Low-Cost, Rapid, Accurate. On-Line and In-Situ Quantification of Chloramines and Ammonia for Improved Operation and Control of a Water Treatment Process.

Oral Presentation

Prepared by M. Benhabib1, M. Peterman2
1 - OndaVia, Inc, 26102 eden landing road suite1, Hayward, CA, 94545, United States
2 - OndaVia, 26102 eden landing rd suite1, Hayward, California, 94545, United States


Contact Information: merwan@ondavia.com; 510-229-9197


ABSTRACT

The US Environmental Protection Agency estimates 68 million Americans drink water disinfected with chloramine. Many water agencies are shifting federal drinking regulations and to protect public health. It has been recognized as a safer disinfectant and a good alternative to chlorine as it forms significantly lower amount of toxic disinfectant byproducts. Additionnally, monochloramine does not contribute significantly to taste or odor and is more stable in solution than free residual chlorine.
Chloramination often is useful in systems with long distribution lines or with large amounts of storage where the water age might be too long to maintain free chlorine residual. Dichloramine is a better disinfectant than monochloramine but contributes undesirable taste and odor. Nitrogen trichloride or trichloramine is undesirable because it has a disagreeable taste and odor and is very unstable in solution.

The key to chloramination is to control the ratio of chlorine to nitrogen to favor formation of monochloramine and prevent formation of dichloramine and trichloramine. As chlorine is added, it reacts with ammonia to form ?monochloramine. The closer free ammonia is to zero, the better the chloramination system will operate. Free ammonia left in the water is a nutrient for microorganisms. Under favorable conditions of temperature, pH, and time, organisms can nourish causing significant operational and aesthetic problems in the water distribution system. Excess ammonia can lead negative health effect due to nitrification and formation of nitrites and nitrates in water.
The problem most commonly associated with chloramination is nitrification: with time and under favorable conditions, a series of reactions can cause monochloramine to deteriorate and result in release of free ammonia adding even more nutrient to the system. To guarantee treatment performance the development of a method capable of continually, accurately and easily measure chloramine and ammonia is required.
The standard laboratory technique to accurately measure trace levels of ammonia or chloramine is gas chromatography coupled to mass-spectrometry. It is an expensive and labor-intensive operation that is not adequate for a timely-response. For rapid analysis, the most common technique used is the colorimetric based on Indophenol. It is a complex, user intensive method that requires to run blanks and calibration standards. The color needs to be is compared with colors of known concentrations. It is not a reliable technique as it is sensitive to interference from organic amines and to factors like pH and temperature.

The quantitative detection of chloramine from 10 ppb to 2 ppm is shown for lab and field samples with an accuracy of 10%. The apparatus, the procedure, its optimization, and its benefits compared to standard techniques are described. No pretreatment process was necessary to remove potential interfering amines or ions. The test consists on a two-steps process and takes a few minutes to complete. Specificity of the analytical procedure to ammonia and chloramine is demonstrated with complete independence toward other organic amines. The technique employed is based on Surface Enhanced Raman Spectroscopy (SERS), it uses active gold- nanoparticles combined with a Berthelot dye: salicylate. As opposed to typical colorimetric tests, this spectroscopy test self-calibrates by means of the use of an internal standard. The internal standard is an isotope of ammonia that is mixed with the Berthelot reagent a long with the sample. The internal standard has a specific Raman shift different from the analyte which makes the measurement of the intensity at that Raman wavelength an accurate tool to standardize the Raman response which then corresponds to the analyte concentration.
Quantitative analysis is demonstrated down to the 10-ppb levels in complex-matrices in lab and in various water samples. A side-by-side comparison with standard analysis equipment proves the high accuracy of this technique.
The successful results obtained for both lab and field samples demonstrates the capabilities of this cost-effective analysis technology to generate quickly meaningful data that can be used to optimize chloramination disinfection processes as both an on-line tool or a deployable handled instrument.