Environmental Engineering

Summary

Environmental engineering is a branch of engineering involving the planning, design, construction, and operation of equipment, systems, and structures to protect and enhance the environment. Major areas of application include wastewater treatment, water pollution control, water treatment, air pollution control, solid waste management, and hazardous waste management. Water pollution control involves physical, chemical, biological, radioactive, and thermal contaminants. Water treatment may be for the drinking water supply or industrial water use. Air pollution control is needed for stationary and moving sources. The management of solid and hazardous wastes includes landfills and incinerators for disposal and identification and management of hazardous wastes.

Definition and Basic Principles

Environmental engineering is a field of engineering that split off from civil engineering as the importance of treating drinking water and wastewater was recognized. This engineering field was first known as sanitary engineering and dealt almost exclusively with water and wastewater treatment. As awareness of other environmental concerns and the need to do something about them grew, this field of engineering became known as environmental engineering, with the expanded scope of dealing with air pollution, solid wastes, and hazardous wastes, in addition to water and wastewater treatment.

Environmental engineering is an interdisciplinary field that makes use of principles of chemistry, biology, mathematics, and physics, along with engineering sciences (such as soil mechanics, fluid mechanics, and hydrology) and empirical engineering correlations and knowledge to plan for, design, construct, maintain, and operate facilities for treatment of liquid and gaseous waste streams, for prevention of air pollution, and for management of solid and hazardous wastes.

The field also includes investigation of sites with contaminated soil or groundwater and the planning and design of remediation strategies. Environmental engineers also provide environmental impact analyses, in which they assess how a proposed project will affect the environment.

Background and History

When environmental engineering, once a branch of civil engineering, first became a separate field in the mid-1800s, it was known as sanitary engineering. Initially, the field involved the water supply, water treatment, and wastewater collection and treatment.

In the mid-twentieth century, people became concerned about environmental quality issues such as water and air pollution. As a consequence, the field of sanitary engineering began to change to environmental engineering, expanding its scope to include air pollution, solid and hazardous waste management, and industrial hygiene.

Several pieces of legislation have affected and helped define the work of environmental engineers. Some of the major laws include the Clean Air Act of 1970, the Safe Drinking Water Act of 1974, the Toxic Substances Control Act of 1976, the Resource Recovery and Conservation Act (RCRA) of 1976, and the Clean Water Act of 1977.

How It Works

Environmental engineering uses chemical, physical, and biological processes for the treatment of water, wastewater, and air, as well as in-site remediation processes. Therefore, knowledge of the basic sciences—chemistry, biology, and physics—is important, along with knowledge of engineering sciences and applied engineering.

Chemistry. Chemical processes are used to treat water and wastewater, to control air pollution, and for site remediation. These chemical treatments include chlorination for disinfection of both water and wastewater, chemical oxidation for iron and manganese removal in water treatment plants, chemical oxidation for odor control, chemical precipitation for removal of metals or phosphorus from wastewater, water softening by the lime-soda process, and chemical neutralization for pH (acidity) control and for scaling control.

The chemistry principles and knowledge needed for these treatment processes include understanding and working with chemical equations, making stoichiometric calculations for dosages, and determining size and configuration requirements for chemical reactors to carry out the various processes.

Biology. The major biological treatment processes used in wastewater treatment are the biological oxidation of dissolved and fine suspended organic matter in wastewater (secondary treatment) and the stabilization of biological wastewater biosolids (sludge) by anaerobic digestion or aerobic digestion.

Biological principles and knowledge that are useful in designing and operating biological wastewater treatment and biosolids digestion processes include the kinetics of the biological reactions and knowledge of the environmental conditions required for the microorganisms. The required environmental conditions include the presence or absence of oxygen and the appropriate temperature and pH.

Physics. Physical treatment processes used in environmental engineering include screening, grinding, comminuting, mixing, flow equalization, flocculation, sedimentation, flotation, and granular filtration. These processes are used to remove materials that can be screened, settled, or filtered out of water or wastewater and to assist in managing some of the processes. Many of these physical treatment processes are designed on the basis of empirical loading factors, although some use theoretical relationships such as the use of estimated particle settling velocities for the design of sedimentation equipment.

Soil Mechanics. Topics covered in soil mechanics include the physical properties of soil, the distribution of stress within the soil, soil compaction, and water flow through soil. Knowledge of soil mechanics is used by environmental engineers in connection with design and operation of sanitary landfills for solid waste, in stormwater management, and in the investigation and remediation of contaminated soil and groundwater.

Fluid Mechanics. Environmental engineers use principles of fluid mechanics to transport water and wastewater through pipes and open channels. Such transport occurs in water distribution systems, sanitary sewer collection systems, stormwater sewers, and wastewater treatment and water treatment plants. The design and sizing of the pipes and open channels use empirical relationships such as the Manning equation for open channel flow and the Darcy-Weisbach equation for frictional head loss in pipe flow. Environmental engineers also design and select pumps and flow-measuring devices.

Hydrology. The principles of hydrology (the science of water) are used to determine flow rates for stormwater management when designing storm sewers or stormwater detention or retention facilities. Knowledge of hydrology is also helpful in planning and developing surface water or groundwater as sources of water.

Practical Knowledge. Environmental engineers make use of accumulated knowledge from their work in the field. Theoretical equations, empirical equations, graphs, nomographs, guidelines, and rules of thumb have been developed based on experience. Empirical loading factors are used to size and design many treatment processes for water and wastewater. For example, the design of rapid sand filters to treat drinking water was based on a specified loading rate in gallons per minute of water per square foot of sand filter. Also the size required for a rotating biological contactor to provide secondary treatment of wastewater was determined based on a loading rate in pounds of biochemical oxygen demand (BOD) per day per one thousand square feet of contactor area.

Engineering Tools. Tools such as engineering graphics, computer-aided drafting (CAD), geographic information systems (GIS), and surveying are available for use by environmental engineers. These tools are used for working with plans and drawings and for laying out treatment facilities or landfills.

Codes and Design Criteria. Much environmental engineering work makes use of codes or design criteria specified by local, state, or federal government agencies. Examples of such design criteria are the storm return period to be used in designing storm sewers or stormwater detention facilities and the loading factor for rapid sand filters. The design and operation of treatment facilities for water and wastewater are also based on mandated requirements for the finished water or the treated effluent.

Applications and Products

Environmental engineers design, build, operate, and maintain treatment facilities and equipment for the treatment of drinking water and wastewater, air pollution control, and the management of solid and hazardous wastes.

Air Pollution Control. Increasing air pollution from industries and power plants as well as automobiles led to passage of the Clean Air Act of 1970. This law led to greater efforts to control air pollution. The two major ways to control air pollution are the treatment of emissions from fixed sources and from moving sources (primarily automobiles).

The fixed sources of air pollution are mainly the smokestacks of industrial facilities and power plants. Devices used to reduce the number of particulates emitted include settling chambers, baghouses, cyclones, wet scrubbers, and electrostatic precipitators. Electrostatic precipitators impart the particles with an electric charge to aid in their removal. They are often used in power plants, at least in part because of the readily available electric power to run them. Water-soluble gaseous pollutants can be removed by wet scrubbers. Other options for gaseous pollutants are adsorption on activated carbon or incineration of combustible pollutants. Because sulfur is contained in the coal used as fuel, coal-fired power plants produce sulfur oxides, particularly troublesome pollutants. The main options for reducing these sulfur oxides are desulfurizing the coal or desulfurizing the flue gas, most typically with a wet scrubber using lime to precipitate the sulfur oxides.

Legislation has greatly reduced the amount of automobile emissions, the main moving source of air pollution. The reduction in emissions has been accomplished through catalytic converters to treat exhaust gases and improvements in the efficiency of automobile engines.

Water Treatment. The two main sources of the water supply are surface water (river, lake, or reservoir) and groundwater. The treatment requirements for these two sources are somewhat different.

For surface water, treatment is aimed primarily at the removal of turbidity (fine suspended matter) and perhaps softening the water. The typical treatment processes for the removal of turbidity involve the addition of chemicals such as alum or ferric chloride. The chemicals are rapidly mixed into the water so that they react with alkalinity in the water, then slowly mixed (flocculation) to form a settleable precipitate. After sedimentation, the water passes through a sand filter and finally is disinfected with chlorine. If the water is to be softened as part of the treatment, lime, Ca(OH)₂, and soda ash, Na₂CO₃, are used in place of alum or ferric chloride, and the water hardness (calcium and magnesium ions) is removed along with its turbidity.

Groundwater is typically not turbid (cloudy), so it does not require the type of treatment used for surface water. At a minimum, it requires disinfection. Removal of iron and manganese by aeration may be needed, and if the water is very hard, it may be softened by ion exchange.

Wastewater Treatment. The Clean Water Act of 1977 brought wastewater treatment to a new level by requiring that all wastewater discharged from municipal treatment plants must first undergo at least secondary treatment. Before the passage of the legislation, many large cities located on a river or along the ocean provided only primary treatment in their wastewater treatment plants and discharged effluent with only settleable solids removed. All dissolved and fine suspended organic matter remained in the effluent. Upgrading treatment plants involved added a biological treatment to remove dissolved and fine suspended organic matter that would otherwise exert an oxygen demand on the receiving stream, perhaps depleting the oxygen enough to cause problems for fish and other aquatic life.

Solid Waste Management. The main options for solid waste management are incineration, which reduces the volume for disposal to that of the ash that is produced, and disposal in a sanitary landfill. Some efforts have been made to reuse and recycle materials to reduce the amount of waste sent to incinerators or landfills. A sanitary landfill is a big improvement over the traditional garbage dump, which was simply an open dumping ground. A sanitary landfill uses liners to prevent groundwater contamination, and each day, the solid waste is covered with soil.

Hazardous Waste Management. The Resource Conservation and Recovery Act (RCRA) of 1976 provides the framework for regulating hazardous waste handling and disposal in the United States. One very useful component of RCRA is that it specifies a very clear and organized procedure for determining if a particular material is a hazardous waste and, therefore, subject to RCRA regulations. If the material of interest is indeed a waste, then it is defined to be a hazardous waste if it appears on one of RCRA's lists of hazardous wastes, if it contains one or more hazardous chemicals that appear on an RCRA list, or if it has one or more of the four RCRA hazardous waste characteristics as defined by laboratory tests. The four RCRA hazardous waste characteristics are flammability, reactivity, corrosivity, and toxicity. The RCRA regulations set standards for secure landfills and treatment processes for disposal of hazardous waste.

Much work has been done in investigating and cleaning up sites that have been contaminated by hazardous wastes in the past. In some cases, funding is available for cleanup of such sites through the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (known as CERCLA or Superfund) or its amendment, the Superfund Amendments and Reauthorization Act (SARA) of 1986.

Careers and Course Work

An entry-level environmental engineering position can be obtained with a bachelor's degree in environmental engineering or civil or chemical engineering with an environmental specialization. However, because many positions require registration as an engineer in training or as a professional engineer, the bachelor's degree program must be accredited by the Accreditation Board for Engineering and Technology (ABET). Students must first graduate from an accredited program before taking the exam to become a registered engineer in training. After four years of experience, the engineer in training can take another exam for registration as a professional engineer.

A typical program of study for an environmental engineering degree at the undergraduate level includes chemistry, calculus-based physics, and mathematics, which is typical of almost all engineering programs in the first two years of study. It also may include biology, additional chemistry, and engineering geology. The last two years of study will typically include hydrology, soil mechanics, an introductory course in environmental engineering, and courses in specialized areas such as water treatment, wastewater treatment, air pollution control, and solid and hazardous waste management.

Master's degree programs in environmental engineering fall into two categories—those designed primarily for people with an undergraduate degree in environmental engineering and those for people with an undergraduate degree in another type of engineering. Some environmental engineering positions require a master's degree. A doctoral degree in environmental engineering is necessary for a position in research or teaching at a college or university.

Social Context and Future Prospects

Many major areas of concern in the United States and worldwide are related to the environment. Issues such as water and air pollution control, global warming, and climate change all require the work of environmental engineers. These issues and the need for environmental engineers are likely to remain concerns for much of the twenty-first century.

Water supply, wastewater treatment, and solid waste management all involve infrastructure that needs repair, maintenance, and upgrading, which all require the help of environmental engineers. In particular, environmental engineers' expertise is needed in areas where drilling for shale gas occurs as massive amounts of water are used in these operations. Concerns about water use efficiency will likely be a new area of job growth for environmental engineers during the twenty-first century as state and local governments work to increase water efficiency.

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