Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewerage.[ Text was copied from this source, which is available under a ] Sub-types of sewage are greywater (from sinks, bathtubs, showers, dishwashers, and clothes washers) and blackwater (the water used to flush , combined with the human waste that it flushes away). 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 , 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.
Sewage usually travels from a building's plumbing either into a sewerage, which will carry it elsewhere, or into an onsite sewage facility. Collection of sewage from several households together usually takes places in either or . The former is designed to exclude stormwater flows whereas the latter is designed to also take stormwater. The production of sewage generally corresponds to the water consumption. A range of factors influence water consumption and hence the sewage flowrates per person. These include: Water availability (the opposite of water scarcity), water supply options, climate (warmer climates may lead to greater water consumption), community size, economic level of the community, level of industrialization, Water metering of household consumption, water cost and water pressure.
The main parameters in sewage that are measured to assess the sewage strength or quality as well as treatment options include: solids, indicators of organic matter, nitrogen, phosphorus, and indicators of fecal contamination.
Management of sewage includes collection and transport for release into the environment, after a Sewage treatment that is compatible with the local requirements for discharge into water bodies, onto soil or for reuse applications.
Terminology
Sewage and wastewater
Sewage (or domestic wastewater) consists of
wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality.
Sewage is a mixture of water (from the community's
water supply),
Human waste (
Human feces and
urine), used water from
, food preparation wastes, laundry wastewater, and other waste products of normal living.
Sewage from municipalities contains wastewater from commercial activities and institutions, e.g. wastewater discharged from , laundry, , , , , stores and establishments serving the local area of larger communities.
Sewage can be distinguished into "untreated sewage" (also called "raw sewage") and "treated sewage" (also called "effluent" from a Sewage treatment).
The term "sewage" is nowadays often used interchangeably with "wastewater" – implying "municipal wastewater" – in many textbooks, policy documents and the literature.[ Spanish and Arabic versions available free online] To be precise, wastewater is a broader term, because it refers to any water after it has been used in a variety of applications.
Blackwater
Greywater
Overall appearance
The overall appearance of sewage is as follows:
The temperature tends to be slightly higher than in drinking water but is more stable than the ambient temperature. The color of fresh sewage is slightly grey, whereas older sewage (also called "septic sewage") is dark grey or black. The
odor of fresh sewage is "oily" and relatively unpleasant, whereas older sewage has an unpleasant foul odor due to
hydrogen sulfide gas and other decomposition by-products.
Sewage can have high
turbidity from suspended solids.
The pH value of sewage is usually near neutral, and can be in the range of 6.7–8.0.
Pollutants
Sewage consists primarily of water and usually contains less than one part of solid matter per thousand parts of water. In other words, one can say that sewage is composed of around 99.9% pure water, and the remaining 0.1% are solids, which can be in the form of either dissolved solids or
suspended solids.
The thousand-to-one ratio is an order of magnitude estimate rather than an exact percentage because, aside from variation caused by dilution, solids may be defined differently depending upon the mechanism used to separate those solids from the liquid fraction.
of settleable solids removed by
settling or
suspended solids removed by
filtration may contain significant amounts of entrained water, while dried solid material remaining after evaporation eliminates most of that water but includes dissolved minerals not captured by filtration or gravitational separation.
The suspended and dissolved solids include organic and inorganic matter plus microorganisms.
About one-third of this solid matter is suspended by turbulence, while the remainder is dissolved or . For the situation in the United States in the 1950s it was estimated that the waste contained in domestic sewage is about half organic compound and half inorganic.
Organic matter
The organic matter in sewage can be classified in terms of form and size: Suspended (particulate) or dissolved (soluble). Secondly, it can be classified in terms of
biodegradability: either inert or biodegradable.
The organic matter in sewage consists of
protein compounds (about 40%),
(about 25–50%), oils and grease (about 10%) and
urea,
,
phenols,
and others (lower quantity).
In order to quantify the organic matter content, it is common to use "indirect methods" which are based on the consumption of oxygen to oxidize the organic matter: mainly the Biochemical Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD).
These indirect methods are associated with the major impact of the discharge of organic matter into water bodies: the organic matter will be food for microorganisms, whose population will grow, and lead to the consumption of oxygen, which may then affect aquatic living organisms.
The mass load of organic content is calculated as the sewage flowrate multiplied with the concentration of the organic matter in the sewage.
Typical values for physical–chemical characteristics of raw sewage is provided further down below.
Nutrients
Apart from organic matter, sewage also contains nutrients. The major nutrients of interest are
nitrogen and
phosphorus. If sewage is discharged untreated, its nitrogen and phosphorus content can lead to pollution of lakes and reservoirs via a process called
eutrophication.
In raw sewage, nitrogen exists in the two forms of organic nitrogen or ammonia. The ammonia stems from the urea in urine. Urea is rapidly hydrolyzed and therefore not usually found in raw sewage.
Total phosphorus is mostly present in sewage in the form of .They are either inorganic (polyphosphates and orthophosphates) and their main source is from and other household chemical products. The other form is organic phosphorus, where the source is organic compounds to which the organic phosphorus is bound.
Pathogens
Human feces in sewage may contain
capable of transmitting diseases.
[ The following four types of pathogens are found in sewage:]
-
Bacteria like Salmonella, Shigella, Campylobacter, or Vibrio cholerae;
-
like hepatitis A, rotavirus, coronavirus,
-
Protozoa like Entamoeba histolytica, Giardia lamblia, Cryptosporidium parvum; and
-
Helminths and their eggs including Ascaris (roundworm), Ancylostoma (hookworm), and Trichuris (whipworm)
In most practical cases, pathogenic organisms are not directly investigated in laboratory analyses. An easier way to assess the presence of fecal contamination is by assessing the most probable numbers of (called thermotolerant coliforms), especially Escherichia coli. Escherichia coli are intestinal bacteria excreted by all warm blooded animals, including human beings, and thus tracking their presence in sewage is easy, because of their substantially high concentrations (around 10 to 100 million per 100 mL).
Solid waste
The ability of a flush toilet to make things "disappear" is soon recognized by young children who may experiment with virtually anything they can carry to the toilet.
Micro-pollutants
Sewage contains environmental persistent pharmaceutical pollutants. can also be present as a result of past disinfection. Sewage may contain microplastics such as polyethylene and polypropylene beads, or polyester and polyamide fragments
Some residential users tend to pour unwanted liquids like used cooking oil,
Typical sewage composition
Factors that determine composition
The composition of sewage varies with climate, social and economic situation and population habits.
Concentrations and loads
Typical values for physical–chemical characteristics of raw sewage in developing countries have been published as follows: 180 g/person/d for total solids (or 1100 mg/L when expressed as a concentration), 50 g/person/d for BOD (300 mg/L), 100 g/person/d for COD (600 mg/L), 8 g/person/d for total nitrogen (45 mg/L), 4.5 g/person/d for ammonia-N (25 mg/L) and 1.0 g/person/d for total phosphorus (7 mg/L).
For high income countries, the "per person organic matter load" has been found to be approximately 60 gram of BOD per person per day.
Values for households in the United States have been published as follows, whereby the estimates are based on the assumption that 25% of the homes have kitchen waste-food grinders (sewage from such households contain more waste): 95 g/person/d for total suspended solids (503 mg/L concentration), 85 g/person/d for BOD (450 mg/L), 198 g/person/d for COD (1050 mg/L), 13.3 g/person/d for the sum of organic nitrogen and ammonia nitrogen (70.4 mg/L), 7.8 g/person/d for ammonia-N (41.2 mg/L) and 3.28 g/person/d for total phosphorus (17.3 mg/L). The concentration values given here are based on a flowrate of 190 L per person per day.
A United States source published in 1972 estimated that the daily dry weight of solid wastes per capita in sewage is estimated as in feces, of dissolved solids in urine, of toilet paper, of greywater solids, of food solids (if garbage disposal units are used), and varying amounts of dissolved minerals depending upon salinity of local water supplies, volume of water use per capita, and extent of water softener use.
Sewage contains urine and feces. The mass of feces varies with dietary fiber intake. An average person produces 128 grams of wet feces per day, or a median dry mass of 29 g/person/day.
Flowrates
The volume of domestic sewage produced per person (or "per capita", abbreviated as "cap") varies with the water consumption in the respective locality.
The production of sewage generally corresponds to the water consumption. However water used for landscape irrigation will not enter the sewer system, while groundwater and stormwater may enter the sewer system in addition to sewage.
With regards to water consumption, a design figure that can be regarded as "world average" is 35–90 L per person per day (data from 1992).
A flowrate value of 200 liters of sewage per person per day is often used as an estimate in high income countries, and is used for example in the design of sewage treatment plants.
For comparison, typical sewage flowrates from urban residential sources in the United States are estimated as follows: 365 L/person/day (for one person households), 288 L/person/day (two person households), 200 L/person/day (four person households), 189 L/person/day (six person households).
Analytical methods
General quality indicators
Specific organisms and substances
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.[ Poliovirus detected from environmental samples in Israel ][ Drug resistant bug review: NDM-1 in New Delhi's sewage, WHO calls to action, recent outbreaks of antibiotic resistant bacteria ][ Raw Sewage Harbors Diverse Viral Populations ] Sequencing DNA from an environmental sample is known as metagenomics.
Sewage has also been analyzed to determine relative rates of use of prescription and illegal drugs among municipal populations.
Collection
Sewage is commonly collected and transported in , either in a sanitary sewer or in a combined sewer. The latter also conveys urban runoff (stormwater) which means the sewage gets diluted during rain events.
Sanitary sewer
Combined sewer
Dilution in the sewer
Infiltration of groundwater into the sewerage system
Infiltration is groundwater entering sewer pipes through defective pipes, connections, joints or .
Stormwater
Combined sewers are designed to transport sewage and stormwater together. This means that sewage becomes diluted during rain events. There are other types of inflow that also dilute sewage, e.g. "water discharged from cellar and foundation drains, cooling-water discharges, and any direct stormwater runoff connections to the sanitary collection system".
Industrial wastewater
Sewage from communities with industrial facilities may include some industrial wastewater, generated by industrial processes such as the production or manufacture of goods. Volumes of industrial wastewater vary widely with the type of industry.
An industry may treat its wastewater and discharge it into the environment (or even use the treated wastewater for specific applications), or, in case it is located in the urban area, it may discharge the wastewater into the public sewerage system. In the latter case, industrial wastewater may receive pre-treatment at the factories to reduce the pollutant load.
Disposal and dilution
Assimilative capacity of receiving water bodies or land
When wastewater is discharged into a Surface water (river, lakes, sea) or land, its relative impact will depend on the assimilative capacity of the water body or ecosystem.
In several cases, a community may partially treat its sewage, and still count on the assimilative capacity of the water body. However, this needs to be analyzed very carefully, taking into account the quality of the water in the receiving body before it receives the discharge of sewage, the resulting water quality after the discharge and the impact on the intended water uses after discharge. There are also specific legal requirements in each country. Different countries have different regulations regarding the specifications of the quality of the sewage being discharged and the quality to be maintained in the receiving water body.
The assimilative capacity depends – among several factors – on the ability of the receiving water to sustain dissolved oxygen concentrations necessary to support organisms Catabolism organic waste.
Application of sewage to land can be considered as a form of final disposal or of treatment, or both.
Other disposal methods
Sewage may be discharged to an evaporation or infiltration basin.
Marine outfall
Global situation
Treatment
Sewage treatment is beneficial in reducing environmental pollution. can remove large solid debris from sewage,
Reuse and reclamation
An alternative to discharge into the environment is to Reclaimed water the sewage in a productive way (for agricultural, urban or industrial uses), in compliance with local regulations and requirements for each specific reuse application. Public health risks of sewage reuse in agriculture can be minimized by following a "multiple barrier approach" according to guidelines by the World Health Organization.
There is also the possibility of resource recovery which could make agriculture more sustainable by using carbon, nitrogen, phosphorus, water and energy recovered from sewage.
Sewage farm
Regulations
Sewage management includes collection and transport for release into the environment after a Sewage treatment that is compatible with the local requirements for discharge into water bodies, onto soil, or for reuse applications.
Sewage management regulations are often part of a country's broader sanitation policies. These may also include the management of human excreta (from non-sewered collection systems), solid waste and stormwater.
See also
-
Fecal sludge management
-
History of water supply and sanitation
-
Reuse of human excreta
-
Urban Waste Water Treatment Directive
-
Wastewater-based epidemiology
External links
