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Article

Inhibition of Urea Hydrolysis in Human Urine for Resource and Energy Recovery: Pharmaceuticals and Their Metabolites as Co-Existing Anticatalyzers

by
Haoran Chi
1,2,
Minshu Chen
3,
Wei Yang
1,
Ya Li
1,
Shuhui Sun
1,
Hualin Wang
1,
Xuejing Yang
1,2,*,
Michael R. Hoffmann
4 and
Lei Guo
1,3,4,*
1
National Engineering Laboratory for Industrial Wastewater Treatment, East China University of Science and Technology (ECUST), Shanghai 200237, China
2
State Key Laboratory of Chemical Engineering, East China University of Science and Technology (ECUST), Shanghai 200237, China
3
Department of Civil Engineering, University of Arkansas, Fayetteville, AR 72701, USA
4
Linde Laboratories, California Institute of Technology, Pasadena, CA 91125, USA
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(7), 630; https://doi.org/10.3390/catal15070630 (registering DOI)
Submission received: 20 May 2025 / Revised: 22 June 2025 / Accepted: 23 June 2025 / Published: 27 June 2025
(This article belongs to the Special Issue Enzyme Catalysis: Innovations and Applications in Sustainable Chemistry)
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Abstract

Urine, which has a high concentration of urea, can be used as a sustainable resource for nutrient recovery and sustainable energy. However, urea undergoes hydrolysis, catalyzed by urease, generating ammonia and carbon dioxide. As ammonia is released during hydrolysis in stored urine, the pH rises progressively until the pKa of ammonium is reached (i.e., 9.3). At elevated pH levels, struvite and other related precipitates are formed. These reactions lower the efficiency of ammonia and urea nitrogen recovery and often cause scaling, pipe blockage, and odors. Herein, we explore an approach to stabilize urea, using pharmaceuticals and their metabolites that are commonly present in human urine. Based on a survey of the urease inhibitory effects of twenty-three pharmaceuticals and metabolites, we determined that the polyphenolic and disulfide-containing compounds had the highest urease inhibition efficiency. Specifically, outstanding inhibitors include catechol (CAT), hydroquinone (HYD), and disulfiram (DSF). Furthermore, when added to urine, these compounds resulted in the retardation of urease-catalyzed hydrolysis, leading to longer-term urine stabilization upon storage. Reaction mechanisms for urease inhibition by polyphenolics and disulfiram are proposed. Evidence is provided that pharmaceutical metabolites can stabilize urea and thus could lead to a sustainable method for nitrogen nutrient recovery from stored urine.

1. Introduction

Human urine is a valuable and sustainable nitrogen nutrient resource in the form of urea. Although urine only accounts for about 1% of domestic wastewater by volume, it constitutes about 80% of the total nitrogen loading [1,2]. As an ideal carrier of hydrogen with a high energy intensity, the thermodynamic equilibrium potential of H2 production in urea-assisted water electrolysis is only 0.37 V versus that of reversible hydrogen electrodes (RHEs), which is much lower than that of traditional water splitting (1.23 V) [3]. From distributed human excrement to scalable energy precursors, urine source separation systems need to be developed and tested [4,5,6,7]. The practical implementation of such systems, however, faces several challenges, such as a low nitrogen recovery efficacy and severe pipe blockage problems [8]. Although urea is quite stable in aqueous solution (e.g., t1/2 = 3.6 y) [9], it can be readily hydrolyzed by urease excreted by fecal microbes and generate ammonia and carbon dioxide (Equation (1)). A series of long-term experiments conducted by the Swiss Federal Water Science Center (EAWAG) showed that the urea hydrolysis rate was 2770 g N m−3·d−1 for untreated urine [8]. Liu et al. also reported that urea hydrolysis was complete after 84 h, as indicated by a stable pH in the solution [10]. The hydrolysis of urea leads to an increase in the pH of the stored urine, usually resulting in the formation of precipitation, scaling, and malodorous organic compounds. In addition, ammonia can be lost via volatilization from collection tanks during long-term storage. Current strategies for urine stabilization include pH adjustment [11,12,13,14,15,16,17,18], chemical and electrochemical oxidation [19,20,21,22], volume reduction [23,24], thermal treatment [25], and the addition of urease inhibitors [14,26]. However, these methods often require the external input of energy or chemicals.
C O ( N H 2 ) 2 + H 2 O → Urease 2 N H 3 + C O 2
Urine source separation systems can also lead to control over micropollutants, such as pharmaceuticals and their metabolites. Pharmaceuticals and their metabolites often lead to antibiotic drug resistance [27], which has an adverse influence on aquatic ecosystems and human health [28,29,30,31]. Approximately 64% of the active ingredients in pharmaceuticals ingested by the human body are excreted in urine [1]. Urine often has 100–500 times higher concentrations of pharmaceuticals and their metabolites than those measured in freshwater [32,33,34,35,36,37]. Thus, urine is a major source of pharmaceutical micropollutants. Traditionally viewed as contaminants, these pharmaceutical-derived micropollutants pose challenges to environmental safety. However, their inherent bioactivity opens up opportunities for beneficial reuse. Specifically, repurposing them as urease inhibitors represents a promising strategy of waste valorization—transforming unwanted residues into functional stabilizers for source-separated urine. For example, catechol and hydroquinone are common urinary metabolites, which are detected in human urine at ppm levels [38]. While electrochemical treatment can directly remove micropollutants, the treatment selectivity can be easily compromised when other organic pollutants dominate in the wastewater [39,40]. On the other hand, alternative treatment processes, which include nanofiltration and adsorption, are often used to concentrate micropollutants for further treatment [41,42,43,44,45].
In this study, we explore the impact of pharmaceuticals and their metabolites as urease inhibitors and evaluate their potential to stabilize urine. Twenty-three pharmaceuticals and their metabolites were examined for their urease inhibition performance. Polyphenolic and disulfide-containing compounds were identified as strong inhibitors, and their inhibitory efficiencies were systematically investigated under a wide range of urine solution conditions. Furthermore, viable mechanisms for non-competitive inhibition pathways to block access to the active site of urease via the covalent attachment of the inhibitors were proposed. This work provides a new perspective on the treatment of urine with source separation systems and the role micropollutants play in this.

2. Results and Discussion

2.1. Survey of Urease Inhibition Efficiencies of Pharmaceuticals

Twenty-three pharmaceuticals and metabolites commonly detected in human urine were screened to determine their urease inhibition efficiencies. As presented in Figure 1, catechol (CAT), hydroquinone (HYD), disulfiram (DSF), and 1,2,4-benzenetriol (BEN) were shown to prevent up to 97% of urine hydrolysis. Acyclovir, metoprolol tartrate, and muconic acid showed inhibitory efficacies of over 50%, while emtricitabine, zidovudine, 4-acetamidophenol, diclofenac, propranolol, atenolol, methyl diethyldithiocarbamate, and ibuprofen had inhibition efficiencies ranging from 10 to 50%. Malonic acid, abacavir, trimethoprim, caffeine, 4-chlorobenzoic acid, lamivudine, carbamazepine, and sulfamethoxazole were ineffective in preventing urea hydrolysis. The shared features of the most effective inhibitors (i.e., CAT, HYD, DSF, and BEN), were the presence of a polyphenolic or disulfide moiety in their chemical structures (Table S1). Thus, more detailed investigations of their urease inhibition capabilities were carried out.

2.2. Long-Term Urine Stabilization Abilities of Pharmaceuticals and Metabolites

The longer-term urine stabilization capacities of CAT, HYD, BEN, and DSF were studied (Figure 2). In the control experiments without pharmaceuticals or metabolites, the ammonium concentration rapidly reached 677 mg/L and continued to increase over the entire course of the experiment, reaching an ammonium concentration of 8045 mg/L at 15 day. In contrast, when CAT, HYD, BEN, and DSF were added into the solutions with their final concentrations set at 1 μM (i.e., much lower than typical concentrations found in human urine) [38,46] approximately one third of the urease inhibition efficiency was obtained. With the concentrations of the pharmaceuticals and metabolites raised to higher levels (0.05 mM and 1 mM), significant urine stabilization could be achieved. As shown in Figure 2, after 15 days of incubation, 1 mM of CAT, HYD, BEN, and DSF could achieve relatively high urease inhibition efficiencies of 98.3%, 90.6%, 97.6%, and 82.4%, respectively. In the case of CAT and BEN, the hydrolysis of urea was inhibited to a large extent. These experiments show that certain pharmaceuticals and metabolites have the potential for long-term urine stabilization in urine source separation systems.

2.3. Influence of pH, Phosphate, and Salinity on Pharmaceuticals’ Urease Inhibition Efficiency

Urine effluents may have a wide range of pH values, variable buffering capacities, and ionic strengths. The effects of variations in these key parameters on the efficacies of CAT and DSF, given their high urease inhibition efficiencies, were evaluated, since they may influence the catalytic activity of urease (Figure S2) over the course of urine storage [23,47,48,49]. Based on the results presented in Figure 3, it is clear that CAT is an effective urease inhibitor over a wide range of pH, buffer capacity, and salinity conditions. However, the inhibitory effects of DSF were more sensitive to changes in pH. As the pH increased from 6 to 7, 7.55, and 8, the urease inhibition efficiency of DSF increased from 27.8% to 47.9%, 85.9%, and 97.6%, respectively. Variations in the total phosphate and NaCl concentrations had less of an impact on the urease inhibition by DSF (i.e., inhibition efficiencies ranging from 75% to 92%). It is quite clear that CAT is an excellent urease inhibitor over a wide range of solution conditions, whereas DSF is more effective for urine stabilization at a higher pH.

2.4. Impact of Water Matrix Composition on Urease Inhibition Efficiency

Urease inhibition by CAT and DSF was investigated in a range of more complex synthetic water matrices, namely, urea solution, fresh urine, dialysis fluid, and partially hydrolyzed urine, to mimic a wide range of possible conditions. In addition to CAT and DSF, HNO3 was included in these experiments as a urease inhibitor [14]. As shown in Figure 4, both CAT and DSF had significant inhibitory effects (ranging from 85 to 99% inhibition efficiencies) in urea solution, fresh urine, and dialysis fluid. In partially hydrolyzed urine, urea hydrolysis did occur, but a significant amount of urea remained (inhibition efficiency varied between 36 and 41%) after treatment. With CAT and DSF set at a concentration of 1 mM, positive inhibition effects in various water matrices were found. In contrast, HNO3 at millimolar levels had a high urease inhibition efficiency only in fresh urine, whereas it had little to almost no inhibition of urease in the urea solution and dialysis fluid. In the partially hydrolyzed urine, millimolar HNO3 actually accelerated urea hydrolysis instead. This is due to the fact that acidification with HNO3 shifted the solution pH toward the optimal pH for jack bean urease activity, since the water matrix composition had a measurable buffering capacity. Therefore, to achieve effective urine stabilization, the addition of strong acids at high concentrations to inactivate urease is required [14]. In comparison, millimolar concentrations of pharmaceuticals and metabolites can inhibit urease.
While synthetic urine provides a controlled system for mechanistic studies, real urine samples exhibit greater complexity due to microbial diversity, dynamic enzymatic activity, and variable organic/inorganic compositions. We acknowledge the need for future works to further validate these findings in real urine matrices, accounting for microbial community dynamics and long-term storage effects. Such studies would further bridge the gap between laboratory-scale observations and practical applications in urine source separation systems.

2.5. Mechanism Study of Urease Inhibition for Phenol and Disulfide Functionalities

Urease inhibition mechanisms for the inhibitors CAT, HYD, BEN, and DSF were explored based on the functionalities in their chemical structure: polyphenolic and disulfide moieties. Jack bean urease has a dinuclear nickel center at its active site, in which one Ni center binds and activates the substrate and the other Ni center binds and activates water [50,51,52]. Urea enters the active site cavity when the mobile flap is open [53,54,55]. Urease inhibition may occur due to (1) competitive inhibition, where the inhibitors have a similar chemical structure with urea (e.g., hydroxyurea) or they have strong chelating effects that can compete with urea for Ni binding [56,57]; or (2) inhibition occurring non-competitively, in which the inhibitors impact the mobile flap such that the substrate (i.e., urea) cannot readily access the active site [58,59].
The polyphenolic reagents BEN, HYD, and CAT along with 1,2,3-benzenetriol, which is an isomer of BEN, were probed initially, as shown in Figure 5. The results confirmed (Figure 5b) that HYD and CAT were efficient urease inhibitors at a concentration of 0.05 mM and resulted in over 95% inhibition of urea hydrolysis. However, BEN and 1,2,3-benzenetriol were found to be less effective urease inhibitors. For example, 1.0 mM of 1,2,3-benzenetriol had a 68.9% efficiency. Furthermore, the inhibition efficiency dropped to 44.8% at a concentration of 0.05 mM. It is previously proposed that aromatic hydroxylated compounds can inhibit the catalytic activity of urease via a radical-based reaction [52]. HYD and CAT are efficient urease inhibitors since they readily react with αCys322 in the active site of urease. In contrast, BEN and 1,2,3-benzenetriol are less effective urease inhibitors since their access to the urease active site is partially impeded due to steric hindrance coupled with additional electronic effects due to the presence of a third hydroxyl group on the dihydroxyphenol ring.
In the case of the inhibition by DSF, the disulfide moiety is reported to react with αCys592 at the active site by immobilizing the flexible flap [60,61]. Alternatively, DSF could inactivate urease by the competitive inhibition of active Ni sites. To further elucidate the mechanism of the inhibition, DSF was added to the urease-spiked urine solutions, producing an 80.6% inhibition of urea hydrolysis. A series of monothiol compounds, namely, L-cysteine (CYS), dithiothreitol (DTT), and 2-mercaptoethanol (ME) (Figure 5c), were added to the urine solution along with DSF. As shown in Figure 5d, the addition of CYS and DTT along with DSF resulted in near-complete urea conversion. In comparison, the combination of DSF and ME allowed for 50% of the urea to be hydrolyzed. This impact is most likely due to the additional thiol groups presented in CYS, DTT, and ME that compete with αCys592 at the active site pocket to react with DSF (Figure 5e). Since thiol groups from these compounds are more accessible than the αCys592 group of urease, DSF will preferentially react with these thiols, allowing urease to remain catalytically functional. ME did not fully block DSF’s inhibition towards urease, which was probably due to the fact that ME itself was also an inhibitor of urease [62]. DSF, CYS, DTT, and ME all have thiol groups that can bind with Ni; however, urease remained active in these experiments. Thus, DSF’s urease inhibition capability is most likely due to the disulfide moiety reacting with αCys592 at the active sites and competitive inhibition is a less likely pathway for urease inhibition for DSF. This conclusion can also explain the phenomenon that the inhibition efficiency of DFS clearly depends on pH (Figure 3c), as thiol–disulfide exchange reactions are also pH-dependent [63]. Thus, at a higher pH, Cys is deprotonated to form a thiolate, which is a better nucleophile than thiol, resulting in faster kinetics of the reaction of DSF with Cys, leading to the more efficient inhibition of urease.

3. Materials and Methods

3.1. Chemicals

Detailed information of the twenty-three pharmaceuticals and metabolites studied in this work is provided in Table S1. Urease (Jack bean) was obtained from Shanghai Yuanju Biotechnology Co., Ltd. (Shanghai, China) Urea and phosphates were supplied by Shanghai Taitan. (Shanghai, China) Ultrapure water with resistivity of 18.2 MΩ cm−1 was produced using purification system provided by the Eped Nanjing Yipu Yida Technology Development Co., Ltd. (Nanjing, China). Reagent-grade chemicals were used directly without further purification.

3.2. Instruments

The extent of urine hydrolysis was determined by measuring ammonium production versus time [64]. Ammonium was quantified using an ammonia gas-sensitive ion electrode (ISE, PNH3-1, Shanghai Lei Magnetic (Shanghai, China)). A calibrated PHS-3E pH meter (Shanghai INESA Scientific Instrument Co., Ltd. (Shanghai, China)). was used to determine pH in all experiments.

3.3. Concentration of Urease in Stock Solutions

Urease concentrations were estimated based on a previous report [8], in which urine was collected using “NoMix” toilets (urine-separating toilets developed by EAWAG) and waterless urinals. Urease was generated by microbes grown in the pipes and were flushed into the collection tanks. Urea hydrolysis rates measured in urine storage tanks were determined to be 2770 g N·m−3·d−1 [8]. Based on this value, synthetic urine and purified urease were employed to mimic urine hydrolysis in urine source separation systems. Hydrolysis rates of synthetic urine with different urease concentrations were calculated based on the concentration of ammonium as a function of time (Figure S1). The average urease-catalyzed hydrolysis rate of urea in synthetic urine was estimated to be 0.06944 g N·m−3·min−1 per mg/L urease. Based on this estimate, a urease stock solution of 30 mg/L was used in subsequent experiments to mimic the reported urea hydrolysis rates in actual urine storage tanks (3000 g N·m−3·d−1). Composition and properties of the synthetic urine, along with those of other urine solutions, are provided in Table 1.

3.4. Preliminary Screening of Pharmaceuticals and Metabolites’ Performance in Inhibition of Urease

The urease inhibition efficiency of each target pharmaceutical was determined using the protocol reported by Quastel et al. [65]. A phosphate-buffer solution (2 mL, 0.2 M, pH 7.55), a urease stock solution (1 mL, 30 mg/L, 305 U/mg), a pharmaceutical stock solution (1 mL, 10 mM), and ultrapure water (5 mL) were added to 10 mL vials and capped with polytetrafluoroethylene-lined lids. The mixed reagent solution was then incubated at room temperature (25 ± 1 °C) for 1 h. After incubation, an aliquot of the urea stock solution (30 wt%, 1 mL) was added to make sure the total volume was 10 mL. This mixture was subsequently incubated for an additional hour. Ammonium concentrations were measured with the NH3 ISE. Control experiments were carried out by replacing the respective pharmaceutical solutions with ultrapure water. Measurements were replicated three times. Inhibition efficiency was determined using Equation (2):
Inhibition   Efficiency   = N 0 − N   N 0 × 100 %
where N0 is the ammonium concentration in the control group, and N is the ammonium concentration in the presence of a target pharmaceutical compound.

3.5. Long-Term Urine Stabilization Experiment

In order to determine the long-term urine stabilization efficacy, pharmaceuticals and metabolites of various concentrations (1.0 μM, 0.05 mM, and 1 mM) were added into a mixture of urease solution (30 mg/L, 10 mL) and ultrapure water (10 mL). The solution was incubated for 1 h at 25.0 °C. Synthetic fresh urine (480 mL) was then added to the mixture. Experiments were carried out for 15 days at 25.0 °C, during which the concentration of ammonium was monitored.

3.6. Impact of pH, Phosphate Concentration, and Salinity on Pharmaceuticals’ Urease Inhibition Efficiencies

To examine the influence of pH on urease inhibition, urease (30 mg/L, 1 mL), pharmaceutical (1 mM, 1 mL), ultrapure water (5 mL), and phosphate buffer of different pH values (0.2 M, 2 mL, pH 6, pH 7, pH 7.55, and pH 8) were incubated for 1 h at 25.0 °C, followed by the addition of urea solution (30 wt%, 1 mL). The mixture was kept at 25.0 °C and concentration of ammonium was measured after 1 h. The impact of phosphate on urease inhibition was explored by adding together urease (30 mg/L, 1 mL), pharmaceutical (1 mM, 1 mL), ultrapure water (5 mL), and phosphate buffers (0.05 M, 0.1 M, 0.2 M, 0.35 M, 0.5 M, and 0.75 M, 2 mL, pH 7.55) and then incubating for 1 h at 25.0 °C. The initial incubation was followed by the addition of a urea solution (30 wt%, 1 mL). The mixture was held at 25.0 °C and concentration of ammonium was measured after 1 h. To determine the effects of salinity on the pharmaceutical’s inhibition of urease, the following solutions were prepared: urease (30 mg/L, 1 mL), pharmaceutical (1 mM, 1 mL), ultrapure water (5 mL), and phosphate buffer (0.2 M, 2 mL, pH 7.55). These solutions were incubated for 1 h at 25.0 °C, followed by the addition of a urea solution (30 wt%, 1 mL) and NaCl solution, such that the final concentration of NaCl was 5 mM, 10 mM, 44 mM, 100 mM, 300 mM, or 500 mM. The salinity mixtures were also held at 25.0 °C while the concentration of ammonium was measured after 1 h.

3.7. Impact of Water Matrix Composition on Urease Inhibition

Four different synthetic water matrices were tested. They were (1) urea solution, (2) fresh urine, (3) partially hydrolyzed urine, and (4) dialysate fluid. All synthetic solutions were prepared based on literature reports [41,66,67,68], and the composition and properties of water matrices are provided in Table 1. Urease (30 mg/L, 1 mL), urine solution (30 wt%, 5 mL), acid or pharmaceuticals (1 mL), and ultrapure water (3 mL) were completely mixed and the concentration of ammonium was measured after 1 hour’s incubation at 25.0 °C.

3.8. Inhibition Mechanisms

The mechanisms of urease inhibition of representative pharmaceuticals were investigated by quantifying the inhibition efficiency of each pharmaceutical under different reaction conditions. For polyphenolic compounds, urease (30 mg/L, 1 mL), polyphenolic compounds (1 mL), ultrapure water (5 mL), and phosphate buffer (0.2 M, 2 mL, pH 7.55) were incubated for 1 h at 25.0 °C, followed by the addition of the urea solution (30 wt%, 1 mL). The final concentrations of the polyphenolic compounds were 0.05 mM, 0.1 mM, and 1 mM. The reaction mixture was kept at 25.0 °C and concentration of ammonium was measured after 1 h. For DSF, thiols (5 mM, 1 mL), DSF (1 mM, 1 mL), urease (30 mg/L, 1 mL), ultrapure water (4 mL), and phosphate buffer (0.2 M, 2 mL, pH 7.55) were incubated for 1 h at 25.0 °C, followed by the addition of the urea solution (30 wt%, 1 mL). The mixture was kept at 25.0 °C and concentration of ammonium was measured after 1 h.

3.9. Inhibition of Urea Hydrolysis of CAT and DSF at Low Concentrations

Representative compounds with high inhibition efficiencies (i.e., CAT and DSF) were tested at low concentrations to mimic realistic conditions. The reaction mixtures included a phosphate-buffer solution (2 mL), pharmaceuticals (1 mL), urease (1 mL), and ultrapure water (5 mL). Urea (1 mL) was added after 1 h and the final concentration of the target pharmaceutical in the solution was adjusted to 0.01 μM, 0.1 μM, 0.5 μM, 1 μM, 10 μM, 0.1 mM, 0.5 mM, and 1 mM. The ammonium concentration in the solution was measured after 1 h to determine the inhibition efficiencies.

4. Implications for Practical Applications

Herein, we demonstrated the bioactivity of selected pharmaceuticals and their metabolites for their urease inhibition potential in stabilizing stored urine. While source-separated human waste offers opportunities for nutrient and energy recovery, urine also contains micropollutants that contribute significantly to aquatic contamination. Catechol (CAT) and hydroquinone (HYQ), which are common metabolic end-products of pharmaceuticals, can be found in urine at high concentrations (e.g., 7700 and 600 ppm, respectively; Table S1) [38]. Remarkably, even low concentrations of these compounds show strong urease inhibition: as little as 0.5 μM CAT (55 ppb) inhibited 90% of urea hydrolysis, and 100 μM disulfiram (DSF, 30 ppm) achieved 82% inhibition (Figure S3). These findings suggest that urine stabilization can be enhanced by concentrating such pharmaceutical inhibitors via nanofiltration or adsorption [41,42,43,44,45]. This strategy is particularly promising for decentralized sanitation systems, where onsite urine stabilization is essential to prevent nitrogen loss and odor formation. Moreover, this approach may also be adapted for the pretreatment of hospital wastewater before it enters centralized treatment facilities.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15070630/s1, Table S1: Structural formulas, molecular weights, purity grades, and suppliers of selected pharmaceuticals, and their concentrations as commonly detected in human urine; Figure S1: Urea hydrolysis rates versus the concentration of urease in synthetic urine; Figure S2: Urea hydrolysis under different pH, phosphate concentration, and salinity without any inhibitor; Figure S3: Urease inhibition efficiencies of CAT and DSF at low levels while maintaining urea concentration. References [69,70,71,72,73,74,75,76,77] are cited in the supplementary materials.

Author Contributions

Conceptualization, X.Y. and L.G.; methodology, H.C., M.C, X.Y. and L.G.; investigation, H.C., W.Y., X.Y. and L.G.; data curation, H.C., M.C., W.Y., Y.L., X.Y. and L.G.; writing—original draft preparation, H.C., M.C., W.Y., Y.L., X.Y. and L.G.; writing—review and editing, S.S., H.W., X.Y., M.R.H., L.G.; supervision, X.Y. and L.G.; project administration, S.S., H.W., X.Y. and L.G.; funding acquisition, X.Y. and L.G. All authors have read and agreed to the published version of the manuscript.

Funding

The authors declare no competing financial interests and acknowledge the financial support from National Key Basic Research Program of China (2019YFA0705800, 2019YFC1906700), National Natural Science Foundation of China (No. 22006039, 21876049 and 91834301), and China Postdoctoral Science Foundation (2019M661412). This work was also supported in part by the Bill & Melinda Gates Foundation [Grant No. INV003227].

Data Availability Statement

The original contributions presented in this study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author(s).

Acknowledgments

Under the grant conditions of the Foundation, a Creative Commons Attribution 4.0 Generic License has already been assigned to the Author Accepted Manuscript version that might arise from this submission. We acknowledge the helpful comments provided by the reviewers, which significantly improved the presented paper.

Conflicts of Interest

There are no conflicts to declare.

References

  1. Wilsenach, J.A.; Van Loosdrecht, M.C.M. Effects of Separate Urine Collection on Advanced Nutrient Removal Processes. Environ. Sci. Technol. 2004, 38, 1208–1215. [Google Scholar] [CrossRef] [PubMed]
  2. Tarpeh, W.A.; Barazesh, J.M.; Cath, T.Y.; Nelson, K.L. Electrochemical Stripping to Recover Nitrogen from Source-Separated Urine. Environ. Sci. Technol. 2018, 52, 1453–1460. [Google Scholar] [CrossRef]
  3. Gao, X.; Zhang, S.; Wang, P.; Jaroniec, M.; Zheng, Y.; Qiao, S.-Z. Urea Catalytic Oxidation for Energy and Environmental Applications. Chem. Soc. Rev. 2024, 53, 1552–1591. [Google Scholar] [CrossRef] [PubMed]
  4. Larsen, T.A.; Alder, A.C.; Eggen, R.I.L.; Maurer, M.; Lienert, J. Source Separation: Will We See a Paradigm Shift in Wastewater Handling? Environ. Sci. Technol. 2009, 43, 6121–6125. [Google Scholar] [CrossRef]
  5. Ishii, S.K.L.; Boyer, T.H. Life Cycle Comparison of Centralized Wastewater Treatment and Urine Source Separation with Struvite Precipitation: Focus on Urine Nutrient Management. Water Res. 2015, 79, 88–103. [Google Scholar] [CrossRef]
  6. Larsen, T.A.; Riechmann, M.E.; Udert, K.M. State of the Art of Urine Treatment Technologies: A Critical Review. Water Res. X 2021, 13, 100114. [Google Scholar] [CrossRef] [PubMed]
  7. Maurer, M.; Pronk, W.; Larsen, T.A. Treatment Processes for Source-Separated Urine. Water Res. 2006, 40, 3151–3166. [Google Scholar] [CrossRef]
  8. Udert, K.M.; Larsen, T.A.; Biebow, M.; Gujer, W. Urea Hydrolysis and Precipitation Dynamics in a Urine-Collecting System. Water Res. 2003, 37, 2571–2582. [Google Scholar] [CrossRef]
  9. Zerner, B. Recent Advances in the Chemistry of an Old Enzyme, Urease. Bioorganic Chem. 1991, 19, 116–131. [Google Scholar] [CrossRef]
  10. Liu, Z.; Zhao, Q.; Wang, K.; Lee, D.; Qiu, W.; Wang, J. Urea Hydrolysis and Recovery of Nitrogen and Phosphorous as MAP from Stale Human Urine. J. Environ. Sci. 2008, 20, 1018–1024. [Google Scholar] [CrossRef]
  11. Hellström, D.; Johansson, E.; Grennberg, K. Storage of Human Urine: Acidification as a Method to Inhibit Decomposition of Urea. Ecol. Eng. 1999, 12, 253–269. [Google Scholar] [CrossRef]
  12. Saetta, D.; Padda, A.; Li, X.; Leyva, C.; Mirchandani, P.B.; Boscovic, D.; Boyer, T.H. Real-Time Monitoring and Control of Urea Hydrolysis in Cyber-Enabled Nonwater Urinal System. Environ. Sci. Technol. 2019, 53, 3187–3197. [Google Scholar] [CrossRef]
  13. Muirhead, D.; Carrier, C. Comparison of Four Strong Acids on the Precipitation Potential of Gypsum in Brines during Distillation of Pretreated, Augmented Urine: Preliminary Results. In Proceedings of the 42nd International Conference on Environmental Systems, San Diego, CA, USA, 15–19 July 2012; American Institute of Aeronautics and Astronautics: Reston, VA, USA, 2012. [Google Scholar]
  14. Ray, H.; Saetta, D.; Boyer, T.H. Characterization of Urea Hydrolysis in Fresh Human Urine and Inhibition by Chemical Addition. Environ. Sci. Water Res. Technol. 2017, 4, 87–98. [Google Scholar] [CrossRef]
  15. De Paepe, J.; De Pryck, L.; Verliefde, A.R.D.; Rabaey, K.; Clauwaert, P. Electrochemically Induced Precipitation Enables Fresh Urine Stabilization and Facilitates Source Separation. Environ. Sci. Technol. 2020, 54, 3618–3627. [Google Scholar] [CrossRef] [PubMed]
  16. Senecal, J.; Vinnerås, B. Urea Stabilisation and Concentration for Urine-Diverting Dry Toilets: Urine Dehydration in Ash. Sci. Total Environ. 2017, 586, 650–657. [Google Scholar] [CrossRef] [PubMed]
  17. Randall, D.G.; Krähenbühl, M.; Köpping, I.; Larsen, T.A.; Udert, K.M. A Novel Approach for Stabilizing Fresh Urine by Calcium Hydroxide Addition. Water Res. 2016, 95, 361–369. [Google Scholar] [CrossRef]
  18. Saetta, D.; Boyer, T.H. Mimicking and Inhibiting Urea Hydrolysis in Nonwater Urinals. Environ. Sci. Technol. 2017, 51, 13850–13858. [Google Scholar] [CrossRef]
  19. Zhang, Y.; Li, Z.; Zhao, Y.; Chen, S.; Mahmood, I.B. Stabilization of Source-Separated Human Urine by Chemical Oxidation. Water Sci. Technol. 2013, 67, 1901–1907. [Google Scholar] [CrossRef]
  20. Lv, Y.; Li, Z.; Zhou, X.; Cheng, S.; Zheng, L. Stabilization of Source-Separated Urine by Heat-Activated Peroxydisulfate. Sci. Total Environ. 2020, 749, 142213. [Google Scholar] [CrossRef]
  21. Ikematsu, M.; Kaneda, K.; Iseki, M.; Yasuda, M. Electrochemical Treatment of Human Urine for Its Storage and Reuse as Flush Water. Sci. Total Environ. 2007, 382, 159–164. [Google Scholar] [CrossRef]
  22. Arve, P.H.; Popat, S.C. Stabilization of Urea for Recovery from Source-Separated Urine Using Electrochemically Synthesized Hydrogen Peroxide. ACS ES T Eng. 2021, 1, 1642–1648. [Google Scholar] [CrossRef]
  23. Hotta, S.; Funamizu, N. Inhibition Factor of Ammonification in Stored Urine with Fecal Contamination. Water Sci. Technol. 2008, 58, 1187–1192. [Google Scholar] [CrossRef] [PubMed]
  24. Pahore, M.M.; Ushijima, K.; Ito, R.; Funamizu, N. Fate of Nitrogen during Volume Reduction of Human Urine Using an On-Site Volume Reduction System. Environ. Technol. 2012, 33, 229–235. [Google Scholar] [CrossRef]
  25. Zhou, X.; Li, Y.; Li, Z.; Xi, Y.; Nazim Uddin, S.M.; Zhang, Y. Investigation on Microbial Inactivation and Urea Decomposition in Human Urine during Thermal Storage. J. Water Sanit. Hyg. Dev. 2017, 7, 378–386. [Google Scholar] [CrossRef] [PubMed]
  26. Svane, S.; Sigurdarson, J.J.; Finkenwirth, F.; Eitinger, T.; Karring, H. Inhibition of Urease Activity by Different Compounds Provides Insight into the Modulation and Association of Bacterial Nickel Import and Ureolysis. Sci. Rep. 2020, 10, 8503. [Google Scholar] [CrossRef]
  27. Calero-Cáceres, W.; Melgarejo, A.; Colomer-Lluch, M.; Stoll, C.; Lucena, F.; Jofre, J.; Muniesa, M. Sludge As a Potential Important Source of Antibiotic Resistance Genes in Both the Bacterial and Bacteriophage Fractions. Environ. Sci. Technol. 2014, 48, 7602–7611. [Google Scholar] [CrossRef]
  28. Schwarzenbach, R.P.; Escher, B.I.; Fenner, K.; Hofstetter, T.B.; Johnson, C.A.; von Gunten, U.; Wehrli, B. The Challenge of Micropollutants in Aquatic Systems. Science 2006, 313, 1072–1077. [Google Scholar] [CrossRef]
  29. Richardson, S.D.; Ternes, T.A. Water Analysis: Emerging Contaminants and Current Issues. Anal. Chem. 2018, 90, 398–428. [Google Scholar] [CrossRef]
  30. Murray, K.E.; Thomas, S.M.; Bodour, A.A. Prioritizing Research for Trace Pollutants and Emerging Contaminants in the Freshwater Environment. Environ. Pollut. 2010, 158, 3462–3471. [Google Scholar] [CrossRef]
  31. Daughton, C.G.; Ternes, T.A. Pharmaceuticals and Personal Care Products in the Environment: Agents of Subtle Change? Environ. Health Perspect. 1999, 107 (Suppl. S6), 907–938. [Google Scholar] [CrossRef]
  32. Luo, Y.; Guo, W.; Ngo, H.H.; Nghiem, L.D.; Hai, F.I.; Zhang, J.; Liang, S.; Wang, X.C. A Review on the Occurrence of Micropollutants in the Aquatic Environment and Their Fate and Removal during Wastewater Treatment. Sci. Total Environ. 2014, 473–474, 619–641. [Google Scholar] [CrossRef]
  33. Zhang, T.; Li, B. Occurrence, Transformation, and Fate of Antibiotics in Municipal Wastewater Treatment Plants. Crit. Rev. Environ. Sci. Technol. 2011, 41, 951–998. [Google Scholar] [CrossRef]
  34. Benotti, M.J.; Trenholm, R.A.; Vanderford, B.J.; Holady, J.C.; Stanford, B.D.; Snyder, S.A. Pharmaceuticals and Endocrine Disrupting Compounds in U.S. Drinking Water. Environ. Sci. Technol. 2009, 43, 597–603. [Google Scholar] [CrossRef]
  35. Hughes, S.R.; Kay, P.; Brown, L.E. Global Synthesis and Critical Evaluation of Pharmaceutical Data Sets Collected from River Systems. Environ. Sci. Technol. 2013, 47, 661–677. [Google Scholar] [CrossRef] [PubMed]
  36. Larsen, T.A.; Lienert, J.; Joss, A.; Siegrist, H. How to Avoid Pharmaceuticals in the Aquatic Environment. J. Biotechnol. 2004, 113, 295–304. [Google Scholar] [CrossRef]
  37. Winker, M.; Tettenborn, F.; Faika, D.; Gulyas, H.; Otterpohl, R. Comparison of Analytical and Theoretical Pharmaceutical Concentrations in Human Urine in Germany. Water Res. 2008, 42, 3633–3640. [Google Scholar] [CrossRef] [PubMed]
  38. Marrubini, G.; Calleri, E.; Coccini, T.; Castoldi, A.F.; Manzo, L. Direct Analysis of Phenol, Catechol and Hydroquinone in Human Urine by Coupled-Column HPLC with Fluorimetric Detection. Chromatographia 2005, 62, 25–31. [Google Scholar] [CrossRef]
  39. Cotillas, S.; Lacasa, E.; Sáez, C.; Cañizares, P.; Rodrigo, M.A. Electrolytic and Electro-Irradiated Technologies for the Removal of Chloramphenicol in Synthetic Urine with Diamond Anodes. Water Res. 2018, 128, 383–392. [Google Scholar] [CrossRef]
  40. Jojoa-Sierra, S.D.; Silva-Agredo, J.; Herrera-Calderon, E.; Torres-Palma, R.A. Elimination of the Antibiotic Norfloxacin in Municipal Wastewater, Urine and Seawater by Electrochemical Oxidation on IrO2 Anodes. Sci. Total Environ. 2017, 575, 1228–1238. [Google Scholar] [CrossRef]
  41. Sendrowski, A.; Boyer, T.H. Phosphate Removal from Urine Using Hybrid Anion Exchange Resin. Desalination 2013, 322, 104–112. [Google Scholar] [CrossRef]
  42. Lazarova, Z.; Spendlingwimmer, R. Treatment of Yellow Water by Membrane Separations and Advanced Oxidation Methods. Water Sci. Technol. 2008, 58, 419–426. [Google Scholar] [CrossRef] [PubMed]
  43. Pronk, W.; Palmquist, H.; Biebow, M.; Boller, M. Nanofiltration for the Separation of Pharmaceuticals from Nutrients in Source-Separated Urine. Water Res. 2006, 40, 1405–1412. [Google Scholar] [CrossRef]
  44. Cristóvão, M.B.; Torrejais, J.; Janssens, R.; Luis, P.; Van der Bruggen, B.; Dubey, K.K.; Mandal, M.K.; Bronze, M.R.; Crespo, J.G.; Pereira, V.J. Treatment of Anticancer Drugs in Hospital and Wastewater Effluents Using Nanofiltration. Sep. Purif. Technol. 2019, 224, 273–280. [Google Scholar] [CrossRef]
  45. Tarpeh, W.A.; Udert, K.M.; Nelson, K.L. Comparing Ion Exchange Adsorbents for Nitrogen Recovery from Source-Separated Urine. Environ. Sci. Technol. 2017, 51, 2373–2381. [Google Scholar] [CrossRef]
  46. Inoue, O.; Seiji, K.; Nakatsuka, H.; Watanabe, T.; Yin, S.; Li, G.L.; Cai, S.X.; Jin, C.; Ikeda, M. Excretion of 1,2,4-Benzenetriol in the Urine of Workers Exposed to Benzene. Br. J. Ind. Med. 1989, 46, 559–565. [Google Scholar] [CrossRef] [PubMed]
  47. Cesareo, S.D.; Langton, S.R. Kinetic Properties of Helicobacter Pylori Urease Compared with Jack Bean Urease. FEMS Microbiol. Lett. 1992, 99, 15–21. [Google Scholar] [CrossRef]
  48. Krajewska, B.; Zaborska, W. The Effect of Phosphate Buffer in the Range of pH 5.80–8.07 on Jack Bean Urease Activity. J. Mol. Catal. B Enzym. 1999, 6, 75–81. [Google Scholar] [CrossRef]
  49. Frankenberger, W.T.; Bingham, F.T. Influence of Salinity on Soil Enzyme Activities. Soil Sci. Soc. Am. J. 1982, 46, 1173–1177. [Google Scholar] [CrossRef]
  50. Dixon, N.E.; Gazzola, C.; Blakeley, R.L.; Zerner, B. Jack Bean Urease (EC 3.5.1.5). Metalloenzyme. Simple Biological Role for Nickel. J. Am. Chem. Soc. 1975, 97, 4131–4133. [Google Scholar] [CrossRef]
  51. Todd, M.J.; Hausinger, R.P. Competitive Inhibitors of Klebsiella Aerogenes Urease: Mechanisms of Interaction with the Nickel Active Site. J. Biol. Chem. 1989, 264, 15835–15842. [Google Scholar] [CrossRef]
  52. Carter, E.L.; Flugga, N.; Boer, J.L.; Mulrooney, S.B.; Hausinger, R.P. Interplay of Metal Ions and Urease. Metallomics 2009, 1, 207–221. [Google Scholar] [CrossRef] [PubMed]
  53. Benini, S.; Rypniewski, W.R.; Wilson, K.S.; Miletti, S.; Ciurli, S.; Mangani, S. A New Proposal for Urease Mechanism Based on the Crystal Structures of the Native and Inhibited Enzyme from Bacillus pasteurii: Why Urea Hydrolysis Costs Two Nickels. Structure 1999, 7, 205–216. [Google Scholar] [CrossRef] [PubMed]
  54. Zambelli, B.; Musiani, F.; Benini, S.; Ciurli, S. Chemistry of Ni2+ in Urease: Sensing, Trafficking, and Catalysis. Acc. Chem. Res. 2011, 44, 520–530. [Google Scholar] [CrossRef] [PubMed]
  55. Ciurli, S.; Benini, S.; Rypniewski, W.R.; Wilson, K.S.; Miletti, S.; Mangani, S. Structural Properties of the Nickel Ions in Urease: Novel Insights into the Catalytic and Inhibition Mechanisms. Coord. Chem. Rev. 1999, 190–192, 331–355. [Google Scholar] [CrossRef]
  56. Tan, L.; Su, J.; Wu, D.; Yu, X.; Su, Z.; He, J.; Wu, X.; Kong, S.; Lai, X.; Lin, J.; et al. Kinetics and Mechanism Study of Competitive Inhibition of Jack-Bean Urease by Baicalin. Sci. World J. 2013, 2013, e879501. [Google Scholar] [CrossRef]
  57. Mazzei, L.; Cianci, M.; Contaldo, U.; Ciurli, S. Insights into Urease Inhibition by N-(n-Butyl) Phosphoric Triamide through an Integrated Structural and Kinetic Approach. J. Agric. Food Chem. 2019, 67, 2127–2138. [Google Scholar] [CrossRef] [PubMed]
  58. Iftikhar, F.; Ali, Y.; Ahmad Kiani, F.; Fahad Hassan, S.; Fatima, T.; Khan, A.; Niaz, B.; Hassan, A.; Latif Ansari, F.; Rashid, U. Design, Synthesis, in Vitro Evaluation and Docking Studies on Dihydropyrimidine-Based Urease Inhibitors. Bioorganic Chem. 2017, 74, 53–65. [Google Scholar] [CrossRef]
  59. Mazzei, L.; Cianci, M.; Vara, A.G.; Ciurli, S. The Structure of Urease Inactivated by Ag(i): A New Paradigm for Enzyme Inhibition by Heavy Metals. Dalton Trans. 2018, 47, 8240–8247. [Google Scholar] [CrossRef]
  60. Díaz-Sánchez, Á.G.; Alvarez-Parrilla, E.; Martínez-Martínez, A.; Aguirre-Reyes, L.; Orozpe-Olvera, J.A.; Ramos-Soto, M.A.; Núñez-Gastélum, J.A.; Alvarado-Tenorio, B.; De la Rosa, L.A. Inhibition of Urease by Disulfiram, an FDA-Approved Thiol Reagent Used in Humans. Molecules 2016, 21, 1628. [Google Scholar] [CrossRef]
  61. Krajewska, B.; Zaborska, W. Jack Bean Urease: The Effect of Active-Site Binding Inhibitors on the Reactivity of Enzyme Thiol Groups. Bioorganic Chem. 2007, 35, 355–365. [Google Scholar] [CrossRef]
  62. Wang, S.; Lee, M.H.; Hausinger, R.P.; Clark, P.A.; Wilcox, D.E.; Scott, R.A. Structure of the Dinuclear Active Site of Urease. X-Ray Absorption Spectroscopic Study of Native and 2-Mercaptoethanol-Inhibited Bacterial and Plant Enzymes. Inorg. Chem. 1994, 33, 1589–1593. [Google Scholar] [CrossRef]
  63. Nagy, P. Kinetics and Mechanisms of Thiol–Disulfide Exchange Covering Direct Substitution and Thiol Oxidation-Mediated Pathways. Antioxid. Redox Signal. 2013, 18, 1623–1641. [Google Scholar] [CrossRef] [PubMed]
  64. Brown, H.H. Determination of Blood Urea with P-Dimethylaminobenzaldehyde. Anal. Chem. 1959, 31, 1844–1846. [Google Scholar] [CrossRef]
  65. Quastel, J.H. The Action of Polyhydric Phenols on Urease; the Influence of Thiol Compounds. Biochem. J. 1933, 27, 1116–1122. [Google Scholar] [CrossRef]
  66. Putnam, D.F. Composition and Concentrative Properties of Human Urine; NASA-CR-1802; NASA: Washington, DC, USA, 1971. Available online: https://ntrs.nasa.gov/citations/19710023044 (accessed on 15 July 2021).
  67. Drukker, W.; Parsons, F.M.; Gordon, A. Practical Application of Dialysate Regeneration: The Redy System. In Replacement of Renal Function by Dialysis; Drukker, W., Parsons, F.M., Maher, J.F., Eds.; Springer: Dordrecht, The Netherlands, 1979; pp. 244–258. ISBN 978-94-009-9327-3. [Google Scholar]
  68. Giordano, C.; Esposito, R.; Bello, P.; Quarto, E.; Gonzalez, F.M. Cold Carbon Apparatus for Hemodialysis. J. Dial. 1976, 1, 165–179. [Google Scholar] [CrossRef] [PubMed]
  69. Baranowska, I.; Wilczek, A. A Rapid Uhplc Method for the Simultaneous Determination of Selected B-Blockers, Nsaids, and Their Metabolites in Human Urine and Water Samples. J. Liq. Chromatogr. Relat. Technol. 2010, 33, 1776–1790. [Google Scholar] [CrossRef]
  70. Ducos, P.; Gaudin, R.; Robert, A.; Francin, J.M.; Maire, C. Improvement in HPLC Analysis of Urinary Trans, Trans-Muconic Acid, a Promising Substitute for Phenol in the Assessment of Benzene Exposure. Int. Arch. Occup. Environ. Health 1990, 62, 529–534. [Google Scholar] [CrossRef]
  71. Bischel, H.N.; Özel Duygan, B.D.; Strande, L.; McArdell, C.S.; Udert, K.M.; Kohn, T. Pathogens and Pharmaceuticals in Source-Separated Urine in EThekwini, South Africa. Water Res. 2015, 85, 57–65. [Google Scholar] [CrossRef]
  72. Cload, P.A. A Review of the Pharmacokinetics of Zidovudine in Man. J. Infect. 1989, 18, 15–21. [Google Scholar] [CrossRef]
  73. Hamilton, M.; Kissinger, P.T. Determination of Acetaminophen Metabolites in Urine by Liquid Chromatography/Electrochemistry. Anal. Biochem. 1982, 125, 143–148. [Google Scholar] [CrossRef]
  74. Pritchard, J.F.; Schneck, D.W.; Hayes, A.H., Jr. Determination of Propranolol and Six Metabolites in Human Urine by High-Pressure Liquid Chromatography. J. Chromatogr. B Biomed. Sci. Appl. 1979, 162, 47–58. [Google Scholar] [CrossRef] [PubMed]
  75. Rybak, M.E.; Sternberg, M.R.; Pao, C.-I.; Ahluwalia, N.; Pfeiffer, C.M. Urine Excretion of Caffeine and Select Caffeine Metabolites Is Common in the US Population and Associated with Caffeine Intake. J. Nutr. 2015, 145, 766–774. [Google Scholar] [CrossRef] [PubMed]
  76. Muschek, L.D.; Grindel, J.M. Review of the Pharmacokinetics and Metabolism of Zomepirac in Man and Animals. J. Clin. Pharmacol. 1980, 20, 223–229. [Google Scholar] [CrossRef] [PubMed]
  77. Ngumba, E.; Gachanja, A.; Nyirenda, J.; Maldonado, J.; Tuhkanen, T. Occurrence of Antibiotics and Antiretroviral Drugs in Source-Separated Urine, Groundwater, Surface Water and Wastewater in the Peri-Urban Area of Chunga in Lusaka, Zambia. Water SA 2020, 46, 278–284. [Google Scholar] [CrossRef]
Catalysts 15 00630 g001
Figure 1. Urease inhibition efficiencies of twenty-three pharmaceuticals and metabolites.
Figure 1. Urease inhibition efficiencies of twenty-three pharmaceuticals and metabolites.
Catalysts 15 00630 g001
Catalysts 15 00630 g002
Figure 2. Ammonium concentration in urine solutions during long-term storage with and without the presence of pharmaceuticals and metabolites at different concentrations.
Figure 2. Ammonium concentration in urine solutions during long-term storage with and without the presence of pharmaceuticals and metabolites at different concentrations.
Catalysts 15 00630 g002
Catalysts 15 00630 g003
Figure 3. Urease inhibition efficiency of CAT and DSF as functions of (a) pH, (b) phosphate concentration, and (c) salinity.
Figure 3. Urease inhibition efficiency of CAT and DSF as functions of (a) pH, (b) phosphate concentration, and (c) salinity.
Catalysts 15 00630 g003
Catalysts 15 00630 g004
Figure 4. CAT, DSF, and HNO3′s urease inhibition effects in different synthetic water matrices.
Figure 4. CAT, DSF, and HNO3′s urease inhibition effects in different synthetic water matrices.
Catalysts 15 00630 g004
Catalysts 15 00630 g005
Figure 5. (a) Chemical structures and (b) inhibition efficiencies of polyphenolic compounds of different concentrations. (c) Chemical structures of DSF and monothiol compounds. (d) Effect of different thiols towards DSF’s urease inhibition. (e) Thiol–disulfide exchange reaction of DSF with thiols.
Figure 5. (a) Chemical structures and (b) inhibition efficiencies of polyphenolic compounds of different concentrations. (c) Chemical structures of DSF and monothiol compounds. (d) Effect of different thiols towards DSF’s urease inhibition. (e) Thiol–disulfide exchange reaction of DSF with thiols.
Catalysts 15 00630 g005
Table 1. Composition and properties of different synthetic water matrices.
Table 1. Composition and properties of different synthetic water matrices.
SpeciesMolecular Weight
(g·mol−1)		Concentration (mol·L−1)
Urea SolutionFresh UrinePartially Hydrolyzed UrineCollected UrineDialysis Fluid
Urea60.060.450.270.180.300.00038
Creatinine113.10-0.0012-0.00970.0012
Uric acid168.11-0.0021-0.00210.000574
NH4OH35.04--0.090.03-
Na2HPO4141.960.02----
NaH2PO4119.980.020.020.0140.02-
KCl74.55-0.040.040.03-
MgCl2·6H2O203.32-0.0042---
CaCl2·2H2O147.02-0.0045-0.0045-
Na2SO4142.04-0.0150.0150.0015-
NH4HCO379.05--0.090.00002-
NaCl58.440.0440.050.060.06-
pH-6.885.207.899.446.44
Buffer capacity 0.00880.00390.01350.01520.0059
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Chi, H.; Chen, M.; Yang, W.; Li, Y.; Sun, S.; Wang, H.; Yang, X.; Hoffmann, M.R.; Guo, L. Inhibition of Urea Hydrolysis in Human Urine for Resource and Energy Recovery: Pharmaceuticals and Their Metabolites as Co-Existing Anticatalyzers. Catalysts 2025, 15, 630. https://doi.org/10.3390/catal15070630

AMA Style

Chi H, Chen M, Yang W, Li Y, Sun S, Wang H, Yang X, Hoffmann MR, Guo L. Inhibition of Urea Hydrolysis in Human Urine for Resource and Energy Recovery: Pharmaceuticals and Their Metabolites as Co-Existing Anticatalyzers. Catalysts. 2025; 15(7):630. https://doi.org/10.3390/catal15070630

Chicago/Turabian Style

Chi, Haoran, Minshu Chen, Wei Yang, Ya Li, Shuhui Sun, Hualin Wang, Xuejing Yang, Michael R. Hoffmann, and Lei Guo. 2025. "Inhibition of Urea Hydrolysis in Human Urine for Resource and Energy Recovery: Pharmaceuticals and Their Metabolites as Co-Existing Anticatalyzers" Catalysts 15, no. 7: 630. https://doi.org/10.3390/catal15070630

APA Style

Chi, H., Chen, M., Yang, W., Li, Y., Sun, S., Wang, H., Yang, X., Hoffmann, M. R., & Guo, L. (2025). Inhibition of Urea Hydrolysis in Human Urine for Resource and Energy Recovery: Pharmaceuticals and Their Metabolites as Co-Existing Anticatalyzers. Catalysts, 15(7), 630. https://doi.org/10.3390/catal15070630

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