Mimicking and Inhibiting Urea Hydrolysis in Nonwater Urinals

Abstract

Nonwater urinals are critical in the implementation of building-scale water conservation and urine diversion systems. However, because of the composition of urine and the prevalence of the urease enzyme that hydrolyzes urea, minerals readily precipitate in nonwater urinals and pipes. This leads to clogging, malodor, and possible replacement of nonwater urinals with flush urinals. Accordingly, the goal of this research was to provide an improved understanding of the urea hydrolysis process in nonwater urinals to benefit water conservation and phosphate recovery efforts. Acetic acid addition was used in nonwater urinals to inhibit the urea hydrolysis reaction by lowering the pH, thereby making the precipitation of calcium- and magnesium-containing minerals less favorable. Of the acids tested, 2.5 mL of 2500 mequiv/L acetic acid added after every urination event was able to inhibit urea hydrolysis in synthetic urine and real urine as indicated by the pH and conductivity of the effluent urine. Acid addition also allowed for 43% more phosphate recovery via struvite precipitation in the acetic acid addition synthetic urine than the synthetic urine with no acid addition.

Water and Wastewater Building CPS: Creation of Cyber-Physical Wastewater Collection System Centered on Urine Diversion

“…The real time measurements were able to capture the increase in pH and conductivity as urine rested in the collection pipes between urination events. Previous studies were only able to show the upward overall trend in measurements, as opposed to the gradual increase in the measurements before the measurements decreased as fresher urine entered the pipes [14], [24].…”

“…Three solutions were delivered to the urinal testbed to mimic urine diversion systems: (1) synthetic fresh urine, (2) urease solution, and (3) acetic acid to the urinals. The synthetic fresh urine was made following the recipe presented in Saetta & Boyer, 2017 [14]. Its major components include 500 mM as N of urea, 20 mM of phosphate, 4 mM of calcium, and 4 mM of magnesium.…”

“…Prior research into urea hydrolysis in nonwater urinals was not able to show the reactor characteristics that the CPS was able to illuminate. Saetta and Boyer, 2017 concluded that a study on nonwater urinal flow dynamics was necessary to illuminate the reactions that occur as urine travels through collection systems [14].…”

“…Implementation of the CPS allowed for enhanced data acquisition, as prior experiments were only able to see the reaction occurring at a lower resolution. Saetta and Boyer, 2017 was only able to show measurements taken every 30 min, which was not specific enough to determine the flow characteristics of the nonwater urinals [14].…”

Life Cycle Assessment of Urine Diversion and Conversion to Fertilizer Products at the City Scale

“…It was assumed each flush would provide enough acetic acid to neutralize the alkalinity of urine, which is described in equation 22. The pH of fresh urine is assumed to be 6.2, [27][28][29] and the concentration of ammonia and phosphate were determined from the nutrient composition of urine. It is assumed that nutrients in potable water were negligible compared to urine.…”