DESIGN AND IMPLEMENTATION OF UV/H2O2 TREATMENT IN A FULL SCALE DRINKING WATER TREATMENT PLANT
Abstract:The presence of pathogenic organisms and micro-pollutants has caused PWN to replace breakpoint chlorination by a-selective barriers in their surface water treatment plants. Feasibility of the application of UV/H2O2 for both disinfection and organic contaminant control was studied.
The UV/H2O2 process treats pre-treated IJssel Lake water with a nitrate content of 6-12 mg/L and a DOC concentration of approximately 2.5 mg/L. To meet disinfection criteria for target micro organisms such as viruses and protozoa, a germicidal UV-dose of 70 mJ/cm2 is necessary. Target micro pollutants are mainly pesticides, endocrine disruptors and pharmaceuticals. The applied UV-dose for organic contaminant control by advanced oxidation is 600 mJ/cm2; the H2O2 dosage is 6 ppm. Applying advanced oxidation process conditions, results in superior disinfection.
Extensive research preceded the implementation. In historic research, no response in the Ames test was observed in UV treated water under disinfection conditions. For atrazine, the formation of primary metabolites was researched in both the disinfection and the oxidative regime. Pilot plant research on byproducts mainly focussed the oxidative regime. Produced byproducts are nitrite and biodegradable compounds (AOC).
Long term pilot scale testing of the UV/H2O2 process, followed by activated carbon filtration (EBCT 30 minutes), was performed to monitor the formation of these products. Formation of 100-300 μg/L nitrate and 100-150 μg/L AOC was observed. Biodegradation by the GAC filters reduced the AOC to 16-18 μg/L. Formed nitrite was completely re-oxidized to nitrate in the GAC filters.
The additional function of the activated carbon, decomposition of the residual hydrogen peroxide, was studied as well. The expected catalytic decomposition of H2O2 by activated carbon was confirmed. Depending on the characteristics of the activated carbon, 6-9 minutes EBCT were required to decompose the residual H2O2 below detection limit.
Available UV-reactors were optimized for disinfection purposes only, based on disinfection modelling and CFD. In this case, both the disinfection and the advanced oxidation process needed to be performed by the same UV-reactor. Trojan Technologies' existing disinfection models and CFD capabilities, combined with collaborative research effort and development of a kinetic model for the advanced oxidation process, resulted in an optimized reactor design.
Based upon the model calculations, a full scale UV-system was designed, constructed and implemented. The full scale UV/H2O2 installation treats pre-treated IJssel Lake water and is located before of the existing activated carbon filters (EBCT 30 minutes). The maximum capacity of the plant is 4,500 m3/h.
The full-scale UV/H2O2 installation is operational since November 2004 and the performance has been monitored since. Earlier pilot results were confirmed.
Document Type: Research Article
Publication date: 2007-01-01
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