Introduction to Environmental Engineering Code No. (PE389) Lec. 3.

WELCOME

DR.KHALED ALI

Introduction to Environmental EngineeringCode No. (PE389)

Lec. 3

Measurement of Water Quality

Introduction● Quantitative measurements of pollutants are obviouslynecessary before water pollution can be controlled.● measurement of these pollutants is burdened by difficulties.1. Sometimes specific materials responsible for the pollutionare not known.2. pollutants are generally present at low concentrations, and2 very accurate methods of detection are required.

• Many water pollutants are measured in terms of milligrams of the substance per liter of water (mg/L).

• In older publications pollutant concentrations are expressed as parts per million (ppm), a weight/weight parameter. If the liquid involved is water, ppm is identical with mg/L, since one liter (L) of water weighs 1000 grams (g).

• A third commonly used parameter is percent, a weight/weight relationship.

• Note that 10,000 ppm = 1% and is equal to 10,000 mg/L only when 1 mL = 1 g

Chemical parameters Of Drinking Water Quality

DISSOLVED OXYGEN (DO)

Dissolved oxygen is inversely proportional to temperature, and the maximum oxygen that can be dissolved in water at most ambient temperatures is about10 mg/L. The saturation value decreases rapidly with increasing water temperature, as shown in Table 4-1.

pH The pH of a solution is a measure of

hydrogen ion concentration, which in turn is a measure of its acidity. Pure water dissociates slightly into equal concentrations of hydrogen and hydroxyl (OH-) ions.

H2O ↔ H+ + OH-

An excess of hydrogen ions makes a solution acidic, whereas any absence of H+ ions, or an excess of hydroxyl ions, makes it basic.

pH The measurement of pH is now almost universally

by electronic means.Electrodes that are sensitive to hydrogen ion

concentration (strictly speaking, the hydrogen ion activity) convert the signal to electric current.

pH is important in almost all phases of water and wastewater treatment. Aquatic organisms are sensitive to pH changes, and biological treatment requires either pH control or monitoring.

In water treatment as well as in disinfection and corrosion control, pH is important in ensuring proper chemical treatment.

ALKALINITY

A parameter related to pH is alkalinity, or the buffering capacity of the water against acids.

Water that has a high alkalinity can accept large doses of an acid without lowering the pH significantly.

Waters with low alkalinity, such as rainwater, can experience a drop in the pH with only a minor addition of hydrogen ion.

physical parameters of drinking water quality.

TURBIDITY

Water that is not clear but "dirty," in the sense that light transmission is inhibited, is considered turbid.

COLOR AND ODOR Color and odor are both important measurements in

water treatment. Along with turbidity they are called physical parameters of drinking water quality.

Color and odor are important from the standpoint of aesthetics (visual). If water looks colored or smells bad, people instinctively (automatically) avoid using it, even though it might be perfectly safe from the public health aspect. Both color and odor may be and often are caused by organic substances

Color is measured by comparison with standards. When multicolored industrial wastes are involved, such color measurement is meaningless.

Odor is measured by successive dilutions of the sample with odor-free water until the odor is no longer detectable. This test is obviously subjective and depends entirely on the olfactory senses of the tester.

SOLIDSWastewater treatment is complicated by

the dissolved and suspended inorganic material the wastewater contains.

In discussion of water treatment, both dissolved and suspended materials are called solids.

The separation of these solids from the water is one of the primary objectives of treatment.

SOLIDSThe usual definition of solids, however, is

the residue after evaporation at 103°C (slightly higher than the boiling point of water).

The solids thus measured are known as total solids (TS).

Total solids are divided into two fractions:

the total dissolved solids (TDS) and the total suspended solids (TSS).

SOLIDSSuspended solids are separated from

dissolved solids by filtering the water through a filter paper .

The suspended material is retained on the filter paper, while the dissolved fraction passes through.

If the initial dry weight of the filter paper is known, the subtraction of this from the total weight of the filter and the dried solids caught in the filter paper yields the weight of suspended solids, expressed in milligrams per liter.

SOLIDSSolids may be classified in another way: 1. Volatile Solids. Those that are volatilized at high

temperature (600°C)2. Fixed Solids. Those are not volatilized at 600°C. Volatile solids are usually organic compounds. Obviously, at 600°C, the temperature at which the

combustion takes place, some of the inorganics are decomposed and volatilized, but this is not considered a serious drawback.

Measurement of the volatile fraction of suspended material, the volatile suspended solids, is made by burning the suspended solids and weighing them again. The loss in weight is interpreted as the volatile suspended solids.

ExampleGiven the following data:Weight of a dish = 48.6212 g.100 mL of sample is placed in a dish and

evaporated. Weight of the dish and dry solids = 48.6432

g.The dish is then placed in a 600°C furnace,

then cooled. Weight = 48.6300 g.Find the total, fixed, and volatile solids

(expressed as mg/L).

QuestionsDefine turbidity? What is its importance

and what is the units of its measurementHow can you determine color & odor?Define pH? Mention two importance of

determining pH? what is the benefit of a high alkaline

water?Mention the classification of solids