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 (1)

Article excerpt

Abstract: 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.

Resume : Les essais a faisceaux collimates permettent des mesures constantes, facilement calculees et reproductibles de la fluence UV; ces essais sont frequemment utilises en recherche et dans la validation du traitement UV. Cependant, puisque les essais avec faisceaux collimates utilisent la distance pour fournir la collimation, l'irradiance au niveau de l'echantillon d'essai est beaucoup plus faible que dans les systemes de traitement UV. Un avantage potentiel de la lumiere pulsee peut decouler du taux de fluence eleve qu'elle produit. Une nouvelle approche de cellule d'essai a irradiance elevee et une technique de modelisation sont presentees pour l'evaluation de ces effets. Le modele predit correctement la fluence dans la cellule d'essais a irradiance elevee en la comparant aux mesures effectuees par faisceaux collimates. Cela demontre que la cellule a irradiance elevee est un outil utile pour evaluer l'effet d'un taux de fluence elevee dans le traitement UV. Cette technique de modelisation pourrait egalement etre utilisee dans la conception de reacteurs.

Mots-cles : ultraviolet a impulsion, faisceau collimate, modelisation, desinfection, rehabilitation.

[Traduit par la Redaction]


Pulsed ultraviolet (UV) sources differ in several ways from continuous UV sources. Pulsed discharges produce very high intensity light during a brief on time (microseconds to milliseconds), followed by a relatively longer off time before the next pulse. In addition, pulsed light emission spectra are less dominated by line emission (more continuum radiation) and, with correct operation, have more emission below 240 nm than mercury lamps. Figure 1 shows the time dependence and output spectrum for a pulsed UV lamp. The temporal behavior of the UV light output is measured with a photodiode (Thorlabs DET210 high speed silicon detector), using a UV bandpass filter (Oriel Model 53330). Light measurements are made with a multi-channel spectrometer with 2048 elements over the wavelength range of 200-800nm (Ocean Optics USB2000).


Pulsed sources may have enhanced efficacy on a delivered-fluence basis over continuous UV sources for both remediation of organic contaminants and disinfection applications, possibly due to either spectral or fluence rate differences (Bohrerova et al. 2005; Grapperhaus et al. 2005; Hillegas and Demirci 2003; Sharma and Demirci 2003; Shemer et al. 2005; Wekhof 2003), but many of these studies lack a good measure of the delivered fluence. Spectral differences can be accounted for by correlating quantitative spectral measurements of the light with the action spectrum of chemicals or microbes being treated. However, this may not account for the enhanced efficacy of the pulsed source (Bohrerova et al. 2005; Grapperhaus et al. 2005). If the difference is caused by the high fluence rate, it may be a threshold effect. Therefore, to compare lamps in a bench-top experiment when fluence rate dependent effects are suspected, it is desirable to replicate the fluence rates in a reactor. …