The use of organic residues and waste for production of biogas as an energy source is a viable option for waste management and reduction of greenhouse gas emissions. However, before any eventual utilization of biogas, hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ) must be removed since those contaminants are highly undesirable in combustion systems. This work deals with the construction and examination of a laboratoryscale, low-cost test stand for quick evaluation of the existing and new methods for H 2 S and CO 2 removal from biogas. The test stand consists of two sections: one based on absorption in liquid phase (barbotage process) and the other adsorption in a bed of solid reagent. Seven different reagents of various concentrations were used in the experiment: sodium hydroxide (NaOH), ethylene glycol (EG), ethanoloamine (EA), diethanoloamine (DEA), and distilled water (H 2 O) in the barbotage section of the test stand, and bog iron ore (BIO) and activated carbon (AC) in the adsorption column. In the absorption tests, treating biogas with 1M NaOH solution and 100% EA resulted in complete removal of H 2 S and CO 2 . For 100% DEA, high H 2 S and moderate CO 2 absorption efficiency were achieved. EG and H 2 O allowed the removal of H 2 S only to a very limited extent. Both reagents used in the tests with adsorption in a bed, BIO and AC, were able to eliminate H 2 S from biogas, but practically did not change the concentration of CO 2 .

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Among the factors influencing tourist trail network development are political issues, including the presence of state borders, the possibility of crossing them and the accessibility of border zones. In the article, it was decided to look at changes in the offer of tourist trails (hiking and cycling) along the entire border of the Czech Republic after the extension of the Schengen area (within this area, crossing the border is possible anywhere, and not only at official border crossings). It should be emphasized here that the borders of the Czech Republic over most of their length run through mountainous areas and, apart from political factors, natural features should have a major impact on the development of tourist routes. In order to determine the coherence of the current network of trails on both sides of the Czech Republic state border, modern tourist maps have been analyzed, determining the number of places where it is possible to cross the state border with the help of a marked tourist trail. Based on that, two indicators were introduced to determine the degree of openness with all neighboring countries as regards the opportunity to cross on a tourist trail. Changes in the historical situation, a comparison of the accessibility of the border area before entering the Schengen area and 2019, were analyzed for two study areas using archival maps. Over a decade after the extension of the Schengen area, the number of places where tourist trails of neighboring countries approach the border has clearly increased. Crossing is more often made possible using hiking trails than cycling routes (trails of the first type cross the border every 7.91 km, while the latter every 13.3 km), but considering the speed of movement, it can be assessed that the openness for cyclists is higher than for hikers. Moreover, in many places there is still significant potential for further integration of tourist trail networks as trails created in one country often do not have a continuation on the other side of the border.

In recent years, a considerable development of the network of hiking trails has taken place in selected parts of the Sudetes. This has occurred both in areas of hitherto poorly developed tourist infrastructure (for example the Orlickie Foothills) as well as in traditional tourist regions with a quite good base (for example the Sowie Mountains). It was decided to analyse more precisely the changes which occurred in 2005-2017 in selected parts of the Middle Sudetes. For this purpose, changes in the density and connectivity of the networks of hiking trails were assessed using elements of the graph theory and, drawn from it, indices used in the topological analysis of spatial structure. A comparative analysis of maps was the basis for these works. Important factors deciding about the validity of marking new hiking trails are: their role in the network of trails and their tourist attractiveness. Those were evaluated using field works and an analysis of maps and tourist (sightseeing) literature. An additional aim was to examine ways of tracing new trails and changing routes of those already existing, taking into account the guidelines for hiking trails presented in literature. Marking new trails has undoubtedly enabled the development of networks, but not necessarily resulted in their higher connectivity (new sections of trails resulted in a higher number of nodes). However, new tourist values have been made accessible (especially scenic and cultural ones) and planning hikes has become simpler, which is particularly important in the vicinity of spas. New hiking trails and changes of routes of those existing earlier must be assessed positively in terms of the relation between natural and artificial (hard) surfaces.

Most of the Polish-Czech borderland is of great tourist attractiveness and has a considerable potential for tourism development. In order for a tourist region to function properly, appropriate public transport is necessary, which in the analysed case also includes cross-border transport. The aim of this paper is to evaluate the level of development of cross-border public transport in the Polish-Czech borderland from the perspective of its attractiveness and the development of tourism functions. Despite the fact that both Poland and Czechia joined Schengen the development of cross-border journeys’ range has been relatively slow (in some cases even diminishing). The coordination of services organised by the two countries is poor in terms of routes and timetables (in the latter case especially taking into account tourists’ needs). Locations where it is possible to cross the border using means of public transport are located irregularly and do not always correspond with the tourist attractiveness of a region. For the tourists who do not have a vehicle or for those who consciously refrain from using the car on holidays, the border is still a barrier.

The political transformation taking place in Central European countries at the turn of 1980s and 1990s influenced, among other aspects, the methods of nature protection and making it available for tourism. The changes taking place at that time have been traced in the article on the example of three sandstone landscapes, which belong to the most popular geotouristic attractions of the Czech Republic and Poland: Prachov Rocks Nature Reserve with adjacent fragments of the Bohemian Paradise Protected Landscape Area, Adršpach-Teplice Rocks National Nature Reserve and the Table Mountains National Park. These changes were analysed on the basis of transformations of the networks of hiking trails and development of other tourism facilities within the boundaries of the protected areas. Analysis covers the entire period from the end of communism (1980s) up to present days. According to the study, in the case of all analysed protected areas, the systemic transformation in Central Europe played an important role as a factor affecting the network of hiking trails. In each case, however, local factors were also important. The biggest changes occurred in the Adršpach-Teplice Rocks and the Table Mountains. In the first case, the number and distribution of visitors needed to be controlled, leading to modification of route network. The main reason of its significant reduction was to separate paid routes from those not charged. In the Table Mountains, the network was substantially developed as a consequence of the establishment of a national park there and the political changes at the turn of twentieth and twenty-first centuries which opened the border zone and forced the marking of new tourist trails. In the Prachov Rocks, the existing layout of hiking trails has been largely kept unchanged because the continuous intensive tourist traffic did not allow any reductions, even if these would help to protect the environment. On the other hand, the network was really well developed, that it did not require further growth. Today's networks of tourist trails in the Prachov Rocks and some parts of the Table Mountains seem too developed, taking into account the protective regime of both areas. In terms of interpretation of geoheritage, the most extensive and targeted offer can be found in the Table Mountains National Park. Referring to the methods used, the graph theory cannot be applied easily to tourist trails networks, especially when a dissected landscape is analysed. A simple but very helpful indicator illustrating the development of the network is the density of tourist trails per square kilometre.

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