Wednesday, 17 May 2017

Soil Erosion: Its Causes and Effects

Introduction

Soil is considered to be one of the most valuable natural resources. Soil is a combination of weathered rock, decayed organic matter, mineral fragments, water, and air. As degraded soil becomes loose and weak, it loses the ability to absorb and retain water, which leads to soil erosion. Ellison (1944) defines soil erosion as the process of detachment and transport of soil particles by erosive agents. 


Soil Erosion Factors

Factors that contribute to erosion include climate, topography, soil characteristics, vegetation, velocity of winds, rainfall intensity, and duration. Knowing the factors that cause erosion assists in identifying the source of erosion and developing a plan to control it. 

Erosion is classified into two major categories: geological erosion and man-made erosion. Geological erosion occurs naturally, while man-made erosion arises when humans alter the land. Soil classification and soil erosion factors are discussed in our FE Environmental exam review course to recap the fundamentals and factors of soil erosion.

Agents of Soil Erosion


Soil Erosion by Water

When a raindrop hits the soil, it destroys the granulation of soil (compaction) and causes a disruption of the soil surface (detachment). The exposed soil particles are dislodged, splashed into the air, and suspended in the rainwater. The rainwater that runs from a slope during heavy rains is referred to as a runoff. This runoff carries away soil particles and nutrient elements along with it.

There are three main types of erosion that occur due to water:

· Sheet erosion is the uniform movement of a thin layer of soil from unprotected land.

· Rill erosion forms when the rainfall is heavy and runoff volume increases. Runoff rain water creates many small, deep channels called rills.

· Gully erosion evolves from rill erosion over time. When runoff is in a single wide and deep channel, it is known as gully erosion. A gully is defined as a scoured-out area that is not crossable with tillage and grading equipment.

Soil erosion by water is thoroughly discussed in our FE Environmental exam refresher course.

Wind Erosion

Wind erosion occurs when land that is bare of vegetation is exposed to high-velocity winds. Soil movement is initiated when the forces of wind are exerted against the surface of the ground. 

For each soil type and surface condition, there is a minimum velocity required to move soil particles; this concept is known as threshold velocity. When wind threshold velocity overcomes the cohesive and gravitational forces of the soil particles, wind can move soil and carry it away in suspension.

Other Forms of Soil Erosion

Gravity erosion is the transfer of rock and soil down a slope due to the direct action of gravity; gravity erosion can cause a mass movement of soil, ice, and rock, which leads to landslides, avalanches, and rock fall. 

Glacier erosion occurs when a huge mass of ice slowly moves over the land. Glaciers erode the earth’s surface and wear down, pick up, and carry sediments that vary in size. 

Sedimentation control methods and the effects of soil erosion are important concepts to understand for the FE Environmental exam.

Wastewater Treatment Methods

Introduction

Water is an ideal solvent with a neutral pH value and is colorless, odorless, and tasteless in its purest form. Any physical or chemical change in water that affects the health of a living organism is known as water pollution. Water can become contaminated due to domestic, industrial, physical, chemical, and biological pollutants. 

Water pollution is a global problem affecting millions of lives.
· 1.8 billion people do not have access to clean water
· 70% of all industrial waste is dumped into bodies of water
· 2 million tons of sewage is disposed of into bodies of water each day throughout the world 
· 840,000 people die each year from water-related diseases

waste water treatment

Sources of Water Pollution

Water pollution comes in different forms and from different sources. 
· Point-source pollution: pollutants derived from a single-known source (pipe or sewer line)
· Nonpoint-source pollution: pollutants that come from many unknown sources (agricultural run-off)
· Trans-boundary pollution: pollutants that affect the environment hundreds of miles away from the source (nuclear incident)

Water pollution and the causes of water pollution are thoroughly reviewed in our PE Environmental exam review courses.

Wastewater Treatment 

The water used for industrial and domestic purposes is degraded with pollutants, and such water must be treated to remove pollutants before being released into bodies of water. The aim of wastewater treatment is to remove suspended solids, salts, nutrients, bacteria, and oxygen-demanding material. Wastewater treatment is a large industry that is worth $20 billion a year. Therefore, it is important to study wastewater treatment methods prior to taking the PE exam. 

Methods of Wastewater Treatment

Wastewater is treated by using different methods to remove pollutants before returning the water to the drinking supply.

Two methods of water treatment are employed based on the need: 
· Conventional method using sewage tanks
· Centralized wastewater treatment plants

Wastewater treatment involves three stages: 
· Primary stage
· Secondary stage 
· Tertiary stage 

The three stages involved in wastewater treatment are explained in the following flow charts:



Primary Treatment

Screening stage: Incoming raw sewage enters the treatment plant and passes through a series of screens to remove large, floating organic material.

Sedimentation stage: In the second stage, water enters the sedimentation tanks to remove sand, small stones, and grit. The particulate matter settles out to form a mud called sludge. In the next step, sludge is removed and transported to a digester. Primary treatment removes about 35% of biochemical oxygen demand (BOD) from the polluted water. 

Secondary Treatment

Secondary treatment is a biological process involving microorganisms. The wastewater is pumped into oxidation ponds where the microorganisms oxidize its organic matter, and then it is transferred from the primary sedimentation tank to the stabilization tank. The partly-treated water then enters the final sedimentation tank where the sludge settles. After the sludge is settled, it is transported to the digester.

Chlorination Stage

At this stage, the pH value of the water is near neutral. The BOD value of water is assessed, and the chlorination process is activated to kill harmful pathogens. After chlorination, water that is safe to use can be discharged. Secondary treatment removes about 90% of BOD. Secondary treatment does not remove all nutrients, heavy metals, solvents and pesticides. To be cautionary in regards to safety, water should be treated in an advanced stage that involves sophisticated methods and technology.

Tertiary Treatment

Tertiary treatment is a physicochemical process aimed to remove the turbidity of wastewater caused by nitrogen, phosphorus, dissolved organic matter, heavy metals, and pathogens. Tertiary treatment involves a chemical oxidation of wastewater using strong oxidizing agents, such as chlorine gas, perchlorate salts, ozone gas, and UV radiation. Tertiary treatment renders the water safe to be discharged back into the environment. 

Wastewater treatment topics are extensively discussed and emphasized in our PE exam review courses for both environmental engineers and water resources engineers.

Thursday, 27 April 2017

The Importance of Soil Erosion Control Measures

Introduction

Soil erosion control is the process of minimizing the potential for soil erosion. Erosion control measures have proven to reduce erosion potential by stabilizing exposed soil and reducing surface runoff flow velocity. 

Erosion and sediment control measures are classified into two categories:
· Temporary control measures
· Permanent control measures

Temporary soil erosion control measures are created to control soil erosion during the construction phase. Once the project has been completed and permanent measures have been installed, the temporary measures are completely removed.

Permanent soil erosion control measures are incorporated into the overall design to address long-term post-construction erosion and sediment control. Soil erosion control measures and stormwater management practices are thoroughly reviewed in our PE Civil exam review courses


Erosion Control Methods:

Source control of runoff flow

The primary goal of source control is to protect exposed earth surfaces from the erosive energy of rain splash and surface runoff flow. Cover is the most effective erosion control method for preventing soil erosion. Cover includes top soiling in conjunction with one or more of the following methods: seeding, mulching, hydroseeding, sodding, erosion control blankets, turf reinforcement matting (TRM), riprap, gabion mat, aggregate cover, and paving.

Runoff control during project work

During the construction of a project, it is not possible to provide surface cover for all disturbed areas. Runoff control methods, such as slope surface modification and slope gradient reduction, are employed to prevent soil erosion. 

Bio-engineering methods

Revegetation of exposed soil with grass and plant growth on topsoil is the main bio-engineering soil erosion control method. This method is a permanent soil erosion control measure that uses the roots, stems, and leaves of vegetation to reduce the potential for soil erosion. 

Bio-engineering involves the introduction of foliage that decreases the impact of rain, leading to infiltration of rainwater into the soil and resulting in anchoring the soil with root systems. As the plants grow, the bio-engineered erosion control system continues to strengthen. Bio-engineering methods provide a simple and cost-effective measure for controlling long-term erosion problems.

Terracing

Terracing prevents and reduces erosion caused by surface runoff by decreasing the incline and length of hillside slopes. Terracing is a land shaping method in which earth embankments and ridges are redesigned for the interception of runoff water, which in turn channels it into a specific direction and outlet. Terraces can be classified by two types: bench and broad base terraces. The bench terrace is the oldest form of terrace and is used to reduce land slope; broad base terraces are used to control and retain surface water on sloping land. 

Vegetated waterways 

Vegetated waterways protect soil against the erosive forces of runoff from sloping lands. These waterways absorb the destructive energy, which causes channel erosion and gully formation. Depending on the climate and functional requirements, waterways can have cross sections in parabolic, trapezoidal, and triangular forms.

Contouring

Contouring involves the tillage and planting of crops on the same elevation or "contour." Water is restrained between the contours, which moderates water erosion and increases soil moisture. With stable soils, contouring leads to reduced soil loss. 

Soil erosion is an important topic to understand for the PE Civil exam. Our PE Civil review courses thoroughly discuss soil erosion and the methods used to prevent it.

Monday, 24 April 2017

Effects of Air Pollution on the Environment

Introduction 

Air pollution occurs when harmful gases, dust, or smoke enters the atmosphere and has a negative impact on plants, animals, and/or humans. Air pollution is the deadliest form of pollution, killing millions of people each year. The World Health Organization reports that more than 92% of the world’s population lives where air pollution exceeds safe limits. Among all other pollutants, air pollution has proven to be a major concern throughout the world. Air pollution and its impact on the environment creates an increasing demand for environmental engineers with their PE license. 

PE Environmental Review Course

Air Pollution Hazards

Air pollution hazards are thoroughly discussed in our PE Environmental review courses. Air pollution can cause many problems including: 

1)Acid rain
2)Eutrophication
3)Haze
4)Negative effects on wildlife
5)Ozone depletion
6)Crop and forest damage
7)Global climate change

Acid Rain

Acid rain is formed when sulfur dioxide and nitrogen oxide in the atmosphere is mixed with rainwater as a weak sulfuric and nitric acid. Acid rain can damage crops, plants, and aquatic life and is even capable of damaging structures. 

Eutrophication

Eutrophication is a condition created by using excessive fertilizers and pesticides that drain into bodies of water. Nutrients, such as nitrogen, stimulate blooms of algae, which in turn endangers aquatic life.

Haze

Haze is formed when sunlight encounters suspended pollutant particles in the air. Haze obstructs our vision, clarity, color, texture, and form of what we visualize in the real world. 

Negative Effects on Wildlife

Like humans, wild animals are also developing health problems as they are exposed to toxic air. Air toxins contribute to birth defects, reproductive failure, and disease in wild animals and aquatic ecosystems.

Ozone Depletion

Ozone is a gas that is present in the earth's upper atmosphere, the stratosphere. Ozone forms a layer that protects life on Earth from the sun's harmful ultraviolet (UV) rays. Ozone is gradually being destroyed due to ozone-depleting substances being released into the atmosphere. The thinning of the protective ozone layer is causing higher amounts of UV radiation to reach the earth, leading to more cases of skin cancer, cataracts, and impaired immune systems. UV rays also damage crops and lead to reduced yields. 

Crop and Forest Damage

Air pollution damages crops and trees in many ways. Air pollution reduces growth and the survivability of plant seedlings and increases plant susceptibility to disease, pests, and other environmental stresses, such as harsh weather. 

Global Climate Change

The earth's atmosphere is a delicate balance of naturally occurring gases that trap excessive heat from the sun. This greenhouse effect protects and maintains a stable temperature on the planet. Throughout time, humans have disturbed this natural balance by producing greenhouse gases, including carbon dioxide and methane. Thus, the earth's atmosphere is trapping more of the sun's heat, leading to the average temperature to rise. This phenomenon is known as “global warming.” Global warming has significant impacts on human health, agriculture, water resources, forests, wildlife, and coastal areas. 

Air pollution and its potential impacts on the environment are fully reviewed in our PE Environmental refresher course.

Sunday, 16 April 2017

Introduction to Basics of Boiler Components for Mechanical Engineers

The most important components of boilers include fuel oil systems, super heaters, and ash removal systems. As a mechanical engineer, it is extremely critical to understand the various components of boilers. Heat transfer is an important topic for undergraduate mechanical engineers preparing to take the FE Mechanical exam to understand. Heat transfer is thoroughly reviewed in our FE Mechanical exam review course. 

FE Mechanical Exam Course

Fuel Oil System

Oil-fired boilers may use a light grade oil, typically diesel, or a heavier grade residual oil that is often referred to as "Bunker Fuel." Light oils have a low viscosity and do not require pre-heating. They are pumped from the storage tank to the burner, which is equipped with an atomizing tip that sprays the oil into the furnace in the form of a fine mist. The mist mixes very rapidly with the combustion air, ensuring efficient and clean furnace operation. Heavy residual fuel oils are viscous and require pre-heating for proper atomization. The most commonly used residual fuels are typically more viscous. The temperature required to achieve optimal atomization may differ between fuels.

Super Heaters

Steam leaving the boiler is routed through the super heater element, which is located in a high-temperature zone of the furnace. The moisture quickly evaporates because the steam is no longer in contact with the water in the drum. The actual difference between the saturation temperature and the actual steam temperature is called the degree of superheat. Although superheating does add additional energy to the steam, the primary objective is to provide a margin of safety by ensuring that the steam does not immediately begin to condense prior to giving up its superheat energy component. Super heaters are commonly used in water tube boilers. The nature of the process determines whether a super heater is required; a super heater is not generally used unless there is a specific need.

Ash Removal 

Environmental legislation in most jurisdictions imposes strict constraints on particulate emissions. Therefore, removing entrained fly ash is usually a mandatory requirement on solid-fuel boilers. For large boilers, electrostatic precipitators, bag houses, and scrubbers are widely used. One of the most common methods employed on small to medium sized boilers is the multi-cyclone grit arrester; it has low capital costs and a degree of efficiency that will satisfy all but the most stringent requirements. Understanding boiler components and heat transfer mechanisms is critical for the FE Mechanical exam. Our FE Mechanical exam review course thoroughly covers the topics of heat exchangers, boiling, and condensation. 

Common Types of Boilers for Engineering Applications 

· Fire tube boilers: 

Fire tube boilers have the advantage of relatively low capital and operating costs. These types of boilers are predominantly used in industries and processes that have modest steam demands at low to medium pressure. Physical size constraints impose limits on operating pressure and because of their large mass, fire tube boilers are not well suited to large, rapid changes in steam loads. 

· Water Tube Boilers 

The water circulation through the tubes of a water tube boiler follows a defined path. This process ensures that a relatively small quantity of water will be rapidly distributed by heat, which results in an efficient operation. Water tube boilers can be brought up to working pressure much more quickly than fire tube equivalents.


Monday, 10 April 2017

Measuring Instruments and Their Performance Characteristics

Introduction

Measuring instruments are used to measure a quantity. When choosing an instrument, the static calibration and static performance of an instrument must be considered. Our PE Electrical exam review course thoroughly covers what to consider when selecting instruments for a given job.

The characteristics of measuring instruments can be classified into the following categories:

1)Static performance characteristics
2)Dynamic performance characteristics

PE Electrical Exam Course

Static Calibration

Static calibration refers to the procedure where an input is constant or a variable is applied to an instrument. Instruments are manufactured based on the property of irreversibility or directionality. This implies that change in an input quantity will cause a corresponding change in the output. A calibration standard must be at least ten times more accurate than the instrument to be calibrated.

Static performance characteristics include the linearity performance of the instrument, static sensitivity of the instrument, repeatability of the same results, hysteresis resolution, and the readability of the results. 

Static performance characteristics influence data acquisition if the instruments are not properly calibrated prior to the measurement. Understanding quality control and quality assurance procedures for handling equipment is essential for the PE exam.

Linearity

If the relationship between the output and input can be expressed by the equation Q0= P + RQ1, where P and R are constants, then the instrument is considered linear. Linearity is never fully achieved in real-world situations, and the deviations from the ideal are referred to as linearity tolerances. For example, 3% independent linearity means that the output will remain within the values set by two parallel lines spaced ± 3% of the full-scale output from the idealized line. If the input-output relationship is not linear for an instrument, it may still be approximated to a linear form when it is used over a very restrictive range. 

Static Sensitivity

Static sensitivity can be defined as the slope of a calibration curve. 

Sensitivity = Q0/Q1

Sensitivity influences the input parameters of an instrument. The sensitivity factor can also be referred to as sensitivity drift or scale factor drift. 

Repeatability Error 

When an instrument is used to measure the same or an identical input many times and at different time intervals, the output is never the same; it deviates from the recorded values. This deviation from the ideal value is referred to as repeatability error.

Hysteresis-Threshold Resolution

When testing an instrument for repeatability, it is often noted that the input-out value does not coincide with the inputs, which are continuously ascending and descending values. This occurs because of hysteresis, which is caused by internal friction, sliding, external friction, and free play mechanisms. Hysteresis can be eliminated by taking readings corresponding to the ascending and descending values of the input and calculating their arithmetic mean.

Professional engineers who work with measurements and instrumentation should understand calibration procedures of various instruments for proper data acquisition.

Monday, 3 April 2017

Importance of Quality Control and Quality Assurance Procedures

Productivity and Quality Control Plan Implementation

In order to enhance client satisfaction during a construction project, the project must meet the expected quality. This expected quality can be ensured through quality assurance and quality control activities. The quality control process confirms that the project outcome meets the client’s standards. The quality assurance process checks the quality plan and quality control process to confirm that quality standards are implemented on the project site. To improve the quality construction of the project, understanding project requirements and standards is essential. This is usually done by a team outside of the project construction team, and the goal of this practice is to maintain quality standards, eliminate practices that are not appropriate and share best practices for quality assurance in the organization and with the project construction team. The project quality plan should be part of the project construction management plan. The quality control plan defines how quality should be handled throughout the duration of the project. Quality and safety are the main concerns for project completion. In large construction projects, management assigns an individual department for quality assurance and safety to ensure the standards of the project; in small projects, the project manager is responsible for quality assurance. Construction productivity and quality control procedures and testing methods are important for PE exam preparation


Project Quality Management Plan for Construction Projects

The success of any project has two key factors: one is the completion of the project on schedule as per the contract document and the quality of the project as per department standards. A failed project cannot lead to achieving business goals, and moreover, it leads to losses. Proper project planning is the first step for the success of the project. The plan describes the number of phases in the project and the list of construction activities to be carried out in each phase. Individual responsibility of each project phase, the duration of the project and the overall project budget are also included in the project plan. Generally, there are four steps in construction project management. The steps are planning, executing, monitoring and quality assurance. Each and every step of project management should contain a document within itself. These four steps help to increase productivity and quality as per the client’s requirements. The team should evaluate the overall project on a regular basis to validate the quality standards of the project. The responsibility of the project engineer is to ensure that quality control is implemented effectively. It is best to have professional engineer exam certified candidates in charge for better productivity and overall quality.

Disadvantages of Inappropriate Quality Control Procedures

Overlooking the quality control procedures of a project incurs additional expenses and project delays. Having to rework increases the maintenance and opportunity costs. Structural elements that are not built according to quality assurance standards have the potential to collapse at any time, which could lead to injuries and death. Professional engineers ensure the quality of the project the first time around. Project quantity takeoffs and scheduling costs should be recapped through a PE exam review course. The project team should maintain good communication with the client. When the project is completed, the essential support and technical arrangements should be given to the client. After completing the project, the project document should be finalized, and the final report of the project should be prepared. If the organization follows a quality management process, completing new projects is not a major ordeal.