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In this work, the sequential Electrocoagulation + Electro-oxidation + Activated carbon adsorption (EC + EO + AC) process was studied as an alternative for the treatment of an industrial textile wastewater (TWW) issuing from a manufacturing company located in Medellín (Colombia). The EC's and EO's operational conditions were optimized using a Box-Behnken experimental design, the Response Surface Methodology and a constrained nonlinear optimization algorithm in terms of organic matter degradation efficiency. The best performance for EC (i. e., dye removal = 94%, COD and TOC degradation of 45 and 40%, respectively) was obtained using Fe anode and Boron Doped Diamond (BDD) cathode, with current density, jEC, equals to 5 mA/cm2, pH = 9.3, 60 RPM and 10 min of electrolysis. After EC treatment, the effluent biodegradability (evaluated as the BOD5/COD ratio) increases from 0.14 to 0.23. Regrettably, EC was not effective for the removal of acute toxicity to Artemia salina since the treated effluent remained very toxic (100%). The treatment of EC's effluent by EO enhanced organic pollutant removal. For EC + EO sequential process, EO optimal operational conditions (jEO = 10 mA/cm2, pH = 3, 240 RPM, BDD as anode and Fe as cathode) allowed reduction of 100% of color, 88% of COD and 79% of TOC after 30 min of electrolysis. Moreover, the BOD5/COD ratio increased from 0.23 to 0.58; however, the treated effluent remained very toxic to the Artemia salina. Consequently, an activated carbon adsorption step was included to complete the treatment process. Thus, by coupling the EC + EO + AC process, effluent's acute toxicity decreased completely. From molecular weight distribution analysis, it was concluded that EC + EO was efficient in eliminating low molecular weight (< 5 kDa) compounds. Finally, the operation cost, which includes chemical reagents, electrodes, energy consumption, and sludge disposal, for the EC + EO + AC sequential process was estimated in 3.83 USD /m3. © 2020 Elsev

Analyses of temperature, conversion, and their sensitivity with respect to the initial temperature were investigated by parametric sensitivity analysis using a dimensionless batch reactor model for the cyclotrimethylene- triamine synthesis. At first, an expression for its reaction rate was fitted from experimental data available in the literature. Then, a new simple sensitivity-based criterion was used to determine critical operating conditions analyzing temperature sensitivity trajectories. The critical condition of runaway reaction corresponds to a Semenov number (F) equals to 0.684, a heat of reaction parameter (B) equals to 15 and an Arrhenius-type number (?) of 20.

In this study, the industrial textile wastewater was treated using a chemical-based technique (coagulation-flocculation, C-F) sequential with an advanced oxidation process (AOP: Fenton or Photo-Fenton). During the C-F, Al2(SO4)3 was used as coagulant and its optimal dose was determined using the jar test. The following operational conditions of C-F, maximizing the organic matter removal, were determined: 700 mg/L of Al2(SO4)3 at pH = 9.96. Thus, the C-F allowed to remove 98% of turbidity, 48% of Chemical Oxygen Demand (COD), and let to increase in the BOD5/COD ratio from 0.137 to 0.212. Subsequently, the C-F effluent was treated using each of AOPs. Their performances were optimized by the Response Surface Methodology (RSM) coupled with a Box-Behnken experimental design (BBD). The following optimal conditions of both Fenton (Fe2+/H2O2) and Photo-Fenton (Fe2+/H2O2/UV) processes were found: Fe2+ concentration = 1 mM, H2O2 dose = 2 mL/L (19.6 mM), and pH = 3. The combination of C-F pre-treatment with the Fenton reagent, at optimized conditions, let to remove 74% of COD during 90 min of the process. The C-F sequential with Photo-Fenton process let to reach 87% of COD removal, in the same time. Moreover, the BOD5/COD ratio increased from 0.212 to 0.68 and from 0.212 to 0.74 using Fenton and Photo-Fenton processes, respectively. Thus, the enhancement of biodegradability with the physico-chemical treatment was proved. The depletion of H2O2 was monitored during kinetic study. Strategies for improving the reaction efficiency, based on the H2O2 evolution, were also tested. © 2017 Elsevier Ltd

The Fenton heterogeneous process in a fluidized bed reactor using Zero Valent Iron (ZVI), in the metallic state, for the treatment of textile wastewater has been used an analyzed. The aim of this work was to optimize the following operating parameters: initial dye concentration, H2O2 concentration, pH, amount of ZVI, and UV radiation, for the removal of dye and organic matter. At first, a fractional factorial experimental design allows defining the most influential factors. After that, they were optimized using the Response Surface Methodology coupled to the Box-Behnken experimental design. The optimal conditions were found to be as follows: initial dye concentration, 881 mg/L; pH 5; ZVI concentration, 5,31 g/L; H2O2 concentration, 0,86 mL/L. At these conditions, the degradation kinetics was performed, reaching 100% and 80,83% of dye and chemical oxygen demand respectively, in 150 minutes of reaction.

Wastewater collected from a local jean manufacturing plant was treated using an electrocoagulation process (EC) coupled with activated carbon (AC) adsorption. The process variables were optimized using multivariate regression coupled with nonlinear programming with nonlinear restrictions to achieve the lowest possible cost while keeping a high enough degradation rate for chemical oxygen demand (COD), color, and turbidity to fulfill the Colombian environmental regulation requirements. Under optimal conditions (pH = 5.4, s =2 mS/cm, j =14 mA/cm2, and t = 11 min) color, COD, and TOC removals of 95%, 63%, and 51%, respectively, were achieved. The biodegradability index also increased from 0.13 to 0.29, whereas toxicity tests showed a remaining toxicity of 45%. A kinetic study was conducted for the EC process. The activated carbon (AC) adsorption process was successfully used to completely remove toxicity, while further increasing color, COD, and TOC removals to 96%, 72%, and 61%, respectively. The conditions for the AC adsorption process (20 g/L of AC and 1 h) were determined by experimental adsorption isotherms and kinetic studies. The optimized EC/AC process led to an effluent satisfying the Colombian regulations and seems technologically viable with lower costs than other similar process that were reported in previous works. © 2020 Elsevier Ltd

In this work, parametric sensitivity and dynamic analysis were combined to determine the thermal instability conditions inherent in the methyl isocyanate hydrolysis reaction. This highly exothermic reaction tragically proved to be very sensible to temperature changes in the so-called Bhopal disaster in 1984. A stirred tank reactor in transient state was considered for simulating the reactive system. First, critical operational conditions were defined from the parametric sensitivity analysis. Subsequently, in a rigorous way, the dynamic analysis determined the thermal instability regions, Hopf bifurcations, and the thermal oscillatory behavior of the reactive system. The Matcont® software was used to solve the differential equations set. It was demonstrated that runaway conditions and the periodic solutions of temperature are closely related with the cooling temperature and the dimensionless parameters (f-dimensionless flow and l-heat transfer term) and their critical parameters were obtained: /c=752.39 and fc=1.57.

Soluble coffee production generates wastewater containing complex mixtures of organic macromolecules. In this work, a sequential Electrocoagulation-Electrooxidation (EC-EO) process, using aluminum and graphite electrodes, was proposed as an alternative way for the treatment of soluble coffee effluent. Process operational parameters were optimized, achieving total decolorization, as well as 74% and 63.5% of COD and TOC removal, respectively. The integrated EC-EO process yielded a highly oxidized (AOS = 1.629) and biocompatible (BOD5/COD approximate to 0.6) effluent. The Molecular Weight Distribution (MWD) analysis showed that during the EC-EO process, EC effectively decomposed contaminants with molecular weight in the range of 10-30 kDa. In contrast, EO was quite efficient in mineralization of contaminants with molecular weight higher than 30 kDa. A kinetic analysis allowed determination of the time required to meet Colombian permissible discharge limits. Finally, a comprehensive operational cost analysis was performed. The integrated EC-EO process was demonstrated as an efficient alternative for the treatment of industrial effluents resulting from soluble coffee production. (C) 2017 Elsevier Ltd. All rights reserved.

The results of a study on the parametric sensitivity of acetic acid production by hydrolysis of acetic anhydride, using acid homogeneous catalysis in a batch reactor, are presented. Dimensionless parameters of mass and energy balances were fitted using experimental data available in the literature that includes the variation of the reaction temperature for different sulfuric acid concentrations (3% to 5%). Then, from the analysis of the intrinsic mathematical properties of the concentration-temperature phase plane, the critical operating conditions were defined. Thus, it was possible to determine the specific values of the safe operating conditions for the catalyzed hydrolysis of acetic anhydride, in the function of catalyst concentration.

In this work, the detailed analysis of HCN volatilization, taking place in tailing storage facilities, was made. Volatilization experiments were performed at conditions typical of gold leaching industrial tailing ponds. The meticulous statistical analysis (including full factorial 33 experimental design) let to determine the variables and their interactions affecting the percentage of HCN volatilization. Volatilization tests were performed in an open, temperature-controlled, continuously-stirred batch reactor. The percentage of HCN volatilization was directly proportional to the temperature and temperature-pH interaction and inversely proportional to the pH, cyanide concentration, and pH-pH and temperature-cyanide concentration interactions. HCN volatilization was promoted at acidic conditions. A first order rate law was used to represent the volatilization rate. The specific rate constant (k) was found to be following function of temperature and pH: k(T,pH) = Ao.exp(-18760/T), where: In(A(0)) = (0.11 +/- 0.11)-pH + (58.08 +/- 0.16). The obtained kinetic model represented properly (R-2 = 0.90) experimental data in a wide range of industrial conditions: cyanide concentration (300-2000 mg.L-1), pH (3-9), and temperature (16-20 degrees C). The increase in temperature, from 16 to 20 C, let to the increase in k, by a factor of ca. 2.5 +/- 0.8. The increase in solution pH, from 3 to 9, provoked its decrease, by a factor of ca. 1.9 +/- 0.3.

The experimental data of CO oxidation over the series of 2 wt.% Au/Ce1-xZrxO2 (x=0, 0.25, 0.5, 0.75, 1) catalyst were analyzed using a variation of the Temperature Scanning Method with the aim of catalyst's composition optimization. The catalysts were prepared by the Direct Anionic Exchange technique. The kinetic of CO oxidation was quantified by conversion-rate-temperature (X, r, T) triplets, calculated from raw data obtained using a plug flow reactor, working at oxygen stoichiometric, rich, and lean conditions. The data were fitted to the Mars-van Krevelen adsorption-reaction model (MvK). The results showed that the MvK model is able to predict the superficial reaction and the re-oxidation of the catalyst surface. Additionally, the data at oxygen lean conditions revealed the distinctive characteristic of Ce-containing catalysts, which act as oxygen buffer by releasing-uptalcing oxygen. The obtained values of the fitted parameters allowed re-mapping raw data onto the conversion-temperature-catalyst composition surface plot and their application as a tool for the optimization of catalyst composition. (C) 2015 Elsevier B.V. All rights reserved.

The capacity of the electro-coagulation (EC) process for the treatment of the wastewater containing Cr3+, resulting from a leather tannery industry placed in Medellin (Colombia), was evaluated. In order to assess the effect of some parameters, such as: the electrode type (Al and/or Fe), the distance between electrodes, the current density, the stirring velocity, and the initial Cr3+ concentration on its efficiency of removal (%RCr+3), a multifactorial experimental design was used. The %RCr3+ was defined as the response variable for the statistical analysis. In order to optimise the operational values for the chosen parameters, the response surface method (RSM) was applied. Additionally, the Biological Oxygen Demand (BOD5), the Chemical Oxygen Demand (COD), and the Total Organic Carbon (TOC) were monitored during the EC process. The electrodes made of aluminium appeared to be the most effective in the chromium removal from the wastewater under study. At pH equal to 4.52 and at 28 degrees C, the optimal conditions of Cr3+ removal using the EC process were found, as follows: the initial Cr3+ concentration=3,596 mg/L, the electrode gap=0.5 cm, the stirring velocity=382.3 rpm, and the current density=57.87 mA/cm2. At those conditions, it was possible to reach 99.76% of Cr3+ removal, and 64% and 61% of mineralisation (TOC) and COD removal, respectively. A kinetic analysis was performed in order to verify the response capacity of the EC process at optimised parameter values.

The statistical optimization of the implementation and operational costs of an electrochemical-oxidation process for treatment of wastewater containing dye Yellow 23 was done. The aim was to optimize the operational parameters for the current density, conductivity, and area of electrodes per unit of volume in order to minimize the net present value (NPV) of the operation while maintaining a defined quality for the treated wastewater. To achieve this, the response surface methodology coupled to the Box-Behnken statistical design was used. The optimal conditions found were: a relationship of treated wastewater volume per area of electrodes of 9.076 mL/cm2, conductivity 4000 µS/cm, and current density 20 mA/cm2. At optimal conditions, the NPV for a 10 year operation is 998636 USD, which corresponds to a cost of 0.68USD/m3 of treated water.

This study examines the electro-oxidation (EO) of cyanide originating from an industrial plant´s gold leaching effluent. Experiments were carried out in a laboratory-scale batch cell reactor. Monopolar configuration of electrodes consisting of graphite (anode) and aluminum (cathode) was employed, operating in galvanostatic mode. Response Surface Methodology (RSM), based on a Box–Behnken experimental Design (BBD), was used to optimize the EO operational conditions. Three independent process variables were considered: initial cyanide concentration ([CN-]0 = 1000–2000 mg L-1), current density (J =7–107 mA cm-2), and stirring velocity (? = 250–750 rpm). The cyanide conversion (XCN-), Chemical Oxygen Demand (COD) removal percentage (%RCOD), and specific Energy Consumption per unit mass of removed cyanide (EC) were analyzed as response variables. Multi-objective optimization let to establish the most effective EO conditions ([CN-]0 = 1000 mg L-1, J = 100 mA cm-2 and ? = 750 rpm). The experimental data (XCN-, %RCOD, and EC) were fitted to second-order polynomial models with adjusted correlation coefficients (Radj2) of ca. 98, 99 and 87%, respectively. The kinetic analysis, performed at optimal EO operational conditions, allowed determination of time required to meet Colombian permissible discharge limits. The predictive capacity of kinetic expressions was verified against experimental data obtained for gold leaching effluent. Total cyanide removal and 96% of COD reduction were obtained, requiring EC of 71.33 kWh kg-1 and 180 min. The BOD5 (biological oxygen demand)/COD ratio increased from 4.52 × 10-4 to 0.5573, confirming effluent biodegradability after EO treatment. Graphic Abstract: [Figure not available: see fulltext.]The variation of cyanide (CN-), cyanate (CNO-) and ammonium (NH4 +) ions concentrations vs. time at alkaline conditions. EO operational conditions: [CN-]0 = 1000 mg/L, J = 100 mA/cm2 , ? = 750 rpm, [NaCl] = 0.15 M and pH 11.1. © 2020, Springer N

In the present work, the operational conditions for methanol synthesis in a Lurgi reactor are analyzed. The industrial data for a packed reactor (consisting of 1620 tubes of 7 m long) are the basis of this study. At first, the industrial reactor is simulated achieving excellent agreement with plant data. Then, the instability region is defined as a boundary in the conversion-temperature diagram and defines the conditions that must be avoided during reactor operation. The optimization of the operational conditions is performed based on the optimal temperature progression from the iso-reaction rate curves. Finally, it was found that the cooling fluid must be at 230 °C and that the heat transfer coefficient must guarantee a value of 118 J/(s.K.m2).

In this study, the potential application of sequential Electrocoagulation + Fenton (F) or Photo-Fenton (PF) + Active carbon adsorption (EC + F/PF + AC) processes were analyzed as alternatives for the treatment of an industrial textile wastewater resulting from an industrial facility located in Medellín (Colombia). In order to maximize the organic matter degradation, each step of the treatment was optimized using the Response Surface Methodology. At first, the optimal performance of EC was achieved with Fe electrodes operating at pH = 7, jEC = 10 mA/cm2 and 60 rpm, during 10 min of electrolysis. At these conditions, EC let to remove 94% of the dye's color, 56% of the COD and 54% of the TOC. Next, sequentially applied Fenton or photo-Fenton process (i.e., EC + F/PF), operating at the optimized conditions (pH = 4.3, [Fe2+] = 1.1 mM, [H2O2] = 9.7 mM, stirring velocity = 100 rpm and reaction time = 60 min.), improved the quality of the treated effluent. The EC + F let to achieve total color reduction, as well as COD and TOC removals of 72 and 75%, respectively. The EC + PF reached 100% of color, 76% of COD and 78% of TOC reductions. The EC + F/PF processes were more efficient than EC in elimination of low molecular weight (<5 kDa) compounds from wastewater. Moreover, the BOD5/COD ratio increased from 0.21 to 0.42 and from 0.21 to 0.46 using EC + F and EC + PF processes, respectively. However, EC + F/PF were not fully effective for the removal of acute toxicity to Artemia salina: 20% and 60% of reduction in toxicity using EC + F and EC + PF, respectively, comparing to very toxic (100%) raw textile wastewater. Thus, activated carbon adsorption was applied as an additional step to complete the treatment. After AC adsorption, the acute toxicity decreased to 10% and 0% using EC + F and EC + PF, respectively. The total operational costs, including chemical reagents, electrodes, energy consumption and sludge disposal, were of 1.65 USD/m3 and 2.3 USD/m3 for EC + F and EC + PF

Photocatalytic degradation of phenol under both UV radiation and visible light, using TiO2 (Degussa P-25) and TiO2 loaded with some transition metal ions (Co, Cu, Fe and Mo) was examined. From the series of metal loaded catalysts, Mo/TiO2 was the most efficient one. In the presence of Mo, neither TiO2 anatase/rutile fraction nor its pore size diameter has been affected. However. Mo made its surface more acidic. The percentage of phenol degradation reached under visible light was significantly lower than that under UV radiation due to the lower degree of light absorption by the catalyst surface. From the series of studied catalysts, 2 wt% Mo/TiO2 was the most efficient one. The synergetic effect between S-BET, mean pore size diameter, catalyst agglomerates size, band gap, ZPC and the type of M0(x)O(y), species on TiO2 surface, depending on Mo loading, created its photocatalytic performance. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

In this work, the operational conditions of the tartrazine electro-oxidation (EO) process were optimized. The batch reactor used has two electrodes: one made of diamond doped with boron and the other one of titanium, working at monopolar configuration. The initial dyestuff concentration (Ci), the current density (i) and the pH were defined as the main factors affecting the EO. Their optimal values were found as follows: Ci=30 ppm, i=5mA/cm2 and pH=6.0. At these conditions, a kinetic analysis was performed in the terms of: the percentage of the dyestuff decolorization (%DC), the percentage of the chemical oxygen demand (%DCOD), and the percentage of the total organic carbon (%TOC). Additionally, the effect of Fe2+ (electro- Fenton process, EF) and Fe2+/UV radiation (electro-photo-Fenton process, EFF) on the studied process were evaluated. The work demonstrates the validity of the hypothesis about the most significant parameters that affect the EO process.

In this work, the response surface methodology was applied as a tool for the optimization of the operational conditions of phenol photo-degradation over TiO2 and 2% wt Mo/TiO2 catalysts. A multifactorial experimental design was proposed, including the following variables: phenol initial concentration (Ci), catalyst loading (Cat) and pH. The apparent reaction rate constant and the percentage of phenol degradation were chosen as the response variables. When TiO2 was used as catalyst, the following optimal operational conditions were found: Ci=10ppm, Cat=0.7g/L and pH=8 for both UV and visible light. For 2% wt Mo/TiO2 catalyst, the optimal operating conditions strongly depended on the applied radiation source. Thus, under UV radiation: Ci=10 ppm, Cat=0.7 g/L and pH=8 were found as the optimum conditions. Using visible light, and the following optimized conditions, Ci=10 ppm, Cat=0.1 g/L, pH =3.6, the Mo containing catalyst showed to be the most efficient. Under these conditions, the amount of 2% wt. Mo/TiO2 was 7 times lower than that of unsupported TiO2.