Sanitary engineering

Last updated
An example of a wastewater treatment system. Steps in a typical wastewater treatment process.png
An example of a wastewater treatment system.

Sanitary engineering, also known as public health engineering or wastewater engineering, is the application of engineering methods to improve sanitation of human communities, primarily by providing the removal and disposal of human waste, and in addition to the supply of safe potable water. Traditionally a branch of civil engineering and now a subset of environmental engineering, in the mid-19th century, the discipline concentrated on the reduction of disease, then thought to be caused by miasma. This was accomplished mainly by the collection and segregation of sewerage flow in London specifically, and Great Britain generally. [1] These and later regulatory improvements were reported in the United States as early as 1865. [2]

Contents

It is also concerned with environmental factors that do not have an immediate and clearly understood effect on public health. Areas outside the purview of sanitary engineering include aesthetic concerns such as landscaping, and environmental conservation as it pertains to plants and animals.

Skills within this field are usually employed for the primary goal of disease prevention within human beings by assuring a supply of healthy drinking water, treatment of waste water, and removal of garbage from inhabited areas.

Compared to (for example) electrical engineering or mechanical engineering which are concerned primarily with closed systems, sanitary engineering is a very interdisciplinary field which may involve such elements as plumbing, fire protection, hydraulics, life safety, constructive modelling, information technology, project design, microbiology, pathology and the many divisions within environmental science and environmental technology. In some cases, considerations that fall within the field of social sciences and urban planning must be factored in as well.

Although sanitary engineering may be most associated with the design of sewers, sewage treatment and wastewater treatment facilities, recycling centers, public landfills and other things which are constructed, the term applies equally to a plan of action to reverse the effects of water pollution or soil contamination in a specific area.

History

Irrigation systems were invented five to seven thousand years ago as a means of supplying water to agriculture-based societies. Aqueducts and irrigation systems were among the first forms of wastewater engineering. As population centers became more dense, they were used to remove sewage from settlements. The Romans were among the first to demonstrate the effectiveness of the aqueduct. The Dark Ages marked a period where progress in water management came to a halt. [3]

As populations grew, the management of human waste became a growing concern and a public health threat. By the 1850s in London, more than 400,000 tons of sewage were flushed into the River Thames each day - around 150 million tons per year. [4] Diseases such as smallpox, diphtheria, measles, scarlet fever, typhus, cholera, and typhoid were spread via the contaminated water supply. [5] During the 19th century, major cities started building sewage systems to remove human waste out of cities and into rivers.

Sanitation in the 1900's

During the 1900s, the activated sludge process was invented. [6] The activated sludge process is a form of water purification that uses bacteria to consume human feces. Chlorine is used later in the process to kill off the bacteria. In the 1950s, the public health reports provided plans for supplying clean water for the public by first looking at potential hazards. The organization looked carefully at water contamination as well as how drinking water was being treated. They also prioritized finding methods that were effective, yet not too costly. [7] Sanitation cost is the main issue for many foreign (not the United States) countries. The average cost of home water and sanitation systems start at $50 a month, when many citizens don't make enough money to use on non-necessities. [8]

Over the centuries, much has changed in the field of wastewater engineering. Advancements in microbiology, chemistry, and engineering have drastically changed the field. Today, wastewater engineers also work on the collection of clean water for drinking, chemically treating it, and using UV light to kill off micro-organisms. They also treat water pollution in wastewater (blackwater and greywater) so that this water may be made safe for use without endangering the population and environment around it. Wastewater treatment and water reclamation are areas of concern in this field.

Harm Huizenga

Prior to modern forms of sanitation in neighborhoods and cities, people would simply leave their trash on the street. In 1892, it was such an issue, that a man named Harm Huizenga volunteered to clean up the mess by himself. The Dutch man went around the streets in his wagon, picking up the garbage of the city of Chicago. Little efforts like that were present throughout the early 1900s, until around 1968. Huizenga's grandson, Wayne Huizenga, made his grandfather's idea into a business, Waste Management. By the seventies, waste management as a whole was seen as a necessary practice by the public. [9]

Sanitation in the United States

California/Counties

In the early 1940s, many counties in the state had problems with their disposal of waste, especially in the Lake Tahoe area. Citizens of these towns feared that their city's poor sewage systems would cause outbreaks in illnesses, like poliomyelitis, cholera, and hepatitis, to name a few. Cholera in particular is the biggest health risk attached to waste management. The illness is caused by bacteria, especially when a person ingests food or water that contain the bacteria. In poorer areas, this is extremely likely due to the cross contamination of waste and drinking water.

Counties

  • El Dorado county has numerous garbage collection facilities, some private companies. In residential areas, the main source of waste is oil. Since then, many waste management facilities have been built in El Dorado county, reducing the risk of these illnesses. Since the fifties, the county has been utilizing the contacts from the companies to provide a low-cost and successful method of keeping the towns clean. Today, there are 7 franchises assigned to the county with different areas of pickup, such as El Dorado Disposal and American River Disposal. [10]
  • San Joaquin valley is very recycling focused. The website for the San Joaquin county's waste management shows many tips for how to recycle all recyclable items, in hopes that their county will comply. One of the tips is to verify that all items in the recycling bins are recyclable, because the load might not get recycled at all. The website is very helpful for the public for to help with waste management in residential areas. [11]

Education

Engineering

Wastewater engineering is not usually its own degree course, but a specialization from degrees such as environmental and sanitary engineering, sanitary engineering, civil engineering, environmental engineering, bio-chemical engineering, or chemical engineering. Formal education for wastewater engineers begins in high school with students taking classes such as chemistry, biology, physics, and higher mathematics including calculus. After high school most jobs require certification from a state agency. Those wanting to advance in the industry should pursue a sanitary engineering, environmental and sanitary engineering, civil engineering, mechanical engineering, environmental engineering, or a facilities engineering degree. Gaining experience through internships and working while in college is a common pathway toward advancement.

Education about waste treatment requires course work in systems design, machinery design principles, water chemistry, and similar coursework. Other classes may include Chemistry of Plant Processes, and various plant operations courses.

Wastewater engineers may advance in their careers through additional education and experience. With additional knowledge and experience one can become the manager of an entire plant. The accreditation body certifying the education for the degree and license is the Accreditation Board for Engineering and Technology (ABET). Over time, some companies may require the wastewater engineer to continue their education to keep up with any changes in technology.

Obtaining one's master's degree is encouraged since many companies list it as a preference in selection. [12] [13]

In this field 76 percent of those employed have a bachelor's degree, 17 percent have a master's degree and three percent have a post-doctoral degree as of 2013. [14] The average annual salary is approximately $83,360. [15]

Plant Operations

Initial employment in wastewater engineering can be obtained by those with and without advanced formal education. The California State Water Resources Control Board (SWRCB), for example, shows how individuals can advance through a progression of certifications as Waste Water Treatment Operators. [16] The Board uses a five level classification system to classify water treatment facilities into categories I-V according to the population served and the complexity of the treatment system.[ citation needed ]

The Operator Certification requirements for water treatment operators and waste water treatment operators are described in detail by State law. To meet certification requirements, operators must submit an application to SWRCB, have the necessary work experience, meet the educational requirements, and pass an examination based on the knowledge, skill, and abilities described in the regulations. Operators are required to renew their certificates every three years. To be eligible for renewal, certified operators must complete a specified number of continuing education hours after the previous issuance of a certificate. [17]

Job description and typical tasks

Important job types working in sanitary engineering include sanitation workers, waste collectors and wastewater engineers.[ citation needed ]

Wastewater engineers use a variety of skills and must have knowledge of mechanical and environmental engineering. They are required to perform tasks and demonstrate knowledge in design, mathematics, English, construction, physics, chemistry, biology, management, and personnel. Wastewater engineers must have skills in complex problem solving, critical thinking, mathematics, active listening, judgement, reading comprehension, speaking, writing, science, and system analysis. [14] Typical work activities include problem solving, communication with management and staff, gathering information, analyzing data, evaluating standards and complying with them, and communicating with others in the field.[ citation needed ]

Wastewater engineers perform these activities by combining their knowledge and skills to perform tasks. These tasks are to understand computer-aided design programs, and to conduct studies for the construction of facilities, water supply systems and collection systems. They may design systems for wastewater collection machinery, as well as system components. They may perform water flow analysis, then select designs and equipment based on government and industry standards. [18] Some are involved with a specific area of concern such as waste collection or the maintenance of waste water facilities and stormwater drainage systems within an area. Others cover a broader scope of activities that might include maintenance of the public water supply, collection of residential yard waste program, disposal of hazardous waste, recycling strategies and even community programs where individuals or businesses "adopt" an area and either maintain it themselves or donate funds for doing so.[ citation needed ]

Wastewater engineers may also map out topographical and geographical features of Earth to determine the best means of collection, design pipe and pumped collection systems, and design treatment processes for collected wastewater.[ citation needed ]

Typical employers

Wastewater engineers work for private companies, state and local governments, and special districts.

Modern challenges

Water scarcity

Water managers confront new challenges and the need for new technology as water levels decrease due to increasingly frequent and extended droughts. Technologies such as sonar mapping are being used in wells to determine the volume of water that they can hold. For example, the United States Geological Survey and the State of New York worked together to map underground aquifers since the 1980s. [19] Today they have thorough maps of these aquifers to assist in water management.

Desalination plants may be required in the future for those regions hardest hit by water scarcity. Desalination is a process of cleaning water by means of evaporation. Water is evaporated and it passes through membranes. The water is then cooled and condenses allowing it to flow either back into the main water line or out to sea. [20]

Climate change

Wastewater treatment contributes to global warming in many ways. One of the factors that contributes to global warming is wastewater treatment facilities and their emissions of greenhouse gases. Some of those gases are carbon dioxide, methane, and nitrous oxide. These gases occur because of the decomposition of organic material from the anaerobic bacteria. These bacteria clean the leftover waste. Even if the anaerobic bacteria decomposition produces these gases, the percentage of greenhouse gases that other equipment produce is still greater than the contribution of the anaerobic bacteria. Also, the power usage from those machinery is very high. That is why many facilities are undergoing renovation to use higher levels of anaerobic bacteria compared to other types of equipment. [21]

Impacts of climate change on sanitary engineering vary based on region and the sanitation solutions employed there. In the Arctic, permafrost melting has caused damage to pipes and other infrastructure. [22] In the Northeastern United States, increased precipitation has overwhelmed aging infrastructure not equipped to handle the massive volume of water from heavy precipitation. [23] In the Western United States, prolonged drought has decreased water availability. This has led some wastewater facilities to expand recycled and reclaimed water programs. [24] Climate change has also affected water distribution pipes. Physical stress from climate change-related conditions such as extreme rainfall or drought increases the rate of pipe corrosion, adding to facility cost. [25]

Related Research Articles

<span class="mw-page-title-main">Environmental engineering</span> Integration of sciences and engineering principles to improve the natural environment for life

Environmental engineering is a professional engineering discipline related to environmental science. It encompasses broad scientific topics like chemistry, biology, ecology, geology, hydraulics, hydrology, microbiology, and mathematics to create solutions that will protect and also improve the health of living organisms and improve the quality of the environment. Environmental engineering is a sub-discipline of civil engineering and chemical engineering. While on the part of civil engineering, the Environmental Engineering is focused mainly on Sanitary Engineering.

<span class="mw-page-title-main">Sanitation</span> Public health conditions related to clean water and proper excreta and sewage disposal

Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems aim to protect human health by providing a clean environment that will stop the transmission of disease, especially through the fecal–oral route. For example, diarrhea, a main cause of malnutrition and stunted growth in children, can be reduced through adequate sanitation. There are many other diseases which are easily transmitted in communities that have low levels of sanitation, such as ascariasis, cholera, hepatitis, polio, schistosomiasis, and trachoma, to name just a few.

<span class="mw-page-title-main">Waste management</span> Activities and actions required to manage waste from its source to its final disposal

Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment and disposal of waste, together with monitoring and regulation of the waste management process and waste-related laws, technologies, economic mechanisms.

<span class="mw-page-title-main">Septic tank</span> Method for basic wastewater treatment (on-site)

A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment efficiency is only moderate. Septic tank systems are a type of simple onsite sewage facility. They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field, which provides further treatment. Nonetheless, groundwater pollution may occur and can be a problem.

<span class="mw-page-title-main">Sanitary sewer</span> Underground pipe for transporting sewage

A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings to a sewage treatment plant or disposal. Sanitary sewers are a type of gravity sewer and are part of an overall system called a "sewage system" or sewerage. Sanitary sewers serving industrial areas may also carry industrial wastewater. In municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. An advantage of sanitary sewer systems is that they avoid combined sewer overflows. Sanitary sewers are typically much smaller in diameter than combined sewers which also transport urban runoff. Backups of raw sewage can occur if excessive stormwater inflow or groundwater infiltration occurs due to leaking joints, defective pipes etc. in aging infrastructure.

<span class="mw-page-title-main">Wastewater treatment</span> Converting wastewater into an effluent for return to the water cycle

Wastewater treatment is a process which removes and eliminates contaminants from wastewater and converts this into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environment or is reused for various purposes. The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater, the treatment plant is called a Sewage Treatment. For industrial wastewater, treatment either takes place in a separate Industrial wastewater treatment, or in a sewage treatment plant. Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate treatment plants.

<span class="mw-page-title-main">Composting toilet</span> Type of toilet that treats human excreta by a biological process called composting

A composting toilet is a type of dry toilet that treats human waste by a biological process called composting. This process leads to the decomposition of organic matter and turns human waste into compost-like material. Composting is carried out by microorganisms under controlled aerobic conditions. Most composting toilets use no water for flushing and are therefore called "dry toilets".

Human waste refers to the waste products of the human digestive system, menses, and human metabolism including urine and faeces. As part of a sanitation system that is in place, human waste is collected, transported, treated and disposed of or reused by one method or another, depending on the type of toilet being used, ability by the users to pay for services and other factors. Faecal sludge management is used to deal with fecal matter collected in on-site sanitation systems such as pit latrines and septic tanks.

Onsite sewage facilities (OSSF), also called septic systems, are wastewater systems designed to treat and dispose of effluent on the same property that produces the wastewater, in areas not served by public sewage infrastructure.

<span class="mw-page-title-main">Secondary treatment</span> Biological treatment process for wastewater or sewage

Secondary treatment is the removal of biodegradable organic matter from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the intended disposal or reuse option. A "primary treatment" step often precedes secondary treatment, whereby physical phase separation is used to remove settleable solids. During secondary treatment, biological processes are used to remove dissolved and suspended organic matter measured as biochemical oxygen demand (BOD). These processes are performed by microorganisms in a managed aerobic or anaerobic process depending on the treatment technology. Bacteria and protozoa consume biodegradable soluble organic contaminants while reproducing to form cells of biological solids. Secondary treatment is widely used in sewage treatment and is also applicable to many agricultural and industrial wastewaters.

<span class="mw-page-title-main">Sewage sludge treatment</span> Processes to manage and dispose of sludge during sewage treatment

Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge treatment is focused on reducing sludge weight and volume to reduce transportation and disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting, or incineration. The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options. Air-drying and composting may be attractive to rural communities, while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities, and economies of scale may encourage energy recovery alternatives in metropolitan areas.

<span class="mw-page-title-main">Sanitary sewer overflow</span> Discharge of untreated sewage

Sanitary sewer overflow (SSO) is a condition in which untreated sewage is discharged from a sanitary sewer into the environment prior to reaching sewage treatment facilities. When caused by rainfall it is also known as wet weather overflow. Causes of sanitary sewer overflows include: Blockage of sewer lines, infiltration/Inflow of excessive stormwater into sewer lines during heavy rainfall, malfunction of pumping station lifts or electrical power failure, broken sewer lines. Prevention of such overflow events involves regular maintenance and timely upgrades of infrastructure.

<span class="mw-page-title-main">Sewage treatment</span> Process of removing contaminants from municipal wastewater

Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage,  using aerobic or anaerobic biological processes.

The CSIR-National Environmental Engineering Research Institute (CSIR-NEERI) is a research institute created and funded by Government of India. It was established in Nagpur in the year 1958 with focus on water supply, sewage disposal and communicable disease and to some extent placed on

<span class="mw-page-title-main">Sewage</span> Wastewater that is produced by a community of people

Sewage is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. Sub-types of sewage are greywater and blackwater. Sewage also contains soaps and detergents. Food waste may be present from dishwashing, and food quantities may be increased where garbage disposal units are used. In regions where toilet paper is used rather than bidets, that paper is also added to the sewage. Sewage contains macro-pollutants and micro-pollutants, and may also incorporate some municipal solid waste and pollutants from industrial wastewater.

<span class="mw-page-title-main">History of water supply and sanitation</span>

The history of water supply and sanitation is one of a logistical challenge to provide clean water and sanitation systems since the dawn of civilization. Where water resources, infrastructure or sanitation systems were insufficient, diseases spread and people fell sick or died prematurely.

Resource recovery is using wastes as an input material to create valuable products as new outputs. The aim is to reduce the amount of waste generated, thereby reducing the need for landfill space, and optimising the values created from waste. Resource recovery delays the need to use raw materials in the manufacturing process. Materials found in municipal solid waste, construction and demolition waste, commercial waste and industrial wastes can be used to recover resources for the manufacturing of new materials and products. Plastic, paper, aluminium, glass and metal are examples of where value can be found in waste.

A marine sanitation device (MSD) is a piece of machinery or a mechanical system that is dedicated to treat, process, and/or store raw, untreated sewage that can accumulate onboard water vessels. It does not refer to portable devices such as portable toilets.

<span class="mw-page-title-main">Fecal sludge management</span> Collection, transport, and treatment of fecal sludge from onsite sanitation systems

Fecal sludge management (FSM) is the storage, collection, transport, treatment and safe end use or disposal of fecal sludge. Together, the collection, transport, treatment and end use of fecal sludge constitute the "value chain" or "service chain" of fecal sludge management. Fecal sludge is defined very broadly as what accumulates in onsite sanitation systems and specifically is not transported through a sewer. It is composed of human excreta, but also anything else that may go into an onsite containment technology, such as flushwater, cleansing materials, menstrual hygiene products, grey water, and solid waste. Fecal sludge that is removed from septic tanks is called septage.

<span class="mw-page-title-main">Decentralized wastewater system</span> Processes to convey, treat and dispose or reuse wastewater from small communities and alike

Decentralized wastewater systems convey, treat and dispose or reuse wastewater from small and low-density communities, buildings and dwellings in remote areas, individual public or private properties. Wastewater flow is generated when appropriate water supply is available within the buildings or close to them.

References

  1. Sanitary Reform of London, The Working Collection of Sir Joseph Bazalgette, British and Commonwealth Literary Studies, Green Library, Stanford University
  2. EUROPEAN SANITARY REFORM.; The British Sanitary Legislation, The New York Times, July 31, 1865
  3. Steinbeck, SG. "An Abridged History of Onsite Wastewater: Early Years to Present" (PDF). REHS Onsite Water Protection Branch. Environmental Health Section, Division of Public Health, NC Department of Health and Human Services. Retrieved April 9, 2015.
  4. "London's Victorian sewer system". Thames Water. Tames Water. Retrieved April 4, 2015.
  5. Hardy, Anne (1984). "Water and the Search for Public Health in London in the Eighteenth and Nineteenth Centuries". Medical History. 28 (3): 250–82. doi:10.1017/s0025727300035936. PMC   1139446 . PMID   6390024.
  6. Matsuo, Tomonori; et al. "Civil Engineering Vol. I" (PDF). Wastewater Management Engineering. Encyclodedia of Life Support Systems. Retrieved April 3, 2015.
  7. Hanson, Harry G. (1956). "Sanitary Engineering". Public Health Reports. 71 (2): 187–190. doi:10.2307/4589388. ISSN   0094-6214. JSTOR   4589388. PMID   13289993.
  8. Rijsberman, Frank; Zwane, Alix Peterson (2012). "WATER & SANITATION". Copenhagen Consensus Center.{{cite journal}}: Cite journal requires |journal= (help)
  9. "Our Story". www.wm.com. Retrieved 2021-12-06.
  10. "Solid Waste Collection and Disposal". www.edcgov.us. Retrieved 2021-12-06.
  11. "Waste Management San Joaquin Valley". www.wm.com. Retrieved 2021-12-06.
  12. "Environmental Engineer". Science Buddies. Science Buddies, Inc. Retrieved March 21, 2015.
  13. "Environmental Engineer: Career Profile". Study.com. Study.com, Mountain View, CA. Retrieved March 21, 2015.
  14. 1 2 "Summary Report for: 17-2081.01 - Water/Wastewater Engineers". O*net Online. U.S. Department of Labor. Retrieved March 23, 2015.
  15. "Wages and Employment Trends". Onetonline.org. U.S. Department of Labor. Retrieved March 25, 2015.
  16. California Environmental Protection Agency. "Operator Certification Requirements TABLE" (PDF). State Water Resources Control Board. State of California. Retrieved March 30, 2015.
  17. "Wastewater Treatment Plant Classification, Operator Certification, and Contract Operator Registration" (PDF). State Water Resources Control Board. State of California. Retrieved April 20, 2015.
  18. Fairfax County Department of Human Resources. "Wastewater Plant Operations Manager Classification Specification". Fairfax County Classifications. Fairfax County, VA. Retrieved March 21, 2015.
  19. "Ground Water Resource Mapping". New York State Department of Resource Conservation. State of New York. Retrieved March 23, 2015.
  20. Lattemann, Sabine; et al. (2008). "Environmental impact and impact assessment of seawater desalination". Desalination. 220 (1): 1–15. doi:10.1016/j.desal.2007.03.009 . Retrieved April 20, 2015.
  21. Cakir, FY (September 26, 2005). "Greenhouse gas production: A comparison between aerobic and anaerobic wastewater treatment technology". Water Research. 39 (17): 4197–4203. doi:10.1016/j.watres.2005.07.042. PMID   16188289.
  22. Schreiber, Melody (10 May 2018). "The Housing Crisis in the Arctic, Caused by Melting Permafrost". Bloomberg.com. Retrieved 2020-04-27.
  23. "Heavy Downpours & Sewage Overflows". medialibrary.climatecentral.org. Retrieved 2020-04-27.
  24. Daniels, Jeff (2015-04-15). "California drought gives 'toilet to tap' a new level of attention". CNBC. Retrieved 2020-04-27.
  25. Jha, Rajan (2016-08-30). "Water pipes, infrastructure could buckle under climate change". GreenBiz. Retrieved 2020-04-27.