Page 24 - Kansas Basics Course: for small public drinking water systems Science Concepts Lesson 2 – Science Concepts is one hour lesson will help you understand the chemical and biological characteristics of water as well as hydraulics related to water. Chemical Characteristics of Water Describes the chemical characteristics of water and its effects on the physical properties of water and constituents in water. The Operator as a Chemist Chemistry is fundamental to the treatment of drinking water. When you treat water, you are basically becoming a chemist by controlling chemical reactions that are important to producing quality drinking water.
Transcript
Page 24 - Kansas Basics Course: for small public drinking water systems
Science Concepts
Lesson 2 – Science ConceptsThis one hour lesson will help you understand the chemical and biological characteristics of water as well as hydraulics related to water.
Chemical Characteristics of WaterDescribes the chemical characteristics of water and its effects on the physical properties of water and constituents in water.
The Operator as a ChemistChemistry is fundamental to the treatment of drinking water. When you treat water, you are basically becoming a chemist by controlling chemical reactions that are important to producing quality drinking water.
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Science Concepts
Chemistry of WaterThe vocabulary of chemistry describes the structure and activities of the things with which we work. As we discuss the chemistry of water you will start to learn this new vocabulary and use the new terms to describe and explain the things that you do every day.
What is Matter?Matter is anything that has mass and occupies space. Air, coffee, water, gasoline, chlorine, rocks and paper are all different forms of matter. It is pretty obvious that all matter is not alike.
States of MatterMatter can be classified into three large groups - solids, liquids, and gases. These three groups are called the physical states of matter.
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Science Concepts
HorsepowerHorsepower is a measurement of the amount of energy required to do work. Motors are rated in horsepower.
-The horsepower of an electric motor is called brake horsepower.
-The horsepower requirements of a pump are dependent on the flow and the total dynamic head.
-The horsepower output of an electric motor is directly reflected to the amperage that the motor draws. Any increase in horsepower requirements will give a corresponding increase in amperage.
-For centrifugal pumps, as the total dynamic head is increased the pump will pump less water and will require less horsepower.
States of MatterSolids have a definite shape with their molecules closely packed together and sticking firmly to each other. A solid does not change its shape to fit a container. If you put a solid on the table it would keep its shape and volume.
States of MatterLiquids maintain a constant volume but will change shape to fit the shape of their container. The molecules of the liquid move freely over one another but still stick together enough to maintain a constant volume. Pour water from a glass into a bowl. You have the same volume of water, but a different shape.
States of MatterGases have no fixed shape and their volume can be expanded or compressed to fill different sizes of containers. The molecules of gases do not stick together at all and they move about freely, filling containers of any shape and size.
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Science Concepts
Elements, Compounds & SolutionsElements
The most basic substances, which cannot be broken down into simpler forms are called elements. Some of these elements exist in nature in pure form; others are combined.
There are 115 known elements. They range from simple, light weight elements to very complex, heavy weight elements.
Many of the elements are quite familiar; oxygen, chlorine, gold, carbon, iron and calcium, for example.
Elements, Compounds & SolutionsCompounds
Most forms of matter in nature are composed of combinations of the elements. Substances composed of two or more elements are called compounds. Unlike elements, compounds can be broken into the simpler substances by chemical changes.
Example
A familiar, common compound is table salt, sodium chloride. It is a combination of sodium and chlorine.
Elements, Compounds & SolutionsSolutions
A solution is a condition in which one or more substances are uniformly and evenly mixed or dissolved. A solution has two components, a solvent and a solute. The solvent does the dissolving. The solute is the component that is dissolved.
Examples
In aqueous solutions water is the solvent. Water can dissolve many other substances; solids, liquids, and gases. When water dissolves substances it creates solutions with many impurities.
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Science Concepts
Water ContaminantsWater can contain a number of substances. When a substance can cause a negative impact to the health of the water user it is called a contaminant.
Water ContaminantsSuspended Solids
Water carries a lot of un-dissolved solids. These solids are non-polar substances and relatively large particles of silt or other material that just will not dissolve. Un-dissolved solids are referred to as suspended solids. If the water is allowed to sit quietly, as it does in a sedimentation basin or clarifier, most of the suspended solids will settle out.
Water ContaminantsDissolved Solids
The material that passes through a filter is defined as dissolved solids.
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Science Concepts
Water ContaminantsTotal Solids
In the water business, total solids are those solids, both suspended and dissolved, that remain behind when the water is removed by evaporation.
Water ContaminantsColloidal Solids
Colloidal solids are suspended solids that are so small they will not settle even if allowed to sit quietly for days or weeks. They are not dissolved but even though they are extremely tiny, they often make the water cloudy. In general anything less than 1 micron (1/1000 of a millimeter) is considered a colloidal particle. Fine silt, tiny particles of vegetation, and bacteria are examples of colloidal particles.
Dissolved GasesGases can also be dissolved in water. Not all gases dissolve to the same extent. Some dissolve easily and others not as well. Oxygen and carbon dioxide are two dissolved gases that are important to water operations.
Gases such as oxygen, carbon dioxide, hydrogen sulfide and nitrogen are examples of gases that dissolve in water.
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D.O. & TemperatureLike other solutions water at a given temperature can be saturated with oxygen. The amount of oxygen that can be dissolved at saturation depends upon the temperature of the water. The higher the temperature the lower the saturation level; the lower the temperature the higher the saturation level.
Carbon DioxideCarbon dioxide is important because of the role it plays in pH and alkalinity. Carbon dioxide is released into the water by microorganisms and consumed by algae and aquatic plants. Carbon dioxide is only slightly soluble in water. Most of the carbon dioxide reacts with the water to form carbonic acid.
MetalsWater often carries metal impurities. Although most metals are not harmful at normal levels, a few metals can cause taste and odor problems or, more seriously, be toxic to humans, animals, and microorganisms.
Most of these metals enter the water as part of compounds which ionize to release the metal as positive ions. When someone says they have iron in their water it is really iron ions.
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Science Concepts
Metal PrecipitatesUnder specific conditions the metal will often come out of solution and a precipitate will be formed. Examples of metal precipitates are the reddish brown iron rust and bluish-green copper stain. This table lists some metals commonly found in water and their potential health concerns.
Chemical Compounds Compounds are divided into two large categories; inorganic compounds and organic compounds.
Chemical Compounds Organic Compounds
Organic compounds (plants and animals) are those that contain the element carbon and are derived from material that was once alive.
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Chemical Compounds Inorganic Compounds
Inorganic compounds (rocks, soil and minerals) are just the opposite. They do not contain carbon and are not derived from living material.
TurbidityTurbidity is defined as the property of water that causes light to be scattered or absorbed. Turbidity in water is caused by suspended solids, usually particles of colloidal size. Materials that cause turbidity can cause taste and odor in drinking water and can provide a place for microorganisms to hide and avoid disinfection.
-High turbidity water appears cloudy whereas low turbidity water often sparkles with clarity.
-Water with low turbidity can still have dissolved solids, because dissolved solids do not cause light to be scattered or absorbed.
ColorColor is considered an aesthetic quality in water and has no direct health impact. Color is divided into two general categories, true color and apparent color.
True color
Color that is the result of dissolved chemicals such as humic acid (from alder leaves) is called true color. It cannot be removed by passing the water through a filter.
Apparent Color
Apparent color is the color that is contributed to the water as a result of the clay, silt or sand carried in the water. The yellow color in a river is often the result of the yellow clay carried by the water.
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Science Concepts
pHpH is a measure of the hydrogen ion (H+) concentration. The pH scale ranges from 0 to 14 with 7 being the center or neutral value. pH values below 7 are acidic and pH values above 7 are basic. The pH scale is an inverse logarithmic scale (pH = -log{H+}). Low pH values are actually high H+ concentration, while high pH values are low H+ concentration. The difference between any two consecutive pH values is ten fold in H+ concenentration.
pH is measured using a pH meter. Any abnormal readings can be an indication of a change in water quality or a problem with the pH meter.
AlkalinityAlkalinity is the measure of water’s ability to neutralize an acid.
-Alkalinity can be defined as a buffer; a chemical that tends to stabilize and prevent fluctuations in pH.
-It is usually beneficial to have significant alkalinity in the water to prevent quick changes in pH.
-Quick changes in pH interfere with the effectiveness of common water treatment processes.
-Low alkalinity also contributes to corrosive tendencies of water. Alkalinity below 80 mg/L is considered low.
-Alkalinity should not be confused with pH. It is the result of carbonate, bicarbonate and hydroxide ions in the water.
-Even water with an acid pH can contain alkalinity.
-Typical water treatment chemicals used to increase alkalinity are quick lime, hydrated lime, and soda ash.
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HardnessHardness is caused by the presence of magnesium and calcium ions in water. Hardness causes soaps and detergents to be less effective and contributes to scale formation in pipes and boilers. Although there are no known health hazards to high hardness, water that contains excessive hardness must often be softened by lime precipitation or ion exchange.
Corrosion/Hardness TableLow hardness contributes to the corrosive tendencies of water. Hardness and alkalinity often occur together because some compounds can contribute both alkalinity and hardness ions. However, hardness can be present when the alkalinity is low, and visa versa.
Hardness can be classified into four levels as identified in this hardness classification table.
Biological Characteristics of WaterA brief discussion of waterborne diseases and the microorganisms which cause those diseases.
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Science Concepts
MicrobiologyMicrobiology is the study of microorganisms; very small living things. Microorganisms of interest to the water industry include bacteria, protozoa, viruses, algae, and fungi.
Waterborne DiseasesWater system operators are mostly concerned about how to control microorganisms, because they are a major health concern; the causes of waterborne diseases. Organisms that cause disease by transmission through contaminated water are called waterborne pathogens.
BacteriaBacteria are among the most common microorganisms in water. Bacteria are primitive, single celled organisms with a variety of shapes and nutritional needs.
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Science Concepts
Disinfection of Bacteria The destruction of pathogenic microorganisms is called disinfection. Disinfection does not mean that all microbial forms are killed. That would be sterilization. However, disinfection does reduce the number of disease causing organisms to an acceptable number. Growing bacteria are fairly easy to control by disinfection. Some bacteria, however, form spores, which are much more difficult to destroy. Spores are survival structures formed by some bacteria to resist harsh, threatening environments.
Waterborne Diseases Caused by Bacteria Bacteria are responsible for a number of the most infamous epidemic diseases. The bacterial pathogens responsible for these diseases enter potential drinking water supplies through fecal contamination and are ingested by humans if the water is not properly treated and disinfected. The table below lists a number of bacterial waterborne diseases.
ProtozoaProtozoa are one celled animal-like organisms with a fairly complex cellular structure. The protozoa are the giants of the microbial world. They are many times larger than bacteria. They range in size from 4 microns to 500 microns. The larger ones can almost be seen with the naked eye.
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Science Concepts
Protozoa Life CycleMost protozoa have a complex life cycle in which they alternate between an active growth phase, when they are called trophozoites, and a resting stage, called cysts. Cysts are an extremely resistant structure that protect the organism from destruction when it encounters harsh environmental conditions.
Disinfection of Protozoa Because of their relative complexity and their ability to form the extremely resistant cysts, control of protozoa requires higher disinfectant concentrations and longer contact time. In fact, some types of protozoa may be completely resistant to chlorination.
Waterborne Diseases Caused by ProtozoaThree protozoan waterborne diseases are listed in the table below.
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Science Concepts
VirusesViruses are the midgets of the microbial world. They are many times smaller than bacteria. They range in size from 0.02 to 0.25 microns in diameter. Viruses are intracellular parasites that must have a host cell in which to multiply. They are extremely simple life forms. A central molecule of genetic material is surrounded by a protein shell called a capsid and sometimes by a second layer called an envelope. They contain no mechanisms by which to obtain energy or reproduce on their own.
Virus Life CycleThere are almost as many kinds of viruses as there are types of other living organisms. Viruses exist that can invade essentially every kind of living cell; animals, plants, insects, fish and even bacteria. After they invade their specific host they take over and multiply. The host cell is destroyed and hundreds of additional viruses are released into the environment.
Disinfection of VirusesBecause viruses lack sensitive cellular machinery and because they have relatively tough capsids and envelopes they are hard to destroy by normal disinfection practices. Increased disinfectant concentration and contact time must be used to effectively destroy viruses.
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Science Concepts
Waterborne Diseases Caused by VirusesThe diseases listed below are caused by waterborne viruses.
Water Hydraulics Describes water hydraulics specific to small drinking water system operations.
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Science Concepts
Weight-Volume RelationshipCubic feet and gallons are both used to describe a volume of water. There is a defined relationship between these two methods of measurement. The specific weight of water is defined relative to a cubic foot.
-One cubic foot of water weighs 62.4 pounds.
-One cubic foot of water contains 7.48 gallons.
-With these two relationships we can determine the weight of one gallon of water.
-This is accomplished by dividing the weight (62.4 lbs) by the volume in gallons (7.48 gallons per cubic foot).
-With this information we can convert cubic feet to gallons by simply multiplying the number of cubic feet by 7.48 gallons per cubic foot.
-Find the number of gallons in a reservoir that has a
Force MeasurementIn the English system force and pressure (or weight) are often used in the same way. The weight of one cubic foot of water is 62.4 pounds. The force exerted on the bottom of the one foot cube is 62.4 pounds. If we have two cubes stacked on top of one another the force on the bottom will be 124.8 pounds.
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Science Concepts
Pressure MeasurementPressure is a force per unit of area, pounds per square inch or pounds per square foot are common expressions of pressure. The pressure on the bottom of our cube is 62.4 pounds per square foot. It is normal to express pressure in pounds per square inch (psi).
-This can be accomplished by determining the weight of one square inch of our cube which is one foot high. Since the cube is 12 inches on each side, the number of square inches on the bottom surface of the cube is 12 X 12 = 144 square inches.
-Now, by dividing the weight by the number of square inches we can determine the weight on each square inch. This is the weight of a column of water one inch square and one foot tall.
-If the column of water were two feet tall, then the pressure would be 2ft X 0.433 psi/ft = 0.866 psi
Force & Pressure Conversions Click the “NEXT” button to work through 2 examples...
We can convert feet of head to psi by multiplying the feet of head times 0.433 psi/ft.
-A reservoir is 40 feet tall. Find the pressure at the bottom of the reservoir.
-The conversion of psi to feet is simply made by dividing the psi by 0.433 psi/ft.
-Find the height of water in a tank if the pressure at the bottom of the tank is 12 psi.
Pressure and HeadPressure is directly related to the height of a column of fluid. This height is called head or feet of head. From this we can see there is a direct relationship between feet of head and pressure. The relationship is that for every 1 foot of head there is a pressure of 0.433 psi.
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Pressure Relative to Water HeightThe pressure at the bottom of a container is only affected by the height of water in the container and not by the shape of the container.
Pressure and Water Level ExampleAdjust the elevation of the water with the slider bars to see how pressure is directly related to the level of water, not the number of gallons, in the tank!
Velocity MeasurementVelocity is the speed at which water is moving along a pipe or through a basin. Velocity is usually expressed in feet per second, ft/sec.
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Science Concepts
Flow MeasurementFlow is commonly expressed in gallons per minute (gpm) and/or cubic feet per second (cfs).
GPM & CFS RelationshipThere is a relationship between gallons per minute and cubic feet per second. One cubic foot per second is equal to 448 gallons per minute.
Flow EquationThe basic equation for determining flow is:
Q = V x A; Where: Q = cfs (ft3/sec); V = ft/sec; A = ft2
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Static Pressure & HeadlossNow, that we familiar with the concepts of velocity and flow, let us understand the concepts of pressure that is related to the flow of water. These concepts are static pressure and headloss.
-The pressure measured when there is no water moving in a line or the pump is not running is called static pressure.
-When water is allowed to run through a pipe and the pressure (called pressure head) measured at various points along the way we find that the pressure decreases the further we are from the sources.
The reason for this reduction in pressure is a phenomenon called headloss. Headloss is the loss of energy (pressure) due to friction.
-In a pipe the factors that contribute to headloss are: roughness of pipe, length, C factor, diameter, and velocity of water.
-Each type of fitting has a specific headloss depending upon the velocity of water through the fitting.
-For instance the headloss through a check valve is two and one quarter times greater than through a ninety degree elbow and ten times greater than the headloss through an open gate valve.
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Science Concepts
Pumping HydraulicsThe mechanics of water is also related to the equipment that used in pumping of water. Let us now learn about pumping hydraulics.
-Static head is the distance between the suction and discharge water levels when the pump is shut off. Static head conditions are often indicated with the letter Z.
-Suction lift is the distance between the suction water level and the center of the pump impeller. This term is only used when the pump is in a suction lift condition. A pump is said to be in a suction lift condition any time the eye (center) of the impeller is above the water being pumped.
-Suction head is the distance between the suction water level and the center of the pump impeller when the pump is in a suction head condition. A pump is said to be in a suction head condition any time the eye (center) of the impeller is below the water level being pumped.
Velocity Head & Total Dynamic HeadVelocity head is the amount of energy required by the pump and motor to overcome inertia and bring the water up to speed.
-Velocity head is often shown mathematically as V2/2g. (g is the acceleration due to gravity - 32.2ft/sec2).
-Total dynamic head (TDH) is a theoretical distance. It is the static head, velocity head and headloss required to get the water from one point to another.
