In 1968, Dr Bindeshwar Pathak, Founder of Sulabh International Social Service Organisation, invented two-pit pour-flush ecological compost toilet technology. Sulabh flush is based on a simple design that is eco-friendly and uses just around 1.5 litres of water to flush.
In the context of developing countries where the sewer systems are almost nonexistent, Sulabh toilets offer an innovative solution to the global sanitation crisis.
In this technology, there are two-pits. When one pit is full, the incoming excreta is diverted to the second pit. In about two years, the excreta gets digested and becomes dry and pathogen-free, and safe for handling as manure. Digested sludge is odourless and is a good manure and soil-conditioner. This technological invention made a path-breaking difference in millions of household – particularly women- who did not have access to safe and hygienic toilet facilities.
The technology offers safe disposal of human excreta on-site. It also meets all the seven criteria of safe on-site disposal of human waste prescribed by the World Health Organization.
Sulabh two-pit pour-flush household toilet
Sulabh two-pit pour-flush household toilet consist of squatting pan of special design set on the floor, a trap with 12 to 20 mm water seal to prevent foul smell and fly mosquito nuisance. Two leach pits retain solid matter and allow the liquid to leach and gases to disperse into the ground. There is a junction box to interconnect system between pit and trap.
Pour-flush toilet requires hardly 1.5 litres to 2 litres of water per wash in place of 10 to 12 litre of water with cistern flush this saving a huge quantity of water. The excreta is carried into subsurface leach pits through pipes or covered drain and one pit is used at one time. The liquid infiltrates into the soil through holes on the leach pit lining. The gases also disperse into the soil.
As such, there is no need for the vent pipe. When one pit is filled, the excreta is diverted to another pit. The filled up pit can be continently emptied after a rest of two years during which the pathogens are inactivated and the organic matter decomposed thus two-pits can be used conveniently and alternately. Pour-flush toilet requires hardly 1.5 litres to 2 litres of water per wash in place of 10 to 12 litre of water with cistern flush this saving a huge quantity of water.
The excreta is carried into subsurface leach pits through pipes or covered drain and one pit is used at one time. The liquid infiltrates into the soil through holes on the leach pit lining. The gases also disperse into the soil. As such, there is no need for the vent pipe. When one pit is filled, the excreta is diverted to another pit. The filled up pit can be continently emptied after a rest of two years during which the pathogens are inactivated and the organic matter decomposed thus two-pits can be used conveniently and alternately.
How it works?
UNCHS declared Sulabh’s Toilet Technology as one of the “Global Best Practices” in 1996 at Habitat Conference in Istanbul, Turkey. Sulabh was conferred Dubai International Award for “Best Practices to Improve Living Environment” in year 2000 for its Toilet Technology.
Know more about Sulabh Technology
The invention by Dr Pathak has been revolutionary not just in transforming the sanitation scenario of the country but also in bringing about behaviour change and change in social attitude. When Sulabh toilet technology was developed, the sanitation situation was dismal in both rural and urban areas. Going out in the open for defecation was a common phenomenon in both rural and urban areas, and women were the worst sufferers. Going out in the field made them vulnerable to all sorts of risks. The harassment that they would endure from anti-social elements meant that they had to compromise with their dignity and shame day in and day out, and they were also prone to snake and animal attacks. Lack of access to sanitation facilities had an enormous toll on the health of mothers and their children.
Children died because of diarrhoea, dehydration and they remained exposed to life-threatening parasites like hookworm, roundworm and tapeworm. Girls dropped out of school because there was no provision of toilets in schools.
Sulabh toilets addressed these issues significantly. In 2004, the UNDP’s Human Development Report gave thrust to the UN’s commitment to diversity by arguing that respect for diversity is an integral part of development. Sulabh’s work across India was recognized by the UNDP as a Global Best Practice and has been described as one such pan-India movement that strongly incorporated the diversity of cultures, beliefs and practices in its development approach.
1. Why two-pits are better than one pit?
Single leach Pits are appropriate only if they can be Desludged Mechanically by a Vacuum Tanker since its contents are not pathogen-free. In 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 the handling of fresh and undigested excreta which is health hazardous.
If a deeper and larger single pit is provided, the desludging operation will be difficult and there would be more chances of pollution especially where the groundwater table is high.
2. Fixing of pan & 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.
To ensure 20mm Water seal, the Trap should be fixed keeping the Top of Inlet and Top Curvature of the Trap Horizontal and the fixing the Pan over it keeping its Rim Horizontal and Flush with the floor.
3. 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 constraints, Pits of Smaller Diameter (not less than 750mm) be provided, but 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 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. (See Drawing No. 2). 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.
4. Spacing between Two-Pits
The Minimum Space between the Two-Pits should be One 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, provide an impervious Barrier like Cut Off Screen or Puddled Wall between the Two-Pits.
5. Lining of Pits
The Pits should be lined to avoid collapsing, Lining could be in Brickwork, Stones, Laterite Bricks, Burnt Clay or Cement Concrete Rings. The 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 of 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.
6. 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 years is 2 metres or more below the Bottom of 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 Cement Concrete stabilised Soil. Normally bacteria do not move beyond 3 metres horizontally in homogenous soil and vertically it does not permeates more than 1 metre, however, there can be marginal deviations depending upon the types and compaction of the soil.
7. Size of Pits
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 and for 3 years Sludge Storage Volume Works out as follows:
|No. of Users/Day||Circular Pits||Combined Rectangular Pit divided|
by Partition Wall in Two Equal
Compartments. Size of each
The above depths are from the Invert of Incoming Pipes of Drains to Bottom of Pit. These depths are to be increased by 225mm to provide a free space above the Invert of Pipes/Drains (See Drawings No. 1 and 2).
8. Pits In High Subsoil, Water Logged 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 around the Pit.
Interconnection between trap and pits
The Trap should be connected to Leach Pits either through ‘U’ Shape Covered Brick Drains of 75mm dia AC or PVC non pressure pipes. In case pipes are used, a Junction 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.
Key Advantages of Sulabh Twin Pit 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 low cost.
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 Septic Tank Toilet System.
Does not need Scavengers for Cleaning the Pits or Disposal of Sludge. This can be done by the Householders.
Makes up for rich manure 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.
Sulabh toilets do not need vent pipes as the gases are dispersed into the soil.
Sulabh’s Affordable Toilet consists of a Pan with a Steep Slope 250 to 280 and specially designed Trap with 20mm Water Seal needing 1.5 to 2 litres of Water for Flushing The Pan and Trap of Conventional Design which is used with Flushing Cisterns should not be used in Pour-flush Toilets with Leach Pits, as it would need more water flushing and the Pit may not function properly.
The Excreta is carried into Leach Pits through Pipes or Covered Drains: One Pit is to be used at a time. The Liquid Infiltrates and Gases Disperse into the Soil through the Holes in the Pit Lining When One Pit is full, excreta is diverted to the Second Pit. In about 18 months curing period, the contents of the First filled up Pit gets Digested and become totally safe for handling. The Pit can then be conveniently emptied and is ready to be put back into use after the Second Pit is full. Thus the Two-Pits can be used alternatively and continuously. The Sludge of the Pit is a good Manure for use in Horticulture/Agriculture. The Cost of Emptying the Pit can be met partially from the Cost of Manure made available. This offers total recycling of Human Waste efficiently and safely.
Government of India, State Governments and various National and International Agencies like UNICEF, World Bank, UNDP, WHO, United Nations Centre for Human Settlement (UNCHS) etc. have endorsed the design. It has been replicated in other developing countries in South-East Asia, Latin America and in Africa.
Sulabh’s technology is designed in such a way that it can be constructed across all geographical terrains in a sustainable manner. Efforts are made to source the building materials locally. Since its design is simple, it can easily be constructed by local masons.
Another advantage is that the naturally occurring bacteria available in the soil converts human waste into the manure which can be used for agricultural purposes.