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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.

Xanthan is a microbial biopolymer with a wide range of industrial applications and it is expected that the demand for this product will significantly increase in the coming decade and for this reason it is important to constantly work on improving all aspects of this biotechnological process. The aim of this research was to examine the kinetics of batch cultivation of Xanthomonas campestris ATCC 13951 using vegetable oil industry wastewaters as a basis for the cultivation medium, in order to produce the biopolymer xanthan. Kinetic modelling is very important for process control, reducing process costs and increasing product quality. By performing xanthan production on a medium with optimized content, the experimental values of content of biomass, carbon source and the desired product were obtained and used to determine the kinetics of biosynthesis. In order to describe biomass multiplication, product formation and carbon source consumption, the logistics, the Luedeking-Piret and modified Luedeking- -Piret equation, respectively, were successfully used. Additionally, using process simulation software (SuperPro Designer®), a process and cost model for a xanthan production facility was developed. The developed model represents the basis for a 21,294.29 and 23,107.97 kg/year xanthan production facility, which uses a vegetable oil industry wastewater-based medium and a semi-synthetic medium. The simulation model of the suggested xanthan production process, developed and based on defined kinetic models, represents an excellent basis for its further improvement and for increasing its efficiency.

The aim of this research was to examine the possibility of using the vegetable oil industry wastewater as the basis of the cultivation media for xanthan production, using Xanthomonas campestris ATCC 13951, in order to reuse the wastewater obtained in one industry as a raw material in another. Furthermore, the aim was to optimize the composition of wastewater based media in terms of carbon, nitrogen, and phosphorus content. Experiments were carried out in accordance with the Box-Behnken design with three factors on three levels (glucose: 10.00- -30.00 g/L; nitrogen: 0.02-0.20 g/L; phosphorus: 0.0045-0.045 g/L) and three repetitions at the central point. The success of biosynthesis was assessed by analysing broths to determine xanthan yield, cultivation broth apparent viscosity, residual carbon, nitrogen, and phosphorus content. Graphical and numerical optimization using response surface methodology was performed to determine the optimal content values of the carbon source, nitrogen, and phosphorus content. The results of graphical optimization suggest that for the defined response interval values, the defined model predicts that the xanthan production is possible when 15.00-16.00 g/L of the carbon source, 0.02-0.09 g/L of nitrogen and 0.01-0.02 g/L of phosphorus are added to the media that as a basis contains vegetable oil industry wastewater.

Wine industry generates large volumes of wastewaters resulting from numerous cleaning operations that occur during the different stages of winemaking. Disposal of these effluents in the environment causes huge problems due to their high organic and inorganic load and seasonal variability. The bioconversion of winery wastewaters in valuable product, such as xanthan, is an important alternative to overcome environmental problems. In this research, the possibility of xanthan production using Xanthomonas campestris on blended wastewaters from different stages of white and rose wine production with initial sugar content of 50 g/L was investigated. In addition to the media parameters (content of sugars, total and assimilable nitrogen, phosphorus, total dissolved salts and apparent viscosity), raw xanthan yield and degree of sugar conversion into product were determined in order to examine the success of xanthan biosynthesis. In applied experimental conditions, xanthan yield of 20.92 and 30.64 g/L and sugar conversion into product of 40.23 and 60.73% were achieved on wastewaters from white and rose wine production, respectively. The results of these experiments suggest that winery wastewaters, after additional optimization of the process in terms of the substrate composition and the cultivation conditions, may be a suitable raw material for industrial xanthan production.

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]