Epsilon Archive for Student Projects

Abstract

Urine, containing nitrogen (N) in the valuable form of urea, has a high fertilizer potential if it
is dehydrated and the nutrients are concentrated. However, urea is not only a valuable N
source for plants but also for microbiota which possess a highly efficient urease enzyme to
degrade urea into volatile ammonia (NH3). Since cross-contamination with microbiota, e.g. by
faeces, cannot be 100 % prevented, it was intended to find feasible options to inactivate the
urease enzyme and retain urea as N fertilizer in the urine. Therefore, faecal-based urease was
examined regarding its sensitivity towards heat and alkaline pH as single and combined
factors and depending on time of exposure. Potential approaches have been found to retain
urea in human urine with the aim to concentrate the nutrients in the urine by dehydration to
use it as a valuable fertilizer for plants. The results of this study emphasize the need to
inactivate the urease enzyme in urine-drying systems and proved the high stability of urease at
high temperatures. Although this study confirmed that urease show a high activity at 60 °C,
has a high stability at high temperatures of ≥ 80 °C and partly regains its activity after being
exposed to pH 12, efficient treatment options for urease inactivation were found. Particularly,
the inexistence of any urea hydrolysation after an exposure to a pH of 13 and the high success
of urease inactivation in the combined treatments of heat and alkaline pH give a direction
towards new system options.