Enhanced MFC power production and struvite recovery by the addition of sea salts to urine

© 2016 The Authors Urine is an excellent fuel for electricity generation in Microbial Fuel Cells (MFCs), especially with practical implementations in mind. Moreover, urine has a high content in nutrients which can be easily recovered. Struvite (MgNH4PO4·6H2O) crystals naturally precipitate in urine, but this reaction can be enhanced by the introduction of additional magnesium. In this work, the effect of magnesium additives on the power output of the MFCs and on the catholyte generation is evaluated. Several magnesium sources including MgCl2, artificial sea water and a commercially available sea salts mixture for seawater preparation (SeaMix) were mixed with real fresh human urine in order to enhance struvite precipitation. The supernatant of each mixture was tested as a feedstock for the MFCs and it was evaluated in terms of power output and catholyte generation. The commercial SeaMix showed the best performance in terms of struvite precipitation, increasing the amount of struvite in the solid collected from 21% to 94%. Moreover, the SeaMix increased the maximum power performance of the MFCs by over 10% and it also changed the properties of the catholyte collected by increasing the pH, conductivity and the concentration of chloride ions. These results demonstrate that the addition of sea-salts to real urine is beneficial for both struvite recovery and electricity generation in MFCs

Droplet size dispersion in the spray cone of jet-swirl atomizers

The burning process in the combustion engines strongly depends on the quality of atomization; hence the microstructure of the atomized fuel is an important factor for designers. Jet-swirl atomizers spray fuel into a wide cone of directions, as quite small droplets, which ensures effective burning. In some applications (e.g. turbine engines) it is important to guarantee that a certain portion of mass of the fuel is atomized in droplets of diameters lower to a fixed critical value Dk. This can be done by creating a quasi-monodispersive distribution of small droplets. The paper presents the results of experimental and statistical investigations into the microstructure of aerosols, with particular interest in the relative standard deviation of droplets diameters d and its relations with the mass portion of droplets of diameters greater the critical value Dk. Diagram of flow through a jet-swirl atomizer with swirling grooves, relative radius is the ratio of radius at which measurements were made, to the spray cone radius, log-normal distribution fitted to a typical experimental data set and the corresponding mass distribution, log-normal distribution fitted to a typical experimental data set and the corresponding mass distribution, Dependence of the mass carried by droplets are illustrated in the paper