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      A novel approach for stabilizing fresh urine by calcium hydroxide addition

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          Abstract

          In this study, we investigated the prevention of enzymatic urea hydrolysis in fresh urine by increasing the pH with calcium hydroxide (Ca(OH) 2) powder. The amount of Ca(OH) 2 dissolving in fresh urine depends significantly on the composition of the urine. The different urine compositions used in our simulations showed that between 4.3 and 5.8 g Ca(OH) 2 dissolved in 1 L of urine at 25 °C. At this temperature, the pH at saturation is 12.5 and is far above the pH of 11, which we identified as the upper limit for enzymatic urea hydrolysis. However, temperature has a strong effect on the saturation pH, with higher values being achieved at lower temperatures. Based on our results, we recommend a dosage of 10 g Ca(OH) 2 L −1 of fresh urine to ensure solid Ca(OH) 2 always remains in the urine reactor which ensures sufficiently high pH values. Besides providing sufficient Ca(OH) 2, the temperature has to be kept in a certain range to prevent chemical urea hydrolysis. At temperatures below 14 °C, the saturation pH is higher than 13, which favors chemical urea hydrolysis. We chose a precautionary upper temperature of 40 °C because the rate of chemical urea hydrolysis increases at higher temperatures but this should be confirmed with kinetic studies. By considering the boundaries for pH and temperature developed in this study, urine can be stabilized effectively with Ca(OH) 2 thereby simplifying later treatment processes or making direct use easier.

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          Highlights

          • •

            Stabilization of source-separated urine refers to the prevention of urea hydrolysis.

          • •

            Calcium hydroxide can be used to stabilize fresh urine.

          • •

            Adding Ca(OH) 2 to fresh urine effectively inhibits enzymatic urea hydrolysis.

          • •

            Keeping the temperature between 14 °C and 40 °C limits chemical urea hydrolysis.

          • •

            The low solubility of Ca(OH) 2 allows for passive dosing.

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          Microbial ureases: significance, regulation, and molecular characterization.

          Victoria L. Mobley, Robert P. Hausinger (1989)
          Microbial ureases hydrolyze urea to ammonia and carbon dioxide. Urease activity of an infectious microorganism can contribute to the development of urinary stones, pyelonephritis, gastric ulceration, and other diseases. In contrast to these harmful effects, urease activity of ruminal and gastrointestinal microorganisms can benefit both the microbe and host by recycling (thereby conserving) urea nitrogen. Microbial ureases also play an important role in utilization of environmental nitrogenous compounds and urea-based fertilizers. Urease is a high-molecular-weight, multimeric, nickel-containing enzyme. Its cytoplasmic location requires that urea enter the cell for utilization, and in some species energy-dependent urea uptake systems have been detected. Eucaryotic microorganisms possess a homopolymeric urease, analogous to the well-studied plant enzyme composed of six identical subunits. Gram-positive bacteria may also possess homopolymeric ureases, but the evidence for this is not conclusive. In contrast, ureases from gram-negative bacteria studied thus far clearly possess three distinct subunits with Mrs of 65,000 to 73,000 (alpha), 10,000 to 12,000 (beta), and 8,000 to 10,000 (gamma). Tightly bound nickel is present in all ureases and appears to participate in catalysis. Urease genes have been cloned from several species, and nickel-containing recombinant ureases have been characterized. Three structural genes are transcribed on a single messenger ribonucleic acid and translated in the order gamma, beta, and then alpha. In addition to these genes, several other peptides are encoded in the urease operon of some species. The roles for these other genes are not firmly established, but may involve regulation, urea transport, nickel transport, or nickel processing.
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            Magnesium transport and function in plants: the tip of the iceberg.

            Orit Shaul (2002)
            The maintenance of Mg2+ homeostasis in the plant is essential for viability. This review describes Mg2+ functions and balancing in plants, with special focus on the existing knowledge of the involved transport mechanisms. Mg2+ is essential for the function of many cellular enzymes and for the aggregation of ribosomes. Mg2+ concentrations also modulate ionic currents across the chloroplast and the vacuolar membranes, and might thus regulate ion balance in the cell and stomatal opening. The significance of Mg2+ homeostasis has been particularly established with regard to Mg2+'s role in photosynthesis. Mg2+ is the central atom of the chlorophyll molecule, and fluctuations in its levels in the chloroplast regulate the activity of key photosynthetic enzymes. Relatively little is known of the proteins mediating Mg2+ uptake and transport in plants. The plant vacuole seem to play a key role in Mg2+ homeostasis in plant cells. Physiological and molecular evidence indicate that Mg2+ entry to the vacuole is mediated by Mg2+/H+ exchangers. The Arabidopsis vacuolar Mg2+/H+ exchanger, AtMHX, is highly transcribed at the vascular tissue, apparently most abundantly at the xylem parenchyma. Inclusion of Mg2+ ions into the vacuoles of this tissue may determine their partitioning between the various plant organs. Impacts of Mg2+ imbalance are described with respect for both plant physiology and for its nutritional value to animal and human.
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              Capturing the lost phosphorus.

              Bruce E Rittmann, Brooke Mayer, Paul Westerhoff … (2011)
              Minable phosphorus (P) reserves are being depleted and will need to be replaced by recovering P that currently is lost from the agricultural system, causing water-quality problems. The largest two flows of lost P are in agricultural runoff and erosion (∼46% of mined P globally) and animal wastes (∼40%). These flows are quite distinct. Runoff has a very high volumetric flow rate, but a low P concentration; animal wastes have low flow rates, but a high P concentration together with a high concentration of organic material. Recovering the lost P in animal wastes is technically and economically more tractable, and it is the focus for this review of promising P-capture technologies. P capture requires that organic P be transformed into inorganic P (phosphate). For high-strength animal wastes, P release can be accomplished in tandem with anaerobic treatment that converts the energy value in the organic matter to CH(4), H(2), or electricity. Once present as phosphate, the P can be captured in a reusable form by four approaches. Most well developed is precipitation as magnesium or calcium solids. Less developed, but promising are adsorption to iron-based adsorbents, ion exchange to phosphate-selective solids, and uptake by photosynthetic microorganisms or P-selective proteins. Copyright © 2011 Elsevier Ltd. All rights reserved.
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                Author and article information

                Contributors
                Dyllon G. Randall
                Kai M. Udert
                Journal
                Journal ID (nlm-ta): Water Res
                Journal ID (iso-abbrev): Water Res
                Title: Water Research
                Publisher: Pergamon Press
                ISSN (Print): 0043-1354
                ISSN (Electronic): 1879-2448
                Publication date PMC-release: 15 May 2016
                Publication date (Print): 15 May 2016
                Volume: 95
                Pages: 361-369
                Affiliations
                [1]Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland
                Author notes
                [∗ ]Corresponding author. kai.udert@ 123456eawag.ch
                [∗∗ ]Corresponding author. dyllonrandall@ 123456gmail.com
                [1]

                These authors contributed equally to this manuscript.

                Article
                Publisher ID: S0043-1354(16)30134-8
                DOI: 10.1016/j.watres.2016.03.007
                PMC ID: 4857702
                PubMed ID: 27055084
                SO-VID: 6001a2ba-89fc-4f8e-98d1-588a48e40581
                Copyright © © 2016 The Authors
                License:

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                History
                Date received : 9 December 2015
                Date revision received : 23 February 2016
                Date accepted : 1 March 2016
                Categories
                Subject: Article

                ScienceOpen disciplines: Oceanography & Hydrology
                Keywords: urine,source separation,stabilization of urea,inhibition of urease,phosphorus recovery
                Data availability:
                ScienceOpen disciplines: Oceanography & Hydrology
                Keywords: urine, source separation, stabilization of urea, inhibition of urease, phosphorus recovery

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