Composting Toilets for Urban Sanitation

Sustainability Problem: Water/Waste

The sustainability problem:

  1. Problem:  In the next few decades, population growth will happen primarily in urban cities in Asia and Africa.  These cities may develop increasing slum-like conditions if there is not sufficient clean water resources, the funds to bring these resources to residents, and the political will and efficacy to implement large scale centralized infrastructure projects.
  2. Solution: Composting toilets for urban sanitation,   Article:  http://www.sciencedirect.com/science/article/pii/S0956053X13004923
  3. There are many different potential designs for a composting toilet but in general, they do not rely on a centralized infrastructure for water and waste management.  Similar to flush toilets, composting toilets have a seat and drainage pipe.  But instead of being connected to a water system for flushing, the flush mechanism relies on gravity.  Only a small amount of water or foam is used to facilitate flushing or washing.  The user may be required to add a bulking agent (such as a cup of sawdust) after use to facilitate composting and prevent anaerobic reactions (which cause odors).  Waste is transported through the pipe to a storage container.  Excess liquid/urine may be drained off to the sewer system to reduce fermentation/smells.  Solid matter remains in the tank with the with the bulking agents where it is aerobically digested by bacteria until it becomes compost.  The storage container has a door for removing the compost.  Additional features such as a mixing arm and vent facilitate the breakdown of solid waste and reducing odors.  More advanced models use separate chambers in the storage container to separate fresh waste with fully mature compost to ensure that only safe product is removed from the tank.

Stakeholders:

    1. Consumers:  receive a middle class amenity for presumably lower lifetime cost (cost of unit, maintenance and future water fees), creates an end product (composting) that can be used in locally if needed.
    2. Local government:  reduces required investment in centralized water resources
    3. Suppliers:  can sell units and provide maintenance packages if consumers don’t want to empty their own compost.  Could potentially have a model where they receive compost back from consumers and further prepare it for resale.

Implementation:

In order for the technology to be adopted there are several barriers that need to be overcome:

      1. Building codes that are based on the assumption that toilets will be connected to a central water system will need to be revised.
      2. City waste management rules regarding the use of biomaterials should be updated with regards to safe vs unsafe human composting (as opposed to assuming that all human compost is unsafe).  For example, multi chamber models that separate fresh waste from mature compost prevent pathogens from fresh waste entering the mature compost.
      3. Affordable pricing plans need to be developed that would allow poorer residents to pay for their unit over a specified number of years rather than upfront due to the high cost of the units and the low income of the residents.
      4. Pilot programs in schools and public buildings should be used to demonstrate successful usage, better understand maintenance requirements and influence public perception as to the cleanliness of the technology.
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