Sewer gas

Source: Wikipedia, the free encyclopedia.
An old sewer gas chimney in Stonehouse, Plymouth, England, built in the 1880s to disperse sewer gas above residents

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.[1]

Sewer gases may include

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

furnaces, water heaters and rooms with underfloor heating. Infrequently used utility sinks, tubs, showers, and restrooms also are common culprits. Trap primers
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 storage tanks, or septic tanks.

In buildings with

air handlers that admit outside air for ventilation
, 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

The cover of an 1882 issue of The Wasp, with an illustration linking sewer gas and disease

During the mid-nineteenth century, when indoor plumbing was being developed, it was a common belief that disease was caused largely by

John Snow, among others, worked to prove that polluted water was the culprit, not the foul smells from sewage pipes or other sources.[3][4] Subsequently, even as the germ theory of disease
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.

headaches, 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.[7] The methane concentration in open sewers is lower (7 to 15 ppmv) than the closed drains (up to 300 ppmv) in samples collected 2 cm (0.8 in) above the level of sewage.[8]

Greenhouse gas contribution

Fully vented sewer gases contribute to greenhouse gas emissions. Septic vent pipes can be fitted with filters that remove some odors.[citation needed]

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 or microbial corrosion. In worst cases, it may lead to the collapse of the structure with significant cost for its rehabilitation.

See also

References

  1. ^ "Sewer Gas". dhs.wisconsin.gov. 10 March 2017.
  2. PMID 11733443
    .
  3. ^ "The Ghost Map by Steven Johnson - Online Resources". www.theghostmap.com.
  4. ISBN 1-59448-925-4
    .
  5. ^ Thad Godish (February 2002). "Indoor Environment Notebook". Ball State University: Department of Natural Resources and Environmental Management. Archived from the original on 2012-01-13.
  6. ISBN 978-3-659-21734-0
  7. ^ "Exposure to sewer gas". www.dhs.wisconsin.gov. 3 March 2017.
  8. ^ 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.
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