

Demonstrating 4‐log adenovirus inactivation in a medium‐pressure UV disinfection reactor

Previous bench‐scale results demonstrated that polychromatic medium‐pressure (MP) ultraviolet (UV) disinfection could achieve 4‐log adenovirus inactivation at equivalent UV doses well below those required under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). These findings were confirmed and extended to a full‐scale UV disinfection reactor using a live adenovirus challenge. The MP UV disinfection system was able to measure &gt; 4‐log adenovirus disinfection at an MS2 coliphage reduction equivalent dose (RED) of &lt; 100 mJ/cm2. The highest observed adenovirus‐based RED achieved, referenced to a low‐pressure (LP) UV dose‐response, was 233 mJ/cm2; the validated RED, including relevant validation factors, was equivalent to that required by the LT2ESWTR for 4‐log virus inactivation credit. These results proved that required virus disinfection doses can be validated and that MP UV is capable of meeting the 4‐log virus disinfection standard in the LT2ESWTR at a measurable and achievable UV dose substantially lower than that of LP UV technology.

Computational fluid dynamics for predicting performance of ultraviolet disinfection – sensitivity to particle tracking inputs

A three-dimensional (3-D) computational fluid dynamic model that predicts the performance of a full-scale medium-pressure lamp ultraviolet (UV) reactor for disinfection of drinking water is described. The model integrates velocity field, fluence rate distribution, and particle trajectory calculations with a microorganism inactivation kinetic model to arrive at predictions of reduction equivalent dose and microorganism inactivation for MS2 coliphage. A rational approach to determining an appropriate number of fluid particles that would generate the required computational precision is presented. Predictions of inactivation and equivalent dose were found to be sensitive to computational mesh geometry (hexahedral versus tetrahedral) but were less sensitive to the value of the Lagrangian empirical constant used in the random walk model and to choice of turbulence model (κ – εε versus Reynolds stress). Non-steady-state (dynamic) simulations produced results that were similar to those of steady-state simulations. Utility of the model for evaluating different lamp operating modes and alternative physical arrangements of the baffles and lamps was demonstrated.Key words: ultraviolet, UV reactor, disinfection, water, computational fluid dynamics, modeling.

Measurement of Ultraviolet Radiation with Biological Dosimeters

The measurement of UV radiation with biological dosemeters is in most cases performed using micro-organisms. The biological effect which may be used in this context is the inactivation of the micro-organisms exposed to UV radiation, the survival curve is measured and is used as the calibration curve for the measurement. As a biodosemeter, for instance, bacterial spores or viruses can be used. In one application biodosimetry is the only method which can be used: in measuring the dose in flow-through UV-disinfection plants for water. The biodosemeter is added to the water flowing into the disinfection plant and from the reduction of the micro-organisms the dose can be calculated as reduction equivalent dose (RED). Because of the inhomogeneous radiation field inside the plant every micro-organism receives a different fluence, this causes a distribution of fluences among the micro-organisms which have passed through the plant. In general the RED is lower than the arithmetic mean of the density function of the fluence distribution.

Biodosimetry: Model calculations for u.v. water disinfection devices with regard to dose distributions

The increasing importance of disinfection of drinking water by u.v. radiation makes it necessary to determine the u.v. dose which is applied to the water by u.v.-disinfection plants. In Austria a minimum microbicidal dose of 400 Jm −2 at a wavelength of 253.7 nm is demanded for drinking water, the control of it shall be assured by type testing. A method was developed in using calibrated spores of Bacillus subtilis as biodosimeter which are added to the inflowing water, and after determination of their survival rate in the plant one can deduce the applied dose from it. This procedure is unproblematic as long as all microorganisms receive the same dose on their way through the reactor. But in some cases, and probably this is the normal case, not all microorganisms receive the same dose. It follows that a dose distribution will exist among the test organisms which have passed through the reactor. The dose (reduction-equivalent dose or RED) which is deduced from the survival rate of the microorganisms passing flow-through systems for u.v.-disinfection of wastewater or drinking water in general is different from the arithmetic mean of the dose distribution. The RED depends on the special form of the dose distribution and on the specific shape of the survival curve of the test organisms. The broader the dose distribution and the higher the u.v.-susceptibility of the microorganisms, the lower is the measured RED. But if the survival curve of the microorganisms used would have a shoulder ( D s > D m), and the dose distribution would overlap with the shoulder the RED may increase. We investigated by calculations and by experiments the influences on the test results obtained by this method.