Ammonia

About: Ammonia is a research topic. Over the lifetime, 16217 publications have been published within this topic receiving 271940 citations. The topic is also known as: NH3 & azane.

Effect of pH, temperature, amount of litter and storage density on ammonia emissions from stable manure

Abstract: In laboratory tests using stable manure consisting of wheat straw and slurry, ammonia emission was found to have two peaks corresponding to the population dynamics of proteolytic bacteria and amino acid-degrading bacteria respectively. Cumulative ammonia emissions over 14 days were 0.8-23.2 % of the initial total nitrogen (N t ) and were both abiotically and biotically induced. Changes in pH had the most significant effect on the abiotically induced ammonia emissions. After 14 days of decomposition, at pH values of 6.0 and 7.5, abiotically induced emissions remained close to the limit of detectability, whereas at pH 9.0 as much as 9.8 % of the initial N t was lost. An increase in storage pressure from 0 to 400 and 800 kp/m 2 generally decreased the biotic emissions to 9.6, 2.8 and 2.3 %; while increasing the amounts of litter (2.5, 5.0 and 15.0 kg straw/LAU per day) led to a decline not only in the biotic (17.1, 12.8, 3.5 %) but also in the abiotic emissions (6.1, 5.5, 1.6%). Varying the temperature (20, 30 and 40 °C) resulted in biotically induced emissions of 7.9, 11.7 and 11.6%, respectively, and abiotically induced emissions of 1.1, 1.4 and 2.2 % of the initial N t . At temperatures of 30 and 40 °C, the amount of microbially digested sources of carbon available was obviously sufficient to permit almost total reincorporation of NH 4 + from 4 days onwards.

Effect of potassium and barium on the stability of a carbon-supported ruthenium catalyst for the synthesis of ammonia

Abstract: The effect of potassium and barium on the activity and thermal stability of a carbon-based ruthenium catalyst for the synthesis of ammonia has been studied. Kinetic measurements in NH 3 synthesis were carried out in a flow differential reactor operating at standard conditions ( p =6 MPa, T =673 K, X NH 3 =8%, H 2 : N 2 =3 : 1). Overheating of the samples was carried out at 793 K for 24 h. The examinations have been supplemented by XRD and chemisorption studies for the characterization of the ruthenium dispersion as well as by studying the catalysts methanation. It has been found that the barium-promoted catalyst is more active in NH 3 synthesis and more resistant to overheating than the catalyst promoted with potassium. The activity of Ba–Ru/C is much higher than that of a commercial fused-iron catalyst. This is important for industrial practice.

Operational boundaries for nitrite accumulation in nitrification based on minimum/maximum substrate concentrations that include effects of oxygen limitation, pH, and free ammonia and free nitrous acid inhibition.

Abstract: Recent studies on shortcut biological nitrogen removal (SBNR), which use the concept of denitrification from nitrite, have reported the key factors affecting nitrite build-up, such as dissolved oxygen (DO) limitation, pH, and free ammonia (FA) and free nitrous acid (FNA) inhibition. This study extends the concept of the traditional minimum substrate concentration (S(min)) to explain the simultaneous effect of those factors. Thus, we introduce the minimum DO concentration (DO(min)) and the maximum substrate concentration (S(max)) that are needed to support a steady-state biological system. We define all three values as the MSC values. The model provides a method to identify good combinations of pH, DO, and total ammonium nitrogen (TAN) to support shortcut nitritation. We use MSC curves to show that the effect of DO-alone and the effect of DO plus direct pH inhibition cannot give strong enough selection against nitrite oxidizing bacteria to work in a practical setting. However, adding the FA and FNA effects gives a strong selection effect that is accentuated near pH 8. Thus, a generalized conclusion is that having pH approximately 8 is favorable in many situations. We defined a specific operational boundary to achieve shortcut nitritation coupled to anaerobic ammonium oxidation (ANAMMOX), in which the effluent concentrations of total nitrite and total ammonium should be approximately equal. Experimental results for alkaline and acidic nitrite-accumulating systems match the trends from the MSC approach. In particular, acidic systems had to maintain higher total ammonium, total nitrite, and DO concentrations. The MSC values are a practical tool to define the operational boundaries for selecting ammonium-oxidizing bacteria while suppressing nitrite-oxidizing bacteria.

Selective Nitrate-to-Ammonia Transformation on Surface Defects of Titanium Dioxide Photocatalysts

Abstract: Ammonia (NH3) is an essential chemical in modern society, currently manufactured via the Haber–Bosch process with H2 and N2 under extremely high pressure (>200 bar) and high-temperature conditions (>673 K). Toxic nitrate anion (NO3–) contained in wastewater is one potential nitrogen source. Selective NO3–-to-NH3 transformation via eight-electron reduction, if promoted at atmospheric pressure and room temperature, may become a powerful recycling process for NH3 production. Several photocatalytic systems have been proposed, but many of them produce nitrogen gas (N2) via five-electron reduction of NO3–. Here, we report that unmodified TiO2, when photoexcited by ultraviolet (UV) light (λ > 300 nm) with formic acid (HCOOH) as an electron donor, promotes selective NO3–-to-NH3 reduction with 97% selectivity. Surface defects and Lewis acid sites of TiO2 behave as reduction sites for NO3–. The surface defect selectively promotes eight-electron reduction (NH3 formation), while the Lewis acid site promotes nonselect...