Papers by Nicolas Kalogerakis
The notion of the relaxed Robust Control Lyapunov Function (relaxed RCLF) is introduced and is ex... more The notion of the relaxed Robust Control Lyapunov Function (relaxed RCLF) is introduced and is exploited for the design of robust feedback stabilizers for nonlinear systems. Particularly, it is shown for systems with input constraints that relaxed RCLFs can be easily obtained, while RCLFs are not available. Moreover, it is shown that the use of relaxed RCLFs usually results to
Scientific Reports, 2015
Two of the largest crude oil-polluted areas in the world are the semi-enclosed Mediterranean and ... more Two of the largest crude oil-polluted areas in the world are the semi-enclosed Mediterranean and Red Seas, but the effect of chronic pollution remains incompletely understood on a large scale. We compared the influence of environmental and geographical constraints and anthropogenic forces (hydrocarbon input) on bacterial communities in eight geographically separated oil-polluted sites along the coastlines of the Mediterranean and Red Seas. The differences in community compositions and their biodegradation potential were primarily associated (P < 0.05) with both temperature and chemical diversity. Furthermore, we observed a link between temperature and chemical and biological diversity that was stronger in chronically polluted sites than in pristine ones where accidental oil spills occurred. We propose that low temperature increases bacterial richness while decreasing catabolic diversity and that chronic pollution promotes catabolic diversification. Our results further suggest that the bacterial populations in chronically polluted sites may respond more promptly in degrading petroleum after accidental oil spills.
Frontiers in Environmental Science, 2014
A dynamic model was developed to simulate the behavior of the biological processes taking place i... more A dynamic model was developed to simulate the behavior of the biological processes taking place in a membrane bioreactor (MBR) pilot plant treating industrial wastewater at the Heraklion Industrial Park including the cake development on the membrane surface. The modified extended CES-ASM3 model has been used. Hydrolysis rates of the soluble microbial products have been added. Membrane fouling was taken into account and trans membrane pressure (TMP) was modeled and compared to experimental data. Simulation results are presented for the operation period between February 2012 and May 2013 and the prediction ability of the model is shown through the computation of the mean relative error of each measured state variable. Overall, the model estimates match the experimental data satisfactorily, as they follow similar trends while for all input variables their mean value was used as a constant input in the simulations. The operation of the MBR was conducted at three different sludge retention times.
The Chemical Engineering Journal, 1992
The assumption of constant axial dispersion coefficient in residence time distribution (RTD) expe... more The assumption of constant axial dispersion coefficient in residence time distribution (RTD) experiments is examined for liquid fluidized beds. Experimental results show this assumption to be violated in short beds. A quantitative criterion is proposed for the constraint required to achieve the ...
Frontiers in Microbiology, 2015
Biosurfactants (BSs) are "green" amphiphilic molecules produced by microorganisms during biodegra... more Biosurfactants (BSs) are "green" amphiphilic molecules produced by microorganisms during biodegradation, increasing the bioavailability of organic pollutants. In this work, the BS production yield of marine hydrocarbon degraders isolated from Elefsina bay in Eastern Mediterranean Sea has been investigated. The drop collapse test was used as a preliminary screening test to confirm BS producing strains or mixed consortia. The community structure of the best consortia based on the drop collapse test was determined by 16S-rDNA pyrotag screening. Subsequently, the effect of incubation time, temperature, substrate and supplementation with inorganic nutrients, on BS production, was examined. Two types of BS -lipid mixtures were extracted from the culture broth; the low molecular weight BS Rhamnolipids and Sophorolipids. Crude extracts were purified by silica gel column chromatography and then identified by thin layer chromatography and Fourier transform infrared spectroscopy. Results indicate that BS production yield remains constant and low while it is independent of the total culture biomass, carbon source, and temperature. A constant BS concentration in a culture broth with continuous degradation of crude oil (CO) implies that the BS producing microbes generate no more than the required amount of BSs that enables biodegradation of the CO. Isolated pure strains were found to have higher specific production yields than the complex microbial marine community-consortia. The heavy oil fraction of CO has emerged as a promising substrate for BS production (by marine BS producers) with fewer impurities in the final product. Furthermore, a particular strain isolated from sediments, Paracoccus marcusii, may be an optimal choice for bioremediation purposes as its biomass remains trapped in the hydrocarbon phase, not suffering from potential dilution effects by sea currents.
Environment international, 2005
The pre-treatment of three different olive oil processing effluents by means of direct flocculati... more The pre-treatment of three different olive oil processing effluents by means of direct flocculation (i.e. without prior coagulation) was investigated. Four cationic and two anionic poly-electrolytes were tested and most of them were found capable of removing nearly completely total suspended solids (TSS) as well as reducing considerably the concentration of chemical (COD) and biochemical oxygen demand (BOD(5)) without altering solution pH. Flocculant dosage was crucial to achieve effective separation. For three cationic and one anionic poly-electrolytes, the minimum dosage required to initiate separation was about 2.5-3 g/L. The remaining two poly-electrolytes failed to cause separation even at dosages as high as 7 g/L. Lime and ferric chloride were also tested as reference coagulants and found quite effective in terms of TSS removal although the degree of COD reduction was generally lower than that with poly-electrolytes. However, lime treatment would require greater dosages and lo...
Journal of Hazardous Materials, 2015
Currently, the treatment of aquaculture-origin effluents is mainly performed through land-based r... more Currently, the treatment of aquaculture-origin effluents is mainly performed through land-based recirculating aquaculture systems (RAS). In this study, we evaluate and introduce a novel immobilized/packed bed bioreactor which uses a synthetic textile as the support medium. A marine microbial consortium was developed on the textile by its inoculation with the microalgae Picochlorum sp. The bioreactor was tested with variable loadings of C and N and showed outstanding performance approaching removal rates up to 95% within a few hours (4-5h) of operation. Pyrosequencing analysis revealed a novel microbial consortium consisting mainly of chitrinomycetes, Pseudomonas sp. and the absence of β-proteobacteria, which is the Class encompassing autotrophic nitrifiers. Quantitative polymerase chain reaction further confirmed these findings suggesting heterotrophic nitrification and aerobic denitrification as the principal mechanisms of N-removal from the bioreactor. Overall our findings reveal the potential of the AdvanTex System for the treatment of marine aquaculture effluents-COD reduction and N-removal, in a single stage.
The greater area of the Asopos river, situated at the Region of Sterea Ellada, north of Athens is... more The greater area of the Asopos river, situated at the Region of Sterea Ellada, north of Athens is a unique case of combined anthropogenic and geogenic origin of chromium contamination. The high concentrations of chromium and hexavalent chromium found at the groundwater system of Asopos have resulted in an increased public concern, since part of the groundwater is used for water abstraction for human consumption and most of it for irrigation purposes. The objective of this work was to organize all available data pertinent to the groundwater flow and chromium transport modeling of the area into maps, using geographical information systems, geotechnical graphics software and geostatistical techniques. The data was collected from various sources such as field campaigns, existing reports, data logs etc. One of the most important parameters that affect chromium transport is the geology of the area, thus a digitized geological map of the main formations encountered in the upper layers of the subsurface of the region was generated. In addition, geological boring logs for a large number of wells were created (using a geotechnical graphics software) and then combined in order to create vertical cross-sections, at various locations in the greater area, that define the geological characteristics of the deeper layers. The combination of the above defines the 3-D representation of the geological stratification of the physical system. Another parameter of interest in the area is the groundwater level and flow direction. In order to create a hydraulic head map of the area, the locations of more than 1000 shallow and deep wells that have been documented in the greater area of the Asopos river basin were defined using GIS software. A kriging technique was then applied to the available data in order to produce hydraulic head contours and consequently define the general groundwater flow direction. The same technique was applied for the generation of chromium concentration contours that provide an indication of the most problematic locations as well as a general chromium background level in the greater area.
Salinity is an expanding worldwide issue that affects agricultural soils and limits the restorati... more Salinity is an expanding worldwide issue that affects agricultural soils and limits the restoration of contaminated sites. In spite of the substantial number of papers about salt and Cd tolerance in a broad range of Brassica juncea cultivars, no accounts about the variety juncea (wild type) have been found. In this study, seeds of B. juncea (var. juncea) were allowed to germinate and grow for 8 days, subjected to the individual and combined effect of Cd (0, 15 and 30 mg L -1 ) and NaCl (0, 60 and 120 mM). Germination was not reduced by any of the treatments, no oxidative stress was registered, and overall the seedlings development was not severely impaired. The synergistic effects of Cd and salt did not appear to have significantly contributed for growth impairment, and signs of decay were solely related to the individual effect of Cd and NaCl. Furthermore, data suggests that mild concentrations of NaCl enhanced Cd uptake. It was concluded that B. juncea (var. juncea) may present moderate tolerance to Cd and salinity during germination and the early growth stage. Additional research in this and upcoming growth phases would be crucial to confirm the moderate tolerance of B. juncea (var. juncea) to Cd and salinity.
ABSTRACT Bisphenol-A (BPA; 2,2-bis(4-hydroxyphenyl) propane) is a monomer used primarily in the p... more ABSTRACT Bisphenol-A (BPA; 2,2-bis(4-hydroxyphenyl) propane) is a monomer used primarily in the production of polycarbonate and epoxy resins that has been reported to have estrogenic activity. The biodegradability of BPA has been previously investigated in several studies designed to simulate surface waters and biological wastewater treatment systems. However, there is little information available about the phytoremediation of groundwater contaminated with BPA. Halophytic species are of special interest for phytoremediation research since these plants are naturally better adapted to cope with environmental stress. Therefore, in the present paper BPA degradation dynamics have been investigated experimentally and through modeling of a rhizodegradation pilot, emulating a shallow aquifer, treating BPA contaminated groundwater by the halophyte Juncus acutus. The mathematical model considers rhizodegradation as the main BPA phytodegradation mechanism but takes also into account BPA removal through plant up-take and hydrolysis. The model calibration has been performed with raw data from two experimental runs of the pilot unit and the simulations match the experimental data for both runs sufficiently well.
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Papers by Nicolas Kalogerakis