Synthesis or humification of humic substances (HSs) is the second widely applied organic compound transformation process after photosynthesis. Peat decomposition process results in a production of a HSs which has a high demand in agriculture, forestry, and gardening areas. Addition of the KOH is good option for environmental protection and K+ belongs to the nitrogen, potassium and phosphorous (NKP) mineral component. A homogenization process in a customize for commerce, where peat treatment technology was improved with the help of the cavitation effect. This effect was provided with the help of the high-speed mixer-disperser (HSMD) developed at Riga Technical University. Mechanical cavitation causes relatively high energy shifts from mechanical movement of cavitation causing elements to the liquid medium which causes efficient destruction of particles inside a suspension. Values of the peat particle diameter at 50 % in the cumulative distribution before and after 1, 2, and 3 homogenization cycles were measured in the present study. The aim of the present study was to find the optimal conditions (KOH concentration, cavitation cycles and reaction temperature) to produce potassium humate (K-HSs) regarding sustainable regenerative approach aspects. Cavitation treatment of the tested peat particle diameter at 50 % in the cumulative distribution (d50) from 267 down to 129 µm; the peak in the size range from 160 up to 409 µm completely disappears and significantly decreases the number of Dalton’s which causes the more efficient formation of fulvic acid caused by increased concentration of carbonyl and carboxyl groups as compared with the conventional homogenization method.

Statistical, morphological and functional approaches have long been used to delineate spatial boundaries of urban agglomerations. This research uses data from the Central Statistical Bureau and the State Revenue Service. The results indicate that morphological and functional approaches are essential when defining the agglomeration, however the outcomes are different. The most relevant consistency was observed in the territorial units adjoining the city of Riga due to the fact that they have a common labour market with Riga and share a strong functional linkage. However, the spatial extent based on the morphological approach confirms and highlights the effects of urban sprawl.

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Belgeo est mis à disposition selon les termes de la licence Creative Commons Attribution 4.0 International.

The effects of polypropylene fibers on the fracture of concrete and steel-fiber-reinforced concrete (SFRC) are studied. Properties of the composites were investigated by conducting four-point bending tests. The experimental data obtained showed a good overall improvement in SFRC properties with addition of polypropylene fibers.

Large housing estates from the socialist era are a characteristic feature of the built environment in the cities of Central and Eastern Europe. Many urban researchers are increasingly interested in residential changes in these areas, showing how demographic and socioeconomic processes interact with the decline or upgrading of this distinct type of housing. In Europe, the debate concerning large housing estates is largely related to a declining and ageing population, as well as to housing conditions. In Latvia, the underdeveloped housing market and the massive privatisation of the housing stock to sitting tenants have contributed, since the late-Soviet period, to inherited socio-spatial structures. During the 2000s, the second decade of post-socialist transition, the increasing residential mobility of affluent people was observed. However, the issue of its impact on residential composition in the large housing estates remains ambiguous. This chapter discusses the patterns of population change and composition in the most distinctive type of housing in the capital city, Riga. We draw our empirical evidence from there due to the widely acknowledged fact that the most notable social changes and the fastest economic growth have tended to be concentrated and much more advanced in capital cities. Moreover, a significant number of city residents continue to live in mass housing built in the Soviet period.

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Fens store significant amounts of organic matter and thus are of high importance from the perspective of the organic carbon biogeochemical cycle. Fen peat comprises moderately to highly decomposed higher plant remains with relatively high mineral matter content. Humic acids form the major part of fen peat organic matter; they are also the most refractory and recalcitrant natural substances to degradation, and thus they contain essential information regarding mire and peat development over large periods of time as well as the organic carbon biogeochemical cycle. Moreover, humic substances in fen peat are a prospective resource for applications in agriculture and other sectors. The aim of this study was to comparatively study properties of humic acids isolated from fen peat of varied botanical compositions and origins and to compare the impact of the precursor biological material on properties of the humification process and the resulting humic acids. The formation of humic acids of varied origins shows similarities; however, at the same time, differences can be found in the further development of humic acids, depending on the environment in which they are present.