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Drying is one of the most efficient processes to reduce sludge volume by lowering moisture content. Vacuum filters are equipment suitable for sludge drying in small wastewater treatment plants. It is known that by reducing pressure in the filter, the vaporization process begins at lower temperature. The aim of this study is to estimate the values of liquid (free water) and gaseous (air) phase ratios in sludge cake during vacuum drying. Numerical results in function of heating temperature and cake initial moisture content are estimated by finite element analysis in a central point situated on cake surface.

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The suspended and settleable particles which exist permanently in the atmosphere have their concentration variation depending on weather conditions, traffic in the collecting area, industrial activities, etc. It is known that once these particles pollute the atmosphere can affect human health so, their collection by efficient filtration air systems is needed in order to proper evaluate them. In this paper the short-term concentration of the suspended particles from air is determined in the collection point located inside the Faculty of Engineering Hunedoara (Romania), in the vicinity of the road. The sampling was done in months May and June of year 2020, during three time intervals. Obtained minimum and maximum suspended particles concentrations were 13.43 &b.mu;g/m3 and 83.96 &b.mu;g/m3, respectively.

The paper presents a case study on wastewater sludge drying in a vacuum filter. Using finite element analysis it is estimated the variation with cake height, along its centerline, of temperature, liquid and gaseous phase ratios. Numerical results are estimated after 30 hours of drying at different temperatures (60°C, 80°C and 100°C), considering a sludge initial moisture content of 20%.