Dionissios Mantzavinos

Removal of residual pharmaceuticals from aqueous systems by advanced oxidation processes.

Over the past few years, pharmaceuticals are considered as an emerging environmental problem due to their continuous input and persistence to the aquatic ecosystem even at low concentrations. Advanced oxidation processes (AOPs) are technologies based on the intermediacy of hydroxyl and other radicals to oxidize recalcitrant, toxic and non-biodegradable compounds to various by-products and eventually to inert end-products. The environmental applications of AOPs are numerous, including water and wastewater treatment (i.e. removal of organic and inorganic pollutants and pathogens), air pollution abatement and soil remediation. AOPs are applied for the abatement of pollution caused by the presence of residual pharmaceuticals in waters for the last decade. In this light, this paper reviews and assesses the effectiveness of various AOPs for pharmaceutical removal from aqueous systems.

New perspectives for advanced oxidation processes

Advanced Oxidation Processes (AOPs) are called to fill the gap between the treatability attained by conventional physico-chemical and biological treatments and the day-to-day more exigent limits fixed by environmental regulations. They are particularly important for the removal of anthropogenic pollutants and for this reason, they have been widely investigated in the last decades and even applied in the treatment of many industrial wastewater flows. However, despite the great development reached, AOPs cannot be considered mature yet and there are many new fields worthy of research. Some of them are going to be briefly introduced in this paper, including hybrid processes, heterogeneous semiconductor photocatalysis, sulphate-radical oxidation and electrochemical advanced oxidation for water/wastewater treatment. Moreover, the use of photoelectrochemical processes for energy production is discussed. The work ends with some perspectives that can be of interest for the ongoing and future research.

Recovery of antioxidants from olive mill wastewaters: A viable solution that promotes their overall sustainable management

Olive mill wastewaters (OMW) are rich in water-soluble polyphenolic compounds that show remarkable antioxidant properties. In this work, the recovery yield of compounds, such as hydroxytyrosol and tyrosol, as well as total phenols (TPh) from real OMW was investigated. Antioxidants were recovered by means of liquid-liquid solvent extraction. For this purpose, a laboratory-scale pilot unit was established and the effect of various organic solvents, namely ethyl acetate, diethyl ether and a mixture of chloroform/isopropyl alcohol, on process efficiency was investigated. It was found that the performance of the three extraction systems decreased in the order: ethyl acetatexa0>xa0chloroform/isopropanolxa0>xa0diethyl ether, in terms of their antioxidant recovery yield. It was estimated that treatment of 1xa0m(3) OMW with ethyl acetate could provide 0.247xa0kg hydroxytyrosol, 0.062xa0kg tyrosol and 3.44xa0kg of TPh. Furthermore, the environmental footprint of the whole liquid-liquid extraction system was estimated by means of the life cycle assessment (LCA) methodology to provide the best available and most sustainable extraction technique. From an environmental perspective, it was found that ethyl acetate and diethyl ether had similar environmental impacts. Specifically, for the production of 1xa0g hydroxytyrosol, tyrosol or TPh, 13.3, 53.1 or 0.949xa0kg CO2 equivalent would be released to the atmosphere, respectively. On the other hand, the chloroform/isopropyl alcohol mixture had detrimental effects onto ecosystems, human health and fossil fuels resources. In total, ethyl acetate yields low environmental impacts and high antioxidant recovery yield and thus it can be considered as the best solution, both from the environmental and technical point of view. Three alternative scenarios to improve the recovery performance and boost the sustainability of the ethyl acetate extraction system were also investigated and their total environmental impacts were estimated. It was found that with small process modifications the environmental impacts could be reduced by 29%, thus achieving a more sustainable antioxidants recovery process.

Kinetics of ethyl paraben degradation by simulated solar radiation in the presence of N-doped TiO2 catalysts.

Ethyl paraben (EP), an emerging micro-pollutant representative of the parabens family, has been subject to photocatalytic degradation under simulated solar radiation at a photon flux of 1.3·10(-4)xa0E/(m(2)xa0s). Six nitrogen-doped titania catalysts synthesized by annealing a sol-gel derived TiO2 powder under ammonia flow and their un-doped counterparts, calcined in air at different temperatures in the range 450-800xa0°C, were compared under solar and visible light and the most active one (N-doped TiO2 calcined at 600xa0°C) was used for further tests. Experiments were performed at EP concentrations between 150 and 900xa0μg/L, catalyst loadings between 100 and 1000xa0mg/L, pH between 3 and 9, different matrices (ultrapure water, water spiked with humic acids or bicarbonates, drinking water and secondary treated wastewater) and hydrogen peroxide between 10 and 100xa0mg/L. For EP concentrations up to 300xa0μg/L, the degradation rate can be approached by first order kinetics but then shifts to lower order as the concentration increases. The rate increases linearly with catalyst loading up to 750xa0mg/L and hydrogen peroxide up to 100xa0mg/L. Near-neutral (pHxa0=xa06.5-7.5) and alkaline conditions (pHxa0=xa09) do not affect degradation, which is reduced at acidic pH. The presence of humic acids at 10-20xa0mg/L impedes degradation due to the competition with EP for the oxidizing species and this is more pronounced in actual wastewater matrices. UPLC-ESI-HRMS and HPLC-DAD were employed to follow EP concentration changes, as well as identify and quantify transformation by-products during the early stages of the reaction. Five such products were successfully detected and, based on their concentration-time profiles, a reaction network for the degradation of EP is proposed. Hydroxyl radical reactions appear to prevail during the initial steps as evidenced by the rapid formation of hydroxylated and dealkylated intermediates.

Sonochemical degradation of ethyl paraben in environmental samples: Statistically important parameters determining kinetics, by-products and pathways.

The sonochemical degradation of ethyl paraben (EP), a representative of the parabens family, was investigated. Experiments were conducted at constant ultrasound frequency of 20 kHz and liquid bulk temperature of 30 °C in the following range of experimental conditions: EP concentration 250-1250 μg/L, ultrasound (US) density 20-60 W/L, reaction time up to 120 min, initial pH 3-8 and sodium persulfate 0-100mg/L, either in ultrapure water or secondary treated wastewater. A factorial design methodology was adopted to elucidate the statistically important effects and their interactions and a full empirical model comprising seventeen terms was originally developed. Omitting several terms of lower significance, a reduced model that can reliably simulate the process was finally proposed; this includes EP concentration, reaction time, power density and initial pH, as well as the interactions (EP concentration)×(US density), (EP concentration)×(pHo) and (EP concentration)×(time). Experiments at an increased EP concentration of 3.5mg/L were also performed to identify degradation by-products. LC-TOF-MS analysis revealed that EP sonochemical degradation occurs through dealkylation of the ethyl chain to form methyl paraben, while successive hydroxylation of the aromatic ring yields 4-hydroxybenzoic, 2,4-dihydroxybenzoic and 3,4-dihydroxybenzoic acids. By-products are less toxic to bacterium V. fischeri than the parent compound.

Photodegradation of ethyl paraben using simulated solar radiation and Ag3PO4 photocatalyst

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP), a representative of the parabens family, was studied using silver orthophosphate, a relatively new photocatalytic material. The catalyst was synthesized by a precipitation method and had a primary crystallite size of ca 70nm, specific surface area of 1.4m2/g and a bandgap of 2.4eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500-1500μg/L), catalyst concentration (100-500mg/L), reaction time (4-30min), water matrix (pure water or 10mg/L humic acid) and initial solution pH (3-9) on EP removal. All individual effects but solution pH were statistically significant and so were the second-order interactions of EP concentration with reaction time or catalyst concentration. The water matrix effect was negative (all other effects were positive) signifying the role of humic acid as scavenger of the oxidant species. Liquid chromatography-time of flight mass spectrometry revealed the formation of methyl paraben, 4-hydroxybenzoic acid, benzoic acid and phenol as primary transformation by-products; these are formed through dealkylation and decarboxylation reactions initiated primarily by the photogenerated holes. Estrogenicity assays showed that methyl paraben was more estrogenic than EP; however, parabens are slightly estrogenic compared to 17β-estradiol.

Sequential treatment of diluted olive pomace leachate by digestion in a pilot scale UASB reactor and BDD electrochemical oxidation.

The efficiency of the anaerobic treatment of olive pomace leachate (OPL) at mesophilic conditions was investigated. Daily and cumulative biogas production was measured during the operational period. The maximum biogas flowrate was 65xa0L/d, of which 50% was methane. In addition, the applicability of electrochemical oxidation as an advanced post-treatment method for the complete removal of chemical oxygen demand (COD) from the anaerobically treated OPL was evaluated. The diluted OPL, having a pH of 6.5 and a total COD of 5xa0g/L, was first treated in a 600xa0L, pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor was operated for 71 days at mesophilic conditions (32xa0±xa02xa0°C) in a temperature-controlled environment at a hydraulic retention time of 3 days, and organic loading rates (OLR) between 0.33 and 1.67xa0g COD/(L.d). The UASB process led to a COD removal efficiency between 35 and 70%, while the particulate matter of the wastewater was effectively removed by entrapment in the sludge blanket of the reactor. When the anaerobic reactor effluent was post-treated over a boron-doped diamond (BDD) anode at 18 A and in the presence of 0.17% NaCl as the supporting electrolyte, complete removal of COD was attained after 7xa0h of treatment predominantly through total oxidation reactions. During electrochemical experiments, three groups of organo-chlorinated compounds, namely trihalomethanes (THMs), haloacetonitriles (HANs) and haloketons (HKs), as well as 1,2-dichloroethane (DCA) and chloropicrin were identified as by-products of the process; these, along with the residual chlorine are thought to increase the matrix ecotoxicity to Artemia salina.

Photocatalytic and photoelectrocatalytic degradation of the drug omeprazole on nanocrystalline titania films in alkaline media: Effect of applied electrical bias on degradation and transformation products.

Photocatalytic and photoelectrocatalytic degradation of the drug omeprazole has been studied in the presence of nanocrystalline titania films supported on glass slides or transparent FTO electrodes in alkaline environment. Its photocatalytic degradation rate was assessed by its UV absorbance and by HPLC, while its transformation products were analyzed by HR-LC-MS. Based on UV absorbance, omeprazole can be photocatalytically degraded at an average rate of 6.7×10(-4)min(-1) under low intensity UVA irradiation of 1.5mWcm(-2) in the presence of a nanoparticulate titania film. This corresponds to degradation of 1.4mg of omeprazole per gram of the photocatalyst per liter of solution per hour. The photodegradation rate can be accelerated in a photoelectrochemical cell by applying a forward bias. In this case, the maximum rate reached under the present conditions was 11.6×10(-4)min(-1) by applying a forward bias of +0.6V vs. Ag/AgCl. Four major transformation products were successfully identified and their profiles were followed by HR-LC-MS. The major degradation path includes the scission of the sulfoxide bridge into the corresponding pyridine and benzimidazole ring derivates and this is accompanied by the release of sulfate anions in the reaction mixture.

Oxidation of bisphenol A in water by heat-activated persulfate.

The heat-activated persulfate oxidation of bisphenol A (BPA), a representative endocrine disrupting compound, was investigated with respect to the effect of several process variables on degradation rates. The activation temperature appears to be the single most important parameter, i.e. a temperature increase from 40 to 70xa0°C results in an 80-fold rate increase. Regarding initial BPA concentration, the reaction follows a pseudo-first order rate expression, where the kinetic constant decreases from 11.5 10-2 to 3.5 10-2xa0min-1 when BPA concentration increases from 110 to 440xa0μg/L. Reactions in actual water matrices, such as bottled water and secondary treated wastewater, are slower than in pure water since various organic/inorganic water constituents compete with BPA for being oxidized by the reactive oxidizing species; this was confirmed with experiments in pure water spiked with humic acid or bicarbonate. Interestingly though, the presence of chloride seems to promote BPA degradation. Furthermore, degradation is favored at near-neutral pH and increased sodium persulfate (SPS) concentrations. Experiments at an increased BPA concentration of 20xa0mg/L were performed to identify transformation by-products (TBPs), as well as assess the mineralization and toxicity of the treated samples. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) revealed the formation of eleven TBPs of BPA and plausible pathways including hydroxylation, oxidation, cleavage and oligomerization reactions are proposed. Mineralization occurs slower than BPA degradation, while the toxicity to marine bacteria Vibrio fischeri increases during the early stages of the reaction but it progressively decreases thereafter.

Boron-doped diamond oxidation of amoxicillin pharmaceutical formulation: Statistical evaluation of operating parameters, reaction pathways and antibacterial activity

The electrochemical oxidation of a commercial amoxicillin formulation over a boron-doped diamond (BDD) anode was investigated. The effect of initial COD concentration (1-2xa0g/L), current density (30-50xa0mA/cm2), treatment time (15-90xa0min), initial pH (3-9) and electrolyte concentration (2-4xa0g/L NaCl) on COD removal was assessed through a factorial design methodology. For the range of conditions in question, the first three single effects, as well as the interaction between COD and time were the most important ones in terms of mass of COD removed. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) was employed to identify major transformation by-products (TBPs); thirteen compounds were detected as TBPs of AMX electrochemical degradation, while several others appear in the original formulation. AMX degradation occurs though the following pathways: (i) hydroxylation mainly in the benzoic ring, (ii) opening of β-lactam ring followed by decarboxylation, hydroxylation and re-arrangement, and (iii) bond cleavage between the carbons of amino and amide groups. Furthermore, the process is accompanied by the release of several ions, i.e. nitrate, sulfate and ammonium. The antibiotic activity of AMX up to 1000xa0mg/L was tested against Klebsiella pneumoniae and Enterococcus faecalis reference strains; both bacteria are completely inactivated at this concentration but the activity is reduced substantially at lower concentrations. Oxidized samples still exhibit some antibacterial activity (50-60%) which is due to TBPs and active chlorine species present in the liquid phase. The latter are generated from chloride ions and enhance considerably AMX degradation rates.