Sewage

Key takeaways

Sewage belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sewage to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sewage from memory before moving on to harder problems.

Reference excerpt

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 sewer system. Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. Sub-types of sewage are greywater (from sinks, bathtubs, showers, dishwashers, and clothes washers) and blackwater (the water used to flush toilets, 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 bidets, 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 sewer, which will carry it elsewhere, or into an onsite sewage facility. Collection of sewage from several households together usually takes places in either sanitary sewers or combined sewers. 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, 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. These can be considered to be the main macro-pollutants in sewage. Sewage contains pathogens which stem from fecal matter. The following four types of pathogens are found in sewage: pathogenic bacteria, viruses, protozoa (in the form of cysts or oocysts) and helminths (in the form of eggs). In order to quantify the organic matter, indirect methods are commonly used: mainly the Biochemical Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD). 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. Disposal options include dilution (self-purification of water bodies, making use of their assimilative capacity if possible), marine outfalls, land disposal and sewage farms. All disposal options may run risks of causing water pollution.

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 excreta (feces and urine), used water from bathrooms, 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 restaurants, laundries, hospitals, schools, prisons, offices, 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 plant). The term "sewage" is nowadays often used interchangeably with "wastewater" – implying "municipal wastewater" – in many textbooks, policy documents and the literature. To be precise, wastewater is a broader term, because it refers to any water after it has been used in a variety of applications. Thus it may also refer to "industrial wastewater", agricultural wastewater and other flows that are not related to household activities.

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. Sludges 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 colloidal. For the situation in the United States in the 1950s it was estimated that the waste contained in domestic sewage is about half organic and half inorganic.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Sewage

Start with the simplest possible case. Write down what Sewage claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sewage before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sewage ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sewage

In research: Sewage appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sewage in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sewage is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anaerobic digestion, Sanitation, Sewerage, so understanding it makes those chapters shorter.
In everyday life: Look for Sewage outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Sewage in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sewage means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sewage out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sewage in simple terms?

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 sewer system.

Why does Sewage matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sewage?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sewage.