Main Parameters and Assays Involved with Organic Pollution of Water

LORENA VIDAL; CLAUDIA E. DOMINI; ANTONIO CANALS

Handbook of Water Analysis Third Edition

London

Año: 2013; p. 453 - 485

The estimation of the organic contamination in a water sample is a complex and delicate problem that involves several determination assays because the organic matter is present under diverse chemical com-pounds and degradation states. The global organic matter balance cannot be obtained by considering a single method, but it must be done by a comparison of the results obtained by different methods [1]. An additional difficulty lies in the fact that, in general terms, no single parameter can be used to quantify the organic matter content. In principle, the carbonated matter is used as a nutrient by aerobic germs, and it is oxidized to carbon dioxide and water, while species such as nitrite and nitrate are used as food by, for example, nitrobacte-ria. In an oxygen-deficient environment, such as sewer or stale water, bacteria take oxygen not only from nitrates and nitrites but also from sulfates, with sulfur hydrogen as residual product. These oxidation CONTENTS 17.1 Introduction ..................................................................................................................................459 17.2 Biochemical Oxygen Demand ..................................................................................................... 460 17.2.1 Dilution Method .............................................................................................................. 460 17.2.2 Instrumental Methods ..................................................................................................... 461 17.2.2.1 Respirometric Methods .................................................................................... 461 17.2.2.2 Biosensors ........................................................................................................ 462 17.2.2.3 Other Methods ................................................................................................. 462 17.3 Chemical Oxygen Demand .......................................................................................................... 465 17.3.1 Classic (Opened Reflux) Method ..................................................................................... 466 17.3.2 Semimicro (Closed Reflux) Method ................................................................................ 466 17.3.3 Other Discontinuous Methods ......................................................................................... 467 17.3.4 Methods Based on Flow Injection Analysis .....................................................................471 17.4 Total Organic Carbon ................................................................................................................... 472 17.4.1 High-Temperature Combustion Methods .........................................................................474 17.4.2 Low-Temperature Oxidation Methods .............................................................................474 17.4.3 Other Methods ..................................................................................................................475 17.4.4 Recent Advances ..............................................................................................................475 17.4.5 Interferences .....................................................................................................................476 17.5 Total Organic Halide .................................................................................................................... 477 17.5.1 Adsorption?Pyrolysis?Titrimetric Method ..................................................................... 477 17.5.2 Direct Measurement of Absorbance ................................................................................ 479 17.5.3 Total Organic Halides as a Part of Disinfection By-Products ......................................... 479 Acknowledgment ...................................................................................................................................481 References ..............................................................................................................................................481 © 2014 by Taylor & Francis Group, LLC 460 Handbook of Water Analysis phenomena that take place in nature are very difficult to reproduce on a laboratory scale. However, some tests (e.g., biochemical oxygen demand, BOD) allow a biological appreciation of the phenomena, although there are some inherent problems, which will be discussed later. Several chemical methods have been developed to obtain a more complete and reproducible oxida-tion of organic matter. Some of them are based on the use of chemical reagents and a methodology that avoids the ambiguity of biological methods. In this way, chemical oxygen demand (COD) has become one of the obtained parameters. Nevertheless, the degradation (i.e., extent and velocity) of organic substances by means of biological methods can be different from that produced by chemical methods. Therefore, the results obtained with both sorts of methods may be difficult to compare. In particular, the extent of oxidation reached when using a strong oxidizing agent (e.g., potassium dichromate) is more complete for many organic compounds than is biological oxidation, although in some cases it is not fully accomplished. As a result, the COD values obtained by this method are so high that, under biological conditions, the complete oxidation of organic matter takes a long time, and it is not always reached. Another way to evaluate organic matter content is to measure the carbon present in a sample. Total organic carbon (TOC) is, in this case, the employed parameter. The rapid evolution of relatively complex techniques introduced in the past few years has promoted the development of these methods. These techniques show, as the most relevant advantage, applicability to almost every category of organic prod-ucts, even to the most resistant oxidizing compounds. Besides, the results are obtained quickly and the determinations can be easily automated. There are other parameters for estimating water contamination. Besides those already mentioned (i.e., BOD, COD, and TOC), total organic halide (TOX) is a very useful parameter. The combination of all these parameters would give complete information for the characterization of the organic matter present in a sample