7. INTRODUCTION TO SANITATION

 7.1 Definition and Role of Sanitation in Maintenance of Health

Sanitation is defined as the process of keeping our environment free from dirt, infection, disease etc. by removing waste, trash and other unwanted materials from our environment.

Major role of sanitation in public health can be listed as below.

• Sanitation keeps our environment tree from wastages.
• Sanitation protects drinking water.
• Sanitation protects air for breathing.
• Sanitation keeps us far from bacteria pathogens and virus.
• Sanitation keeps land hygiene etc.

 7.2 Systems of Sanitation

Sanitation systems are a combination of different functional units that together allow managing and reusing or disposing the different waste flows from households, institutions, agriculture or industries in order to protect people and the environment. 

The procedure of sanitation system is shown in following diagram.

For the disposal of waste product of a town two major works are required:

a. Collection Works and                 b. Disposal Works.

Collection works are the works, which are done to collect waste product. The disposal works are the works are the works which are done to treat waste and dispose to the suitable location. The disposal is done in such a way that. It will not disturb human health. For such collection and disposal works system of sanitation defines the major tasks. So, systems of sanitation are as follow:

1.   1. Waterless or Dry System             2. Water Carriage or Wet System

1. Waterless or Dry System: In this system, Various types of refuse and storm water are collected conveyed and disposed of separately by different methods. Garbage or dry refuse of a town/city is collected in dust-bins placed along the roads and streets. From dust-bins the refuse is transported by trucks twice in a day to the point of disposal. All the noncombustible portion of garbage such as sand, dust, clean ashes etc are used for filling the low-level areas. The combustible pertains of garbage such as dry leaves, waste paper, broken furniture etc. are burnt. The decaying fruits, vegetables, grass and other such things are first dried and disposed of by drying or in manufacture of manure. Human excreta are collected separately in privies or latrines. This system has following advantages and disadvantages:

Advantages

• It is cheaper in initial cost.
• Quantity of sewage reaching at the treatment plant before disposal is low.
• The storm water goes in open drain so that the section of sewer will be small.

Disadvantages

• Storm water may enter sewer line that may cause heavy load on treatment plant.
• For burning human extra-large space is required.
• Liquid refuse may get an access in the subsoil and may contaminate grained.

2. 2. Water Carriage or Wet System: In this system, water is used for the collection and conveyance of the sewage. In this system, water is the main substance therefore it is called water carriage system or wet system. The refuse from the city is taken out through properly designed sewerage system after necessary treatment. This system has following advantages and disadvantages.

     Advantages

• It is hygienic method.
• There is no nuisance in the streets of towns.
• It occupies less space.
• Land required for disposal is less.
• This system does not depend on manual labour at every time.

Disadvantages

• This system is very costly initially.
• The maintenance of this system is also costly.
• During monsoon large quantity of sewage water is to be treated where age very small volume is to be treated in the remaining period of year.

Define valves and fittings

Valves and fittings are essential components of sewer systems, helping to control the flow of wastewater and prevent the backflow of sewage. Here are some commonly used valves and fittings in sewer systems:

a. Gate valves

These valves are used to regulate the flow of sewage through pipes. They are typically used in large-diameter pipes and can be operated manually or through an actuator.

b. Check valves
These valves are used to prevent backflow of sewage into a building or other structure. They allow flow in only one direction, preventing sewage from backing up into the building.

c. Ball valves
These valves are used to control the flow of sewage and are often used in smaller pipes. They are easy to operate and require little maintenance.

d. Couplings
Couplings are used to join two pieces of pipe together. They are often used in sewer systems to repair damaged or broken pipes.

e. Elbows
Elbows are fittings that allow pipes to change direction. They are commonly used in sewer systems to navigate around obstacles or change the direction of the flow.

f. Tees
Tees are fittings that allow pipes to branch off in different directions. They are commonly used in sewer systems to connect multiple pipes together.

g. Reducers
Reducers are used to transition from one pipe size to another. They are commonly used in sewer systems to connect pipes of different sizes together.

7.3 System of sewerage 

A sewerage system, or wastewater collection system, is a network of pipes, pumping stations, and appurtenances that convey sewage from its points of origin to a point of treatment and disposal. Generally, sewerage systems are classified as follows:

1.    1. Combined System         2. Separate System         3. Partially Separate System

3.    1. Combined System
When only one set of sewers is laid, carrying both the sanitary sewage and storm water. It is called combined system. This system is suitable in small rainfall areas. It is also suitable in crowded areas. It has following advantages and disadvantages: 

Advantages 

• Sewage treatment is economical.
• More quantity of sewage is available so no needs of flushing system.
• More suitable in narrow streets.

Disadvantages 

• Initial cost is high.
• It is not suitable in heavy rainfall areas.

2. Separate System      

When the domestic and industrial sewage are taken in one set of sewer and storm water is taken in another set of sewers, the system of sewerage is separate system. This system has following advantages and disadvantages:

Advantages 

• Quantity of sewage to be treated is low.
• It is cheaper than combined system.
• There is no fear of stream pollution etc.

Disadvantages 

• Flushing is required for continuous flow of sewage.
• There is risk of overflow of sewage due to entering of storm water.
• Maintenance cost is more.
• Difficult for laying in heavy traffic areas.

3. Partially Separate System

In the separate system, if a portion of storm water is allowed to enter in the sewers carrying sewages and the remaining storm water flows in separate set of sewers, it is called partially separate system. It has following advantages and disadvantages:

Advantages 

• The sewer becomes economical.
• No flushing is required etc.

Disadvantages 

• There is possibility of overflow.
• In dry weather there may be possibility of clogging sewer etc.

7.4 Types of sewers 

The conduit or closed system that carries sewage from its origin to treatment plant and up to disposal area is called sewer. Sewers are made up of so many types of materials according to purpose and degree of waste present. In general, sewers are classified as following: 

A. According to materials 

·         a. Asbestos Cement (AC)(AC) Sewers: Asbestos cement sewers are manufactured from a mixture of cement and asbestos fiber. Asbestos cement (AC)(AC) sewers are suitable for carrying domestic sanitary sewage. Asbestos cement sewer is best as vertical pipe for carrying sullage from upper floors of multistory buildings.

·         b. Brick Sewers: These types of sewers are made at site and used for construction large size sewer. Brick sewers are very useful for construction of storm sewer and combined sewer.

·         c. Cement Sewers: These are made of cement sand and coarse aggregates. Cement concrete sewers are manufactured with reinforcement and without reinforcement both. PCCPCC (Without reinforcement) Sewers are constructed up to diameter of 60 cm these are suitable for small storm drains. These are not durable. On the other hand, RCCRCC sewers are suitable for diameter greater than 60 cm. Concrete Reinforced sewers can resist heavy loads. They can resist corrosion and high pressure. These are very heavy and difficult to transport.

·         d. Cost Iron (CI)(CI) Sewers: These sewers are high strength and durability water thought. Cast Iron (CI) sewers can withstand high internal pressure and can bear external load. These are suitable for the following condition.

• When the sewage is conveyed high pressure.
• When sewer line is subjected to heavy external load.
• When there is considerable difference in pressure.

·         e. Plastic Sewers: Nowadays plastic sewers are used for carrying sewerage. Plastic sewers are resistant to corrosion. Such types of sewers are light in weight, smooth and can be bent easily. But these types of sewers are having high coefficient of thermal expansion and cannot be used at very hot areas.

·         f. Steel Sewers: These types of sewers are imperious and water light. These are light in weight. Steel pipes can resist high pressure. These are flexible and suitable in following conditions:

• When the sewage is carried under pressure.
• When the sewage is to be carried across river under water.
• When the sewer has to cross under a railway track etc.

B. According to purpose

a. Sanitary Sewer: Sanitary sewer carries sewage from municipality including domestic and industrial sewage water.

b. Storm Sewer: Storm sewer carries storm sewage including run off and street wash.

c. Combined Sewer: Combine sewer carries domestic, industrial and storm sewage.

d. House Sewer: It is the sewer conveying sewage from planning system of a building to common sewer.

e. Lateral Sewer: The sewer carries sewage from house sewers.

f. Main Sewer: It is the sewer that carries sewage from two or more sub mains.

g. Sub Main Sewer: The sewer that carries sewage from two or more than two laterals.

h. Outfall Sewer: Outfall sewer receives sewage from all collecting system and convey it to point of final disposal.

C. According to shape of sewer

a. Circular Shaped Sewers- Circular sewers are the most commonly utilised sewers and are preferred for all sorts of sewage. This sewer shape is simple to build, takes fewer resources, and is cost-effective. 

b. Parabolic-Shaped Sewer- A parabolic-shaped sewer is utilised for smaller amounts of sewage discharge. The sewer is modest in size, and the upper border is shaped like a parabola. This sewer's inverted section could be parabolic or elliptical in shape. It is also cost-effective. 

c. Horseshoe-Shaped Sewer- As the name implies, its shape resembles a horseshoe. A horseshoe-shaped sewer is a big size sewer that is commonly used in locations where substantial discharge is necessary. The invert can be round, parabolic, or flat. The height of such sewers is greater than its width. Maintenance of these types of sewers is simple because of their great size. 

d. Standard Egg-Shaped Sewer- These types of sewers are appropriate for low flow conditions as these types of sewers give higher flow velocities as compared to circular sewers. These types of sewers are preferred for combined sewerage systems. The construction of these types of sewers is cumbersome and costly as it requires large amounts of construction materials. 

e. Semi-Elliptical Shaped Sewer- These types of sewers are adopted for carrying large amounts of sewage. The upper arch of these types of sewers is elliptical in shape and the invert may be elliptical or parabolic. 

f. Rectangular-Shaped Sewer- A rectangular-shaped sewer is used for discharging stormwater and large quantities of sewage. The construction and maintenance of these types of sewers are quite cheaper. 

g. U-shaped Sewer- Its shape is identical to the English capital letter "U". The U-shaped sewer is utilised for highvolume sewage outflow. Because of its size, it is also used to transport stormwater. The inverted component of such sewers has a semi-circular form. It also serves as a combined sewer. Its upkeep or maintenance work is simple due to its enormous size. 

7.5 Laying of sewers 

The trench is excavated between two manholes and the bedding layer of concrete is provided for soft soil while in case of rocky or hard soil, bedding is not required. The sewers are laid down between two manholes. Sewers are generally laid starting from their outfall ends towards starting ends. The various steps on lying of sewers are as follows:

• First locate the positions of man hole on the ground along longitudinal section of sewer line. It is common practice that, one sewer line is lying between manholes.
• Mark the centre line of sewer line and the center line pegs of the sewer are driven at a distance every 7.5 m or 15 m.
• The center line of the sewer line should be properly maintained by providing an offset line usually market at a distance of 2 m to 3 m.
• The trench is excavated between two manholes and the bedding layer of concrete is provided for soft soil. In case of rocky or hard soil no bedding provided. The sewers are then laid down between two manholes.
• After completing the lying of sewer pipe between two manholes, further excavations are mad for lying of sewer pipe between the next consecutive manholes. The process is consecutive manholes. The process continued from the outfall end of the sewer towards the starting end till entire sewer lay out.
• The refilling/backfilling of trenches is started after the sewer line is properly laid in position, aligned, jointed and test for leakage on alignment.