Plamena Zlateva

Phenol and cresol mixture degradation by the yeast Trichosporon cutaneum

Most industrial wastes contain different organic mixtures, making important the investigation on the microbial destruction of composite substrates. The capability of microbes to remove harmful chemicals from polluted environments strongly depends on the presence of other carbon and energy substrates. The effect of mixtures of phenol- and methyl-substituted phenols (o-, m-, p-cresol) on the growth behaviour and degradation capacity of Trichosporon cutaneum strain was investigated. The cell-free supernatants were analysed by HPLC. It was established that the presence of o-, m- and p- cresol has not prevented complete phenol assimilation but had significant delaying effect on the phenol degradation dynamics. The mutual influence of phenol and p-cresol was investigated. We developed the kinetic model on the basis of Haldane kinetics, which used model parameters from single-substrate experiments to predict the outcome of the two-substrate mixture experiment. The interaction coefficients indicating the degree to which phenol affects the biodegradation of p-cresol and vice versa were estimated. Quantitative estimation of interaction parameters is essential to facilitate the application of single or mixed cultures to the bio-treatment of hazardous compounds.

Phenol utilization by filamentous yeast Trichosporon cutaneum

Abstract The investigated strain Trichosporon cutaneum shows well expressed capability for metabolizing high concentrations of phenol, up to 1 g/l, utilizing it as the sole carbon source for the growth and development of the population. The data reported, prove the good perspectives for its application in protecting the environment from phenol pollution. No data about modelling the process of cultivation of Trichosporon cutaneum in phenol media is available in scientific literature up to now. The mathematical model, reported here, consists of two nonlinear differential equations, describing cell growth and substrate consumption. The unknown parameters are estimated following the method of Hooke and Jeeves. A number of simulation investigations are carried out. They prove the adequacy of the model and its applicability in further studies on the processes of growth and phenol uptake of Trichosporon cutaneum.

Kinetic Parameters Determination of the Phenolic Derivatives Assimilation by Trichosporon Cutaneum R57

ABSTRACT The kinetic parameters characteristic of the growth and degradation capacity of Trichosporon cutaneum R57 strain in relation to o-, m-, p-chlorophenol, o-, m-, p-cresol and o-, m-, p-nitrophenol are presented in this study. The investigated strain degraded up to 0.1 g/l of all mono-chlorophenols. A concentration of 0.2 g/l p- cresol was completely degraded whereas m- cresol was degraded to an extent of 32%. No degradation of o- cresol was observed. O- nitrophenol in concentration of 0.1 g/l was less readily degraded than the same concentration of m-nitrophenol and p- nitrophenol was not degraded. The Haldane equation has frequently been used to describe the biodegradation of toxic substrates but little is known about the kinetic constants for the biodegradation of aromatic compounds. The coefficients obtained confirmed the higher toxicity of the investigated phenol derivatives on Trichosporon cutaneum R57. The yield coefficient (Y) was least of all in the medium supplemented with o- chlorophenol where μmax was also minimum. The highest value of Ki characteristic of p-cresol assimilation correlated with the ability of Trichosporon cutaneum R57 to degrade up to 0.4 g/l of this compound. The model prediction was compared with experimental data. It was found that the designed model described the trend of experimental data satisfactorily.

Cloud infrastructure security

Cloud computing can help companies accomplish more by eliminating the physical bonds between an IT infrastructure and its users. Users can purchase services from a cloud environment that could allow them to save money and focus on their core business. At the same time certain concerns have emerged as potential barriers to rapid adoption of cloud services such as security, privacy and reliability. Usually the information security professionals define the security rules, guidelines and best practices of the IT infrastructure of a given organization at the network, host and application levels. The current paper discusses miscellaneous problems of providing the infrastructure security. The different aspects of data security are given a special attention, especially data and its security. The main components of cloud infrastructure security are defined and the corresponding issues and recommendations are given.

Influence of phenolic substrates utilised by yeast Trichosporon cutaneum on the degradation kinetics

The degradation kinetics of different phenolic substrates utilised by Trichosporon cutaneum R57 was studied. The following compounds were used as substrates: phenol, resorcinol, hydroquinone, 3-nitrophenol, 2,6-dinitrophenol, 3-chloro phenol and p-cresol. The specific degradation rates (Qs) were described by a Haldane kinetic model. The unknown model parameters were estimated using the mathematical optimisation procedure for direct search. The results obtained demonstrated that Qs varied greatly in the experiments carried out. The level of biodegradability depended on the different structure and toxicity of compounds used as carbon substrates. The highest Qs values were observed for less toxic hydroxylated phenols (0.77–0.85 h−1), while the most toxic chlorinated phenols were characterised with the lowest Qs values (0.224 h−1). The results obtained with different concentrations of resorcinol (from 0.2 to 0.8 g L−1) and 2,6-dinitrophenol (from 0.2 to 0.7 g L−1) demonstrated a growing inhibitory effect directly correlating with the extended time necessary for complete degradation of both compounds.

GROWTH OF TRAMETES VERSICOLOR IN NITRO AND HYDROXYL PHENOL DERIVATIVES

ABSTRACT This is the first report on the ability of Trametes versicolor to utilize hydroxyl and nitro aromatic compounds as a sole carbon source. The cultivation was carried out in Czapek salt medium supplemented with 0.5 g/l 2-,3-,4-nitrophenol as well as benzene-1,3-diol (resorcinol), benzene-1,2-diol (catechol) and benzene-1,4-diol (hydroquinone), respectively. The hydroxylated phenols were completely utilized for 80–96 hours. The best degradation of the investigated nitrophenols was registered with 2-nitrophenol. The strain was able to degrade it completely in 216 hours. The dynamics of all degradation processes were investigated and characterized by specific growth rate (μmax), metabolic coefficient (k) and rate of degradation (Q). The kinetic parameters established for the best utilized compounds were as follows: benzene-1,3-diol—μmax = 0.065 h−1, k = 9.0, Q = 0.075 h−1; and 2-nitrophenol—μmax = 0.048 h-1, k = 8.5, Q = 0.033 h−1. The intracellular phenol hydroxylase [EC 1.14.13.7], catechol-1,2-dioxygenase [EC 1.13.11.1], and cis, cis-muconate lactonizing enzyme [EC 5.5.1.5] activities were determined in cells cultivated in medium complemented with the best utilized compounds—resorcinol and 2-nitrophenol. The obtained data showed that the substrate specificity of the first enzyme—phenol hydroxylase, is decisive for the rate of degradation of the studied toxic aromatic compounds.

A Model for Fuzzy Logic Assessment of Real Estate Investment Risks

Assessing the real estate investment risks is a major issue for the responsible management and the sustainable regional development. The paper proposes a fuzzy logic model for complex estimation of the real estate investment risks, based on the available information sources and the expert knowledge. The fuzzy logic model is designed as a hierarchical system that includes several variables. This model is intended to be implemented as a Web service in a cloud computing environment as a next natural step for increasing the span and efficiency of real estate manager activities.

Mathematical Modelling and Simulation of Fermentation Process for Citric Acid Production

ABSTRACTThe modelling of citric acid production in batch culture was made on the basis of experimental studies. The unknown kinetics coefficients were estimated by least squares identification technique minimizing a quadratic performance index by the method of Hooke and Jeeves. The influence of the integration method and the step, and of the initial optimization step on the accuracy of modelling and on the time for one simulation was investigated.

Comparison of the Biodegradation Capacity of Two Fungal Strains Toward a Mixture of Phenol and Cresol by Mathematical Modeling

ABSTRACT The examined strains of Aspergillus awamori NRRL 3112 and Trametes versicolor 1 were cultured in a culture medium containing phenol, p-cresol and a mixture of them as single carbon substrates. Both strains were able to utilize both examined compounds. The results showed that the strain of Trametes versicolor 1 degraded p-cresol much faster than the strain Aspergillus awamori NRRL 3112. In the experiments on degradation of the mixture of phenol and p-cresol by both strains, complete carbon utilization was also observed. The influence of the mixed substrate on the growth of microbial cultures was studied. A positive influence of phenol on the degradation of cresol by Aspergillus awamori NRRL 3112 and Trametes versicolor 1 was observed. SKIP models (Sum kinetics with interaction parameters) expressing the total kinetics of the degradation of a mixture of phenol/p-cresol in Aspergillus awamori NRRL 3112 and Trametes versicolor 1 were created. The obtained values of the interaction coefficients in the model (Iph/cr and Icr/ph) corresponded to the influence exerted by each of the investigated mixed compounds on the development and degradation capacities of both fungal strains.

Stability and bifurcation analysis of a nonlinear model of bioreactor

The stability characteristics of a nonlinear model of a continuously stirred tank bioreactor with cell recycle are studied. Assuming that some practically important model parameters are uncertain, existence of bifurcations of equilibrium points is shown. The dynamic behaviour of the system near bifurcation points is also demonstrated. Numerical simulations in the computer algebra system Maple are presented.