Core Concepts for the Civil PE Exam Water Resources and Environmental Depth

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Civil PE Exam Water Resources and Environmental  Depth

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Civil PE Exam Water Resources Online Study Guide
Click below to expand each topic. All of this is included in the paperback version of the Water Resources Depth

Analysis and Design

Stream Degradation


Stream Degradation is the wearing away and lowering of a stream bed over time due to erosion from the flow of water within a stream. Often flow rates and velocities which are too high can cause this. The removal of the soil can affect the water quality by increasing the amount of sediment in the water and therefore decreasing clarity and oxygen in the stream.




Oxygen Dynamics


Oxygen dynamics is related to the amount of oxygen present in flowing water. More specifically this type of oxygen is referred to as Dissolved Oxygen (DO). Simply put dissolved oxygen is the amount of gaseous oxygen present in a moving volume of water. DO is also affected by the temperature and must be adjusted appropriately

Dissolved Oxygen is one of the more relevant parameters when determining the quality of a mass of water so it is important to be able to understand and analyze its content. Typical concentrations of DO may vary greatly throughout the year for a given body of water. Concentrations may range anywhere from 1 mg/L to 20 mg/L. The level that is appropriate is based on the type of life that needs to be sustained. Certain organisms require a larger content of DO to survive than others. For example, larger marine animals such as trout or salmon may require 12-14 mg/L whereas others like pike may only need 3-4 mg/L.

Re-aeration is a process used to increase the Dissolved Oxygen content of a specific water source. This is where oxygen from the air is dissolved into the water by causing turbulence in the water. Turbulence causes the water to move rapidly by forces such as a physical force, wind or currents. This causes a mixing of the water and air in which increased amounts of oxygen will begin to dissolve into the body of water. Turbulence can be used to mix bottom and top areas of water which may have uneven amounts of dissolved oxygen. Often the top portion of water will have higher concentrations. Mixing them will more evenly distribute the dissolved oxygen. To determine the final DO concentration resulting from the mixing of two sources, use the following:

C = Concentration

Q = Flow rate




Total Maximum Daily Load (TMDL)


Total Maximum Daily Load often referred to as TMDL, relates to the Clean Water Act of 1972 which set the standards for pollutants in water. TMDL in accordance with this legislation provides the maximum amount of a pollutant which a body of water can receive that will not violate the quality standards. Some of the pollutants which are of concern are nitrogen, phosphorous, and sediment among others.

TMDL is the sum of all the pollutants entering a system and the inclusion of a factor of safety:

TMDL=WLA+LA+MOS+SV

WLA = Waste Land Allocation (Direct flow into the body such as pipes and ditches)

LA = Land Allocation (Pollutants from land areas)

MOS = Margin of Safety

SV = Seasonal Variation




Biological Contaminants


Biological contaminants refers to the amount of organisms in the water. These organisms are also sometimes referred to as microbes. The microbes, because they are living, will reproduce if there is a sufficient supply of food. The food is called the substrate and may or may not be limited to facilitate the biological growth. The Monod equation is used to determine the rate at which substrate is converted into biomass which is simply the total mass of microorganisms in a given volume of water. The equation is as follows:




Chemical Contaminants


Chemical contaminants are a severe concern in water as they may impose health risks to the public. Water should be tested regularly for the presence of such chemicals and action taken immediately. Since chemicals pose a risk to human life, acceptable levels of risk need to be identified and associated with the concentrations of the chemical. The following equation can be used:





Hydraulics-Closed Conduit

Stream Degradation


Stream Degradation is the wearing away and lowering of a stream bed over time due to erosion from the flow of water within a stream. Often flow rates and velocities which are too high can cause this. The removal of the soil can affect the water quality by increasing the amount of sediment in the water and therefore decreasing clarity and oxygen in the stream.




Oxygen Dynamics


Oxygen dynamics is related to the amount of oxygen present in flowing water. More specifically this type of oxygen is referred to as Dissolved Oxygen (DO). Simply put dissolved oxygen is the amount of gaseous oxygen present in a moving volume of water. DO is also affected by the temperature and must be adjusted appropriately

Dissolved Oxygen is one of the more relevant parameters when determining the quality of a mass of water so it is important to be able to understand and analyze its content. Typical concentrations of DO may vary greatly throughout the year for a given body of water. Concentrations may range anywhere from 1 mg/L to 20 mg/L. The level that is appropriate is based on the type of life that needs to be sustained. Certain organisms require a larger content of DO to survive than others. For example, larger marine animals such as trout or salmon may require 12-14 mg/L whereas others like pike may only need 3-4 mg/L.

Re-aeration is a process used to increase the Dissolved Oxygen content of a specific water source. This is where oxygen from the air is dissolved into the water by causing turbulence in the water. Turbulence causes the water to move rapidly by forces such as a physical force, wind or currents. This causes a mixing of the water and air in which increased amounts of oxygen will begin to dissolve into the body of water. Turbulence can be used to mix bottom and top areas of water which may have uneven amounts of dissolved oxygen. Often the top portion of water will have higher concentrations. Mixing them will more evenly distribute the dissolved oxygen. To determine the final DO concentration resulting from the mixing of two sources, use the following:

C = Concentration

Q = Flow rate




Total Maximum Daily Load (TMDL)


Total Maximum Daily Load often referred to as TMDL, relates to the Clean Water Act of 1972 which set the standards for pollutants in water. TMDL in accordance with this legislation provides the maximum amount of a pollutant which a body of water can receive that will not violate the quality standards. Some of the pollutants which are of concern are nitrogen, phosphorous, and sediment among others.

TMDL is the sum of all the pollutants entering a system and the inclusion of a factor of safety:

TMDL=WLA+LA+MOS+SV

WLA = Waste Land Allocation (Direct flow into the body such as pipes and ditches)

LA = Land Allocation (Pollutants from land areas)

MOS = Margin of Safety

SV = Seasonal Variation




Biological Contaminants


Biological contaminants refers to the amount of organisms in the water. These organisms are also sometimes referred to as microbes. The microbes, because they are living, will reproduce if there is a sufficient supply of food. The food is called the substrate and may or may not be limited to facilitate the biological growth. The Monod equation is used to determine the rate at which substrate is converted into biomass which is simply the total mass of microorganisms in a given volume of water. The equation is as follows:




Chemical Contaminants


Chemical contaminants are a severe concern in water as they may impose health risks to the public. Water should be tested regularly for the presence of such chemicals and action taken immediately. Since chemicals pose a risk to human life, acceptable levels of risk need to be identified and associated with the concentrations of the chemical. The following equation can be used:





Hydraulics-Open Channel

Drinking Water Distribution Systems


As the name suggests, systems are developed so that drinking water can be safely and efficiently distributed to the populations. These systems may consist of many components such as pipes, reservoirs, pumps, storage tanks and many others. These components carry water from a centralized distribution plant which maintains regulated levels of safe drinking water.




Drinking Water Treatment Process


There is a large number of processes which can be performed to get water meeting quality standards. The selection of which processes are performed depends heavily on the characteristics of the water specific to a certain plant. The procedure can be divided into 3 components: Pretreatment, Treatment, and Special Treatment. Here we will provide a breakdown of what may be involved in each portion depending on the type of water that needs to be treated.

Pretreatment

Screening: As the name suggests suspended solids which are large enough to be physically removed by allowing water to flow through fine screens is an initial process that is necessary to remove any debris.

Microstraining: A second level of screening used to remove the more finer debris. This process is very effective in the removal of algae.

Plain Settling: A removal of sediment by allowing the water to sit and the natural movement of sediments to fall to the bottom to occur.

Aeration: The rapid moving of water to allow mixing or the infusion of oxygen into the water. Aeration can have many benefits depending on the desired result. It can increase dissolved oxygen, decrease dissolved gases, reduce iron and manganese, or decrease odor and taste compounds.

Treatment

Lime Softening: As the name suggests this is the process of adding lime water (calcium hydroxide) to soften water. This additive will react with the calcium and manganese to form precipitates.

Coagulation and Sedimentation: This process is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. This process is essential to the treatment of water and is covered in greater detail later on.

Rapid Sand Filtration/Pressure Sand Filtration: See section on filtration.




Demands


Water demands need to be measured and analyzed so that distribution systems may be properly designed. Water demand is most often specified as gallons per capita per day (gpcd). It can also be expressed as Average Annual Daily Flow (AADF) which as the name suggests is the average daily use of water per person averaged over a year time period. A common value used for basic design purposes is often taken as 165 gpcd but should be adjusted based on the intended water use whether it be residential, commercial, or industrial.

Besides the average flow demand throughout a day, there may be increased demands instantaneously which systems must have adequate capacity for. The average annual daily flow times a specified multiplier is often used to determine the instantaneous demand:

Qinstant=M(AADF)

It is also important to note that per capita demand needs to account for the entire population but it must often be specified at what time period. Because of growth, a distribution system should meet some future predicted growth of population.




Storage


Water supplies need to be stored for a variety of uses and as well as to ensure adequate supply in times of growth or emergency. Water can be distributed from storage either through gravity or pumping. Gravity is available when there is a sufficiently high point in elevation relative to the population. Otherwise pumping is necessary. Water is most often stored in surface or elevated tanks. Within these tanks the elevation of the surface water is monitored to determine the appropriate distribution pressure. These are often monitored by altitude valves.




Rapid Mixing


This process as mentioned above is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. For this reason we have combined two of the NCEES syllabus items since it is most appropriate to discuss these topics together. The most common type of coagulates are aluminum sulfate commonly referred to simply as alum. Others include ferrous sulfate and chlorinated copperas. Alum is often provided in doses in the range of 5-50 mg/L. There are three requirements for Alum to be effective:

  1. A large enough quantity of Alum must be present to neutralize the negative particles present in the water
  2. Enough alkalinity must be present to facilitate the reaction of aluminum sulfate to aluminum hydroxide
  3. The PH must be within the acceptable range which is a function of the type on contaminant. Typically it is taken between 6-7

The amount of coagulate to successfully form floc must be determined. The equation for the feed rate is:

F = Feed Rate

D = Dose

Q = Flow Rate

P = Purity

G = Availability (1.0 is not specified)




Taste and Odor Control


There are many processes which can aid in the elimination of undesirable taste and odor in water. Some include chlorination, aeration and micro straining. To identify the presence of taste or order, the threshold odor number (TON) is established and can be calculated as per below:

TON= (V Raw Sample+V Dilution Water)/VRaw Sample

Typically, a TON of less than 6 is desirable




Sedimentation


A plain sedimentation tank is used to allow water which includes suspended sediments to settle out. The time and velocity for the particles to settle is a function of the temperature of the water, the particle size and the specific gravity of the particles (however this is often taken as 2.65 for analysis). Assumed settling velocities can be taken as the following to calculate the actual settling velocities:

Gravel: 3.28 ft/s

Coarse Sand: 0.328 ft/s

Fine Sand: 0.0328 ft/s

Silt: 0.000328 ft/s

Then the approach to determining the settlement time can be determined by first calculating the Reynolds number:




Filtration


Filtration is used to remove excess floc, precipitates from softening, algae, debris and any other suspended byproducts remaining in the treated water. The most common is rapid sand filtration. Rapid Sand Filtration is the filtering of water through a bed of sand and gravel as a medium for removing suspended particles. Water moves through a layer of sand in which the suspended particles will be held back by the sand. Depending on the type of filter, the loading rate can be anywhere from 2 – 10 gpm/ft2. The loading rate can be determined by the following equation:

Load Rate= Flow Rate/Area

Filters often need to be cleaned and therefore there is a high maintenance cost. The pores between the filters will become clogged and need to get washed out. To counteract this is a process called back washing. This is where water is pumped slowly in the reverse direction of the water to be filtered so that the pores in the sand can be expanded to release any trapped material. It is important during backwashing to monitor the rise rate of the water to ensure it does not exceed the settling velocity of the smallest particle intended to be left in the filter. These rates are often taken as about 1-3 ft/min. The amount of backwash needed can be determined by:

V= Area Filter(Rise Rate)(t Backwash)




Hardness and Softening


Hardness is a measure of the presence of calcium and magnesium ions expressed as calcium carbonate (CaCO3). Practically, hardness in water does not provide any health concerns but does have an effect on the usefulness of the water. One of the main concerns is often that hardness in water will greatly reduce the effectiveness of soap. It also has a detrimental effect on the pipes and storage facilities of a water distribution system.

There are two types of hardness:

Carbonate Hardness: Water containing Bicarbonate (HCO3-)

Noncarbonate Hardness: Remaining hardness not carbonate due to sulfates, chlorides, and nitrates.

Hardness can also be expressed as total hardness which is the sum of carbonate and noncarbonate hardness in mg/L as CaCO3. There is a clear connection between the alkalinity of water and the hardness. The following assumptions can be made:

  • If Total Hardness = Alkalinity, all hardness is carbonate and there are no sulfates, chlorides, or nitrates present
  • If Total Hardness > Alkalinity, noncarbonate hardness is present
  • If Total Hardness < Alkalinity, all hardness is carbonate and the remainder of the bicarbonate is from additional sources

Water softening is the removal of hardness through the use of lime and soda ash in mg/L as CaCO3. It is important to note that lime will attack any carbon dioxide in water first and then begin with the removal of any carbonate hardness before the noncarbonate.




Disinfection


Disinfectants were defined earlier in the wastewater section. Here we will discuss by products.

Chlorine in water produces the following chemical reaction depending on PH

PH > 4: Cl2+ H2O →HCl+HOCl

PH > 9: HOCl → H++ OCl-

HCl and HOCL are hydrochloric and hypochlorous acids respectively. You can see that at PH greater than 9, the hypochlorous acid becomes hydrogen and hypochlorite ions.





Hydrology

Drinking Water Distribution Systems


As the name suggests, systems are developed so that drinking water can be safely and efficiently distributed to the populations. These systems may consist of many components such as pipes, reservoirs, pumps, storage tanks and many others. These components carry water from a centralized distribution plant which maintains regulated levels of safe drinking water.




Drinking Water Treatment Process


There is a large number of processes which can be performed to get water meeting quality standards. The selection of which processes are performed depends heavily on the characteristics of the water specific to a certain plant. The procedure can be divided into 3 components: Pretreatment, Treatment, and Special Treatment. Here we will provide a breakdown of what may be involved in each portion depending on the type of water that needs to be treated.

Pretreatment

Screening: As the name suggests suspended solids which are large enough to be physically removed by allowing water to flow through fine screens is an initial process that is necessary to remove any debris.

Microstraining: A second level of screening used to remove the more finer debris. This process is very effective in the removal of algae.

Plain Settling: A removal of sediment by allowing the water to sit and the natural movement of sediments to fall to the bottom to occur.

Aeration: The rapid moving of water to allow mixing or the infusion of oxygen into the water. Aeration can have many benefits depending on the desired result. It can increase dissolved oxygen, decrease dissolved gases, reduce iron and manganese, or decrease odor and taste compounds.

Treatment

Lime Softening: As the name suggests this is the process of adding lime water (calcium hydroxide) to soften water. This additive will react with the calcium and manganese to form precipitates.

Coagulation and Sedimentation: This process is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. This process is essential to the treatment of water and is covered in greater detail later on.

Rapid Sand Filtration/Pressure Sand Filtration: See section on filtration.




Demands


Water demands need to be measured and analyzed so that distribution systems may be properly designed. Water demand is most often specified as gallons per capita per day (gpcd). It can also be expressed as Average Annual Daily Flow (AADF) which as the name suggests is the average daily use of water per person averaged over a year time period. A common value used for basic design purposes is often taken as 165 gpcd but should be adjusted based on the intended water use whether it be residential, commercial, or industrial.

Besides the average flow demand throughout a day, there may be increased demands instantaneously which systems must have adequate capacity for. The average annual daily flow times a specified multiplier is often used to determine the instantaneous demand:

Qinstant=M(AADF)

It is also important to note that per capita demand needs to account for the entire population but it must often be specified at what time period. Because of growth, a distribution system should meet some future predicted growth of population.




Storage


Water supplies need to be stored for a variety of uses and as well as to ensure adequate supply in times of growth or emergency. Water can be distributed from storage either through gravity or pumping. Gravity is available when there is a sufficiently high point in elevation relative to the population. Otherwise pumping is necessary. Water is most often stored in surface or elevated tanks. Within these tanks the elevation of the surface water is monitored to determine the appropriate distribution pressure. These are often monitored by altitude valves.




Rapid Mixing


This process as mentioned above is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. For this reason we have combined two of the NCEES syllabus items since it is most appropriate to discuss these topics together. The most common type of coagulates are aluminum sulfate commonly referred to simply as alum. Others include ferrous sulfate and chlorinated copperas. Alum is often provided in doses in the range of 5-50 mg/L. There are three requirements for Alum to be effective:

  1. A large enough quantity of Alum must be present to neutralize the negative particles present in the water
  2. Enough alkalinity must be present to facilitate the reaction of aluminum sulfate to aluminum hydroxide
  3. The PH must be within the acceptable range which is a function of the type on contaminant. Typically it is taken between 6-7

The amount of coagulate to successfully form floc must be determined. The equation for the feed rate is:

F = Feed Rate

D = Dose

Q = Flow Rate

P = Purity

G = Availability (1.0 is not specified)




Taste and Odor Control


There are many processes which can aid in the elimination of undesirable taste and odor in water. Some include chlorination, aeration and micro straining. To identify the presence of taste or order, the threshold odor number (TON) is established and can be calculated as per below:

TON= (V Raw Sample+V Dilution Water)/VRaw Sample

Typically, a TON of less than 6 is desirable




Sedimentation


A plain sedimentation tank is used to allow water which includes suspended sediments to settle out. The time and velocity for the particles to settle is a function of the temperature of the water, the particle size and the specific gravity of the particles (however this is often taken as 2.65 for analysis). Assumed settling velocities can be taken as the following to calculate the actual settling velocities:

Gravel: 3.28 ft/s

Coarse Sand: 0.328 ft/s

Fine Sand: 0.0328 ft/s

Silt: 0.000328 ft/s

Then the approach to determining the settlement time can be determined by first calculating the Reynolds number:




Filtration


Filtration is used to remove excess floc, precipitates from softening, algae, debris and any other suspended byproducts remaining in the treated water. The most common is rapid sand filtration. Rapid Sand Filtration is the filtering of water through a bed of sand and gravel as a medium for removing suspended particles. Water moves through a layer of sand in which the suspended particles will be held back by the sand. Depending on the type of filter, the loading rate can be anywhere from 2 – 10 gpm/ft2. The loading rate can be determined by the following equation:

Load Rate= Flow Rate/Area

Filters often need to be cleaned and therefore there is a high maintenance cost. The pores between the filters will become clogged and need to get washed out. To counteract this is a process called back washing. This is where water is pumped slowly in the reverse direction of the water to be filtered so that the pores in the sand can be expanded to release any trapped material. It is important during backwashing to monitor the rise rate of the water to ensure it does not exceed the settling velocity of the smallest particle intended to be left in the filter. These rates are often taken as about 1-3 ft/min. The amount of backwash needed can be determined by:

V= Area Filter(Rise Rate)(t Backwash)




Hardness and Softening


Hardness is a measure of the presence of calcium and magnesium ions expressed as calcium carbonate (CaCO3). Practically, hardness in water does not provide any health concerns but does have an effect on the usefulness of the water. One of the main concerns is often that hardness in water will greatly reduce the effectiveness of soap. It also has a detrimental effect on the pipes and storage facilities of a water distribution system.

There are two types of hardness:

Carbonate Hardness: Water containing Bicarbonate (HCO3-)

Noncarbonate Hardness: Remaining hardness not carbonate due to sulfates, chlorides, and nitrates.

Hardness can also be expressed as total hardness which is the sum of carbonate and noncarbonate hardness in mg/L as CaCO3. There is a clear connection between the alkalinity of water and the hardness. The following assumptions can be made:

  • If Total Hardness = Alkalinity, all hardness is carbonate and there are no sulfates, chlorides, or nitrates present
  • If Total Hardness > Alkalinity, noncarbonate hardness is present
  • If Total Hardness < Alkalinity, all hardness is carbonate and the remainder of the bicarbonate is from additional sources

Water softening is the removal of hardness through the use of lime and soda ash in mg/L as CaCO3. It is important to note that lime will attack any carbon dioxide in water first and then begin with the removal of any carbonate hardness before the noncarbonate.




Disinfection


Disinfectants were defined earlier in the wastewater section. Here we will discuss by products.

Chlorine in water produces the following chemical reaction depending on PH

PH > 4: Cl2+ H2O →HCl+HOCl

PH > 9: HOCl → H++ OCl-

HCl and HOCL are hydrochloric and hypochlorous acids respectively. You can see that at PH greater than 9, the hypochlorous acid becomes hydrogen and hypochlorite ions.





Groundwater and Wells

Wastewater Collection Systems


Wastewater is collected by a network of pipes known as sanitary sewer. Some residents may not be connected to the sewer line and may resort to septic tanks for their wastewater disposal. Wastewater in sewer networks is transported to the wastewater treatment plants to be treated. Lift stations are pump stations which can be used to facilitate the transportation of the waste water to the treatment plant.

Smoke testing is a method of determining if there are leaks in a wastewater system. Smoke is pumped into a pipe and will seep through any cracks which can then be identified.

Infiltration is water which enters the system due to imperfections in the system such as cracks in the line or improperly constructed portions.

Inflow is water that enters the system from unanticipated or illegal means.




Wastewater Treatment Process


Wastewater treatment processes are the procedures for treating wastewater so that it may be used again. This process will remove sediments, sludge, taste, odors, and any other undesirable characteristics of the water. The process can be divided into preliminary, primary, and secondary treatment which will be discussed further below.




Wastewater Flow Rates


The quantity of wastewater from a municipal needs to be determined to properly design the treatment system. This is based on anticipated discharge from residential, commercial and other buildings. In addition, the system must account for infiltration and inflow as defined previously.

Flow rate can be approximated as the average flow or the peak flow. The peak flow is the highest daily flow rate. The average and peak flow are related by the peaking factor:

The peak factor can also be approximated by the population using the Harmon equation: P is the population in thousands of people




Preliminary Treatment


Preliminary treatment is the first step in the wastewater treatment process. This portion of the process is mostly the mechanical removal of debris and other large objects which may be caught in the flow. Heavy chemicals and large amounts of oil are also removed during this process. In general, anything that can be identified with the naked eye and easily screened will be removed during the preliminary treatment process. This process is often performed with large mechanical screens or filters. These large obstructions must also be removed so that they do not damage or impede the subsequent processes.




Solids Treatment


Mixed Liquor Suspended Solids (MLSS) is the concentration of bacteria, solids, and any other undesirable material in sludge. To remove sludge, the MLSS is considered food for the activated microorganisms in the aeration process. It is often important to determine the food to microorganism ratio from the equation below:




Phosphorous Removal


Phosphorous removal can be separated into two different types. A small percentage is insoluble and can be removed during primary settling. The remaining amount is soluble and must be chemically converted to an insoluble material for removal.

Often aluminum sulfate, ferric sulfide, and lime is used to complete this process so that the phosphorous can precipitate and settle for removal. The most common is aluminum sulfate. The Chemical equations for removal are:




Nitrification and Dentrification


Nitrification is the use of oxygen by autotrophic bacteria. In this process the bacteria oxidizes ammonia to nitrites and nitrates. This process is important to understand as it relates to determining the Biochemical Oxygen Demand (BOD) of a particular sample and more specifically, the Ultimate Biochemical Oxygen Demand (BODu). To test for BOD, samples are diluted and dissolved oxygen is measured initially and typically after a 5-day period. The following equation is used to determine the Biochemical Oxygen Demand after that 5-day period (BOD5):

DOi = Initial Dissolved Oxygen content

DOf = Final Dissolved Oxygen content

V = Volume

The process of nitrification causes a deviation from the trajectory of the carbonaceous process of oxygen demand as it relates to time. This must be accounted for when determining the Ultimate BOD. The BOD at any time t is called the BOD exertion and is related to the ultimate by the following equation:

It is important to note that at initially in a sample there is only a small amount of autotrophic bacteria present and the process of nitrification is delayed from having a significant effect on the BOD process. For reference the chemical equation for nitrification is:

Denitrification is the removal or loss of nitrogen by the means of bacteria. The chemical equation is:




Secondary Treatment


The most intensive of the levels of wastewater treatment is the secondary treatment. This may involve biological treatment in tickling filters and sludge treatment. The most amount of BOD will be removed in this stage.




Primary Treatment


Primary treatment is the second level in wastewater treatment. In this portion the wastewater is allowed to settle to remove any remaining oils and any solids which are able to separate. Typically about half of the solids will be removed during this portion of the process. It is also expected that this level of the process will remove 25%-35% of the Biochemical Oxygen Demand (BOD) in the wastewater.




Digestion


Digestion is a process of treating sludge that is too thick or bulky to be easily worked with for disposal. In other words if the sludge is too thick it can be further broken down by digestion so that it can be moved more easily. There are 2 processes of digestion: aerobic and anerobic.

Aerobic digestion is putting the sludge in a large open holding tank for a period of time. In this tank the sludge is stirred and left open to air. This allows bacteria to consume the sludge reducing the solids. Often, up to 70% of the solids can be removed through this process.

Anaerobic digestion as the name suggests occurs without the use of oxygen. This process is more delicate in nature and proper care must be taken during as to not upset the desired result. However, it is often a more economical solution. Bacteria which does not require oxygen is introduced to the system. These bacteria, in a three-stage process, convert the sludge to gases which can then be released.




Disenfection


Disinfectants are chemicals which are used to kill bacteria that is present in water. In general when disinfectants are discussed, the chemical referred to is chlorine. Chlorine is easily the most widely used mainly because of the cost comparative to other types of disinfectants. Chlorine however is a toxic substance and can be extremely dangerous to public health. It must be handled safely and properly.

In wastewater chlorine can be used to destroy common bacteria such as coliform. This is the presence of fecal matter in water supply.




Advanced Treatment


Advanced treatment also known as tertiary treatment and is a final level of the wastewater treatment process. This phase handles any remaining pollutants that are still above allowable levels that have not been removed during the previous stages. Here are some of the pollutants that may be removed during this level.

Suspended Solids – At this point any solids remaining are very small in size and would need to be removed by more advanced techniques. This may involve microstrainers or filter beds which are able to remove very high gradation solids.

Phosphorous – This stage may require the removal of phosphorous. This is done through the use of chemical precipitation. This process utilizes aluminum, iron, and lime coagulates.

Ammonia – There are many processes for use of removal of ammonia to acceptable levels. These may include stripping, biological denitrification, breakpoint chlorination, anion exchange, and algae ponds.





Wastewater Collection and Treatment

Stream Degradation


Stream Degradation is the wearing away and lowering of a stream bed over time due to erosion from the flow of water within a stream. Often flow rates and velocities which are too high can cause this. The removal of the soil can affect the water quality by increasing the amount of sediment in the water and therefore decreasing clarity and oxygen in the stream.




Oxygen Dynamics


Oxygen dynamics is related to the amount of oxygen present in flowing water. More specifically this type of oxygen is referred to as Dissolved Oxygen (DO). Simply put dissolved oxygen is the amount of gaseous oxygen present in a moving volume of water. DO is also affected by the temperature and must be adjusted appropriately

Dissolved Oxygen is one of the more relevant parameters when determining the quality of a mass of water so it is important to be able to understand and analyze its content. Typical concentrations of DO may vary greatly throughout the year for a given body of water. Concentrations may range anywhere from 1 mg/L to 20 mg/L. The level that is appropriate is based on the type of life that needs to be sustained. Certain organisms require a larger content of DO to survive than others. For example, larger marine animals such as trout or salmon may require 12-14 mg/L whereas others like pike may only need 3-4 mg/L.

Re-aeration is a process used to increase the Dissolved Oxygen content of a specific water source. This is where oxygen from the air is dissolved into the water by causing turbulence in the water. Turbulence causes the water to move rapidly by forces such as a physical force, wind or currents. This causes a mixing of the water and air in which increased amounts of oxygen will begin to dissolve into the body of water. Turbulence can be used to mix bottom and top areas of water which may have uneven amounts of dissolved oxygen. Often the top portion of water will have higher concentrations. Mixing them will more evenly distribute the dissolved oxygen. To determine the final DO concentration resulting from the mixing of two sources, use the following:

C = Concentration

Q = Flow rate




Total Maximum Daily Load (TMDL)


Total Maximum Daily Load often referred to as TMDL, relates to the Clean Water Act of 1972 which set the standards for pollutants in water. TMDL in accordance with this legislation provides the maximum amount of a pollutant which a body of water can receive that will not violate the quality standards. Some of the pollutants which are of concern are nitrogen, phosphorous, and sediment among others.

TMDL is the sum of all the pollutants entering a system and the inclusion of a factor of safety:

TMDL=WLA+LA+MOS+SV

WLA = Waste Land Allocation (Direct flow into the body such as pipes and ditches)

LA = Land Allocation (Pollutants from land areas)

MOS = Margin of Safety

SV = Seasonal Variation




Biological Contaminants


Biological contaminants refers to the amount of organisms in the water. These organisms are also sometimes referred to as microbes. The microbes, because they are living, will reproduce if there is a sufficient supply of food. The food is called the substrate and may or may not be limited to facilitate the biological growth. The Monod equation is used to determine the rate at which substrate is converted into biomass which is simply the total mass of microorganisms in a given volume of water. The equation is as follows:




Chemical Contaminants


Chemical contaminants are a severe concern in water as they may impose health risks to the public. Water should be tested regularly for the presence of such chemicals and action taken immediately. Since chemicals pose a risk to human life, acceptable levels of risk need to be identified and associated with the concentrations of the chemical. The following equation can be used:





Water Quality

Stream Degradation


Stream Degradation is the wearing away and lowering of a stream bed over time due to erosion from the flow of water within a stream. Often flow rates and velocities which are too high can cause this. The removal of the soil can affect the water quality by increasing the amount of sediment in the water and therefore decreasing clarity and oxygen in the stream.




Oxygen Dynamics


Oxygen dynamics is related to the amount of oxygen present in flowing water. More specifically this type of oxygen is referred to as Dissolved Oxygen (DO). Simply put dissolved oxygen is the amount of gaseous oxygen present in a moving volume of water. DO is also affected by the temperature and must be adjusted appropriately

Dissolved Oxygen is one of the more relevant parameters when determining the quality of a mass of water so it is important to be able to understand and analyze its content. Typical concentrations of DO may vary greatly throughout the year for a given body of water. Concentrations may range anywhere from 1 mg/L to 20 mg/L. The level that is appropriate is based on the type of life that needs to be sustained. Certain organisms require a larger content of DO to survive than others. For example, larger marine animals such as trout or salmon may require 12-14 mg/L whereas others like pike may only need 3-4 mg/L.

Re-aeration is a process used to increase the Dissolved Oxygen content of a specific water source. This is where oxygen from the air is dissolved into the water by causing turbulence in the water. Turbulence causes the water to move rapidly by forces such as a physical force, wind or currents. This causes a mixing of the water and air in which increased amounts of oxygen will begin to dissolve into the body of water. Turbulence can be used to mix bottom and top areas of water which may have uneven amounts of dissolved oxygen. Often the top portion of water will have higher concentrations. Mixing them will more evenly distribute the dissolved oxygen. To determine the final DO concentration resulting from the mixing of two sources, use the following:

C = Concentration

Q = Flow rate




Total Maximum Daily Load (TMDL)


Total Maximum Daily Load often referred to as TMDL, relates to the Clean Water Act of 1972 which set the standards for pollutants in water. TMDL in accordance with this legislation provides the maximum amount of a pollutant which a body of water can receive that will not violate the quality standards. Some of the pollutants which are of concern are nitrogen, phosphorous, and sediment among others.

TMDL is the sum of all the pollutants entering a system and the inclusion of a factor of safety:

TMDL=WLA+LA+MOS+SV

WLA = Waste Land Allocation (Direct flow into the body such as pipes and ditches)

LA = Land Allocation (Pollutants from land areas)

MOS = Margin of Safety

SV = Seasonal Variation




Biological Contaminants


Biological contaminants refers to the amount of organisms in the water. These organisms are also sometimes referred to as microbes. The microbes, because they are living, will reproduce if there is a sufficient supply of food. The food is called the substrate and may or may not be limited to facilitate the biological growth. The Monod equation is used to determine the rate at which substrate is converted into biomass which is simply the total mass of microorganisms in a given volume of water. The equation is as follows:




Chemical Contaminants


Chemical contaminants are a severe concern in water as they may impose health risks to the public. Water should be tested regularly for the presence of such chemicals and action taken immediately. Since chemicals pose a risk to human life, acceptable levels of risk need to be identified and associated with the concentrations of the chemical. The following equation can be used:





Drinking Water Distribution and Treatment

Drinking Water Distribution Systems


As the name suggests, systems are developed so that drinking water can be safely and efficiently distributed to the populations. These systems may consist of many components such as pipes, reservoirs, pumps, storage tanks and many others. These components carry water from a centralized distribution plant which maintains regulated levels of safe drinking water.




Drinking Water Treatment Process


There is a large number of processes which can be performed to get water meeting quality standards. The selection of which processes are performed depends heavily on the characteristics of the water specific to a certain plant. The procedure can be divided into 3 components: Pretreatment, Treatment, and Special Treatment. Here we will provide a breakdown of what may be involved in each portion depending on the type of water that needs to be treated.

Pretreatment

Screening: As the name suggests suspended solids which are large enough to be physically removed by allowing water to flow through fine screens is an initial process that is necessary to remove any debris.

Microstraining: A second level of screening used to remove the more finer debris. This process is very effective in the removal of algae.

Plain Settling: A removal of sediment by allowing the water to sit and the natural movement of sediments to fall to the bottom to occur.

Aeration: The rapid moving of water to allow mixing or the infusion of oxygen into the water. Aeration can have many benefits depending on the desired result. It can increase dissolved oxygen, decrease dissolved gases, reduce iron and manganese, or decrease odor and taste compounds.

Treatment

Lime Softening: As the name suggests this is the process of adding lime water (calcium hydroxide) to soften water. This additive will react with the calcium and manganese to form precipitates.

Coagulation and Sedimentation: This process is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. This process is essential to the treatment of water and is covered in greater detail later on.

Rapid Sand Filtration/Pressure Sand Filtration: See section on filtration.




Demands


Water demands need to be measured and analyzed so that distribution systems may be properly designed. Water demand is most often specified as gallons per capita per day (gpcd). It can also be expressed as Average Annual Daily Flow (AADF) which as the name suggests is the average daily use of water per person averaged over a year time period. A common value used for basic design purposes is often taken as 165 gpcd but should be adjusted based on the intended water use whether it be residential, commercial, or industrial.

Besides the average flow demand throughout a day, there may be increased demands instantaneously which systems must have adequate capacity for. The average annual daily flow times a specified multiplier is often used to determine the instantaneous demand:

Qinstant=M(AADF)

It is also important to note that per capita demand needs to account for the entire population but it must often be specified at what time period. Because of growth, a distribution system should meet some future predicted growth of population.




Storage


Water supplies need to be stored for a variety of uses and as well as to ensure adequate supply in times of growth or emergency. Water can be distributed from storage either through gravity or pumping. Gravity is available when there is a sufficiently high point in elevation relative to the population. Otherwise pumping is necessary. Water is most often stored in surface or elevated tanks. Within these tanks the elevation of the surface water is monitored to determine the appropriate distribution pressure. These are often monitored by altitude valves.




Rapid Mixing


This process as mentioned above is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. For this reason we have combined two of the NCEES syllabus items since it is most appropriate to discuss these topics together. The most common type of coagulates are aluminum sulfate commonly referred to simply as alum. Others include ferrous sulfate and chlorinated copperas. Alum is often provided in doses in the range of 5-50 mg/L. There are three requirements for Alum to be effective:

  1. A large enough quantity of Alum must be present to neutralize the negative particles present in the water
  2. Enough alkalinity must be present to facilitate the reaction of aluminum sulfate to aluminum hydroxide
  3. The PH must be within the acceptable range which is a function of the type on contaminant. Typically it is taken between 6-7

The amount of coagulate to successfully form floc must be determined. The equation for the feed rate is:

F = Feed Rate

D = Dose

Q = Flow Rate

P = Purity

G = Availability (1.0 is not specified)




Taste and Odor Control


There are many processes which can aid in the elimination of undesirable taste and odor in water. Some include chlorination, aeration and micro straining. To identify the presence of taste or order, the threshold odor number (TON) is established and can be calculated as per below:

TON= (V Raw Sample+V Dilution Water)/VRaw Sample

Typically, a TON of less than 6 is desirable




Sedimentation


A plain sedimentation tank is used to allow water which includes suspended sediments to settle out. The time and velocity for the particles to settle is a function of the temperature of the water, the particle size and the specific gravity of the particles (however this is often taken as 2.65 for analysis). Assumed settling velocities can be taken as the following to calculate the actual settling velocities:

Gravel: 3.28 ft/s

Coarse Sand: 0.328 ft/s

Fine Sand: 0.0328 ft/s

Silt: 0.000328 ft/s

Then the approach to determining the settlement time can be determined by first calculating the Reynolds number:




Filtration


Filtration is used to remove excess floc, precipitates from softening, algae, debris and any other suspended byproducts remaining in the treated water. The most common is rapid sand filtration. Rapid Sand Filtration is the filtering of water through a bed of sand and gravel as a medium for removing suspended particles. Water moves through a layer of sand in which the suspended particles will be held back by the sand. Depending on the type of filter, the loading rate can be anywhere from 2 – 10 gpm/ft2. The loading rate can be determined by the following equation:

Load Rate= Flow Rate/Area

Filters often need to be cleaned and therefore there is a high maintenance cost. The pores between the filters will become clogged and need to get washed out. To counteract this is a process called back washing. This is where water is pumped slowly in the reverse direction of the water to be filtered so that the pores in the sand can be expanded to release any trapped material. It is important during backwashing to monitor the rise rate of the water to ensure it does not exceed the settling velocity of the smallest particle intended to be left in the filter. These rates are often taken as about 1-3 ft/min. The amount of backwash needed can be determined by:

V= Area Filter(Rise Rate)(t Backwash)




Hardness and Softening


Hardness is a measure of the presence of calcium and magnesium ions expressed as calcium carbonate (CaCO3). Practically, hardness in water does not provide any health concerns but does have an effect on the usefulness of the water. One of the main concerns is often that hardness in water will greatly reduce the effectiveness of soap. It also has a detrimental effect on the pipes and storage facilities of a water distribution system.

There are two types of hardness:

Carbonate Hardness: Water containing Bicarbonate (HCO3-)

Noncarbonate Hardness: Remaining hardness not carbonate due to sulfates, chlorides, and nitrates.

Hardness can also be expressed as total hardness which is the sum of carbonate and noncarbonate hardness in mg/L as CaCO3. There is a clear connection between the alkalinity of water and the hardness. The following assumptions can be made:

  • If Total Hardness = Alkalinity, all hardness is carbonate and there are no sulfates, chlorides, or nitrates present
  • If Total Hardness > Alkalinity, noncarbonate hardness is present
  • If Total Hardness < Alkalinity, all hardness is carbonate and the remainder of the bicarbonate is from additional sources

Water softening is the removal of hardness through the use of lime and soda ash in mg/L as CaCO3. It is important to note that lime will attack any carbon dioxide in water first and then begin with the removal of any carbonate hardness before the noncarbonate.




Disinfection


Disinfectants were defined earlier in the wastewater section. Here we will discuss by products.

Chlorine in water produces the following chemical reaction depending on PH

PH > 4: Cl2+ H2O →HCl+HOCl

PH > 9: HOCl → H++ OCl-

HCl and HOCL are hydrochloric and hypochlorous acids respectively. You can see that at PH greater than 9, the hypochlorous acid becomes hydrogen and hypochlorite ions.





Engineering Economics

Drinking Water Distribution Systems


As the name suggests, systems are developed so that drinking water can be safely and efficiently distributed to the populations. These systems may consist of many components such as pipes, reservoirs, pumps, storage tanks and many others. These components carry water from a centralized distribution plant which maintains regulated levels of safe drinking water.




Drinking Water Treatment Process


There is a large number of processes which can be performed to get water meeting quality standards. The selection of which processes are performed depends heavily on the characteristics of the water specific to a certain plant. The procedure can be divided into 3 components: Pretreatment, Treatment, and Special Treatment. Here we will provide a breakdown of what may be involved in each portion depending on the type of water that needs to be treated.

Pretreatment

Screening: As the name suggests suspended solids which are large enough to be physically removed by allowing water to flow through fine screens is an initial process that is necessary to remove any debris.

Microstraining: A second level of screening used to remove the more finer debris. This process is very effective in the removal of algae.

Plain Settling: A removal of sediment by allowing the water to sit and the natural movement of sediments to fall to the bottom to occur.

Aeration: The rapid moving of water to allow mixing or the infusion of oxygen into the water. Aeration can have many benefits depending on the desired result. It can increase dissolved oxygen, decrease dissolved gases, reduce iron and manganese, or decrease odor and taste compounds.

Treatment

Lime Softening: As the name suggests this is the process of adding lime water (calcium hydroxide) to soften water. This additive will react with the calcium and manganese to form precipitates.

Coagulation and Sedimentation: This process is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. This process is essential to the treatment of water and is covered in greater detail later on.

Rapid Sand Filtration/Pressure Sand Filtration: See section on filtration.




Demands


Water demands need to be measured and analyzed so that distribution systems may be properly designed. Water demand is most often specified as gallons per capita per day (gpcd). It can also be expressed as Average Annual Daily Flow (AADF) which as the name suggests is the average daily use of water per person averaged over a year time period. A common value used for basic design purposes is often taken as 165 gpcd but should be adjusted based on the intended water use whether it be residential, commercial, or industrial.

Besides the average flow demand throughout a day, there may be increased demands instantaneously which systems must have adequate capacity for. The average annual daily flow times a specified multiplier is often used to determine the instantaneous demand:

Qinstant=M(AADF)

It is also important to note that per capita demand needs to account for the entire population but it must often be specified at what time period. Because of growth, a distribution system should meet some future predicted growth of population.




Storage


Water supplies need to be stored for a variety of uses and as well as to ensure adequate supply in times of growth or emergency. Water can be distributed from storage either through gravity or pumping. Gravity is available when there is a sufficiently high point in elevation relative to the population. Otherwise pumping is necessary. Water is most often stored in surface or elevated tanks. Within these tanks the elevation of the surface water is monitored to determine the appropriate distribution pressure. These are often monitored by altitude valves.




Rapid Mixing


This process as mentioned above is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. For this reason we have combined two of the NCEES syllabus items since it is most appropriate to discuss these topics together. The most common type of coagulates are aluminum sulfate commonly referred to simply as alum. Others include ferrous sulfate and chlorinated copperas. Alum is often provided in doses in the range of 5-50 mg/L. There are three requirements for Alum to be effective:

  1. A large enough quantity of Alum must be present to neutralize the negative particles present in the water
  2. Enough alkalinity must be present to facilitate the reaction of aluminum sulfate to aluminum hydroxide
  3. The PH must be within the acceptable range which is a function of the type on contaminant. Typically it is taken between 6-7

The amount of coagulate to successfully form floc must be determined. The equation for the feed rate is:

F = Feed Rate

D = Dose

Q = Flow Rate

P = Purity

G = Availability (1.0 is not specified)




Taste and Odor Control


There are many processes which can aid in the elimination of undesirable taste and odor in water. Some include chlorination, aeration and micro straining. To identify the presence of taste or order, the threshold odor number (TON) is established and can be calculated as per below:

TON= (V Raw Sample+V Dilution Water)/VRaw Sample

Typically, a TON of less than 6 is desirable




Sedimentation


A plain sedimentation tank is used to allow water which includes suspended sediments to settle out. The time and velocity for the particles to settle is a function of the temperature of the water, the particle size and the specific gravity of the particles (however this is often taken as 2.65 for analysis). Assumed settling velocities can be taken as the following to calculate the actual settling velocities:

Gravel: 3.28 ft/s

Coarse Sand: 0.328 ft/s

Fine Sand: 0.0328 ft/s

Silt: 0.000328 ft/s

Then the approach to determining the settlement time can be determined by first calculating the Reynolds number:




Filtration


Filtration is used to remove excess floc, precipitates from softening, algae, debris and any other suspended byproducts remaining in the treated water. The most common is rapid sand filtration. Rapid Sand Filtration is the filtering of water through a bed of sand and gravel as a medium for removing suspended particles. Water moves through a layer of sand in which the suspended particles will be held back by the sand. Depending on the type of filter, the loading rate can be anywhere from 2 – 10 gpm/ft2. The loading rate can be determined by the following equation:

Load Rate= Flow Rate/Area

Filters often need to be cleaned and therefore there is a high maintenance cost. The pores between the filters will become clogged and need to get washed out. To counteract this is a process called back washing. This is where water is pumped slowly in the reverse direction of the water to be filtered so that the pores in the sand can be expanded to release any trapped material. It is important during backwashing to monitor the rise rate of the water to ensure it does not exceed the settling velocity of the smallest particle intended to be left in the filter. These rates are often taken as about 1-3 ft/min. The amount of backwash needed can be determined by:

V= Area Filter(Rise Rate)(t Backwash)




Hardness and Softening


Hardness is a measure of the presence of calcium and magnesium ions expressed as calcium carbonate (CaCO3). Practically, hardness in water does not provide any health concerns but does have an effect on the usefulness of the water. One of the main concerns is often that hardness in water will greatly reduce the effectiveness of soap. It also has a detrimental effect on the pipes and storage facilities of a water distribution system.

There are two types of hardness:

Carbonate Hardness: Water containing Bicarbonate (HCO3-)

Noncarbonate Hardness: Remaining hardness not carbonate due to sulfates, chlorides, and nitrates.

Hardness can also be expressed as total hardness which is the sum of carbonate and noncarbonate hardness in mg/L as CaCO3. There is a clear connection between the alkalinity of water and the hardness. The following assumptions can be made:

  • If Total Hardness = Alkalinity, all hardness is carbonate and there are no sulfates, chlorides, or nitrates present
  • If Total Hardness > Alkalinity, noncarbonate hardness is present
  • If Total Hardness < Alkalinity, all hardness is carbonate and the remainder of the bicarbonate is from additional sources

Water softening is the removal of hardness through the use of lime and soda ash in mg/L as CaCO3. It is important to note that lime will attack any carbon dioxide in water first and then begin with the removal of any carbonate hardness before the noncarbonate.




Disinfection


Disinfectants were defined earlier in the wastewater section. Here we will discuss by products.

Chlorine in water produces the following chemical reaction depending on PH

PH > 4: Cl2+ H2O →HCl+HOCl

PH > 9: HOCl → H++ OCl-

HCl and HOCL are hydrochloric and hypochlorous acids respectively. You can see that at PH greater than 9, the hypochlorous acid becomes hydrogen and hypochlorite ions.





 
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