Sewage: Wastewater and Its Management

Sewage is typically a type of wastewater or a mixture of water and wastes containing ions, solids wastes, or harmful bacteria produced by domestic and industrial life and is flushed into the sewer.

• Generally, it is referred to as liquid waste, it also includes the rainwater that runs down the street and the water that washes off the roads and rooftops.
• Many harmful impurities and chemicals are dissolved and suspended in such water.
• In order to retrieve the precious water, the sewage is treated and cleaned, in “Sewage water treatment plants”.

Key Terms: Sewage, Sewage wastewater treatment, Domestic sewage, Industrial sewage, Organic material, Plant nutrients, Sewage treatment, Wastewater disposal system

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What is Sewage?

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Water is the basic need of every individual. One cannot survive without water. It is used in cooking, bathing, cleaning, washing clothes and dishes, and for many other purposes. After use, this water gets dirty and is termed wastewater or sewage.

Sewage (also known as domestic sewage, domestic wastewater, or municipal wastewater) is wastewater produced by a community of people. It is generally transported through the sewage system. 

Sewage includes wastes from domestic, municipal, industrial, commercial, and other public facilities. Waste comprises the following:

• The lather of Soaps and detergents
• Food waste from the washing of dishes
• Blackwater gushes down from showers, toilets, laundries, etc.
• Toilet papers
• Macro pollutants (like organic matter, solids, fecal matter, etc.) and micropollutants

Sewage

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Types of Sewage

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Sewage is divided into three major categories, namely:

Domestic Sewage

It is also known as Sanitary Sewage, this sewage is carried off by the people living in residential areas in the form of laundry wastes, urine, excreta, etc.

It is further divided into two sub-categories:

• Greywater: It comes from bathtubs, sinks, washing machines, showers, etc.
• Blackwater: It comes from the water which is used to flush toilets and human excreta.

Industrial Sewage

It originated from industrial processes such as manufacturing or production of goods, chemical processes, etc.

Storm Sewage

Storm sewage (also known as stormwater) is the rainwater that traverses down the rooftops and over the ground to a defined channel. While dissolving it carries all the chemicals from the atmosphere, and other organic materials and solids are picked up as it travels over the ground.

Types of Sewage

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Pollutants of Sewage

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Untreated sewage has various hazardous substances like PAHs, PCBs, pesticides, etc.

Given below is a detailed view of the principal pollutants of the sewage:

Organic Material

It is indicated by the BOD (Biochemical Oxygen Demand), the amount of oxygen utilized by the microorganisms to decompose the organic material. The more organic matter present in the sewage, the more its BOD.

Suspended Solids

It is present in the sewage and is directly proportional to the volume of muck produced in a treatment plant. Industrial and storm sewage generally may have higher concentrations of suspended solids than sanitary waste

Plant Nutrients

The sewage contains two essential elements for plant growth: phosphorous and nitrates. Too much of these elements supports fast algae growth, which accelerates the natural aging of lakes through a process known as eutrophication.

Microbes

Billions of microorganisms are found in domestic sewage mainly as Coliform bacteria, which come from the human intestinal tract, and many other microbes.

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Disposal Methods of Sewage

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Sewage disposal methods constitute the major components of a sewage management system, wherein it disposes the used water from households, industries, etc., and again helps to keep the environment clean. Some of the well-known sewage disposal methods that are practiced around the globe are:

Municipality Systems

This is a treatment plant, in the municipality wastewater system, connected to the source of wastewater. By treating the used water, this plant efficiently removes around 95% of waste/ impurities. Moreover, by an anaerobic process, the sludge is again treated to assure the safety of using this water.

Off-Site Sewage System

The off-site sewage system was initially developed as the result of increased urbanization.

• In urban areas, the houses are built on plots, where each plot is connected to a wastewater line.
• These wastewater lines collect waste from households and flow towards a community sewage treatment plant.
• Here, once the treatment is done, excess water is directed toward a nearby river/ irrigation area.

On-Site Sewage System

An on-site sewage system or septic system is composed of a septic tank where the sewage can be settled, treated, and similarly slurred in the same place of waste generation.

• In this process, the wastewater is disposed of and treated in natural ways.
• Usually, an on-site system comprises a septic tank along with a disposal field that is the soil absorption place. 

Full Wastewater System

In a full wastewater disposal system, the sewage water is collected from households and then directed to various sewer pipes. Here, all solid wastes go through multiple sharp blades or macerators, which helps to decrease the dimension of solid waste before further processing.

Lagoons

Lagoons denote large open ponds that can collect wastewater from households and these water bodies contain microorganisms to a great extent that decompose the waste. Sunlight and wind that act as catalysts in this process, accelerate the decomposition process.

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Sewage Treatment

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There are basically four types of sewage treatment:

Sewage Treatment Plants (STPs)

It receives sewage waste from residential and commercial buildings and rainwater and debris from storm sewers.

• Its main work is to remove contaminants from the sewage with a combination of physical, chemical, and biological treatment before discharging it into the environment.
• It performs its function in three main steps and hence is known as the three-stage plant.

Effluent Treatment Plants (ETPs)

These are used in cleaning industrial sewage- the sewage which flows out as a by-product of industries.

• It is used in sectors with extensive chemical contamination such as pharmaceuticals, textile and dye manufacturing, etc.
• These are beneficial for large operations and often require specialized technicians for operations and maintenance.

Activated Sludge Plants (ASPs)

It treats sewage by using primarily activated sludge to digest biological contaminants and dissolved oxygen to promote the growth of clumps of organic matter. Activated sludge has less odor as compared to anaerobic sludge and hence, is used in less-isolated settings where the smell is a concern.

Common and Combined Effluent Treatment Plants (CEPTs)

These are used by smaller manufacturing companies that cannot always afford to run their own effluent treatment plants. It allows the different industrial cluster to pool their effluent in a centralized plant for treatment. CEPT's maintenance is shared by all the small facilities that send its sewage to it.

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Health and Environmental Aspects of Sewage

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The following are the Health and Environmental aspects of sewage

Health Aspects

According to GESAMP (2001), sewage pollution in the coastal marine environment causes the spread of various infectious diseases.

• These are associated with swimming and bathing in marine waters, as well as the consumption of seafood.
• When humans are exposed to various algae-related toxins, serious health hazards arise. 
• The majority of diseases are caused by pathogens, which are infectious or biological organisms that transmit disease.
• The acute diseases caused by them include diarrhea, typhoid fever, cholera, and hepatitis A.
• These bacteria are known to survive in the water for several weeks. 

Environmental Aspects

Organisms need chemical nutrients to reproduce and survive. Excess nutrients are discharged into the marine environment as a result of agricultural fertilizers and nitrogen oxides produced by fossil fuel combustion.

• In cities, sewage is the main source of nutrients, whereas agriculture is the primary source in rural regions.
• Eutrophication is a process in which increased nutrients cause a wide variety of plants to grow and decay.

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Things to Remember

• Sewage includes wastes from domestic, municipal, industrial, commercial, and other public facilities.
• Sewage has a slightly higher temperature than groundwater or drinking water because heat is released during the breakdown of organic substances.
• The color of sewage determines its power and lifetime.
• Fresh sewage is slightly greyish in color whereas older sewage( or septic sewage) is dark grey or black.
• Domestic sewage, also known as sanitary sewage, is released by people living in residential areas in the form of laundry waste, urine, excreta, and so on.
• Industrial wastes originate from industrial processes such as manufacturing or production of goods, chemical processes, etc.
• Storm sewage or stormwater is the rainwater that traverses down the rooftops and over the ground to a defined channel.