Sewage Disposal in Nigeria

Introduction

Environmental hazards of varying magnitude dangerously threaten human and animal lives in most urban and rural centers in Nigeria. With human/solid waste decorating street corners and public space everywhere in Nigeria, this paper teased out the institutional measures taken to confront waste management in Nigeria.
Among the characteristics of living things is excretion, which is basically the ejection of harmful waste products from the body. These waste products include sweat, urine and faeces. The last two could be termed as sewage, although sewage actually is the waste water of a community (Feachem et al, 2007). Everybody knows that the sight of sewage of a community is unbearable if proper disposal measures are not taken. In Nigeria people sometimes dispose their wastes into streams, a habit hazardous to human health.
Sewage should be treated before its disposal in order to prevent pollution of the surface and groundwater’s, and to reduce the spread of communicable diseases caused by pathogenic organisms present in sewage (Ogedengbe, 2001). The treatment of sewage is mostly a combination of physical and biological processes and sometimes a chemical process is included when the sewage is very concentrated (e.g. sewage from residential and industrial buildings) or mixed with industrial wastes. The biological process involves the action of bacteria, protozoa and algae on sewage under ideal conditions.
In a developing country like Nigeria with old cities and communities, wastewater or sewage generated are often discharged into pit latrines in rural areas while they are discharged into septic tanks, soak ways and cesspools in towns and cities. These systems are problematic as soils become saturated with pollutants and effluents with very high suspended and dissolved solids causing environmental pollution and even groundwater pollution in some cases. Environmental pollution from wastes generated by human activities has been a major challenge and problem to environmental engineers all over the world.
Types of Sewage Disposal system in Nigeria:
Domestic sewage, produced in urban residences, institutions, and businesses, is usually collected by pipes and conduits called sanitary sewers, which lead to a central discharge point. In rural residences domestic sewage is often collected in a septic tank on the property. Industrial wastes, which consist of liquids produced in manufacturing processes, are sometimes collected in sanitary sewers, but the nature of many industrial wastes may make it dangerous or difficult to do so. Often industries dispose of their own wastes. Storm sewage, which comes from rain and groundwater, is collected either in a storm sewer or, with domestic sewage and industrial wastes, in what is called a combined sewer.
Sewer pipe must be strong enough to withstand the structural stresses to which it is subjected by being buried in the ground. In addition, the pipe itself and the joints between sections of pipe must be capable of withstanding at least moderate water pressure without significant leakage of sewage into the environment. Materials used for sewer pipe include plastics, vitrified clay, cast iron and steel, corrugated iron, concrete, and asbestos cement. Although usually circular, pipes are also made egg-shaped or semi-elliptical so that suspended solids do not accumulate even at a relatively low rate of flow, about 2 ft (.6 m) per second. Sewer pipes are usually inclined downward toward the central collection point so that sewage will flow to it naturally, although pumping stations may be required.
Sewage is eventually discharged into underground or surface watercourses that naturally drain an area. In past centuries, the dilution produced by discharging sewage into large bodies of water was considered sufficient to render harmless any toxic substances contained in it. However, the volume of sewage is now so great that dilution is no longer considered an adequate safeguard.

Sewage Treatment
The biochemical processes that take place in water bodies have also been relied on to neutralize sewage. Aerobic, or oxygen-requiring, bacteria feed on the organic material in sewage, decomposing it. However, this process uses the oxygen that is dissolved in water. Often the concentration of organic waste is so great that the biochemical oxygen demand (BOD) depletes the water’s oxygen supply, killing fish and plants. In order to avoid these problems, it is now recognized that all sewage except unmixed storm sewage must be treated before it is discharged.
Sewage treatment is classified as primary, secondary, or tertiary, depending on the degree to which the effluent is purified. Primary treatment is removal of floating and suspended solids. Secondary treatment uses biological methods such as digestion. Complete, or tertiary, treatment removes all but a negligible portion of bacterial and organic matter. Industrial wastes are treated by a number of methods, depending on the specific nature of the waste. Increasingly, governments are forcing industries to process effluents either chemically or mechanically, or both ways, so that harmful substances are removed.
Domestic sewage must be treated to produce discharge water that is free of odors, suspended solids, and objectionable bacteria. (Coliform bacteria, which inhabit the lower intestines of mammals, while not pathogenic of themselves, are taken as an index of contamination of watercourses.) In rural areas, sewage can be stored in a holding tank, e.g., a septic tank; naturally occurring anaerobic bacteria can decompose the solids, which then settle to the bottom. While suitable for small systems, this method has several disadvantages. First, anaerobic decomposition produces noxious gaseous effluents, and it is fairly slow. Second, harmful bacteria may still be present in the liquid effluent.
In large urban systems, a combination of processes must be used. Decomposition can be speeded by forcing air through the mass so that aerobic bacteria can be used. This oxidation process is typically combined with filtration, either in sand or in granular activated carbon, and with several hours of aeration. The liquid can then be discharged, often after being disinfected with chlorine. The liquid may be also treated by microfiltration, reverse osmosis, and hydrogen peroxide and ultraviolet light to produce very clean water that can be reused. Another method of removing solids is to allow the liquid to stand in large tanks until the solids fall out and form sediment, but the process is slow and requires the accumulation of large volumes of liquid.
The increasing pact of reports of epidemic diseases at various states in Nigeria has become a source of worry to every right thinking citizen. A phase from the recent effort being embarked by the government to stem the trend the sporadic spread to other states, it is necessary to look in wards on the possible primary causes of the epidemic diseases with a view to fashioning workable solutions.
Without mincing words, the way sewage is managed in the country could be the reason for the dilemma being experienced in our health sector .The solid waste; waste water and also industrial accumulated waste have to be given adequate attention. It is based on this that I intend to focus on the key points for effective sewage management and control of epidemic diseases.

Sewage Disposal in Nigeria: Methods of sewage treatment in Nigeria
Every community should have a way of disposing of sewage so that people, animals and flies cannot touch it. This is called a sewage system. There are different types of sewage systems which can be described as on-site systems and sewage or effluent systems.
An on-site system is one which treats the sewage in a septic tank so that most of the sewage becomes effluent and is disposed of in an area close to the house or buildings. An example of an on-site disposal system consists of a septic tank and leach drains. A sewage or wastewater system disposes of the effluent from a community at a central place usually called a sewage lagoon or effluent pond. The sewage can be treated:
• in a septic tank at each building
• just before the lagoon in a large septic tank or macerator system, or
• in the lagoon itself
8.1 On-site disposal systems
All the liquid waste from the toilet, bathroom, laundry and sink goes into pipes which carry it to a septic tank. The effluent from the tank is then disposed of through effluent disposal drains often referred to as leach or French drains. Both of these methods of disposing of liquid waste are on-site disposal systems. They must be installed and maintained properly.
In these systems, the effluent is soaked into the surrounding soil. Some soils don’t allow good soakage such as clay or similar soils; if there are any problems with this disposal system a local government EHO should be consulted to talk about the problem.

Effluent (wastewater) disposal system
In this method the effluent from the community is carried by large pipes to the lagoon. These pipes serve all the houses and other buildings in the community. The sewage may be either be treated in septic tanks at the houses or buildings or at the lagoon. There are no leach or French drains.
Full sewage system
All the sewage from the toilet, shower, laundry and other areas enters waste and sewer pipes directly and is pumped to a lagoon.
• There are three types of full sewage system:
• The sewage enters the lagoon without treatment
• The sewage goes through a series of cutting blades which help break up the solid matter before it enters the lagoon. These blades are called macerators.

Conclusion
The term sewer refers to conduit usually underground for carrying off drainage water and sewage. Sewage means waste matter conveyed in sewers. Epidemic refers to widespread occurrence of a disease in a community at a particular time. Besides Abuja (FCT), I have not heard of or witnessed a functional centralized sewage system in many states in the country.
What obtains is a decentralized system where every resident constructs outlets at ground level to discharge waste water, and also each resident construct septic tank for the solid waste matter. Because population density was low, privies constructed in this way did not create sanitation problems or unbearable nuisance in most of our colonial built cities.
Ironically, as population increased, so did the sanitation problems and nuisanses; majority of residents accepted the sanitation problem as urban life except during epidemics or following a disease outbreak when sanitation was given considerable attention.
The proliferation of domestic well at almost every residence as a result of acute water scarcity, apart from domestic safety hazards, has been found to pose serious health problems. The problem of waste water from septic tank of the sewage entering underground into the well water thereby contaminating the water is a possible cause of epidemic disease.

References
1. American society of Civil Engineers (ASCE), (1982) Gravity Sewer Design and Construction ASCE MOPS 50 (WEF MOP FD- 5) Reston, VA: American Society of Civil Engineers
2. Anonymous, (2008) International Source Book on Environmental Sound Technology for Waste Water and Storm water Management https://www.unep.or.jp/ietc/publications/Tech publications/Techpub-15/3-Afrca/1-2-3, asp
4. Awoyemi, A.E (2009) “Perception of Students in Tertiary Institution of Poverty as an Index Intellectual Dwarfism” An Unpublished Ph.D Thesis in the Department of Statistics, Faculty of Science, University of Ibadan.
5. Feachem, R. McGarry, M. and Mara, D, (2007): Water, Wastes and Health in Hot Climate. John Wiley and Sons, Chichester.
6. Koren, H, (1980): Handbook of Environmental Health and Safety. Pergamon Press, Paris.
7. Ogedengbe, M.O., (2001) Waste Management Systems Potential impacts, Paper presented during a course on Environmental Impact Assessment by National centre for Technology Management, OAU, Ile-Ife
8. West African Health Examination Board,(1991). Waste Disposal and Environmental Hazard Control. Clarerianium Press, Ibadan.
9. Wise, A. F. (2009): Water, Sanitary and Waste Services for Building. B. T. Batsford Limited, London

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