My current project 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 1m length plastic pipe (angle is variable but can be fixed for a trial ~ 40 degrees from horizontal). I want to measure: 1. Number of users and what volume they contribute to the pit (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) The NGO would prefer if the device is something which fits on/around the pipe i.e. minimum interference..plus keeps it safe. The timing of events is useful (but not compulsory) because (in theory) through some manipulation of the data I can start to link up a ‘use’ with a volume e.g. if a trigger which says 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. It would allow analysis of peak usage times in the day. 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! From the very basic mechanical options to advanced electronics...all ideas welcome. Budget strictly <$200 (preferable $50 for a basic logger counting uses) 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.p.s please be patient and clear- civil engineer speaking here ;-)
I think you would have to use a single board computer or microcontroller and a strain gauge for weight, with a sensor for detecting a height above where fluids would be expected. Batteries would be a problem, sealing could be a problem, keeping sensors clean would be a problem. Detecting water vs urine vs 'other fluids' (multiphase) would also be hard. I think you would have to make some assumptions about water used per use. Alternatively mechanical counters are cheap, a tension spring above the pipe and a mechanical counter below, might work.
Immediate thoughts that enter my head. Do you have power at the site? Is the site accessible? If it is in Uganda and rural, you may have to use a solar panel. You need to get advise from the medical side - how to handle stuff like eColi etc, also talk to waste management companies - many do portable toilelts - there would be similarities. I would build the apparatus 1st (in a modular design), then ship it to the site and fit it. This way you are not testing anything on-site, only taking measurements. Also who wants the information, and what do they want to do with it? regards Patrick
another thought, this kind of measurement can be done accurately using Coriolis mass flow measuring devices. There is no intervention in the fluid being measured. It would be simple to attach a logging device and then you would have to analyse the data mmm quite a bit of work here, and of course you would need power. A mechanical system like a load cell or spring may be more tricky - someone must have done this before (civil engineering)- I would suggest a thorough literature survey.
For under $200 you might get a basic counter of uses, but that's about it... any volume measurement or data transmission is going to cost a lot more. If you can measure the total volume after, say, a week or month of use you can probably get a pretty good average per use so no further measurement should be needed. A capacitive ring sensor around the pipe might suffice. You'd want to ignore repeated detection within some period of time. Or you could count the users entering rather than any direct measurement on the pipe.
$50 USD is about £30.50 GBP, in the UK that is just about enough for a mechanical counter and a spring. For a mechanical counter that would need someone to phone in the count, probably with many false counts. You couldn't get a frame fabricated to mount them to in the UK for that money, maybe for $200. https://drive.google.com/file/d/0BzZ74AapicmQMjdqT3F2a0NOVWM/edit?usp=sharing
