Collimated Beam Tests Research Articles

Fluence requirements in existing UV disinfection facilities to comply with EU validation performance targets for reclaimed water: a case study.

Since 2020, there is a new European Regulation (EU, 2020/741) on minimum requirements for water reuse, where routine and validation monitoring requirements (log reductions of indicator microorganisms and reference pathogens) have been established. Many reclamation facilities that are already in operation might have difficulties to comply with these performance targets. Existing disinfection systems must be expanded and upgraded. In the case of UV disinfection systems, fluence requirements must be determined to properly design with a focus on the safety and economic-environmental viability of reclaimed water. This study can be used as a reference to develop fluence-response curves for Clostridium perfringens spores, Escherichia coli, and total and F-specific coliphages, indicator microorganisms referred to in the new European Regulation. Eight UV-LED collimated beam tests were performed. Samples were obtained from filtered effluent of secondary treatment from two wastewater treatment plants (WWTPs) which ranged between 30 and 54%. Results showed UV sensitivity of 33.46 mJ/cm2 log I for C. perfringens spores and 2.86 mJ/cm2 log I for E. coli, both from environmental origin. Coliphages were inactivated below the limit of quantitation. The non-dominance of MS2 phages in environmental F-specific coliphages was observed.

UV disinfection audit of water resource recovery facilities identifies system and matrix limitations

The use of ultraviolet (UV) light as a disinfectant in water resource recovery facilities is a well-accepted and increasingly popular disinfection option. Different assessment techniques, such as collimated beam testing, biodosimetry, fluorescent microspheres, and computational fluid dynamic modelling, exist to evaluate suitability and validate fluence of full-scale UV systems; however, each of these techniques has limitations. UV auditing overcomes these limitations by concurrently estimating the minimum fluence required to meet effluent discharge limits, providing direct inactivation results of the regulated organism, and estimating the minimum fluence achieved by an installed full-scale system. Four wastewater facilities with various treatment technologies and flowrates were selected to be audited. Bench-scale collimated beam performance fluence-response curves were developed for E. coli and the modeled data was compared to plant performance to determine system versus matrix limitations. The results found that UV auditing successfully identified system and matrix limitations for each of four different wastewater treatment facilities. Furthermore, seasonal differences between two sampling locations were confirmed via UV auditing. Seasonal water quality analysis of WWTF-C resulted in a more challenging wastewater matrix to treat with increasing influent E. coli during the Fall. The UV audit identified that WWTF-C was undersized and limited in its capacity. In summary, UV auditing provides a clear and robust method to better understand how wastewater treatment facilities perform and provides a novel approach to determine the fluence of an installed full-scale reactor.

Optimizing UV Disinfection Design and Energy Consumption Through Collimated Beam Testing

Optimizing UV Disinfection Design and Energy Consumption Through Collimated Beam Testing

Microbial UV fluence-response assessment using a novel UV-LED collimated beam system

A research study has been performed to determine the ultraviolet (UV) fluence-response of several target non-pathogenic microorganisms to UV light emitting diodes (UV-LEDs) by performing collimated beam tests. UV-LEDs do not contain toxic mercury, offer design flexibility due to their small size, and have a longer operational life than mercury lamps. Comsol Multiphysics was utilized to create an optimal UV-LED collimated beam design based on number and spacing of UV-LEDs and distance of the sample from the light source while minimizing the overall cost. The optimized UV-LED collimated beam apparatus and a low-pressure mercury lamp collimated beam apparatus were used to determine the UV fluence-response of three surrogate microorganisms ( Escherichia coli, MS-2, T7) to 255 nm UV-LEDs, 275 nm UV-LEDs, and 254 nm low-pressure mercury lamps. Irradiation by low-pressure mercury lamps produced greater E. coli and MS-2 inactivation than 255 nm and 275 nm UV-LEDs and similar T7 inactivation to irradiation by 275 nm UV-LEDs. The 275 nm UV-LEDs produced more efficient T7 and E. coli inactivation than 255 nm UV-LEDs while both 255 nm and 275 nm UV-LEDs produced comparable microbial inactivation for MS-2. Differences may have been caused by a departure from the time-dose reciprocity law due to microbial repair mechanisms.

Collimated beam tests: their limitations for assessing wastewater disinfectability by UV, and a proposal for an additional evaluation parameter

This study examines the effects of the liquid matrix on the disinfectability of waters and wastewaters by ultraviolet (UV) light. Collimated beam (CB) curves, which are routinely used to assess disinfectability, and to provide the average fluence (in microjoules per square centimetre) necessary to reach a target effluent microbial count, eliminate the effect of UV transmission (UVT), using the Morowitz equation. However, this calculation has the consequence of masking the differences between samples of differing UVT, which may indeed require the same average UV fluence to reach the target, but require considerably different energy input and number of lamps in the full-scale system. An additional parameter, called herein an "energy factor'', is proposed in addition to the CB curve to evaluate disinfectability. The energy factor is the applied UV energy per unit volume divided by the average fluence experienced by the microbes in the liquid matrix. Synthetic data and actual CB curves from various types of samples are used to assess the effects of UVT, the depth of sample in the petri dish, the slope of the CB curve, the target microbial count, and, finally, the original microbial count on the energy factor. Key words: ultraviolet disinfection, collimated beam, energy factor.

Modeling of a new UV test cell for evaluation of lamp fluence rate effects in regard to water treatment, and comparison to collimated beam tests

Collimated beam (CB) tests allow for consistent, easily calculated and reproducible measurements of UV fluence, and are widely used in UV treatment research and validation testing. However, because CB tests employ distance to provide collimation, the irradiance at the test sample is much lower than in UV treatment systems. A potential benefit of pulsed light may arise from the high fluence rate it produces. A new high-irradiance (HI) test cell approach and modeling technique are presented for use in evaluating these effects. The model is shown to correctly predict the fluence in the HI test cell by benchmarking it to CB measurements. This demonstrates that the HI cell is a useful tool in evaluating the effect of high fluence rate in UV treatment. This modeling technique also has application in reactor design.Key words: pulsed UV, collimated beam, modeling, disinfection, remediation.

Fouling Mechanisms in a Laboratory‐Scale UV Disinfection System

The fouling of quartz sleeves surrounding UV disinfection lamps is a perennial problem affecting both drinking water and wastewater applications. The mechanisms of fouling are not fully understood, but factors promoting fouling are believed to include heat, high hardness and/or high iron concentrations, and hydrodynamic forces. The role of UV radiation itself is unclear. The goal of this paper is to attempt to isolate the fouling mechanisms and to provide key information about those induced by UV radiation, using a unique laboratory-scale continuous-flow UV reactor. Its design allowed for irradiated and nonirradiated zones and control of both temperature and UV intensity at the fouling surface. Synthetic wastewater samples were tested with two levels of calcium, iron, phosphorus, and biochemical oxygen demand (as beef broth), and constant levels of magnesium and nitrogen to assess the effects of the four key variables. Average UV fluence before fouling exceeded 35 mJ/cm2, based on collimated beam tests. Foulant accumulation was monitored by UV intensity measurements and by mass and composition of foulant collected after an average of 56 hours of continuous operation. Tests showed that relative UV intensity dropped by as much as 100% when iron was present. Detailed results were assessed and yielded support for the following three UV-induced fouling mechanisms: (a) precipitation of ferric hydroxide [Fe(OH)3], (b) release of calcium from calcium-organics complexes followed by precipitation of iron-organics complexes, and (c) calcium carbonate precipitation. Other fouling mechanisms, such as sedimentation of preformed particles and sorption of calcium onto preformed colloids of Fe(OH)3, occurred outside the zone of UV radiation. Hence, these could be confused with concurrent UV-induced mechanisms in full-scale reactors. Iron and/or calcium undoubtedly created the most favorable conditions for fouling to occur; in the absence of both, fouling would be unlikely. The rates of fouling were enhanced when organics were also present; however, when phosphorus was present, fouling in the UV section was reduced. Indeed, UV may be viewed as inhibiting the fouling caused by phosphate complexes.

UV Systems for Reclaimed Water Disinfection – From Equipment Validation to Operation

The Sanitation Districts of Los Angeles County (Districts) operate seven tertiary water reclamation plants (WRPs) with a combined treatment capacity over 200 million gallons per day (MGD). Although chloramination has provided reliable and effective disinfection, the Districts decided to change this disinfection practice at one of the WRPs to ultraviolet (UV) irradiation to minimize N-nitrosodimethylamine (NDMA) formation. During the process of designing the UV disinfection system, the Districts had an opportunity to participate in an equipment validation study that was conducted by a third party consultant. A pilot scale UV system equipped with low-pressure high-output UV lamps was validated according to Ultraviolet Disinfection Guidelines for Drinking Water and Wastewater Reclamation, and the equipment validation report was approved by the California Department of Health Services (DHS). Following the equipment validation testing, the Districts conducted additional UV disinfection studies, using the same pilot system, at two WRPs in 2004 and 2005. The objectives of these studies were to verify the UV dose regression model developed from equipment validation testing, and to determine if the UV dose regression model developed at one WRP could be used for design of a full-scale UV disinfection system at another WRP with similar treatment processes and water quality. Results showed that the delivered UV doses from the Districts’ tests were different from those calculated using the dose regression model. Factors that may attribute to this apparent discrepancy include differences in collimated beam testing procedures, water quality, data analysis procedures, and assumptions made to calculate doses of multiple-bank systems. The findings from this study have implications on UV system design and operation which rely on the dose regression model. It is recommended that the factors discussed in this study be considered in UV equipment validation and full-scale UV system design and operation to ensure that the full-scale UV systems function as designed and provide adequate safety factor for protection of human health.

Closure to “Standardized Collimated Beam Testing Protocol for Water∕Wastewater Ultraviolet Disinfection” by Jeff Kuo, Ching-lin Chen, and Margaret Nellor

Closure to “Standardized Collimated Beam Testing Protocol for Water∕Wastewater Ultraviolet Disinfection” by Jeff Kuo, Ching-lin Chen, and Margaret Nellor

Discussion of “Standardized Collimated Beam Testing Protocol for Water∕Wastewater Ultraviolet Disinfection” by Jeff Kuo, Ching-lin Chen, and Margaret Nellor

Discussion of “Standardized Collimated Beam Testing Protocol for Water∕Wastewater Ultraviolet Disinfection” by Jeff Kuo, Ching-lin Chen, and Margaret Nellor

Technical and sanitary aspects of wastewater disinfection by UV irradiation for landscape irrigation

Water reuse for landscape irrigation requires the production of high quality virus-free effluents to minimize risk for human health. In order to establish the relevance of MS2 phages as an appropriate biodosimeter for UV design, a pilot plant study has been carried out with different types of wastewater effluents. The two pilot systems tested (low-pressure high output and medium-pressure UV units) were able to achieve 4 and 5 log MS2 reduction in tertiary filtered effluent at high calculated UV doses of 170 _ 10 and 300 mJ/cm2, respectively. UV disinfection was extremely efficient for MS2 inactivation in high quality effluents after reverse osmosis: detention times as low as one second and UV dose of 40 mJ/cm2 were sufficient to reach 5 log inactivation of MS2. UV irradiation also produced rapid inactivation of human pathogens such as poliovirus type 1 and indigenous enteroviruses at UV doses up to 3 times lower that those for MS2 disinfection. It was concluded that accurate UV unit design for a given type of wastewater could be ensured by pilot tests using laboratory-propagated MS2 as biodosimeter and collimated-beam tests as the calibration-check.

Effect of Low Turbidity and Algae on UV Disinfection Performance

It is well‐recognized that changes in ultraviolet (UV) absorbance or significant concentrations of amorphous biological wastewater solids in a water matrix can affect UV disinfection performance. However, the effects of low concentrations of drinking water particulates (turbidity) and algae on UV disinfection effectiveness are more poorly understood. This article presents the results of continuing studies at the University of New Hampshire (Durham) on the effects of particles on UV disinfection. The research was conducted in two phases of medium‐pressure UV collimated beam tests. The first phase compared the dose–response of seeded MS2 bacteriophage in waters with montmorillonite clay turbidity up to 12 ntu and algal content up to 42 μg/L as chlorophyll a (~42,000 cells/mL) to the dose–response of seeded MS2 in deionized water. The second phase compared phase 1 results with the inactivation of MS2 in the presence of naturally occurring turbidity in reservoir waters. Results indicated UV light was effective for inactivating MS2 in the presence of montmorillonite clay, algae, and naturally occurring turbidity in collimated‐beam testing.

Standardized Collimated Beam Testing Protocol for Water/Wastewater Ultraviolet Disinfection

Ultraviolet (UV) irradiation has emerged as a viable alternative for water/wastewater disinfection. Laboratory dose-response data from collimated-beam tests are commonly used as a basis for determining the necessary delivered UV dose for full-scale UV systems as measured by UV intensity and exposure time. While researchers often think that germicidal dose can be estimated confidently in a collimated beam system, the reported dose-response relationships vary considerably. Numerous factors may affect the test results to some extent. They include apparatus setup, column dimensions, UV lamp type and output, intensity measurement, shutter type and operation, petri dish specifications, sample volume and depth of the liquid, mixing condition, laboratory settings, microbial organism preparation and testing, and water quality. The methodology used to calculate the UV dose for collimated beam tests is also a critical factor. To ensure reproducibility or to have a meaningful comparison of results from different collimated beam tests, a standardized protocol for collimated beam testing and its dose calculation is necessary. The standardized collimated beam test can then serve as a tool to calibrate the dose calculation models for field-scale UV reactors and, consequently, to meaningfully compare the dose values derived from these models. A comprehensive standardized collimated beam testing protocol is warranted to advance applications of UV disinfection for water/wastewater. However, development of such a protocol is a significant research effort that will require input from researchers of various technical and disciplinary backgrounds. In addition, some technical issues still need to be clarified by further research. This paper presents important issues associated with collimated beam testing in the context of developing a standard protocol as well as future research needs. The main objective is to serve as a starting point for development of a standardized collimated beam testing protocol that is universally acceptable by researchers, industries, and regulatory agencies.

UV disinfection of wastewater coagulated with ferric chloride: recalcitrance and fouling problems

Collimated beam and pilot tests using low pressure or medium pressure UV lamps were conducted to assess the disinfection performance of a municipal wastewater which had been pretreated by ferric chloride coagulation followed by sedimentation. The feed to the UV systems contained high levels of Fe (often above 3 mg/l); suspended solids and UV254 transmission values were also not ideal (mean approximately 30 mg/l and 32% respectively). The collimated beam tests indicated that the target level of 2,500 coliform forming units/100 ml often could not be reached, and the pilot tests revealed significant fouling after only a few hours. Thus physicochemical effluents of this nature likely require upstream filtration (or a relaxation of the target level) and a continual, automated cleaning system to ensure that performance levels can be maintained.

UV disinfection of wastewater coagulated with ferric chloride: Recalcitrance and fouling problems

Collimated beam and pilot tests using low pressure or medium pressure UV lamps were conducted to assess the disinfection performance of a municipal wastewater which had been pretreated by ferric chloride coagulation followed by sedimentation. The feed to the UV systems contained high levels of Fe (often above 3 mg/l); suspended solids and UV254 transmission values were also not ideal (mean approximately 30 mg/l and 32% respectively). The collimated beam tests indicated that the target level of 2,500 coliform forming units/100 ml often could not be reached, and the pilot tests revealed significant fouling after only a few hours. Thus physicochemical effluents of this nature likely require upstream filtration (or a relaxation of the target level) and a continual, automated cleaning system to ensure that performance levels can be maintained.