Eawag, the Swiss Federal Institute of Aquatic Science and Technology, recently developed a new and highly efficient composting toilet called Blue Diversion. Human waste has significant value, since it can provide fertilizer and phosphorus and the Blue Diversion toilet is able to successfully harvest both. These byproducts can also be sold at a profit, so this toilet does more than just provide water efficiency or off-the-grid-living.
The goal for creating the Blue Diversion Toilet was bringing sustainable and affordable sanitation services to urban slum neighborhoods in low-income countries. The toilet is designed so that it is capable of recovering all the resources that go into it, and can operate independent of a grid.
The Blue Diversion toilet works on the core principle of first separating the urine from the feces into different containers. After that, water is added which can be used for both personal hygiene and for cleaning the toilet bowl. The water, which is already less contaminated than it would be in a regular toilet, is then chemically treated and repurposed.
As a first step, the water is biologically treated in the toilet itself. Pathogens are removed via the process of water passing through a specially designed membrane. This passage of water is driven by gravity and requires no additional mechanics to work. The next step in making the water fit for repurposing is production of chlorine by solar-powered electrolysis. This process stops the re-growth of undesirable bacteria in the recycled water, which is of drinking quality. The toilet needs a total of 11.5W of electrical energy to function, but this energy is provided by a 60Wp solar panel.
The fact that the urine and feces are harvested separately makes it much easier to process them and turn them into fertilizer and phosphorus. Here is where the Blue Diversion toilet becomes more than just a toilet. The collected feces and urine can be transported to an off-site resource recovery plant, where they are turned into fertilizers that can be sold at a profit.
The company is currently in the process of developing a second toilet, which will have the capability of creating all the useful byproducts on-site. This toilet is called the Autarky Toilet and the user interface of this toilet will be the same as the Blue Diversion one, but the treatment of the byproducts will differ. The company is currently developing a special chemical urine stabilization method, using hydrated lime, which will yield a liquid phosphorous nutrient solution. After further drying this solution will become a dry phosphorous fertilizer end product. The volume of urine following this process will be further reduced though a special evaporation method.
For the Autarky Toilet, the feces treatment technology and the thermal feces dewatering and drying followed by combustion is still being developed in cooperation with other grantees of the Reinvent the Toilet Challenge, which is a project funded by the Bill & Melinda Gates Foundation.