Sewage
[1]: 175 Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality.
Sewage contains macro-pollutants and micro-pollutants, and may also incorporate some municipal solid waste and pollutants from industrial wastewater.
[2]: 36 Management of sewage includes collection and transport for release into the environment, after a treatment level that is compatible with the local requirements for discharge into water bodies, onto soil or for reuse applications.
As greywater contains fewer pathogens than blackwater, 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.
Greywater may still have some pathogen content from laundering soiled clothing or cleaning the anal area in the shower or bath.
[10]: 9–38 The organic matter in sewage can be classified in terms of form and size: Suspended (particulate) or dissolved (soluble).
[2]: 35 The organic matter in sewage consists of protein compounds (about 40%), carbohydrates (about 25–50%), oils and grease (about 10%) and urea, surfactants, phenols, pesticides and others (lower quantity).
If sewage is discharged untreated, its nitrogen and phosphorus content can lead to pollution of lakes and reservoirs via a process called eutrophication.
[2]: 43 Total phosphorus is mostly present in sewage in the form of phosphates.They are either inorganic (polyphosphates and orthophosphates) and their main source is from detergents and other household chemical products.
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).
The privacy of a toilet offers a clandestine means of removing embarrassing evidence by flushing such things as drug paraphernalia, pregnancy test kits, combined oral contraceptive pill dispensers, and the packaging for those devices.
Sewage may contain microplastics such as polyethylene and polypropylene beads, or polyester and polyamide fragments[15] from synthetic clothing and bedding fabrics abraded by wear and laundering, or from plastic packaging and plastic-coated paper products disintegrated by lift station pumps.
Pharmaceuticals, endocrine disrupting compounds, and hormones[16][17][18] may be excreted in urine or feces if not catabolized within the human body.
Some residential users tend to pour unwanted liquids like used cooking oil,[19]: 228 lubricants,[19]: 228 adhesives, paint, solvents, detergents,[19]: 228 and disinfectants into their sewer connections.
[6] This is called the population equivalent (PE) and is also used as a comparison parameter to express the strength of industrial wastewater compared to sewage.
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).
An average person produces 128 grams of wet feces per day, or a median dry mass of 29 g/person/day.
[20] The volume of domestic sewage produced per person (or "per capita", abbreviated as "cap") varies with the water consumption in the respective locality.
[5]: 163 Even inside a country, there may be large variations from one region to another due to the various factors that determine the water consumption as listed above.
Sewage has also been analyzed to determine relative rates of use of prescription and illegal drugs among municipal populations.
[5]: 163 The "direct inflows" can result in peak sewage flowrates similar to combined sewers during wet weather events.
[2]: 27 Industrial wastewater may contain very different pollutants at much higher concentrations than what is typically found in sewage.
In principle, the higher the dilution capacity (ratio of volume or flow of the receiving water and volume or flow of sewage discharged), the lower will be the concentration of pollutants in the receiving water, and probably the lower will be the negative impacts.
[30] In several cases, a community may treat partially its sewage, and still count on the assimilative capacity of the water body.
This could lead to satisfactory results if the assimilative capacity of the ecosystem is sufficient which is nowadays not often the case due to increasing population density.
[19]: 446 Primary treated sewage usually contains less than half of the original solids content and approximately two-thirds of the BOD in the form of colloids and dissolved organic compounds.
[44] Water disinfection may be attempted to kill pathogens prior to disposal, and is increasingly effective after more elements of the foregoing treatment sequence have been completed.
[45] 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.
[46][4] Sewage management includes collection and transport for release into the environment after a treatment level that is compatible with the local requirements for discharge into water bodies, onto soil, or for reuse applications.
[2]: 156 In most countries, uncontrolled discharges of wastewater to the environment are not permitted under law, and strict water quality requirements are to be met.
