Decomposition pathways and rates of human urine in soils

Fate of nitrogen and phosphorus from source-separated human urine in a calcareous soil

Human urine concentrates 88% of the nitrogen and 50% of the phosphorus excreted by humans, making it a potential alternative crop fertilizer. However, knowledge gaps remain on the fate of nitrogen in situations favouring NH₃ volatilization and on the availability of P from urine in soils. This study aimed at identifying the fate of nitrogen and phosphorus supplied by human urine from source separation toilets in a calcareous soil. To this end, a spinach crop was fertilized with 2 different doses of human urine (170 kgN ha^-1 + 8.5 kgP ha^-1 and 510 kgN ha^-1 + 25.5 kgP ha^-1) and compared with a synthetic fertilizer treatment (170 kgN ha^-1 + 8.5 kgP ha^-1) and an unfertilized control. The experiment was conducted in 4 soil tanks (50-cm depth) in greenhouse conditions, according to a randomized block scheme. We monitored soil mineral nitrogen over time and simulated nitrogen volatilization using Hydrus-1D and Visual Minteq softwares. We also monitored soil phosphorus pools, carbon, nitrogen and phosphorus (CNP) in microbial biomass, soil pH and electrical conductivity. Only an excessive input of urine affected soil pH (decreasing it by 0.2 units) and soil conductivity (increasing it by 183%). The phosphorus supplied was either taken up by the crop or remained mostly in the available P pool, as demonstrated by a net increase of the resin and bicarbonate extractable P. Ammonium seemed to be nitrified within about 10 days after application. However, both Visual Minteq and Hydrus models estimated that more than 50% of the nitrogen supplied was lost by ammonia volatilization. Overall, our results indicate that direct application of urine to a calcareous soil provides available nutrients for plant growth, but that heavy losses of volatilized nitrogen are to be expected. Our results also question whether long-term application could affect soil pH and salinity.

Intense rainfalls trigger nitrite leaching in agricultural soils depleted in organic matter

Nitrate and ammonium are common inorganic contaminants of anthropogenic origin in many shallow aquifers around the world, while nitrite is less common, but it is most harmful than nitrate and ammonium due to its high reactivity. This paper presents evidence of nitrite accumulation after intense rainfalls in soil samples collected in an agricultural field characterized by organic matter chronic depletion. Moreover, an intact core from the same site was also collected to perform an unsaturated column experiment (60 cm long and 20 cm outer diameter) mimicking heavy rainfalls (230 mm in 2 days). Results from the field site showed nitrite accumulation (up to 0.45 mmol/kg) at 50-70 cm depth, just below the plough layer. The column experiment showed very high initial concentrations of nitrate and nitrite in the leachate and a progressive decrease of nitrate due to denitrification. The numerical flow model was calibrated versus the observed volumetric water contents and leachate flow rates. The numerical reactive transport model was calibrated versus the leachate concentrations of six dissolved species (ammonium, nitrate, nitrite, dissolved organic carbon, chloride and bromide). The optimized model resulted to be robustly calibrated providing insights on the kinetic rates driving the production, accumulation and leakage of nitrite, showing that incomplete denitrification is the source of nitrite. As far as the authors are aware, this is the first study reporting a clear link between high nitrite leaching rates and extreme rainfall events in lowland agricultural soils depleted in organic matter. The proposed methodology could be applied to quantify nitrite cycling processes in many other agricultural areas of the world affected by extreme rainfall events.

A urine-fuelled soil-based bioregenerative life support system for long-term and long-distance manned space missions

A soil-based cropping unit fuelled with human urine for long-term manned space missions was investigated with the aim to analyze whether a closed-loop nutrient cycle from human liquid wastes was achievable. Its ecohydrology and biogeochemistry were analysed in microgravity with the use of an advanced computational tool. Urine from the crew was used to supply primary (N, P, and K) and secondary (S, Ca and Mg) nutrients to wheat and soybean plants in the controlled cropping unit. Breakdown of urine compounds into primary and secondary nutrients as well as byproduct gases, adsorbed, and uptake fractions were tracked over a period of 20 years. Results suggested that human urine could satisfy the demand of at least 3 to 4 out of 6 nutrients with an offset in pH and salinity tolerable by plants. It was therefore inferred that a urine-fuelled life support system can introduce a number of advantages including: (1) recycling of liquids wastes and production of food; (2) forgiveness of neglect as compared to engineered electro-mechanical systems that may fail under unexpected or unplanned conditions; and (3) reduction of supply and waste loads during space missions.

In-situ atrazine biodegradation dynamics in wheat (Triticum) crops under variable hydrologic regime

A comprehensive biodegradation reaction network of atrazine (ATZ) and its 18 byproducts was coupled to the nitrogen cycle and integrated in a computational solver to assess the in-situ biodegradation effectiveness and leaching along a 5m deep soil cultivated with wheat in West Wyalong, New South Wales, Australia. Biodegradation removed 97.7% of 2kg/ha ATZ yearly applications in the root zone, but removal substantially decreased at increasing depths; dechlorination removed 79% of ATZ in aerobic conditions and 18% in anaerobic conditions, whereas deethylation and oxidation removed only 0.11% and 0.15% of ATZ, respectively. The residual Cl mass fraction in ATZ and 4 byproducts was 2.4% of the applied mass. ATZ half-life ranged from 150 to 247days in the soil surface. ATZ reached 5m soil depth within 200years and its concentration increased from 1×10^-6 to 4×10^-6mg/kg_dry-soil over time. The correlation between ATZ specific biomass degradation affinity Φ₀ and half-life t_1/2, although relatively uncertain for both hydrolyzing and oxidizing bacteria, suggested that microorganisms with high Φ₀ led to low ATZ t_1/2. Greater ATZ applications were balanced by small nonlinear increments of ATZ biodegraded fraction within the root zone and therefore less ATZ leached into the shallow aquifer.

Kinetics of atrazine, deisopropylatrazine, and deethylatrazine soil biodecomposers

Twenty-two experimental sets were used to determine the biodecomposition parameters of atrazine (ATZ), deisopropylatrazine (DIATZ), and deethylatrazine (DEATZ) by inverse solution of Michaelis-Menten-Monod kinetic equations. The averaged maximum specific growth rate (μ), Michaelis-Menten half-saturation concentration (K), and biomass yield (Y) ranged between 2.00 × 10^-7 and 4.62 × 10^-5 1/s, 3.43 × 10^-6 and 1.39 × 10¹ mol/L, and 1.20 × 10² and 2.98 × 10⁵ mg-wet-Bio/mol-Subs, respectively. Parameters grouped by reaction pathway appeared clustered by aerobic and anaerobic catabolic breakdown, and were poorly correlated between each other (R ranging from -0.27 to 0.63, p ≥ 0.05). The tested bacterial strains decomposed ATZ, DIATZ, and DEATZ relatively rapidly in laboratory conditions, with an half-life (t_1/2) ranging between 3 and 6 days. Numerical modeling showed that ATZ, DIATZ, and DEATZ half-lives were particularly sensitive to their initial concentration and the initial microbial biomass concentration. This study suggests that these bacterial strains can effectively be used or enhanced for bioremediation of agricultural soils where atrazine has been applied as long as these bacteria already coexist in or can integrate with the local soil microbial population at a given location.

Evaluation of storage and evaporation in the removal efficiency of D-norgestrel and progesterone in human urine

Pharmaceuticals are emerging contaminants and it must be noted that approximately 70 % of them are excreted via urine. Therefore, urine usage implies the risk of transfer of pharmaceutical residues to agricultural fields and environment contamination. Thus, this study aimed on the development and validation of a LC-MS/MS method for D-norgestrel (D-NOR) and progesterone (PRO) determination in human urine, as well as the evaluation of the removal efficiency of two methods (storage and evaporation), and the effects of acidification with sulfuric acid. The storage process was evaluated for 6 weeks, while the evaporation was assessed at three different temperatures (50, 75, and 100 °C). All experiments were done with normal urine (pH = 6.0) and acidified urine (pH = 2.0, with sulfuric acid). The results of validation showed good method efficiency. In the second week of storage, higher hormone degradation was observed. In the evaporation method, both D-NOR and PRO were almost completely degraded when the volume was reduced to the lowermost level. Results also indicate that acidification did not affect degradation. Overall, the results showed that combination of two methods can be employed for more efficient hormone removal in urine.