Passive evaporation of source-separated urine from dry toilets: UES optimization and dry product accumulation over time

A urine evaporation system (UES) was optimized and evaluated in a laboratory by adding 5 L of urine at the same time each day for 65 days. The UES consisted of a wooden box that is open at the front only with tracks for 22 vertically stacked cafeteria-type trays and a fan and chimney at the back. Urine flowed from tray to tray via gravity exiting each tray via a weir along the long side of the tray. A distinctive physical and chemical zonation in the solid urine product was observed from the upper to lower trays due to leaching of precipitated minerals in the upper trays and mineral accumulation in the lower trays. The redox conditions became increasingly oxidizing from the top to bottom trays due to contact with the atmosphere thus favouring more stable mineralized forms of nitrogen (ammonium and nitrate) and sulphur (sulphate) and disfavouring the less stable and volatile ammonia, nitrogen gas and hydrogen sulphide. The quality of the fertilizer product is higher in the upper trays with higher levels of nitrogen, phosphorus and potassium, whereas the lower trays have higher levels of sodium chloride. Nitrogen losses due to ammonia volatilization were approximately 35%.

Production of ammonia by Tritrichomonas foetus and Trichomonas vaginalis

Production of ammonia is difficult to find among the various studies of amino acid metabolism in protozoa. Several studies suggest that catabolism of arginine to ammonium is important for the growth of trichomonads. Trichomonads are amitochondriate zooflagellates that thrive under microaerophilic and anaerobic conditions. The authors were able to detect accumulation of ammonium ions and ammonia in cultures of Tritrichomonas foetus and Trichomonas vaginalis, including those resistant to metronidazole. Ammonium ions and ammonia were detected using the indophenol colorimetric method. Cells incubated overnight under an ambient oxygen gas phase had 0·9 mM soluble ammonium (NH4 + and NH3) or a 20 % greater concentration of ammonium relative to sterile growth medium that had been incubated similarly. Production of ammonia itself was confirmed by analysis of a wick that was moistened with sulfuric acid (20 mM) and placed above the liquid in sealed cultures of a strain of Trichomonas vaginalis. The wicks from these cultures captured the equivalent of 0·048 mM volatile ammonia (NH3) from the liquid as compared to 0·021 mM volatile ammonia from sterile medium after overnight incubation. Intact trichomonads, 0·7×106 cells ml−1 equivalent to 0·7 mg protein ml−1, incubated in Doran's buffer with or without (1 mM) l-arginine produced significant amounts of soluble ammonium (0·07 mM and 0·04 mM, respectively) during 60 min. The results indicate that ammonium ions and the more irritating ammonia are significant metabolites of trichomonads. In addition, based upon end-product amounts, it appears that the rate of arginine metabolism is of the same order of magnitude as that for carbohydrate metabolism by trichomonads.

Ammonia Pulses and Metabolic Oscillations Guide Yeast Colony Development

On solid substrate, growing yeast colonies alternately acidify and alkalinize the medium. Using morphological, cytochemical, genetic, and DNA microarray approaches, we characterized six temporal steps in the “acid-to-alkali” colony transition. This transition is connected with the production of volatile ammonia acting as starvation signal between colonies. We present evidence that the three membrane proteins Ato1p, Ato2p, and Ato3p, members of the YaaH family, are involved in ammonia production in Saccharomyces cerevisiae colonies. The acid-to-alkali transition is connected with decrease of mitochondrial oxidative catabolism and by peroxisome activation, which in parallel with activation of biosynthetic pathways contribute to decrease the general stress level in colonies. These metabolic features characterize a novel survival strategy used by yeast under starvation conditions prevalent in nature.

Yeast colonies synchronise their growth and development

The ability to emit and receive signals over long distances is one of the characteristic attributes of multicellular organisms. Such communication can be mediated in different manners (by chemical compounds, light waves, acoustic waves etc.) and usually is reflected in the behaviour of the communicating organisms. Recently, we reported that individual yeast colonies, organised multicellular structures, can also communicate at long distance by means of volatile ammonia, which is produced by colonies in pulses separated by acidification of the medium. Here, we demonstrate that the colony that first reached the stage of intense ammonia production induces ammonia production response in surrounding colonies regardless of their age, causing the synchronisation of their NH(3) pulses and, consequently, the mutual affection of their growth. Also an artificial source of ammonia (but neither NH(4)(+) nor NaOH gradients) can immediately induce the ammonia production even in the colony starting its acidic stage of the development. The repeated transition of Candida mogii colonies from the acidic phase to the phase of intensive ammonia production is accompanied by dramatic changes in colony morphology and also in cell morphology and growth. Relatively smooth colonies in the acidic phase are formed by growing pseudohyphae. After ammonia induction, pseudohyphae decompose into non-dividing yeast-like cells, which rearrange themselves into ruffled spaghetti-like structures. The synchronisation of colony growth, that also exists between yeast colonies of different genera, could be important in establishing their optimal distribution in a natural habitat.