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Friday, 23 November 2018

Sewage Disposal







An efficient method of disposing sewage, which involved minimum handling, is necessary to control the spread of the water and food borne diseases. It act as s barrier that isolated the pathogens in the faeces and urine and prevents them from spreading and infecting healthy people.

      The common sewage disposal systems include

• the direct disposal method, e.g. pit latrine;

• the conservancy method, e.g. the bucket latrine and chemical latrine; and 

• the water carriage system.

       As with refuse disposal, sewage disposal in urban areas and villages is carried out by the public health authorities.

Pit latrine :

In rural areas, a pit latrine is used to dispose of human faeces and urine. It is simply a hole in the ground about 3 metres deep and 1 metre wide. The opening is always kept covered when not in use. The solid matter in the faeces is acted upon by bacteria turned into a liquid which seeps into the surrounding soil. When yhr contents of the pit reach with in 1 to 2 metres of the surface, it is filled in pit latrines should be at least 3 to 4 metres away from the nearest subsoil water supply.

      A pit latrine is a hygienic method of sewage disposal as there is no handling of human wastes. However, a badly constructed and maintained pit latrine may contaminate water supplies and act as a breeding ground for vectors.

Note : In some places, bore hole latrine are used. Here, the holes are bout 6 to 7 metre deep. Borehole latrines last longer than pit latrines.

Bucket latrine :

The bucket latrine system is a common method of disposing sewage In the urban areas of developing countries like Nigeria. A night soil worker empties this waste daily into his bucket. The house hold bucket is washed, disinfected and put back in its place. The human waste that is collected from all the houses in the urban area is transported to a dumping ground and emptied into a pit.

     The bucket latrine system is unhygienic especially as one latrine is usually used by many people. It involved handling which increases the risk of faecal contamination of soil, water and food. It is difficult to keep the bucket clean and free of pathogens, and prevent flies from visiting the latrines. As a result, control of diseases spread through flies, food, water and contact is difficult.

Chemical latrine :

In this type of latrine, the faeces fall into a water tight tank, containing a disinfectant and a liquefier. The contents of the latrine are disposed of either continuously by percolation into the surrounding soil, or removed by interval for burial.

    This type of latrine is useful for isolated houses where the daily servicing of an ordinary bucket latrine is not possible. It is also used in aircraft and railway trains.

Water carriage system :

This is the most efficient a d hygienic method of sewage disposal. It is the system used in the urban areas of most developed countries. 

    In this system, faeces and urine deposited in a water closet are flushed with clean water from a cistern. The raw Segar is conveyed by drains to 

• a septic tank, or

• sewers (,large underground pipes).

Some of the clean water used for flushing away the waste remains in the water closet, trapped by a u shaped bend in the pipe. This forms a water seal that prevents the smells from the sewers PR septic tank from entering the house.

Septic tank :

In Durban and rural areas, sewage from the water closers is emptied into a septic tank. This is a convenient way of disposing sewage from a single house or a few houses.

    A septic tank is a large air tight hole in the ground line with bricks or concrete. It had an inlet pipe for incoming sewage SNF outlet for treated effluent. It had a removable concrete cover with air vents for gases to escape. Sewage entering the tank is decomposed anaerobically by bacteria. Most of the suspended solids is removed by this action, the denser materials sink to the bottom to form sludge and scum. The liquid layer in between the scum and sludge passes out of the outlet pipe into the surrounding soil or sometimes into a seepage pit. In a seepage pit , aerobic bacteria bring about further decomposition, making the effluent harmless. The sludge in a septic tank had to be removed periodically (usually every three years).

Sewage and sewage work :

In some places, sewers empty their contents directly into the sea, where decomposers usually break down the organic matter into harmless products. This works as long as  the natural nutrient cycles can handle the amount of sewage that is being dumped; IG not the water becomes polluted.

    In many countries, sewers lead to a central sewage worms. Here, the sewage is first screened to remove large debris. Chemicals are added to coagulate the raw sewage, which then settles down is register by anaerobic and aerobic bacteria. After many staged of treatment, the original sewage is changed into

• a harmless liquid form which is drained into ponds or lakes into the sea, and

• a solid form called sludge which is used as a fertilizer.

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