Sanitary Engineering

               Introduction to Sanitary Engineering

1.      What is Sanitary Engineering?

-          Explain Sanitary Engineering and mention its importance. (Dec 2006 5m)

Ans. Sanitary engineering is defined as the branch of public health engineering which deals with the removal and disposal of the sewage (liquid waste) without causing nuisance to the society by preventing communicable diseases.

Following are the importance of Sanitary Engineering:

·         To protect water supply from pollution.

·         To collect and dispose-off the waste of the city.

·         To remove rain water from city/town.

·         To prevent the pollution of water resources.

·         To maintain healthy environment.

·         To prevent the occurrence of disease. Ex:  Malaria, typhoid, etc.

2.      Explain the Principles of sanitation.

Ans. The following are the Principles of sanitation:

a)      Collection: The waste matters like garbage and sewage should be removed as early as possible after its formation.

b)      Conveyance: The collected waste is removed by providing underground conduits up to the disposal works so that it may not create nuisance to the public.

c)      Building Orientation: It should provide fresh air and sufficient light in all the rooms of a building and buildings should be made damp-proof.

d)     Water requirements: Water supply should be regular and sufficient so that the flushing of lavatories may be done properly.

e)      Disposal: The sewage must be disposed-off in a satisfactory manner after making it harmless.

3.      What is refuse? Explain its various categories. (May 2010 5m)

-          List the components of refuse.

-          What is meant by garbage?

Ans. The term refuse is used to indicate what is rejected or left over as waste. It is divided into five categories:

a)      Garbage: The garbage includes all sorts of bio-degradable organic wastes obtained from kitchens, hotels, restaurants, etc. The waste articles of food, vegetables, fruits, peeling waste meat, etc. is called garbage. It may be solid or semi-solid.

b)      Sullage:  The term is used to indicate the waste water from bathrooms, kitchens, etc. It is merely waste water and does not create bad smell.

c)      Sewage: The term sewage is used to indicate the liquid waste from the community and it includes sullage, discharge from latrines, urinals, stables, industrial waste and storm water, etc.

d)     Storm water: The term is used to indicate rain water.

e)      Sub-soil water: This indicates the ground water which finds its entry into sewers through leaks.

4.      List out the aims and objectives of sewage disposal.

-          What are the objects of sewage disposal?

Ans. The following are the aims and objectives of sewage disposal:

1)      Proper disposal of human excreta to a safe place, before it decomposes.

2)      To drain out all types of wastes from the locality so that mosquitoes, flies, bacteria, etc. may not breed.

3)      Final disposal of sewage on land or in nearby water courses after some treatment so that the receiving land or water is not polluted.

4)      As far as possible the fertilizing elements of sewage may be used for growing crops through sewage forming and get the benefit of income, in addition to disposal of sewage.

5)      If the sewage is disposed-off on land, it should be treated to the extent that it does not affect the subsoil.

5.      Explain the methods of sewage collection.

Ans. The collection works are meant for collecting all types of waste products. The solid and liquid wastes are collected and conveyed to suitable spots for treatment and disposal. The following are the two types of sewage collection methods:

a.      Conservancy System:

·         This is also called as dry system. In this system, different types of wastes, wet or dry, foul or non-foul are collected manually and transported in vehicles to the points of ultimate disposal. 

·         At the dumping ground, the garbage is separated in to two categories, such as flammable and inflammable.

·         The waste water from kitchens, bathrooms, etc., are carried separately in open or closed drain up to the disposal.

·         This system is out of date in modern cities. It is, however, still adopted in small towns, villages, etc.

b.      Water Carriage System:

·         In this system, the wastes from water closets get mixed with sufficient quantity of water by flushing and this water is used to transport the wastes for treatment and disposal.

·         The sewage formed in this system will consist of 99.9% of water and remaining 0.1% of solid matters.

·         This method is very advantageous and is universally employed in practice.

6.      Discuss the merits and demerits of conservancy and water carriage systems.

-          List down the advantages and disadvantages of methods of sewage collection.

Ans. The following are the advantages and disadvantages of Conservancy system.

Advantages:

a)      It is cheaper in initial cost.

b)      The storm water can pass in open drains and conservancy latrines are economical.

c)      The quantity of sewage to be treated is low.

d)     There will not be silting or deposition in sewers

e)      If water level at outfalls increases in case of floods then the pumping of sewage will not be costly.

Disadvantages:

a)      In crowded lanes it is very difficult to lay two different sewers.

b)      Construction of roadside drains, cause great inconvenience to the traffic.

c)      More land is required to bury human excreta.

d)     The building cannot be designed as one compact unit.

e)      There is possibility of liquid refuse reaching the subsoil surface

f)       It pollutes the underground water.

g)      It can spoil the aesthetic appearance of a city.

h)      Decomposition of sewage causes insanitary conditions which is dangerous to health.

i)        This system completely depends on manual laborers.

The following are the advantages and disadvantages of Water carriage system.

Advantages:

a)      This is a hygienic method of collection.

b)      The risk of epidemics is reduced.

c)      This system can obtain self-cleansing velocity even at less gradients.

d)     It can take more quantity of sewage.

e)      For disposal, the land area required is less.

f)       This allows the construction of latrines and bath rooms together.

g)      This occupies less space which leads to compact design.

h)      It does not depend on manual labors quite often.

i)        The sewage after proper treatment can be used for various purpose.

j)        It can be used as manure.

Disadvantages:

a)      Initial cost is very high.

b)      The maintenance cost is more.

c)      During the monsoon season, a large volume of sewage has to be treated, whereas a very small volume has to be treated during the rest of the year.

d)     In case of any break of water supply, the system is highly affected. 

7.      Give a comparison between conservancy and water carriage system. (Nov 2006 5m, Nov 2007 5m, May 2008 5m)

Ans. The comparison between conservancy and water carriage system are given below:

Sl. No.	Conservancy System	Water Carriage System
1	Very low initial cost	Costly initial cost
2	It reduces aesthetic appearance of the city	Better aesthetic appearance of the city
3	Latrines should be constructed far away from the buildings due to foul smell	Latrines remain clean and hygienic since water is used abundantly for flushing
4	Compact design of building is not possible	Buildings can be designed compact
5	Large area is required for disposal	Less area is required
6	If excreta is not removed immediately it starts giving out bad smell	Excreta is removed immediately with flush of water
7	Chances of underground water pollution is high	There is no risk of pollution of underground water

8.      Define the following

a.       Sewer: A pipe or conduit or drains which carries sewage.

b.      Sewerage: The network of collecting and conveying sewage by water carriage system through the underground sewers is known as sewerage.

c.       Rubbish: it means all the unwanted solid wastes as paper, leaves, grass, broken furniture, waste building material and debris, etc., comparatively inert in chemical action. Most of these types of wastes are discarded on a regular basis from homes, offices and commercial buildings.

d.      Dry weather flow (D.W.F): The flow of sewage during the dry season of the year is termed as dry weather flow.

e.       Wet weather flow (W.W.F): The flow of sewage during the rainy season is termed as Wet weather flow.

f.       Invert: The lowermost level or surface of a sewer is known as its invert.

g.      Drain: It is a pipe carrying sewage plus rain water. Open drains, however carrying only rainwater and sullage.

h.      Septic sewage: This indicates sewage undergoing the treatment process.

i.        Weak or Dilute sewage: This term is used for sewage containing less suspended solid matters.

j.        Trunk sewage: The sewer which receives the discharge from two or more main sewers is known as trunk sewage.

k.      Soil waste: This is the discharge from water closets, urinals, sinks, cowsheds, gullies, and other such sources.

l.        Sanitary sewer: It is a sewer which carries sanitary sewage and it avoids carry of storm sewage, surface water and ground water.

m.    Outfall sewers: The length of main or trunk sewer between the connection of the lowest branch and final point of disposal.

n.      Intercepting sewer: It is the sewer that intercepts the discharge from a number of main or outfall sewers and carries the flow to the point of treatment and disposal.

o.      Relief or overflow sewer: The sewer which carries the excess discharge from existing sewer is termed as relief sewer.

(NOTE: For more details on terminologies and its definitions refer Environmental Engineering-II by H.S. Vishwanath, Pg no. 02 to 05).

Reference:

·         Water supply and Sanitary Engineering, by Rangwala, New Delhi, India.

·         Environmental Engineering II, by B.C. Punmia, Pande, B.B. Lal. Lakshmi Publications, New Delhi, India.

·         Water supply and Sanitary Engineering, by Birde.