Data logging from a Ugandan toilet - please help

[NicNakNoe]

A tricky one for you: I’m working on a project and am quite stuck.

It is for an NGO in Uganda who want to know to get a better idea of what goes into their basic pit latrines (essentially a hole in the ground where waste is flushed into via flushing with a bucket of water).

The setup is pretty much this: http://www.unep.or.jp/ietc/publicati.../2-4/4-1-3.asp

The waste enters via a 110 mm plastic pipe (angle is variable but can be fixed for a trial). The NGO would prefer if the device is something which fits on/around the pipe
I want to measure:
1. At the very least – an approximation of what total combined volume of liquids plus solids is entering the pit (plus timings would be great)
2. In the ideal world – the proportions of water vs urine vs solids entering the pit (and at what time)

I guess the time is useful because maybe through some manipulation of the data I can start to link up a ‘use’ with a volume e.g. if the ‘switch’ which say something passes is activated 3 times in one minute – this could be attributed to one user (the distinction between ‘uses’ and ‘volume’ is difficult in my mind.
This would ideally be transmitted via phone or have collectable data. No mains electricity available.

Any help greatly appreciated – this data will hopefully enable the NGO to work more effectively for provision of sanitation. Keep in mind the basic and rough conditions in a Ugandan toilet pit!

Nicola

p.s. I am not being payed for this work - just trying to help them out.
p.p.s I have some ideas but this post was already too long so if someone joins me for a chat about this I'll explain my initial thoughts.
p.p.s please be patient - i have no electronics background - civil engineer

 

[KJ6EAD]

An array of capacitive proximity sensors, a strain guage and an infrared thermal sensor attached to a fixed length of pipe may provide the data you need but it won't be cheap.

 

[NicNakNoe]

Yes - that is a massive constraint worth mentioning. They work in dollars and want something <$200 at very most...with closer to $50 being an aim for the simple one. Can you explain why you think the combination of those would work?

 

[KJ6EAD]

The capacitive sensors should allow you to get a reasonable measure of the solid portion of the sample standing higher than liquids in a sloped pipe, the infrared sensor will mainly serve as a use counter by seeing the thermal edges of the water slug and the strain gauge will give a relative weight of the sample. Some of these sensing methods may seem redundant but if you want good data, you need to correlate the input from multiple sources. Testing and calibration would not be trivial.

 

[OLIVE2222]

Hi,

Because of the massive constrains having only one logger system at the pipes collector end can ease to keep the budget low.

Dishwasher have system to measure the waste quantity, can be a start.
Also why don't use a translucide pipe, a web cam and a cheap, yet powerfull CPU board like the BeagleBoard black http://be.mouser.com/ProductDetail/...wNMONnDuAbTwbrIHVw4R/%2bth5Q2M/X2Gs60muroNw== yes still not enough for the urine. Maybe a reactive can be added to the water to color it, just ideas.

Olivier

 

[NicNakNoe]

Mmm the thoughts of calibrating are interesting for this - so many unknowns.

At what point to do you think a strain gauge could be inserted in a way that it wouldn't get soiled?

The combination of the capacitor and IR makes sense to me...is capacitance through a plastic pipe something I can do?

Apologies for the basic level of these questions.

I'll have to do a bit of a hunt about this dishwasher option and get back to you!

 

[duke37]

Perhaps the resistivity of the liquid could give an indication of urine content. Electrodes in the liquid would get contaminated but it may be possible to measure using inductance.

 

[jpanhalt]

Urine specific gravity varies form about 1.000 to1.030. Moreover, solutes in stool mixed with it would, I believe, make a simple conductivity measurement meaningless for calculating the proportion of urine.

Since the primary source of urea excretion, which is produced as a waste product from amino acid metabolism, is in the urine, one might measure the amount of urea to determine very roughly the amount of urine.

Of course, diet affects the amount of urea excreted. On a Western diet, one might expect an average adult to excrete about 27 g per day dissolved in 1.5 to 2.0 L of urine. (https://www.inkling.com/read/medical-physiology-boron-boulpaep-2nd/chapter-36/urea). Thus, if you knew the average diet or did a calibration, you might get a very rough estimate of the volume of urine by measuring the total amount of urea in the waste stream. With the budget and other constraints you mention, I do not think getting any meaningful estimate of the volume of urine would be possible.

Glucose and bacteria are in stool (http://www.ncbi.nlm.nih.gov/pubmed/2169303), but not typically in urine.One might consider either of them as a marker for the proportion of stool in the effluent, but again, there are wide variations between individuals and high dependence on diet. Also, any delay in analysis would lead to changes in composition. I don't think that would be practical in the setting.

As for measuring total volume, one could use a tip bucket or similar device for measuring a number of known aliquots, e.g, any holding tank that is emptied at various intervals when full.


John

 

[KJ6EAD]

All of the sensors I mentioned could be on the exterior of a typical ABS pipe. The strain gauge would be between the bottom of the pipe and a stationary stanchion to measure the downward deflection of the pipe.