Fouling of quartz surfaces in potable water ultraviolet disinfection reactors
Although ultraviolet (UV) disinfection of drinking water has been shown to be effective and cost efficient, one barrier to more widespread adoption is uncertainty surrounding the possible accumulation of fouling materials on quartz surfaces within UV reactors. These quartz surfaces serve as protection for the UV lamps that are immersed in the water being treated, and in many cases they can become coated with precipitated minerals and impacted particles that limit the transmission of germicidal UV radiation from the lamp into the water that is to be treated. While much of the past research on the subject of quartz fouling in UV systems has investigated the formation of foulants in reactors treating wastewater, differences in reactor geometry, lamp type, and water chemistry between these scenarios and drinking water treatment applications makes it difficult to understand how past research may apply to drinking water. Currently, there is limited information available about the chemical composition, rate of formation, and means of predicting the formation of the foulant materials that accumulate. Laboratory and field experiments were conducted at several locations to investigate the relationship between water chemistry and foulant composition, formation, and UV absorbance characteristics. Low Pressure High Output (LPHO) lamp sleeves in a parallel flow configuration were examined for metals accumulation, UV transmittance, and rate of accumulation, and models of solution chemistry were used to understand the formation of mineral species. Zero order kinetics for foulant accumulation were consistently observed. Medium Pressure (MP) lamp sleeves were utilized in a perpendicular flow reactor configuration disinfecting a surface water to determine variations in fouling that can occur when reactor geometry and higher UV intensities are used. Regression modeling was utilized to develop an understanding of the absorbance characteristics of foulant components, and iron and calcium were found to be primary contributors to radiation absorption of germicidal UV radiation by fouled lamp sleeves. Comparisons of foulant buildup and fouling effects among multiple groundwater based treatment facilities highlighted the impact of treatment steps that cause changes in oxidation reduction potential, mineral solubility, and fouling rate.
Blatchley, Purdue University.
Civil engineering|Environmental engineering
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