Total Organic Carbon Mineralization Research Articles

Photocatalytic ozonation under visible light for the remediation of water effluents and its integration with an electro-membrane bioreactor

Photocatalysis and photocatalytic ozonation under visible light have been applied for the purification of a complex aqueous matrix such as the grey water of Masdar City (UAE), by using N-doped brookite-rutile catalysts. Preliminary runs on 4-nitrophenol (4-NP) solutions allowed to test the reaction system in the presence of a model pollutant and to afford the relevant kinetic parameters of the process. Subsequently, the remediation of grey water effluent has been evaluated in terms of the reduction of total organic carbon (TOC) and bacterial counts. The concentration of the most abundant inorganic ionic species in the effluent has been also monitored during reaction. Photocatalytic ozonation under visible light allowed to reduce the TOC content of the grey water by ca. 60% in the optimized experimental conditions and to reduce the total bacterial count by ca. 97%. The extent of TOC mineralization reached ca. 80% when the photocatalytic ozonation occurred downstream to a preliminary electro-membrane bioreactor (eMBR). Coupling the two processes enhanced the global efficiency. In fact, the eMBR treatment lowered the turbidity and the organic load of the effluent entering the photocatalytic ozonation treatment, which in turn enhanced the extent of purification and disinfection.

Photo Degradation of Methyl Orange by Persulfate Activated with Zero Valent Iron

The oxidative degradation of Methyl Orange (MO) subjected to direct photolysis (Solar) and various oxidative systems was studied. The comparative experiments have shown that MO conversion and mineralization increases in the following order: Solar ∼ Solar/Fe0 ∼ Solar/S2O82- < S2O82-/Fe0 < Solar/S2O82-/Fe0. The influence of the main factors (duration of exposure, the ratio of initial concentrations of MO:S2O82-:Fe0, pH and temperature of the reaction medium) on the degree of MO conversion and mineralization was studied. The optimal pH and temperature of the reaction medium were 5.8 and 25°C, respectively. The rate of MO decomposition and mineralization increased proportionally to the initial concentration of the oxidant at the molar ratios [S2O82-] :[MO] ≤ 12. Judging by the nature of the kinetic curves, a further increase of this ratio is impractical. However, an increase in the oxidant concentration had a positive effect on the degrees of conversion and mineralization of total organic carbon (TOC). Thus, at the ratios of 12:1 and 48:1, the conversion efficiency of TOC was 23 and 60 %, respectively. The optimal concentration of Fe0 was 100 mg/l.

Spinel manganites synthesized by combustion method: Structural characterization and catalytic activity in the oxidative degradation of organic pollutants

Two spinel-type oxides, CuMn2O4 and CoMn2O4 were synthesized by a simple combustion method. The oxides were characterized by X-ray Diffraction, infrared spectroscopy, scanning electron microscopy and atomic absorption spectroscopy. The structures of the obtained oxides were refined by the Rietveld method. The obtained samples were tested in the catalytic degradation of phenol and methyl orange. Two different oxidants were employed: potassium persulfate and peroxymonosulfate. The catalytic activity was tested, as well as the degradation efficiencies. The best results were obtained with the copper substituted oxides, using oxone as oxidant. With this system, mineralization of total organic carbon (TOC) reached more than 94% within 120min of reaction. For cobalt mixed oxides, the TOC mineralization reached as much as 68% in the same condition. The activation mechanisms for the different systems studied in this work are discussed and two different pathways are proposed depending on the oxidant and/or the substitution metal.

Boron doped micro/nanocrystalline diamond electrodes used on the electrochemical flow reactor to degrade brilliant green dye

ABSTRACTA systematic study was performed concerning the production, characterization, and application of BDD and BDND films grown on Ti substrate to degrade brilliant green dye using an electrochemical flow reactor. Films were grown in a hot filament chemical vapour deposition (HFCVD) reactor using H2/CH4 (BDD) and H2/CH4/Ar (BDND) gas mixtures. Boron doping was performed by dissolution of B2O3 in methanol in the appropriate B/C ratio to obtain good conductive electrodes. The electrolysis was carried out using BDD/Ti and BDND/Ti as anode material analyzing the influence of different current densities and flow rates. During the electrolysis, aliquots of the treated solution were analyzed by UV-Vis and Total Organic Carbon (TOC) measurements. The electrode efficiencies were compared considering the color removal as well as the TOC mineralization in the end of each electrolysis. The absorption bands intensity from UV/Vis spectra clearly decreased up to their completely vanishing at current density of 100 mA/cm2 for both electrodes. These results were corroborated by TOC measurements where 50% of the organic material was removed.

Heterogeneous photo-Fenton degradation of methyl orange by Fe2O3/TiO2 nanoparticles under visible light

A novel heterogeneous photo-Fenton catalyst Fe2O3/TiO2 nanoparticle was successfully prepared by sol-gel method and characterized by X-ray diffraction (XRD), UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and porosimetry analysis. The characterization results showed that the nano-sized Fe2O3 particles appeared on the TiO2 support and the Fe2O3/TiO2 nanoparticle exhibited enhanced absorption in the broad visible-light region together with an apparent red shift in the optical absorption edge. The XPS results revealed that the presence of Ti4+ and Fe3+ in Fe2O3/TiO2 materials. The activity of heterogeneous photo-Fenton catalyst Fe2O3/TiO2 combined with the photocatalytic and photo-Fenton was assayed in the degradation of methyl orange (MO) in the presence of visible light and H2O2. The results showed that the heterogeneous photo-Fenton was much faster and higher removal of methyl orange than the photocatalytic degradation alone. The mineralization of the organic pollutant was investigated by total organic carbon (TOC) measurements. The Fe2O3/TiO2+H2O2 showed the highest TOC mineralization of MO. All these results indicate the possibility of the practical application of this photocatalyst for water treatment.

Sonochemical degradation of perfluorinated chemicals in aqueous film-forming foams

Aqueous film-forming foams (AFFFs) are complex mixtures containing 1–5% w/w fluorocarbons (FCs). Here, we have investigated degradation of two commercial AFFF formulations, 3M and Ansul, using sound field at 500kHz and 1MHz, with varying initial concentrations ranging from 200 to 930× dilution. The foams were readily degraded by 1MHz, with percentage of defluorination ranging from 11.1±1.4% (200× dilution of 3M) to 47.1±5.8% (500× dilution of Ansul). Removal of total organic carbon (TOC) ranged from 16.0±1.4% (200× dilution Ansul) to 39.0±7.2% (500× dilution Ansul). Degradation of AFFF was affected by sound frequency with rates of defluorination 10-fold greater when the frequency was 1MHz than when it was 500kHz. Mineralization of TOC was 1.5- to 3.0-fold greater under 1MHz than 500kHz. Rate of fluoride release was 60% greater for the greatest initial concentration of FC in Ansul compared to the least initial concentration. While the rate of mineralization of AFFF was directly proportional to the initial concentration of Ansul, that was not the case for 3M, where the rates of mineralization were approximately the same for all three initial concentrations. Results of the study demonstrate that sonolysis is a promising technology to effectively treat AFFFs.

Degradation of acesulfame in aqueous solutions by electro-oxidation

The electrochemical oxidation of acesulfame (acesulfame potassium (ACE-K)) on different electrodes or in various aqueous solutions was investigated in this study. The performance in terms of ACE-K degradation and total organic carbon (TOC) removal of tested anodes was in the order boron-doped diamond (BDD) > PbO2 > Pt, although ACE-K could not be directly oxidized on these electrodes in cyclic voltammetric analysis. At the same electrolysis time, the ACE-K degradation and TOC removal efficiencies increased with an increasing current density or anode area, but decreased with the increase of initial ACE-K concentration. The ACE-K degradation was slightly influenced by temperature at 25−50°C. The apparent pseudo-first-order rate constants of ACE-K oxidation were similar in ACE-K-spiked 1M Na2SO4 solution and municipal wastewater matrices (influent (IN), before biological treatment (BBT), and after biological treatment (ABT)) ((1.73 – 2.32) × 10−3 s−1). Although the TOC removal (consistent with mineralization current efficiency) in these wastewater matrices followed the order ABT ≈ IN > BBT, the complete mineralization of ACE-K and TOC was achieved. Accordingly, the electrooxidation process has great potential to be used to improve the biodegradation-resistant ACE-K degradation and TOC removal in secondary biological wastewater treatment.

Assessing benthic oxygen fluxes in oligotrophic deep sea sediments (HAUSGARTEN observatory)

Benthic oxygen fluxes, an established proxy for total organic carbon mineralization, were investigated in oligotrophic deep sea sediments. We used three different in situ technologies to estimate the benthic oxygen fluxes at an Arctic deep sea site (2500m depth, HAUSGARTEN observatory) with limiting conditions of low oxygen gradients and fluxes, low turbulence and low particle content in the benthic boundary layer. The resolved eddy covariance turbulent oxygen flux (−0.9±0.2 (SD)mmol O2m−2d−1) compared well with simultaneous dissolved oxygen flux measurements carried out with a microprofiler (−1.02±0.3 (SD)mmol O2m−2d−1) and total oxygen uptake obtained by benthic chamber incubations (−1.1±0.1 (SD)mmol O2m−2d−1). The agreement between these different techniques revealed that microbial-mediated oxygen consumption was dominant at this site. The average benthic flux equals a carbon mineralization rate of 4.3g Cm−2yr−1, which exceeds the annual sedimentation of particulate organic matter measured by sediment traps.The present study represents a detailed comparison of different in situ technologies for benthic flux measurements at different spatial scales in oligotrophic deep sea sediments. The use of eddy covariance, so far rarely used for deep sea investigations, is presented in detail.

Decolorization and mineralization of azo dye Acid Blue 113 by the UV/Oxone process and optimization of operating parameters

A UV/Oxone advanced oxidation process was proposed to degrade and mineralize a synthesized Acid Blue 113 (AB113) dyeing wastewater. Various operating parameters which affected the removal efficiencies of AB113 and total organic carbon (TOC) such as reaction time, Oxone dosage, initial AB113 concentration, initial pH, and UV intensity were studied. Results presented effective removal of AB113 azo dye by UV/Oxone process based on both AB113 and TOC indicators. The reaction kinetics was shown to be pseudo-second-order reaction. In UV/Oxone process, the higher the Oxone dosage applied, the higher the AB113 and TOC removal efficiencies can be obtained up to 6.3mM Oxone concentration. The AB113 removal efficiency and pseudo-second-order rate constant decreased with increase in the initial dye concentration. However, the proposed UV/Oxone process was proved to be able to degrade high AB113 concentration up to 400 mg l−1. The initial pH showed no significant effect on AB113 removal efficiency. UV intensity affected TOC mineralization efficiency significantly. In contrast, UV intensity presented less important factors on degradation of AB113.

The change in fractions of organic substances in water in the intermediate oxidation process

This article presents the results of a study on the changes in the content of both biodegradable and non-biodegradable fractions of dissolved total organic carbon. The studies were conducted on a technical scale in surface and mixed water (underground water after aeration mixed with surface water after micro sieve) purification plants, and the oxidation process was performed with ozone and a mixture of chlorine and chlorine dioxide, respectively. The study demonstrated a significant increase in the biodegradability of organic substances in the oxidation process regardless of the type of oxidant used. Ozone turned out to be the most effective oxidant in eliminating and transforming organic substances, compared with chlorine and chlorine dioxide. In the case of the utilization of a mixture of chlorine and chlorine dioxide, a greater reactivity of chlorine dioxide with organic matter, especially refractive substances, was determined. In both water treatment plants, the transformation of high molecular weight organic substances to smaller ones dominated over the mineralization of total organic carbon. The type and size of the transformation of organic matter depended mainly on the type of oxidant utilized, and not on the level of water contamination.

Investigation of the synergistic effects for p-nitrophenol mineralization by a combined process of ozonation and electrolysis using a boron-doped diamond anode

Electrolysis and ozonation are two commonly used technologies for treating wastewaters contaminated with nitrophenol pollutants. However, they are often handicapped by their slow kinetics and low yields of total organic carbon (TOC) mineralization. To improve TOC mineralization efficiency, we combined electrolysis using a boron-doped diamond (BDD) anode with ozonation (electrolysis-O3) to treat a p-nitrophenol (PNP) aqueous solution. Up to 91% TOC was removed after 60min of the electrolysis-O3 process. In comparison, only 20 and 44% TOC was respectively removed by individual electrolysis and ozonation treatment conducted under similar reaction conditions. The result indicates that when electrolysis and ozonation are applied simultaneously, they have a significant synergy for PNP mineralization. This synergy can be mainly attributed to (i) the rapid degradation of PNP to carboxylic acids (e.g., oxalic acid and acetic acid) by O3, which would otherwise take a much longer time by electrolysis alone, and (ii) the effective mineralization of the ozone-refractory carboxylic acids to CO2 by OH generated from multiple sources in the electrolysis-O3 system. The result suggests that combining electrolysis with ozonation can provide a simple and effective way to mutually compensate the limitations of the two processes for degradation of phenolic pollutants.

Characteristic mechanism of ceramic honeycomb catalytic ozonation enhanced by ultrasound with triple frequencies for the degradation of nitrobenzene in aqueous solution

Ceramic honeycomb catalytic ozonation enhanced by ultrasound with triple frequencies was carried out in semi-continuous mode to investigate the degradation efficiency of nitrobenzene in aqueous solution. The combination process can enhance remarkably the degradation efficiency of nitrobenzene compared to the additive effects of single operations, and the degradation of nitrobenzene follows the mechanism of hydroxyl radical (OH) oxidation. The enhancement function is even more pronounced in the presence of ultrasound with orthogonal triple frequencies due to the obvious synergetic effect which can accelerate the transformation and the decomposition of ozone, increase the utilization efficiency of ozone, and enhance the initiation of OH and the formation of H2O2, resulting in the rapid formation of an increasing diversity of byproducts and the higher degree of mineralization of total organic carbon. The investigation of enhanced mechanism indicates the introduction of ultrasound can prevent deactivation by continuously cleaning the surface of catalyst, and can accelerate the cleavage of the bond as well as speed up the diffusion of oxidative intermediate from the heterogeneous surface to the aqueous solution due to the weakening of the bond derived from the ultrasonic shock, leading to the production of the synergetic effect among ozone, ceramic honeycomb and ultrasound.

Quantum efficiencies of the photo-Fenton degradation of atrazine in water

An experimental work in a well-stirred batch recycling reactor for the photo-Fenton degradation of atrazine in water is presented. A study of the quantum efficiency is performed to assess the effectiveness of the photo-Fenton process on the atrazine degradation and total organic carbon (TOC) mineralization. Apparent and absolute quantum efficiencies of degradation and mineralization of an atrazine-based commercial herbicide are determined under different experimental conditions. Higher apparent efficiencies were found for both atrazine degradation and TOC mineralization when the ferric ion and hydrogen peroxide concentrations are increased. Because of the well known stability of the triazine ring, atrazine was not completely mineralized by the photo-Fenton process. However, a TOC reduction of 40% was achieved, being 62.5% of the maximum value that can be reached.

Enhancement of the advanced Fenton process (Fe0/H2O2) by ultrasound for the mineralization of phenol

In this study, a successful mineralization of phenol was achieved by means of coupling zero-valent iron (ZVI) particles, hydrogen peroxide and a short input of ultrasonic irradiation. This short sono-advanced Fenton process (AFP) provided a better performance of ZVI in a subsequent silent degradation stage, which involves neither extra cost of energy nor additional oxidant. The short input of ultrasound (US) irradiation enhanced the activity of the Fe0/H2O2 system in terms of the total organic carbon (TOC) removal. Then, the TOC mineralization continued during the silent stage, even after the total consumption of hydrogen peroxide, reaching values of ca. 90% TOC conversions over 24h. This remarkable activity is attributed to the capacity of the ZVI/iron oxide composite formed during the degradation for the generation of oxidizing radical species and to the formation of another reactive oxidant species, such as the ferryl ion. The modification of the initial conditions of the sono-AFP system such as the ultrasonic irradiation time and the hydrogen peroxide dosage, showed significant variations in terms of TOC mineralization for the ongoing silent degradation stage. An appropriate selection of operation conditions will lead to an economical and highly efficient technology with eventual large-scale commercial applications for the degradation organic pollutants in aqueous effluents.

The phage‐driven microbial loop in petroleum bioremediation

SummaryDuring the drilling process and transport of crude oil, water mixes with the petroleum. At oil terminals, the water settles to the bottom of storage tanks. This drainage water is contaminated with emulsified oil and water‐soluble hydrocarbons and must be treated before it can be released into the environment. In this study, we tested the efficiency of a continuous flow, two‐stage bioreactor for treating drainage water from an Israeli oil terminal. The bioreactor removed all of the ammonia, 93% of the sulfide and converted 90% of the total organic carbon (TOC) into carbon dioxide. SYBR Gold staining indicated that reactor 1 contained 1.7 × 108 bacteria and 3.7 × 108 phages per millilitre, and reactor 2 contained 1.3 × 108 bacteria and 1.7 × 109 phages per millilitre. The unexpectedly high mineralization of TOC and high concentration of phage in reactor 2 support the concept of a phage‐driven microbial loop in the bioremediation of the drainage water. In general, application of this concept in bioremediation of contaminated water has the potential to increase the efficiency of processes.

Heterogeneous photo-Fenton treatment for the reduction of pharmaceutical contamination in Madrid rivers and ecotoxicological evaluation by a miniaturized fern spores bioassay

Fifty-six pharmaceuticals of various chemical groups, such as anti-inflammatory, antibacterial and cardiovascular drugs, were detected in four selected river waters receiving sewage effluents in the Community of Madrid (Spain). A promising approach for the degradation of those residues is the application of a photo-Fenton treatment. Several new bioassays using fern spores were employed for the evaluation of acute and chronic toxicity based on mitochondrial activity, DNA and chlorophyll quantifications of as-received river water and photo-Fenton-treated samples. photo-Fenton treatment provided a high degree of total organic carbon mineralization with up to 70% reduction for river water samples. In addition, the elimination of most of the studied pharmaceutical compounds was confirmed. A few compounds, however (salicylic acid, ofloxacin, caffeine, cotinine and nicotine), seemed more resistant, with after-treatment concentrations between 4 and 44 ng L −1. Nicotine showed the most refractory behaviour with concentrations ranging from 29 to 224 ng L −1 for treated samples. Photo-Fenton treatment yielded a significant decrease in acute and chronic toxicity, even though some residual toxicity remained after treatment. This fact seemed to be related to the presence of toxicants in the water matrix, probably of inorganic nature, rather than the toxic effect of the studied pharmaceutical compounds, as revealed by the effective removal of these compounds and high TOC mineralization of photo-Fenton treatments.

The effect of surfactants on the ozonation of o‐cresol in aqueous solutions in a rotating packed contactor

Steady‐state dissolved ozone concentrations were maintained relatively constant for experiments on ozone dissolution conducted in the presence of various amounts of sodium dodecyl sulphate (SDS) and Triton X‐100 (TX‐100), an anionic surfactant and a nonionic surfactant, respectively. Ozonation in a rotating packed contactor has been shown to be feasible for achieving nearly complete decomposition of o‐cresol within about 10 minutes of reaction time for most experiments conducted. The temporal decomposition behaviour of o‐cresol in aqueous solution by ozonation was described by a two‐step pseudo‐first‐order reaction kinetics. Even though the presence of SDS and TX‐100 slightly affected the decomposition rate constant of o‐cresol by ozonation in the rotating packed contactor, the mineralization of total organic carbon was apparently reduced with the addition of SDS and TX‐100.

Enhanced mechanism of catalytic ozonation by ultrasound with orthogonal dual frequencies for the degradation of nitrobenzene in aqueous solution

The experiments have been performed with a semi-continuous batch reactor to investigate the degradation efficiency of nitrobenzene in aqueous solution by ultrasound with the different orthogonal dual frequencies catalytic ozonation. The introduction of ultrasound can enhance the degradation efficiency of nitrobenzene compared to the results obtained from the processes of ozonation alone and ultrasound alone. The degradation of nitrobenzene is found to be zero-order in the two systems of ultrasound alone, and the reactions follow the pseudo-first-order kinetic model in the processes of ozone alone and ozone/ultrasound. The investigation confirms that the degradation of nitrobenzene follows the mechanism of hydroxyl radical ( •OH) oxidation, and the enhancement function is even more pronounced in the presence of ultrasound with the greater difference between the orthogonal dual frequencies due to the obvious synergetic effect between ozone and ultrasound, which increases the utilization efficiency of ozone, and accelerates the initiation of •OH and the formation of H 2O 2, resulting in the rapid formation of an increasing diversity of byproducts and the advancement degree of mineralization of total organic carbon (TOC). The oxidative byproducts have been, respectively identified in the different processes selected, including o, p, m-nitrophenols, phenol, malonic acid, 4-nitrocatechol, nitrate ion, maleic acid, oxalic acid, hydroquinone, p-quinone, 1,2,3-trihydroxy-5-nitrobenzene and acetic acid.

Synergetic Effect of Ultrasound with Dual Fields for the Degradation of Nitrobenzene in Aqueous Solution

Experiments have been performed with a semicontinuous batch reactor to compare the degradation efficiency of nitrobenzene in aqueous solution by the ultrasonic processes of single field, opposite dual fields, and orthogonal dual fields. Ultrasound with dual fields can improve the degradation efficiency of nitrobenzene compared to that of single field, and the improvement phenomenon is even more pronounced in the orthogonal dual-field system. The degradation reactions of nitrobenzene in the three processes all follow the pseudofirst-order kinetic model. The mechanism investigation indicates the degradation proceeds via hydroxyl radical (*OH) oxidation. The enhancement efficiency of orthogonal dual fields is attributed to an obvious synergetic effect, which accelerates the *OH initiation from 0.28 micromol L(-1) min(-1) for a single field to 0.98 micromol L(-1) min(-1) compared with 0.42 micromol L(-1) min(-1) for opposite dual fields, resulting in rapid formation of an increased diversity of byproducts and an advanced degree of mineralization of total organic carbon (TOC). The introduction of an ultrasonic field placed in the different spatial position causes a variable kinetic order during the removal of TOC. The degradation byproducts are identified by gas chromatography mass spectrometry and ion chromatography, including p-, m-nitrophenol, malonic acid, nitrate ion, 4-nitrocatechol, phenol, maleic acid, oxalic acid, hydroquinone, 1,2,3-trihydroxy-5-nitrobenzene, and acetic acid.

Industrial wastewater treatment using hydrodynamic cavitation and heterogeneous advanced Fenton processing

A combination of hydrodynamic cavitation and heterogeneous advanced Fenton process (AFP) based on the use of zero valent iron as the catalyst has been investigated for the treatment of real industrial wastewater. The effect of various operating parameters such as inlet pressure, temperature, and the presence of copper windings on the extent of mineralization as measured by total organic carbon (TOC) content have been studied with the aim of maximizing the extent of degradation. It has been observed that increased pressures, higher operating temperature and the absence of copper windings are more favourable for a rapid TOC mineralization. A new approach of latent remediation has also been investigated where hydrodynamic cavitation is only used as a pre-treatment with an aim of reducing the overall cost of pollutant degradation. It has been observed that approach of latent remediation works quite well with about 50–60% removal of TOC using only minimal initial treatment by hydrodynamic cavitation.