Twin pit pour flush latrines in India - is it timely to call into question the design and operating principles?


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  • mchalej
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Re: New SATO Connection System for Twin-Pit Pour Flush Latrines

Dear Dean,

Twin Pit Pour Flush Latrines have been utilized in India for at least 40 years. Roughly 50,000 per day are currently being constructed under the Swachh Bharat Mission. Our intention was to develop something that would eliminate some common breakdowns and enable them to be implemented and operated more effectively, not to change the composting mechanism or basic operating principle itself.

For background information on twin pit latrine construction and composting process please see reports from World Bank and India Ministry of Drinking Water and Sanitation below.

World Bank Report
India MDWS



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  • goeco
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  • Self employed innovator with an interest in wastewater treatment systems and recycling of nutrients
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Twin pit pour flush latrines in India - is it timely to call into question the design and operating principles?

Note by moderator: this post used to be in this thread about the "New SATO Connection System for Twin-Pit Pour Flush Latrines"


I'd like to ask about the specific purpose of these twin chamber pits used in India (see image below). It looks like wet composting whereby the intent is for lack of soakage to be overcome by rotating when buildup of liquid/sludge fills one side? Can the design be improved?

My initial observation is that capacity comes at a cost and for sanitary "compost" the resting period needs to be sufficient for destruction of pathogens, in particular helminths. The faster the pit fills the greater the required capacity for a sufficient resting period, which increases cost.

How can this be improved? Enhancing decomposition with earthworms would mean the pits fill slower, increasing the rotation period. However, any excess of liquids would be unfavourable for digestion - adequate drainage being the key to rapid digestion. Seems to me that if those pits were wider and shallower, then you'd have the same capacity but an increased soil surface area and therefore improved percolation... to directly improve digestion and extend rotation length or lower cost. If the environment were optimised for worms, the solids would get digested rapidly, allowing rotation every 3-5 years instead of 1-2 years, therefore producing a sanitary compost.

Also, by lining your pits with shadecloth the soil surface would not become "sealed" with sludge because the bricks would isolate the solids from the soil and only liquid would filter through to the wall soil surface for soakage. What was the space between the bricks and clay wall filled with? I guess I'm just wondering if there is active work on optimising this system for rapid digestion?

The SATO diverter is a fantastic innovation for twin pits, I'd like to see systems in place that really take advantage of it so sludge becomes a thing of the past. Now that would be more than just a fantastic innovation, that would be nothing short of revolutionary.

Dean Satchell, M For. Sc.
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