The pandemic of the COVID-19 virus disease has resulted in significant changes in everyday life. As a result, two-thirds of the urban population has been forced to alter previously established travel habits. With this in mind, the international scientific community wonders if the newly formed travel habits could be maintained after the pandemic is over. This paper presents the findings of a survey conducted among students in Kragujevac prior to and during the COVID-19 virus pandemic. Furthermore, the citizens' expectations regarding the change in travel habits following the end of the pandemic are presented. For a period of five years, the survey was conducted once a year on students at the Faculty of Engineering in Kragujevac (Serbia). According to the survey results, during the pandemic, the car was considered a more comfortable mode of transportation than before. When compared to before the pandemic, the share of student families with two cars increased by 15%. The number of cyclists has also increased, making the lack of bike paths during the pandemic a more visible issue than previously. The students polled believe that once the pandemic is over, they will walk more and continue to rely on public transportation as before.
More and more attention in sewage sludge management is being devoted to its environmental utilization. This approach is justified both from economic and environmental points of view. However, as with any method, there are certain possibilities and limitations. The goal of the natural utilization of sewage sludge is to recover the valuable agronomic properties and fertilizing potential of the sludge. The main aspect limiting the possibility of using sludge as a fertilizer is the heavy metal content. In this paper, an analysis of the risk of environmental contamination in the case of application of sewage sludge with different forms of sludge treatment was carried out. Risk indices such as Igeo and PERI, based on the comparison of total metal content in sludge and soil, as well as RAC and ERD indices, which take into account the mobility of metals in soil, were calculated. It was shown that high levels of potential risk and geoaccumulation indicators do not necessarily disqualify the use of sewage sludge, the key aspect is the form of mobility in which the heavy metals are found in the sludge, and this should be the only aspect taken into account for the possibility of their environmental use.
To improve solar collector (SC) efficiency, a variety of designs and
materials have been introduced into production practice. Studies describing
SC specifics, therefore, are particularly valuable to the scientific
community as they contribute to the overall body of knowledge and constant
improvement the in the scientific field. In that regard, the study presented
in this paper analyses the thermal performance of the fixed flat-plate
collector (fFPSC) with an Sn-Al2O3 selective absorber. The fFPSC design
utilizes gravity water flow in an open loop system. A two-month study was
conducted to perform the analysis. The experiment was based on measurements
of water flow in the fFPSC, the water temperature at the fFPSC inlet and
outlet, and solar radiation intensity on a horizontal surface. Results for
three randomly selected measurement days have shown that fFPSC can achieve
relatively satisfactory values for average daily specific heat power,
thermal efficiency, and inlet-outlet water temperature gradient,
respectively: June 29 (381.78 W/m2, 60.67%, and 9.06 ?C), June 30 (364.33
W/m2, 59.43%, and 7.46 ?C), and July 15 (373.06 W/m2, 59.85%, and 8.69 ?C).
Apart from the relatively good measurement results, this type of SC does not
require circulating pumps for operation, which brings a double advantage:
energy saving and energy production.
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