In this paper, the authors identified key elements important for circularity: (1) Background: The primary goal of circularity is to eliminate waste and to prove the constant use of resources. In the paper, we classify studies according to circular approaches. The authors identified main elements and classified them into categories important for circularity, starting with the managing and reducing waste and the recovery of resources; and ending with the circularity of material, and general circularity-related topics and presented scientific works dedicated to each of the above-mentioned categories. The authors analyzed several core elements from the first category aiming to investigate and connect different waste streams and provided a regression model; (2) Methods: The authors used a dynamic regression model to identify relationships among variables and selected the ones, which has an impact on the increase of biowaste. The research was delivered for the 27 European Union countries during the period between 2020 and 2019; (3) Conclusions: The authors indicated that the recycling rate of wasted electrical equipment in the previous year has an impact on the increase of recycling biowaste next year. This is explained as non-metallic spare parts of electronic equipment are used as biowaste for fuel production. And the separation process of the composites of electric equipment takes some time, on average the effect is evident in one year period.

Sharing activity is getting higher attention due to increasing popularity in recent years. In the paper, the authors investigated the main elements affecting the sharing activity. (1) Literature review: The theoretical part starts from the revision of definitions of sharing activity; description of the links between sharing and sustainable development, policy recommendations and relevant regulation in the field; later on, the study emphasises the key elements important for sharing. Finally, the authors investigated how the Covid-19 pandemic affected sharing activity; (2) Methods: During empirical research, the authors revised the list of 37 variables. The study uses data for each of the 27 EU countries from 2011 to 2020. The authors investigated correlation between macroeconomics variables to determine key variables for the regression model; (3) Results: The authors constructed a dynamic regression model that can be applied to predict the number of participants visiting sharing platforms in the European Union (EU); (4) Conclusions: The study shows that seeking to forecast the number of visits to sharing platforms it is necessary to use values of main macroeconomic variables such as consumer price index, productivity index, total unemployment rate, the number of users and households connected to the Internet, etc.

The authors have revised the circularity of materials, which is important to stimulate circular activity processes. The theoretical part starts with describing the characteristics of the circular activity and the comparison of circular and linear systems in terms of recycling. Later on, the authors examined key elements important for the circularity and the results of an examination of various sectors. The authors formed a correlation matrix and used a dynamic regression model to identify the circular material use rate. The authors suggested a three-level methodology, using it provided a dynamic regression model which could be applied for forecasting the size of circular material use rate in European Union countries. The results show that private investments into recycling and the recycling of electronic waste and the recycling of other municipal waste categories are important in seeking to increase the usage rate of circular materials.