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Republic of Srpska (RS) is one of the two entities in Bosnia and Herzegovina (BiH). It is located in South-eastern Europe, in the western part of the Balkan Peninsula. As in most developing countries, waste management is based on landfilling. The constant increase in waste generation creates a growing burden on the existing waste management system and the environment. Comparing the amount of waste with GDP, despite a much lower standard, RS/BiH residents, compared to EU residents, generate far more waste for the same amount of money. All generated waste is disposed of in landfills, which causes greenhouse gas emissions and has a negative effect on the environment. On the other side, untreated waste deposited in landfills represents the loss of potential of waste as a renewable energy source. In this study, an attempt has been made to represent the possibilities of sustainable waste-to-energy management in RS with the goal to provide reliable support to decision makers to direct waste management in a sustainable framework.

Xanthomonas euvesicatoria is a worldwide causer of pepper bacterial spot, a bacterial plant disease responsible for massive losses of fresh pepper fruits. Considering the current problems in management of bacterial plant diseases, biological control using antagonistic microbial strains with high potential for plant pathogens suppression emerges as a possible solution. The aim of this study was to select suitable antagonists for suppression of X. euvesicatoria among the bacteria, yeast and fungi from the genera Pseudomonas, Lactobacillus, Saccharomyces and Trichoderma, based on in vitro antimicrobial activity testing using the diffusion disc method. The results of this study have revealed that cultivation broth samples of the antagonists Lactobacillus MK3 and Trichoderma reseii QM 9414, as well as supernatant samples of the antagonist Pseudomonas aeruginosa I128, have showed significant potential to be applied in biological control of X. euvesicatoria. Further research would be required to formulate suitable cultivation medium and optimize bioprocess conditions for production of the proposed pepper bacterial spot biocontrol agents.

The application of antifungal compounds produced by microorganisms in the control of plant diseases caused by phytopathogenic fungi is a promising alternative to synthetic pesticides. Among phytopathogenic fungi, Alternaria alternata and Fusarium avenaceum are significant pathogens responsible for the storage rot of apple fruits. During storage, transport and marketing A. alternata and F. avenaceum can cause significant losses of apple fruits and their control is of great importance for the producers and consumers. In the present study, the effects of agitation rate on the production of antifungal methabolite( s) by Streptomyces hygroscopicus in a 3-L lab-scale bioreactor (Biostat® Aplus, Sartorius AG, Germany) against two isolates of A. alternata and two isolates of F. avenaceum were investigated. The cultivation of S. hygroscopicus was carried out at 27°C with agitation rates of 100 rpm and 200 rpm during 7 days. The aim was to analyze the bioprocess parameters of biofungicide production in a medium containing glycerol as a carbon source, and examine the effect of agitation rate on the production of antifungal metabolite(s). The in vitro antifungal activity of the produced metabolites against fungi from the genera Alternaria and Fusarium grown on potato dextrose agar medium was determined every 24 h using wells technique. In the experiments conducted in the bioreactor at different stirring speeds, it was found that the maximum production of antifungal metabolites occurred after 96 hours of cultivation. A higher consumption of nutrients and a larger inhibition zone diameter was registered in the experiment with an agitation rate of 200 rpm. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR-31002]

The biocontrol agents are a very promising alternative to synthetic pesticides that are presently used to control plant diseases caused by phytopathogenic microorganisms. Members of the Bacillus genera are soil bacteria that produce significant quantities of agriculturally important bioactive compounds. Production of these compounds can be improved by changing the nutritional and environmental conditions. The aim of this study was the optimization of medium composition, using response surface methodology, for the production of compounds effective against Xanthomonas campestris ATCC 13951 by Bacillus subtilis ATCC 6633. To study the production of antimicrobial compounds by selected Bacillus strain, the producing microorganisms were cultivated on nutrient broth. The inhibition zone diameter of 18.0 mm obtained by the diffusion-disc method indicated that the used Bacillus subtilis strain produces compounds with antimicrobial activity against Xanthomonas campestris ATCC 13951. To optimize the composition of the cultivation medium in terms of glycerol, sodium nitrite and phosphates content, experiments were carried out in accordance with Box-Behnken design, and optimization of multiple responses was performed using the concept of desirability function. The developed model predicted that the maximum inhibition zone diameter (26.23 mm) against tested phytopathogen is achieved when the initial content of glycerol, sodium nitrite and phosphate were 50.00 g/L, 2.85 g/L and 11.00 g/L, respectively. To minimize the consumption of medium components and costs of effluents processing, additional optimization set was made. The techno-economic analysis of the obtained results has to be done to select optimal medium composition for industrial production of antimicrobial compounds.

Methods that can provide adequate accuracy in the estimation of variables from incomplete information are desirable for the prediction of fermentation processes. A feed-forward back-propagation artificial neural network was used for modelling of thick juice fermentation. Fermentation time and starting sugar content were usedas input variables, i.e. nodes. Neural network had one output node (ethanol content, yeast cell number or sugar content). The hidden layer had nine neurons. Garson's algorithm and connection weights were used for interpreting neural network. The inadequacy of Garson's algorithm can be seen by comparing with the results of regression analysis, which indicates that the influence of the fermentation time is higher. A better agreement of the results was obtained using network connection weights, a method that can be used to determine the relative importance of input variables.

The present study examines xanthan production by Xanthomonas campestris under aerobic conditions on spent grains liquor based cultivation media containing four different amounts of maltose. All four experiments were performed simultaneously, so that all stages of the biotechnological process would be carried out under identical conditions. In addition to the cultivation parameters (pH value, contents of dissolved oxygen, reducing sugars and assimilable nitrogen, turbidity and trickling time), xanthan yield and sugar conversion percentage were also determined. Based on the results of the experiments maltose addition up to 5% to spent grains liquor does not hinder the cultivation course. On the other hand, the conversion of sugars into xanthan decreases with the increase of maltose content to 5% and a large amount of sugars lags in the cultivation broth.