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Concentrated fertilizer production

Research Question: How can we reduce the volume of urine for efficient transport?

Dates: 2015-present

An adult typically produces 150 gallons (570 liters) of urine each year. This urine contains most of the fertilizer needed to grow a year’s worth of food, but its large volume makes it difficult to store and transport to farms where it can be used — particularly if urine is collected in cities far from agricultural areas.

A variety of strategies have been tried by other researchers for removing water from urine and reducing its volume to create a concentrated product. These include distillation, evaporation, freeze/thaw, and reverse osmosis. Reverse osmosis is the most energy efficient, but it has one major drawback: because the nitrogen in stored urine is largely in the form of ammonia, a portion of it is able to pass through the membrane instead of being retained in the concentrate.

The Rich Earth Institute acquired an 800-gallon-per-day marine reverse osmosis machine and began concentrating stored urine in early 2015. The process worked, but as expected roughly 20% of the nitrogen was passing through the membrane in the form of ammonia and being lost. Our ongoing original research focuses on new techniques to reduce the levels of ammonia in the urine to increase the effectiveness of reverse osmosis at concentrating all the available nutrients into the final fertilizer product.

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