Sanitary Engineering

Summary

Sanitary engineering is the discipline of civil engineering that addresses matters of public health, including water quality (such as potable drinking water, wastewater treatment, storm-sewer drainage, and swimming pool cleanliness), sewage collection, recycling, and disposal. In some jurisdictions, sanitary engineering is now called environmental engineering and also covers issues of air pollution, water pollution, hazardous waste management, and land management. The importance of this discipline, which involves the practical application of engineering and life sciences, is its responsibility for providing a healthy environment for people.

Definition and Basic Principles

Sanitary engineering is the practical application of science and engineering to provide a safe, natural environment where people can live free from disease. It requires knowledge of organic and inorganic chemistry, biology, and bacteriology to recognize the health risks of various water impurities to humans and animals and the means to eliminate them. It also requires knowledge of mathematics (algebra, geometry, quantitative analysis, statistical significance), engineering (drafting, surveying, mechanics, materials, design, and construction), and environmental science (water supplies, topography, land management). Knowledge of the latter fields is necessary to develop and maintain the appropriate water transport, purification, and distribution infrastructure.

Sanitary engineering works on large scales (a municipal water-treatment tank can hold more than one million gallons of wastewater) and small scales (lead in drinking water is measured in parts per billion per liter). Sanitary engineers are responsible for upholding public health regulations related to disease prevention in public venues that have toilets, drinking fountains, showers, swimming pools, Jacuzzis, and hot tubs. They may also review and approve plans for the installation of private septic systems and wells, taking into consideration the results of soil percolation tests and well water quality tests.

Background and History

The Romans created aqueducts, intentionally constructed channels for water transport for drinking and bathing, in the third century BCE. Most aqueducts were built in underground tunnels to protect them from contamination by enemies and diseases on the ground's surface. This was the archetype of the modern plumbing system.

Sanitary engineering arose from the contemporary scientific recognition that plumbing was related to cleanliness and thus had an impact on public health and disease prevention. Plumbing inspectors were trained to recognize and protect society from the use of inferior materials, reckless installation, and unsanitary water pathways. The American Society of Sanitary Engineering for Plumbing and Sanitary Research was formed on January 29, 1906. Henry B. Davis, the chief plumbing inspector for Washington, DC, convened with twenty-five plumbing inspectors from other states to form this national association to standardize plumbing practices to prevent the transmission of diseases.

The 1970s brought significant legislation in the practice of sanitary engineering. In the Safe Drinking Water Act of 1974, the Environmental Protection Agency (EPA) established standards for drinking-water quality. In the Clean Water Act of 1977, the EPA established standards for the quality of surface waters into which foreign, polluting materials are discharged.

How It Works

Water Treatment. Water treatment is the overall process of removing contaminants from water to make it safe for drinking, bathing, cooking, and swimming. Without water treatment, waterborne diseases can cause illness and death, often from dehydration following diarrhea. Waterborne pathogens include Cryptosporidium, Escherichia coli, hepatitis A virus, and Giardia intestinalis parasite.

People expect clean water to be clear, colorless, odorless, and tasteless. This requires particulates be removed; microbes such as bacteria, viruses, and other parasites be killed; and minerals such as iron, calcium, magnesium, manganese, and sulphur be bound and removed. To achieve this, a series of specific processes must be performed: physical separation of solids by settling and filtration, chemical reactions of coagulation and disinfection, and biological methods such as aeration, bacterial digestion of sludge, and filtration through natural materials.

The choice of processes depends on the nature and volume of the water to be purified. Analytical survey must be performed initially. There are two original sources of water: surface water and groundwater. Surface water encompasses rivers, lakes, streams, and ponds. Groundwater is accessible by digging wells and generally requires less water treatment than surface water, which contains more debris and pollutants.

Coagulation. When water is first received at the water-treatment plant, large pieces of solid material, such as sewage, are removed by a coarse screen and discarded. Then smaller solid particles are induced to bind together to form larger particles through coagulation. Ions with multiple charges (polyelectrolytes) change the pH of the water and trigger chemical reactions that cause aggregation. Alum is frequently added to attract dirt particles, which may contain herbicides and pesticides. Lime and soda ash cause calcium and magnesium to precipitate, thus “softening” the water.

Sedimentation. The material resulting from coagulation, called floc, has sufficient weight that it sinks to the bottom of the settling tank. This separation of solids by sedimentation is a time-consuming step. Algae rise to the top, where they may be skimmed. The clearer water on the top is then slowly siphoned off for filtration. Aerobic and anaerobic bacteria may be added to the withheld solids (sludge) to digest organic waste matter and neutralize pollutants. Carbon dioxide, ammonia, and methane gases are generated. The digested sludge may then be used as a fertilizer supplement in farming.

Filtration. Remaining particles in the water may be removed by filters made of artificial membranes, nets, or natural materials. Water may be filtered by passing it through beds of sand, gravel, or pulverized coal. Activated charcoal may be added to the water first to remove color, odor, taste, and radioactivity.

As another method of removing calcium and magnesium, water may be passed through ion-exchange columns, in which sodium ions compete with these cations for binding to porous material.

Aeration is used to remove dissolved elements such as iron, sulphur, and manganese. Air is forced into the water, and the oxygen removes carbon dioxide, hydrogen sulfide, and other gases. In diffused aeration, air is bubbled through the water. In spray aeration, water is sprayed through the air.

Desalination, the process of removing salt from the water, is often employed to make ocean water drinkable in places where freshwater is scarce. The salt is removed by microfiltration and reverse osmosis.

Disinfection. Disinfection is the general method of killing pathogens such as bacteria, viruses, and parasites. The most common method is chlorination of the water with sodium hypochlorite bleach. Less frequently used are ultraviolet light and ozone aeration. Water may be boiled at home for disinfection in cases of emergency.

Storage. Treated water must then be stored and delivered under clean conditions to prevent recontamination. It is stored in closed tanks or reservoirs; from there, it is piped to homes and businesses. Minimal chlorine may be added to maintain cleanliness. Fluoride may also be added to water to improve dental health since it helps prevent tooth decay.

Applications and Products

Water Treatment for Medical Purposes. Water used in medical, dental, and pharmaceutical procedures must meet exceptionally high quality standards. This ultrahigh quality of water is achieved with multiple technologies beyond chlorination, nanofiltration, and carbon adsorption. These technologies include reverse osmosis, deionization, ozonation, and ultraviolet irradiation.

Home Filtration Systems. The same filtration and purification methods used in large water treatment plants have been downscaled for home use. Faucet-mount filters use carbon filtration, ion-exchange filtration, and submicron filtration to reduce sediment, chlorine, lead, mercury, iron, herbicides, pesticides, insecticides, industrial solvents, volatile organic compounds, synthetic organic compounds, and trihalomethanes (THMs, chlorine and its by-products). These apparatuses rapidly provide filtered water that tastes and smells better with less cloudiness. Shower filters typically use copper-zinc oxidation media and carbon filtration to remove chlorine for softer skin and hair. Whole-house-use water filters are plumbed into the main water line and commonly include a sediment pre-filter, then copper-zinc oxidation media and crushed mineral stone or natural pumice to reduce chlorine, then activated carbon to remove other chemicals.

Home Water Softeners. Home water softeners are water-treatment systems that address hard water problems. Hard water contains high levels of dissolved magnesium, calcium, manganese, and iron. These minerals react with soap ingredients to create a filthy coating in sinks, bathtubs, and showers. They also react with detergent ingredients to make clothes, towels, and sheets feel abrasive. Drinking glasses washed in hard water may show spotting, streaking, or a cloudy coating. These minerals may accumulate to form crusty deposits inside pipes, showerheads, and teakettles, obstructing water flow. Home water softeners use ion exchange to replace the metal ions with sodium ions, which do not react with soap ingredients or accumulate in pipes.

Low-Flow Toilets. The Energy Policy Act of 1992 contained a mandate for low-flow toilets. This mandate went into effect in 1994 and stipulated that toilets be redesigned to reduce the water use from five to seven gallons of water per flush to 1.6 gallons of water per flush. In 2016, the state of California mandated that toilets and faucets cannot exceed more than 1.28 gallons per flush—a figure lower than the federal standard. Design adjustments were made, such as a wider flapper valve through which water flows from the tank into the bowl and a wider trap way through which water flows from the bowl to the sewage pipe. These modifications allowed the reduced amount of water to move with greater force and efficiency. Later high-efficiency toilets reduced the water use further still, to as little as 1.28 gallons per flush. Dual-flush models, introduced in Europe before the United States, enable users to select a greater amount of water for flushing solid waste and a smaller amount for liquid waste.

Low-Flow Showerheads. In keeping with the water conservation movement, showerheads were redesigned to reduce the water use by thirty to forty percent with a flow of up to two gallons per minute. Design modifications were made such as enlarging the faceplate and increasing the water pressure locally so that the reduced amount of water is dispersed with increased spray power. Some heads are still adjustable to allow for a brisk massage or a gentle rinse.

Careers and Course Work

Students interested in sanitary engineering typically pursue a bachelor of science degree in civil, chemical, or mechanical engineering, followed by a master of science degree in sanitary engineering. Doctorate degree programs are also available. To specialize in sanitary engineering, graduate students take classes in geographic information systems, hydrology, public health, urban water management and drainage, wastewater treatment processes, solid waste management, and water transport and distribution. Elective courses should include those in writing and public speaking, logic and problem-solving, computer modeling, societal governance, and regulatory compliance.

Sanitary engineers typically work for public health departments and government regulatory agencies. Some become professors and conduct academic research. Some work in private testing laboratories and research firms. Some operate water-treatment plants and pollution-control facilities. Others work as consultants to manufacturers, corporations, and private homeowners. Others may work abroad in countries where basic sanitation needs are unmet. A professional engineering license is generally required for employment. This license distinguishes one's education and proficiency from that of a draftsman, machinist, mechanic, technician, plumber, or surveyor. Engineering is considered to be a safety-related practice, and licensure holds an engineer to legal liability.

Social Context and Future Prospects

Research projects in sanitary engineering include seeking processes and equipment for improved purification efficiency. One example is the development of large, portable water-treatment systems that are suitable for providing clean water to survivors of natural disasters and the bivouac medical units that treat them. Another example is a nanofiltration system that desalinates ocean water for use on naval ships, especially during times of conflict and extended private offshore operations such as oil drilling. A related nanofiltration system is necessary for oil spill cleanup. A third example is the specialized absorbent removal of microcontaminants that may be present in small yet detrimental amounts. These may include elements such as arsenic and lead, industrial solvents, and radioactive particles.

Most water treatment plants are not prepared to remove pharmaceuticals, including natural and synthetic hormones, that are flushed down the sink or toilet. Those that use chemical oxidative processes to remove estrogens and other medications generate disinfection by-products in the water supply that pose potential risks to human health. Some communities organize collections of unused or unwanted over-the-counter and prescription medications for disposal by authorized incineration.

In some arid countries, wastewater has been filtered and treated for safe drinking water use for decades. As urbanization continues apace, and as water scarcity is expected to worsen from climate disruption, sanitary engineers in places like Perth, Western Australia, and Orange County, California, have begun to implement water recycling measures, such as reverse osmosis, UV irradiation, desalination, and aquifer storage. In other areas lacking wastewater treatment infrastructure, such as Uganda and Madagascar, pilot systems that convert human waste into biogas and fertilizer or electricity are being trialed.

Other current and future challenges facing sanitary engineers include an increasing world population, intensive water use for and pollution from industrial and agricultural operations, and over-withdrawal of freshwater aquifers. To address these issues, they will likely need a more interdisciplinary approach.

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