Inactivation of the urease enzyme by heat and alkaline pH treatment : retaining urea-nitrogen in urine for fertilizer use

Sammanfattning: 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.