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Real-Time Monitoring and Control of Urea Hydrolysis in Cyber-Enabled Nonwater Urinal System

Saetta, Daniella, Padda, Arsh, Li, Xiushuang, Leyva, Carlos, Mirchandani, Pitu B., Boscovic, Dragan, Boyer, Treavor H.
Environmental science & technology 2019 v.53 no.6 pp. 3187-3197
acetic acid, hydrolysis, mixing, models, monitoring, off odors, pH, regression analysis, urea, urination, urine, United States
This research used a cyber-physical system (CPS) to monitor and control the extent of urea hydrolysis in nonwater urinals. Real-time pH and conductivity data were used to control urea hydrolysis inhibition under realistic restroom conditions with acetic acid addition. Variable urination frequencies and urination volumes were used to compare three conditions that affect the progression of urea hydrolysis. Mechanistic and conceptual models were created to evaluate the factors that influence the progression of urea hydrolysis in nonwater urinals. It was found that low urination volumes at low frequencies created ideal conditions for urea hydrolysis to progress. Alternatively, high urination volumes at high frequencies created pseudo-inhibitory conditions because it did not allow for sufficient reaction time or mixing with older urine in the urinal trap. The CPS was used to control urea hydrolysis inhibition by two logics: (1) reactively responding to a pH threshold and (2) predictively responding to past measurements using four lasso regression models. Results from the control logic experiments showed that acid was added once per hour under low use conditions and once in a 4 h experiment for high use conditions. The CPS allowed for full control of urine chemistry in the nonwater urinal, reducing the conditions (i.e., clogging and malodor) that have led to the removal of nonwater urinals in the United States.