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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This article is a result of measuring the dielectric constant of a dielectric used in studying the influence of dielectrics on the antennae reflection coefficients. A paper having a density of 0.797 g/cm3, moisture content of 0% and temperature of 210C, is used as a dielectric. Although the literature provides a lot of data on the dielectric properties of wood and paper, without direct measurement of the dielectric constant it is impossible to know its amount for the dielectric used in the defined frequency range. Dielectric constant measurements are performed in the frequency range from 100 Hz to 100 kHz, while the frequency range of its impact on the aperture antenna reflection coefficients is up to 2 GHz. The frequency range from 100 KHz to 10 GHz is interpolated and fitted by using measurements and available literature data and by respecting physical influences and phenomena and functional changes of the dielectric constant of paper within the given range

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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.