Science of Water : Concepts and Applications

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Environmental Biomonitoring, Sampling, and Testing 255 DO fi eld kits using the Winkler method are relatively inexpensive, especially compared to a meter and probe. Field kits run between $35 and $200, and each kit comes with enough reagents to run 50–100 DO tests. Replacement reagents are inexpensive, and you can buy them already measured out for each test in plastic pillows. You can also purchase the reagents in larger quantities in bottles, and measure them out with a volumetric scoop. The pillows’ advantage is that they have a longer shelf life and are much less prone to contamination or spillage. Buying larger quantities in bottles has the advantage of considerably lower cost per test. The major factor in the expense for the kits is the method of titration used—eyedropper, syringetype titrator. Eyedropper and syringe-type titration is less precise than digital titration, because a larger drop of titrant is allowed to pass through the dropper opening, and on a micro-scale, the drop size (and thus volume of titrant) can vary from drop to drop. A digital titrator or a burette (a long glass tube with a tapered tip like a pipette) permits much more precision and uniformity for the titrant it allows to pass. If a high degree of accuracy and precision in DO results are required, a digital titrator should be used. A kit that uses an eyedropper-type or syringe-type titrator is suitable for most other purposes. The lower cost of this type of DO fi eld kit might be attractive if several teams of samplers and testers at multiple sites at the same time are relied on. Meter and Probe A DO meter is an electronic device that converts signals from a probe placed in the water into units of DO in milligrams per liter. Most meters and probes also measure temperature. The probe is fi lled with a salt solution and has a selectively permeable membrane that allows DO to pass from the stream water into the salt solution. The DO that has diffused into the salt solution changes the electric potential of the salt solution, and this change is sent by an electric cable to the meter, which converts the signal to milligrams per liter on a scale that the user can read. Methodology If samples are to be collected for analysis in the laboratory, a special APHA sampler or the equivalent must be used. This is the case because, if the sample is exposed or mixed with air during collection, test results can change dramatically. Therefore, the sampling device must allow collection of a sample that is not mixed with atmospheric air and allows for at least 3X bottle overfl ow (see Figure 8.12). Again, because the DO level in a sample can change quickly, only grab samples should be used for DO testing. Samples must be tested immediately (within 15 min) after collection. √ Note: Samples collected for analysis using the modifi ed Winkler titration method may be preserved for up to 8 h by adding 0.7 mL of concentrated sulfuric acid or by adding all the chemicals required by the procedure. Samples collected from the aeration tank of the activated sludge process must be preserved using a solution of copper sulfate–sulfamic acid to inhibit biological activity. The disadvantage of using the DO oxygen meter method is that the meter can be used to determine DO concentration directly (see Figure 8.13). In the fi eld, a direct reading can be obtained using a probe (see Figure 8.14) or by collection of samples for testing in the laboratory using a laboratory probe (see Figure 8.15). √ Note: The fi eld probe can be used for laboratory work by placing a stirrer in the bottom of the sample bottle, but the laboratory probe should never be used in any situation where the entire probe might be submerged. The probe used in the determination of DO consists of two electrodes, a membrane, and a membrane fi lling solution. Oxygen passes through the membrane into the fi lling solution and causes a change in the electrical current passing between the two electrodes. The change is measured and displayed as the concentration of DO. To be accurate, the probe membrane must be in proper operating condition, and the meter must be calibrated before use.
256 The Science of Water: Concepts and Applications Temp Zero Off FIGURE 8.13 Dissolved oxygen meter. Membrane (inside cap) FIGURE 8.14 Dissolved oxygen-fi eld probe. Dissolved oxygen meter-digital readout DO 0.1 mg/L DO 0.01 mg/L DO % Sat. Zero 4.14 mg/L Cable to meter Weighed cap Probe body Protective cap Calibration The only chemical used in the DO meter method during normal operation is the electrode fi lling solution. However, in the Winkler DO method, chemicals are required for meter calibration. Calibration prior to use is important. Both the meter and the probe must be calibrated to ensure accurate results. The frequency of calibration is dependent on the frequency of use. For example, if the meter is used once a day, then calibration should be performed before use. There are three
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Second Edition THE SCIENCE OF WATER
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Cover Image: Falling Spring at Fall
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Contents Preface ..................
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Contents ix Velocity Head .........
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Contents xi Specifi c Conductance .
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Contents xiii (5) Beetles (Order: C
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Contents xv Chlorine Residual Testi
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Contents xvii Water Filtration Calc
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To the Reader In reading this text,
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1 Introduction When color photograp
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Introduction 3 On second look, we s
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Introduction 5 As mentioned earlier
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Introduction 7 This scream of lost
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Introduction 9 Metcalf & Eddy, Inc.
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12 The Science of Water: Concepts a
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3 Water Hydraulics Anyone who has t
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Water Hydraulics 47 Another relatio
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Water Hydraulics 49 • • 1 ft 3
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Water Hydraulics 51 √ Important P
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Water Hydraulics 53 FIGURE 3.4 Thru
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Water Hydraulics 55 Example 3.8 Pro
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Water Hydraulics 57 FIGURE 3.6 Lami
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Water Hydraulics 59 With regard to
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Water Hydraulics 61 or hydraulic gr
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Water Hydraulics 63 E 1 smaller fl
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Water Hydraulics 65 √ Note: In de
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Water Hydraulics 67 • Cone of dep
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Water Hydraulics 69 • • • •
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Water Hydraulics 71 The Darcy-Weisb
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Water Hydraulics 73 Of course, pipe
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Water Hydraulics 75 In this section
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Water Hydraulics 77 Slope (S) The s
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Water Hydraulics 79 and important c
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Water Hydraulics 81 and the depth o
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Water Hydraulics 83 TYPES OF DIFFER
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Water Hydraulics 85 √ Important P
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Water Hydraulics 87 Meter backpress
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Water Hydraulics 89 VELOCITY FLOWME
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Water Hydraulics 91 The positive-di
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Water Hydraulics 93 Solution: 1200g
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Water Hydraulics 95 Water and Waste
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100 The Science of Water: Concepts
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6 Water Ecology The subject of man
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Water Ecology 157 The environment i
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Water Ecology 159 FIGURE 6.2 Notone
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Water Ecology 161 H 2 O O 2 FIGURE
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Water Ecology 163 FeS FIGURE 6.6 Th
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Water Ecology 165 Algae FIGURE 6.8
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Water Ecology 167 2. Likewise, biom
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Water Ecology 169 Population densit
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Water Ecology 171 succession can be
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Water Ecology 173 dark winter month
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Water Ecology 175 In rain events wh
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Water Ecology 177 long profi le, cr
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Water Ecology 179 THE FLOODPLAIN A
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Water Ecology 181 It is important t
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Water Ecology 183 Specifi c Adaptat
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Water Ecology 185 serve to indicate
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Water Ecology 187 UNITS OF ORGANIZA
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Water Ecology 189 FIGURE 6.20 Stone
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Water Ecology 191 FIGURE 6.22 Midge
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Water Ecology 193 FIGURE 6.25 Riffl
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Water Ecology 195 They push their m
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Water Ecology 197 FIGURE 6.32 Damse
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Water Ecology 199 Darwin, C., 1998.
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10 Water Treatment Calculations Gup
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