Eating is an agricultural act - Wendell Berry

Sunday, February 07, 2010

managing sanitation at pR

sustainable design (like permaculture) mandates that 'nothing goes to waste' including 'waste', i.e., there is nothing that is waste, i.e.^2, everything has a use.

a potentially queasy problem in going off-the-grid is the management of human waste (note - not disposal, but management)

lets get to the evolution of the toilet design at pR.

stage 1
the simplest toilet in the world in the hole in the ground.
this hole is connected to a tank/pit which collects the faeces/urine/water.
in cities with areas not connected by sewarage systems, this tank is called the septic tank and the municipal authorities arrange to empty them at designated intervals.
in villages, sulabh's bindeshwar pathak and safai vidyalaya's ishwarbhai patel have pioneered the two-pit latrine system aka pour-flush-compost latrine.
this is how this system has been installed at pR. the pic on the right shows the top covers of the two pits.

the key short-coming of this system, is the potential contamination of the ground water (by leaching) as the faeces is mixed with the flush-water and the urine (total approx 3 litres per use).
also, in the case of heavy flooding, there is a risk of leakage into the over-ground fresh water systems (lakes, tanks, etc).

stage 2
it was clearly evident that we would need to address the above shortcomings.
1. the faeces should be kept separate from water and urine.
2. the faeces collection should be safe from flooding.

enter the urine diverting ecopan from paul calvert's eco-solutions.
here it is installed at pR.
this is the indian style version. the wooden frame (pic on right) is for holding.

explanation of this design (refer to the pic on the left).
1. the middle of the long pan is for the urine colletion.
2. the lid (with red knob) covers the pit into which the faeces drops (there are 2 pits on either side of the urine collector - the knobbed one is in use and the other is closed).
3. the short pan on the left of the pic is for washing the backside post dropping.

this entire system is mounted (with brick and mortar) at a height of around 2 feet. so the faeces collection pit is above ground.
sawdust is used extensively to line the bottom of the pit prior to usage and after each use to cover the faeces. this will absorb excess moisture and prevent odours, etc.
the urine and wash water could be directly led to plant beds just outside the toilet.
Note: - we will be running the urine through a charcoal bed as we feel that it is too concentrated to be directly given to plants.

now the important part - what happens to the faeces.
the capacity of the collection pit is approx 5 cu ft.
and 5 people can use it for over 6 months without even hitting 50%.
at this stage, the in-use pit will be closed (after generous dumping of sawdust) and the sitting position is reversed and the other pit will be start being used.
within 6 months, the faeces in the closed pit will have decomposed and can be easily and safely removed and used as manure (very high quality).

the key shortcoming of this system is the physical discomfort involved in the perpendicular swivel move to reach the backside wash pan. and not too appropriate for saree wearers.

Stage 3
the Ecosan urine diverting toilet from biome solutions is a better design with the backside wash pan comfortably placed just behind the faeces pit. so a simple shuffle of around 3 inches behind will place the user right above this pan.

this design will be optimised shortly in Stage 4.


SurveySan said...

i am a nature lover.
but this could be a deterrent for people like me to do an extended stay in PR :)

when big cities can have millions of septic tanks and deal with leakage/etc.., why cant pR do the same?

once the septic tank contents decompost, does it still provide a threat of leakage and ground water contamination?

in PR, is the main idea to conserve water?

i personally think, this is over engineering ;)

csm said...

ss -thanks for the note and Qs. human waste is a delicate (!!) issue for majority and needs to be addressed such that there is no unease over its management.

1. am not sure big cities do a good job in handling sewage. in most indian cities, untreated sewage is let out in large quantities into nearby water bodies.

2. even the septic tank system in cities do not allow for any composting at all. the municipalities se

2. even the septic tank system in cities do not allow for any composting at all (as they are fully cemented and hence the water remains in the tank). the municipalities send trucks to empty the residential septic tanks and then take it to their treatment center.

3. the classic 2-pit system septic tank is just a pit in the ground (no cement). Hence the water will separate into the ground and then the waste will compost. This is the basic difference in city based septic tank systems and the 2-pit system.

4. post composting there is no danger in leaching, contamination, etc.

5. in pR, the reason for this evolution stems from water conservation, speed to compost (septic tank contents will take much longer to decompose due to the higher levels of water) , ease of handling the compost, ability to use the urine directly as fertiliser as well as de-risking ground water contamination. As pR's water-harveting systems get more and more robust (refer swales note on, the water table will rise, especially post monsoon.

Hope the above is clear in answering your queries :-)

SurveySan said...

//2. even the septic tank system in cities do not allow for any composting at all (as they are fully cemented and hence the water remains in the tank).//

interesting. this is news to me. but, the clearing happens only every 5 years or so for a household. i thought it would compost by then.

thanks for the details.
fun fun fun. :) - Explore Indian blogs said...

Thanks for this article. I'm glad that was able to take your message far accross and could do our bit for a good cause.

Arvind said...

I identify with the issue but the system you've documented seems too much of a compromise. Have you thought about installing a gobar gas plant and feeding the waste from the toilets to it? This should result in slurry that composts much faster. You may need to keep cows to ensure enough feed for the digester though.

csm said...

hi arvind,
why is it a compromise?
it is finally a question of using human waste effectively. and the eco-san does that remarkably better than the other system mentioned.

gobar gas plant is certainly another method of using slurried human waste, but as you your self have indicated, we need cows.
in the absence of cows (raising cows = raising babies in my farming dictionary), the eco-san options are simple, effective and efficient.

would love to hear your thoughts on the compromise statement.

Arvind said...

To give a little bit of background, I'm reading your post as someone who wants to construct a home on farm land. I'm trying to avoid a septic tank at all costs.

I felt that for the common person, this system demands a very different mindset than the one they are currently used to. Trying to separate urine and faeces, asking them to shuffle around to a different wash pit etc. Also, the fact that such a bathroom cannot normally be situated inside the confines of a home is quite restrictive. As a person, I might be willing to go through with this. However, when you try to get buy-in from wife, kids, extended family etc. it runs into a brick wall.

I feel there are many people out there who would be more sympathetic to composting human waste and avoiding septic tanks, if they are presented with alternatives that are not too different from conventional systems in usage.

As for my personal situation, like I mentioned before, I am leaning towards a gobar gas plant. Yes, raising cows is a chore but that will be the sacrifice I make to ensure that the waste we generate is composted and does not pollute our land.

csm said...

hi arvind - stage 4 of the evolution will tackle the switching etc.
yes, we are designing for a rural homestead and this system will naturally have the batroom as a separate unit and not part of the house.
for your requirement, you should consider the sawdust toilet (
also read the humanure handbook and so much more (
these would address your concerns and give you a suitable design for a composting toilet.

at some stage in this learning, your family will have to learn to be less queasy about shit. thats as important as the design of the toilet (in terms of your effort).

i think that our conventional systems are deeply flawed and will have to drastically changed.
how can any system which pumps in billions of kilolitres of sewage into our waterbodies be termed conventional.
this is my stance, will not thrust this down anyone's throat :-)

the question with cows (which many are unable to answer) is what to do when they age?
almost all cows (including those raised by temples) end up as beef. this is just for info in terms of your sustainability of the gobar gas unit etc.
good luck with the building and do keep in touch.
love - csm

Jacob said...

HOpe this info is relevant in your context: Septic tank effluent is not pathogen free (potentially harmful) and methane is released into the air which depletes ozone (20 times more harmful than CO2). Methane produced in the Biogas plant can be used for cooking and the effluent is pathogen free. sullage (Kitchen & Bath waste) should be separated from sewage (excreta) Dr.Mapuskar of Appa Patwardhan Safai & Paryavaran Tantra Niketan, Dehu Rd, Pune have sucessfully executed several such systems.

csm said...

jacob - precisely why we do not use a septic tank and have written against it.
the eco-san system is superior to most systems due to zero water mixing with the faeces. it takes around 12-18 months for full and safe composting.
our bathwater, kitchen water go directly into vegetable growing areas.
if you noticed our set up, we are totally off-the-grid in rural TN.
you should read the humanure handbook. it is a phenomenal tome on managing human waste.
we are considering a bio-gas system and have the tech specs from ESI/safai vidyalaya in gujarat.
thanks for the leads.