Cold Gas Microthruster Characterization in Vacuum, using a High Precision Microbalance

In the framework of the development of a cold gas micropropulsion system, pursued since 2005 in the aerospace laboratories of the II Faculty of Engineering of the University of Bologna, a microbalance was designed, assembled, calibrated and characterized. This project, entirely developed by the University of Bologna, under a contract with Carlo Gavazzi Space (CGS), was aimed at the evaluation of the thrust generated by a MEMS (micro electromechanical systems) based cold gas micropropulsion system to be flown on-board the first microsatellite of the University of Bologna (ALMASat-1)1 for attitude and orbit control experiments. The microbalance is based on the pendulum principle and makes use of a Laser Optical Displacement Sensor to measure the pendulum displacement generated by the thruster. The force exerted by the thruster, together with its own weight, identifies an equilibrium condition whose angular displacement with respect to its initial vertical position is proportional to the measured thrust. The interface between the thruster and the Optical Sensor was designed with the aim of minimizing the friction on the hinge point, so an Aluminium sheet was used. A software interface was developed in LabVIEW\uae environment in order to evaluate the real time thrust generated by the microthruster. This paper presents the results of the measurements, fully characterizing the balance in terms of accuracy, resolution and thrust range. Finally, the experimental results in vacuum condition (10-2 mbar) are compared to the fluid dynamic simulations carried out on the microdevices manufactured in collaboration with Carlo Gavazzi Space (CGS) and the IMM section of the Italian National Research Council (CNR) of Bologna, using a Deep Reactive Ion Etching (DRIE) technique and successive bonding

Recycling nitrogen from liquid digestate via novel reactive struvite and zeolite minerals to mitigate agricultural pollution

Recycling nutrients is of paramount importance. For this reason, struvite and nitrogen enriched zeolite fertilizers produced from wastewater treatments are receiving growing attention in European markets. However, their effects on agricultural soils are far from certain, especially struvite, which only recently was implemented in EU Fertilizing Product Regulations. In this paper, we investigate the effects of these materials in acid sandy arable soil, particularly focusing on N dynamics, evaluating potential losses, transformation pathways, and the effects of struvite and zeolitic tuffs on main soil biogeochemical parameters, in comparison to traditional fertilization with digestate. Liming effect (pH alkalinization) was observed in all treatments with varying intensities, affecting most of the soil processes. The struvite was quickly solubilized due to soil acidity, and the release of nutrients stimulated nitrifying and denitrifying microorganisms. Zeolitic tuff amendments decreased the NOx gas emissions, which are precursors to the powerful climate altering N2O gas, and the N enriched chabazite tuff also recorded smaller NH3 emissions compared to the digestate. However, a high dosage of zeolites in soil increased NH3 emissions after fertilization, due to pronounced pH shifts. Contrasting effects were observed between the two zeolitic tuffs when applied as soil amendments; while the chabazite tuff had a strong positive effect - increasing up to ∼90% the soil microbial N immobilization - the employed clinoptilolite tuff had immediate negative effects on the microbial biomass, likely due to the large quantities of sulphur released. However, when applied at lower dosages, the N enriched clinoptilolite also contributed to the increase of microbial N. From these outcomes, we confirm the potential of struvite and zeolites to mitigate the outfluxes of nutrients from agricultural systems. To gain the best results and significantly lower environmental impacts, extension practitioners could give recommendations based on the soils that are planned for zeolite application

Short-Term response of soil microbial biomass and gaseous emissions to different chabazite zeolitite amendments

Zeolitites (ZTs) are rocks containing more than 50 % of zeolites and are worldwide recognized as a suitable and valuable soil amendment. Once homogenized in the soil or in the cultivation substrate, ZTs enhance soil physicochemical properties and nitrogen (N) use efficiency. However, little is known about their effects on soil microbial biomass and on how they influence soil gaseous emissions, which may represent an important contribution of greenhouse effect. This study aims at i) evaluating short-term effects of different chabazite-rich ZT (CHAZT) amendments on soil microbial biomass and activity and ii) evaluating the effects of different CHAZT amendments on soil gaseous emissions (CO2, N2O, NOx and NH3) soon after the application. To reach these goals a silty-clay agricultural soil was amended with different percentages of natural CHAZT (NZ, at 5 and 15 wt%) and NH4-enriched CHAZT (CZ, at 10 wt%) in two separate incubation experiments. In the first incubation experiment, soil dissolved organic carbon (C), total dissolved N, NH4, NO3, NO2, microbial biomass C and N, and ergosterol were measured periodically over a 16 day period. To verify the microbial immobilization of the N derived from CZ, a naturally high 15N source (pig slurry) was used for enriching the mineral and microbial biomass 15N signature was monitored over the incubation. In the second incubation experiment, an investigation of soil CO2, N2O, NOx and NH3 fluxes was carried out for a total of 24 h both immediately after the application of urea and without a further N input. Concerning the effect on soil microbial biomass (first experiment), ergosterol content increased in the soil amended with 5 % NZ while no clear trends were observed in the soil amended with 15 % NZ, suggesting that fungal biomass was favored at lower application rate. CZ amended soil showed evidence of nitrification, since microbial biomass N was directly related to NO3 production and inversely related to NH4. Isotopic measurements confirmed immediate assimilation of N derived from CZ. In the second experiment, immediate CO2, N2O, NOx and especially NH3 emissions after fertilizer application were generally reduced (up to 60 %) in soils amended with NZ, indicating it as a valuable material for reducing soil C-N gaseous losses. CZ application lowered CO2 and N2O emissions, but very high NOx fluxes occurred even without applying any further N input. NH3 emissions were higher in NH4-enriched zeolites amended soil, but if the amendment is performed without further N inputs, the emissions can be significantly lowered with respect to a conventional urea fertilization. These results suggested that the CZ used in this study supplied an immediately available N pool to the microbial biomass and that NZ can be a suitable material for mitigating gaseous N and C losses from soil or substrates