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Modular Sanitation System

Problem Statement // 

There is no way for dense urban areas in Nairobi, Kenya to have proper sanitation due to the lack of sewage systems and a small amount of open land. The willingness to pay for proper sanitation is low because it is the user themselves or the landlord that will have to pay for the cost and maintenance of any proper solution. Design a sanitation module that satisfies the requirements of a modern-day human and falls within strict constraints. 

Requirements  // 

Must be affordable (total less than around $100 USD 

Little / Low Maintenance and no inputs to keep the system running 

Easy assembly & small amount of parts; all parts must be easily replaceable 

Problem Space Ideation // 

I went out and talked to a TON of people in the sanitation space - from people working at companies that were creating solutions to everyday local Kenyans, all the way up to the landlords and around to sewage companies. I learned everything you could need to know about the space (does not sound like an appealing search but it was necessary). 

The major problem was that with current solutions being pit-latrines, it was too expensive to upkeep the cost of constantly emptying it. Then, I thought about the fact that waste is 90% water... so how about we just get rid of all that weight at the source and only remove the 10% that needs to be removed. So, the problem I was now solving was: how do you treat waste on-site so that it is portable and safe for people to remove? 

Solution Space Exploration // 

When I came into the project, there was a "left - over prototype that they were trying to make work with this design. It was involving a vertical chain mechanism that tried to eject waste into a drying mechanism... but that was not working with humidity levels in Kenya. So, I started to do two things simultaneously -- (1) do small improvements to the current system and (2) completely redesign a new mechanism. 

Task (1) was a lot of studying of materials and new ways to beat thermodynamics. I was trying to remove humidity in levels with the highest humidity on the planet. I worked with active and passive airflows, ventilation systems, and materials that would absorb humidities.

 

Here is the first level prototype we were working with - you can see ventilation on the sides and the chain mechanism going up to a separate chamber ontop. 

IMG_4969.HEIC

Second Solution and Prototype 

This prototype had a lot of problems, and it eventually felt like my solutions were just becoming band-aids for problems that would continually come up. 

So, I sat there with an awesome colleague for 3 hours one day, toying with problems, a lot of geometry, space, and airflows to create this new prototype: 

Screen Shot 2022-09-28 at 2.19.11 PM.png

(Not Included in this version of the CAD) 

  • Scraper on the top left pulley to remove material 

  • Piping from the blue spout on the right side of the pulley 

  • Airflow fan on the upper left corner and ventilation in lower right corner 

To quickly explain how it works, it sits on top of an interface that will divert waste into feces and urine. The urine will be removed to the right side (not shown in the CAD) and the feces will be dried out passively through a series of belts. Belts will move at varying speeds depending on the time of day, humidity levels, and time of year (programmed with an Arduino). 

The driven pulleys were prototyped to be on 3 out of the 6 pulleys due to constraints in cost and materials- powered by 5kW motors with a solar module on top of the restroom. 

Side Note- the bottom 2 were chosen as places to have the pulleys because there was the highest mechanical advantage to pulling up the heaviest material (when it was wet) if that motor was placed in the bottom left corner. This is due to the lever arm that we would be getting from the taut belt. 

Dried material would accumulate in the green basket and have a holding capacity of about 6 months for an 8 person household. 

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