The system in which excreta are removed from bucket latrines (also called nightsoil latrines or earth closets) is one of the oldest forms of organized sanitation. Bucket latrines are still found in many towns and cities in Africa, Latin America and Asia, because their low capital cost makes them attractive to underfunded local authorities.
In some rural and periurban areas, members of households take nightsoil to manure heaps or apply it directly to fields as fertilizer. In towns and cities, nightsoil is often collected by sweepers engaged by householders on contract, or by the local authorities. Buckets are usually emptied into larger containers near the latrine. In some places labourers carry these containers by hand or on their heads; hand-carts, animal-drawn carts, bicycles and tricycles are also used.
For the reasons given in Chapter 4, nightsoil collection should never be considered as an option for sanitation improvement programmes, and all existing bucket latrines should be replaced as soon as possible.
The number of bucket latrines is declining rapidly. However, for many years to come, some people will have to rely on bucket latrines as their only form of sanitation. The following paragraphs give suggestions for improvements to existing systems until they can be replaced by more acceptable forms of sanitation.
A container made of non-corrosive material is placed beneath a squatting slab or seat in the bucket chamber, with rear doors which should be kept shut except during removal and replacement of the bucket. The bucket chamber should be cleaned whenever the bucket is removed. The squat hole should be covered by a flyproof cover when not in use. The cover of the seat should be hinged (Fig. 6.37) and the cover of the squatting slab should have a long handle.
Fig. 6.37. Bucket latrine (A)
Fig. 6.37. Bucket latrine (B)
At regular intervals (preferably each night) the container should be removed and replaced by a clean one. Full containers should be taken to depots or transfer stations where they are emptied, washed and disinfected with a phenol or cresol type of disinfectant. In some towns it is the practice to provide two buckets painted in different colours for each latrine. Containers should be kept covered with tight-fitting lids while in transit and the operators should be provided with full protective clothing. Proper supervision and management are essential. Defective buckets should be repaired or replaced and transport vehicles should be kept in good order.
In some systems, urine is diverted away from the buckets to reduce the volume to be dealt with. It is usually channelled to soakpits, but may be collected separately and used directly as fertilizer. Water used for washing latrines and bucket-chambers should pass to soakpits, and should not be allowed to pollute the ground around the latrines.
The practice of dumping nightsoil indiscriminately into streams or on open land is objectionable and causes health hazards.
Bucket latrines are sometimes found in towns that are partially provided with sewers, in which case it may be convenient to discharge the nightsoil into a main sewer. Tipping points on sewers require careful design to prevent contamination of surrounding areas and should be as near to the sewage works as possible. Extra water may have to be added to prevent blockage of the sewers.
Sewage treatment works
Nightsoil may be discharged into the sewage flow at the works inlet, at sedimentation or aeration tanks, or directly to waste stabilization ponds or sludge digestion tanks.
Trenches about 1 m deep and 1 m wide may be filled with nightsoil to within not less than 300 mm of the top. The trench is then backfilled with excavated soil, which should be well compacted to prevent the emergence of flies or the excreta being dug up by animals (Fig. 6.38). At the end of each day any exposed excreta must be covered with at least 200 mm of soil, well compacted. After backfilling, the trench should remain untouched for at least two years, after which it can be re-excavated for reuse and the contents used as fertilizer. The trenching site should be close to the collection area but away from residential areas. It should have deep and porous soil, be well above the water table, and not be subject to flooding.
Fig. 6.38. Disposing of excreta from bucket latrines by trenching (A)
Fig. 6.38. Disposing of excreta from bucket latrines by trenching (B)
Nightsoil can be used as a fertilizer after all pathogens have been destroyed. It may also be added to ponds for fish cultivation (see Annex 1).
Vault latrines are a way of overcoming the problem of frequent emptying needed with bucket latrine systems. A watertight tank or vault below or close to a latrine is used to collect faeces, urine and sometimes sullage. The capacity of the vault is often sufficient for 2-3 weeks' accumulation of excreta, after which time the vault is emptied. The system is satisfactory if collection is reliable and hygienic, and the vaults are properly flyproofed, vented and fitted with water-seal toilets.
In some places, the contents of vaults are bailed out by hand and taken away in tanks mounted on carts. This is highly undesirable. Trials with manually operated pumps to empty vault contents have not been very successful because with a low pumping rate (about 400 litres per hour) complete evacuation of the vault is a long and tedious operation. This method is obviously also undesirable.
Motorized vacuum tankers can provide safe removal but must be backed up by good institutional support for operation and maintenance. Most vacuum tankers cannot lift vault contents if the proportion of solids exceeds about 12%, but some have facilities for adding water to vaults before lifting the contents.
Sufficient extra space to allow for irregularities in collection time should be planned for in designing vault capacity. In communities where finance, spare parts and good maintenance are available, the additional space needed may be only 15-20%. However, where vehicle maintenance is poor, an allowance of 50% may be advisable.
The performance of vaults has been mixed, mainly dependent on the levels of finance and vehicle maintenance. Poorly constructed vaults are common, leading to problems with odour and flies, ground pollution and thickening of the vault contents. It is not recommended that new vault latrines be constructed.
Cesspits, like vaults, are watertight tanks with sealed covers (to keep out mosquitos). They differ from vaults in that they are usually located outside the premises and collect sullage as well as the wastes from water closets. The capacity may be sufficient for up to several months' use (Fig. 6.39). The cost of providing a regular removal service for all the wastewater from a house with a good supply of piped water can be very high, making cesspits an expensive form of sanitation.
Fig. 6.39. Cesspit
Modern chemical toilets are normally of the following types:
• a cylindrical bucket fitted with a plastic seat and lid; the capacity is usually 20-30 litres; after the bucket has been emptied and cleaned, about 50 mm depth of fluid is put in;
• two tanks: the flushing-liquid reservoir contains a mixture of fresh water and a deodorizing chemical which is pumped manually to the rim of the pan; discharge is to the waste-storage tank (Fig. 6.40);
• a single tank in which a flushing pan is fitted; a manual or electrically operated pump recirculates oil, drawing it from the base of the tank through a filter and discharging it around the rim of the pan; the pan has a counter-balanced flap so that the contents cannot be seen (Fig. 6.41).
Fig. 6.40. Manually flushed chemical toilet
Fig. 6.41. Recirculating oil toilet
The fluid is normally a chemical diluted with water which renders excreta harmless and odourless. When containers are full, the contents are tipped into pits or sewers, or pumped into storage tanks.
Chemical toilets are used in aircraft, long-distance coaches, caravans, vacation homes and construction sites. The chemical is expensive.
An overhung latrine consists of a superstructure and floor built over water (Fig. 6.42). A squat hole in the floor allows excreta to fall into the water. A chute is sometimes provided from the floor to the water. Overhung latrines should never be built in places where pit latrines can be provided. However, they may be the only possible form of sanitation for people living on land that is continuously or seasonally covered with water.
Fig. 6.42. Overhung latrine
Wagner & Lanoix (1958) suggested that such latrines might be acceptable provided the following conditions are met.
• The receiving water is of sufficient salinity all year round to prevent human consumption.
• The latrine is installed over water that is sufficiently deep to ensure that the bed is never exposed during low tide or the dry season.
• Every effort is made to select a site from where floating solids will be carried away from the village.
• The walkways, piers, squatting openings, and superstructures are made structurally safe for adults and children.
• The excreta are not deposited in still water or into water that will be used for recreation.