Quantifying soil N2O emissions from soil and anaerobically digested swine manure, nitrification and denitrification using 15N isotope labeling method.

Increasing use of anaerobically digested swine manure in the farmland makes it necessary to understand its impact on N2O emissions, regarding the source of N2O and the corresponding mechanism of action. We used a 15N-labeled sulfate modifying the soil in order to identify the sources of N2O and the pathways of nitrification and denitrification. Three soil moisture contents (50% WHC, 75% WHC, and 100% WHC) along with three levels of anaerobically digested swine manure (0 g·kg-1, 10 g·kg-1, and 25 g·kg-1) were tested using randomized block design. Although the combined effect of contents of anaerobically digested swine manure and the soil moisture contents added to the system stimulated the utilization of soil N and promoted denitrification, the process of nitrification dominated. In anaerobically digested swine manure-treated soils, the rate of contribution of anaerobically digested swine manure to N2O accounted for 68.6-99.8%. In the 25 g·kg-1 treatment, the maximum of N2O produced by denitrification and nitrification were 14.1% and 93.1%.

Localized Electrochemical Impedance Measurements on Nafion Membranes: Observation and Analysis of Spatially Diverse Proton Transport Using Atomic Force Microscopy.

The distribution of ion conductive channels on the Nafion membrane surface, which determines the formation of the three-phase boundary, plays a very important role in improving the performance of proton-exchange membrane fuel cells. Therefore, understanding the microstructures at the catalyst layer/membrane interfaces of proton-exchange membranes is essential. Although current-sensing atomic force microscopy (AFM) can present some surface conductance data, localized impedance measurement providing more accurate proton-transport information is desirable. To obtain this information, in our study, localized electrochemical impedance spectroscopy was measured automatically with a home-built AFM-electrochemical impedance spectroscopy setup in which AFM was coupled with an impedance tester by a customized procedure. By this method, the localized proton-transport resistance at different humidities was observed in spatially diverse locations, and the value decreased as the membrane became hydrated. Furthermore, the microstructure of the Nafion membrane was numerically reconstructed at different hydration levels to examine the relationship between the membrane microstructural morphology and proton-transport resistance. The results showed that the spatial diversity of proton-transport resistance arose from the variable concentration of hydrophilic groups at the contact location of the AFM tip and the membrane, and from the heterogeneity of dry sulfonic acid groups in the membrane that creates local variation in water content.

Anaerobic digestion performance of sweet potato vine and animal manure under wet, semi-dry, and dry conditions.

Sweet potato vine (SPV) is an abundant agricultural waste, which is easy to obtain at low cost and has the potential to produce clean energy via anaerobic digestion (AD). The main objectives of this study were to reveal methane production and process stability of SPV and the mixtures with animal manure under various total solid conditions, to verify synergetic effect in co-digestion of SPV and manure in AD systems, and to determine the kinetics characteristics during the full AD process. The results showed that SPV was desirable feedstock for AD with 200.22 mL/g VSadded of methane yield in wet anaerobic digestion and 12.20 Lmethane/Lworking volume in dry anaerobic digestion (D-AD). Synergistic effects were found in semi-dry anaerobic digestion and D-AD with each two mixing feedstock. In contrast with SPV mono-digestion, co-digestion with manure increased methane yield within the range of 14.34-49.11% in different AD digesters. The values of final volatile fatty acids to total alkalinity (TA) were below 0.4 and the values of final pH were within the range of 7.4-8.2 in all the reactors, which supported a positive relationship between carbohydrate hydrolysis and methanogenesis during AD process. The mathematical modified first order model was applied to estimate substrate biodegradability and methane production potential well with conversion constant ranged from 0.0003 to 0.0953 1/day, which indicated that co-digestion increased hydrolysis efficiency and metabolic activity. This work provides useful information to improve the utilization and stability of digestion using SPV and livestock or poultry manure as substrates.