Master’s thesis proposal spring 2018 – Urine drying – technical evaluation of pilot system

In the sanitation sector, there is growing recognition that we are in urgent need of a new paradigm that transforms the way in which we handle, treat and recycle human wastes in our environment. Every year, each of us excrete 550 kg of urine which contains 4 kg nitrogen, 0.4 kg phosphorous, & 1 kg potassium; nutrients that can be recovered and recycled back to agricultural areas where they can potentially replace chemical fertilisers. Instead, these nutrients are flushed down in our toilets using potable water. Urine, however is a very dilute fertiliser and is in fact, mostly water (95%).

The Environmental Engineering Group at SLU has developed an exciting technology that converts liquid urine, a wastewater stream into a high-value, dry fertiliser. The technology, alkaline dehydration, involves adding urine to an alkaline material such as wood ash or lime, after which it is dried using a stream of air which removes water from the urine. The alkaline material however retains most of the urine nutrients.

The City of Malmö, VA SYD and Sweden Water Research are also working on urine separation as a solution to increase nutrient recovery from municipal wastewater.

The aim of this Master’s thesis project is to evaluate the function of a pilot scale urine drying system implemented in offices regarding their conservation of plant nutrients and dehydration rate in relation to the design and the drying media.

Several new toilet systems will be installed. In the project these systems will be monitored regarding evaporation rate and nutrient conservation. The monitoring of the system is based on observations and chemical modelling.

The project will be a part in the development of a new sanitation system that are optimise with the focus on nutrient recovery and function of the drying bed in a standard toilet room.

Spring 2018

Björn Vinnerås, associate professor, SLU, Uppsala (
David Gustavsson, research leader, Sweden Water Research (