Ammonia Recovery from Digestate Using Gas-Permeable Membranes: A Pilot-Scale Study

The reduction and recovery of nitrogen (N) from anaerobically digested manure (digestate) is desirable to mitigate N-related emissions, mainly ammonia and nitrate, derived from digestate land application in nutrient-saturated zones. This work reports the results of a gas-permeable membrane (GPM) pilot-scale plant to recover ammonia from digestate in the framework of the EU project Ammonia Trapping. The total ammonia nitrogen (TAN) concentration in digestate was reduced by 34.2% on average (range 9.4–57.4%). The recovery of TAN in the trapping solution in the form of a (NH4)2SO4 solution averaged 55.3% of the removed TAN, with a TAN recovery rate of 16.2 g N m−2 d−1 (range between 14.5 and 21.0 g N m−2 d−1). The TAN concentration in the trapping solution achieved a value of up to 35,000 mg N L−1. The frequent change of the trapping solution has been proven as an efficient strategy to improve the overall performance of the GPM technology.

Determination of Formaldehyde Yields in E-Cigarette Aerosols: An Evaluation of the Efficiency of the DNPH Derivatization Method

Recent reports have suggested that (1) formaldehyde levels (measured as a hydrazone derivative using the DNPH derivatization method) in Electronic Nicotine Delivery Systems (ENDS) products were underreported because formaldehyde may react with propylene glycol (PG) and glycerin (Gly) in the aerosol to form hemiacetals; (2) the equilibrium would shift from the hemiacetals to the acetals in the acidic DNPH trapping solution. In both cases, neither the hemiacetal nor the acetal would react with DNPH to form the target formaldehyde hydrazone, due to the lack of the carbonyl functional group, thus underreporting formaldehyde. These reports were studied in our laboratory. Our results showed that the aerosol generated from formaldehyde-fortified e-liquids provided a near-quantitative recovery of formaldehyde in the aerosol, suggesting that if any hemiacetal was formed in the aerosol, it would readily hydrolyze to free formaldehyde and, consequently, form formaldehyde hydrazone in the acidic DNPH trapping solution. We demonstrated that custom-synthesized Gly and PG hemiacetal adducts added to the DNPH trapping solution would readily hydrolyze to form the formaldehyde hydrazone. We demonstrated that acetals of PG and Gly present in e-liquid are almost completely transferred to the aerosol during aerosolization. The study results demonstrate that the DNPH derivatization method allows for an accurate measurement of formaldehyde in vapor products.

A Sensitive and Quantitative Isotope-Dilution LC-MS/MS Method for Analysis of Hydrazine in Tobacco Smoke

A new isotope dilution liquid chromatography/tandem mass spectrometric method was developed for the analysis of potential hydrazine present in tobacco smoke. The sample preparation was performed via an optimized derivatization method using an aqueous buffer:methanol solution of 2-nitrobenzaldehyde (10 g/L) used as a derivatizing agent. The mainstream smoke of cigarettes was passed through a glass fiber filter pad followed by a trapping solution containing an isotopically labeled 15N2-hydrazine used as internal standard. After smoking, the filter pad was extracted with the trapping solution and then incubated for 30 minutes at 35°C. An aliquot of the extract was centrifuged and the resultant hydrazone was quantified by liquid chromatography tandem mass spectrometry (LC-MS/MS). The isotope dilution standard calibration curve demonstrated good linearity (R2 > 0.999) from 0.079 to 248 ng/mL, with limits of quantification in mainstream smoke of 0.2 and 0.4 ng/cig for ISO and Canadian Intense smoking regimens, respectively. The method recovery was assessed using samples spiked with solutions of known amounts of hydrazine. The results showed good accuracy with recoveries ranging from 98 to 111%. Although there were no detectable levels of hydrazine in the reference cigarettes used in the validation (KR3R4F), the method precision was estimated to be ~10% based on the variability observed in the spiked samples. Trapping efficiencies were assessed using a hydrazine permeation tube providing a known amount of hydrazine vapor such that the distribution between the vapor phase and particulate phase of mainstream smoke could be determined.

Effect of the Type of Gas-Permeable Membrane in Ammonia Recovery from Air

Animal production is one of the largest contributors to ammonia emissions. A project, “Ammonia Trapping”, was designed to recover gaseous ammonia from animal barns in Spain. Laboratory experiments were conducted to select a type of membrane most suitable for gaseous ammonia trapping. Three types of gas-permeable membranes (GPM), all made of expanded polytetrafluoroethylene (ePTFE), but with different diameter (3.0 to 8.6 mm), polymer density (0.45 to 1.09), air permeability (2 to 40 L·min−1·cm2), and porosity (5.6 to 21.8%) were evaluated for their effectiveness to recover gas phase ammonia. The ammonia evolved from a synthetic solution (NH4Cl + NaHCO3 + allylthiourea), and an acidic solution (1 N H2SO4) was used as the ammonia trapping solution. Replicated tests were performed simultaneously during a period of 7 days with a constant flow of acidic solution circulating through the lumen of the tubular membrane. The ammonia recovery yields were higher with the use of membranes of greater diameter and corresponding surface area, but they were not affected by the large differences in material density, porosity, air permeability, and wall thickness in the range evaluated. A higher fluid velocity of the acidic solution significantly increased—approximately 3 times—the mass NH3–N recovered per unit of membrane surface area and time (N-flux), from 1.7 to 5.8 mg N·cm−2·d−1. Therefore, to optimize the effectiveness of GPM system to capture gaseous ammonia, the appropriate velocity of the circulating acidic solution should be an important design consideration.

Soil CO2 flux: a method comparison of closed static chambers in a sugarcane field

A large variety of techniques have been used to measure soil CO2 released from the soil surface, and much of the variability observed between locations must be attributed to the different methods used by the investigators. Therefore, a minimum protocol of measurement procedures should be established. The objectives of this study were (a) to compare different absorption areas, concentrations and volumes of the alkali trapping solution used in closed static chambers (CSC), and (b) to compare both, the optimized alkali trapping solution and the soda-lime trapping using CSC to measure soil respiration in sugarcane areas. Three CO2 absorption areas were evaluated (7; 15 and 20 % of the soil emission area or chamber); two volumes of NaOH (40 and 80 mL) at three concentrations (0.1, 0.25 and 0.5 mol L-1). Three different types of alkaline traps were tested: (a), 80 mL of 0.5 mol L-1 NaOH in glass containers, absorption area 15 % (V0.5); (b) 40 mL of 2 mol L-1 NaOH retained in a sponge, absorption area 80 % (S2) and (c) 40 g soda lime, absorption area 15 % (SL). NaOH concentrations of 0.5 mol L-1 or lower underestimated the soil CO2-C flux or CO2 flux. The lower limit of the alkali trap absorption area should be a minimum of 20 % of the area covered by the chamber. The 2 mol L-1 NaOH solution trap (S2) was the most efficient (highest accuracy and highest CO2 fluxes) in measuring soil respiration.

Investigation on Nanorod TCO Light-trapping for a-Si:H Solar Cells in Superstrate Configuration

ABSTRACTLight trapping due to rough transparent conductive oxide (TCO) surfaces is a common and industrially applied technique in thin film silicon solar cells. In this study, we demonstrate a novel light trapping solution using electrochemically deposited, highly doped zinc oxide (ZnO) nanorod arrays which goes beyond standard light management concepts. The n-doped ZnO rods enable the application as front electrode in superstrate configuration. We explain our experimental results by multidimensional solar cell simulations and show how the nanorod array geometry influences the cell performance. The requirement is demonstrated to choose an appropriate average nanorod distance which strongly influences the electrical cell characteristics. The results clearly outline the potential of TCO nanorod technology for enhanced light trapping.

Determination of Hydrogen Cyanide in Cigarette Mainstream Smoke by LC/MS/MS

An LC/MS/MS method is presented for the determination of hydrogen cyanide in cigarette mainstream smoke. Cyanide is derivatized with 2,3-naphthalenedicarboxaldehyde and taurine to form a benzo[f]isoindole derivative, which is then analyzed by LC/MS/MS. Isotopic KCN (K13C15N) was used as an internal standard. The regression equation was linear within the range 2.4331 ng/mL for cyanide with a correlation coefficient >0.999. The LOD was calculated as 4.1 ng/cigarette. The influence of the sodium hydroxide trapping solution concentration on the results is discussed. A 1 M solution showed the best results in terms of sample stability and trapping efficiency. The method proved to be robust, reliable, and more selective than current methods, making it a logical choice for determination of total cyanide in cigarette smoke.

Measurement of exogenous carbohydrate oxidation: a comparison of [U-14C]glucose and [U-13C]glucose tracers

The purpose of this study was to assess the level of agreement between two techniques commonly used to measure exogenous carbohydrate oxidation (CHOEXO). To accomplish this, seven healthy male subjects (24 ± 3 yr, 74.8 ± 2.1 kg, V̇O2max 62 ± 4 ml·kg−1·min−1) exercised at 50% of their peak power for 120 min on two occasions. During these exercise bouts, subjects ingested a solution containing either 144 g glucose (8.7% wt/vol glucose) or water. The glucose solution contained trace amounts of both [U-13C]glucose and [U-14C]glucose to allow CHOEXO to be quantified simultaneously. The water trial was used to correct for background 13C enrichment. 13C appearance in the expired air was measured using isotope ratio mass spectrometry, whereas 14C appearance was quantified by trapping expired CO2 in solution (using hyamine hydroxide) and adding a scintillator before counting radioactivity. CHOEXO measured with [13C]glucose ([13C]CHOEXO) was significantly greater than CHOEXO measured with [14C]glucose ([14C]CHOEXO) from 30 to 120 min. There was a 15 ± 4% difference between [13C]CHOEXO and [14C]CHOEXO such that the absolute difference increased with the magnitude of CHOEXO. Further investigations suggest that the difference is not because of losses of CO2 from the trapping solution before counting or an underestimation of the “strength” of the trapping solution. Previous research suggests that the degree of isotopic fractionation is small (S. C. Kalhan, S. M. Savin, and P. A. Adam. J Lab Clin Med89: 285–294, 1977). Therefore, the explanation for the discrepancy in calculated CHOEXO remains to be fully understood.

Determination of Crude Protein in Animal Feed, Forage, Grain, and Oilseeds by Using Block Digestion with a Copper Catalyst and Steam Distillation into Boric Acid: Collaborative Study

A collaborative study was conducted to evaluate the repeatability and reproducibility of an extension of AOAC Official Method 991.20, Nitrogen (Crude) in Milk, to animal feed, forage (plant tissue), grain, and oilseed materials. Test portions are digested in an aluminum block at 420°C in sulfuric acid with potassium sulfate and a copper catalyst. Digests are cooled and diluted, and concentrated sodium hydroxide is added to neutralize the acid and make the digest basic; the liberated ammonia is distilled by using steam distillation. The liberated ammonia is trapped in a weak boric acid solution and titrated with a stronger standardized acid, hydrochloric acid; colorimetric endpoint detection is used. Fourteen blind samples were sent to 13 collaborators in the United States, Denmark, Sweden, Germany, and the United Kingdom. Recoveries of nitrogen from lysine, tryptophan, and acetanilide were 86.8, 98.8, and 100.1%, respectively. The within-laboratory relative standard deviation (RSDr, repeatability) ranged from 0.40 to 2.38% for crude protein. The among-laboratories (including within-) relative standard deviation (RSDR, reproducibility) ranged from 0.44 to 2.38%. It is recommended that the method be adopted First Action by AOAC INTERNATIONAL. A lower concentration (1% H3BO3) of trapping solution was compared with the concentration specified in the original protocol (4% H3BO3) and was found comparable for use in an automatic titration system in which titration begins automatically as soon as distillation starts. The Study Directors recommend that 1% H3BO3 as an optional alternative to 4% boric acid trapping solution be allowed for automatic titrators that titrate throughout the distillation.