Yovana Todorova

Long-term assessment of the self-purification potential of a technologically managed ecosystem: the Middle Iskar cascade.

The Middle Iskar cascade is situated along the middle course of the Iskar River (Bulgaria) after the capital city Sofia and has three small hydroelectric power plants that were put into operation by the end of 2012. The aim of this study was to evaluate the self-purification potential of water in the reservoirs of these plants as an important and necessary condition for their ecological functioning. The assessment was made by hydrochemical parameters (dissolved suspended solids, insoluble suspended solids, total suspended solids, nitrites, nitrates, ammonium, phosphates, chemical oxygen demand, dissolved oxygen) and microbiological parameters (aerobic heterotrophic bacteria and bacteria growing in an Endo medium) and covered a period of three years (2010, 2011 and 2012). Standard methods were applied, mainly colorimetric and microbiological cultivation methods. The obtained results showed high levels of some of the tested indicators during 2012. In the section of the Middle Iskar cascade a high self-purification potential was observed in the reservoirs which maintain good water quality.

EVOLUTION OF THE EXPERIMENTAL PLAN IN DATA COLLECTION AND VERIFICATION TACTICS IN MODELLING OF RIVER WATER QUALITY

ABSTRACT Modeling is one of the basic approaches for preventive management of the water quantity and quality, as well as for the ecological sufficiency of the river. The approach for selection of parameters and data collection, specific and unique for each model, is an important element in this aspect. This data plays a critical role for the calibration and verification of models. In this paper two years of investigations of the gradual adaptation of the experimental plan of data collection as well as the adequate development according to the HSPF (EPA) model and specificity of Iskar River (Bulgaria) have been presented. The 8—degree experimental evolution was accomplished in line with the principles of EMS, ISO-14000, WFD, ecological complexity and interdisciplinary approach. The obtained results confirmed that mathematical instruments of the model require individual experimental scenario for data collection, specific for each catchment parameter, application of variety of approaches for measurement of the real rate of the processes—opposite scaling up, physical and analogous modeling, selection of critical control points, parameters and temporal scheme.

Contamination and Ecological Risk Assessment of Long-Term Polluted Sediments with Heavy Metals in Small Hydropower Cascade

The identification of contamination level and ecological risks, associated with heavy metal pollution of sediments in small hydropower cascade was done on the base of index analyses approach. The concentration of As, Cd, Cu, Hg, Pb, Zn, total organic carbon and percentage of fines were determined in sediments of two habitats in cascade sequence – river and dam. Correlation and multivariate analyses suggest that As, Cu, Pb and Zn are associated with similar anthropogenic source. Cadmium and mercury originate from different source and have specific moving. Based on the contamination and background indices the sediments in Middle Iskar cascade are moderate contaminated at least and are subject of intensive hydrological and technological mixing. The potential ecological risk index (PERI) classifies the sediments in dam site with the higher risk level. Suitable indicators for express assessment of metal pollution in “river” sediments are contamination/enrichment indices which are more sensitive for local concentration increase of less toxic metals. In “dam” sites the process of sedimentation affects strongly the degree of metals accumulation and differences in toxicity are clearly presented – PER/PERI in combination with content of fine sediment fractions and TOC have a potential for rapid identification of sediment-associated risks.

Surface-wave-sustained plasma torch for water treatment

In this study the effects of water treatment by surface-wave-sustained plasma torch at 2.45 GHz are studied. Changes in two directions are obtained: (i) changes of the plasma characteristics during the interaction with the water; (ii) water physical and chemical characteristics modification as a result of the plasma treatment. In addition, deactivation of Gram positive and Gram negative bacteria in suspension are registered. A number of charged and excited particles from the plasma interact with the water. As a result the water chemical and physical characteristics such as the water conductivity, pH, H2O2 concentration are modified. It is observed that the effect depends on the treatment time, wave power, and volume of the treated liquid. At specific discharge conditions determined by the wave power, gas flow, discharge tube radius, thickness and permittivity, the surface-wave-sustained discharge (SWD) operating at atmospheric pressure in argon is strongly non-equilibrium with electron temperature T e much higher than the temperature of the heavy particles (gas temperature T g). It has been observed that SWD argon plasma with T g close to the room temperature is able to produce H2O2 in the water with high efficiency at short exposure times (less than 60 sec). The H2O2 decomposition is strongly dependant on the temperature thus the low operating gas temperature is crucial for the H2O2 production efficiency. After scaling up the device, the observed effects can be applied for the waste water treatment in different facilities. The innovation will be useful especially for the treatment of waters and materials for medical application.

Evaluation of the effect of cold atmospheric plasma on oxygenases’ activities for application in water treatment technologies

ABSTRACT Plasma-based technologies take an increasing place in the new conceptions of wastewater management as a promising tool for the treatment of persistent organic pollutants with low biodegradability. Plasma major advantage is the synergy of diverse active components with high oxidative action and additional benefits as disinfection of treated water. But the bactericidal effect of plasma can influence the treatment effectiveness when this technology is used in combination with biological methods for the removal of pollutants. The aim of this paper is to study the effect of non-thermal atmospheric plasma torch on key enzymes from phenol biodegradation pathways in Pseudomonas aureofaciens (chlororaphis) AP-9. The strain was isolated from contaminated soils and had a high potential for biodegradation of aromatic compounds. The used plasma source is surface-wave-sustained discharge operating at 2.45 GHz in argon produced by an electromagnetic wave launcher surfatron type. The enzyme activities of phenol 2-monooxygenase (P2MO), catechol 1,2-dioxygenase (C12DO), catechol 2,3-dioxygenase (C23DO), protocatechuate 3,4-dioxygenase (P34DO) and succinate dehydrogenase (SDH) were measured in control and after plasma treatment of 10, 30 and 60 s. At short-time treatment, the activities of intradiol dioxygenases increased with 26% and 59% for C12DO and P34DO, respectively. Other oxygenases and SDH were inhibited with 35% even at 10 s treatment. Longer treatment times had a clear negative effect but SDH kept the higher activity at 60 s treatment compared to the oxygenases. Our data suggest that plasma-based technologies are a useful approach for post-treatment of aryl-containing wastewater in order to increase the effectiveness of biological removal. GRAPHICAL ABSTRACT

Innovative sterilization technology - bacterial inactivation by cold argon plasma

Non-thermal (cold) plasma is subject of intensive scientific interest as an alternative sterilization technique for advanced control of microbial quality and safety in food biotechnology. The cold plasma is a flow of weakly ionized gas at atmospheric pressure that includes radicals, H O , O , ultraviolet radiation, charged particles, exited metastable atoms, electric fields. One of the major benefits of plasma-based technologies is the synergy between the strong effects of these highly active components that provides a high bactericidal efficiency at low costs, time-saving and non-toxicity. The aim of this study is to assess the bactericidal effect of cold argon plasma in liquids and surfaces, contaminated with Gram-negative and Gram-positive spore-forming bacteria. The used plasma source is surface-wave-sustained discharge (SWD) operating at 2.45 GHz in argon (plasma torch) produced by an electromagnetic wave launcher surfatron type. The bactericidal effect was studied by direct contact treatment of contaminated liquids and agar plates with Pseudomonas aureofaciens AP-9 and Brevibacillus laterosporus BT-271. The results show that the cold argon plasma is able to inactivate bacteria at short exposure time (under 1 min). The clear sterilization zones on treated surfaces with diameter depending on exposure time and initial bacterial density were obtained. In bacteria-contaminated liquids ‡ ‡ ‡ § | | ¶

Analogous Modeling of Nutrient Transformation in Iskar River Sediments at Different Moisture Content: Microbiological and Enzymological Indicators

ABSTRACT This study was focused on the R&D of the elements of the systems for early warning of risk events as well as on the selection of the mechanisms and indicators for their management. The aim was to derive the mathematical dependences, bioalgorithms, and indicative correlations for upgrading of the HSPF hydrological model. For this purpose analogous modeling of transformation of organics in the river sediments of the parafluvial zone as a function of moisture (in%) was performed. This upgrading can be applied for correct and effective prognosis of the rate of self-purification in the Iskar River in the section from Beli Iskar Reservoir to Iskar Reservoir. The results showed that the combination of total dehydrogenase, nitrate reductase and phosphatase activities could be considered an effective instrument for water quality management and for prediction of the rate of transformation processes. The derived linear mathematical dependences can be applied to calculate other microbiological and kinetic indicators important for monitoring, as well as to create special modules for the HSPF model with a well-functioning verification strategy.

Biodegradation of Phenol by Immobilized in Peo-Cryogel Bacillus Laterosporus BT-271 in Sequencing Batch Biofilter

ABSTRACT A long (20 days) model process of phenol biodegradation was performed in biofilters in sequencing batch regime and with active biological system—polyethylene oxide cryogels (PEO-cryogel) with immobilized bacteria Bacillus laterosporus BT-271. The model waste water, containing mineral medium and phenol as the only source of carbon and energy with 300 mg/l in the effluent, was used. One of the key investigated parameters was the manner of immobilization of the bacteria in polyethylene oxide cryogels. The two variants of the experiment were: 1) direct immobilization of the inoculation material (SBB-D) and 2) inoculation of the biomass after preliminary separation and further concentration (SBB-S). The process was characterized on the basis of the following parameters: concentration of phenol in the influent, efficiency of phenol biodegradation, rate of phenol biodegradation, debit of purified water, loading of biofilters, rate of phenol degradation and efficiency, oxygenase enzyme activity of the cells immobilized in the cryogel and of the free cells in the effluent. The implantation of the gel with the immobilized microorganisms in a sequencing batch biofilter showed good biodegradation, kinetic, enzymological characteristics, as well as self-renovating adequate biofilm structure in laboratory conditions. The two biofilters functioned well and the efficiency of phenol elimination reached 100% in 15 days. The variant SBB-D showed a more stable process, as well as an easier way of preparing the initial PEO-plate biofilm. The SBB-D system is suitable for scaling and future implementation of the water purification processes in practice.