Sewage

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Raw sewage arriving at a sewage treatment plant in Syria Influent raw wastewater (note grey colour in glass jar) (3232393634).jpg
Raw sewage arriving at a sewage treatment plant in Syria

Sewage, or domestic/municipal wastewater, is a type of wastewater that is produced by a community of people. It is characterized by volume or rate of flow, physical condition, chemical and toxic constituents, and its bacteriologic status (which organisms it contains and in what quantities). It consists mostly of greywater (from sinks, bathtubs, showers, dishwashers, and clothes washers), blackwater (the water used to flush toilets, combined with the human waste that it flushes away); soaps and detergents; and toilet paper (less so in regions where bidets are widely used instead of paper).

Contents

Sewage usually travels from a building's plumbing either into a sewer, which will carry it elsewhere, or into an onsite sewage facility (of which there are many kinds). Whether it is combined with surface runoff in the sewer depends on the sewer design (sanitary sewer or combined sewer). The reality is that most wastewater produced globally remains untreated, causing widespread water pollution, especially in low-income countries: a global estimate by UNDP and UN-Habitat is that 90% of all wastewater generated is released into the environment untreated. [1] In many developing countries the bulk of domestic and industrial wastewater is discharged without any treatment or after primary treatment only.

The term sewage is nowadays regarded as an older term and is being more and more replaced by "wastewater". [2] In general American English usage, the terms "sewage" and "sewerage" mean the same thing. [3] [4] [5] In common English usage, and in American technical and professional English usage, "sewerage" refers to the infrastructure that conveys sewage. [6]

Overview

Before the 20th century, sewers usually discharged into a body of water such as a stream, river, lake, bay, or ocean. There was no treatment, so the breakdown of the human waste was left to the ecosystem. Today, the goal is that sewers route their contents to a wastewater treatment plant rather than directly to a body of water. In many countries, this is the norm; in many developing countries, it may be a yet-unrealized goal.

Current approaches to sewage management may include handling surface runoff separately from sewage, handling greywater separately from blackwater (flush toilets), and coping better with abnormal events (such as peaks stormwater volumes from extreme weather).

Proper collection and safe, nuisance-free disposal of the liquid wastes of a community are legally recognized as a necessity in an urbanized, industrialized society. [7]

Types

Greywater samples before and after treatment in a constructed wetland in Peru Greywater samples before and after treatment in a VFB (5547295000).jpg
Greywater samples before and after treatment in a constructed wetland in Peru

Pollutants

Organic pollutants and nutrients

Sewage is a complex mixture of chemicals, with many distinctive chemical characteristics. These include high concentrations of ammonium, nitrate, nitrogen, phosphorus, high conductivity (due to high dissolved solids), high alkalinity, with pH typically ranging between 7 and 8. The organic matter of sewage is measured by determining its biological oxygen demand (BOD) or the chemical oxygen demand (COD).

Pathogens

Sewage contains human feces, and therefore often contains pathogens of one of the four types: [8] [9]

Sewage can be monitored for both disease-causing and benign organisms with a variety of techniques. Traditional techniques involve filtering, staining, and examining samples under a microscope. Much more sensitive and specific testing can be accomplished with DNA sequencing, such as when looking for rare organisms, attempting eradication, testing specifically for drug-resistant strains, or discovering new species. [11] [12] [13] Sequencing DNA from an environmental sample is known as metagenomics.

Micro-pollutants

Sewage also contains environmental persistent pharmaceutical pollutants. Trihalomethanes can also be present as a result of past disinfection.

Sewage has also been analyzed to determine relative rates of use of prescription and illegal drugs among municipal populations. [14] General socioeconomic demographics may be inferred as well. [15]

Health and environmental aspects

All categories of sewage are likely to carry pathogenic organisms that can transmit disease to humans and animals. Sewage also contains organic matter that can cause odor and attract flies.

Sewage contains nutrients that may cause eutrophication of receiving water bodies; and can lead to ecotoxicity.

Collection

A medieval waste pipe in Stockholm Old Town formerly deposited sewage on the street to be flushed away by rain. Nygrand 2 mars 2007.JPG
A medieval waste pipe in Stockholm Old Town formerly deposited sewage on the street to be flushed away by rain.
Sewage canal of a medieval house as depicted in 1447 St. Barbara Altarpiece in the National Museum in Warsaw. Kalteysen St. Barbara Altarpiece (detail) 01.jpg
Sewage canal of a medieval house as depicted in 1447 St. Barbara Altarpiece in the National Museum in Warsaw.

A system of sewer pipes (sewers) collects sewage and takes it for treatment or disposal. The system of sewers is called sewerage or sewerage system (see London sewerage system) in British English and sewage system in American English. Where a main sewerage system has not been provided, sewage may be collected from homes by pipes into septic tanks or cesspits, where it may be treated or collected in vehicles and taken for treatment or disposal. Properly functioning septic tanks require emptying every 2–5 years depending on the load of the system.

Treatment

Sewage treatment is the process of removing the contaminants from sewage to produce liquid and solid (sludge) suitable for discharge to the environment or for reuse. It is a form of waste management. A septic tank or other on-site wastewater treatment system such as biofilters or constructed wetlands can be used to treat sewage close to where it is created.

Sewage treatment results in sewage sludge which requires sewage sludge treatment before safe disposal or reuse. Under certain circumstances, the treated sewage sludge might be termed "biosolids" and can be used as a fertilizer.

In developed countries sewage collection and treatment is typically subject to local and national regulations and standards.

Disposal

Raw sewage is also disposed of to rivers, streams, and the sea in many parts of the world. Doing so can lead to serious pollution of the receiving water. This is common in developing countries and may still occur in some developed countries, for various reasons – usually related to costs.

Ships at sea are forbidden from discharging their sewage overboard unless three miles or more from shore. [16]

Reuse of treated or untreated sewage

Sewage can be converted to biogas using anaerobic digestion. [17] Increasingly, agriculture is using untreated wastewater for irrigation. Cities provide lucrative markets for fresh produce, so are attractive to farmers. Because agriculture has to compete for increasingly scarce water resources with industry and municipal users, there is often no alternative for farmers but to use water polluted with urban waste, including sewage, directly to water their crops. There can be significant health hazards related to using water loaded with pathogens in this way, especially if people eat raw vegetables that have been irrigated with the polluted water.

The International Water Management Institute has worked in India, Pakistan, Vietnam, Ghana, Ethiopia, Mexico and other countries on various projects aimed at assessing and reducing risks of wastewater irrigation. They advocate a ‘multiple-barrier’ approach to wastewater use, where farmers are encouraged to adopt various risk-reducing behaviours. These include ceasing irrigation a few days before harvesting to allow pathogens to die off in the sunlight, applying water carefully so it does not contaminate leaves likely to be eaten raw, cleaning vegetables with disinfectant or allowing fecal sludge used in farming to dry before being used as a human manure. [18] The World Health Organization has developed guidelines for safe water use.

Legislation

European Union

Council Directive 91/271/EEC on Urban Wastewater Treatment was adopted on 21 May 1991, [19] amended by the Commission Directive 98/15/EC. [20] Commission Decision 93/481/EEC defines the information that Member States should provide the Commission on the state of implementation of the Directive. [21]

Etymology

The words "sewage" and "sewer" came from Old French essouier "to drain", which came from Latin exaquāre. Their formal Latin antecedents are exaquāticum and exaquārium.

Both words are descended from Old French assewer, derived from the Latin exaquare, "to drain out (water)".

See also

Related Research Articles

Environmental engineering integration of sciences and engineering principles to improve the natural environment for life

Environmental engineering is a professional engineering discipline that takes from 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, chemical engineering and mechanical engineering.

Sanitation public health conditions related to clean drinking water and adequate disposal of human excreta and sewage

Sanitation refers to public health conditions related to clean drinking water and adequate 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 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.

Greywater A type of wastewater generated in households without toilet wastewater

Grey water or sullage is all the wastewater generated in households or office buildings from streams without fecal contamination, i.e. all streams except for the wastewater from toilets. Sources of grey water include sinks, showers, baths, washing machines or dishwashers. As grey water contains fewer pathogens than domestic wastewater, it is generally safer to handle and easier to treat and reuse onsite for toilet flushing, landscape or crop irrigation, and other non-potable uses.

Wastewater Water that has been contaminated by human use

Wastewater is any water that has been contaminated by human use. Wastewater is "used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff or stormwater, and any sewer inflow or sewer infiltration". Therefore, wastewater is a byproduct of domestic, industrial, commercial or agricultural activities. The characteristics of wastewater vary depending on the source. Types of wastewater include: domestic wastewater from households, municipal wastewater from communities and industrial wastewater. Wastewater can contain physical, chemical and biological pollutants.

Septic tank 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 treatment. Settling and anaerobic processes reduce solids and organics, but the treatment efficiency is only moderate. Septic tank systems are a type of simple onsite sewage facility (OSSF). 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.

Sanitary sewer Underground pipe or tunnel system for transporting sewage from houses or buildings to treatment facilities or disposal

A sanitary sewer or foul sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings to treatment facilities or disposal. Sanitary sewers are part of an overall system called a sewage system or sewerage.

Wastewater treatment Converting wastewater into an effluent for return to the water cycle

Wastewater treatment is a process used to remove contaminants from wastewater or sewage and convert it into an effluent that can be returned to the water cycle with minimum impact on the environment, or directly reused. The latter is called water reclamation because treated wastewater can be used for other purposes. The treatment process takes place in a wastewater treatment plant (WWTP), often referred to as a Water Resource Recovery Facility (WRRF) or a Sewage Treatment Plant (STP). Pollutants in municipal wastewater are removed or broken down.

Human waste refers to the waste products of the human digestive system and the human metabolism, namely feces and urine. 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. Fecal 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.

Combined sewer Sewage collection system of pipes and tunnels designed to also collect surface runoff

A combined sewer is a sewage collection system of pipes and tunnels designed to simultaneously collect surface runoff and sewage water in a shared system. This type of gravity sewer design is no longer used in almost every instance worldwide when constructing new sewer systems. Modern-day sewer designs exclude surface runoff from sanitary sewers, but many older cities and towns continue to operate previously constructed combined sewer systems.

Sewage farm

Sewage farms use sewage for irrigation and fertilizing agricultural land. The practice is common in warm, arid climates where irrigation is valuable while sources of fresh water are scarce. Suspended solids may be converted to humus by microbes and bacteria in order to supply nitrogen, phosphorus and other plant nutrients for crop growth.

Secondary treatment A treatment process for wastewater or sewage

Secondary treatment is a treatment process for wastewater to achieve a certain degree of effluent quality by using a sewage treatment plant with physical phase separation to remove settleable solids and a biological process to remove dissolved and suspended organic compounds. After this kind of treatment, the wastewater may be called as secondary-treated wastewater.

Sewage sludge treatment Processes used to manage and dispose of sewage sludge produced during sewage treatment

Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers. Secondary sludge separated in secondary clarifiers includes treated sewage sludge from secondary treatment bioreactors.

Sanitary engineering 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

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. These and later regulatory improvements were reported in the United States as early as 1865.

Sewage treatment Process of removing contaminants from municipal wastewater

Sewage treatment is the process of removing contaminants from municipal wastewater, containing mainly household sewage plus some industrial wastewater. Physical, chemical, and biological processes are used to remove contaminants and produce treated wastewater that is safe enough for release into the environment. A by-product of sewage treatment is a semi-solid waste or slurry, called sewage sludge. The sludge has to undergo further treatment before being suitable for disposal or application to land.

A marine outfall is a pipeline or tunnel that discharges municipal or industrial wastewater, stormwater, combined sewer overflows, cooling water, or brine effluents from water desalination plants to the sea. Usually they discharge under the sea's surface. In the case of municipal wastewater, effluent is often being discharged after having undergone no or only primary treatment, with the intention of using the assimilative capacity of the sea for further treatment. Submarine outfalls are common throughout the world and probably number in the thousands. The light intensity and salinity in natural sea water disinfects the wastewater to ocean outfall system significantly. More than 200 outfalls alone have been listed in a single international database maintained by the Institute for Hydromechanics at Karlsruhe University for the International Association of Hydraulic Engineering and Research (IAHR) / International Water Association (IWA) Committee on Marine Outfall Systems.

Effluent sewer type of sewerage system in which each premise has its own septic tank, and the effluent from the on-premise septic tank flows into the sewerage system

Effluent sewer systems, also called septic tank effluent drainage (STED) or solids-free sewer (SFS) systems, have septic tanks that collect sewage from residences and businesses, and the effluent that comes out of the tank is sent to either a centralized sewage treatment plant or a distributed treatment system for further treatment. Most of the solids are removed by the septic tanks, so the treatment plant can be much smaller than a typical plant. In addition, because of the vast reduction in solid waste, a pumping system can be used to move the wastewater rather than a gravity system.

Reuse of excreta Safe, beneficial use of animal or human waste

Reuse of excreta refers to the safe, beneficial use of animal or human excreta, i.e. feces and urine. Such beneficial use involves mainly the nutrient, organic matter and energy contained in human waste, rather than the water content. Reuse of human waste can involve using it as a soil conditioner or fertilizer in agriculture, gardening, aquaculture, or horticultural activities. Excreta can also be used as a fuel source or as a building material.

Fecal sludge management Collection, transport, and treatment of fecal sludge from onsite sanitation systems

Fecal sludge management (FSM) is the collection, transport, and treatment of fecal sludge from pit latrines, septic tanks or other onsite sanitation systems. Fecal sludge is a mixture of human excreta, water and solid wastes that are disposed of in pits, tanks or vaults of onsite sanitation systems. Fecal sludge that is removed from septic tanks is called septage.

Decentralized wastewater system 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 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

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