Urine nitrification robustness for application in space: Effect of high salinity and the response to extreme free ammonia concentrations

Urine nitrification is one of the possibilities for the future recovery of water and elements for soilless crop production in space systems. The start-up of artificial urine nitrification was conducted for over 85 days in a sequencing batch reactor (SBR). Two free ammonia (FA) incidents occurred, which gave the opportunity to demonstrate the impressive ability of nitrifiers to resist temporary inhibition by FA without long lasting adverse effects. The failures led to very high FA concentrations of 280 and 84 gN-NH3/m(3), respectively. Sludge was exposed to FA for 19 and 27 h. It was possible to restore nitrification with simple remedy actions (dilution and pH restoration). No inhibitory effects on the nitrification rate were seen after implementation of the remedy actions and the nitrification rate increased considerably (up to 300% of the pre-failure value) due to decrease in salinity. After a few days of normal operation and salt concentration, the nitrification rate returned to the pre-failure values in both cases.

Automated summary

The study demonstrates the impressive ability of nitrifiers to resist temporary inhibition by free ammonia (FA) and restore nitrification with simple remedy actions. High FA concentrations were successfully treated without long lasting adverse effects, leading to a considerable increase in nitrification rate.