Biodosimetry testing of a simplified computational model for the UV disinfection of wastewater

Abstract

A simplified computational model of the ultraviolet (UV) disinfection dose delivered to wastewater was developed and the model outputs were compared with pilot-scale biodosimetry data. The model assumed plug flow, an assumption that may apply for some open channel UV reactors designed for wastewater disinfection and in which case may eliminate the need for involved and expensive computational fluid dynamics analyses of flow patterns. The reactor residence times derived from this assumption were combined with the output from a two-dimensional, point-source summation UV irradiance model to calculate UV dose. The output from the irradiance model was adapted to account for the cross-sectional distribution of UV irradiance within the reactor. Two UV reactor configurations were modeled and pilot-tested at two UV transmittance (UVT) values that are typical for wastewater. The simplified model predicted doses that fell within the range of the observed UV doses under some flow and UVT conditions, however it did so inconsistently and over-predicted the doses at the highest tested flow rates. This was concluded to be due to a breakdown of the simplified plug flow assumption due to deviations in the velocity field distribution at higher flows. Therefore, while this modeling approach may provide "back of the envelope" initial estimates of the UV doses supplied to wastewater and may allow a qualitative evaluation of the effect of adjusting UV reactor design parameters (e.g., channel width, lamp spacing) on the resulting UV dose, the precise quantitative prediction of UV dose must continue to rely on more sophisticated models. Key words: ultraviolet disinfection, computational modeling, wastewater treatment.

Field investigation of advanced oxidation of secondary effluent from municipal wastewater treatment plant

“…[2,6,8] This is because of the variation in the feed characteristics in this field study, such as turbidity, UVT, and concentrations of total suspended solids and biological indicators (Table 1). This suggests that in arranging laboratory studies, the experiments should be designed statistically to capture possible variations and make the output convincing and reliable.…”

“…[2,5,6,8,14,19,22] There is insufficient information on the impacts observed from practical field application of the AOT to water and wastewater treatment. The objectives of this study were to test the field applicability of AOT at a pilot scale to a secondary effluent from an activated sludge process without nutrient removal, and to investigate the effect of AOT on inactivation and on changes in nitrate-nitrite concentrations in the product water under field conditions.…”

Assessment of UV Disinfection and Advanced Oxidation Processes for Treatment and Reuse of Hydraulic Fracturing Produced Water

“…These control experiments were carried out by placing a test water containing cultured microorganisms into the collimated beam system (UV light turned off) and measuring the microbial counts at time 0 and the time required to achieve a dose of 30 mJ/cm 2 (up to 5 min) with an incident irradiance of approximately 0.75 mW/cm 2 . A fluence of 30 mJ/cm 2 was used because fluence levels between 20 mJ/cm 2 and 45 mJ/cm 2 are commonly applied to meet disinfection requirements for secondary and tertiary wastewater (i.e., 200 fecal coliforms per 100 mL on a 30-day geometric mean). , Microbial counts were then measured following the same plating and counting techniques described above. Microbial counts (∼10 7 CFU/mL) were similar at time 0 and 30 mJ/cm 2 .…”

On-Site Determination and Monitoring of Real-Time Fluence Delivery for an Operating UV Reactor Based on a True Fluence Rate Detector

“…The performance of a UV reactor is governed by the UV fluence or, more precisely, by the fluence distribution. The initial (nominal) fluence determination (as measured by biodosimetry) of an ex-factory UV reactor has been investigated by many researchers. − Fluence estimation during subsequent operation is often based on initial fluence and monitoring of flow rate, UVT, and conventional detector readings. Monitoring protocols based on this approach have been proposed and applied. − …”