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Sewer gas is a complex, generally obnoxious smelling mixture of toxic and nontoxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes, typical components of sewage. Sewer gases may include hydrogen sulfide,
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
,
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
,
esters In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
,
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
, sulfur dioxide and
nitrogen oxides Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral *Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide *Nitrogen dioxide (), nitrogen(IV) oxide * Nitrogen trioxide (), or ...
. Improper disposal of petroleum products such as
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
and mineral spirits contribute to sewer gas hazards. Sewer gases are of concern due to their odor, health effects, and potential for creating fire or explosions.


In homes

Sewer gas is typically restricted from entering buildings through plumbing traps that create a water seal at potential points of entry. In addition, plumbing
vents Vent or vents may refer to: Science and technology Biology *Vent, the cloaca region of an animal *Vent DNA polymerase, a thermostable DNA polymerase Geology *Hydrothermal vent, a fissure in a planet's surface from which geothermally heated water ...
allow sewer gases to be exhausted outdoors. Infrequently used
plumbing fixture A plumbing fixture is an exchangeable device which can be connected to a plumbing system to deliver and drain water. Common fixtures Supply The most common plumbing fixtures are: *Bathtubs *Bidets * Channel drains * Drinking fountains * Hose b ...
s may allow sewer gas to enter a home due to evaporation of water in the trap, especially in warm weather. The result is the most common means of sewer gas entering buildings and can be solved easily by using the fixtures regularly or adding water to their drains. One of the most common traps to dry out are floor drains such as those typically placed near home furnaces, water heaters and rooms with underfloor heating. Infrequently used utility sinks, tubs, showers, and restrooms also are common culprits.
Trap primer A trap primer (or trap seal primer) is a plumbing device or valve that adds water to traps. The water seals in traps are needed to prevent sewer gases from entering buildings, but because this water is exposed to the air, it is subject to evapor ...
s are available that automatically add water to remote or little used traps such as these. Blocked plumbing vents, typically at the roof, also can cause water seals to fail via siphoning of the water. Exposure to sewer gas also can happen if the gas seeps in via a leaking plumbing drain or vent pipe, or even through cracks in a building’s foundation. Sewer gas is typically denser than atmospheric gases and may accumulate in basements, but may eventually mix with surrounding air. Individuals who work in sanitation industries or on farms might be exposed on the job if they clean or maintain municipal sewers,
manure Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists of animal feces; other sources include compost and green manure. Manures contribute to the Soil fertility, fertility of soil by adding organic ma ...
storage tanks, or
septic tank 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 treatm ...
s. In buildings with HVAC air handlers that admit outside air for
ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Ventilator, a m ...
, plumbing vents placed too closely to air intakes or windows can be a source of sewer gas odors. In some cases airflow around buildings and wind effects may contribute to sewer gas odor problems even with appropriately separated vents and air intakes. Increasing vent heights, adding vent pipe filters, or providing powered dilution and exhaust can help reduce occurrences.


History

During the mid-nineteenth century, when indoor plumbing was being developed, it was a common belief that disease was caused largely by miasmas, or literally "polluted air." (Malaria, a disease spread by mosquitoes that breed in marshy areas, got its name from the Italian words for "bad air" because people initially blamed it on marsh gas.) Originally, traps in drain pipes were designed to help keep this bad air from passing back into living spaces within buildings. However, during the Broad Street cholera outbreak in London, in the summer of 1854, physician John Snow, among others, worked to prove that polluted water was the culprit, not the foul smells from sewage pipes or other sources. Subsequently, even as the
germ theory of disease The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can lead to disease. These small organisms, too small to be seen without magnification, invade ...
developed, society was slow to accept the idea that odors from sewers were relatively harmless when it came to the spread of disease.


Health effects

In most homes, sewer gas may have an unpleasant odor, but does not often pose a significant health hazard. Residential sewer pipes primarily contain the gases found in
air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
(
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
,
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
, etc.). Often,
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
is the gas of next highest concentration, but typically remains at nontoxic levels, especially in properly vented systems. However, if sewer gas has a distinct “rotten egg” smell, especially in sewage mains, septic tanks, or other sewage treatment facilities, it may be due to hydrogen sulfide content, which can be detected by human olfactory senses in concentrations as low as
parts per billion In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they ...
. Exposure to low levels of this
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...
can irritate the eyes, cause a cough or sore throat,
shortness of breath Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing di ...
, and fluid accumulation in the lungs. Prolonged low-level exposure may cause fatigue, pneumonia, loss of appetite,
headaches Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
, irritability, poor memory, and dizziness. High concentrations of hydrogen sulfide (>150 ppm) can produce olfactory fatigue, whereby the scent becomes undetectable. At higher concentrations (>300 ppm), hydrogen sulfide can cause loss of consciousness and death. Very high concentrations (>1000 ppm) can result in immediate collapse, occurring after a single breath.


Explosion risk

Sewer gas can contain methane and hydrogen sulfide, both highly flammable and potentially explosive substances. As such, ignition of the gas is possible with flame or sparks. The methane concentration in open sewers is lower (7 to 15 ppmv) than the closed drains (up to 300 ppmv) in samples collected above the level of sewage.N N Purkait and D K Chakrabarty. Methane Emission from open drain; Indian journal of Radio and Physics; vol 4, March 2015: pp 56-59 ( M K Mitra centre for research in Space Environment, Institute of Radiophysics and electronics, University of Clacutta, Kolkata.


Greenhouse gas contribution

Fully vented sewer gases contribute to
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
. Septic vent pipes can be fitted with filters that remove some odors. Sewer gas can be used as a power source, thus reducing the consumption of fossil fuels. The gas is piped into a cleaning system and then used as a fuel to power a generator or combined heat and power (CHP) plant.


Impact on sewerage

Gases present in sewerage can strongly impact material durability due to the action of microorganisms. The most deleterious one is associated to hydrogen sulfide that can result in
biogenic sulfide corrosion Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is biochemically ox ...
or
microbial corrosion Microbial corrosion, also called microbiologically influenced corrosion (MIC), microbially induced corrosion (MIC) or biocorrosion, is "corrosion affected by the presence or activity (or both) of microorganisms in biofilms on the surface of the cor ...
. In worst cases, it may lead to the collapse of the structure with significant cost for its rehabilitation.


See also

*
Fire protection Fire protection is the study and practice of mitigating the unwanted effects of potentially destructive fires. It involves the study of the behaviour, compartmentalisation, suppression and investigation of fire and its related emergencies, as we ...
*
Indoor air quality Indoor air quality (IAQ) is the air quality within and around buildings and structures. IAQ is known to affect the health, comfort, and well-being of building occupants. Poor indoor air quality has been linked to sick building syndrome, reduce ...
* Louisville sewer explosions *
Plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water deliv ...
* Potable cold and hot water supply * Rainwater, surface, and subsurface water drainage *
Septic system 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. A septic tank a ...
s * Sewer gas destructor lamp *
Marsh gas Marsh gas, also known as swamp gas or bog gas, is a mixture primarily of methane and smaller amounts of hydrogen sulfide, carbon dioxide, and trace phosphine that is produced naturally within some geographical marshes, swamps, and bogs. The surfac ...


References

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