Chemical Oxygen Demand By Dichromate

Potassium dichromate is a relatively cheap compound that can be obtained in a high state of purity. The analytical-reagent grade, after drying at 103 C, can be used to prepare solutions of an exact normality by direct weighing and dilution to the proper volume. The dichromate ion, is a very potent oxidizing agent in solutions that are strongly acidic. The reaction involved in the usual case, where organic nitrogen is all in a reduced state (oxidation number of -3), may be represented in a...

Methods Of Chlorine Residual Determination

It was not until about 1940 that the difference in disinfecting power of chloramine and free chlorine residuals was demonstrated. Prior to that time no attempt had been made to develop analytical procedures for differentiation. Therefore, methods for measuring chlorine residuals may be classed into old methods that measure total chlorine and new methods that allow measurement of free and combined forms. CHAPTER 20 Residual Chlorine and Chlorine Demand AH common methods of measuring chlorine...

Environmental Significance Of Dissolved Oxygen

In liquid wastes, dissolved oxygen is the factor that determines whether the biological changes are brought about by aerobic or by anaerobic organisms. The former use free oxygen for oxidation of organic and inorganic matter and produce innocuous end products, whereas the latter bring about such oxidations through the reduction of certain inorganic salts such as sulfate, and the end products are often very obnoxious. Since both types of organisms are ubiquitous in nature, it is highly important...

General Considerations

AH living organisms are dependent upon oxygen in one form or another to maintain the metabolic processes that produce energy for growth and reproduction. Aerobic processes are the subject of greatest interest because of their need for free oxygen. Humans are vitally concerned with the oxygen content of the air that they breathe, since they know from experience that an appreciable reduction in oxygen content will lead to discomfort and possibly death. For this reason, the number of occupants...

Application Of Chloride Data

In many areas the level of chloride in natural waters is an important consideration in the selection of supplies for human, industrial, and agricultural uses. Where brackish waters must be used for domestic purposes, the amount of chloride present is an important factor in determining the type of desalting apparatus to be used. The chlo- ride determination is used to control pumping of groundwater from locations where intrusion of seawater is a problem. In areas where the discharge of...

Methods Of Determination

There are several Standard Methods procedures for measurement of chloride. Among these are a potentiometric procedure (Sec. 12.3) using silver nitrate as a ' tjtrant to complex chloride with silver and employing a silver-silver chloride electrode system to detect the end point, and ion chromatography (Sec. 12.4), which is useful for determining concentrations of several common anions in one analysis. These instrumental methods require somewhat expensive equipment. Two other procedures that are...

Air Pollution And Global Environmental Change

Although the problems of water supply and liquid-waste disposal are of major importance to urban populations, their solution alone does not ensure a completely satisfactory environment. Pollution of the atmosphere increases in almost direct ratio to the population density and is largely related to the products of combustion from heating plants, incinerators, and automobiles, plus gases, fumes, and smokes arising from industrial processes. The intensity of most air pollution problems is usually...

Ch cr cr

p-Xylene It exists in three isomeric forms ortho-xylene, meta-xylene, and paxa-xylene. All i are isomeric with ethylbenzene in that they have the same general formula, CgH10. j Together with benzene, these compounds are commonly referred to as the BTEX j group. The benzene-series hydrocarbons are used extensively as solvents and in chem- i ical synthesis, and are common constituents of petroleum products (e.g., gasoline), j Although they are relatively insoluble in water, wastewaters and...

O o c

If' iCOOH jr , * H + 4IT + 4e (6.32) Side chains such as the CH2COOH group in 2,4-D are typically removed before the fe aromatic ring is cleaved. These carboxylic acids are eventually mineralized to C02. As described, halogenated xenobiotic compounds can often be oxidized by bac-ii' teria. In general, the more chlorine atoms a compound has, the less susceptible it is Si t0 oxidation and the more susceptible it is to reduction. For example, hexa-If-'chloroethane (C2C16) is very resistant to...

[H [OH [Ac

Note that in mass balance, charge balance, and proton condition relationships, molar concentrations and not activities are required. - V- . The ionic strength must now be calculated so that activity corrections can be made. Since HAc is a weak acid, its ionization can be ignored ( Ac- - 0) and we can assume that the ionic strength is due entirely to the added NaCl. ,V P- Sc.z 0.5 0.01(1)2 + O.Ol(-l)2 0.01 M Using the Guntelberg approximation Eq. (4.2) . log 7 -0.5Z2 V5 L -0.0455Z2 ' 1 + VOOl...

Basic Concepts from Equilibrium Chemistry

A knowledge of equilibrium chemistry has become increasingly important for determining quantitatively the relationships between the various constituents in natural and contaminated waters, and for understanding the effect of alterations in the water on the various chemical species present. This is a matter of growing importance because of the use of physical-chemical methods for treating wastewaters and sanitary-landfill leachates and the need to understand the fate and transport of both...

Methods Of Expressing Alkalinity

Alkalinity measurements are made on a wide variety of materials. These range from relatively pure waters through polluted waters, such as municipal and industrial wastewaters, to digesting sludges. The methods of expressing alkalinity values vary considerably therefore, it is necessary to explain the methods in some detail and to indicate the areas where the various methods are employed. Phenolphthalein and Total Alkalinity Inspection of the titration curves for a strong base (hydroxide...

K um K kb[ ORT

Care must be taken to ensure that the units used in these rate expressions are The concept of half-life is often used to describe the persistence of an organic in the environment. Half-life (i1 2) was defined in Sec. 3.10 as 0.693Ik, where k is a grst-orderrate coefficient. With hydrolysis, k is represented by kh or kh N , Hydrolysis reactions may be quite slow (half-lives of years) or quite rapid (half-lives of seconds) depending on the organic and the environmental conditions. The following...

Discrepancy Between L0 Values And Theoretical Oxygen Demand Values

The ultimate BOD, or L0, value of organic substances is often considered to be equal to the theoretical oxygen demand as calculated from the chemical equation involved see Eq. (23.1) . For example, oxidation of glucose to carbon dioxide and water requires 192 g of oxygen per mole or 1.065 mg of oxygen per milligram of glucose. c6h1206 + 602 6c02 + 6h20 (23.15) A great deal of BOD work has been done with glucose solutions in a concentration of 300 mg L. Such a solution has a theoretical oxygen...

Chapter

Basic Concepts from Organic Chemistry 212 5.1 Introduction 212 Aliphatic Compounds 5.8 Alkyl Halides and Other Halogenated Aliphatic Compounds 237 5.9 Simple Compounds Containing Nitrogen 242 5.10 Cyclic Aliphatic Compounds 245 5.11 Mercaptans or Thioalcohols 245 Aromatic Compounds 5.15 Alcohols, Aldehydes, Ketones, and Acids 254 5.16 Simple Compounds Containing Nitrogen 256 Heterocyclic Compounds 5.17 Heterocyclic Compounds 258 The Common Foods and Related Compounds 5.22 Proteins and Amino...

Volumetric Analysis

Early methods of volumetric analysis employed separate measurement of carbon dioxide and oxygen, followed by a slow simultaneous combustion of hydrogen and methane. The analysis was completed by measuring the amount of carbon dioxide produced during the combustion of the methane and then employing a knowledge of Gay-Lussac's law of combining volumes (Sec. 2.9) to determine the amounts of methane and hydrogen present in the mixture. In the past an apparatus was sometimes used that employed a...

The Safe Drinking Water

The critical nature of the water supply problem brought congressional action resulting in Public Law 93-523, known as the Safe Drinking Water Act (SDWA), which was signed into law in 1974, It then became incumbent upon the newly formed Environmental Protection Agency (EPA) to interpret the law and establish Drinking Water Standards that apply to all public water systems in the United States, not just those that supply common carriers, as did the U.S. Public Health Standards. The SDWA was...

Types Of Hardness

In addition to total hardness, it is desirable and sometimes necessary to know the types of hardness present. Hardness is classified in two ways (1) with respect to the metallic ion and (2) with respect to the anions associated with the metallic ions. Calcium and magnesium cause by far the greatest portion of the hardness occurring in natural waters. In some considerations it is important to know the amounts of calcium and magnesium hardness in water. For example, it is necessary to know the...

Computer Methods For Solving Equilibrium Problems

The chemical equilibrium problems presented in this chapter are relatively simple ones involving only a few species and equilibrium expressions. They have been solved using equilibrium constants, mass balances, charge balances, and sometimes proton conditions, and spreadsheets or by making simplifying assumptions and generating quadratic equations or by drawing log concentration diagrams. However, for more complex problems where many species are involved (say more than 15 to 20), where several...

Significance Of Carbon Dioxide And Mineral Acidity

Acidity is of little concern from a sanitary or public health viewpoint. Carbon dioxide is present in malt and carbonated beverages in concentrations greatly in excess of any concentrations known in natural waters, and no deleterious effects due to the carbon dioxide have been recognized. Waters that contain mineral acidity are so unpalatable that problems related to human consumption are nonexistent. Acid waters are of concern because of their corrosive characteristics and the expense involved...

Methods Of Determining Volatile Acids

Two methods of deteimining volatile acids are currently described in Standard Methods. One uses column-partition chromatography, and the other involves distillation. Several laboratories today also use gas chromatography or ion chromatography (Sec. 12.4) for the measurement of the concentration of individual volatile acids, although these procedures are not yet considered as standard. They may be in the future as we leam more about the significance of individual volatile acids in the control of...

Significance Of Chloride

Chloride in reasonable concentrations is not harmful to humans. At concentrations above 250 mg L it gives a salty taste to water, which is objectionable to many people. For this reason a secondary standard of 250 mg L for chloride in drinking water has been set by the U.S. EPA, the same value contained in the WHO guidelines. In many areas of the world where water supplies are scarce, sources containing as much as 2000 mg L are used for domestic purposes without the development of adverse...

Oxidationreduction Reactions

Oxidation-reduction reactions are among the most important with which environmental engineers and scientists deal. Many reactions of interest in wastewater treatment such as organic oxidation and methane fermentation, nitrification, and denitri-fication are of this type and are mediated by bacteria. Oxidation-reduction reactions are important in the solubilization and precipitation of iron and manganese. Oxidants such as chlorine and ozone are added to water and wastewater to bring about...

Methods Of Determining Fluoride

There are four standard methods for determination of fluoride at the present time the electrode method, two colorimetric procedures, and ion chromatography. The electrode method is the simplest but does require use of an expanded-scale pH meter and a special electrode. The principles behind and limitations of the electrode method are described under Crystalline Membrane Electrode in Sec. 12.3. The ion chromatographic technique, described in Sec. 12.4, permits analysis for fluoride and several...

Chcl2ch2br Name

Chapter 5 Basic Concepts from Organic Chemistry ch2 ch ch ch3 ch3ch2ch5cooh ch3 A contaminated groundwater contains 50 (j,g L chlorobenzene, 25 Ag L dichloromethane, and 85 xg L ethylbenzene. Using the simplified equilibrium model developed in Sec. 5.34, estimate the air-to-water ratio required to reduce the concentration of each of these compounds below 5 ig L, Assume a temperature of 25 c. If you were to design a stripping tower to remove these contaminants, would you expect your design...

Cause And Source Of Hardness

Hardness is caused by multivalent metallic cations. Such ions are capable of reacting with soap to form precipitates and with certain anions present in the water to form scale. The principal hardness-causing cations are the divalent calcium, magnesium, strontium, ferrous iron, and manganous ions. These cations, plus the most important anions with which they are associated, are shown in Table 19.1 in the order of their relative abundance in natural waters. Aluminum and ferric ions are sometimes...

Colloidal Dispersions In Liquids

Colloidal dispersions of solids, liquids, and gases in liquids are commonly encountered in environmental engineering and science. The nomenclature and behavior of each type differ somewhat consequently, discussions of each will be given. Colloidal dispersion's of solids in liquids are generally of two types, those that bind j strongly with the liquid and those that do not. Dispersions binding strongly with the I liquid are generally more stable and difficult to separate from the liquid than...

Problems

3.1 Determine the net heat of combustion of ethane gas from standard enthalpies of formation. Give the answer in kilojoules per mole of ethane. 3.2 A small quantity of hydrogen gas is sometimes present in the gas from an anaerobic digester. Determine the net heat value in kilojoules per mole available from burning this gas. 3.3 A waste containing 1 percent sulfuric acid (10,000 mg L) is neutralized by the addition of a concentrated lime slurry made by dissolving Ca(OH)2Cr) in water . If the...

Method Of Measuring

The BOD test is based upon determinations of dissolved oxygen consequently, the accuracy of the results is influenced greatly by the care given to its measurement. BOD may be measured directly in a few samples, but in general, a dilution procedure is required. For samples with 5-day BOD less than 7 mg L, it is not necessary to dilute them, provided that they are aerated to bring the dissolved-oxygen level nearly to saturation at the start of the test. Many river waters fall into this category....

Method Of Determining Alkalinity

Alkalinity Titration Curve

Alkalinity is measured volumetrically by titration with N 50 or 0.020 N H2S04 and is reported in terms of equivalent CaC03. For samples whose initial pH is above 8.3, the titration is made in two steps. In the first step the titration is conducted until the pH is lowered to 8.3, the point at which phenolphthalein indicator turns from pink to colorless. The second phase of the titration is conducted until the pH is lowered to about 4.5, corresponding to the bromcresol green end point. When the...