Publications by authors named "Dimitris V Vayenas"

9 Publications

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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

Treatment of real industrial-grade dye solutions and printing ink wastewater using a novel pilot-scale hydrodynamic cavitation reactor.

J Environ Manage 2021 Nov 16;297:113301. Epub 2021 Jul 16.

Department of Chemical Engineering, University of Patras, Rio, GR-26504, Patras, Greece; Institute of Chemical Engineering and High Temperature Chemical Processes (FORTH/ ICE-HT), Stadiou Str., Platani, GR-26504, Patras, Greece. Electronic address:

A novel pilot-scale hydrodynamic cavitation (HC) reactor was used to decolorize industrial-grade dye solutions and printing ink wastewater (PIW). The effect of the orifice plate geometry (1 hole plate of 1 mm and 2 mm in diameter, 31 holes of 1 mm and 2 mm in diameter, 62 holes of 1 mm and 2 mm in diameter), inlet pressure (4, 5 bar), initial dye concentration (0.3 and 0.6 OD), and the synergistic effect of HC and hydrogen peroxide concentration (0.0, 0.5, 1.0, 2.0 g/L) were investigated. The results showed that the highest color removal was obtained using 31 holes orifice plate of 2 mm holes' diameter, at 4 bar inlet pressure. Furthermore, although HC could not degrade completely all the industrial-grade dyes, efficiency was enhanced in the presence of HO. The optimum concentration of hydrogen peroxide was 1.0 g/L regardless of the initial concentration of the dyes studied. Under optimum operating conditions, color removal reached up to 68% for black, 39% for red, 43% for yellow, 55% for green, and 51% for cyan dye, while color removal in the PIW reached only 15%. The black dye solution presented almost 100% COD removal, while 38%, 25%, 67%, and 78% COD removal values were obtained for the red, yellow, cyan and green dyes, respectively. 55% COD removal was recorded from the PIW. Concerning cavitation yields, black, red, yellow, green, cyan dye yields reached 2.5E(-7), 1.1E(-7), 1.5E(-7), 2.0E(-7), 1.7E(-7) OD⋅L/J, respectively, while PIW yield was 6.3E(-8) OD⋅L/J. The present study demonstrates that HC combined with green oxidants such as hydrogen peroxide could be an alternative treatment approach for real industrial wastewater streams. However, a combination with a post-treatment method should be applied to maximize both color and COD removal.
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http://dx.doi.org/10.1016/j.jenvman.2021.113301DOI 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

Two-step treatment of brewery wastewater using electrocoagulation and cyanobacteria-based cultivation.

J Environ Manage 2020 Jul 8;265:110543. Epub 2020 Apr 8.

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.

This study combines electrocoagulation (EC) and cyanobacteria-based cultivation for the two-step treatment of brewery wastewater (BW), with the aim to develop a viable alternative to conventional activated sludge technology. The first step applied EC as a pretreatment method, using different electrode materials (aluminum and iron), to remove color and some pollutant load from the BW. After 30 min of EC treatment, decolorization of BW exceeded 80% for both electrode materials and a 100% reduction of total suspended solids was achieved. In the second step, the electrochemically pretreated BW was used as substrate for a cyanobacteria-based cultivation. After 15 days of cultivation total biomass concentrations (containing up to 50% carbohydrates) reached 525.0 mg L and 740.0 mg L, for aluminum- and iron-pretreated BW, respectively. Moreover, the cyanobacterial community assimilated most of the residual aluminum and iron produced by the EC process, therefore verifying its bioremediation abilities. The combined process also proved effective at pollutant removal (89.1%, 100%, 89.4%, 98.5% and 91.6% of nitrate, ammonium, total Kjeldahl nitrogen, total phosphorus and chemical oxygen demand, respectively). The two-stage treatment method proposed could offer a promising alternative to conventional BW treatment technologies as it combines both efficiency and sustainability.
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http://dx.doi.org/10.1016/j.jenvman.2020.110543DOI Listing
July 2020

A hybrid system for groundwater denitrification using electrocoagulation and adsorption.

J Environ Manage 2019 Nov 6;249:109355. Epub 2019 Sep 6.

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

The treatment of nitrate-contaminated groundwater was studied using a hybrid system comprising an electrocoagulation unit and a zeolite adsorption reactor. In the electrocoagulation (EC) process, aluminum alloy electrodes were used in an undivided cell. Experiments in the laboratory-scale reactor were carried out in unregulated temperature conditions to treat synthetic groundwater solutions containing initial nitrate concentrations of 10-100 mg NO-N·L in batch mode and without using additional pH buffers. Various operating variables, such as applied current density (about 20 mA cm to 80 mA cm), concentration of NaCl electrolyte (0.0-1.0 g L) and treatment time (up to 120 min), were tested for their effects on nitrate removal. Results showed that initial NO-N concentration, current density and electrolyte concentration, play important roles in EC. For all initial NO-N concentrations and current densities tested, the highest NO-N removal rates (up to 2.374 g L·d) were achieved without additional electrolyte and/or with the lowest electrolyte concentration of 0.1 g L. In these experiments, EC reduced NO-N to below the standard limit of 10 mg L after 10-60 min of electrolysis. A significant quantity of by-products, ammonium and dissolved aluminum, formed during the process, however these were successfully removed by zeolite adsorption in the post-treatment step. The electrochemical reactor using the specific anode/cathode combination and an environmentally-friendly post-treatment step such as zeolite adsorption, can be used to efficiently remove nitrate from groundwaters because of its high efficiency.
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http://dx.doi.org/10.1016/j.jenvman.2019.109355DOI Listing
November 2019

Treatment of printing ink wastewater using electrocoagulation.

J Environ Manage 2019 May 27;237:442-448. Epub 2019 Feb 27.

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:

The present study investigates the treatment of real printing ink wastewater by using the electrocoagulation (EC) process. Effects of initial chemical oxygen demand (COD) concentrations, electrode materials and current densities were examined to determine the maximum COD and color removal from the wastewater. In parallel, raw and treated printing ink wastewater toxic potential was further estimated via the application of toxicity tests using the freshwater crustacean Thamnocephalus platyurus for assessing EC process efficiency. According to the results, it was observed that the EC is efficient under most of the operating conditions used, as COD and color removal ranged between 72.03 to 85.81% and 98.7-100%, respectively. The total cost of the EC process, considering the treatment time, applied current, applied voltage and the total anode electrode mass consumption was also estimated. The Fe electrode proved to be of lower cost than the Al electrode, however the use of Al electrode produced better decolorization results in the solutions. Moreover, toxicity tests currently performed with the use of larvae of the fairy shrimp Thamnocephalus platyurus revealed a substantial decrease in the toxic potential of printing ink wastewater, thus indicating the efficiency of the proposed EC process.
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http://dx.doi.org/10.1016/j.jenvman.2019.02.080DOI Listing
May 2019

Modelling of biological Cr(VI) removal in draw-fill reactors using microorganisms in suspended and attached growth systems.

Water Res 2013 Feb 2;47(2):623-36. Epub 2012 Nov 2.

Department of Environmental and Natural Resources Management, University of Western Greece, 2 Seferi Str., 30100 Agrinio, Greece.

The kinetics of hexavalent chromium bio-reduction in draw-fill suspended and attached growth reactors was examined using sugar as substrate and indigenous microorganisms from the industrial sludge of the Hellenic Aerospace Industry. Initially, experiments in suspended growth batch reactors for Cr (VI) concentrations of 1.4-110 mg/l were carried out, to extensively study the behaviour of a mixed culture. The maximum Cr(VI) reduction rate of 2 mg/l h was achieved for initial concentration 12.85 mg/l with biomass production rate 4.1 mg biomass/l h. Analysis of the microbial structure in the batch reactor culture indicated that the dominant bacterial communities were constituted by bacterial members of Raoultella sp., Citrobacter sp., Klebsiella sp., Salmonella sp., Achromobacter sp. and Kerstersia sp. while the dominant fungal strain was that of Pichia jadinii. Experiments using the same mixed culture were also carried out in packed-bed reactors with plastic support media. High removal rates were achieved (2.0 mg/l h) even in high initial concentrations (109 mg/l). A combination of the model of Tsao and Hanson for growth enhancement and that of Aiba and Shoda for growth inhibition was used in order to describe and predict the process of Cr(VI) bio-reduction in suspended growth and packed-bed reactors. Kinetic constants of the equation obtained from both batch (or draw-fill) culture experiments. In the draw-fill experiments at the packed-bed reactor, hexavalent chromium inhibitory effects were minimized increasing the inhibitory constant value K(i)' at 148.5 mg/l, compared to suspended growth experiments which was K(i) = 8.219 mg/l. The model adequately predicts hexavalent chromium reduction in both batch reactors for all initial concentrations tested.
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http://dx.doi.org/10.1016/j.watres.2012.10.034DOI Listing
February 2013

The effect of carbon source on microbial community structure and Cr(VI) reduction rate.

Biotechnol Bioeng 2010 Oct;107(3):478-87

Department of Environmental and Natural Resources Management, University of Ioannina, 2 Seferi Street, Agrinio 30100, Greece.

In the present work, the effect of the carbon source on microbial community structure in batch cultures derived from industrial sludge and hexavalent chromium reduction was studied. Experiments in aerobic batch reactors were carried out by amending industrial sludge with two different carbon sources: sodium acetate and sucrose. In each of the experiments performed, four different initial Cr(VI) concentrations of: 6, 13, 30 and 115 mg/L were tested. The change of carbon source in the batch reactor from sodium acetate to sucrose led to a 1.3-2.1 fold increase in chromium reduction rate and to a 5- to 9.5-fold increase in biomass. Analysis of the microbial structure in the batch reactor showed that the dominant communities were bacterial species (Acinetobacter lwoffii, Defluvibacter lusatiensis, Pseudoxanthomonas japonensis, Mesorhizium chacoense, and Flavobacterium suncheonense) when sodium acetate was used as carbon source and fungal strains (Trichoderma viride and Pichia jadinii), when sodium acetate was replaced by sucrose. These results indicate that the carbon source is a key parameter for microbial dynamics and enhanced chromium reduction and should be taken into account for efficient bioreactor design.
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http://dx.doi.org/10.1002/bit.22837DOI Listing
October 2010

Complex dynamics of microbial competition in the gradostat.

J Biotechnol 2009 Jan 3;139(1):38-46. Epub 2008 Sep 3.

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

We examine the conditions necessary for the emergence of complex dynamic behavior in systems of microbial competition. In particular, we study the effect of spatial heterogeneity and substrate-inhibition on the dynamics of such a system. This is accomplished through the study of a mathematical model of two microbial populations competing for a single nutrient in a configuration of two interconnected chemostats. Microbial growth is assumed to follow substrate-inhibited kinetics for both species. Such a system with sterile feed has been shown in a previous work to exhibit stable periodic states. In the present work we study the system for the case of non-sterile feed, i.e., when the two species are present in the feed of the chemostats. The analysis is done by numerical bifurcation theory methods. We demonstrate that, in addition to periodic states, the system possesses stable quasi-periodic states resulting from Neimark-Sacker bifurcations of limit cycles. Also, periodic states may undergo successive period doublings leading to periodic states of increasing period and indicating that chaotic states might be possible. Multistability is also observed, consisting in the coexistence of several stable steady states and possibly stable periodic or quasi-periodic states for given operating conditions. It appears that substrate-inhibition, spatial heterogeneity and presence of microorganisms in the inflow are all necessary conditions for complex dynamics to arise in a microbial system of pure and simple competition.
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http://dx.doi.org/10.1016/j.jbiotec.2008.08.006DOI Listing
January 2009
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