Principle of sanitation
Sanitary Engineering: It is the branch of public health engineering which deal with the prevention & maintenance of the health of individual & the community. Its studies methodical collection, conveyance, treatment & disposal of waste water to land or water bodies meeting the criteria of pollution load as prescribed by the national guidelines.
Major goals of sanitary engineering:
- Protect the public health: Waste water is nuisance, carries disease spreading pathogens, harmful toxic compounds, and heavy metal. Proper collection, treatment and disposal of such waste are the major objective of sanitary engineering.
- Protecting the environment: Untreated waste water when discharged directly to receiving water or land body leads to the deterioration of surface and groundwater quality and pollutes the soil.
- Reuse of treated waste water and solid: Treated waste water that is free of harmful impurities can be used for agricultural, industrial and ground water recharge. This helps in addressing growing concern water scarcity and water stress. Similarly, the treated solid particles when treated and stabilized can be used as manure or filling material.
Basic terminology
- Black water: Water from flush toilet (faeces and urine with flushwater)
- Gray Water: Washing water from kitchen, bathroom, laundry (without excreta)
- Rubbish: Dry and combustible waste from office eg: Building broken material, broken furniture, paper etc.
- Refuse: Refuse includes all rejected solid, semi solid and liquid waste.
- Garbage: It indicates dry refuse & it includes decayed fruit, grass, leaves, paper pieces, sweeping, vegetables etc.
- Sullage: It indicates the waste water from the bathroom, kitchen (human excreta not mixed)
- Night soil: Waste water mixed with human excreta.
- Infiltration: It is the water which inters the sewers from ground water through Leaks from loose joints or cracks.
- Sewer: Sewers are underground pipes or conduits which carry sewage.
- Trunk or main sewer: Sewer receiving sewage from branch or sub mains and serves as an outlet for a large area.
- Branch sewer: Sewer receiving sewage from a no of lateral sewers and delivering to main sewer.
- Lateral sewer: Sewer receiving sewage from house though house sewer and delivering it to a branch or sub main sewer.
- Sewage/waste water: The Liquid waste from a community is called sewage. Sewage is classified into domestic and non-domestic sewage. The non domestic sewage is classified into industrial, commercial, institutional and any other sewage that is not domestic.
- Sewerage: The entire system used for collection, treatment and disposal of Liquid waste. This includes pipes, manholes, and all structures used for the above mentioned purposes.
- Manholes: A supporting structure for connecting sewers.
- Outfall: The last point of sewer network.
Historical development of waste water and solid waste management
The history of sanitation records back to the 26th century BC, in Iraq. The well documented sanitation practices are after the outbreak of cholera in 1848, 1849, 1852, 1853, and 1854. With understanding of water borne disease by poor sanitation, the sector started receiving attention. In England, Chadwick, known as father of sanitation, promoted house and cesspools connection to the sewers. Likewise, in 1868 experiments on the intermittent sand filter was carried out in England followed by experiment in aeration in 1882. Contact bed filtration was tried in Massachisetts in 1889. Digestion of sludge in lagoons was developed in Germany in 1891. First grit chamber was developed in 1904 in USA, disinfection by chlorination was developed in USA in 1906. The first municipal trickling filter was installed in USA in 1908.
Nepal stance on sanitary
“Nepal achieved its one of the most important goals of being declared as an Open Defecation Free (ODF) country in September 2019. The journey toward becoming an ODF free country commenced after the introduction of community led total sanitation (CLTS) and school led total sanitation (SLTS) in 2005. International year of sanitation 2008 was a breakthrough in shaping the robust national campaign of sanitation and hygiene. Then in 2011 Government of Nepal provided Sanitation and Hygiene Master Plan, a nationwide guideline, with a target to declare ODF Nepal by 2017. The declaration of ODF in 2019 is the result of combined cooperation and collaborative action of Nepal’s Government and different donor organizations.
The first sewers line in Nepal was constructed during RANA regime. In the heavily dense urban setting, Nepal has adopted water carriage system, however in rural area the practice is still conservancy system with septic tanks as treatment unit.
System of sanitation
The following are the two methods which are employed for the collection & disposal of refuse of a locality.
1) Conservancy system
This is a primitive system where refuse are collected manually & then suitably disposed off to the safe point of disposal. Conveyance is generally done by carts or trucks. The night soil is collected in pans, carried by labor in carts, truck etc & then buried into the ground & is thus converted into manure. The storm water & sullage are collected & conveyed separately by closed or open channel. They are discharged in natural rivers or stream.
Advantage:
- A primitive method with no sophisticated technology needed. It cartered the need of the time when the idea of water carriage system was not conceived.
- The system does not pollute water.
Disadvantage
- Insanitary condition: The decomposition of sewage starts about 4 to 5 hrs after its production and hence causes insanitary condition. There is direct contact between waste collection team and waste, hence the risk of disease spreading is high.
- Labor Problem: It entirely depends upon labor. if the labor goes on strike due to any reason, the public health is put into great danger.
- Land for disposal: The sewage, especially night soil require considerable land for its disposal.
- Night soil carts: It is highly undesirable to allow the night soil cart to pass through main road of the city.
- Open drains: If the storm water & sullage is carried in open drain. it create unsanitary condition.
- Pollution of water: There is a chances of liquid waste as it may soak in ground then the underground supply of water will be polluted.
- Risk of epidemic: If the sewage is not properly disposed then there is a chance of outbreak of epidemic.
2) Water Carriage system (sewerage system)
In this system, water is used as a medium to convey the sewage from the point of generation to treatment to the final point of disposal. Sewer lines are the conveyance structure.
Advantages
- The system facilitates compact unit as waste is not collected and carries in buckets and carts, as is required to be done in the conservancy system.
- The system is hygienic in nature as the sewage is transported in closed pipe i.e sewer line preventing contacts with waste water.
- Based on the availability of land, suitable type of treatment unit can be adopted.
Disadvantages:
- Large quantity of water is polluted.
- Unnecessary conveyance of waste water if the treatment system is central.
- Cost intensive and requires high skilled technology in designing and operation
Classification of water carriage system/sewerage systems
1)Separate system
In this system, storm water and sewage are conveyed separately in two different sets of conduits.
Advantages
- The size of pipes is much smaller than the combined system sewers. This gives the advantage of good hydraulics in the pipe (the pipe is Designed to have a minimum velocity to prevent sedimentation of sand)
- Separation of wastewater from storm water minimize the total quantity of sewage which has the following advantages :
- Smaller pumping stations are needed.
- Smaller and more efficient treatment plants are needed.
- Overflow of combined sewers in the storm events produces pollution to environment which is not the case in separate sewer. Only unavoidable Storm water inters the system which protects the system from the accumulation of sand in the sewers in the non-paved areas.
Disadvantages:
- Separate set of plumbing work required for collection of storm water and sewage, starting from the household unit.
- If the sewer length is very high in compare to the quantity, laying two sets of pipe can increase the total project cost.
2)Combined system
In this system, single pipe is used to carry both storm water and sewage.
Advantage:
- Unlike separate system, there is no need of two set of plumbing work.
- Suitable for regions where wet seasons is short.
- Only option in the areas where it is difficult to construct two pipelines. crowded streets.
- Cost of the overall system is less than separate system.
- Sewage is diluted.
- Self cleaning velocity is maintained most of the time. Especially in the cases where sewage quantity is low.
Disadvantages:
- Since the system carries both storm and sanitary waste, the pipe size is generally large and hence it is difficult to meet the requirement of hydraulic characteristics (such as self cleaning velocity) when only sewage is considered.
- In dry season, sedimentation of organic matter may lead to anaerobic digestion expelling hydrogen sulphide and other gases. These gases corrode the pipe material and as thus the life of pipe is decreased.
- Unnecessary pollution of rain water which could have been discharge directly to the river.
3)Partially combined system
In this system a portion of storm water is allowed to enter in the sanitary sewage carrying sewer and remaining storm sewage into another sewer. Storm water from roof, pavement and yards are allowed to enter sewer and remaining sewage is drained off from other drain.
Advantage:
- This is the most preferred system as it offers benefits of both systems.
- There is no need of separate plumbing work in each household or receiving units.
- The storm water collected from the road and public spaces can be directly discharged to the river through open drain.
- The storm water entering to the sewer helps in flushing deposited sediments that can possibly occur at the beginning part of the sewer line due to low sewage quantity.
Disadvantage:
- Self cleaning velocity may not be achieved in dry season.
- The loads on the treatment plant may increase.
- Only suitable for area with proper rainfall.
References:
- Modi, P.N. Environmental Engineering, Volume II : Waste Water Treatment, Disposal and Air Pollution Engineering. Delhi: Standard Book House.
- Garg. S.K. Environmental Engineering (Vol. II): Waste Water Engineering. Delhi: Khanna Publishers.