Screening of Local Wild Xanthomonas Species for Xanthan Production on Crude Glycerol-based Medium

In this study, the effect of cultivation time on xanthan biosynthesis by different Xanthomonas campestris and Xanthomonas euvesicatoria strains, isolated from crucifers and pepper leaves, respectively, was examined. Xanthan was produced by submerged cultivation on crude glycerol-based medium at a laboratory level under aerobic conditions at 30 °C and 150 rpm for 168 h and 240 h. Bioprocess efficacy was estimated based on the xanthan concentration in media at the end of bioprocess and its average molecular weight. According to the obtained results, Xanthomonas strains have statistically significant effect on xanthan concentration in cultivation media when biosynthesis is performed by X. euvesicatoria strains, and cultivation time has significant effect on this parameter only when bioprocess is performed by X.campestris strains. The combination of Xanthomonas strains and cultivation time has a statistically significant effect on xanthan concentration in medium for both groups of isolates. The obtained results show that all applied Xanthomonas strains and cultivation time as well as their combination have statistically significant effect on average molecular weight of xanthan produced in applied experimental conditions. It is found that X. euvesicatoria strains produce higher amount of xanthan in a shorter period of time (168 h) when compared to the X.campestris strains. Xanthan of higher average molecular weight was produced when cultivation of both groups of isolates was performed for 240 h in applied experimental conditions. Results obtained in this research suggest that X. euvesicatoria strains have the greatest potential for application in biotechnological production of xanthan on crude glycerol-based medium

Microbiological quality of fresh vegetable salads from the Novi Sad market

Increased consumption, big production units and very efficient delivery service networks of fresh vegetables and salads caused a higher number of foodborne illnesses in the last two decades all over the world. In this study 15 fresh vegetable salads from different marketplaces in Novi Sad were tested by reference microbiological methods (detection of Salmonella spp., enumeration of Listeria monocytogenes, mesophilic aerobic bacteria, yeasts and molds, sporogenic mesophilic aerobic bacteria, sporogenic sulfite-reducing bacteria, Bacillus cereus, Enterobacteriaceae, Escherichia coli and coagulase positive staphylococci). Salmonella spp. was found in one sample which, according to the safety criteria for such a product (if treated as ready-to-eat), was considered to be microbiologically unsafe. The number of Listeria monocytogenes in all tested samples was <100 cfu/g, which is a satisfactory result according to the safety criteria. E. coli was detected in only one sample, and the number of Enterobacteriaceae was in the range from 4.4 to 6.9 log CFU/g. The isolated Enterobacteriaceae strains were identified as Enterobacter cloacae, Klebsiella pneumoniae ssp. pneumoniae and Citrobacter spp

Comparation of corrosion and mechanical properties of commercial and recycled 6060 and 6082 aluminium alloys

Although the same quality of various metals from the recycling process is considered for granted, obtaining aluminum of high purity and aluminum alloys with identical properties as from production from pure raw materials is a very challenging process, especially if the sources for recycling are numerous materials that contain different impurities. In this study, recycled alloys were produced by melting of aluminum scrap with the addition of the required components. This paper aims to compare two commercial Al alloys with their analogs from the recycling process. Both of the alloys belong to the aluminum series 6000, with designations 6060 and 6082. The results of comparing corrosion and physical characteristics are presented in this study. Physical characterization was performed by measuring the alloys' hardness and electrical conductivity. The electrochemical investigation used several corrosion methods, OCP (open circuit potential), measuring polarization curves in apparent Tafel region with extrapolation of results, and LRP (linear polarization resistance). The corrosion environment was acidulated 0.5M Na2SO4 with pH=2.5. The received results have confirmed insignificant differences between the properties of the commercial and alloys produced by the recycling. Recycled alloys have achieved almost identical mechanical properties and even slightly better corrosion characteristics, which was the consequence of the lower concentration of impurities in recycled alloys or higher concentration of microalloying components

Analysis of the treatment of plastic from electrical and electronic waste in the republic of Serbia and the testing of the recycling potential of non-metallic fractions of printed circuit boards

This paper presents the analysis of the quantity of plastic and waste printed circuit boards obtained after the mechanical treatment of electrical and electronic waste (E-waste) in the Republic of Serbia, as well as the recycling of non-metallic fractions of waste printed circuit boards. The aim is to analyze the obtained recycled material and recommendation for possible application of recyclables. The data on the quantities and treatment of plastics and printed circuit boards obtained after the mechanical treatment of WEEE, were gained through questionnaires sent to the operators who treat this type of waste. The results of the questionnaire analysis showed that in 2014 the dismantling of E-waste isolated 1,870.95 t of plastic and 499.85 t of printed circuit boards. In the Republic of Serbia, E-waste recycling is performed exclusively by using mechanical methods. Mechanical methods consist of primary crushing and separation of the materials which have a utility value as secondary raw materials, from the components and materials that have hazardous properties. Respect to that, the recycling of printed circuit boards using some of the metallurgical processes with the aim of extracting copper, precious metals and non-metallic fraction is completely absent, and the circuit boards are exported as a whole. Given the number of printed circuit boards obtained by E-waste dismantling, and the fact that from an economic point of view, hydrometallurgical methods are very suitable technological solutions in the case of a smaller capacity, there is a possibility for establishing the facilities in the Republic of Serbia for the hydrometallurgical treatment that could be used for metals extraction, and non-metallic fractions, which also have their own value. Printed circuit boards granulate obtained after the mechanical pretreatment and the selective removal of metals by hydrometallurgical processes was used for the testing of the recycling potential. Granulometric analysis as well analysis of chemical composition of obtained fractions was performed. Subsequently, the manual classification of different types of polymeric material contained in the granulate was made, and both the apparent specific gravity and the chemical composition of the classified types of polymeric materials were determined. Chemical composition of granulate was determined by X-Ray Fluorescence (XRF) using Thermo Scientific Niton XL 3t, while the identification of residual polymers was determined by the FTIR (Fourier Transform Infrared Spectroscopy) method on the Bomen MB 100 device in range 4000 to 400 cm(-1). Based on the results of this study, it can be concluded that after the hydrometallurgical treatment of printed circuit boards, and the separation of metals that have the highest value, the residual non-metallic fraction have the utility value and can be used for various purposes, such as developing new polymer materials for technical purposes that have been investigated by many researchers and mentioned in this article

Determination of culture medium composition for maximizing the biomass production of Pseudomonas stutzeri

In the recent years, extensive studies have been conducted on the application of bioremediation in order to prevent and solve the global problem of nitrate accumulation especially in water and soil. In the studies related to the biological denitrification, Pseduomonas stutzeri is usually used as a model microorganism due to its ability of performing a complete reduction of nitrate. The aim of this work is to establish a culture medium at a laboratory level for maximizing the biomass production of Pseduomonas stutzeri ATCC 17588 and Pseudomonas stutzeri D1, previously isolated from the Danube (Novi Sad, Serbia) by using a Box-Bhenken experimental design and response surface methodology. The selected independent variables (+, 0, - levels) were: glucose (0, 1 and 2 g/L), KNO3 (1, 2 and 3 g/L), and peptone (0.4, 2 and 4 g/L), while the number of viable cells (log/mL) was chosen as a dependent factor (response). Based on the obtained results, it can be noticed that the maximum number of P. stutzeri ATCC 17588 viable cells is achieved when the initial content of glucose, KNO3 and peptone in the medium are 0 g/L, 2 g/L and 4 g/L, respectively. In the case of P. stutzeri D1, the most appropriate media for enhancing the biomass production consists of glucose (1 g/L), KNO3 (3 g/L) and peptone (4 g/L). Тhe obtained results can be used for further technoeconomic analysis and scale up of the P. stutzeri biomass production. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III45008