Sewage

Sewage is defined as the liquid and solid waste that is excreted by a community and is produced by factories, industries, street and yard washings, and houses. It smells bad and looks like dirty water. Sewage contains 99.9% waste and 0.1% partially organic, partially inorganic, and partially suspended particles.

Sullage: Waste water that is free of human waste. It is produced by everyday tasks like doing laundry, cleaning dishes, and taking a shower, and it may be recycled on site for things like landscape irrigation and artificial wetlands.

Sludge: Sludge is the leftover, semi-solid substance from sewage or industrial waste water treatment procedures. It can also apply to the settled suspension produced by a variety of industrial processes, including those used to treat drinking water. As a result, it is thick and contains 95% water and 5% other organic substances.

Process of Sewage Decomposition

Nicely learned There are two methods through which organic stuff in sewage decomposes:

• The aerobic process is the most effective way to break down organic stuff. Free dissolved oxygen must be available continuously for the process to work. By the action of bacterial organisms, including protozoa, the organic matter is broken down into simpler components, such as carbon dioxide, water, ammonia, nitrites, nitrates, & sulphate.
• Anaerobic process: This method works best when the sewage is extremely concentrated and contains a lot of particles. Methane, ammonia, carbon dioxide, and water are the final byproducts of the breakdown process. Anaerobic decomposition has slower reactions and a more complicated mechanism than aerobic decomposition.

Modern Sewage Treatment

Modern sewage treatment facilities are built around the biological principles of bacterial aerobic and anaerobic action in sewage purification. Sewage treatment can be separated into two stages:

• Primary treatment
• Secondary treatment

Primary Treatment:

Anaerobic digestion, the initial step in purification, is used in primary treatment to remove the particles from the sewage in part through screening and in part through sedimentation.

• Screening: The community's sewage and sludge are first run through a metal screen to remove large objects like wood, rags, piles of debris, and dead animals. This keeps the treatment plants from clogging. Steel bars that are either vertical or incline are typically spaced 2 inches apart to make the screen. There are some plants that have moving screens. Periodically, the screenings are removed manually or mechanically and disposed of by trenching or burying.
• Grit chamber: After passing through the "grit chamber," which is a long, thin room, sewage is discharged. This chamber has a length of between 10 and 20 meters and a constant velocity of around 1 foot per second. The purpose of the grit chamber is to permit the passage of organic matter while allowing the settlement of heavier solids, such as sand and gravel. The grit that gathers at the bottom of the chamber is periodically removed or continuously dumped or trenched out.
• The sewage is now introduced into the primary sedimentation tank. It has a rectangular shape, and sewage is permitted to move gently through it at a speed of 1-2 feet per minute. The sewage remains in this tank for 6 to 8 hours. Approximately 50–70% of solids gravitationally sink to the ground. Sludge is the term for the organic material that settles to the bottom and is removed using machinery without interfering with the tank's functioning. Some fat and oil rise to the surface and produce scum, which is periodically cleaned and disposed of. Chemicals such as lime, aluminum sulfate, and ferrous sulfate are used to treat sewage that contains organic trade wastes. 3.

Secondary Treatment:

The primary sedimentation tank's effluent still has a significant amount of living organisms and organic matter in solution or colloidal form. It has a high demand for organs and, if not properly treated, can pollute soil or water. As a result, the following approaches should be used: (Bacterial oxidation)

• Depending on the size of the population, the trickling filter, also known as the percolating filter, is a bed of clinker or crushed stone that is 4–8 feet deep and 6-100 feet in diameter. A rotating mechanism evenly and constantly spreads the primary sedimentation tank's effluent over the bed's surface. The tool is made out of hollow pipes, each with a row of holes. These pipes continue to turn, spraying a thin film of effluent over the filter's surface. The "zoogleal layer" is a very comprehensive biological growth made up of algae, fungus, and protozoa. The bacterial flora of the zoogleal layer oxidizes the effluent as it passes through the filter bed.
• Aeration tank: The aeration tank is the "heart of the activated sludge process." Sludge and the effluent from the primary sedimentation tank are combined, and the mixture has a 6- to 8-hour rating. Mechanical agitation or the continual passage of compressed air from the chamber's bottom are also methods of aeration. The organic stuff in the sewage is converted during this process into carbon dioxide, nitrate, and water. Most microbes, including those that cause cholera and typhoid, have been eliminated. Large cities are the greatest places for this process because it calls for trained labor.
• Secondary (final) sedimentation: The trickling filter or aeration chamber sends the oxidized sewage into the secondary sedimentation tank, where it is held for two to three hours. Aerated sludge is the name given to the sedimented sludge. From the primary sedimentation tank, it is different. It is flavorless, abundant in bacteria, nitrogen, and phosphates, and can be dried and used as manure. In the activated sludge process, some of the activated sludge is pumped back into the "aeration tanks" while the remaining is pumped into the sludge digestion tanks for cleaning and disposal. The organic material in the sewage is oxidized during this process, yielding carbon dioxide, nitrate, and water. Most organisms, including those that cause cholera and typhoid, have been eliminated. Large cities are the best places for this process because it calls for skilled labor.

Sludge Digestion

The handling and disposal of the generated sludge is one of the biggest issues with sewage treatment. 15-20 tons of sludge are produced by one million gallons of sewa e. The sludge is a heavy, black mass that is 95% water and has an offensive odor. There are several ways to dispose of sewage:

• Sludge is treated by being digested in contemporary sewage treatment facilities. Sludge can go through anaerobic auto-digestion, in which complex materials are broken down into water, carbon dioxide, methane, and ammonia when incubated under favorable temperature and PH conditions. Sludge volume is also significantly decreased. The digestion of sludge takes three to four weeks or more to be finished. The residue is a flavorless, tarry, sticky muck that rapidly dries and makes excellent manure. In specialized tanks referred to as "sludge digestion tanks," sludge is digested. Sludge digestion produces methane gas, which can be used for lighting and heating.
• Sludge can be pumped into the sea for disposal in seacoast cities and towns.
• Land-based disposal: Sludge can be disposed of by composting it with municipal waste.

Disposal of Effluent

• Disposal by dilution: "Disposal by dilution" refers to the disposal of waste into water bodies like rivers and streams. Before releasing the effluent into a river or body of water, it is vital to take into account the river's capacity for dilution and the amount of dissolved oxygen present. If river water is used for drinking, sufficient chlorination must be used to rid the effluent of pathogenic organisms. Today's industry has created hundreds of new compounds that biological therapy cannot eliminate. As a result, the effluent may contain compounds that are hazardous to humans or that can harm crops, kill fish, or interfere with a stream's regular flow.
• Land disposal: The wastewater can be used for irrigation if there is adequate land available.

Bagmati Civilization Conservation and Development Committee Guheshwori is an illustration of contemporary sewage treatment.

Methods of Sewage Disposal

• Sea outfall: Seacoast cities and towns have the option of dumping their sewage into the sea. The sewage is diluted in the sea water due to the increased depth of the ocean, and the solid gradually oxidizes. This method has the disadvantage that objectionable solid waste may wash back to the coast and cause a public nuisance. The sewage outfall is constructed to discharge the sewage into deep water through a lengthy sewerage system in order to avoid this. For countries like Nepal that are landlocked, this approach is ineffective.
• The majority of the Kathmandu Valley and other cities in Nepal use this technique, which contaminates the rivers and streams. However, close to Pashupati, the Bagmati Civilization Conservation and Development Committee (previously known as the High Powered Committee for Integrated Development of the Bagmati Civilization) Guheshwori treats the sewage as per modern sewage treatment process & as per modern sewage treatment process then falls at Pingalasthan in the Bagmati River, beneath the Pashupati Temple.
• Sewage may be applied to the land after grit removal, screening, and a brief period of settlement if sufficient and adequate land (porous soil) is available. The term "wide irrigation" also applies to this approach. Through the use of a conduit, the sewage is directed to land. The ground is first divided into ridges and furrows, then crops are planted on the ridges and sewage is intermittently fed into the furrows. The best crops are ones that are likely to be consumed raw and don't come into contact with sewage. It is possible to produce fruit trees with fruits that hang high above the ground. However, crops that will come into touch with sewage, such as sugarcane, coriander, cucumber, tomato, and onion, shouldn't be cultivated. The farm ought to fall under
• Using an oxidation pond to dispose of waste is less expensive. Other names for it include sewage lagoons, redox ponds, and waste stabilization ponds. The oxidation pond is an open, shallow pool that is between 3 and 5 feet deep and has an outlet. An oxidation pond requires the following elements to qualify:
  • Specific bacterial species that feed on organic waste that has decomposed
  • Sun-light 
  • Algae
• Bacteria convert the organic content in sewage to simple chemical components like carbon dioxide, ammonia, and water. The carbon dioxide, water, and inorganic minerals are used by the algae along with sunshine to fuel their growth. Algae and bacteria coexist in oxidation ponds in a biological equilibrium that is mutually beneficial. The most crucial component of life, oxygen, is mostly obtained from algae that release oxygen when exposed to sunshine. So, on sunny days, oxidation ponds operate effectively. Purification is carried out by anaerobic means at night and aerobic means during the day. Thus, both aerobic and anaerobic species of bacteria work together to purify sewage in oxidation ponds.
• Open drainage is used by the vast majority of persons in our neighborhood. A health hazard is an open drainage because it:
  • Assists in fly reproduction
  • Food is contaminated
  • Pollutes water, soil, and air
  • Pollutes the environment Typhoid, paratyphoid, fever, dysentery, diarrhea, cholera, hookworm, ascariasis, and viral hepatitis are among the illnesses brought on by unhygienic conditions.