Sewage | Types, Treatment, Advantages & Disadvantages

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Sewage is a process for the purification of mixtures of human and other domestic wastes from water and the process to purify is aerobic or anaerobic.

It also may be defined as a type of wastewater or utilized water that is produced by a community of people.

Sewage is often converted to biogas using anaerobic digestion. Increasingly, agriculture is using untreated wastewater for irrigation. Cities provide lucrative markets for fresh produce, so are attractive to farmers.

Because agriculture has got to compete for increasingly scarce water resources with industry and municipal users, there’s often no alternative for farmers but to use water polluted with urban waste, including sewage, to water their crops.

There are often significant health hazards associated with using water loaded with pathogens in this way, especially if people eat raw vegetables that are irrigated with polluted water.


The International Water Management Institute has worked in India, Pakistan, Vietnam, Ghana, Ethiopia, Mexico, and other countries on various projects aimed at assessing and reducing the risks of wastewater irrigation.

They advocate a multiple-barrier approach to wastewater use, where farmers are encouraged to adopt various risk-reducing behaviors.

These include ceasing irrigation a couple of days before harvesting to permit pathogens to die out within the sunlight, applying water carefully so it doesn’t contaminate leaves likely to be eaten raw, cleaning vegetables with disinfectant, or allowing facials sludge utilized in farming to dry before getting used as a person’s manure. Health Organization has developed guidelines for safe water use.





  1. Domestic Sewage  

Domestic sewage means human excrement, greywater (from home laundry, bathing, showers, dish-washing, and food preparation), other wastewater from household drains, and waterborne waste normally discharged from the sanitary conveniences of dwellings (including apartment houses and hotels), office buildings, retail and commercial establishments, factories, and institutions, that’s free from industrial waste.





  2. Industrial Sewage  

Fossil-fuel power stations, particularly coal-fired plants, are a serious source of commercial wastewater. Many of those plants discharge wastewater with significant levels of metals like lead, mercury, cadmium, and chromium, also as arsenic, selenium, and nitrogen compounds (nitrates and nitrites).




  3. Storm sewage  

 Storm sewage, or stormwater, is runoff from precipitation that is collected in a system of pipes or open channels.





  4. Aerobic Wastewater Treatment 

Aerobic treatment of sewage water is the best organic process which uses oxygen to interrupt down organic contaminants and other pollutants like nitrogen and phosphorous.

Oxygen is continuously mixed into the wastewater or sewage by a mechanical aeration device, like an air blower or compressor. Aerobic microorganisms then prey on the wastewater’s organic matter, converting it into CO2 and biomass which may be removed.

Aerobic treatment is typical and won’t polish industrial wastewater pre-treated by anaerobic processes. This process ensures the wastewater is fully degraded and may be safely discharged following strict environmental regulations.

Aerobic treatment processes are suitable for a variety of industries like food & beverage, chemical, and municipal. Aerobic treatment of sewage water is a stable, simple, and efficient process that produces high-quality secondary effluent. The resulting sludge is odor-free and may be sold as excellent agricultural fertilizer.





  3. Anaerobic Wastewater Treatment  

Anaerobic wastewater treatment is an organic process where microorganisms break down organic contaminants in the absence of oxygen. During a basic anaerobic treatment cycle, wastewater enters a bioreactor receptacle.

The bio-reactor contains a thick, semi-solid substance referred to as sludge, which is comprised of anaerobic bacteria and other microorganisms. These anaerobic microorganisms, or “anaerobes,” digest the biodegradable matter present within the wastewater, leading to an effluent with lower biological oxygen demand (BOD), chemical oxygen demand (COD), and/or total suspended solids (TSS), also as biogas byproducts.





  4. Importance of Sewage  

The procedure for removing contaminants from the wastewater basically from household sewage is named sewage treatment. It’s to undergo chemical, physical and biological procedures to get rid of these contaminants and provide an environmentally safe treated effluent.

A semi-solid slurry called sewage sludge is the by-product of sewage treatment. This sludge is further processed before it’s suitable for land application.

Sewage treatment is additionally called wastewater treatment, i.e. It also includes treatment of wastewater from industries. In many cities, the sewer carries a proportion of commercial wastewater to the sewage water treatment plant which has already undergone treatment within the factories for reducing the pollutant. If it’s a combined sewer it’ll also carry stormwater alongside it.

The sewage waters visit the sewage water treatment plants through pipes and pumps. The sewage within the sewage water treatment plant undergoes the subsequent basic processes.




  5. Types of Sewage  

There are mainly 2 types of sewage which are as follows:


a. Treated sewage  

Treated sewage refers to wastewater or sewage that has already been purified by the water treatment plant. Sewage goes through several stages within the treatment process ensuring that each harmful bacteria, pollutant, and contaminant are eliminated.

The Process of sewage treatment contains pretreatment, primary, secondary, and tertiary sewage treatment. The last stage usually involves the utilization of UV light to make sure all bacteria and/or viruses are removed.

After treatment, the water will usually pass into rivers or seas or be reused for irrigation and agricultural purposes.

Coming into contact with treated sewage is rare, but can arise if large flooding events affect sewage treatment plants or in very rare cases there’s a pump or other breakdown that leads to wastewater spreading over land and potentially into the property.


b. Untreated sewage  

Untreated sewage refers to wastewater that contains harmful waterborne pathogens and bacteria and which has not yet skilled a sewage treatment plant. Raw sewage usually arises from broken toilet pipes, overspills, industry leakages, and heavy storms.

It poses a particularly high risk to human and animal health and therefore the longer it sits and stagnates a home or a business, the greater amount of bacteria it’ll contain.

Quite often, within the poorer areas of the planet, sewage can get dumped anywhere and this is often unfortunate as people haven’t any access to proper treatment plants, therefore increasing health risks in those areas.

When a flood occurs, more often than not, the water contains untreated sewage and it, therefore, must be addressed immediately.

Clean Safe Services respond immediately and we can get to you within but 2 hours, reducing business interruption and majorly decreasing the danger of injury to your health and your property.





  6. Stages of Sewage treatment  

Sewage treatment is done in three stages: primary, secondary, and tertiary treatment.


a. Primary treatment  

In the primary sedimentation stage, sewage flows through large tanks, commonly called “pre-settling basins”, “primary sedimentation tanks” or “primary clarifiers”. The tanks are wont to settle sludge while grease and oils rise to the surface and are skimmed off.

Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge toward a hopper within the base of the tank where it’s pumped to sludge treatment facilities. Grease and oil from the floating material can sometimes be recovered for saponification (soap-making).


b. Secondary treatment  

Secondary treatment is meant to substantially degrade the biological content of the sewage which is derived from body waste, garbage, soaps, and detergent. the bulk of municipal plants treats the settled sewage liquor using aerobic biological processes.

To be effective, the biota requires both oxygen and food to measure. The bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules) and bind much of the less soluble fractions into floc.

Secondary treatment systems are classified as fixed-film or suspended-growth systems.

Fixed-film or attached growth systems include trickling filters, constructed wetlands, bio-towers, and rotating biological contactors, where the biomass grows on media and therefore the sewage passes over its surface.

The fixed-film principle has further developed into moving bed biofilm reactors (MBBR)and Integrated Fixed-Film Activated Sludge (IFAS) processes. An MBBR system typically requires a smaller footprint than suspended-growth systems.

Suspended-growth systems include activated sludge, where the biomass is mixed with the sewage and may be operated in a smaller space than trickling filters that treat an equivalent amount of water.

However, fixed-film systems are more ready to deal with drastic changes within the amount of biological material and may provide higher removal rates for organic material and suspended solids than suspended growth systems.

Some secondary treatment methods include a secondary clarification to settle out and separate biological Floc or filter material grown within the secondary treatment bioreactor.


c. Tertiary treatment  

The purpose of tertiary treatment is to supply a final treatment stage to further improve the effluent quality before it’s discharged to the receiving environment (sea, river, lake, wetlands, ground, etc.).

Quite one tertiary treatment process could also be used at any treatment plant. If disinfection is practiced, it’s always the ultimate process. it’s also called “effluent polishing”.





  7. Sludge treatment  

The sludge that’s accumulated within the treatment is further treated and disposed of in a safe manner. The sludge is skilled thickeners that dewater it. This sludge is then transported for disposal during a landfill or used for agriculture soil amendment.





  8. Advantages of Sewage Treatment  

The Benefits of a Contemporary Wastewater Treatment System

1. Rids Potential Diseases.

2. Low-Cost.

3. Minimal Odour Emissions.

4. No Water Bills.

5. Little Maintenance.

6. Break Down Solids Faster.

7. Less Wasteful.





  9. Disadvantages of Sewage Treatment  

There are 7 potential disadvantages of the Swage Treatment sludge process to be discussed below.

1. Hydraulic Retention Time.

2. Sludge Retention Time / Recycling.

3. Size.

4. Changes in Volume or Character of Sewage.

5. Sludge Disposal.

6. Operation / Supervision.

7. Issues with Sludge Settling.





  10. Odor Control  

Odors emitted by sewage treatment are typically a sign of an anaerobic or “septic” condition. Early stages of processing will tend to supply foul-smelling gases, with sulfide being the commonest in generating complaints.

Large process plants in urban areas will often treat the odors with carbon reactors, a contact media with bio-slimes, small doses of chlorine, or circulating fluids to biologically capture and metabolize the noxious gases.

Other methods of odor control exist, including the addition of iron salts, peroxide, nitrate, etc. to manage sulfide levels. High-density solids pumps are suitable for reducing odors by conveying sludge through hermetic closed pipework.





  11. Conclusion  

Our earth is surrounded by 70% of water. Out of which only 2.5% is water. 70% of this water is frozen in Antarctica and Greenland. Therefore, just one of the water is out there for our usage.

We use water in our lifestyle for nearly everything like cooking, washing, bathing, toilet, etc. If we recycle water for these purposes, the demand for water is often reduced.

Therefore, it’s important to treat sewage and reuse this treated effluent for laundry, floor cleaning, etc.




  12. References  

1. Content Filter & Authenticity Checking Team, Dream Civil International

(Our team checks every content & detail to maintain quality.)




Read More: Waterlogging



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