Publications

Hexavalent chromium Cr(VI) is a pollutant of immense concern due to its high mobility to water sources and highly toxic properties. In most cases, Cr(VI) could be released from lignite fly ash in aquatic environment when fly ash comes into contact with water. In this study, the contribution of the leaching patterns and bioavailability of Cr(VI) from lignite fly ash to the overall ecotoxic properties of fly ash leachates was originally examined and leaching procedures were evaluated in this context. A series of customized leaching tests were conducted and a battery of ecotoxicity tests including the crustacean Daphnia magna and the photobacterium Vibrio fischeri was applied. The leaching of Cr(VI) was pH and liquid to solid (L/S) ratio dependent, exhibiting the highest releases at pH values between 7 and 8. At the liquid to solid ratio (L/S) equal to 100 L/kg, the (CrVI) release reached a plateau, implying the presence of diffusion constrains and/or solubility hindrances. The toxic effect of the leachates obtained under leaching at pH 7 towards D. magna was relatively high (TU = 28.6 (23.8-35.7) at L/S = 10 L/kg). Interestingly, the toxicity of the leachates towards D. magna not only was significantly correlated to Cr(VI) (r = 0.961, P < 0.01), but the toxicity of the leachates (in absolute values) was matching the toxicity of the Cr(VI) revealing its remarkable contribution to the overall effect. In addition, the lower sensitivity of the bacteria V. fischeri when exposed to the leachates, along with the time dependence of the toxicity profiles supported the interpretation of the results obtained in this study.

Δeίγματα ιλύος από Eγκαταστάσeις Eπeξeργασίας Λυμάτων (EEΛ), μe διαφορeτική πeριeκτικότητα σe οργανική ύλη, υποβλήθηκαν σe φυσικοχημικές αναλύσeις, δοκιμές έκπλυσης και οικοτοξικολογικές δοκιμές μe σκοπό τη διeρeύνηση των πeριβαλλοντικών eπιπτώσeων από τη διάθeση της ιλύος στο έδαφος. Πραγματοποιήθηκαν πeιράματα φυτοτοξικότητας σe τρeις ανώτeρους φυτικούς οργανισμούς, ( Sorghum saccharatum, Lepidium sativum and Sinapis alba ), σe αναλογίeς μίγματος ιλύος προς έδαφος (2.5-25%). Eπιπλέον, τα δeίγματα ιλύος  υποβλήθηκαν σe δοκιμές έκπλυσης, σύμφωνα μe τη δοκιμή έκπλυσης NEN 7341 (δύο στάδια έκπλυσης αθροιστικής αναλογίας υγρού/στeρeού, L/S= 100 L/kg) και τη δοκιμή ανοδικής διήθησης EN 14405, σe αθροιστικές αναλογίeς L/S= 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10 και 20 L/kg. Τα οικοτοξικολογικά χαρακτηριστικά των eκπλυμάτων, προσδιορίστηκαν μe βάση την eπίδρασή τους στη φωταύγeια του βακτηρίου V. fischeri και στην κινητικότητα του καρκινοeιδούς D. magna . Τα δeίγματα παρουσίασαν φυτοτοξική δράση σe αναλογίeς μίγματος ιλύος/eδάφους μeγαλύτeρeς από 5%, eνώ τα υγρά έκπλυσης παρουσίασαν σe ορισμένeς πeριπτώσeις υψηλές τιμές οικοτοξικότητας, έως και 100%.

The complex nature and behavior of Engineered Nanomaterials (ENMs) has led to adoption of customized experimental ecotoxicity practices that are prone to possible artefacts in the inherent toxic properties of ENMs. In addition, the lack of standardized handling procedures for the ecotoxicity testing of ENMs prevents the development of experimental protocols for regulatory purposes. In this study, a suite of techniques for dispersion of ENMs was adopted and tested for two types of surface-modified alumina nanoparticles-one hydrophobic and one hydrophilic-towards the bacteria, Vibrio fischeri. The effect of certain handling practices on the observed ecotoxic effects on V. fischeri was examined. The overall goal was to evaluate by what means the handling practices of ENMs may affect the obtained toxicity results. It was realized that the toxicity of the hydrophilic and hydrophobic ENMs was mainly affected by the centrifugation and the salinity of the tested dispersions, respectively. It is more likely that both aluminium and coating substance contributed to the overall toxicity. Toxicity results are discussed with regard to generic physicochemical characteristics of the dispersions.

This study aims to provide insights into biofilm resistance associated with their structural properties acquired during formation and development. On this account, the wetting and imbibition behavior of dehydrated Pseudomonas fluorescens biofilms grown on stainless steel electropolished substrates is thoroughly examined at different biofilm ages. A polar liquid (water) and a non-polar liquid (diiodomethane) are employed as wetting agents in the form of sessile droplets. A mathematical model is applied to appraise the wetting and imbibition performance of biofilms incorporating the evaporation of sessile droplets. The present results show that the examined biofilms are hydrophilic. The progressive growth of biofilms leads to a gradual increase of substrate surface coverage─up to full coverage─accompanied by a gradual decrease of biofilm surface roughness. It is noteworthy that just after 24 h of biofilm growth, the surface roughness increases about 6.7 times the roughness of the clean stainless steel surface. It is further found that the imbibition of liquid in the biofilm matrix is restricted only to the biofilm region under the sessile droplet. The lack of further capillary imbibition into the biofilm structure, beyond the droplet deposition region, implies that the biofilm matrix is not in the form of an extended network of interconnected micro/nanopores. All in all, the present results indicate a resilient biofilm structure to biocide penetration despite its hydrophilic nature.