In the estimation of distribution of annual maximum flows it is a generally accepted assumption that the sequence of observations originates from a homogeneous population. This assumption, however, is rarely met. The observed annual maximum flow are only in part generated by flood events. The remaining ones are the result of the effect of other hydrological processes that do not have that character. For this reason, a new solution to this problem is proposed in the paper. It is assumed that the sought distribution is a mixture of two probability distributions: a three-parameter GEV distribution, describing flows generated by events with flood character, and a two-parameter gamma distribution, accounting for maximum annual flows that do not have such a character. The paper presents both the method of estimation of the mixture distribution and its application for gauging stations selected so as to take into account possible the most diverse conditions of meteorological, hydrological and geomorphological character. The area with such a high diversification, selected for the study, is the catchment basin of upper and central river Odra (South-West Poland). In the studied water gauge profiles the proposed mixture distribution indicates correct fit. Its advantages and limitations are presented through a comparative analysis with results obtained during estimation of distributions of maximum annual flows by means of standard methods.

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A lot of different chemical reactions take place in the biochemical process of biogas formation but the most important of them include the reaction of bonding carbon dioxide with hydrogen and the decomposition of acetic acid. Other factors, such as temperature, pH, etc., only limit the amount of methane or, in extreme cases, they even stop the process of methane formation. The paper presents an analysis of the influence of the amount of available carbon in the substrate and inoculum on biogas production, as well as of the validity of the relation between methane production and carbon/hydrogen ratio which is often mentioned in the literature. The analyses were made on the basis of the results of several dozen laboratory experiments on methane production for five groups of substrates: cultivated plants, animal faeces, plant waste, animal waste and municipal waste. This provided the basis for the formulation of the conclusion that there is no significant relation between the carbon/hydrogen ratio and methane production, and an alternative biogas calculator was suggested to estimate methane production with the known content of carbon in the substrate and inoculum. This calculator was also adapted to the conditions of agricultural biogas plants, and then it was tested in those conditions. It should also be mentioned that the innovative aspect of the study presented herein is the model developed for the estimation of methane production on the basis of carbon content only, providing estimates with a smaller error than in the case of the calculators!

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From the producers’ point of view, there is no universal and quick method to predict bruise area when dropping an apple from a certain height onto a certain type of substrate. In this study the authors presented a very simple method to estimate bruise volume based on drop height and substrate material. Three varieties of apples were selected for the study: Idared, Golden Delicious, and Jonagold. Their weight, turgor, moisture, and sugar content were measured to determine morphological differences. In the next step, fruit bruise volumes were determined after a free fall test from a height of 10 to 150 mm in 10 mm increments. Based on the results of the research, linear regression models were performed to predict bruise volume on the basis of the drop height and type of substrate on which the fruit was dropped. Wood and concrete represented the stiffest substrates and it was expected that wood would respond more subtly during the free fall test. Meanwhile, wood appeared to react almost identically to concrete. Corrugated cardboard minimized bruising at the lowest discharge heights, but as the drop height increased, the cardboard degraded and the apple bruising level reached the results as for wood and concrete. Contrary to cardboard, the foam protected apples from bruising up to a drop height of 50 mm and absorbed kinetic energy up to the highest drop heights. Idared proved to be the most resistant to damage, while Golden Delicious was medium and Jonagold was least resistant to damage. Numerical models are a practical tool to quickly estimate bruise volume with an accuracy of about 75% for collective models (including all cultivars dropped on each of the given substrate) and 93% for separate models (including single cultivar dropped on each of the given substrate).

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