Related Experiment Videos
Estimating the precipitation potential in urine-collecting systems
Kai M Udert1, Tove A Larsen, Willi Gujer
1Swiss Federal Institute for Environmental Science and Technology (EAWAG), Urban Water Management, P.O. Box 611, 8600 Dübendorf, Switzerland. udert@eawag.ch
Water Research
|May 20, 2003
Summary
Precipitation in urine-separating toilets can be predicted using a new computer model. This model helps understand how urea hydrolysis and water dilution impact mineral scale formation, crucial for preventing maintenance issues.
Area of Science:
- Environmental Engineering
- Water Chemistry
- Materials Science
Background:
- Precipitation in urine-separating toilets (NoMix toilets) and waterless urinals leads to significant maintenance challenges.
- This precipitation can substantially decrease soluble phosphate content in collected urine.
Purpose of the Study:
- To develop and present a computer model for estimating precipitation potential (PP) in urine-collecting systems.
- To predict the composition and mass concentration of precipitates using the developed model.
Main Methods:
- Utilized a computer model to simulate the effects of urea hydrolysis and varying flushing water volumes on urine precipitation.
- Investigated the influence of microbial urea hydrolysis (ureolysis) and mineral limitations (calcium, magnesium) on precipitate formation.
- Analyzed the impact of urine dilution with tapwater and rainwater on precipitate composition and concentration.
Main Results:
- Confirmed that microbial ureolysis triggers precipitation, with calcium and magnesium limiting the amount of precipitates.
- Identified struvite and hydroxyapatite (HAP) as primary precipitate compounds, with calcite forming at high tapwater dilution.
- Demonstrated that increased flushing water volume reduces precipitate mass concentration, thereby diminishing blockage risk.
- Showed rainwater flushing is more effective than tapwater, which causes significant phosphate fixation.
Conclusions:
- The developed computer model accurately predicts precipitation potential and mineral composition in urine-collecting systems.
- Urea hydrolysis is a key driver of precipitation, and dilution significantly impacts the severity of scale formation.
- Findings provide valuable insights for designing and maintaining efficient urine-collecting systems, optimizing phosphate recovery, and preventing blockages.