Publications by authors named "Alexandros Katsaounis"

11 Publications

  • Page 1 of 1

Nitrate removal from groundwater using a batch and continuous flow hybrid Fe-electrocoagulation and electrooxidation system.

J Environ Manage 2021 Nov 28;297:113387. Epub 2021 Jul 28.

Department of Chemical Engineering, University of Patras, Rio, GR-26504, Patras, Greece; Institute of Chemical Engineering Sciences (ICE-HT), Stadiou Str., Platani, GR-26504, Patras, Greece.

During the last two decades nitrate contaminated groundwater has become an extensive worldwide problem with wide-reaching negative effects on human health and the environment. In this study, a combination of electrocoagulation (EC) and electrooxidation (EO) was studied as a denitrification process to efficiently remove nitrates and ammonium (a by-product produced during EC) from real polluted groundwater. Initially, EC experiments under batch operating mode were performed using iron electrodes at different applied current density values (20-40 mA cm). Nitrate percentage removal of 100 % was recorded, however high ammonium concentrations were performed (4.5-6.5 mg NH-Ν L). Therefore, a continuous flow system was examined for the complete removal of both nitrates and EC-generated ammonium cations. The system comprised an EC reactor, a settling tank and an EO reactor. The applied current densities to the EC process were the same as those in the batch experiments, while the volumetric flow rates were 4, 6 and 8 mL min. Regarding the current density of the EO process was kept constant at the value of 75 mA cm. The percentage nitrate removal recorded during the EC process ranged between 52.0 and 100 %, while the NH-N concentration at the outlet of the EO reduced significantly (53-100 %) depending on the applied current density and the volumetric flow rate. Also, the dissolved iron concentration in the treated water was always below the legislated limit of 0.2 mg L (up to 0.027 mg L). These results indicate that the proposed hybrid system is capable of denitrifying real nitrate contaminated groundwater without generating toxic by-products, therefore making the water suitable for human consumption.
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http://dx.doi.org/10.1016/j.jenvman.2021.113387DOI Listing
November 2021

Combined electrocoagulation and electrochemical oxidation treatment for groundwater denitrification.

J Environ Manage 2021 May 10;285:112068. Epub 2021 Feb 10.

Department of Chemical Engineering, University of Patras, Rio, GR-26504, Patras, Greece; Institute of Chemical Engineering Sciences (ICE-HT), Stadiou Str., Platani, GR-26504, Patras, Greece. Electronic address:

Electrocoagulation (EC) with an aluminum electrode arrangement as anode-cathode was applied to denitrify groundwater and electrooxidation (EO) was examined as a post-treatment step to remove the produced by-products. Initially, EC experiments were performed under batch operating mode using artificially-polluted tap water to investigate the effects of initial pH (5.5, 7.5, 8.5), initial NO-N concentration (25, 35, 45, 55 mg L) and applied current density (10, 20 mA cm) on process efficiency. The effect of initial solution pH on ammonium cation concentration was also investigated as their generation (as a by-product) is the main drawback preventing wide-scale application of these treatment processes. Experimental results revealed high nitrate removal percentages (up to 96.3%) for initial pH 7.5 and all initial concentrations and current densities, while the final ammonium concentrations ranged between 5.3 and 9.2 mg NH-N L (for initial NO-N of 25 mg L). Therefore, EO was examined to oxidize the ammonium cations to nitrogen gas on iridium oxide coated titanium electrodes (IrO/Ti) anode surface. The effects of cathode material (aluminum, stainless steel), total current density and anode surface area (3.3-30 mA cm and 12-36 cm, respectively) were investigated, and lead to NH-N percentage removals of between 25% (10 mA cm, 12 cm) and 100% (30 mA cm, 24 cm) for an initial NH-N concentration of 10 mg L. The optimum EC (20 mA cm, natural initial pH 7.5-7.8) and EO parameters (30 mA cm, 24 cm surface area anode, Al cathode) were combined into a hybrid system to treat two real nitrate-polluted groundwaters with initial NO-N concentrations of 25 and 75 mg L. Results revealed that the proposed hybrid treatment system can be used to efficiently remove nitrate from groundwaters.
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http://dx.doi.org/10.1016/j.jenvman.2021.112068DOI Listing
May 2021

Electrochemical treatment of biologically pre-treated dairy wastewater using dimensionally stable anodes.

J Environ Manage 2017 Nov 20;202(Pt 1):217-224. Epub 2017 Jul 20.

Department of Chemical Engineering, University of Patras, Caratheodory 1, GR-26504 Patras, Greece; Institute of Chemical Engineering Sciences, Foundation for Research and Technology, PO Box 1414, GR-26504 Patras, Greece.

In this work, electrochemical oxidation of aerobically pre-treated dairy wastewaters using IrO-Pt coated dimensionally stable anodes was investigated. It was found that IrO/Ti electrode outperforming Pt/Ti and IrO-Pt/Ti at lower current densities, while Pt/Ti achieved better efficiency at higher current density. Among the different parameters which were studied, the current density was the most crucial for the efficiency of the process. A current density of 100 mA/cm led to almost complete removal of 3700 mg/L COD after 360 min of treatment using IrO/Ti electrode and 0.2 M of sodium chloride while complete decolorization was achieved in less than 60 min. Electrolytes also found to significantly affect the process. More specific, the use of sodium chloride instead of sodium sulfate enhanced both COD and color removal due to the formation of active chlorine species. The effect of temperature was relative low; the process was favourable at elevated temperatures while increasing COD loading resulted in a decrease of COD and color removal.
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http://dx.doi.org/10.1016/j.jenvman.2017.07.046DOI Listing
November 2017

Boron-doped diamond electrooxidation of ethyl paraben: The effect of electrolyte on by-products distribution and mechanisms.

J Environ Manage 2017 Jun 1;195(Pt 2):148-156. Epub 2016 Jul 1.

Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece.

Ethyl paraben (EP), a representative emerging pollutant of the parabens family, was subject to electrochemical oxidation over a boron-doped diamond (BDD) anode. Experiments were carried out in a single-compartment cell at 10-70 mA cm current density, 200-600 μg L EP concentration, initial solution pH 3-9 and 0.1 M electrolyte concentration. The degradation rate is favored at increased current densities and in the presence of NaCl as the supporting electrolyte, while the pH effect is inconsiderable. For instance, the first order rate constant for the degradation of 200 μg L EP at 30 mA cm was 0.25, 0.1 and 0.07 min with NaCl, NaSO and HClO, respectively. Degradation in secondary treated wastewater was faster than in pure water presumably due to the action of chloride ions present in the effluent. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) was employed to determine major transformation by-products (TBPs). The route of EP degradation with NaSO involves hydroxylation and demethylation reactions, signifying the role of electrogenerated hydroxyl radicals in the process. Twenty one TBPs were identified with NaCl as the electrolyte, including several chlorinated and non-chlorinated dimers and trimers; these findings suggest that indirect oxidation mediated by chlorine radicals and other chlorine active species also takes place. In this view, the role of the supporting electrolyte is crucial since it can influence both reaction kinetics and pathways.
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http://dx.doi.org/10.1016/j.jenvman.2016.06.044DOI Listing
June 2017

Photoelectrocatalytic disinfection of water and wastewater: performance evaluation by qPCR and culture techniques.

J Water Health 2013 Mar;11(1):21-9

Department of Environmental Engineering, Technical University of Crete, Polytechneioupolis, GR-73100 Chania, Greece.

Photoelectrocatalytic oxidation (PEC) was evaluated as a disinfection technique using water and secondary treated wastewater spiked with Escherichia coli and Enterococcus faecalis. PEC experiments were carried out using a TiO(2)/Ti-film anode and a zirconium cathode under simulated solar radiation. Bacterial inactivation was monitored by culture and quantitative polymerase chain reaction (qPCR). Inactivation rates were enhanced when the duration of the treatment was prolonged and when the bacterial density and the complexity of the water matrix were decreased. E. coli cells were reduced by approximately 6 orders of magnitude after 15 min of PEC treatment in water at 2V of applied potential and an initial concentration of 10(7) CFU/mL; pure photocatalysis (PC) led to about 5 log reduction, while electrochemical oxidation alone resulted in negligible inactivation. The superiority of PEC relative to PC can be attributed to a more efficient separation of the photogenerated charge carriers. Regarding disinfection in mixed bacterial suspensions, E. coli was more susceptible than E. faecalis at a potential of 2V. The complex composition of wastewater affected disinfection efficiency, yielding lower inactivation rates compared to water treatment. qPCR yielded lower inactivation rates at longer treatment times than culture techniques, presumably due to the fact that the latter do not take into account the viable but not culturable state of microorganisms.
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http://dx.doi.org/10.2166/wh.2012.208DOI Listing
March 2013

Removal of faecal indicator pathogens from waters and wastewaters by photoelectrocatalytic oxidation on TiO(2)/Ti films under simulated solar radiation.

Environ Sci Pollut Res Int 2012 Nov 3;19(9):3782-90. Epub 2012 Oct 3.

Department of Environmental Engineering, Technical University of Crete, Polytechneioupolis, 73100, Chania, Greece.

Purpose: The disinfection efficiency of water and secondary treated wastewater by means of photoelectrocatalytic oxidation (PEC) using reference strains of Enterococcus faecalis and Escherichia coli as faecal indicators was evaluated. Operating parameters such as applied potential (2-10 V), initial bacterial concentration (10(3)-10(7) CFU/mL), treatment time (up to 90 min) and aqueous matrix (pure water and treated effluent) were assessed concerning their impact on disinfection.

Methods: PEC experiments were carried out using a TiO(2)/Ti film anode and a zirconium cathode in the presence of simulated solar radiation. Bacterial inactivation was monitored by the culture method and real-time SYBR green PCR.

Results: A 6.2 log reduction in E. faecalis population was achieved after 15 min of PEC treatment in water at 10 V of applied potential and an initial concentration of 10(7) CFU/mL; pure photocatalysis (PC) led to only about 4.3 log reduction, whilst negligible inactivation was recorded when the respective electrochemical oxidation process was applied (i.e. without radiation). PEC efficiency was generally improved increasing the applied potential and decreasing initial bacterial concentration. Regarding real wastewater, E. coli was more susceptible than E. faecalis during treatment at a potential of 5 V. Wastewater disinfection was affected by its complex composition and the contained mixed bacterial populations, yielding lower inactivation rates compared to water treatment. Screening the results obtained from both applied techniques (culture method and real-time PCR), there was a discrepancy regarding the recorded time periods of total bacterial inactivation, with qPCR revealing longer periods for complete bacterial reduction.

Conclusions: PEC is superior to PC in terms of E. faecalis inactivation presumably due to a more efficient separation and utilization of the photogenerated charge carriers, and it is mainly affected by the applied potential, initial bacterial concentration and the aqueous matrix.
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http://dx.doi.org/10.1007/s11356-012-0768-5DOI Listing
November 2012

Reprint of: Electrochemical oxidation of stabilized landfill leachate on DSA electrodes.

J Hazard Mater 2012 Mar 1;207-208:73-8. Epub 2012 Feb 1.

Department of Environmental Engineering, University of Padua, 35100 Padua, Italy.

The electrochemical oxidation of stabilized landfill leachate with 2960 mgL(-1) chemical oxygen demand (COD) over a Ti/IrO2-RuO2 anode was investigated in the presence of HClO4 as the supporting electrolyte. Emphasis was given on the effect of electrolysis time (up to 240 min) and temperature (30, 60 and 80 °C), current density (8, 16 and 32 mAcm(-2)), initial effluent's pH (0.25, 3, 5 and 6), HClO4 concentration (0.25 and 1M) and the addition of NaCl (20 and 100 mM) or Na2SO4 (20 mM) as source of extra electrogenerated oxidants on performance; the latter was evaluated regarding COD, total carbon (TC), total phenols (TPh) and color removal. Moreover, the anode was studied by scanning electron microscopy and cyclic voltammetry. The main parameters affecting the process were the effluent's pH and the addition of salts. Treatment for 240 min at 32 mAcm(-2) current density, 80 °C and the pH adjusted from its inherent value of 0.25 (i.e., after the addition of HClO4) to 3 yielded 90% COD, 65% TC and complete color and TPh removal at an electricity consumption of 35kWhkg(-1) COD removed. Comparable performance (i.e. 75% COD reduction) could be achieved without pH adjustment but with the addition of 100mM NaCl consuming 20 kWhkg(-1) COD removed.
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http://dx.doi.org/10.1016/j.jhazmat.2012.01.083DOI Listing
March 2012

Anodic oxidation of textile dyehouse effluents on boron-doped diamond electrode.

J Hazard Mater 2012 Mar 4;207-208:91-6. Epub 2011 Apr 4.

Department of Environmental Engineering, Technical University of Crete, Polytechneioupolis, GR-73100 Chania, Greece.

The electrochemical oxidation of textile effluents over a boron-doped diamond anode was investigated in the present study. Experiments were conducted with a multi-component synthetic solution containing seventeen dyes and other auxiliary inorganics, as well as an actual effluent from a textile dyeing process. The effect of varying operating parameters, such as current density (4-50 mA/cm2), electrolyte concentration (0.1-0.5 M HClO4), initial solution pH (1-12.3) and temperature (22-43 °C), on process efficiency was investigated following changes in total organic carbon (TOC), chemical oxygen demand (COD) and color. Complete decolorization accompanied by significant mineralization (up to 85% depending on the conditions) could be achieved after 180 min of treatment. Performance was improved at higher electrolyte concentrations and lower pH values, while the effect of temperature was marginal. Energy consumption per unit mass of COD removed was favored at lower current densities, since energy was unnecessarily wasted to side reactions at higher densities.
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http://dx.doi.org/10.1016/j.jhazmat.2011.03.107DOI Listing
March 2012

Electrochemical oxidation of stabilized landfill leachate on DSA electrodes.

J Hazard Mater 2011 Jun 29;190(1-3):460-5. Epub 2011 Mar 29.

Department of Environmental Engineering, University of Padua, 35100 Padua, Italy.

The electrochemical oxidation of stabilized landfill leachate with 2960 mg L(-1) chemical oxygen demand (COD) over a Ti/IrO(2)-RuO(2) anode was investigated in the presence of HClO(4) as the supporting electrolyte. Emphasis was given on the effect of electrolysis time (up to 240 min) and temperature (30, 60 and 80°C), current density (8, 16 and 32 mA cm(-2)), initial effluent's pH (0.25, 3, 5 and 6), HClO(4) concentration (0.25 and 1M) and the addition of NaCl (20 and 100mM) or Na(2)SO(4) (20mM) as source of extra electrogenerated oxidants on performance; the latter was evaluated regarding COD, total carbon (TC), total phenols (TPh) and color removal. Moreover, the anode was studied by scanning electron microscopy and cyclic voltammetry. The main parameters affecting the process were the effluent's pH and the addition of salts. Treatment for 240 min at 32 mA cm(-2) current density, 80°C and the pH adjusted from its inherent value of 0.25 (i.e. after the addition of HClO(4)) to 3 yielded 90% COD, 65% TC and complete color and TPh removal at an electricity consumption of 35 kWh kg(-1) COD removed. Comparable performance (i.e. 75% COD reduction) could be achieved without pH adjustment but with the addition of 100mM NaCl consuming 20 kWh kg(-1) COD removed.
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http://dx.doi.org/10.1016/j.jhazmat.2011.03.085DOI Listing
June 2011

Electrochemical enhancement of solar photocatalysis: degradation of endocrine disruptor bisphenol-A on Ti/TiO2 films.

Water Res 2011 Apr 21;45(9):2996-3004. Epub 2011 Mar 21.

Department of Environmental Engineering, Technical University of Crete, Polytechneioupolis, Chania, Greece.

The photoelectrocatalytic oxidation over immobilized Ti/TiO(2) films in the presence of simulated solar light was investigated for the degradation of bisphenol-A (BPA) in water. The catalyst, consisting of 75:25 anatase:rutile, was prepared by a sol-gel method and characterized by cyclic voltammetry, X-ray diffraction and scanning electron microscopy. Experiments were conducted to assess the effect of applied current (0.02-0.32 mA/cm(2)), TiO(2) loading (1.3-9.2 mg), BPA concentration (120-820 μg/L), initial solution pH (1 and 7.5) and the aqueous matrix (pure water and treated effluent) on BPA photoelectrocatalytic degradation which was monitored by high performance liquid chromatography equipped with a fluorescence detector. The reaction was favored at anodic currents up to 0.04 mA/cm(2) and lower substrate concentrations, but it was hindered by the presence of residual organic matter and radical scavengers (e.g. bicarbonates) in treated effluents. Moreover, a pseudo-first order kinetic model could fit the experimental data well with the apparent reaction constant taking values between 2.9 and 32.4 10(-3)/min. The degradation of BPA by pure photocatalysis or electrochemical oxidation alone was also studied leading to partial substrate removal. In all cases, the contribution of applied potential to photocatalytic degradation was synergistic with the photocatalytic efficiency increasing between 24% and 97% possibly due to a more efficient separation and utilization of the photogenerated charge carriers. The effect of photoelectrocatalysis on the ecotoxic and estrogenic properties of BPA was also evaluated measuring the bioluminescence inhibition of Vibrio fischeri and performing the yeast estrogen screening assay, respectively.
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http://dx.doi.org/10.1016/j.watres.2011.03.030DOI Listing
April 2011

Boron-doped diamond anodic treatment of olive mill wastewaters: statistical analysis, kinetic modeling and biodegradability.

Water Res 2009 Sep 17;43(16):3999-4009. Epub 2009 Apr 17.

Department of Environmental Engineering, Technical University of Crete, Polytechneioupolis, GR-73100 Chania, Greece.

The electrochemical treatment of olive mill wastewaters (OMW) over boron-doped diamond (BDD) electrodes was investigated. A factorial design methodology was implemented to evaluate the statistically important operating parameters, amongst initial COD load (1000-5000 mg/L), treatment time (1-4h), current intensity (10-20A), initial pH (4-6) and the use of 500 mg/L H(2)O(2) as an additional oxidant, on treatment efficiency; the latter was assessed in terms of COD, phenols, aromatics and color removal. Of the five parameters tested, the first two had a considerable effect on COD removal. Hence, analysis was repeated at more intense conditions, i.e. initial COD values up to 10,000 mg/L and reaction times up to 7h and a simple model was developed and validated to predict COD evolution profiles. The model suggests that the rate of COD degradation is zero order regarding its concentration and agrees well with an electrochemical model for the anodic oxidation of organics over BDD developed elsewhere. The treatability of the undiluted effluent (40,000 mg/L COD) was tested at 20A for 15h yielding 19% COD and 36% phenols' removal respectively with a specific energy consumption of 96 kWh/kg COD removed. Aerobic biodegradability and ecotoxicity assays were also performed to assess the respective effects of electrochemical treatment.
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http://dx.doi.org/10.1016/j.watres.2009.04.007DOI Listing
September 2009
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