Long-term observation of a urine-collection system at Eawag

A NoMix system with 37 urine-diverting toilets, 7 waterless urinals and 2 collection tanks is installed in the new Eawag main building 'Forum Chriesbach'. The system allows gaining full-scale experience with urine separation in an office building for 150 employees. Since the opening of the building in 2006, the toilets, pipes and tanks have been monitored continuously.

Clogging by precipitates is a known problem of NoMix systems, therefore, several precautionary measures were taken: all pipes have wide diameters, the slopes of horizontal pipes are steeper than usual, the urine pipes of the NoMix toilets have been flushed regularly (once a month) with citric acid and soft rainwater has been used for toilet flushing. Thanks to these measures, no major clogging problems have occurred in the first four years of operation.

One type of NoMix toilets (Roediger) and waterless urinals from five different companies (Keramik Laufen/Geberit, Urimat, F.Ernst Ingenieur, Hellbrok, Uridan) are installed in 'Forum Chriesbach'

Chemical analysis of the collected urine shows that dilution with flushing water is low: concentrations of ions such as chloride, sodium or potassium are similar to literature values for fresh urine. As expected, phosphate concentrations are lower than in fresh urine due to spontaneous precipitation of struvite and calcium phosphate.

One of the two urine collection tanks in Forum Chriesbach (photo: Kai Udert)

In addition to phosphorus, nitrogen concentrations are also much lower than in fresh urine (by more than 50%). Gas measurements at the roof opening of the rising main revealed that the nitrogen loss is caused by ammonia volatilization. The load of gaseous ammonia in the outgoing air follows a pronounced diurnal cycle, which shows that most of the ammonia volatilizes in the rising main and not in the collection tank.

In collaboration with Wst21

Literature

Goosse P., Steiner M., Udert K.M., Neuenschwander W. (2009) NoMix-Anlage. Erste Monitoringergebnisse im Forum Chriesbach. Gas Wasser Abwasser 7/2009, 567-574 (in German).

Lienert, J., Larsen, T.A., (2007) Pilot projects in bathrooms: a new challenge for wastewater professionals. Water Practice & Technology 2 (3).