For the disposal of night soil or excretal waste without the help of water carriage system different types of privies or laterines may be constructed.
The different types of privies which may be used in rural areas are as follows: 1. Trench Privy (Shallow Type) 2. Pit Privy, or Dug Well Privy 3. Bore Hole Privy 4. Pale or Can Privy 5. Concrete Vault Privy 6. Aqua Privy 7. Chemical Toilet 8. Pour Flush Water Seal Laterine.
Type # 1. Trench Privy (Shallow Type):
ADVERTISEMENTS:
These are used as a temporary measure during fairs, camps, etc. These consist of rows of parallel trenches 0.9 m long, 0.3 m wide and 0.3 to 0.6 m deep and provided with privacy screens. A distance of about 0.6 m is maintained between each trench.
The faeces, urine and ablution water fall directly into the trench. The excavated earth is piled round the trench, and each user after use throws some quantity of earth on the faecal matter. Each trench may be used for about 100 faecal droppings.
Type # 2. Pit Privy or Dug Well Privy:
It consists of a pit 0.9 to 1.2 m in diameter (or 1 m x 1 m in plan) and 2 to 4 m deep. The pit may be lined or unlined but its bottom is unlined. The pit is covered with a squatting slab with a hole or squatting plate. A cover may also be provided to cover the hole. The user discharges excreta into the pit by sitting on the squatting slab.
The faeces, urine and ablution water fall directly into the pit. The faeces are stored in the pit while the urine and ablution water seeps into the soil. A superstructure may be built over the privy (see Fig. 21.2). A capacity of 40 to 60 litres per person per year is provided. Storage period may be 4 to 6 years. A pit capacity of 1.5 m3 can serve an average sized family for several years.
When the pit gets filled up, the squatting slab and the superstructure are shifted to another pit. The filled pit is covered with earth and its contents may be taken out after about couple of months and may be used as manure.
Type # 3. Bore Hole Privy:
Bore hole privy is constructed where the space available is very little. It is similar to pit privy except that it is smaller than the pit privy while its depth is much larger. It consists of a circular hole of 0.3 to 0.4 m diameter and 5 to 6 m deep dug in the ground by means of auger. The bore hole is covered with a suitable concrete squatting slab of about 0.85 m diameter with a central opening and foot rests. The upper portion of the bore hole is lined with clay (see Fig. 21.3). A superstructure may be built over the privy.
ADVERTISEMENTS:
When the bore hole gets filled up, the squatting slab (or squatting pan with trap) and the superstructure are shifted to another bore hole and the filled bore hole is covered with earth and its contents may be taken out after about couple of months and may be used as manure.
Type # 4. Pail or Can Privy:
This is also known as removable receptacle privy. This is the oldest and the primitive type of privy, which is still widely used in rural areas. In this privy excreta is collected in iron pails or cans. The pails or cans are 40 cm x 30 cm x 20 cm in size and are water tight. Fig. 21.4 shows such a privy in which the pail or can is placed under the seat or squatting plate for the collection of the faeces, urine and ablution water. The excreta is collected from this container once or twice in a day by scavengers for further disposal.
ADVERTISEMENTS:
The initial cost of the pail or can privy is low, but the servicing cost by the scavengers is high. Further it has several other disadvantages like, major health hazards and social stigma for the scavengers, foul smell, breeding of flies and mosquitoes.
Type # 5. Concrete Vault Privy:
This is an improved form of pit or bore hole privy, used in sandy soils or in locations where ground watertable is high. Fig. 21.5 shows a concrete vault privy which consists of a watertight concrete vault or chamber constructed underground for collection and storage of faecal matter. The squatting seat is provided over the top of the vault.
ADVERTISEMENTS:
The capacity of vault is sufficient for six months storage. After every sitting soil is thrown over the excreta so that bad odours are prevented. The squatting pan is so constructed that no water enters the vault. When the vault is filled up, either fully or partially, it is emptied through the manhole.
Type # 6. Aqua Privy:
Aqua privy is also known as wet latrine in order to distinguish it from the other types of latrines which are known as dry latrines.
As shown in Fig. 21.6 an aqua privy consists of three interconnected underground chambers:
(i) Anaerobic digestion chamber,
(ii) Aerobic digestion/clarifying chamber, and
(iii) Filter chamber.
The anaerobic and aerobic digestion chambers are of equal size and are filled with water while the filter chamber is of smaller size and is filled with brick bats/ clinker to act as filter media. The squatting pan is placed on the top of the anaerobic digestion chamber and its discharge pipe is taken about 10 cm below the water level in the anaerobic digestion chamber to provide water seal.
The faeces, urine and ablution water fall directly into the anaerobic digestion chamber, and is decomposed by the action of anaerobic bacteria. The gases produced during the decomposition escape through the vent pipe provided in the aerobic digestion chamber. In the aerobic digestion chamber further decomposition takes place by the action of aerobic bacteria.
The digested sludge gets settled in both anaerobic and aerobic digestion chambers which may be cleared once in two years. The effluent from the aerobic digestion chamber flows to the filter chamber through a pipe whose outlet is taken down upto somewhat near the bottom of the filter chamber. As the effluent rises in the filter chamber, it gets purified. The purified effluent from the filter chamber is led out through the effluent channel and may be used for gardening or fanning.
To compensate for evaporation and leakage losses and to maintain the water seal, i.e., submergence of the discharge pipe of the squatting pan in the water, water is to be added every time after its use. In practice water seal maintenance has proved to be difficult.
Absence of effective water seal may result in foul smell, mosquito and fly breeding, visibility of floating excreta through the pipe, splashing of water, etc. In addition the excreta may stick to the pipe and thus encourage breeding of flies and mosquitoes. In view of these reasons aqua privies are not commonly adopted.
Type # 7. Chemical Toilet:
In the chemical toilet, the concrete vault is replaced by an acid proof metal tank. The tank is generally of 600 litres capacity, and in this 10 kg of caustic soda dissolved in 40 to 60 litres of water is placed. The caustic soda helps to stabilize the organic matter present in the excreta.
The night soil is liquefied and sterilized in the tank and pathogens are also destroyed. The spent chemical and accumulating liquids and solids are removed periodically and drained out in a cesspool. There is no odour problem in this case. However, the cost of these toilets is more, and hence these are not commonly used in rural areas. These types of toilets are usually used in aircrafts.
Type # 8. Pour Flush Water Seal Laterine:
In a pour flush laterine, as the name indicates, the excreta is hand flushed by pouring about 1.5 to 2 litres of water. As shown in Fig. 21.7 a pour flush laterine consists of a squatting pan with a trap which discharges the excreta into a leaching pit located slightly away from the pan. Usually two leaching pits are provided, but at a time squatting pan is connected to only one pit.
The leaching pits are provided with a lining of brick work in cement mortar 1:6 with honey combing in alternate layers. When one pit gets filled up, the excreta are diverted to the second pit. The filled up pit may be emptied after one to two years when the excreta gets completely digested and most of the pathogens die off. The digested excreta may be used as manure. Thus the two pits can be used alternately and perpetually.
With simple care, pour-flush water-seal laterine is a very satisfactory and hygienic sanitation system for rural and other areas where sewerage system does not exist. This laterine can be located inside the house since the water seal would prevent odour and insect nuisance.
Requirements of a Good Privy:
The requirements of a good privy are as follows:
(1) It should be located away from the building on the leeward side.
(2) The squatting pan should be well above the ground surface to prevent entry of rain water.
(3) It should be well ventilated.
(4) The receptacle to receive excreta should be of sufficient capacity so as to hold at least 24 hours the faeces, urine and ablution water.
(5) It should remain closely covered so that flies do not reach there.
(6) Contents should not be visible to the user.
(7) It should have moderate cost.