Biomass availability is one of the key factors for biogas production in the future. The current status and possibilities for utilizing harvest residues (soybean straw, corn stover and sunflower stalk) in Croatia for biogas production is given. In the last few decades, different pretreatment methods have been developed for the degradation of different lignocellulosic biomass, but many of them are environmentally unfriendly and sometimes very expensive. More research and development is necessary in order to find both economically and environmentally friendly pretreatment methods. This paper provides a review on the mechanical, physical, and biological methods used for different lignocellulose material pretreatment. Harvest residues are usually left in the field, but with the improvement of the pretreatment process along with soil protection, they could be used for the production of huge amounts of energy in the future.

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Several batch experiments were conducted on the anaerobic co-digestion of dairy cow manure (DCM) with three harvest residues (HR) (soybean straw, sunflower stalks, and corn stover). The influence of thermal pretreatment of HR on biogas production was investigated, where the HR were thermally pretreated at two different temperatures: T = 121 °C and T = 175 °C, during t = 30 and t = 90 min, respectively. All anaerobic co-digestion batch experiments were performed simultaneously under thermophilic regime, at T = 55 °C. Biogas and methane yields were significantly improved in experiments performed with corn stover thermally pretreated at 175 °C for 30 min (491.37 cm/g VS and 306.96 cm/g VS, respectively), if compared to experiments performed with untreated corn stover. The highest VS and COD removal rates were also observed in the same group of experiments and were 34.5 and 50.1%, respectively. The highest biogas and methane yields with soybean straw (418.93 cm/g VS and 261.44 cm/g VS, respectively) were obtained when soybean straw pretreated at 121 °C during 90 min. The highest biogas and methane yields with sunflower stalk (393.28 cm/g VS and 245.02 cm/g VS, respectively) were obtained when sunflower stalk was pretreated at 121 °C during 90 min.

We wished to determine protein and lipid content in pelleted raw fish food, necessary for optimal growth of European catfish (Silurus glanis). Experiments were set up in 20 cages, each holding 30 young catfish. Fishes in each cage received a different food combination over a 98-day period at favourable physical and chemical water conditions. Food protein content varied between 37.5 and 45%, while lipid content, added in the form of soybean oil, varied between 3 and 11%. The oil contained an adequate x-fatty acids concentration, necessary for fish growth. The main growth indicators determined at the end of experiment were total body gain, specific growth rate and feed conversion ratio. There was a high statistical difference among the experimental groups receiving variable food combinations for each growth parameter (P < 0.001). Both protein and lipid food content affected growth parameters, but in a different manner. Further analysis -percentage of change depending on lipid to protein ratio and bivariate surface analysis -allowed us to recognize the most economical combination: 39.5% protein + 9% lipid content. The addition of 9% soybean oil to the fish food reduces the necessary protein concentration by 5.5%, with resulting identical catfish growth effects.