Initial Organic Concentration Research Articles

Electrochemical degradation of atrazine on Pt anode with cathodic electro-generation of H2O2

This study investigated the degradation of atrazine by anodic oxidation with cathodic eletrogeneration of H2O2 (AO—H2O2). A series of trials were conducted in an undivided cylindrical glass cell using Pt anode and graphite cathode, air was compressed into working solution at atmospheric pressure. The oxidation experiments were carried out to assess the influence of primary parameters (current intensity, air feeding flow rate, cathode—to— anode area ratio and initial organic concentration) on atrazine removal. During all trials performed, the concentration of atrazine declined significantly, and in the best operating parameters found (current intensity 80 mA, air feeding flow rate 0.9 L min-1, cathode—to— anode area ratio 12), 72% of atrazine removal was obtained within 120 min oxidation time. CV tests exhibited that the intensity of anodic peak was strengthened when the working solution is O2—saturated, implying that O2 might play an important role in the anodic oxidation of atrazine.

ANN model for predicting acrylonitrile wastewater degradation in supercritical water oxidation

The discharged acrylonitrile wastewater had aroused more and more attention due to the increasingly serious water pollution. Supercritical water oxidation (SCWO) was an effective and fast way to degrade it completely without secondary pollution. To better illustrate the performances of SCWO of acrylonitrile wastewater, the experimental research covered the effects of different operation conditions on TOC reduction, such as reduced temperature (T/Tc), reduced pressure (P/Pc), initial total organic carbon concentration (TOC0), stoichiometric ratio (SR) and residence time (t). For a more accurate prediction of the emissions, two kinds of artificial neural network (ANN) models were adopt to simulate the TOC reductions in the processes of SCWO of acrylonitrile wastewater, including the Cascade-forward back propagation neural network (CFBPNN) and Feed-forward back propagation neural network (FFBPNN). The input parameters of ANN models were T/Tc, P/Pc, TOC0, SR and t. The output parameter was TOC reduction (η). The mean square error (E2) and the coefficient of determination (R2) were used to evaluate the model performances, respectively. Both the model and the experiment results had shown the TOC reduction could be greatly improved by reduced temperature, reduced pressure, initial TOC concentration, stoichiometric ratio and residence time. The FFBPNN model with the hidden neurons numbers of 12 was shown much better performances than the CFBPNN model.

Nonlinear behavior of organic aerosol in biomass burning plumes: a microphysical model analysis

Abstract. Organic aerosol (OA) is a major component of smoke plumes from open biomass burning (BB). Therefore, adequate representation of the atmospheric transformations of BB OA in chemistry-transport and climate models is an important prerequisite for accurate estimates of the impact of BB emissions on air quality and climate. However, field and laboratory studies of atmospheric transformations (aging) of BB OA have yielded a wide diversity of observed effects. This diversity is still not sufficiently understood and thus not addressed in models. As OA evolution is governed by complex nonlinear processes, it is likely that at least a part of the observed variability in the BB OA aging effects is due to the factors associated with the intrinsic nonlinearity of the OA system. In this study, we performed a numerical analysis in order to gain a deeper understanding of these factors. We employ a microphysical dynamic model that represents gas–particle partitioning and OA oxidation chemistry within the volatility basis set (VBS) framework and includes a schematic parameterization of BB OA dilution due to dispersion of an isolated smoke plume. Several VBS schemes of different complexity, which have been suggested in the literature to represent BB OA aging in regional and global chemistry-transport models, are applied to simulate BB OA evolution over a 5 d period representative of the BB aerosol lifetime in the dry atmosphere. We consider the BB OA mass enhancement ratio (EnR), which is defined as the ratio of the mass concentration of BB OA to that of an inert tracer and allows us to eliminate the linear part of the dilution effects. We also analyze the behavior of the hygroscopicity parameter, κ, that was simulated in a part of our numerical experiments. As a result, five qualitatively different regimes of OA evolution are identified, which comprise (1) a monotonic saturating increase in EnR, (2) an increase in EnR followed by a decrease, (3) an initial rapid decrease in EnR followed by a gradual increase, (4) an EnR increase between two intermittent stages of its decrease, or (5) a gradual decrease in EnR. We find that the EnR for BB aerosol aged from a few hours to a few tens of hours typically increases for larger initial sizes of the smoke plume (and therefore smaller dilution rates) or for lower initial OA concentrations (and thus more organic gases available to form secondary OA – SOA). However, these dependencies can be weakened or even reversed, depending on the BB OA age and on the ratio between the fragmentation and functionalization oxidation pathways. Nonlinear behavior of BB OA is also exhibited in the dependencies of κ on the parameters of the plume. Application of the different VBS schemes results in large quantitative and qualitative differences between the simulations, although our analysis suggests also that the main qualitative features of OA evolution simulated with a complex two-dimensional VBS scheme can also be reproduced with a much simpler scheme. Overall, this study indicates that the BB aerosol evolution may strongly depend on parameters of the individual BB smoke plumes (such as the initial organic aerosol concentration and plume size) that are typically not resolved in chemistry-transport models.

Metal-free catalysts of graphitic carbon nitride–covalent organic frameworks for efficient pollutant destruction in water

Novel metal-free catalysts via integration of covalent organic framework (COF) and graphitic carbon nitride (g-C3N4@COF) with a high graphitization degree and nitrogen content were fabricated and exhibited an outstanding activity in a wide pH range for peroxymonosulfate (PMS)-driven oxidation of refractory organic pollutants in water. Scanning electron microscopy images showed many aggregated COFs crystals anchored on the irregular g-C3N4 surface to form 3D structures. The precursors (urea, melamine, and dicyandiamide) of g-C3N4 determined the porous structures and properties of the g-C3N4@COF materials. The hybrids possessed superior reactivity in Orange II removal (100%) compared to pristine g-C3N4 (10%) and COF (5%), benefiting from high-temperature pyrolysis to generate crystal carbon and modulate nitrogen doping. Besides, removal efficiency of target pollutants depended on the oxidant dosages (0.33–1.30 mM), initial concentrations of organics (10–40 mg/L), temperatures (5–45 °C), pHs (1.72–10.3), and anions (Cl−, SO42-, NO3-, HCO3-, CO32-, and HCOO-). Quenching experiments and electron paramagnetic resonance demonstrated that non-radical singlet oxygen (1O2) was the dominant species for the oxidation of organic pollutants via electron transfer in the g-C3N4@COF/PMS system. It was inferred that the good balance between graphitization degree and nitrogen content benefited to enhancing the catalytic performance for the refractory pollutant degradation. The present investigation provides a new avenue for the design and construction of metal-free hybrid composites for environmental remediation.

Effectiveness of humic substance removal during the coagulation process

This study concerns the utility of the coagulation process in removing humic substances and its dependence on the properties of these substances and their concentrations. The coagulation process was performed on model solutions of natural humic acids. Polyaluminum chloride (PAX XL3) and aluminum sulfate were used for this study, which allowed for a comparison of the effectiveness of pre-hydrolyzed and hydrolyzing coagulants. The coagulant dosages were determined as gram aluminum per gram carbon, thanks to which it was possible to compare the process effectiveness for different initial organic carbon concentrations, whose values were in the range of 5.51–21.23 gC/m3. The obtained values of reductions in organic carbon concentrations point to a significant process effectiveness (37.2–59.4% and 20.0–41.5% for pre-hydrolyzed and hydrolyzing coagulants, respectively), which increased with increasing molecular mass of the humic substances present in water. These results are analogous to those found for coagulation of surface waters and point to a greater effectiveness of pre-hydrolyzed coagulant in removing humic substances (at the same coagulant dosage). The effectiveness in removing organic substances increased with coagulant dosage and the initial total organic carbon concentration. The coagulation process most effectively removed aromatic substances absorbing UV light. The content of substances absorbing UV light in raw and post-coagulation water was proportional to the dissolved organic carbon content.

New insights into the effect of direct interspecies electron transfer on syntrophic methanogenesis through thermodynamic analysis

Effects of redox materials, and types and concentrations of organic carbons on direct interspecies electron transfer (DIET) were thermodynamically analyzed. Redox materials with a low redox potential (below +0.033 V) and increasing substance concentrations could increase the reaction rate of DIET. The reaction rate of DIET reached 0.3390 h−1 with the addition of ferroferric oxide (Fe3O4), which was much higher than that of acetoclastic and hydrogentrophic methanogenesis. Ethanol was the most favorable organic carbon in DIET, and the facilitation of DIET could be achieved with redox materials like c-type cytochromes and Fe3O4. Addition of redox materials with a negative redox potential and increasing initial organic carbon concentrations could promote DIET and improve the efficiency of methanogenesis. A mechanism of combined organic carbon and redox mediators affecting DIET was proposed. Furthermore, a new parameter, σ · η · cRM / (γ · VSS + η · cRM), representing electron transfer rate via DIET with the addition of redox mediators, was proposed for DIET modelling.

High performance of PAN/GO-ZnO composite nanofibers for photocatalytic degradation under visible irradiation

In this work, Polyacrylonitrile nanofibers were enhanced by graphene oxide and zinc oxide, in terms of enhanced the photocatalytic activity and mechanical properties for the composite nanofibers. Photocatalytic degradation of two organic dyes methylene blue dye and indigo carmine dye from the simulated industrial wastewaters has been investigated under visible light irradiation. Composite nanofibers fabricated by using electrospinning technique followed by chemical cross-linking with zinc oxide. The surface sensitization and morphology changes of the fabricated composite nanofibers were studied using Fourier transform infrared spectroscopy analysis, Scanning Electron Microscopy and transmission electron microscope. Sensitized zinc oxide with graphene oxide showed higher efficiency in the degradation of MB with a 96% of degradation efficiency after 70 min and 98% for IC after merely 27 min. The optimum catalytic parameters such as initial organic dye concentration and pH were discussed. The efficacy of degradation of methylene blue dye and indigo carmine increased as initial concentration decreased. The optimal pH was around 5 where the reaction rate decreases above and under this pH value.

Microbial Electrosynthesis of Bioalcohols through Reduction of High Concentrations of Volatile Fatty Acids

The efficiency and characteristics of conversion of volatile fatty acids (VFAs) into alcohols by a microbial electrosynthesis (MES) process were significantly influenced by the initial organic loading concentration and operational period. The acetate and butyrate concentrations ranged from 2 to 8 g-COD/L, and alcohol and other product formations were determined over a 5 day operation. The highest yield of 0.218 g-CODAlcohol/g-CODVFAs was obtained for 4 g-COD/L after a 1 day operation. A gradual decrease over time in alcohol recovery was noticed for all VFA concentrations due to methane generation under elevated pH conditions. At the end of the operation, a higher bioalcohol yield was achieved at a relatively lower VFA concentration of 2 g-COD/L. A large fraction of initial VFAs remained unchanged without bioenergy production from higher substrate concentrations (6 and 8 g-COD/L). The energy recovery of total products (alcohols and methane) based on the input power was less than about 24% at the end of the...

Supercritical water oxidation of octol – containing wastewater

<p>This study investigated optimum operating conditions of supercritical water oxidation (SCWO) for octol and compared the degradation of its components TNT (2,4,6-trinitrotoluene) and HMX (octahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine, octogen) under the same conditions. Pilot scale experiments were conducted at various temperatures, reaction times and oxidant amounts. Removal efficiency, by-product analysis and toxicity tests were selected as the performance criteria for the SCWO. Optimum conditions were determined as a temperature of 500 C, 120 s of oxidation time and an oxidant ratio of 150%. Removal of octol was achieved at a rate of 99.99%, while TNT and HMX were removed individually at a rate of ~85% when they existed in the wastewater. No toxicity was observed at the end of the octol oxidation, whereas toxicity was found in the TNT and HMX oxidation due to the formation of TNT isomer and aniline. Higher initial organic material concentrations promoted the removal rates. These results demonstrated that SCWO can be effectively used for the degradation of ammunition wastewater even when concentrations are high.</p>

Uncertainty analysis of parameters in non‐point source pollution simulation: case study of the application of the Soil and Water Assessment Tool model to Yitong River watershed in northeast China

AbstractUncertainty analysis of the model parameters in non‐point source pollution (NPSP) simulation is important because of its great effects on predictions and decision‐making. Understanding the main parameters that effect the uncertainty of NPSP is necessary to provide the basis for formulating control measures. In this study, two methods were applied to conduct parameter uncertainty analysis for Soil and Water Assessment Tool (SWAT). Sobol’ method was used to screen out the model parameters with great effects on the runoff, sediment, total nitrogen (TN) and total phosphorus (TP). The results obtained by sensitivity analysis were used subsequent model calibration and further uncertainty analysis. Monte Carlo (MC) method was employed to analyse the effects of parameter uncertainty on the model outputs. However, such problems are time‐consuming because the MC method required to invoke simulation model thousands of times. To address this challenge, a kriging surrogate model was developed to improve the overall calculation efficiency. The results obtained by sensitivity analysis showed that curve number value (CN2), soil evaporation compensation factor (ESCO), universal soil loss equation support practice factor (USLE_P) and initial organic nitrogen concentration in soil layer (SOL_ORGN) had significant effects on the SWAT outputs. The uncertainty analysis results showed that the uncertainty of runoff is the lowest, followed by TP and TN, and the uncertainty of sediment was the greatest. The kriging surrogate model has the ability to solve this time‐consuming problem rapidly with a high degree of accuracy, and thus it is very robust.

Effect of Aquatic Particles on the Flocculation of M. aeruginosa and Nitzschia

Abstract Effects of size and concentration of aquatic particles collected from Lake Poyang, as well as initial algal cell density and organic matter concentration, on flocculation of Microcystis ae...

Catalytic ozonation of organic contaminants in petrochemical wastewater with iron-nickel foam as catalyst

This work investigated the removal of organic contaminants in actual petrochemical wastewater by catalytic ozonation with iron-nickel foam as catalyst. Under different conditions, the DOC removal percentages ranged from 40% to 61%, the sCOD removals were from 73% to 96% in the reaction time of 120 min. Two thirds of the 66 detected organic compounds disappeared in the treated wastewater. The biodegradability of the petrochemical wastewater was greatly improved after catalytic ozonation. TP, TN, NO3-N, Cl− and some heavy metals in the petrochemical wastewater were also removed to some extent. The influence of pH and initial organic matter concentration on the performance of catalytic ozonation was limited. Increase of aqueous ozone concentration and catalyst dosage was advantageous for organic contaminants removal. The probable mechanism of catalytic ozonation was proposed as that the iron-nickel foam was oxidized by ozone into the mixture of oxides, hydroxides, and hydroxyoxides. On one hand, the hydroxyl groups on the catalyst surface motivated the formation of OH. On the other hand, the electrons transferred among different valences of transition metals facilitated the decomposition of ozone. The generated OH diffused into bulk solution, working together with ozone to degrade the organic contaminants. From theoretical modeling, the residue ozone in the off gas can be reduced from 98% to 11% by using iron-nickel foam as the catalyst.

One-step preparation of FexOy/N-GN/CNTs heterojunctions as a peroxymonosulfate activator for relatively highly-efficient methylene blue degradation

Persulfate decontamination technologies utilizing radical-driven processes are powerful tools for the treatment of a broad range of impurities. However, the design of high-performance catalytic activators with multi-functionality remains a great challenge. Therefore, in this study, three-dimensional multifunctional FexOy/N-GN/CNTs (N-GN: nitrogen-doped graphene, CNTs: carbon nanotubes) heterojunctions, which can be employed as microwave absorbers and catalysts, were synthesized via a solvothermal method and applied to activate peroxymonosulfate for the degradation of methylene blue (MB). X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), and X-ray photoelectron microscopy (XPS) analyses revealed that the FexOy were anchored in-situ onto the N-GN network. Using MB as the model organic dye, various factors, such as degradation systems, PMS loading, initial organic pollutant concentration, and catalyst dosage were optimized. The results revealed that the remarkable efficiency was attributable to the synergistic effects of carbon, nitrogen, and iron-based species. The oxidation system corresponded to the pseudo-first-order kinetic with a k value of ∼0.33 min−1. It was demonstrated that both SO4•− and OH• were the predominant reactive species through quenching experiments. Because these heterojunctions were employed as microwave absorbers and have a semiconductor-like texture, the Fe/N co-rich hierarchical porous carbon skeleton favored electron transport and storage. These heterojunctions increase the options for transitional metal catalysts and highlights the importance of designing other heterojunctions for specific applications, such as supercapacitors, energy storage, CO2 capture, and oxygen reduction electrocatalysts.

Organic pollutants removal from oily wastewater using clean technology economically, friendly biosorbent (Phragmites australis)

A cost operative and favorable technology has been revealed for the removal of (COD, BOD and Oil & Grease) from oily industrial wastewater effluents. Batch scale studies for the biosorption potential of novel biosorbent Phragmites australis (Reeds). The study was supported at different constraints to obtain prime conditions of biosorbent dose, time of contact, pH, agitation speed and initial organic loads concentration. To dissect the propriety of the procedure and decided amount of organic loads removal, Langmuir and Freundlich isotherms were connected. The ideal estimations of contact time and agitation speed were found at 120 min and 150 rpm respectively. The ideal biosorption limits were seen at pH 7. Both pseudo-first and pseudo-second order models were connected and it was discovered that information fitting best to the pseudo-second-arrange active model. The outcomes demonstrated that Phragmites australis was an empowering adsorbent for the biosorption treatment of oily derivatives industrial wastewater.

Feasibility of bio-hythane production by co-digesting skim latex serum (SLS) with palm oil mill effluent (POME) through two-phase anaerobic process

Hydrogenogenic batch fermentation without nutrients addition was investigated at different SLS: POME mixing ratios of 100:0, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45,50:50, and 0:100 (Volatile Solid, VS basis) at initial organic concentrations of 21 and 7 g-VS/L. Satisfactory hydrogen yield of 84.5 ± 0.7 mL H2/g-VSadded was achieved from 7 g-VS/L batch having SLS: POME-VS mixing ratio of 55:45. Adding NaHCO3 3 g/L or 0.43 g-NaHCO3/g-VS) in the two-stage anaerobic system at 7 g-VS/L could provide sufficient buffering capacity. Hydrogenogenic effluent from 7 g-VS/L batch at SLS: POME mixing ratio of 55:45 (VS basis) could further generate rather high methane yield of 311.2 ± 8.0 mL- CH4/g-VSadded in themethanogenic stage.According to the experimental results, bio-hythane approximately 55.5 × 106 m3/year with 21% (V/V) of hydrogen, equivalent to51.0 × 106 l-gasoline could be produced potentially from 3.88 × 106 m3 of mixed SLS and POME through the two-stage anaerobic co-digestion.

Dynamic model of organic pollutant degradation in three dimensional packed bed electrode reactor

A dynamic model of semi-batch three-dimensional electrode reactor was established based on the limiting current density, Faraday's law, mass balance and a series of assumptions. Semi-batch experiments of phenol degradation were carried out in a three-dimensional electrode reactor packed with activated carbon under different conditions to verify the model. The factors such as the current density, the electrolyte concentration, the initial pH value, the flow rate of organic and the initial organic concentration were examined to know about the pollutant degradation in the three-dimensional electrode reactor. The various concentrations and logarithm of concentration of phenol with time were compared with the dynamic model. It was shown that the calculated data were in good agreement with experimental data in most cases.

Experimental and Modeling Study of Organic Chloride Compounds Removal from Naphtha Fraction of Contaminated Crude Oil Using Sintered γ-Al2O3 Nanoparticles: Equilibrium, Kinetic, and Thermodynamic Analysis

Because of destructive effects of organic chlorides, elimination of these compounds from contaminated crude oil and its distillates is very crucial for oil refiners. Despite the importance of the subject, limited researches in this field are performed and most of the proposed removal methods are operationally difficult and costly. In the present study, an adsorption process as an efficient technology is proposed and employed to eliminate the organic chlorides compounds from the naphtha fraction of contaminated crude oil. The γ-Al2O3 nanoparticles as an adsorbent are prepared and characterized by XRD, SEM–EDS, and BET analyses. Adsorption experiments are carried out at different operating temperatures and also various initial organic chloride concentrations. The experimental results indicated that the adsorption efficiency reaches to more than 96%, when the initial concentration of the organic chloride in the sample is 8.5 mg/L. The adsorption equilibrium analysis revealed that the Freundlich isotherm mode...

Removal of Organic material contaminants from wastewater of a petroleum refinery by Employing Ultrasound

In this study, the reduction of organic pollutants from wastewater was investigated. Ultrasonic radiation was approved as the usage method. Effective parameters such as the period of ultrasonic radiation (10-35min), ultrasonic power (40-200watt) and initial organic material concentration (123-150 mg/l) were tested to determine their effects on organic material removal percentage and turbidity regress. It has been found that a time interval of 30 minutes of continuous exposition of dissolved organic material to the field of ultrasound come to 76% removal at initial organic material concentration of 123 mg/l. Significant temperature change occurred which was about (20-33 ) rise in 35 minutes. However, this temperature change had no significant influence on efficiency of the treatment .Also it was found that the turbidity deceases with time from 98 to 34 at 35 min of exposure to Ultrasonic irradiation.

Mechanism and Kinetic Model for Autocatalysis in Liquid–Liquid System: Oxidation of Dibutyl Sulfide with Aqueous Hydrogen Peroxide

The oxidation of dibutyl sulfide with aqueous hydrogen peroxide as a liquid–liquid reaction was investigated. The autocatalysis, solubility of H2O2 in organic phase, and effects of temperature, stirring speed, initial organic DBSO concentration, and initial aqueous H2O2 concentration were studied. Solvent effect of dibutyl sulfoxide was proposed for liquid–liquid autocatalysis. The intrinsic reaction was considered as the determining step, and all the other steps were considered as equilibrium processes. Considering interfacial reaction and dynamic equilibrium of hydrogen peroxide between the two phases, the reaction was divided into exterior and interior stages. Exterior and interior mechanisms were proposed for the corresponding stages, and kinetic models were established. The parameters of kinetic model were estimated with the experimental data, and the activation energies of exterior and interior reaction were 30.62 and 73.50 kJ/mol. The validity of the kinetic models with estimated parameters was stu...

Effects of low molecular weight organic acids and fulvic acid on 2,4,4′-trichlorobiphenyl degradation and hydroxyl radical formation in a goethite-catalyzed Fenton-like reaction

The effects of different organic acids on 2,4,4′-trichlorobiphenyl (PCB28) degradation, H2O2 decomposition and OH formation in a goethite-catalyzed Fenton-like reaction were investigated at different pH and initial organic acid concentrations. In general, organic acid addition had a similar effect on PCB28 degradation and OH formation, but there was a significant difference between its effect on PCB28 degradation and H2O2 decomposition. This indicates that OH was responsible for PCB28 degradation in the heterogeneous Fenton reaction. Oxalic, citric, malic and succinic acid addition decreased PCB28 degradation, H2O2 decomposition and OH formation. Their inhibitory effect followed the order oxalic acid>citric acid>malic acid>succinic acid, according to their sorption affinity for a goethite surface. Catechol and gallic acid addition had a considerable inhibitory effect on PCB28 degradation and OH formation, and the opposite effect was observed with 2,6-dimethoxylphenol and caffeic acid addition, although the addition decreased the H2O2 decomposition. The addition of low-concentration fulvic acid (FA) could promote PCB28 degradation and OH formation at pH 3 and pH 7, but an inhibitory effect was observed with increasing concentrations of FA. The inhibitory effect of added FA on H2O2 decomposition increased with decreasing pH and with increasing FA concentrations.