Ioannis D. Manariotis

Selection of microalgae for wastewater treatment and potential lipids production.

In the present study, ten microalgal strains found in fresh and saline waters were cultured, and used to conduct batch experiments in order to evaluate their potential contribution to nutrient removal and biofuel production. The growth rate of microalgae was inversely analogous to their initial concentration. Three freshwater strains were selected, based on their growth rate, and their behavior with synthetic wastewater was further investigated. The strains studied were the Scenedesmus rubescens (SAG 5.95), the Neochloris vigensis (SAG 80.80), and the Chlorococcum spec. (SAG 22.83), and higher growth rate was observed with S. rubescens. Total phosphorus removal at an initial phosphate concentration of 6-7 mg P/L in the synthetic wastewater, was 53%, 25% and 11% for N. vigensis, Chlorococcum spec., and S. rubescens, respectively. Finally, the lipid content was determined at 20th and 30th day of cultivation, and the highest amount was observed at the 20th day.

Degradation of PAHs by high frequency ultrasound

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic compounds, which have been reported in the literature to efficiently degrade at low (e.g. 20 kHz) and moderate (e.g. 506 kHz) ultrasound frequencies. The present study focuses on degradation of naphthalene, phenanthrene, and pyrene by ultrasound at three different relatively high frequencies (i.e. 582, 862, and 1142 kHz). The experimental results indicate that for all three frequencies and power inputs ≥ 133 W phenanthrene degrades to concentrations lower than our experimental detection limit (<1 μg/L). Phenanthrene degrades significantly faster at 582 kHz than at 862 and 1142 kHz. For all three frequencies, the degradation rates per unit mass are similar for naphthalene and phenanthrene and lower for pyrene. Furthermore, naphthalene degradation requires less energy than phenanthrene, which requires less energy than pyrene under the same conditions. No hexane-extractable metabolites were identified in the solutions.

Virus inactivation by high frequency ultrasound in combination with visible light

In this study, the effects of high frequency ultrasound (US) and visible light (VL) on virus inactivation were investigated. The bacteriophages ΦX174 and MS2 were used as model viruses. The experiments were performed at room temperature at three different, relatively high US frequencies (i.e., 582, 862, and 1142 kHz) with and without the use of VL, and different initial virus concentrations. The two bacteriophages were diluted in phosphate-buffered saline solution to a titer of 10(3)-10(4)pfu/mL. The experimental virus inactivation data were satisfactorily represented by a simple first-order kinetic expression. Virus inactivation was faster at the lower frequencies (582 and 862 kHz). Furthermore, it was observed that MS2 was inactivated faster than ΦX174. The simultaneous use of US and VL was found to be more effective than US alone for MS2 inactivation, indicating the existence of a synergistic effect. However, the use of VL in conjunction with high frequency US hindered the inactivation of ΦX174.

Effect of cultivation media on the toxicity of ZnO nanoparticles to freshwater and marine microalgae.

The aim of this work was to investigate the effect of zinc oxide nanoparticles (ZnO NPs) on freshwater and marine microalgae cultivated in different media. Freshwater species Chlorococcum sp. and Scenedesmus rubescens were cultivated in modified Blue-Green medium (BG-11) and Bolds Basal Medium (BBM), and marine species Dunaliella tertiolecta, and Tetraselmis suesica, cultured in salt modified BG-11 and f/2 medium. The microalgae species were exposed for 96 h with a daily reading of algal growth rate, to different ZnO NPs concentrations (0.081-810 mg/L). Significant differences were observed on microalgae growth rates, with the marine being more sensitive than the freshwater species, as revealed by their half inhibitory concentration values (IC50). The IC50 values in freshwater species were affected by the culture medium. The lowest IC50 values (<2.57 mg/L) were observed in the marine species. S. rubescens showed the less toxic effect in cultures with modified BG-11, compared to BBM cultures, with IC50 values >810 mg/L and 14.27 mg/L after 96 h exposure time, respectively. ZnO nanoparticles appeared to have toxic effects in all species tested, depended on the species type, the exposure time, the NPs concentration, and mainly the culture medium.

Design and analysis of a solar reactor for anaerobic wastewater treatment

The aim of this research was to design a solar heated reactor system to enhance the anaerobic treatment of wastewater or biological sludge at temperatures higher than the ambient air temperature. For the proposed reactor system, the solar energy absorbed by flat plate collectors was transferred to a heat storage tank, which continuously supplied an anaerobic-filter reactor with water at a maximum temperature of 35 degrees C. The packed reactor was a metallic cylindrical tank with a peripheral twin-wall enclosure. Inside this enclosure was circulated warm water from the heat storage tank. Furthermore, a mathematical model was developed for the prediction of the temperature distribution within the reactor under steady state conditions. Preliminary results based on model simulations performed with meteorological data from various geographical regions of the world suggested that the proposed solar reactor system could be a promising and environmentally friendly approach for anaerobic treatment of wastewater and biological sludge.

Anaerobic Treatment of Low-Strength Wastewater in a Biofilm Reactor

Abstract A 3.9-L (70-cm high) upflow anaerobic filter (AF) packed with corrugated plastic rings was employed to evaluate the direct treatment of low-strength wastewater over a long period of operation (32 months at 25.4°C and 2 months at 15.5°C). The AF was fed four complex synthetic-type wastewaters with a low-solids content [chemical oxygen demand (COD) 325–403 mg L−1 soluble COD (SCOD) 86–339 mg L−1 and total suspended solids (TSS) 65–156 mg L−1] at organic loading rates (OLR) ranging from 0.02 to 0.91 kg COD m−3 d−1. Operation with filtered municipal wastewater supplemented with a sugar-nutrient based substrate (OLR 0.27–0.91 kg COD m−3 d−1) yielded removal efficiencies in the range of 72–80% for COD and 80–92% for TSS, and use of a completely synthetic substrate resulted in improved effluent quality. Under these test conditions, removal of organic matter and solids occurred within the first 40 cm of column height and accumulation within the reactor was not substantial or affected by the length of operation.

Mediated effect of ultrasound treated Diclofenac on mussel hemocytes: First evidence for the involvement of respiratory burst enzymes in the induction of DCF-mediated unspecific mode of action

The present study investigates the toxic behavior of diclofenac (DCF) before and after its ultrasound (US) treatment, as well as the involvement of intracellular target molecules, such as NADPH oxidase and NO synthase, in the DCF-induced adverse effects on hemocytes of mussel Mytilus galloprovincialis. In this context, appropriate volumes (350 and 500mL) of DCF solutions (at concentrations of 2, 2.5, 5 and 10mgL(-1)) were treated under different ultrasound operating conditions (frequency at 582 and 862kHz, electric power density at 133 and 167W) for assessing US method efficiency. In parallel, DCF and US DCF-mediated cytotoxic (in terms of cell viability measured with the use of neutral red uptake/NRU method), oxidative (in terms of superoxide anions/(.)O2(-), nitric oxides such as NO2(-) and lipid peroxidation products, such as malondialdehyde/MDA content) and genotoxic (DNA damage measured by the use of Comet assay method) effects were investigated in hemocytes exposed for 1h to 5, 10 and 100ngL(-1) and 1, 10 and 20μgL(-1) of DCF. The involvement of NADPH oxidase and NO synthase to the DCF-induced toxicity was further investigated by the use of 10μΜ L-NAME, a NO synthase inhibitor and 10μΜ DPI, a NADPH oxidase inhibitor. According to the results, 350mL of 2mgL(-1) DCF showed higher degradation (>50%) under 167W electric power density and frequency at 862kHz for 120min, compared to degradation in all other cases, followed by a significant elimination of its toxicity. Specifically, US DCF-treated hemocytes showed a significant attenuation of DCF-mediated cytotoxic, oxidative and genotoxic effects, which appeared to be caused by NADPH oxidase and NO synthase activation, since their inhibition was followed by a significant elimination of (.)O2(-) and NO2(-) generation and the concomitant oxidative damage within cells. The results of the present study showed for the first time that unspecific mode of action of DCF, associated with the induction of NADPH oxidase and NO synthase in mussel hemocytes, could be significantly diminished after partial US degradation of DCF, at least under optimized operating conditions currently tested.

Anaerobic Treatment of Low-Strength Wastewater by a Biofilm Reactor

A 3.9-L (70-cm high) upflow anaerobic filter (AF) packed with corrugated plastic rings was employed to evaluate the direct treatment of low-strength wastewater over a long period of operation (32 months at 25.4 degrees C and 2 months at 15.5 degrees C). The AF was fed four complex synthetic-type wastewaters with a low-solids content [chemical oxygen demand (COD) 325-403 mg L(-1), soluble COD (SCOD) 86-339 mg L(-1) and total suspended solids (TSS) 65-156 mg L(-1)] at organic loading rates (OLR) ranging from 0.02 to 0.91 kg COD m(-3) d(-1). Operation with filtered municipal wastewater supplemented with a sugar-nutrient based substrate (OLR 0.27-0.91 kg COD m(-3) d(-1)) yielded removal efficiencies in the range of 72-80% for COD and 80-92% for TSS, and use of a completely synthetic substrate resulted in improved effluent quality. Under these test conditions, removal of organic matter and solids occurred within the first 40cm of column height and accumulation within the reactor was not substantial or affected by the length of operation.

Long-term toxicity of ZnO nanoparticles to Scenedesmus rubescens cultivated in different media

The aim of this work was to investigate the long-term toxic effect of zinc oxide (ZnO) nanoparticles (NPs) on freshwater microalgae, combined with the nutrient consumption in the culture. For this purpose, two common microalgae media (Blue-Green 11, BG-11, and Bold’s Basal Medium, BBM) were used. Scenedesmus rubescens was used as freshwater microalgae model species and was exposed to ZnO NPs at different concentrations (0.081 to 810 mg/L) for a period up to 28 d. The experimental results revealed that microalgae growth was affected by the time of exposure and the NPs concentrations, but mainly the culture medium used. Differences in microalgae growth rates were observed and attributed to the selected culture medium. The toxic effect of ZnO NPs was higher on microalgae cultured in modified BG-11 compared to BBM, despite the fact that S. rubescens exhibited higher growth rate in modified BG-11 without the exposure of ZnO NPs.

Assessment of the effectiveness of a solar system heating an anaerobic bioreactor.

The performance of a solar system designed to heat a packed bed reactor for anaerobic treatment of municipal wastewater was evaluated, and the feasibility of employing low-scale solar reactors in small settlements or enterprises was investigated. An energy balance was performed using a simple reactor model previously proposed by Yiannopoulos et al. (Bioresource Technology 99:7742–7749, 2008) to estimate the size of a solar system in Patras, Greece. The main objective is to feed the reactor with warm water produced by solar energy and achieve an increase of temperature close to 35°C for the majority of the year. Model simulations indicated that the heat demand of the reactor could be balanced practically by a number of flat plate solar collectors supplying warm water at above 20°C for over 95% of the year. Therefore, the proposed system can offer a viable alternative to enhancing anaerobic treatment in wastewater facilities.