Technical Evaluation of Urine Drying in Pilot Scale – a Field Experiment in Finland

The master thesis, Technical Evaluation of Urine Drying in Pilot Scale – a Field Experiment in Finland (author Caroline Karlsson), is now published at the DiVA portal. In this interesting master project the urine drying technology was tested for the first time in field conditions at a military base in southwestern Finland. For more information: http://www.diva-portal.org/smash/record.jsf?pid=diva2:1374211

ABSTRACT

Of all global processes that regulate the earth system, the biogeochemical flows of
nitrogen (N) and phosphorus (P) are the most affected by human activities. Inert forms of
N and P are converted into reactive forms that are dispersed in the environment, causing
eutrophication and affecting marine ecosystems. The majority of the reactive N and P are
used for the production of mineral fertilizers. An alternative way of producing fertilizers
is to recycle nutrients from the sewage. A technology that reuses nutrients in urine is
alkaline urine drying. The technology stabilizes urea with an alkaline drying medium
and concentrates the nutrients by evaporating the water in urine. The end-product is a dry
fertilizer in powder form.

In this master project, the alkaline urine drying technology was tested for the first time in
field conditions. A system for urine drying with the capacity to evaporate
40 kg of urine day-1 m-2 was constructed and integrated into an existing dry sanitation
system for use over a period of three months. The master project evaluated the system
for 13 days of the 3 months. The results showed that 24 kg of urine was collected in the
system, significantly less than what the system had been designed to dry. Furthermore,
the results showed that the system functioned smoothly recovering 97 % of the urine-N
in the end-product. The nutrient content in the end-product and the dry matter of the
end-product was low due to the low amount of urine that was collected.

However, the system had the potential to dry much larger quantities of urine. If the
system would have been operated to function at full potential (drying 40 kg of urine
day-1 m-2) the N- and P-content in the end-product would be much higher than that
observed during the 13 days. Furthermore, the system if operated at lower temperatures
has the potential to recover more N.

The system’s energy consumption was high, as the system had a continuous energy
consumption. In comparison with the conventional wastewater treatment and the
production of mineral fertilizers, the system has a high energy consumption, but
compared to an incineration toilet, the system’s energy consumption is equivalent. In
order to reduce the energy consumption, automatic control could be implemented so that
the energy is switched off when the system is not used. The system’s energy
consumption may also be set in relation to the problems that today’s systems for food
production and sanitation entail. Unlike the aforementioned systems, the urine
dehydration technology does not consume drinking water, it enables recycling of
nutrients as well as a reduced impact on aquatic life.”

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