Watercapes Spring 2006 - Laserfiche WebLink

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Detectin Hydrogen Peroxide Concentration in Advance Oxidation Treatment Processes By Philip Brandhuber, Ph.D. ncreasing wastewater reuse presents a number of technical challenges, large and small, for utilities. When it is possible for reuse water to indirectly enter a potable water supply, great care must be taken to preserve the drinking water source integrity. To maximize protection of public health, increasingly sophisticated techniques are being used to treat reuse water. In the case of indirect potable reuse, additional treatment of reuse water by an advanced oxidation process (AOP) is gaining popularity. AOP couples either ultraviolet (UV) irradiation or ozonation of the reuse water in the presence of hydrogen peroxide. Both the ozone /peroxide and UV/peroxide processes stimulate formation of a highly reactive chemical called a hydroxyl radical. Hydroxyl radicals are widely known for their capability to destroy a number of contaminants in water. AOPs are capable of treating trace contaminants which may be present in reuse water such as 1,4- dioxone, and N- nitrosodimethylamine (NDMA), as well as many pharmaceutically active compounds (PhACs) and personal care products (PCPs). Problems Measuring AOP Performance When operating an AOP, it would be advantageous to directly measure the concentration of hydroxyl radicals the process is producing. This would provide a direct measure of AOP performance. Yet the short life and high reactivity of hydroxyl radicals makes them very difficult to measure. To get around this problem, the performance of an AOP system can be verified indirectly by monitoring the residual concentration of peroxide in the treated water exiting the system. In addition to monitoring performance, being able to accurately measure hydrogen peroxide residual may also provide an economic benefit. This is because AOP systems could then be operated on the basis of residual peroxide concentration rather than applied dose. Doing so would permit the ability to "fine tune' the process to varying oxidant demands of the water. Surprisingly, a simple and inexpensive laboratory method for the detection of low concentrations of hydrogen peroxide, which is free of interferences from constituents found in reuse water, does not exist. To address this analytical issue, HDR has teamed with the University of Washington to develop a simple, inexpensive and reliable analytical method to accurately detect hydrogen peroxide in reuse water, using equipment available in the water quality lab of most utilities. The project is being funded through the WateReuse Foundation and with contributions from the West Basin Municipal Water District and the Orange County Water District. A Review of Existing Peroxide Detection Methods At present, Standard Methods for the Examination of Water and Wastewater does not include a procedure for measuring hydrogen peroxide concentration. However, numerous non - standard methods for hydrogen peroxide detection are published in the literature. While these methods have been successfully used for specific applications, they frequently lack simplicity or are subject to positive or negative interferences from contaminants typically present in reuse water. In addition, the performance of these methods in the presence of combined chlorine is generally unknown. Laboratory methods for the determination of hydrogen peroxide concentrations fall into five categories. The categories include: • Titration; • Spectrophotometry; • Fluorescence; • Chemiluminescence; and • Electrochemical. In general, titration methods are not accurate in the range of peroxide concentration (0.5 mg/L to 5 mg/L) used by AOPs. They are also time consuming and require a moderate level of skill. Spectrophotometric methods generally are rapid and well suited for water quality analysis by utilities. If free from interference, or if the extent of interference can be quantified and corrected for, Spectrophotometric methods are likely to be the most effective for determining peroxide concentrations in AOPs. Fluorescence and chemiluminescence methods have been widely used to quantify peroxide concentration in environmental samples. In general, these methods have the lowest detection limits. However, they are more complex and require instru- ments and equipment not available in most utility water quality laboratories. Electrochemical detection methods are primarily used to measure the concen- tration of peroxide in biological samples and for other specialized purposes. Electrochemical methods typically are very sensitive, but require expensive equipment, extensive calibration and operator training. Progress to Date The development of a detection method suitable for meeting the needs of utilities is underway. Initial experiments have focused on two Spectrophotometric methods. The first peroxide detection method under investigation is based on the reduction of copper (II) ions to copper (1) ions in the presence of excess 2, 9- diemethyl- 1,10 - phenanthroline (DMP). The copper (1) forms a bright yellow cationic complex with DMP that is easily detected by a spectropho- tometer. This peroxide detection method appears to be simple, robust and rather insensitive to interference. The second detection peroxide method under investigation is based on the reaction of peroxide with potassium titanium oxalate. This reaction forms a yellowish peroxotitanium complex with a maximum absorbance at 400 nm. This complex can also be easily detected by a spectrophotometer. Initial experiments with both methods have been promising. Experimental work is continuing. At the completion of this project, the results of the study will be discussed in a future issue of Waterscapes. Philip Brandhuber, Ph.D., is a project manager specializing in water quality and drinking water treatment. He can be reached in HDR's Denver office at (303) 764 -1520 orphilip.brandhuber @hdrinc.com.