Key advantages of Sulabh flush composting toilets are:
- Hygienically and technically appropriate, and socio-culturally acceptable.
- Affordable and easy to construct with locally available materials.
- Design and specifications can be modified to suit householder’s needs and affordability.
- Eliminates mosquito, insect and fly breeding.
- Can be constructed in different physical, geological and hydrogeological conditions.
- Free from health hazards and does not pollute surface or ground water, if proper precautions and safeguards are taken during construction.
- Can be located within the premises as it is free from foul smell and fly/mosquito nuisance etc.
- Can be constructed on upper floors of houses.
- Pits are generally designed for 3-year desludging interval, but if desired, it can be designed for longer periods or it can be reduced even to two years.
- Maintenance is easy, simple and costs very little.
- Needs only 1.5 to 2 litres of water for flushing, while conventional flush toilet needs 12 to 14 litres of water.
- Needs less space than a septic tank toilet system.
- Does not need scavengers for cleaning the pits or disposal of sludge. This can be done by the householder.
- Makes available rich fertilizer and soil conditioner.
- Can be easily connected to sewers when introduced in the area.
- A low volume flushing cistern could be attached to avoid pour flushing.
No Need of Vent Pipe
Sulabh flush compost toilets do not need vent pipes as gases are dispersed into the soil.
Why Two Pits are Better Than One Pit
Single leach pit is appropriate only if they can be desludged mechanically by a vacuum tanker, since its contents are not pathogen-free. In the two-pit system, since one pit is used at a time, the filled up pit can be cleaned manually even by the householder himself because of the long period of digestion which makes it free of foul smell and safe for handling. In the single pit system, desludging has to be done almost immediately after the pit has been filled to enable its reuse; this involves handling of fresh and undigested excreta which is hazardous for health. If a deeper and larger single pit is provided, desludging operation will be difficult and chances of pollution would be more especially where the ground water table is high.
Fixing of Pan and Trap
Squatting pan of design specified for pour flush and trap with 20mm water seal should be used in Sulabh toilets. The pan can be of ceramic, fibre glass, PVC, mosaic or cement concrete. With fibre glass pan, traps of HDPE are used. With ceramic and PVC pans, traps of the same material are used. For mosaic and cement concrete pans, traps are of cement concrete.
Shape of Two Pits
As far as possible, separate circular pits should be constructed as these are structurally more stable and the sludge is dry and safe to handle. Where separate circular pits of standard sizes can not be constructed due to space constraint, pits of smaller diameter (not less than 750mm) be provided, but the depth should be increased suitably to provide required storage volume and infiltration surface area. If it is not possible to construct small diameter pits, combined oval, square or rectangular pits divided into two equal compartments by a partition wall can be provided. The partition wall should be taken 300mm below the bottom of the pit and be plastered on both sides with cement mortar of 1:6 ratio. The partition wall and pit lining in 300mm width adjoining the partition wall should not have holes. However the possibility of water from one pit finding its way to the other pit is very much there. Therefore the desludging of the filled up pit has to be done with care to avoid health hazards.
Spacing Between Two Pits
The minimum space between the two pits should beone metre or equal to the depth of pits below the level of incoming pipe or drain, whichever is more. Where it is not possible to maintain this space, an impervious barrier like cut off screen or a mud wall may be provided between the two pits.
Lining of Pits
The pits should be lined to avoid collapsing. Lining could be in brick work, stones, laterite bricks, burnt clay or cement concrete rings. Lining could be done with treated bamboos, wooden logs, tar drums depending upon availability etc. 50mm wide holes should be provided in alternate brick courses by laying bricks 50mm apart. Above the invert of incoming pipes or drains, no holes should be provided. Where the soil is sandy, sand envelope is provided or where there are chances of damage by field rats, the width of the holes should be reduced to 12-15mm.
Prevention of Pollution
To check pollution of drinking water sources, the pits in fine soils (effective size 0.2mm or less) should be located at a minimum distance of 3 metres from open wells and shallow hand pumps provided ground water table throughout the year is 2 metre or more below the bottom of the pit; if water table is higher, the distance should be increased to 10 metres. In coarser soils (effective size more than 0.2mm), the same safe distances can be maintained by providing 500mm thick sand envelope of 0.2mm sand all round the pit and sealing the pit bottom by some impervious material like puddled clay, polythene sheet, lean cementconcrete or cement stabilised soil.
Normally bacteria do not move beyond 3 metres horizontally in homogeneous soil and vertically they do not permeate more than 1 metre, however there can be marginal deviations depending upon the types and compaction of the soil. It may be noted that chances of ground water occur due to higher hydraulic load. Since in this system hydraulic load is only 1.5 to 2 litres per use, there is no such chance of ground water pollution.
The sizes of pits where ground water level is always below the bottom of the pit and infiltration rate of soil is 30 1/m2/day, for 3 years sludge storage volume works out as follows:
|Circular Pits||Combined rectangular pit divided by partition wall in two equal compartments. Size of each compartment|
|No. Of Users per day||Diameter mm||Depth mm||Length mm||Breadth mm||Depth mm|
The above depths are from the invert of incoming pipes or drains to the bottom of the pit. These depths are to be increased by 225mm to provide free space above the invert of the pipes/drains.
Pits in High Subsoil
Waterlogged and Flood Prone areas in waterlogged, flood prone and high subsoil water areas, the pits should be raised so that the invert of pipe or drain is just above the likely water level. The raising of pits will necessitate raising of toilet floor also. Earth should be filled and well compacted all round the pit. Interconnection Between Trap And Pits The trap should be connected to leach pits through ‘U’ shape covered brick drains of 75mm dia PVC non pressure pipes. In case pipes are used, a junction pit. Keeping the basic design unchanged, Sulabh has a number of such toilet models for demonstration.
Manure From Human Excreta
One of the major difficulties for the use of human excreta as manure is the presence of bacterial and other pathogens. Human excreta contains a full spectrum of pathogens causing various infections. It should be free from pathogens before being used as manure. Another problem is psychological/chamber (250mm x 500mm internal size) should be constructed at the place from where the pipe is bifurcated to connect the two pits. The pipes of drains should have a minimum gradient of 1:15.
Uses of Pit Cover for Household Purposes
Since the pits are covered air tightly with RCC slabs, they can be used for different household purposes or even for running a small shop and so forth.
Cost of Sulabh Flush Compost Toilet
The cost of Sulabh flush composting toilets varies widely to suit people of every economic stratum. The cost ranges from US$ 10 to US$ 1000 per unit. It depends upon materials of construction of pits and seat as well as of the superstructure. The pits can be constructed with bricks or any locally available materials like stones, woodlogs, burnt clay rings, concrete rings or even used coaltar drums. Similarly, the quality of superstructure ranges from simple gunny bag sheets, or thatch to well finished tiles with R.C.C. roof, doors, wash basin, etc. Cost varies also due to size and capacity of the pits, varying from 2 years to 20 years capacity for each pit. Keeping the basic design unchanged, Sulabh has a number of such toilet models for demonstration.
Manure From Human Excreta One of the major difficulties for the use of human excreta as manure is the presence of bacterial and other pathogens. Human excreta contains a full spectrum of pathogens causing various infections. It should be free from pathogens before being used as manure. Another problem is psychological/ religious taboos associated with it. The studies carried out by the Sulabh have revealed that the content of a Sulabh toilet pit is almost free from pathogens when taken out after two years of resting period. To make it completely pathogen free, digested sludge is sun dried for 2 to 3 weeks. During drying of sludge big lumps are formed making it difficult to mix in soil homogeneously. Sulabh developed a technology to granulate such dried lumps into small size graded granules which look like processed tea leaves. Before granulating, it is processed in a ball mill to break it into small pieces. Then it is passed through the mass mixer where the moisture content of manure is regulated by adding water. Such manure has a good percentage of plant nutrients. Besides, it increases humus and water holding capacity of the soil. The Institute has carried out experiments to monitor its manurial effects on different vegetables and flowering plants. In all the cases tested, the effect of manure on the growth of plants was very encouraging.
Operation and Maintenance
- Before use, wet the pan by pouring only a little quantity of water.
- After defecation, pour 1.5 to 2 litres of water in the pan for flushing.
- Pour about half litre of water in the pan after urination.
- The pan should be cleaned once a day with a brush or a broom and with soap powder periodically.
- One of the pits is to be used at a time by plugging the drain for the other pit.
- Kitchen, bathroom waste water or rain water should not be allowed to enter the pits.
- Other solid wastes like kitchen waste, rags, cotton, sweepings etc. should not be thrown in the pan, this could block the toilet.
- When the first pit in use is full, the flow should be diverted to the second pit and the filled up pit should be desludged after 1.5 to 2-year rest period. The first pit can then be put to reuse, when the second pit fills up.