Sanitary Engineering

Sanitary Engineering is the branch of public health engineering that deals with the preservation and maintenance of the health of the individual and the community, by preventing communicable diseases.

It consists of scientific and methodical collection, conveyance, treatment, and disposal of waste matter so that public health can be protected from offensive and injurious substances.

Sanitation is the prevention of the sporadic outbreak of diseases and can be achieved by either controlling or eliminating such environmental factors that contribute in some form or other to the transmission of diseases.

If the waste matter, created and given out by human and animal life, and also by industries, etc, is allowed to accumulate, it will get decompose and will contaminate or pollute air, water, and food. Hence sanitary disposal of waste, either in solid form or in liquid form, is essential.

Sanitary sewage includes excreta (i.e. waste matter eliminated from the body), domestic sewage ( i.e. used water from home or community which includes toilet, bath, laundry, lavatory, and kitchen-sink wastes), and industrial wastes.

The improper disposal of human excreta and sewage is the major factor threatening the health and comfort of individuals where satisfactory sewerage systems are not available.

Also Read: Theory of Structure You Must Know In 2023

Important Terms and Definitions

1. Refuse: refuse is a general term used to indicate what is rejected or left out as worthless. It may be in liquid, semi-solid, or solid form, and may be divided into six categories: (i) garbage (ii) rubbish  (iii) sullage  (iv) sewage (v)subsoil water, and (vi) stormwater.
2. Garbage: garbage indicates dry refuse. It includes waste paper decayed fruits and vegetables, glass, and sweeping from streets, markets, and other public places. Thus, garbage contains large amounts of organic and putrifying matter.
3. Rubbish: rubbish indicates sundry solid wastes from offices, residences, and other buildings. It also includes waste building materials, Brocken furniture, paper, rags, etc. Generally, rubbish is dry and is of combustible nature.
4. Sullage: sullage is a term used to indicate the wastewater from bathrooms, kitchens, washing places, wash basins, etc. It does not create a foul smell since the organic matter in it is either absent or negligible.
5. Sewage:  sewage indicates the liquid waste from the community. It includes sullage, discharge from lavatories, urinals, stables industrial waste, and also the ground surface and stormwater that may be admitted into the sewer. It is extremely putrescible; its decomposition produces large quantities of malodorous gases and it may contain numerous pathogenic or disease-producing bacteria.
6. Sub-soil water: It is the groundwater that finds its entry into sewers through leaks.
7. Stormwater: It indicates the rainwater of the locality.
8. Sanitary sewage: Sanitary or domestic sewage indicates sewage mainly derived from residential buildings and industrial establishments. It is extremely foul in nature. Sanitary sewage may be classified as (i) domestic sewage and (ii) industrial sewage
9. Domestic sewage: It is the sewage obtained from the lavatory basins, urinals, and water closets of residential buildings, office buildings, theatres, and other institutions. Since it contains  human excreta and urine, it is extremely foul in nature
10. Industrial sewage: It is wastewater obtained from industrial and commercial establishments. It may contain objectionable organic compounds that may not be amenable to conventional treatment processes.
11. Night soil: It is a term used to indicate human and animal excreta.
12. Sewer: It is an underground conduit or drain through which sewage is carried to a point of discharge or disposal. Separate sewers are those that carry household and industrial wastes only. Stormwater drains are those which carry rainwater from the roofs and street surface. Combined sewers are those which carry both sewage and stormwater. A House sewer (or drain) is a pipe carrying away the sewage from a building to a street sewer. The main sewer or trunk sewer is a sewer that receives sewage from many tributary branches and sewers, serving as an outlet for a large territory.  A branch sewer or sub-main sewer is a sewer that receives sewage from a relatively small area, usually, a few laterals, and discharges into a main sewer. A lateral sewer is a sewer that collects sewage directly from the houses. It indicates the first stage of sewage collection. A depressed sewer is a section of the sewer constructed lower than the adjacent section to pass beneath an obstacle or obstruction. It runs fully under the force of gravity and at great than atmospheric pressure, the sewage entering and leaving atmospheric pressure, sewage entering and leaving atmospheric pressure. Intercepting sewer is a sewer laid transversely to the general sewer system to intercept the dry-weather flow of sewage and such additional surface and stormwater and may be desirable. An intercepting sewer is usually a large sewer, flowing parallel to a natural drainage channel, into which a number of main or outfall sewers discharge. An Outfall sewer is a sewer that receives sewage from the collecting system and conducts it to a point of final discharge or to a disposal plant. A relief sewer or overflow sewer is a sewer built to carry the flow in excess of the capacity of an existing sewer.
13. Sewerage: The term sewerage is a noun, that means the structures, devices, equipment, and appurtenances intended for the collection, transportation, and pumping of sewage and liquid wastes, but excluding works for the treatment of sewage. The term sewage also includes the science of collecting and carrying sewage by water carriage system through sewers.
14. Wastewater: The term wastewater is now increasingly used in place of sewage. Wastewater includes both organic and mineral matter carried through liquid media. While the organic portion of the wastewater is putrescible, undergoing biological decomposition, the mineral matter may combine with water to form dissolved solids, create unsightly sludge deposits, and contribute to the hardness of the water in the effluent.

Wastewater Treatment Systems

Wastewater treatment or sewage treatment is a broad term that applies to any process, operation, or combination of processes and operations, that can reduce the objectionable properties of water-carried waste and render it less dangerous and repulsive to man.

Thus, wastewater should be treated before its ultimate disposal in order to:

1. reduce the spread of infectious diseases caused by the pathogenic organism in the sewage and
2. prevent the pollution of surface and groundwater. Wastewater treatment is a combination of physical, chemical, and biological processes.

Methods of treatment in which the application of physical forces predominate are known as unit operation, while the methods of treatment in which chemical or biological activity is involved are known as unit processes. These are three types of unit operations and processes.

• physical unit operation
• Chemical unit processes
• Biological unit processes

Physical unit operations are those in which the application of physical forces predominates. They consist of screening, mixing, flocculation, sedimentation, flotation, etc. Chemical unit processes are those in which the removal of contaminants is brought about by chemical activity.

Common examples of chemical unit processes are chemical precipitation, gas transfer, adsorption, ion exchange, electrodialysis, etc. Biological unit processes are those in which the removal of contaminants is brought about by biological activity. Common examples of such processes are the activated sludge process, trickling filtration, sludge digestion, etc.

          Conventional treatment is the term used to describe the standard method of sewage treatment in a temperature climate. It comprises the following stages of treatment:

1. Preliminary processes/ treatment
2. Primary treatment
3. Secondary (or biological) treatment

The preliminary processes consist of removing floating materials as well as a heavy settleable inorganic solid; these also include pumping and flow measurement.

The primary treatment is aimed at the sedimentation of organic suspended solids.

In secondary treatment, biological processes are used to remove most of the organic matter.

Sometimes, the wastewater is also subjected to tertiary treatment (also known as advanced treatment) with the aim of removing the pollutants not removed in primary and secondary treatment.

These pollutants may include soluble inorganic compounds (such as phosphorus and nitrogen ) remaining organic material, pathogens, colloidal solids, soluble minerals, and other toxic substances.

In addition to the various stages of treatment of wastewater mentioned above, the processing and disposal of sludge obtained from the above treatment method is of equal importance. Disposal of the accumulated waste sludge is a major economic factor since the cost of its processing is about one-third of that involved in the treatment plants.

Also Read: Engineering Disciplines

Wastewater Management

There are three constituents and interrelated aspects of wastewater management:

1. Collection
2. Treatment
3. Disposal/ Reuse

Collection of domestic and industrial wastewater is best achieved by a fully developed sewerage or water carriage system.

The planning and design of wastewater collection facilities involve determining wastewater flow rates; the hydraulic design of sewers’ large conduits and junction and diversion structures; the selection of sewer appurtenances and pumping stations.

Most sewers are laid under roads to avoid interference with private property when connections and repairs have to be made.

Sewers are commonly laid in straight lines, manholes being provided at all changes of direction, gradient, and diameter.

With modern developments in other fields, many recent changes have been made in wastewater collection – notable amongst them being the photogrammetric and computer techniques to the design of sewers, the improvement of construction materials, and the application of computers in the control of storm sewers.

Treatment of wastewater is essential in order to reduce the spread of infectious diseases caused by the pathogenic organisms in the sewage and to prevent the pollution of surface and groundwater.

The wastewater treatment is carried out by a combination of physical unit operation and chemical and biological unit processes before the end products can be safely disposed of.

The form of treatment normally adopted consists of providing an environment in which natural processes of decay can be intensified and controlled so as to take place in the least objectionable manner.

After the treatment, the problems of disposal arise. The most important recent trend in the field of disposal is the establishment of increasingly stringent requirements to protect the environment.

Currently used effluent disposal methods are;

• dilution in streams and rivers,
• land application, and
• re-use in aquaculture and crop irrigation.

The most striking example of agricultural re-use of domestic wastes is in China in which over 90% of national night soil production is after treatment applied to the land and it represents about one-third of the nutrients actually used by the crops.

The sludge and concentrated pollutants are disposed of in lagoons, sludge drying beds, or sanitary landfills, for small treatment plants, and by vacuum, filtration followed by heat drying and incineration in large treatment plants.

Performance criteria for wastewater management system

Ideal wastewater management, consisting of collection, treatment, and disposal/reuse, should satisfy the following criteria.

1. Health criteria. The system should be so designed that pathogenic organisms do not spread either by direct contact with the night soil or sewage or indirectly via soil, water, or food. The treatment method chosen should be such that a high degree of pathogen destruction is achieved and other harmful chemical pollutants are removed or neutralized to the largest extent possible.
2. Reuse criteria. The treatment processes used should be such that the treatment is safe to be reused for aquaculture, agriculture, industrial cooling, and groundwater recharge
3. Ecological criteria. If the treated effluent is not re-used, but is disposed of in the receiving waster, its characteristics should be such that the aquatic environment is protected and the self-purification capacity of the recipient water is not exceeded. For this, a high degree of removal of organic matter (BOD) is required in order to prevent pollution of the receiving watercourse by oxygen depletion 
4. Nuisance criteria. The treatment system should be so designed that either it does not release objectionable odor or the degree of odor released must be below the nuisance thresh hold. No part of the system should be aesthetically offensive.
5. Cultural criteria. The methods chosen for collection, treatment, disposal, and reuse should be such that they match with local habits, social customs, and religious practices of the people of the area.
6. Operational criteria: The system should be such that it may operate with minimum difficulties, and a greater degree of a spill is not required. It should be such that operation is possible with locally available staff, with minimum possible training.
7. Cost criteria: The system should have minimum possible capital and running costs, which can be easily paid by the community. The return of the reuse of the end products is an important factor. If the end products are not reused, their disposal should be achieved with the minimum possible cost.

Systems of Waste and Sewage Disposal

Wastes or refuse are of two types: solid waste and liquid waste. Night soil consists of human or animal excrement and areas, originating at private water- closets, urinals, and stables.

Garbage dictates dry refuse from a town, and includes sweepings from houses, streets, markets, and other public places, wastepaper, leaves, grass, parings from vegetables, decaying fruit, etc. constitute garbage.

Sullage indicates wastewater from bathrooms, kitchens, washing places, wash basins, etc sewage indicates the liquid waste from the community.

It includes sullage, discharge from latrines, urinals, stable, and industrial waste. It is extremely putrescible; its decomposition produces large quantities of malodorous gases and may contain numerous pathogenic or disease-producing bacteria.

The refuse, consisting of all the above items, formed in any sanitary system should be rapidly and safely carried to its disposal site so as to maintain a clean environment. Excreta and sewage are satisfactorily disposed of if the following conditions are satisfied.

1. The waste does not pollute the ground surface, nor is it exposed to the atmosphere when inadequately treated
2. It should also not be accessible to children or house hoi pets
3. It does not pollute or contaminate the drinking water supply
4. It does not be a too dour nuisance.  
5. It does not give unsightly appearances
6. It does not give rise to mosquito nuisances. It should also not be accessible to insects and rodents.
7. It does not pollute or contaminate the bathing beach or streams used for domestic water supply.    

Depending upon the type of waste, two systems may be employed for its collection, conveyance, and disposal:

1. Conservancy system,
2. Water carriage system.

Also Read: Engineer | Definition and History You Should Know Right Now

Conservancy System

This is an old system in which various types, such as nigh soil, garbage, etc are collected separately from vessels or deposited in pools or pits and then removed periodically at least once in 24 hours.

On account of this method of handling independently the different types of refuse from a place the term conservancy system. The following are the methods of collection of various types of waste in the system.

1. Night soil. Night soil or human excreta in latrines, privies or cesspools, etc. is collected separately in pails and carried on heads of sweepers to a central place from where it is transported in bullock carts or motor vans to a place away from the town for its final disposal. Normally, it is buried in the ground, in trenches, to give excellent manure in one or two years.
2. Garbage. Garbage is collected separately, in dust bins and conveyer on handcarts or motor vans once or twice a day. It may consist of waste matter of both non-combustible as well as combustible types. The two are therefore sorted out.  Garbage disposal methods include the open dump, hog feeding incineration, dumping into the sanitary fill, fermentation, or biological digestion. Incineration, If properly controlled, Is satisfactory for burning combustible refuse.
3. Sullage and stormwater.    Sullage and stormwater are collected and conveyed separately in closed or open gutters. The liquid and semi-liquid mass of filth frequently overflows the  receptacle in privies  which carry it to drain  from the privies, which carry it to drains carrying sullage and storm water along the public lanes or streets        

There was a time when the conservancy system was favored and the agriculturists because of a fear of contamination of the soil by leakage from the sewers and the possible pollution of the water receiving the sewage, and possible nuisance where sewage was distributed on land.

However, the conservancy system in India is still in vogue in all the villages and small towns. Only a few have a water carriage system.

Also Read: 16 Different Types of Concrete You Should Know Right Now

The disadvantage of the conservancy system:

The conservation system has the following disadvantage:

1. Hygiene and sanitary: The conservancy system is highly unhygienic and causes unsanitary conditions since the excreta starts decomposing within a few hours of its production. Even if it is assumed that cleaning will take place twice a day, the excreta remaining in the privies will emit a bad smell and will give rise to fly nuisance
2. Transportation aspect: transportation of nigh soil takes place in open carts through streets and other crowded localities  This is highly undesirable
3. Labor aspect: The working of the system depends entirely on the mercy of labor (sweepers). If they go on strike even for one day for any reason whatsoever, the privies can not be used because of foul smell. The whole locality will smell very badly  
4. Building design aspect:  The lavatories or proves are to be located outside the houses and slightly away from the main building. The compact design is therefore not possible
5. Condition of drains: Insanitation may be there due to the carriage of sullage through open drains laid in the streets
6. Human aspect: In the present day world, when a man has progressed much, it is highly humiliating to ask a human being to transport night soil, in pails on their heads.
7. Risk of the epidemic: Due to improper or careless disposal of night soil, there are more chances of an outbreak of epidemic
8. Pollution problem: The liquid wastes from lavatories etc, during the washing, may soak in the ground, thus contaminating the soil. If groundwater is at a shallow depth, it may also be polluted due to the percolation of wastewater.   
9. Cost consideration: Through the system is quite cheap in the beginning, its maintenance and establishment costs (i.e. recurring expenditure) are very high
10. Disposal land requirement: The system requires considerable land for the disposal of sewage.

Also Read: Cement | Types, Composition, And All You Need to Know

Water Carriage System

In this system, the collection, conveyance, and disposal of various types of waste are carried out with the help of water. Thus water is used as a medium to convey the waste from its point of production to the point of its treatment or final disposal.

A sufficient quantity of water is required to be mixed with the wastes so that the dilution ratio is so great that the mixture may flow just like water.

In this system, specially designed latrines, called water closets (W.C.) are used which are flushed with 5 to 10 liters of water after use by every person. The human excreta is thus flushed away and led to suitable designed and maintained sewers.

The wastes from ketches, baths, washbasins, etc. are also led to the servers. The sewers are the underground closed pipes that are laid on suitable

Longitudinal gradient so that flow takes under gravity and proper flow velocity are maintained to keep the sewer clean. The sewers lead the sewerage so collected, to a suitable site where it is treated suitably and then disposed of by irrigation or by dilution, it should be noted that the garbage is collected separately and conveyed in the same manner as is done in the case of conservancy system. If garbage is permitted in the sewers, it may be clogged.

The system requires a large initial cost of installation and it requires a large quantity of water also to create efficient flow conditions. if the financial condition of people is poor, it may be difficult to adopt this system.

However, this is the most efficient and hygienic system of sewage disposal and may be adopted in stages if sufficient funds are not available in the beginning.

Also Read: Water Supply Design | Water Sources and Storage Tanks

Advantages of water carriage system:

The water carriage system is the most modern system of drainage, and has the following advantages:

1. Hygiene and sanitary aspect: The system is very hygienic since the night soil and other wastewater are conveyed through closed conduits which are not directly exposed to the atmosphere. There is no bad smell because of continuous flow.
2. Epidemic aspect: There are no chances of an outbreak or epidemic because flies and other insects do not have direct access to the sewage
3. Pollution aspect: The liquid waste etc is directly conveyed through the sewers, and therefore there are no changes in the wastewater being soaked in the ground thus contaminating the soil. The wastewater does not percolate down to join the groundwater. There is no chance of pollution of water of wells in individual houses if any.
4. Compactness in design: Since the latrines are flushed after every use, excreta do not remain and there are no foul smells. The latrines can therefore be attached to the living and bedrooms. This permits a compact design. The lavatories can be accommodated in any part of the house.
5. Labor aspect: The labor required for the operation and maintenance is extremely small. In fact, the functioning of the system is practically automatic, except for the operation of certain pumps, etc. Where there is no labor problem. In individual houses, the latrines/ lavatories can be conveniently cleaned by occupants themselves.
6. Treatment aspect: The system permits the use of modern methods of treatment of the sewage collected through the sewers. The treated wastewater and sewage can be safely disposed of without any risk
7. Land disposal requirements: Because of treatment facilities the land required for the disposal of the treated wastewater is very much smaller than that required for the conservancy system
8. Cost consideration: Through the initial cost of installation of the system are very high, the running costs are very small since manual labor is very much reduced

Comparison and Choice of the Two Systems

The water carriage system is the most modern and hygienic system of sewage disposal and should be invariably adopted wherever sufficient funds are available. Table 1 gives a comparison between the two systems.

Trending

Walls: Load Bearing Wall and Non Load Bearing Wall

Classification of Water Carriage System

The water carriage system can be divided into the following types:

• Separate system
• Combined system
• Partially separate system

      The above three types are commonly referred to as the three systems of sewage.

1. Separate system

The separate system provided two separate systems of sewers – the one intended for the conveyance of foul sewage only, such as faucal matter, domestic wastewater, the washing, and draining of places such as slaughterhouses, laundries, stables, and the wastewater derived from the manufacturing processes; and the other for the rainwater, including the surface washing from certain streets, overflow from public baths and foundations, etc.

The sewage from the flow from the first system of sewers can be the second system of sewers can be discharged directly to natural streams etc without any treatment.

Table 1: Comparison between the conservancy and water carriage system.

Advantages

The separate system has the following advantages:

1. The cost of installation is low. Stormwater can be disposed of through the open channels along the open along the load sides. Old sewers may also be suitably converted to carry rainwater. Thus, the actual sewers carrying foul sewage will be of smaller size.
2. The load on the treatment unit will be lowered since only the foul sewage carried by the separate sewer need to be treated.
3. If there is the necessity of lifting the sewage mechanically, the system will prove to be economical both from the point of view of capital costs as well  as from the point of view of running costs
4. The sewage in the separate system will be of more uniform character, and so will lend itself more easily to purification.
5. There is no necessity of providing tanks, for use in dry weather, because the flow in a sewer of the smaller section is much more efficient.
6. The sewage of smaller sections can be easily ventilated than those of larger section
7. The night flow will be comparatively small this may facilitate operations at the outfall works.
8. Rainwater can be discharged into streams or rivers without any treatment.

Also Read: Structural Engineer | All You Need To Know

Disadvantages

1. Since the sewers are of small size, it isn’t easy to clean them.
2. They are likely to get choked.
3. Two sets of sewers may ultimately prove to be costly.
4. There is a likely hood of connections beings wrongly made through the confusion of the system.
5. Strom water sewer or drains comes in use only during the rainy season. During another part of the year, these may serve as dumping places for garbage and may get choked.
6. Because of lesser air contact in small sewers, foul smell may be due to the sewage gas formed.

2. Combined system   

The combined system provides only one sewer to carry both foul sewage as well as rainwater. The sewage and rainwater are carried to the sewage treatment plant, before their final disposal.

The combined system is advocated on the ground that the street surface is the sewage itself, and should therefore be suitably treated before being allowed to enter the natural stream.

Advantages

1. The system required only one set of sewers. Hence the maintenance costs are reduced.
2. The sewers are of larger size, and therefore the chances of their choking are rare; it is easy to clean them.
3. The strength of the sewage is reduced by dilution.
4. The is more air in the larger sewers than in smaller ones of the separate system. Hence the sewer gas that may be formed gets deluded. Thus the chances of foul smell are reduced.

Disadvantages

1. The cost of construction is very high because of the large dimensions of the sewers to be constructed at sufficient depth to receive the sewage from the basement.
2. Because  of the large size of sewers, their handling and transportation are difficult
3. Due to the inclusion of stormwater, the load on the treatment plant increases.
4. The system is uneconomical in circumstances when pumping is required for the lifting of sewage.
5. During heavy rains, the sewers may overflow, and may thus create unhygienic conditions and cause pollution problems.
6. Stormwater is unnecessarily polluted.
7. The large sewers get easily silted if not properly designed. They may become foul in dry weather, when rainwater, is not available.
8. Large sewers are more difficult to be ventilated than smaller ones.

Also Read: Types of Heavy Construction Equipment You Should Know

3. Partially combined system

In this system, only one set of underground sewers is laid. These sewers admit the foul sewage as well as the early washings by rains.

As soon as the quantity of stormwater exceeds a certain limit, the stormwater overflows and is thus collected and covered in open drains to the natural streams. The foul sewage, however, continues to flow in the sewers.

Advantage

1. The sewers are of reasonable size. Their cleaning is therefore not very difficult.
2. It combines the advantage of both separate as well as integrated systems.
3. The stormwater permitted in the sewers eliminates its chances of choking. The tailors are thoroughly cleaned during the rainy season.
4. The problem of disposing of stormwater from homes is simplified.

 Disadvantages

1. During dry weather, when there is no rainwater the velocity of flow will be low. Thus self-cleansing velocity may not be achieved.
2.  The stormwater increases the load on treatment units.
3. The stormwater also increases the cost of pumping.

Factors governing choice of a separate system.

The separate system is adopted under the following conditions:

1. Financial aspect:  If sufficient funds are not available initially, sewers may be constructed to carry only domestic sewage, and the rainwater may be covered thro’ the open drains. These drains can be converted into regular sewers when sufficient funds are available.
2. Flat topography:  If the country is flat, the sewers must be laid at a depth to achieve a reasonable gradient. In such circumstances, separate sewers are more economical. A combined sewer of a bigger size, applied at a significant depth will be costlier.
3. Rainfall pattern:  if the rainfall is there for a shorter duration and does not occur throughout the year. It is more economical to adopt a separate system.
4. Outlet conditions: A separate system is best suited if a river or natural stream is nearby. The stormwater can be directly conveyed to the stream. At the same time, the foul sewage can be led to the treatment plant.
5. Pumping aspects: the separate system is best suited under the conditions when the sewage has to be lifted up by pumping. The  separate sewers  for the stormwater will reduce the load on the pumps
6. Steep topography: If the ground has steep slopes, it is easier to convert stormwater through open drains, to natural streams.
7. Subsoil conditions:  If the subsoil is hard, it is difficult and costlier to lay a combined sewer of larger size.
8. Development pattern: If the sewers are laid before the area is developed, it is preferable to adopt a separate system

Also Read: Construction Estimating: Types, Opportunities, The Estimator, and More

Factors governing the choice of the combined system

A combined system is adopted under the following conditions:

1. Space considerations: the combined system is preferred when space available for laying the sewer is restricted
2. Integrated development: If the sewers are laid along with the overall development of the area, a combined system is preferred.
3. Even rainfall pattern: a combined system is preferred if the rainfall is evenly distributed throughout the year and when the rain during the monsoon season is not that intensive.
4. Conversion of existing stormwater drains: The combined system is preferred if an existing stormwater drain is being converted into a combined sewer. This is possible only if the quantity of sewage is small.   
5. Pumping requirement: If the ground slopes are such that it is necessary to lift both the sewage as well as the stormwater, it is preferable to use the combined system.

Choice of the system.

The factors governing the choice of any system are so vast and varied that no generalization can be done regarding the final choice. The condition varies from place to place.

If the availability of funds is the main factor, then one may conclude that a separate system may be adopted if sufficient funds are not available in the beginning.

In that case, the sewer may be designed to carry the foul sewage and rainwater may flow through the open drains along the roads and streets. This suggestion may be more appropriate for small cities.

For large metropolitan cities, however, a comminuted system is highly desirable. It is possible to design combined sewers such that reasonable velocities are maintained in them throughout the year.

Alternatively, a partially separate system may be adopted for these big metropolitan cities.

Short Note on Sanitary Engineering:

What is Sanitary Engineering?

Sanitary Engineering is the branch of public health engineering that deals with preserving and maintaining the health of the individual and the individual and community by preventing infectious diseases.

What are the important terms and definitions used in Sanitary Engineering?

1. Refuse: refuse is a general term used to indicate what is rejected or left out as worthless. It may be in liquid, semi-solid, or solid form, and may be divided into six categories: (i) garbage (ii) rubbish  (iii) sullage  (iv) sewage (v)subsoil water, and (vi) stormwater.
2. Garbage: garbage indicates dry refuse. It includes waste paper decayed fruits and other public places. Thus, garbage contains large amounts of organic and purifying matter.
3. Rubbish: rubbish indicates sundry solid wastes from offices, residences, and other buildings it also includes waste building materials, Brocken furniture, paper, rags, etc. Generally, rubbish is dry and is of combustible nature
4. Sullage: sullage is a term used to indicate the wastewater from bathrooms, kickers, washing places and wash basins, etc. It does not create a bad smell since the organic matter in it is either absent or is of negligible amount
5. Sewage:  sewage indicates the liquid waste from the community. It includes sullage, discharge from latrines, urinals, stables industrial waste, and also the ground surface and stormwater that may be admitted into the sewer. Its decomposition produces large quantities of malodorous gases and may contain numerous pathogenic or disease-producing bacteria.
6. Sub-soil water: It is the groundwater that finds its entry into sewers through leaks.
7. Stormwater: It indicates the rainwater of the locality.
8. Sanitary sewage: sanitary sewage or domestic sewage indicates sewage mainly derived from residential buildings and industrial establishments. It is extremely foul in nature sanitary sewage may be classified as (i) domestic sewage and (ii) industrial sewage
9. Domestic sewage: It is the sewage obtained from the lavatory basins, urinals, and water closets of residential buildings office buildings, theatres, and other institutions since it contains  human excreta and urine, it is extremely foul in nature
10. Industrial sewage: It is water obtained from industrial and commercial establishments It may contain objectionable organic compounds that may not be amenable to conventional treatment processes.
11. Night soil: It is a term used to indicate the human and animal excreta
12. Sewer: It is an underground conduit or drain through which sewage is carried to a point of discharge or disposal.

What are the three constituents and interrelated aspects of wastewater management?

There are three constituents and interrelated aspects of wastewater management:

1. Collection
2. Treatment
3. Disposal / Reuse

What are the disadvantages of the conservancy system?

The conservation system has the following disadvantage:

1. Hygiene and sanitary: The conservancy system is highly unhygienic and causes unsanitary conditions since the excreta starts decomposing within a few hours of its production. Even if it is assumed that cleaning will take place twice a day, the excreta remaining in the privies will emit a bad smell and will give rise to fly nuisance
2. Transportation aspect: transportation of nigh soil takes place in open carts through streets and other crowded localities  This is highly undesirable
3. Labor aspect: The working of the system depends entirely on the mercy of labor (sweepers). If they go on strike even for one day for any reason whatsoever, the privies can not be used because of foul smell. The whole locality will smell very badly  
4. Building design aspect:  The lavatories or proves are to be located outside the houses and slightly away from the main building. The compact design is therefore not possible
5. Condition of drains: Insanitation may be there due to the carriage of sullage through open drains laid in the streets
6. Human aspect: In the present day world, when a man has progressed much, it is highly humiliating to ask a human being to transport night soil, in pails on their heads.
7. Risk of the epidemic: Due to improper or careless disposal of night soil, there are more chances of an outbreak of epidemic
8. Pollution problem: The liquid wastes from lavatories etc, during the washing, may soak in the ground, thus contaminating the soil. If groundwater is at a shallow depth, it may also be polluted due to the percolation of wastewater.   
9. Cost consideration: Through the system is quite cheap in the beginning, its maintenance and establishment costs (i.e. recurring expenditure) are very high
10. Disposal land requirement: The system requires considerable land for the disposal of sewage.

What are the factors governing the choice of a separate system?

The separate system is adopted under the following conditions:

1. Financial aspect:  If sufficient funds are not available initially, sewers may be constructed to carry only domestic sewage, and the rainwater may be covered thro’ the open drains. These drains can be converted into regular sewers when sufficient funds are available.
2. Flat topography:  If the country is flat, the sewers must be laid at a depth to achieve a reasonable gradient. In such circumstances, separate sewers are more economical. A combined sewer of a bigger size, applied at a significant depth will be costlier.
3. Rainfall pattern:  if the rainfall is there for a shorter duration and does not occur throughout the year. It is more economical to adopt a separate system.
4. Outlet conditions: A separate system is best suited if a river or natural stream is nearby. The stormwater can be directly conveyed to the stream. At the same time, the foul sewage can be led to the treatment plant.
5. Pumping aspects: the separate system is best suited under the conditions when the sewage has to be lifted up by pumping. The  separate sewers  for the stormwater will reduce the load on the pumps
6. Steep topography: If the ground has steep slopes, it is easier to convert stormwater through open drains, to natural streams.
7. Subsoil conditions:  If the subsoil is hard, it is difficult and costlier to lay a combined sewer of larger size.
8. Development pattern: If the sewers are laid before the area is developed, it is preferable to adopt a separate system

We hope this article helped you learn more about Sanitary Engineering. You may also want to learn Water Supply Design | Water Sources and Storage Tanks, Engineer | Definition, History, Walls: Load Bearing Wall and Non-Load Bearing Wall, and Types of Heavy Construction Equipment You Should Know.

If you liked this article, please Join WebsiteForEngineers on Telegram, and you can also find us on Pinterest, Twitter, and Facebook.

Popular On Website for Engineers Right Now!